ICS Supersedes EN : A1:2009, EN :2005. English version

Transcription

1 EUROPEAN STANDARD EN NORME EUROPÉENNE EUROPÄISCHE NORM December 2012 ICS Supersedes EN : A1:2009, EN :2005 English version Overhead electrical lines exceeding AC 1 kv - Part 1: General requirements - Common specifications Lignes électriques aériennes dépassant AC 1 kv - Partie 1: Règles générales - Spécifications communes Freileitungen über AC 1 kv - Teil 1: Allgemeine Anforderungen - Gemeinsame Festlegungen This European Standard was approved by CENELEC on CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung Management Centre: Avenue Marnix 17, B Brussels 2012 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members. Ref. No. EN :2012 E

2 EN : Contents Foreword Introduction Detailed structure of the standard Part 1: General requirements - Common specifications Part 2: National Normative Aspects A-deviations Special national conditions (snc) National complements (NCPTs) Language Scope General Field of application Structure of the European Standard EN Normative references, definitions and symbols Normative references Definitions Symbols Basis of design Introduction Requirements of overhead lines Basic requirements Reliability requirements Security requirements Safety requirements Strength coordination Additional considerations Design working life Durability Quality assurance Limit states General Ultimate limit states Serviceability limit states Actions Principal classifications Classification of actions by their variation in time...48

3 - 3 - EN : Classification of actions by their nature and/or the structural response Characteristic values Characteristic value of an action Action (F) Permanent action (G) Variable action (Q) Accidental action (A) Characteristic value of a material property Design values General Design value of an action Design value of a material property Combination value of a variable action Partial factor method and design formula Partial factor method Basic design formula Total design value of the effect of combined actions General Design situations related to permanent and variable actions Design situations related to permanent, variable and accidental actions Structural design resistance Actions on lines Introduction Permanent loads Wind loads Field of application and basic wind velocity Mean wind velocity Mean wind pressure Turbulence intensity and peak wind pressure Wind forces on any overhead line component Wind forces on overhead line components Wind forces on conductors General Structural factor Drag factor...63

4 EN : Wind forces on insulator sets Wind forces on lattice towers General Method Method Wind forces on poles Ice loads General Ice forces on conductors Combined wind and ice loads Combined probabilities Drag factors and ice densities Mean wind pressure and peak wind pressure Equivalent diameter D of ice covered conductor Wind forces on support for ice covered conductors Combination of wind velocities and ice loads Extreme ice load I T combined with a high probability wind velocity V IH Nominal ice load I 3 combined with a low probability wind velocity V IL Temperature effects Security loads General Torsional loads Longitudinal loads Mechanical conditions of application Safety Loads Construction and maintenance loads Loads related to the weight of linesmen Forces due to short-circuit currents Other special forces Avalanches, creeping snow Earthquakes Load cases General Standard load cases Partial factors for actions...80

5 - 5 - EN : Electrical requirements Introduction Currents Normal current Short-circuit current Insulation co-ordination Classification of voltages and overvoltages General Representative power frequency voltages Representative temporary overvoltages Representative slow-front overvoltages Representative fast-front overvoltages Minimum air clearance distances to avoid flashover General Application of the theoretical method in Annex E Empirical method based on European experience Load cases for calculation of clearances Load conditions Maximum conductor temperature Wind loads for determination of electric clearances Wind load cases Nominal wind loads for determination of internal and external clearances Extreme wind loads for determination of internal clearances Ice loads for determination of electric clearances Combined wind and ice loads Coordination of conductor positions and electrical stresses Internal clearances within the span and at the top of support External clearances General External clearances to ground in areas remote from buildings, roads, etc External clearances to residential and other buildings External clearances to crossing traffic routes External clearances to adjacent traffic routes External clearances to other power lines or overhead telecommunication lines External clearances to recreational areas (playgrounds, sports areas, etc.) Corona effect...103

6 EN : Radio noise General Design influences Noise limits Audible noise General Design influences Noise limit Corona loss Electric and magnetic fields Electric and magnetic fields under a line Electric and magnetic field induction Interference with telecommunication circuits Earthing systems Introduction Purpose Requirements for dimensioning of earthing systems Earthing measures against lightning effects Transferred potentials Ratings with regard to corrosion and mechanical strength Earth electrodes Earthing and bonding conductors Dimensioning with regard to thermal strength General Current rating calculation Dimensioning with regard to human safety Permissible values for touch voltages Touch voltage limits at different locations Basic design of earthing systems with regard to permissible touch voltage Measures in systems with isolated neutral or resonant earthing Site inspection and documentation of earthing systems Supports Initial design considerations Introduction Structural design resistance of a pole...113

7 - 7 - EN : Buckling Resistance Materials Steel materials, bolts, nuts and washers, welding consumables Cold formed steel Requirements for steel grades subject to galvanising Holding-down bolts Concrete and reinforcing steel Wood Guy materials Other materials Lattice steel towers General Basis of design Materials Durability Structural analysis Ultimate limit states General Resistance of cross section areas Tension, bending and compression resistance of members Buckling resistance of members in compression Buckling resistance of members in bending Serviceability limit states Resistance of connections Design assisted by testing Fatigue Steel poles General Basis of design (EN :2005 Chapter 2) Materials (EN :2005 Chapter 3) Durability (EN :2005 Chapter 4) Structural analysis (EN :2005 Chapter 5) Ultimate limit states (EN :2005 Chapter 6) General...118

8 EN : Resistance of cross section areas Serviceability limit states (EN :2005 Chapter 7) Resistance of connections Basis Bolts (other than holding-down bolts) Slip joint connections Flanged bolted connections Welded connections Direct embedding into the concrete Base plate and holding-down bolts Design assisted by testing Wood poles General Basis of design Materials Durability Ultimate limit states Basis Calculation of internal forces and moments Resistance of wood elements Decay conditions Serviceability limit states Resistance of connections Design assisted by testing Concrete poles General Basis of design General rules Design load Lateral reinforcement Materials Ultimate limit states Serviceability limit states Design assisted by testing...124

9 - 9 - EN : Guyed structures General Basis of design Materials Ultimate limit states Basis Calculation of internal forces and moments Second order analysis Maximum slendernesses Serviceability limit states Design details for guys Other structures Corrosion protection and finishes General Galvanising Metal spraying Paint over galvanising in plant (Duplex system) Decorative finishes Use of weather-resistant steels Protection of wood poles Maintenance facilities Climbing Maintainability Safety requirements Loading tests Assembly and erection Foundations Introduction Basis of geotechnical design (EN :2004 Section 2) General Geotechnical design by calculation Design by prescriptive measures Load tests and tests on experimental models Soil investigation and geotechnical data (EN :2004 Section 3) Supervision of construction, monitoring and maintenance (EN :2004 Section 4)...133

10 EN : Fill, dewatering, ground improvement and reinforcement (EN :2004 Section 5) Interactions between support foundations and soil Conductors and earth-wires Introduction Aluminium based conductors Characteristics and dimensions Electrical requirements Conductor service temperatures and grease characteristics Mechanical requirements Corrosion protection Test requirements Steel based conductors Characteristics and dimensions Electrical requirements Conductor service temperatures and grease characteristics Mechanical requirements Corrosion protection Test requirements Copper based conductors Conductors and ground wires containing optical fibre telecommunication circuits Characteristics and dimensions Electrical requirements Conductor service temperatures Mechanical requirements Corrosion protection Test requirements General requirements Avoidance of damage Partial factor for conductors Minimum cross-sections Sag - tension calculations Test reports and certificates Selection, delivery and installation of conductors Insulators Introduction...140

11 EN : Standard electrical requirements RIV requirements and corona extinction voltage Pollution performance requirements Power arc requirements Audible noise requirements Mechanical requirements Durability requirements General requirements for durability of insulators Protection against vandalism Protection of ferrous materials Additional corrosion protection Material selection and specification Characteristics and dimensions of insulators Type test requirements Standard type tests Optional type tests Sample test requirements Routine test requirements Summary of test requirements Test reports and certificates Selection, delivery and installation of insulators Hardware Introduction Electrical requirements Requirements applicable to all fittings Requirements applicable to current carrying fittings RIV requirements and corona extinction voltage Magnetic characteristics Short circuit current and power arc requirements Mechanical requirements Durability requirements Material selection and specification Characteristics and dimensions of fittings Type test requirements Standard type tests Optional type tests Sample test requirements Routine test requirements Test reports and certificates Selection, delivery and installation of fittings...147

12 EN : Quality assurance, checks and taking-over Quality assurance Checks and taking-over Annex A (informative) Strength coordination A.1 Recommended design criteria A.2 Proposed strength coordination Annex B (informative) Conversion of wind velocities and ice loads B.1 Definition of symbols used in this annex B B.2 Evaluation of extreme wind velocity data B.3 Evaluation of extreme ice load data B.4 Statistical ice parameters B.4.1 Basic ice load, I B B.4.2 Yearly maximum ice load, I m B.4.3 Maximum ice load over several years, I max B.4.4 Mean value, I mm of yearly maximum ice loads B.4.5 Coefficient of variation, v I for yearly maximum ice loads B.5 Extreme ice load evaluation based on various data sources B.5.1 Data sources for statistical evaluation B.5.2 Yearly maxima ice loads, I m during periods of at least 10 years are available B.5.3 Maximum ice load, I max is known only for a limited number of years B.5.4 Yearly maximum ice load, I m, based on meteorological analyses Annex C (informative) Application examples of wind loads - Special forces C.1 Application examples of the calculation of wind loads as defined in 4.3 and C.1.1 Example 1 : Typical 24 kv wood pole tangent support C.1.2 Example 2 : Typical 225 kv suspension lattice tower C.2 Special forces C.2.1 Definition of symbols used in this annex C C.2.2 Forces due to short-circuit currents C.2.3 Avalanches, creeping snow C.2.4 Earthquakes Annex D (informative) Statistical data for the Gumbel distribution of extremes D.1 Definition of symbols used in this annex D.2 The Gumbel distribution D.3 Example of using C 1 and C D.4 Calculation of C 1 and C Annex E (normative) Theoretical method for calculating minimum air clearances E.1 Definition of symbols used in this annex...169

13 EN :2012 E.2 Insulation co-ordination E.2.1 Development of theoretical formulae for calculating electrical distances E.2.2 Representative voltages and overvoltages U rp E.2.3 Co-ordination withstand voltage U cw E.2.4 Required withstand voltage of the air gap, U rw E.2.5 Relationship with the clearance distance of the air gap E Statistical approach E Deviation factors E Gap factors E Insulation response to overvoltages E.3 Calculation formulae for the minimum air clearances E.4 Examples of calculation of D el, D pp and D 50 Hz for different U S voltages (informative) E.4.1 Range I: 90 kv system equipped with insulator strings composed of 6 units E.4.2 Range I: 90 kv system equipped with insulator strings composed of 9 units E.4.3 Range II : 400 kv system Annex F (informative) Empirical method for calculating mid span clearances F.1 Empirical method for the determination of clearances within the span F.2 Approximate method for conductors with different cross-sections, materials or sags 184 F.3 Contribution of the insulator set to the determination of clearances at supports Annex G (normative) Calculation methods for earthing systems G.1 Definition of symbols used in this annex G.2 Minimum dimensions of earth electrodes G.3 Current rating calculation G.4 Touch voltage and body current G.4.1 Equivalence between touch voltage and body current G.4.2 Calculation taking into account additional resistances Annex H (informative) Installation and measurements of earthing systems H.1 Definition of symbols used in this annex H.2 Basis for the verification H.2.1 Soil resistivity H.2.2 Resistance to earth H.3 Installation of earth electrodes and earthing conductors H.3.1 Installation of earth electrodes H Earth electrodes H Horizontal earth electrodes H Vertical or inclined driven rods H Jointing the earth electrodes...197

14 EN : H.3.2 Installation of earthing conductors H General H Installing the earthing conductors H Jointing the earthing conductors H.4 Measurements for and on earthing systems H.4.1 Measurement of soil resistivities H.4.2 Measuring touch voltages H.4.3 Measurement of resistances to earth and impedances to earth H.4.4 Determination of the earth potential rise H.4.5 Reduction factor related to earth wires of overhead lines H General H Values of reduction factor of overhead lines Annex J (normative) Angles in lattice steel towers J.1 Definition of symbols used in this annex J.2 General J.3 Tension resistance of angles connected through one leg (see ) J.4 Buckling resistance of angles in compression (see ) J.4.1 Flexural buckling resistance J.4.2 Effective non-dimensional slenderness for flexural buckling J General J Slenderness, λ J Non-dimensional slenderness, λ J Effective non-dimensional slenderness, λ eff J.4.3 Slenderness of members J General J Leg members and chords J Primary bracing patterns J Compound members J.4.4 Secondary (or redundant) bracing members J.5 Design resistance of bolted connections (see 7.3.8) J.5.1 General J.5.2 Block tearing resistance of bolted connections Annex K (normative) Steel poles K.1 Definition of symbols used in this annex K.2 Classification of cross sections (EN : )...217

15 EN :2012 K.3 Class 4 cross-sections (EN : and EN : K.4 Resistance of circular cross sections K.5 Resistance of polygonal cross sections K.5.1 Class 3 cross-sections (EN : ) K.5.2 Class 4 cross-sections (EN : ) K.6 Design of holding-down bolts Annex L (informative) Design requirements for supports and foundations L.1 Structural requirement L.2 Configuration requirements: types of supports and uses L.3 Phase conductor and earth wire attachment L.4 Foundation steelwork L.5 Erection/maintenance facilities L.6 Mass-length restrictions Annex M (informative) Geotechnical and structural design of foundations M.1 Typical values of the geotechnical parameters of soils and rocks M.1.1 General M.1.2 Definitions M.1.3 Symbols, definitions and units of some ground parameters M.2 Sample analytical models for uplift resistance calculation M.2.1 General M.2.2 Calculation of R W M.2.3 Calculation of R S M.2.4 Analytical evaluation of R d M.3 Sample semi-empirical models for resistance estimation M.3.1 Geotechnical design by calculation M General M Monoblock foundations M Slab foundations M Grillage-type slab foundations M Single-pile foundations M Separate stepped block foundations, pad and chimney foundations M Auger-bored and excavated foundations M Separate grillage foundations M Pile foundations M.3.2 Structural design of concrete foundations Annex N (informative) Conductors and overhead earth wires N.1 Specification of conductors and earth wires...245

16 EN : N.1.1 Factors influencing the specification of conductors and earth wires N.1.2 Operational factors N.1.3 Maintenance requirements N.1.4 Environmental parameters N.2 Selection of conductors and earth wires N.3 Packing and delivery of conductors and earth wires N.4 Precautions during installation of conductors and earth wires Annex P (informative) Tests on insulators and insulators sets Annex Q (informative) Insulators Q.1 Specification of insulators Q.1.1 Factors influencing the specification of insulators Q.1.2 Operational factors Q.1.3 Maintenance requirements Q.1.4 Environmental parameters Q.2 Selection of insulators Q.3 Packing and delivery of insulators Q.4 Precautions during installation of insulators Annex R (informative) Hardware R.1 Specification and selection of fittings R.1.1 Factors influencing specification and selection R.1.2 Operational factors R.1.3 Maintenance requirements R.1.4 Environmental parameters R.2 Packing and delivery of fittings R.3 Precautions during installation of fittings...253

17 EN :2012 Foreword This document (EN :2012) has been prepared by CLC/TC 11 "Overhead electrical lines exceeding 1 kv a.c. (1,5 kv d.c.)". The following dates are fixed: latest date by which this document has to be implemented at national level by publication of (dop) an identical national standard or by endorsement latest date by which the national standards conflicting with this document have to be withdrawn (dow) This document supersedes EN : A1:2009 and EN :2005. The most significant technical changes that have been made are: - EN takes into account distribution and transmission overhead lines by merging EN : A1:2009 and EN ; - EN is consistent with recent editions of Eurocodes; - one unique method is described concerning the determination of actions on line; - new design methods and new developments are included. EN is divided into the following parts: EN , Overhead electrical lines exceeding AC 1 kv Part 1: General requirements Common specifications EN , Overhead electrical lines exceeding AC 1 kv Part 2: National Normative Aspects Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.

18 EN : Introduction 0.1 Detailed structure of the standard The standard comprises two parts, numbered Part 1 and Part Part 1: General requirements - Common specifications This part, also referred to as the Main Body, includes clauses common to all countries. These clauses have been prepared by Working Groups and approved by CLC/TC 11. The Main Body is available in English, French and German. 0.3 Part 2: National Normative Aspects The index lists the existing National Normative Aspects (NNAs) related to the different countries; a NNA for a country is normative in that country and informative in other countries. The National Normative Aspects (NNAs) reflect national practices. They generally include A-deviations, special national conditions and national complements. 0.4 A-deviations A-deviations are required by existing national laws or regulations, which cannot be altered at the time of preparation of the standard. Reference is made to CENELEC Internal Regulations Part 2, definition Special national conditions (snc) Special national conditions are national characteristics or practices that cannot be changed even over a long period, e.g. those due to climatic conditions, earth resistivity, etc. Reference is made to CENELEC Internal Regulations, Part 2, definition National complements (NCPTs) National complements reflect national practices, which are neither A-deviations, nor special national conditions. It has been agreed within CLC/TC 11 that NCPTs should be gradually adapted to the Main Body, aiming at the usual EN standard structure including only a Main Body, A-deviations and special national conditions. 0.7 Language The NNAs are published in English and may be published additionally in the national language(s) of the respective country.

19 EN : Scope 1.1 General This European Standard applies to new overhead electric lines with nominal system voltages exceeding AC 1 kv and with rated frequencies below 100 Hz. The extent of the application of this standard by each country in respect of existing overhead lines is subject to the requirements of the National Normative Aspects (NNA) applicable to that country. The specific definition as to the meaning and extent of a new overhead line is to be identified by each National Committee (NC) within their own NNA. At the least, it shall mean a totally new line between two points, A and B. 1.2 Field of application This European Standard also applies to covered conductor overhead lines and overhead insulated cable systems with nominal system voltage exceeding AC 1 kv up to and including AC 45 kv and with rated frequencies below 100 Hz. Additional requirements and simplifications are specified that apply only for this voltage range. Design and construction of overhead lines with insulated conductors, where internal and external clearances can be smaller than specified in the standard, are not included for lines exceeding 45 kv. Other requirements of the Standard may be applicable, and where necessary NNAs should be consulted. This European Standard is applicable for optical Ground Wires (OPGWs) and optical Conductors (OPCONs). However the standard is not applicable to telecommunication systems which are used on overhead transmission lines either attached to the transmission line conductor/earth wire system (e.g. wraparound, etc.) or as separate cables supported by the transmission supports for example All Dielectric Self Supporting (ADSS) or for telecommunication equipment mounted on individual transmission line structures. When such cases are necessary, requirements can be given in the NNAs. This European Standard does not apply to: overhead electric lines inside closed electrical areas as defined in EN ; catenary systems of electrified railways, unless explicitly required by another standard. 1.3 Structure of the European Standard EN Normative references, definitions and symbols with their significations are listed in Clause 2 below. In Clause 3, the basis of design according to this standard is given. The standard specifies in Clauses 4 to 6 the general requirements that shall be met for the structural and electrical design of overhead lines to ensure that the line is suitable for its purpose with due consideration given to safety of public, construction, operation, maintenance and environmental issues. Clauses 7 to 11 of this standard consider the structural and electrical requirements that shall be met for the design, installation and testing of overhead line components including supports, foundations, conductors, insulator strings and hardware as determined by the relevant design parameters of the line. Finally, Clause 12 considers the quality assurance requirements during design, manufacturing and construction. Flowchart 1.1 summarises the structure of the European Standard EN , its Clauses 1 to 12 and its Annexes A to R.

20 EN : EN Scope 2 Normative references, definitions and symbols 3 Basis of design Requirements for overhead lines Requirements for line components Structural requirements 5 Electrical requirements 7 Supports 4 Actions on lines 6 Earthing systems 8 Foundations 12 Quality assurance, check and taking-over 9 Conductors 10 Insulators 11 Hardware Annexes A - D Annexes E - H Annexes J - R Flowchart 1.1 Structure of the European Standard EN Normative references, definitions and symbols 2.1 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

21 EN :2012 Eurocodes: Reference EN 1990:2002 EN :2005 EN :2005 EN :2004 EN :2005 EN :2006 EN :2006 EN :2005 EN :2006 EN :2006 EN :2004 EN :2004 EN :2007 Title Eurocode Basis of structural design Eurocode 1: Actions on structures Part 1-4: General actions Wind actions Eurocode 1 Actions on structures Part 1-6: General actions Actions during execution Eurocode 2: Design of concrete structures Part 1-1: General rules and rules for buildings Eurocode 3: Design of steel structures Part 1-1: General rules and rules for buildings Eurocode 3: Design of steel structures Part 1-3: General rules Supplementary rules for cold-formed members and sheeting Eurocode 3: Design of steel structures Part 1-5: Plated structural elements Eurocode 3: Design of steel structure Part 1-8: Design of joints Eurocode 3 Design of steel structures Part 1-11: Design of structures with tension components Eurocode 3 Design of steel structures Part 3-1: Towers, masts and chimneys Towers and masts Eurocode 5: Design of timber structures Part 1-1: General Common rules and rules for buildings Eurocode 7: Geotechnical design Part 1: General rules Eurocode 7: Geotechnical design Part 2: Ground investigation and testing EN :2005 Eurocode 8: Design of structures for earthquake resistance Part 6: Towers, masts and chimneys Other European Standards: Reference EN ISO 1461:2009 EN ISO 2063 Title Hot dip galvanized coatings on fabricated iron and steel articles Specifications and test methods (ISO 1461:2009) Thermal spraying Metallic and other inorganic coatings Zinc, aluminium and their alloys (ISO 2063) EN ISO 9001 Quality management systems Requirements (ISO 9001)

22 EN : Reference EN ISO (all parts) Title Zinc coatings Guidelines and recommendations for the protection against corrosion of iron and steel in structures (ISO 14713, all parts) EN Execution of steel structures and aluminium structures Part 1: Requirements for conformity assessment of structural components EN (all parts) EN EN EN 50182:2001 EN EN EN EN EN 50522:2010 EN Steel wire ropes Safety Precast concrete products Masts and poles Structural timber Wood poles for overhead lines Conductors for overhead lines Round wire concentric lay stranded conductors Conductors for overhead lines Aluminium-magnesium-silicon alloy wires Conductors for overhead lines Zinc coated steel wires Conductors for overhead lines Characteristics of greases Covered conductors for overhead lines and the related accessories for rated voltages above 1 kv a.c. and not exceeding 36 kv a.c. Part 1: Covered conductors Earthing of power installations exceeding 1 kv a.c. Specification for radio disturbance and immunity measuring apparatus and methods Part 1-1: Radio disturbance and immunity measuring apparatus Measuring apparatus EN CENELEC standard voltages (IEC 60038) EN Insulation co-ordination Part 1: Definitions, principles and rules (IEC ) EN :1997 Insulation co-ordination Part 2: Application guide (IEC :1996) EN EN EN Insulators for overhead lines with a nominal voltage above 1 kv Ceramic or glass insulator units for a.c. systems Characteristics of insulator units of the cap and pin type (IEC 60305) Locking devices for ball and socket couplings of string insulator units Dimensions and tests (IEC 60372) Insulators for overhead lines with a nominal voltage above 1 kv Part 1: Ceramic or glass insulator units for a.c. systems Definitions, test methods and acceptance criteria (IEC )

23 EN :2012 Reference EN EN Title Insulators for overhead lines with a nominal voltage above 1 kv Part 2: Insulator strings and insulator sets for a.c. systems Definitions, test methods and acceptance criteria (IEC ) Insulators for overhead lines with a nominal voltage above 1 kv Ceramic insulators for a.c. systems Characteristics of insulator units of the long rod type (IEC 60433) EN Radio interference tests on high-voltage insulators (IEC 60437) EN Artificial pollution tests on high-voltage insulators to be used on a.c. systems (IEC 60507) EN Loading tests on overhead line structures (IEC 60652) EN EN EN :2003 EN EN Optical fibre cables Part 1-1: Generic specification - General (IEC ) Optical fibre cables Part 1-2: Generic specification Basic optical cable test procedures (IEC ) Optical fibre cables Part 4: Sectional specification Aerial optical cables along electrical power lines (IEC ) Optical fibre cables Part 4-10: Aerial optical cables along electrical power lines Family specification for OPGW (Optical Ground Wires) (IEC ) Short circuit currents Calculation of effects Part 1: Definitions and calculation methods (IEC ) EN Hard-drawn aluminium wire for overhead line conductors (IEC 60889) EN EN EN Short circuit currents in three-phase a.c. systems Part 0: Calculation of currents (IEC ) Insulators for overhead lines Composite suspension and tension insulators for a.c. systems with a nominal voltage greater than 1 000V Definitions, test methods and acceptance criteria (IEC 61109) Insulators of ceramic material or glass for overhead lines with a nominal voltage greater than 1 000V Impulse puncture testing in air (IEC 61211) EN Aluminium-clad steel wires for electrical purposes (IEC 61232) EN Overhead lines Requirements and tests for fittings (IEC 61284) EN Insulators for overhead lines with a nominal voltage above 1 kv Ceramic or glass insulator units for d.c. systems Definitions, test methods and acceptance criteria (IEC 61325)

24 EN : Reference EN EN EN EN EN Title Overhead electrical conductors Creep test procedures for stranded conductors (IEC 61395) Composite string insulator units for overhead lines with a nominal voltage greater than 1 kv Part 1: Standard strength classes and end fittings (IEC ) Composite string insulator units for overhead lines with a nominal voltage greater than 1 kv Part 2: Dimensional and electrical characteristics (IEC ) Insulators for overhead lines Insulator strings and sets for lines with a nominal voltage greater than V AC power arc tests (IEC 61647) Live working Minimum approach distances for a.c. systems in the voltage range 72,5 kv to 800 kv A method of calculation (IEC 61472) EN Overhead lines Testing of foundations for structures (IEC 61773) EN Overhead lines Requirements and tests for spacers (IEC 61854) EN EN EN EN EN HD 474 S1 Overhead lines Requirements and tests for Stockbridge type aeolian vibration dampers (IEC 61897) Power installations exceeding 1 kv a.c. Part 1: Common rules (IEC ) Insulators for overhead lines Composite line post insulators for A.C. systems with a nominal voltage greater than 1 000V Definitions, test methods and acceptance criteria (IEC 61952) Thermal-resistant aluminium alloy wire for overhead line conductor (IEC 62004) Overhead electrical conductors Formed wire, concentric lay, stranded conductors (IEC 62219) Dimensions of ball and socket couplings of string insulator units (IEC 60120) Other publications: Reference Title ICAO Regulations-annex 14 Volume 1 Aerodrome Design and Operations Chapter 6 Visual aids for denoting obstacles IEC IEC International Electrotechnical Vocabulary. Switchgear, controlgear and fuses International Electrotechnical Vocabulary. Chapter 466: Overhead lines

25 EN :2012 Reference IEC IEC IEC IEC IEC IEC/TS :2005 IEC/TR IEC IEC IEC IEC/TS IEC/TS IEC/TS IEC IEC/TR IEC/TR ISO CISPR/TR 18-2 Title International Electrotechnical Vocabulary Part 471: Insulators International Electrotechnical Vocabulary. Chapter 601: Generation, transmission and distribution of electricity General International Electrotechnical Vocabulary. Chapter 604: Generation, transmission and distribution of electricity Operation Electric cables Calculation of the current rating Part 3-1: Sections on operating conditions Reference operating conditions and selection of cable type Dimensions of clevis and tongue couplings of string insulator units Effects of current on human beings and livestock Part 1: General aspects Thermal-mechanical performance test and mechanical performance test on string insulator units Characteristics of line post insulators Short-circuit temperature limits of electric cables with rated voltages of 1 kv (Um = 1,2 kv) and 3 kv (Um = 3,6 kv) Residual strength of string insulator units of glass or ceramic material for overhead lines after mechanical damage of the dielectric Selection and dimensioning of high-voltage insulators intended for use in polluted conditions Part 1: Definitions, information and general principles Selection and dimensioning of high-voltage insulators intended for use in polluted conditions Part 2: Ceramic and glass insulators for a.c. systems Selection and dimensioning of high-voltage insulators intended for use in polluted conditions Part 3: Polymer insulators for a.c. systems Design criteria of overhead transmission lines Overhead electrical conductors Calculation methods for stranded bare conductors Overhead lines Meteorological data for assessing climatic loads Atmospheric icing of structures Radio interference characteristics of overhead power lines and highvoltage equipment Part 2: Methods of measurement and procedure for determining limits

26 EN : Reference CISPR/TR 18-3 Title Radio interference characteristics of overhead power lines and high voltage equipment Part 3: Code of practice for minimizing the generation of radio noise 2.2 Definitions For the purposes of this European Standard, the terms and definitions given in the International Vocabulary (IEC 60050) Chapters 441, 466, 471, 601, 604, in the Eurocodes (EN 1990 to EN 1999) and the following apply action a) force (load) applied to the (mechanical) system (direct action) Note 1 to entry: An action can be permanent, variable or accidental. b) imposed or constrained deformation or imposed acceleration caused for example, by temperature changes, moisture variation, uneven settlement or earthquakes (indirect action) accidental action action, usually of short duration, which is unlikely to occur with a significant magnitude during the design working life Note 1 to entry: An accidental action can be expected in many cases to cause severe consequences unless special measures are taken anti-cascading tower tension or suspension tower specially designed with higher strength to avoid cascade failures and installed at a nominated frequency of towers to limit damage and permit quick restoration of failed towers and conductor(s) bonding conductor conductor providing equipotential bonding box values numerical values identified by Note 1 to entry: Other values may be specified by NCs in NNAs. box values are given as indication characteristic resistance value of mechanical resistance calculated using characteristic values of material properties and which may be obtained from EN , EN or EN characteristic value of a material property value of a material property which has a prescribed probability of not being attained in a hypothetical unlimited test series and which generally corresponds to a specified fraction of the assumed statistical distribution of the particular property of the material Note 1 to entry: A nominal value is used as the characteristic value in some circumstances characteristic value of an action principal representative value of an action which, insofar as this characteristic value can be fixed on statistical bases, is chosen so as to correspond to a prescribed probability of not being exceeded on the unfavourable side during a "reference period" taking into account the design working life of the system and the duration of the design situation

27 EN : clearance distance between two conductive parts along a string stretched the shortest way between these conductive parts [SOURCE: IEV ] coefficient of variation ratio of the standard deviation to the mean value combination of actions set of design values of actions used for the verification of the structural reliability for a limit state under the load case combination factor for an action factor used for the determination of the combination value for an action combination value for an action value which is associated with the use of combinations of actions to take account of a reduced probability of simultaneous occurrence of the most unfavourable values of several independent actions, and which is obtained by multiplying the characteristic value of an action by the combination factor for an action or, in special circumstances, by direct determination component one of the different principle parts of the overhead electrical line system having a specified purpose Note 1 to entry: Typical components are supports, foundations, conductors, insulator strings and hardware composite insulator insulator made of at least two insulating parts, namely a core and a housing equipped with end fittings Note 1 to entry: Composite insulators, can consist for example either of individual sheds mounted on the core, with or without an intermediate sheath, or alternatively, of a housing directly moulded or cast in one or several pieces onto the core conductor (of an overhead line) a wire or combination of wires not insulated from one another, suitable for carrying an electric current Note 1 to entry: One or more aluminium, aluminium alloy, copper, zinc coated or aluminium clad steel wires, or combinations thereof, wrapped together which collectively have the function of conducting an electric current. [SOURCE: IEV ] covered conductor conductor surrounded by a covering made of insulating material to protect against accidental contact between other covered conductors and with earthed parts Note 1 to entry: Due to being unscreened, covered conductors are not sufficiently insulated to be touch-proof overhead insulated cable system system in which each conductor is surrounded by a covering made of insulating material, which fully protects against all leakage currents phase to phase or to earthed parts Note 1 to entry: In the majority of cases, each phase conductor will have a core screen. EXAMPLE Examples of such overhead insulated cable system include: aerial bundled conductors (ABC); selfsupporting and lashed underground cable; and Universal cable systems corona luminous discharge due to ionisation of the air surrounding an electrode caused by a voltage gradient exceeding a certain critical value

28 EN : Note 1 to entry: Electrodes may be conductors, hardware, accessories or insulators current to earth current flowing to earth via the impedance to earth design resistance structural resistance associating all structural properties with the respective design value of the material properties design situation set of physical conditions representing a reference period for which the design will demonstrate that the relevant limit states are not exceeded design value of a material property value obtained by dividing the characteristic value of a material property by the partial factor for the material property or, in special circumstances, by direct determination design value of an action value obtained by multiplying the characteristic value of an action by the partial factor for an action design working life assumed period for which a structure is to be used for its intended purpose with anticipated maintenance but without substantial repair being necessary dynamic action action which causes significant acceleration of the structure or structural elements earth term for the earth as a location as well as for earth as a conductive mass, for example types of soil, humus, loam sand, gravel and stone earth electrode conductor which is embedded in the earth and conductively connected to the earth, or a conductor which is embedded in concrete, which is in contact with the earth via a large surface (for example foundation earth electrode) earth fault conductive connection caused by a fault between a phase conductor of the main circuit and earth or an earthed part. The conductive connection can also occur via an arc Note 1 to entry: Earth faults of two or several phase conductors of the same electrical system at different locations are designated as double or multiple earth faults earth fault current current which flows from the main circuit to earth or earthed parts if there is only one earth fault point at the fault location (earth fault location) earth potential rise voltage between an earthing system and reference earth

29 EN : earth rod earth electrode which is generally buried or driven in vertically to a greater depth, and which, for example, can consist of a pipe, round bar or other profile material earth surface potential voltage between a point on the earth surface and reference earth earthing all means and measures for making a proper conductive connection to earth earthing conductor conductor which connects that part of the installation which has to be earthed to an earth electrode as far as it is laid outside of the soil (earth wire) or buried in the soil earthing system locally limited electrical system of conductively connected earth electrodes or earthing conductors and of bonding conductors, or metal parts effective in the same way, for example tower footings, armourings, metal cable sheaths earth wire conductor connected to earth at some or all supports, which is suspended usually but not necessarily above the line conductors to provide a degree of protection against lightning strokes [SOURCE: IEV ] Note 1 to entry: An earth wire may also contain metallic wires for telecommunication purposes effective field strength square root of the sum of the squares of the three root mean square (r.m.s.) mutually perpendicular components of the field effect of action effect of actions on structural elements for example: internal force, moment, stress, and strain. The design value of the effect of action is the total effect of the respective design values of actions electric field constituent of an electromagnetic field which is characterised by the electric field strength E together with the electric flux density D [SOURCE: IEV ] element one of the different parts of a component Note 1 to entry: For example, the elements of a steel lattice tower are steel angles, plates and bolts equipotential bonding conductive connection between conductive parts, to reduce the potential differences between these parts exclusion limit probability of a variable value of a variable taken from its distribution function and corresponding to an assigned probability of not being exceeded

30 EN : external clearances all clearances which are not "internal clearances" and which include those to the ground plane, roads, buildings and installations (if they are permitted by National Statute) and to objects which can be on any of these failure (structural) state of a structure whose purpose is terminated, i.e. in which a component has failed by excessive deformation, loss of stability, overturning, collapse, rupture, buckling, etc fixed action action which has a fixed distribution over the structure such that the magnitude and direction of the action are determined unambiguously for the whole structure if this magnitude and direction are determined at one point on the structure foundation earth electrode conductor which is embedded in concrete and is in contact with the earth via a large surface free action action which may have any spatial distribution over the structure within given limits frequently occupied area area which people will occupy so frequently that risk of simultaneous earth fault shall be considered (examples: playgrounds, pavements of public roads, close vicinity of residences, etc.) Note 1 to entry: Utilities should define these areas glu-lam wood poles abbreviation for glued laminated wood poles and which as a term refers to wood poles manufactured from such glued laminations in contrast to naturally grown timber poles highest system voltage highest (r.m.s.) value of voltage which occurs at any time and at any point of the overhead line under normal operating conditions and for which the overhead electrical line shall be designed horizontal earth electrode electrode which is generally buried at a low depth and which, for example, can consist of strip, round bar or stranded conductor and can be carried out as radial, ring or mesh earth electrode or as a combination of these impedance to earth of an earthing system impedance between the earthing system and reference earth internal clearance clearance between phase conductors and earthed parts such as steel structural elements and earth wires and also those between phase conductors Note 1 to entry: Also included are clearances to other circuits on the same support limit state (structural) state beyond which the structure no longer satisfies the design performance requirements load arrangement identification of the position, magnitude and direction of a free action

31 EN : load case compatible load arrangements, sets of deformations and imperfections considered simultaneously with defined variable actions and permanent actions for a particular verification magnetic field constituent of an electromagnetic field which is characterised by the magnetic field strength H together with the magnetic flux density B [SOURCE: IEV ] magnetic flux density magnetic flux density, also known as the magnetic induction, is the force exerted on a charge moving in the field and has the unit tesla (T) Note 1 to entry: One tesla is equal to 1 Vs/m², or 1 weber per square metre (Wb/m²) maintenance total set of activities performed during the design working life of the system to maintain its purpose nominal system voltage voltage by which the overhead electrical line is designated and to which certain operating characteristics are referred optical conductor OPCON conductor containing optical telecommunication fibres optical groundwire OPGW optical conductor used solely as an earth wire Note 1 to entry: The conductor component may be stranded or may be tubular or a combination of both partial factor for an action factor depending on the selected reliability level, taking in account the possibility of unfavourable deviations from the characteristic value of actions, inaccurate modelling and uncertainties in the assessment of the effects of actions partial factor for a material property factor covering unfavourable deviations from the characteristic value of material properties, inaccuracies in applied conversion factors and uncertainties in the geometric properties and the resistance model permanent action action which is likely to be present throughout a given design situation and for which the variation in magnitude with time is negligible in relation to the mean value, or for which the variation is always in the same direction (monotonic) until the action attains a certain limit value potential grading influencing of the earth potential, especially the earth surface potential, by means of earth electrodes potential grading earth electrode conductor which due to shape and arrangement is principally used for potential grading rather than for establishing a certain resistance to earth

32 EN : Project Specification document which is supplied by the client to the contractor and containing adequate details of all the requirements for materials, design, manufacture and erection for a particular system or for a component of a line, which may supplement the requirements of the standard, but shall not relax their technological requirements, which shall not supersede the minimum requirements specified in this standard and which shall be reduced to a minimum for each project, i. e. to truly unique or specific details purpose function of the system (overhead electrical line), i.e. to transmit electrical power between its two ends, or of a part of the system quasi-static action dynamic action that can be described by static models in which the dynamic effects are included radio interference effect on the reception of a required radio signal due to an unwanted disturbance within the radiofrequency spectrum. Radio interference is primarily of concern for amplitude-modulated systems (AM radio and television video signals) since other forms of modulation, such as frequency modulation (FM) used for VHF radio broadcasting and television audio signals, are generally much less affected by disturbances that emanate from overhead lines reduction factor of a three phase line ratio, r, of the earth fault current (or earth return current) over the sum of the zero sequence currents in the phase conductors of the main circuit reference earth (remote earth) parts of the earth outside the influence area of an earth electrode or an earthing system, where, between any two points, no perceptible voltages due to the current to earth occur reference period period taking into account the design working life of the system or of one of its elements and/or of the characteristic value of an action reliability (electrical) ability of a system to meet its supply function under stated conditions for a given time interval reliability (structural) probability that a system performs a given purpose, under a set of conditions, during a reference period and that is thus a measure of the success of a system in accomplishing its purpose resistance (structural) mechanical property of a component, of a cross-section or of an element of a structure, e.g. bending resistance, buckling resistance. Resistance is the capacity to withstand collapse, or any other form of structural failure, which may endanger the safety of people or have a deleterious effect on the functioning of the system Note 1 to entry: Resistance against the following effects may require consideration: - loss of equilibrium of the structure or any part of it, considered as a rigid body, - failure by excessive deformation, rupture, or loss of stability of the structure or any part of it, including supports and foundations resistance to earth of an earth electrode electrical resistance of the earth between the earth electrode and the reference earth which, in practice, is a pure resistance

33 EN : return period mean interval between successive recurrencies of a climatic action of at least defined magnitude Note 1 to entry: The inverse of the return period gives the probability of exceeding the action in one year safety ability of a system not to cause human injuries or loss of lives during its construction, operation and maintenance security ability of a system which is to be protected from a major collapse (cascading effect) if a failure is triggered in a given component and which may be caused by electrical or structural factors serviceability limit state state beyond which specified service criteria for a structure or structural element are no longer met soil resistivity specific electrical resistance of the earth sparkover disruptive discharge static action action which does not cause significant acceleration of the structure or structural elements step voltage part of the earth potential rise which can be picked up by a person with a step-width of 1 m, i.e. the current flowing through the human body from foot to foot strength mechanical property of a material, usually given in units of stress structure organised combination of connected elements designed to provide some measure of rigidity support general term for different types of structure that support the conductors of the overhead electrical line support, angle suspension or tension support used at an angle point of a line support, section tension support with or without a line angle serving additionally as rigid point in a line support, suspension support equipped with suspension insulator sets support, tangent suspension or tension support used in straight line

34 EN : support, tension support equipped with tension insulator sets support, terminal (dead-end) tension support capable of carrying the total conductor tensile forces in one direction system (mechanical) set of components connected together to form an overhead electrical line system (electrical) all items of equipment which are used in combination for the generation, transmission and distribution of electricity system with isolated neutral system (electrical) in which the neutrals of transformers, generators and earthing transformers are not intentionally connected to earth, except for high impedance connections for signalling, measuring or protection purposes system with low-impedance neutral earthing system (electrical) in which at least one neutral of a transformer, earthing transformer or generator is earthed directly or via an impedance designed such that due to an earth fault at any location the magnitude of the fault current leads to a reliable automatic tripping system with low-impedance neutral or phase earthing system (electrical) with isolated neutral or resonant earthing, in which in case of a non-selfextinguishing earth fault a neutral or phase conductor of the main circuit is earthed directly or via low impedance a few seconds after the occurrence of an earth fault system with resonant earthing system (electrical) in which at least one neutral of a transformer or earthing transformer is earthed via an arc suppression coil and the combined inductance of all arc suppression coils is essentially tuned to the capacitance of the system to earth for the operating frequency television interference special case of radio interference for disturbances affecting the frequency ranges used for television broadcasting temporary line line that is installed for a short duration, no more than one year Note 1 to entry: Temporary lines can have the function of Emergency Restoration Systems touch voltage part of the earth potential rise across the human body from hand to feet (assumed to be at a horizontal distance of 1 m from the exposed part of the installation) transferred potential potential rise of an earthing system caused by a current to earth transferred by means of a connected conductor (for example cable metal sheath, pipeline, rail) into areas with low or no potential rise to reference earth

35 EN : ultimate limit state state associated with collapse, or with other forms of structural failure which may endanger the safety of people Note 1 to entry: It corresponds generally to the maximum load-carrying resistance of a structure or a structural element unavailability inability of a system to accomplish its purpose, and unavailability of an overhead electrical line that results from structural failure or insufficient electrical reliability as well as from failure due to other unforeseeable events such as landslides, impact of objects, sabotage, defects in material, etc unreliability (structural) complement to (structural) reliability or the probability of (structural) failure variable action action which is unlikely to act throughout a given design situation or for which the variation in magnitude with time is neither negligible in relation to mean value nor monotonic voltage difference voltage acting as a source voltage in the touching circuit with a limited value that guarantees the safety of a person when using additional known resistances (for example footwear or standing on surface insulating material) 2.3 Symbols Symbol Signification Reference A Accidental action A K Characteristic value of an accidental action A K Characteristic residual conductor tension A ins Projected area of an insulator set A m Effective area of a tower member A pol Projected area of a pole A t Effective area of the elements of a lattice tower panel face A tc Effective area of the elements of a lattice crossarm face A tn Effective area of the elements of lattice tower panel face, n A x Area of any line component, projected on a plane perpendicular to the wind direction a Spacing of two poles at half structure height a som Minimum discharge gap between live parts and earthed parts 5.5.3

36 EN : Symbol Signification Reference B 2 Background factor B I Reduction factor of wind velocity associated with icing b 1, b 2 Width of a lattice tower panel C Ic Drag factor for ice covered conductors C T Conversion factor for wind velocity or ice load C c Drag factor for conductors C ins Drag factor for insulator sets C m Drag factor for tower members C n Chord length of span n of a line section C pol Drag factor for poles C tc Drag factor for lattice crossarms in a wind perpendicular to the crossarm face C tn Drag factor for lattice tower panel face, n C x Drag factor (or force coefficient) for any line component c dir Wind directional factor c 0 Orography factor c season Seasonal coefficient D Equivalent diameter of ice covered conductor D el Minimum air clearance required to prevent a disruptive discharge between phase conductors and objects at earth potential during fast-front or slow-front overvoltages D pp Minimum air clearance required to prevent a disruptive discharge between phase conductors during fast-front or slow-front overvoltages D 50Hz_p_e Minimum air clearance required to prevent a disruptive discharge at power frequency voltage between a phase conductor and objects at earth potential 5.5.1

37 EN :2012 Symbol Signification Reference D 50Hz_p_p Minimum air clearance required to prevent a disruptive discharge at power frequency voltage between phase conductors d Diameter of a conductor d Clearance distance of the air gap necessary to obtain the required withstand voltage 5.3 d Distance from the top of a pole d m Average of the mean diameters from two separate poles E Electric field strength E d Total design value of the effect of actions F Action (force or imposed deformation) F K Characteristic value of an action F R,d Design load for the ultimate limit state F d Design value of an action F test, R Minimum test load G Permanent action G K Characteristic value of a permanent action G c Structural factor for conductors or span factor G ins Structural factor for insulator sets G m Structural factor for tower members G pol Structural factor for poles G t Structural factor for lattice towers G tc Structural factor for lattice cross-arms G x Structural factor for any line component H Reference altitude for determination of air density H Magnetic field strength

38 EN : Symbol Signification Reference H Total length of concrete pole H t Total height of a lattice tower h Reference height above ground I Ice load per conductor length I T Ice load per conductor length with return period, T I v Turbulence intensity I 3 Nominal (or high probability) ice load per conductor length with return period of 3 years I 50 Extreme (or low probability) ice load per conductor length with reference return period of 50 years K g Gap factor k a Atmospheric factor k p Peak factor k r Terrain factor L Turbulent length scale L Length of tower leg L R Ruling span L m Mean value of two adjacent span lengths L n Span length of span, n L wn Weight length of span, n n Number of variable Q Variable action Q I Vertical ice force on a support from each sub-conductor Q K Characteristic value of a variable action Q P Construction and maintenance load 4.9.1

39 EN :2012 Symbol Signification Reference Q WIc Wind force on ice covered conductor Q WK Characteristic value of a wind action Q WT Wind force with return period, T and a 10 minutes mean wind velocity for the determination of minimum air clearances Q Wc Wind force on conductor Q Wins Wind force on insulator set Q Wm Wind force on a tower member Q Wpol Wind force on a pole Q Wt Wind force on a lattice tower panel Q Wtc Wind force on a lattice crossarm Q Wx Wind force on any line component Q W3 Q W50 Nominal wind load with a 10 minutes mean wind velocity for the determination of minimum air clearances with return period of 3 years Extreme wind load with a 10 minutes mean wind velocity for the determination of minimum air clearances with reference return period of 50 years Q n Variable action, n Q nk Characteristic value of variable action, n Q 1 Dominant variable action q Ih Mean wind pressure associated with icing at reference height, h above ground q Ip Peak wind pressure associated with icing at reference height, h above ground q h Mean wind pressure at reference height, h above ground q p Peak wind pressure at reference height, h above ground R a Additional electrical resistance R b Backflashover rate 5.4.5

40 EN : Symbol Signification Reference R d Structural design resistance R sf Shielding failure flashover rate R 2 Resonance response factor Re Reynolds number r Reduction factor of a three phase line T Return period of a climatic action T n Return period of variable action, n T o Initial horizontal tension in a conductor T 1 Return period for a dominant variable action T Absolute temperature at a reference altitude, H t F Duration of the fault current U D Voltage difference acting as a source voltage in the touching circuit with a limited value that guarantees the safety of a person when using additional known resistances (e.g. footwear, standing surface insulating material) U E Earth potential rise U T Touch voltage U Tp Permissible touch voltage, i.e. the voltage across the human body U cw Co-ordination withstand voltage 5.3 U m Highest voltage for equipment U n Nominal system voltage 5.3 U rp Representative overvoltage 5.3 U rw Required withstand voltage 5.3 U s Highest system voltage V IH High probability wind velocity associated with icing 4.6.1

41 EN :2012 Symbol Signification Reference V IL Low probability wind velocity associated with icing V Ih Mean wind velocity associated with icing at a reference height, h above ground V T Wind velocity with return period, T V b,0 Basic wind velocity V h Mean wind velocity at reference height, h above ground V 3 Nominal wind velocity with return period of 3 years V 50 Extreme wind velocity with reference return period of 50 years X K Characteristic value of a material property X d Design value of a material property X nk Characteristic value of material property, n X nd Design value of material property, n z 0 Roughness length α Reduction factor for ice loads β Reduction factor for conductor tension γ Partial factor 4.13 γ A Partial factor for an accidental action γ F Partial factor for an action γ G Partial factor for a permanent action γ I Partial factor for an ice action γ M Partial factor for a material property γ P Partial factor for construction and maintenance loads 4.13 γ Pt Partial factor for action on prestressing force γ Q Partial factor for a variable action 3.6.2

42 EN : Symbol Signification Reference γ Q1 Partial factor for a dominant variable action γ W Partial factor for a wind action θ Angle of line direction change ν Kinematic viscosity of the air ρ Air density ρ E Resistivity of the ground near the surface ρ I Ice density ρ ' Air density corresponding to an absolute temperature, T and a reference altitude, H φ Angle between wind direction and the longitudinal axis of the cross-arm φ m Angle between the wind direction and the normal axis plane of member m χ Solidity ratio of a tower panel Ψ Combination factor for an action 4.13 Ψ I Combination factor for an ice action Ψ Q Combination factor for a variable action Ψ Qn Combination factor for variable action, n Ψ W Combination factor for a wind action

43 EN : Basis of design 3.1 Introduction This clause of the standard provides the basis and the general principles for the structural, geotechnical and mechanical design of overhead lines. The clause shall be read in conjunction with Eurocodes 1, 2, 3, 5, 7 and 8. The provisions in this standard supersede the corresponding clauses in the said Eurocodes. The general principles of structural design are based on the limit state concept used in conjunction with the partial factor method. Subclause 3.2 gives an overview of the general requirements for overhead lines, including the basic requirements regarding reliability, security and safety. The reliability levels for wind and ice actions correspond to a given theoretical return period of the climatic actions. Subclause 3.3 declares the distinction between ultimate and serviceability limit states. Subclause 3.4 distinguishes actions according they are permanent, variable or accidental. An action is defined as either a load or a deformation. Subclause 3.5 introduces the characteristic value for an action and for a material property. Subclause 3.6 shows how a design value for an action and for a material property can be developed by using the characteristic value in conjunction with a partial factor. Finally, subclause 3.7 provides the basic design formula following the partial factor method. The total design value of the effect of actions which occur simultaneously, as well as the corresponding structural design resistance, are given. These subclauses are valid for bare overhead lines exceeding AC 1 kv. They also apply to: covered conductor overhead lines; overhead insulated cable systems exceeding AC 1 kv up to and including AC 45 kv. Flowchart 3.1 summarises the structure of this Clause 3.

44 EN : Basic requirements of overhead lines Reliability level Security Safety Partial factor method 3.3 Limit states Partial factor, γ ULS SLS 3.4 Action, F 3.5 Characteristic value, F K Partial factor for actions, γ F Partial factor for material property γ M 3.5 Material property, X 3.5 Characteristic value, X K Design value of an action, F d = γ F F K Clause 4.13 Table 4.7 Clauses 7 to 11 & EC Design value of a material property, X d = X K/γ M Combination value Combination factor, Ψ Total design value of the effect of actions, E d Structural design resistance, R d Basic design equation E d R d Flowchart 3.1 Structure of Clause 3 on the Basis of Design 3.2 Requirements of overhead lines Basic requirements An overhead electrical line shall be designed and constructed in such a way that during its intended life: it shall perform its purpose under a defined set of conditions, with acceptable levels of reliability and in an economic manner. This refers to aspects of reliability requirements; it shall be designed to avoid a progressive collapse (cascading) if a failure is triggered in a defined component. This refers to aspects of security requirements; it shall be designed to avoid human injuries or loss of life during construction and maintenance. This refers to aspects of safety requirements.

45 EN :2012 An overhead line shall also be designed, constructed, and maintained in such a way that due regard is given to safety of the public, durability, robustness, maintainability, environmental considerations and appearance. The above requirements shall be met by appropriate design and detailing, by the choice of suitable materials and by specifying control procedures for design, manufacturing and construction relevant to the particular project. The selected design scenarios, represented by differing load cases, shall be sufficiently severe and varied as to encompass all conditions, which can reasonably be foreseen to occur during the construction and the design working life of the overhead line Reliability requirements The reliability level required for overhead lines, including all of its components and elements, is achieved by design according to this standard and Eurocodes 1, 2 3, 5, 7 and 8, and appropriate quality assurance measures. Three different reliability levels for overhead lines may generally be considered as defined in Table 3.1, each corresponding to a given theoretical return period T of the climatic actions. Reliability level Table 3.1 Reliability levels Theoretical return period T of climatic actions [Year] 1 (reference) Overhead line supports shall be classified as structures of class 1 according to EN 1990 for safety issues. These three reliability levels, used for service continuity issues, shall be considered as three sub-classes of class 1 according to EN Deviations from these levels may be made in accordance with the specific requirements for the project in question. However, the level selected shall at least correspond to reliability level 1 except for temporary constructions and for line components installed temporarily. An absolute reliability of an overhead line will generally be difficult to determine. Therefore, reliability level 1 can be regarded as a reference reliability level whereas the higher reliability levels are to be understood as relative to the reference one. Due to the lower height of lower voltage electrical overhead lines, the applied loadings on these structures will vary due to ground roughness, line height and accidental action factors (falling trees). These factors should be varied as the topography dictates, however minimum reliability level of the lines shall not be less than 1. NOTE 1 The relationship between reliability levels given in Table 3.1 and partial factors for actions given in 4.13, Table 4.7 are also explained in B.2 for wind velocities and in B.3 for ice loads. NOTE 2 For temporary lines, the return period of the climatic actions can be reduced due to the reduced design life exposure as indicated in the following table, which is an extract from EN : Table 3.2 Return period for temporary lines Duration Return periods (years) 3 days 2 3 months (but > 3 days) 5 1 year (but > 3 months) 10

46 EN : For lines installed less than 3 months, it is also possible to take seasonal or current climatic conditions into account: loading assumptions, based on statistical meteorological data, may be defined in the NNAs. For instance: - a seasonal coefficient c season, as defined in the National Annex of EN , may be used to reduce wind loads; - for seasons, where ice accretion does not occur, the ice load need not be considered. This period of the year should be defined in the NNAs, if relevant. If the extreme wind velocity for the reference 50 years return period, V 50, is known, the extreme wind velocity for a theoretical return period of T years, V T, can be determined by using the conversion factor, C T, as developed in Annex B.2 and Table B.1. For reduced return periods, the term nominal wind velocity is used. Similarly, if the extreme ice load per conductor length for the reference 50 years return period, I 50, is known, the extreme ice load per conductor length for a theoretical return period of T years, I T, can be determined by using the conversion factor, C T, as developed in Annex B.3 and Table B.2. For reduced return periods, the term nominal ice load is used. Reliability levels for wind and ice actions are given in the NNAs. It is important to note that increasing the reliability level is not the only way to improve continuity of service of an overhead line. The reference reliability level is generally regarded as providing an acceptable reliability level in respect of continuity of service and safety, but in fact a designer should also consider the following two aspects: Safety of the public: the reference return period of 50 years gives a high level of reliability. The probability of failure is acceptable in respect of public safety, because the combined probability resulting in human injury is very low. Moreover, as components are designed as complete systems rather than individually in isolation, and because they are usually designed prior to specific knowledge of the real line parameters (e.g. span length), the use factor has a positive influence on actual line reliability. Continuity of service: it is possible to increase the reliability by increasing the return period but it is not the only solution. It is also possible to increase the service life by creating redundancy, constructing other overhead lines, or having more lines radiating from substations thereby improving design by strength coordination, limiting damage, installing anti-cascading towers, and by setting an emergency restoration plan to repair damage very quickly. Overall costs are not only determined by the probability of failure, but mostly by the possible consequence of failure, including the uncontrollable propagation of failure and this may extend well beyond the initial failure. Such consequences can be reduced significantly by the following costeffective measures such as: strength coordination, design of supports to resist torsional and longitudinal security loadings, load control devices, de-icing methods, anti-cascading towers, and construction of other overhead lines, etc. (i.e. proactive solutions); emergency restoration structures, training of linemen, etc. (i.e. reactive solutions) Security requirements Security requirements correspond to special loads and/or measures intended to prevent uncontrollable progressive (or cascading) failures. Should a line fail either due to material defects, unforeseeable events (e.g. impact of an object, landslide, etc.) or an unusual climatic action, it is essential that the failure is contained within, or very close to, the line section where overloads, exceeding the strength of line components, have occurred. In order to prevent cascade failures, some simulated actions and loading condition provisions are detailed in 4.8. A higher level of security may be justified for some overhead lines either due to their importance in the network, or because they are subjected to severe climatic loads. In such cases, additional measures may be applied for increasing security according to experience and with reference to the type of line to be designed. Insertion of section supports at specified intervals may be adopted to limit a progressive collapse.

47 EN : Safety requirements Safety requirements are intended to ensure that construction and maintenance operations do not pose safety hazards to people. The safety requirements in this standard consist of special loads, as defined in 4.9, for which line components (mostly supports) have to be designed Strength coordination Regarding an overhead line as a system, requires coordination of the strength of its individual components. In this standard specific requirements for strength coordination are referred to in the NNAs. NOTE Strength coordination is in practice generally obtained by matching the partial factors and/or the loading cases. Annex A gives details of the concept of strength coordination based on IEC Additional considerations Consideration of an overhead line as an element in the environment shall take account of the environmental and legal situations existing in a particular region or country. Safety of human beings and protection of wild life and livestock, (e.g. birds, cattle, etc.) shall be properly considered. Specific requirements may be given in NNAs Design working life The design working life is the assumed period for which an overhead line is to be used for its intended purpose with anticipated maintenance but without substantial repair being necessary. The design working life of overhead lines is generally considered to be 50 years, unless otherwise defined in the Project Specification. NOTE The operating period will normally be in the range of 30 years to 80 years Durability The durability of a support, or part thereof, shall be such that it remains fit for use during its design working life assuming that it is given maintenance appropriate to the environment in which it is located. The environmental, atmospheric and climatic conditions shall be appraised at the design stage to assess their significance in relation to durability and to enable adequate provisions to be made for protection of the materials Quality assurance In order to provide an overhead line corresponding to the requirements and to the assumptions made in the design, appropriate quality assurance measures during design and construction shall be adopted. NOTE Quality assurance is described in EN ISO Limit states General Limit states are states beyond which the overhead line no longer satisfies the design performance requirements. Generally, a distinction is made between ultimate limit states and serviceability limit states Ultimate limit states Ultimate limit states are those associated with collapse or with other similar forms of structural failure due to excessive deformation, loss of stability, overturning, rupture, buckling, etc. A severe damage state prior to structural collapse, may for simplicity, be treated in the same manner as an ultimate limit state. Ultimate limit states concern the selected loading conditions determined by reliability, security and safety requirements, likely to affect the resistance of overhead line components such as supports, foundations, conductors, insulator strings and hardware.

48 EN : Serviceability limit states Serviceability limit states correspond to certain defined conditions beyond which specified service requirements for an overhead line are no longer met. Serviceability limit states, which may require consideration include: unacceptable frequency and duration of electrical flashovers, occurring either at the support or due to the proximity of conductors in mid span; excessive deformations and displacements of supports, which would affect the appearance or effective use of the supports or cause infringements of electrical clearance limits; levels of vibration, which would cause damage to conductors, supports or equipment or limit their functional effectiveness; damage to surface finishes or surface cracking of concrete, likely to affect the durability or the function of the supports, conductors, insulators and line accessories adversely. Reference should be made to NNAs and the Project Specification for recommendations on serviceability limit states and performance criteria. 3.4 Actions Principal classifications An action, F, is: a direct action, i.e. a force or a load applied to the overhead line components such as supports, foundations, conductors, insulator strings and hardware; an indirect action, i.e. an imposed or constrained deformation, caused, for example, by temperature changes, ground water variation or uneven settlement, if applicable. Actions are classified: by their variation in time (see 3.4.2); by their nature and/or the structural response (see 3.4.3) Classification of actions by their variation in time 1) permanent action, (G), i.e. self weight of supports including foundations, fittings and fixed equipment. Self-weight of conductors and the effects of the applicable conductor tension at the reference temperature, see Clause 4, as well as uneven settlements of supports are regarded as permanent actions. 2) variable actions, (Q), i.e. wind loads, ice loads or other imposed loads. Wind loads and ice loads as well as applicable temperatures are climatic conditions which can be assessed: - by applying the reliability concept; - or on a deterministic basis. Conductor tension effects due to wind and ice loads and temperature deviations from the reference temperature are variable actions. The vertical reaction from self-weight of the conductor at the support (in other words, the weight span) is affected by deviations from the reference state of the conductor tension due to conductor creep and temperature variations. As mentioned, this variation from the reference state is a variable action. Where critical for the design, and especially if no other climatic conditions are present, a partial factor on the conductor mass (or weight span) should be considered due to the uncertainty in such a variation (whether unfavourable or favourable). Imposed loads arising from conductor stringing, climbing on the structures, etc. are assessed on a deterministic basis and relate to the safety of construction personnel. 3) accidental actions, (A), i.e. failure containment loads, avalanches, etc. which relate to the security of the whole line.

49 EN : Classification of actions by their nature and/or the structural response 1) static actions, which do not cause significant acceleration of the components or elements; 2) dynamic actions, which cause significant acceleration of the components or elements. It is usually sufficient to consider the equivalent static effect of quasi-static actions, such as wind loads, in the design of overhead line supports (including foundations). Special attention shall be paid to extraordinarily tall and/or slender supports. 3.5 Characteristic values Characteristic value of an action Action (F) For an action, F, the characteristic value, F K, is the main representative value of F used for limit state verifications Permanent action (G) The characteristic value of a permanent action, G in the design of overhead lines can normally be determined as one value, G K, as the variability of G is very small Variable action (Q) For a variable action, Q, the characteristic value, Q K, corresponds to: either an upper value with an intended probability of not being exceeded (e.g. wind and ice loads) and in the case of, for example, temperatures, a lower value with an intended probability of not being lower, during a reference period of one year. In this standard a value of probability of 0,02 per year is assumed (i.e. a return period of 50 years); or a nominal value used for deterministic based actions Accidental action (A) For an accidental action, A, the representative value is generally a characteristic value, A K, corresponding to a specified value Characteristic value of a material property A material property, X is represented by a characteristic value, X K, which corresponds to that value of the material property having a prescribed probability of not being attained in a hypothetical unlimited test series. It generally corresponds for a particular material property to a specified exclusion limit of the assumed statistical distribution of that material property of the material as used in the system. A material property value shall normally be determined from standardised tests performed under specified conditions. A conversion factor shall be applied where it is necessary to convert the test results into values, which can be assumed to represent the behaviour of the material in the overhead line. In some circumstances a nominal value is used as the characteristic value. 3.6 Design values General Design values are generally obtained by using characteristic values in conjunction with partial factors, γ as defined in this standard and Eurocodes 2, 3, 5, 7 and 8. In some cases, it may be appropriate to determine design values directly. These values should be chosen cautiously and shall correspond to at least the same level of reliability for the various limit states as implied in the partial factors in this standard Design value of an action The design value of an action, F d, is expressed in general terms as F d = γ F F K

50 EN : The partial factor for an action, γ F, depends on the selected reliability level and takes account of the possibility of unfavourable deviations of the actions, inaccurate load modelling and uncertainties in the assessment of the effects of actions. NOTE 1 The design values of the different actions G, Q and A classified in are calculated as γ G G K, γ Q Q K and γ A A K, respectively. NOTE 2 Partial factors for actions are generally based on theoretical considerations, experience and calibration by retrospective calculations on existing designs. National values, stated by National Committees as required, appear in the NNAs or Project Specification. The selection of a reliability level leads to the choice of the partial factor recommended values given in 4.13, Table 4.7. Those partial factors are to be applied to the loads determined in Clause 4 from climatic actions based on a reference 50-year return period. When calculating the effect of the action on the conductor tension, the partial factors are applied to the characteristic values of the action, i.e. directly on the wind and/or ice action acting on the conductor. The computed value of the conductor tension is then the final design value. For deterministic calculations, including security and safety load conditions, the partial factor may, however, be applied to the action effect of the characteristic values of the actions, i.e. on the conductor tension, as specifically mentioned in Clause 4 regarding actions Design value of a material property The design value of a material property, X d, is generally defined as X d = X K / γ M The partial factor for a material property, γ M, covers unfavourable deviations from the characteristic value of the material property, X K, inaccuracies in applied conversion factors and uncertainties in the geometric properties and the resistance model. Partial factors for line components are specified in this standard. Partial factors stated in the Eurocodes 2, 3, 5, 7 and 8 generally apply, if not specifically amended in this standard or determined otherwise in the NNAs or Project Specification. Partial factors for a material property can also depend on the coordination of strength envisaged for the line Combination value of a variable action Combination values, Ψ are associated with the use of combinations of actions, to take account of a reduced probability of simultaneous occurrence of the most unfavourable values of several independent actions. The combination value of a variable action, Q is: generally represented as a product of a combination factor and a characteristic value, Ψ Q Q K ; or directly by an action with a reduced return period, Q (T); or may be directly specified in Clause 4. The combination value, (Ψ Q Q K ) is considered to be the design value. Where the occurrence of actions is correlated with each other, this is reflected in the combination factor. The combination factor recommended values are given in 4.13, Table 4.7. NOTE In this standard the combination factor for a variable action, Ψ Q, is principally derived on the basis of a reduced return period and, therefore, includes the partial factor used in the Eurocode format as well as any other reduction factors. 3.7 Partial factor method and design formula Partial factor method Calculations shall be performed using appropriate design models involving relevant variables. The models shall be appropriate to predict the structural behaviour and the limit states considered. Design models shall normally be based on established engineering theory and practice verified experimentally, if necessary.

51 EN :2012 In the partial factor method, it shall be verified that in all relevant design situations the limit states are not reached when design values for actions, material properties and geometrical data are used in the design models. In particular it shall be verified that: the effects of design actions do not exceed the design resistance of the overhead line at the ultimate limit state; the effects of design actions comply with the performance requirements of the overhead line for the serviceability limit state. Simplified verifications based on the limit state concept may be used by considering only limit states and load combinations which from experience are known to govern the design Basic design formula When considering a limit state of rupture or excessive deformation of a component, element or connection, it shall be verified that where E d R d E d is the total design value of the effect of actions, such as internal force or moment, or a representative vector of several internal forces or moments, see 3.7.3; R d is the corresponding structural design resistance, see Total design value of the effect of combined actions General Permanent actions, G, the values of variable actions, Q 1, Q 2, Q 3, etc. which occur simultaneously and accidental actions, A as relevant are combined in accordance with the design situation considered. For each critical load case, the total design value of the effect of combined actions, E d, shall be determined as given by Formulae (3.1) and (3.3) below. Alternative Formulae (3.2) and (3.4) apply when the variable actions, Q n are determined directly. In Formula (3.2) the dominant variable action, Q 1 with the return period, T 1 corresponding to the selected reliability level (e.g. 150 years) is combined with variable actions, Q n (n > 1), which have reduced return periods, T n (e.g. 3 years). In Formula (3.4) the accidental actions, A are combined with variable actions, Q n (n 1) which are present, and all of which have reduced return periods, T n. Imposed deformations shall be considered where relevant Design situations related to permanent and variable actions The total design value of the effect of permanent and variable actions is in symbolic forms: where E d = f {Σ γ G G K, γ Q1 Q 1K, Σ n>1 Ψ Qn Q nk } (3.1) E d = f {Σ γ G G K, Q 1 (T1), Σ n>1 Q n (Tn) } (3.2) γ Q1 Q 1K is the design value of the dominant variable action, i.e. normally either wind or ice; Ψ Qn Q nk is the combination value of other variable actions with reduced return periods, T n (n > 1) Design situations related to permanent, variable and accidental actions The total design value of the effect of permanent, variable and accidental actions is in symbolic forms: E d = f {Σ γ G G K, γ A A K, Σ n 1 Ψ Qn Q nk } (3.3) E d = f {Σ γ G G K, γ A A K, Σ n 1 Q n (Tn) } (3.4) where

52 EN : γ A A K is the design value of an accidental action; Ψ Qn Q nk is the combination value of variable actions with reduced return periods, T n (n 1) Structural design resistance The structural design resistance, R d, associating all structural properties with the respective design values, X nd, is as follows: R d = f {X 1d, X 2d,...} or alternatively as defined in each case, the respective characteristic values, X nk : R d = f {X 1K, X 2K,...} / γ M

53 EN : Actions on lines 4.1 Introduction The purpose of this clause is to give guidance on the calculation of all types of loads on overhead lines and their components. They include climatic loads such as wind, ice and combined wind and ice loads on conductors, insulator sets, lattice towers and poles. Each National Committee is responsible for providing climatic data in their NNA, which can be associated with the requirements of Clause 4. If the NNAs related to Clause 4 do not provide sufficient climatic data, the Project Specification shall include such data from available sources to determine a reliable design. In principle, there are three approaches to assess the climatic data to determine numerical values for actions. Approach 1: the first approach is based on the use of European or National standards which supply reference data such as basic wind velocity given in the EN National Annex and directly usable with Clause 4. Approach 2: the second approach is based on the use of sufficient statistical experimental data due to field observations. This data can then be converted into reference data to be used with Clause 4. Region or site specific issues shall be taken into account to obtain reliable data. Reference to Annex B or standards such as IEC 60826, may be useful to make the necessary conversion of the extreme wind velocity or extreme ice load associated to a reference 50 year return period, into another wind velocity or ice load associated to another return period T. Approach 3: the third approach is based on the use of data calibrated by a long and successful history in overhead line designing that can be found in national regulations, which have existed in some countries since about This data can be basic wind velocity, peak wind pressure, basic ice load, etc., but such data shall lead at least to a reliability level corresponding to level 1 as mentioned in Clause 3 (reference return period of 50 years). If necessary, partial factors given in 4.13 may be modified in the NNAs to obtain the desired reliability level when such empirical data is employed. As a countercheck with action values obtained with approach 3 data, comparison with action values obtained with approach 1 or approach 2 data may be carried out. Subclause 4.2 deals with permanent loads. Subclause 4.3 shows how wind forces acting on any overhead line component (4.3.5) can be determined by calculating respectively the basic wind velocity (4.3.1), the mean wind velocity (4.3.2), the mean wind pressure (4.3.3) and the peak wind pressure (4.3.4). Subclause 4.4 deals with wind forces on overhead line components, respectively on conductors (4.4.1), insulator sets (4.4.2), lattice towers (4.4.3) and poles (4.4.4). Subclauses 4.5 and 4.6 contain rules for determining ice loads and combined wind and ice loads on overhead line conductors. Subclauses 4.7 to 4.11 deal respectively with temperature effects on loads (4.7), security loads (4.8), safety loads (4.9), forces due to short-circuit currents (4.10) and other special forces (4.11). Finally, subclauses 4.12 and 4.13 provide the standard load cases as well as the partial factors and combination factors for actions in the ultimate limit state. Application examples of wind loads (4.3 and 4.4) are given in Annex C.1. Flowchart 4.1 summarises the structure of subclause 4.3 on wind loads.

54 EN : Three approaches to supply climatic data to determine numerical values for actions Approach 1: Reference data EN National Annex Approach 2: Statistical meteorological data: Wind velocity, V T Approach 3: Historical NNA: V b,0 or q p (h) B.2.1 Conversion factor, C T Basic wind velocity, V b,0 10 minutes mean wind velocity 10 m above ground level Terrain category II Return period T = 50 years Mean wind velocity, V h (h) Wind directional factor, c dir EN or NNA Orography factor, c o EN or NNA Roughness length, z 0 (Terrain category table 4.1) Reference height above ground, h Mean wind pressure, q h (h) Air density, ρ (Altitude H) Peak wind pressure, q p (h) Turbulence intensity, I v (h) NNA Wind force on any line component, Q Wx Drag factor, C x 4.4 Wind force on conductor Q Wc, insulator set, Q Wins, lattice tower panel, Q Wt and pole, Q Wp Structural factor, G x Area of line component, A x EN Flowchart 4.1 Structure of 4.3 on Wind Loads

55 EN : Permanent loads Self-weight of supports, insulator sets and other fixed equipment and of the conductors resulting from the adjacent spans act as permanent loads. Aircraft warning spheres and similar elements are to be considered as permanent dead loads. 4.3 Wind loads Field of application and basic wind velocity Subclause 4.3 contains rules for determining design wind loads acting on any overhead line component, based on meteorological data. These rules cover reference heights above ground (see 4.4) up to those as specified in the NNAs. If no requirements are stipulated in the NNA, 60 m is generally acceptable. The rules have been extracted from EN models (EUROCODE 1 Actions on structures general actions, wind actions) and defines the basic wind velocity (V b,0 ) as a 10 minutes mean wind velocity, irrespective of wind direction and time of year, at 10 m above ground level in open country with low vegetation, such as grass and isolated obstacles, and with a separation of at least 20 times obstacle heights. NOTE 1 This terrain corresponds to terrain category II in Table 4.1. This basic wind velocity, V b,0 is a characteristic value having an annual probability of exceedence of 0,02, which is equivalent to a mean return period of 50 years and may be detailed in EN National Annex. Different wind velocity values may be specified in the NNAs, but in these cases, they shall conform to the above basic wind velocity definition. Wind velocity fluctuation due to gusts is taken into account in the wind load design of this standard through the turbulence intensity (see 4.3.4). The rules given in 4.3 and 4.4 are not available for localised high intensity winds as tornadoes or downdrafts. NOTE 2 Information about such winds is available in CIGRE Technical Brochure n 350 "How overhead lines respond to localised high intensity winds Basic understanding". When EN National Annexes already specify peak wind pressures depending on height above ground, these values should be used directly as peak wind pressures q p to design overhead lines without applying subclauses to In these cases, reference shall be made to the NNAs, where such values shall be given Mean wind velocity Mean wind velocity,v h (h) depends on: basic wind velocity (V b,0 ) defined in 4.3.1; wind directional factor (c dir ); reference height above ground (h) of the line component to be studied (see 4.4); roughness length (z 0 ); orography factor (c o ). The value of the wind directional factor, c dir, for various wind directions may be specified in the NNAs. Values can be found in the EN National Annex. The recommended value is 1,0. The reference height above ground, h, that is necessary to be considered depends on the line component on which the wind load is applied. The choice of this reference height above ground is given for each component in 4.4, but the minimum value to be considered is 10 m. The roughness length, z 0, and the terrain factor, k r, which is directly linked to the roughness length, characterise the terrain roughness, which modifies mean wind velocity, V h (h) and turbulence intensity, I v (h). Values of z 0 and k r can be found in Table 4.1 below, in conformity with EN

56 EN : Table 4.1 Terrain categories, roughness length, z 0 and terrain factor, k r Terrain category z 0 [m] k r 0 Sea or coastal area exposed to the open sea 0,003 0,155 I II III IV Lakes or flat and horizontal area with negligible vegetation and without obstacles Area with low vegetation such as grass and isolated obstacles (trees, buildings) with separations of at least 20 times obstacle heights Area with regular cover of vegetation or buildings or with isolated obstacles with a separation of maximum 20 times obstacle heights (such as villages, suburban terrain, permanent forest) Area in which at least 15 % of the surface is covered with buildings which average height exceeds 15 m 0,01 0,169 0,05 0,189 0,3 0, ,233 NOTE The terrain categories are illustrated in EN :2005, A.1. Different terrain categories with different roughness length, z 0 may be specified in the NNAs. Terrain factor, k r can be determined for different roughness lengths, z 0 using expression: k r = 0,189 (z 0 / 0,05) 0,07 The effects of topography may be neglected when the average slope of the upwind terrain is small. In that case, the recommended value for the orography factor, c o is 1. Average slopes smaller than 5 % should be considered as small. Where topography (e.g. hills, cliffs etc.) increases wind velocities by more than 5 % the effects should be taken into account using the orography factor c o. The upwind terrain may be considered for a distance up to 10 times the reference height above ground, h of the component. The procedure to be used for determining c o may be given in the NNAs. A procedure is given in EN :2005, Annex A.3. Mean wind velocity, V h (h), in m/s at the reference height above ground, h is determined using expression: V h (h) = V b,0 c dir c o k r ln (h / z 0 ) For elements associated with structures with nominal voltage exceeding AC 1 kv up to and including AC 45 kv and with a maximum height of 20 m a constant value of the mean wind velocity calculated at 10 m height above ground, as noted above, is allowed. Specific regulations should be specified in the NNAs Mean wind pressure The mean wind pressure, q h (h), in N/m² at the reference height above ground h is determined using: q h (h) = ½ ρ V² h (h) ρ is the air density in kg/m 3, which depends on the altitude, temperature and barometric pressure to be expected in the region during windstorms. ρ is equal to 1,225 kg/m 3 at 15 C and atmospheric pressure of 1013 hpa. For other values of temperature and atmospheric pressure specified in the NNAs, the air density can be calculated or the relative values from Table 4.2 may be used. NOTE A conservative value is given for the air density in EN : ρ = 1,25 kg/m 3.

57 EN :2012 Table 4.2 Relative value of air density ρ as a function of altitude H and temperature T Temperature T NOTE Altitude H C 0 m 600 m m m ,18 1,10 1,02 0, ,13 1,05 0,97 0,91-5 1,08 1,00 0,93 0,87 5 1,04 0,96 0,90 0, ,00 0,93 0,86 0, ,96 0,89 0,83 0,77 The values in this table are derived from 288 ρ ' / ρ = e T ' 1,2 10 where ρ is the air density corresponding to an absolute temperature, T at an altitude, H, H is the reference altitude in m for determination of air density, T is the absolute temperature in degrees Kelvin at an altitude, H. Some countries, through long experience and thorough investigation, have found that certain values of the mean wind pressure are representative for their wind climate (Approach 3). In these cases, reference should be made to the NNAs, where such values are given Turbulence intensity and peak wind pressure The turbulence intensity, I v (h), at reference height above ground, h is defined as the standard deviation of the wind turbulence divided by the mean wind velocity. The rule for the determination of I v (h) are given in expression: I v (h) = 1 / [ c 0 ln (h / z 0 ) ] Roughness length, z 0 and orography factor, c 0 are determined in The peak wind pressure, q p (h), at reference height above ground, h, which takes into account turbulence intensity, I v (h), is given in expression: 4 q p (h) = [ I v (h) ] q h (h) Some countries, through long experience and thorough investigation, have found that certain values of the peak wind pressure are representative for their wind climate (Approach 3). In these cases, reference should be made to the NNAs, where such values are given Wind forces on any overhead line component The value of the wind force, Q Wx due to wind blowing horizontally at reference height above ground, h, perpendicular to any line component, is given by: where Q Wx = q p (h) G x C x A x q p (h) is the peak wind pressure given in 4.3.4; H h G x C x is the reference height above ground to be used for the structural line component being considered; is the structural factor for the structural line component being considered, calculated following the method given in EN ; NOTE 1 Symbol for G x is c s c d in EN is the drag factor (or force coefficient) depending on the shape of the line component being considered;

58 EN : A x is the area of the line component being considered, projected on a plane perpendicular to the wind direction. All those parameters are determined for each line component in the following subclauses. Alternative method (Approach 3). An alternative method, based on another expression of the peak wind pressure, may be specified in the NNAs. In that case, structural factors given in 4.4 do not apply. NOTE 2 A full example to help designers to understand clearly how to evaluate wind loads is given in C.1. The expression for the wind force above is valid for the reference return period of 50 years. For the determination of minimum air clearances in Clause 5, wind loads on the conductors and insulators have to be considered with a 10 minutes mean wind velocity (see 4.3.1). The expression for the extreme wind load with the reference return period of 50 years for minimum clearances, Q W50, can be obtained by multiplying the wind force Q Wx with the ratio of the mean wind pressure, q h (h) and the peak wind pressure, q p (h). Assuming a conservative value of G x = 1, we obtain: Q W50 = Q Wx (q h / q p ) = q h (h) C x A x Similarly, the expression for the nominal wind load with a return period of 3 years for minimum clearances, Q W3, can be obtained by multiplying the wind force, Q Wx with the ratio of the mean wind pressure, q h and the peak wind pressure, q p and with the ratio squared of the wind velocities, V 3 and V 50 with a return period of 3 and 50 years (see C² T in Annex B.2). Assuming a conservative value of G x = 1, we obtain: Q W3 = Q Wx (q h /q p ) (V 3 / V 50 ) 2 = q h (h) C x A x C 2 T 4.4 Wind forces on overhead line components Wind forces on conductors General Wind pressure on conductors causes forces transverse to the direction of the line as well as increased tensions in the conductors. The total wind force on the bundle of phase conductors is defined as the sum of the forces on the individual sub-conductors, without taking into account possible sheltering effects on leeward conductors. In general, the wind force on a support from each sub-conductor from the two adjacent spans is given as follows (see Figure 4.1.a): - in the direction of the cross-arm: Q Wc_V = q p (h) G c C c d ± L1 2 θ1 θ1 L2 2 θ 2 θ 2 cos φ + cos + cos φ cos perpendicular to the cross-arm: Q Wc_U = q p (h) G c C c d L ± cos 2 θ1 θ1 L2 φ + sin θ2 cos φ 2 2 sin θ where q p (h) is the peak wind pressure given in 4.3.4; h G c C c is the reference height to be used for the conductor; is the structural factor for the conductor (also termed span factor); is the drag factor (or force coefficient) for the conductor;

59 EN :2012 d L 1, L 2 φ θ 1, θ 2 is the diameter of the conductor; are the lengths of the two adjacent spans; is the angle between wind direction and the longitudinal axis of the cross-arm defined in Figure 4.1.a; (θ 1 + θ 2 ) / 2 = θ is the angle of line direction change defined in Figure 4.1.a. Figure 4.1.a Wind forces on conductors General case In case of a tangent support, the angle θ = θ 1 = θ 2 is zero. Therefore, and Q Wc_U = 0 Q Wc_V = q p (h) G c C c d cos²φ ( L 1 + L 2 ) / 2 When considering a wind direction along the bisector of the line deviation, the resulting wind force on an angle support from the two adjacent spans is (see Figure 4.1.b): Q Wc_V = q p (h) G c C c d cos 3 (θ/2) ( L 1 + L 2 ) / 2 and Q Wc_U = q p (h) G c C c d sin(θ/2) cos 2 (θ/2) ( L 1 - L 2 ) / 2 If L 1 = L 2 then Q Wc_U = 0 The formula assumes the same diameter, d of the conductors in adjacent spans. Otherwise, the formulae should be modified respectively.

60 EN : Figure 4.1.b Wind forces on conductors wind direction along the bisector of the line deviation The reference height above ground, h, to be considered for the calculation of wind forces on conductors shall be determined according to methods that shall be given in the NNAs. One of the nine following methods, dispatched from the less conservative proposal 1 and the most conservative proposal 9 in Table 4.3 may be used. Table 4.3 Determination of the reference height above ground, h of the conductors 9 methods Reference height above ground h of the conductor or earth wire Individual height, h i Mean weighted height, h w Mean arithmetical height, h a located at h = h i h = h w = i 1 n i 1 i n d i i d h i i h = h a = i 1 n i 1 i n h i i centre of gravity (1) attachment point at the insulator set attachment point of the insulator set at the support (1) located at the lower third of the sag of the conductor or earth wire in a vertical plan where h i h w h a is the reference height above ground of the centre of gravity of the conductor or appropriate attachment point of the conductor at the height level i; is the mean weighted height of all conductors; is the mean arithmetical height of all conductors; d i is the diameter of the conductor at the height level i; n i is the number of the conductors of the same diameter d i at the height level i; In the application example of Annex C.1.2 method 8 from Table 4.3 is used. The calculation for the mechanical tension in a section will take into account the effect of wind forces on the conductor, assuming constant values for conductor reference heights and for span lengths should be used. These values shall be specified in the NNAs. For the calculation of the conductor tension a reduction in the effect of the wind pressure due to the section length may be taken into account if the terrain conditions and the conductor height above ground remain the same. In such a case, a structural factor (span factor) based on the section length of the line can be applied Structural factor The structural factor, G c is given by the expression: G c = 1+ 2 k p I ( h) v 1+ 7 I v ( h) B² + R² where

61 EN :2012 k p is the peak factor defined as the ratio of the maximum value of the fluctuating part of the response to its standard deviation. Its recommended value is 3, but a different value may be specified in the NNAs; I v (h) is the turbulence intensity given in 4.3.4; B² is the background factor, allowing for the lack of full correlation of the pressure on the span; R² is the resonance response factor, allowing for turbulence in resonance with the vibration mode. The recommended value for R² is 0 because resonance in the wind direction can be neglected for a line conductor. Another value may be specified in the NNAs. The value of B² shall be determined from the expression of Annex C of EN :2005: B² = 1 3 L 1 + m 2 L( h) where L m is the mean value of the two adjacent span lengths: L m = (L 1 + L 2 ) / 2; L (h) is the turbulent length scale (average size of gust in m) at the reference height, h of the conductors, given by the expression of Annex B of EN :2005: L (h) = h ,67+ 0,05 ln ( z0 ) with z 0 the roughness length defined in Structural factor, G c for conductor is given, for the recommended values of this subclause, for differing reference heights and differing span lengths in Table 4.4 a, b, c, d and e (one table for each terrain category as defined in 4.3.2). Structural factor, G c for span lengths less than 100 m shall be assumed as equal to 100 m. Table 4.4.a G C values for terrain category 0 Reference height h for conductor [m] z 0 [m] L m [m] , ,78 0,80 0,81 0,82 0,83 0,83 0,84 0,84 0,85 0,85 0, ,73 0,75 0,76 0,77 0,78 0,79 0,79 0,80 0,80 0,80 0, ,70 0,72 0,73 0,74 0,75 0,76 0,76 0,77 0,77 0,78 0, ,68 0,70 0,71 0,72 0,73 0,74 0,74 0,75 0,75 0,76 0, ,67 0,69 0,70 0,71 0,72 0,72 0,73 0,73 0,74 0,74 0, ,66 0,68 0,69 0,70 0,71 0,71 0,72 0,72 0,73 0,73 0, ,65 0,67 0,68 0,69 0,70 0,70 0,71 0,71 0,72 0,72 0, ,64 0,66 0,67 0,68 0,69 0,70 0,70 0,71 0,71 0,71 0,72

62 EN : Table 4.4.b G C values for terrain category I Reference height h for conductor [m] z 0 [m] L m [m] , ,75 0,77 0,79 0,80 0,81 0,81 0,82 0,82 0,83 0,83 0, ,69 0,72 0,73 0,74 0,75 0,76 0,77 0,77 0,78 0,78 0, ,66 0,69 0,70 0,71 0,72 0,73 0,74 0,74 0,75 0,75 0, ,64 0,67 0,68 0,69 0,70 0,71 0,72 0,72 0,73 0,73 0, ,63 0,65 0,67 0,68 0,69 0,69 0,70 0,71 0,71 0,72 0, ,62 0,64 0,66 0,67 0,68 0,68 0,69 0,70 0,70 0,70 0, ,61 0,63 0,65 0,66 0,67 0,67 0,68 0,69 0,69 0,70 0, ,60 0,63 0,64 0,65 0,66 0,67 0,67 0,68 0,68 0,69 0,69 Table 4.4.c G C values for terrain category II Reference height h for conductor [m] z 0 [m] L m [m] , ,70 0,73 0,74 0,76 0,77 0,78 0,79 0,79 0,80 0,80 0, ,63 0,66 0,68 0,70 0,71 0,72 0,73 0,74 0,74 0,75 0, ,60 0,63 0,65 0,67 0,68 0,69 0,70 0,70 0,71 0,72 0, ,58 0,61 0,63 0,64 0,66 0,66 0,67 0,68 0,69 0,69 0, ,57 0,59 0,61 0,63 0,64 0,65 0,66 0,66 0,67 0,68 0, ,56 0,58 0,60 0,61 0,63 0,64 0,64 0,65 0,66 0,66 0, ,55 0,57 0,59 0,61 0,62 0,63 0,63 0,64 0,65 0,65 0, ,54 0,57 0,58 0,60 0,61 0,62 0,63 0,63 0,64 0,64 0,65 Table 4.4.d G C values for terrain category III Reference height h for conductor [m] z 0 [m] L m [m] , ,62 0,66 0,68 0,70 0,72 0,73 0,74 0,75 0,76 0,77 0, ,55 0,59 0,61 0,63 0,65 0,66 0,67 0,68 0,69 0,70 0, ,51 0,55 0,58 0,60 0,61 0,63 0,64 0,65 0,66 0,66 0, ,49 0,53 0,55 0,57 0,59 0,60 0,61 0,62 0,63 0,64 0, ,47 0,51 0,54 0,55 0,57 0,58 0,59 0,60 0,61 0,62 0, ,46 0,50 0,52 0,54 0,56 0,57 0,58 0,59 0,60 0,61 0, ,45 0,49 0,51 0,53 0,55 0,56 0,57 0,58 0,59 0,59 0, ,45 0,48 0,50 0,52 0,54 0,55 0,56 0,57 0,58 0,58 0,59

63 EN :2012 Table 4.4.e G C values for terrain category IV Reference height h for conductor [m] z 0 [m] L m [m] , ,54 0,59 0,63 0,65 0,67 0,69 0,70 0,71 0,72 0,73 0, ,47 0,52 0,55 0,58 0,60 0,61 0,63 0,64 0,65 0,66 0, ,43 0,48 0,51 0,54 0,56 0,57 0,59 0,60 0,61 0,62 0, ,41 0,45 0,49 0,51 0,53 0,55 0,56 0,57 0,58 0,59 0, ,39 0,44 0,47 0,49 0,51 0,53 0,54 0,55 0,56 0,57 0, ,38 0,42 0,45 0,48 0,50 0,51 0,52 0,54 0,55 0,56 0, ,37 0,41 0,44 0,47 0,48 0,50 0,51 0,52 0,53 0,54 0, ,36 0,41 0,43 0,46 0,47 0,49 0,50 0,51 0,52 0,53 0, Drag factor The drag factor, C C for the conductor can be determined using one of the following methods: Method 1: the drag factor is 1 for the generally considered stranded conductors and wind velocities, Method 2: the drag factor is derived from wind tunnel tests, Method 3: the drag factor is evaluated according to the following EN method: Reynolds number Re C C = 1,2 Reynolds number Re 10 5 C C = 0,9 For intermediate values of Re, C C should be obtained by linear interpolation. NOTE Reynolds number, Re is given by expression: Re = with V ( h) ν d V (h) = 2 ( h) q p as defined in EN ρ and where d ν is the diameter of the conductor; is the kinematic viscosity of the air (recommended value: ν = m²/s); ρ is defined in 4.3.3; q p is defined in The method to be used shall be specified in the NNAs Wind forces on insulator sets Wind forces on insulator sets result from wind forces on the conductors as well as from wind pressure on the insulators themselves. Wind forces due to wind pressure on the insulator sets themselves may be neglected for the design of supports, but the NNAs may nonetheless indicate this be taken into account. In that case, wind force acting in the wind direction at each attachment point on the support is given by the expression:

64 EN : where Q Wins = q p (h) G ins C ins A ins q p (h) is the peak wind pressure given in 4.3.4; h G ins C ins A ins is the reference height above ground to be used for the insulator set which is the height of the attachment point in the support. Another reference height may be specified in the NNAs; is the structural factor for the insulator set. The recommended value is 1, but another value may be specified in the NNAs; is the drag factor for the insulator set. The recommended value is 1,2, but another value may be specified in the NNAs; is the area of the insulator set projected horizontally on a vertical plane parallel to the axis of the string Wind forces on lattice towers General Wind forces on lattice towers result from forces transferred from conductors and insulators as well as wind pressures directly on the tower itself. Wind forces on the tower itself can be determined by one of the following methods: Method 1: the tower is divided into sections. The drag factor is linked to the frames of the tower sections, taking into account a sheltering effect of windward frames on leeward frames. Method 2: each individual member of the tower considered. The drag factor is linked to the members of the tower without taking into account any sheltering effect. This method is recommended for irregular tower geometries, especially for cross-arms. The method to be used shall be specified in the NNAs. The reference height above ground, h to be considered for the calculation of wind forces on lattice towers shall be determined according to methods that shall be given in the NNAs. One of the following methods may be used: The tower is considered as a vertical structure such as buildings as defined in EN and the unique reference height for each tower section or each tower member corresponds to a percentage of the total height of the tower. Recommended value is 60% but another value may be specified in the NNAs. Reference height of each tower section or each tower member is the height above ground of the geometrical centre of the tower section or the tower member being considered. NOTE For towers with triangular cross-section and/or for tower with circular elements, alternative methods to determine wind loads can be found in EN Method 1 For lattice towers of rectangular cross-sections, the wind force is acting at the centre of gravity of each tower section. The force component, Q Wt acting in the wind direction is given by the following expression. The force component transverse to the wind direction may be neglected: where Q Wt = q p (h) G t (1 + 0,2 sin²2φ) (C t1 A t1 cos²φ + C t2 A t2 sin²φ) q p (h) is the peak wind pressure given in 4.3.4; h is the reference height above ground to be taken into account for the lattice tower section being considered;

65 EN :2012 G t is the structural factor for lattice tower. The recommended value is 1, but another value may be specified in the NNAs; G t may be calculated as follows if the recommended conservative value of 1 is not required: with: G t = 1+ 6 Iv ( h) B² 1+ 7 I ( h) v B² = 1 3 H 1 + t 2 L ( h) H t is the total height of the tower; L (h) is defined in These formulae are based on EN :2005, Annex C and give values of G t smaller than 0,9. C t1, C t2 is the drag factor for lattice tower panel face 1 (respectively face 2) of the section being considered in a wind perpendicular to this panel; A t1, A t2 is the effective area of the elements of lattice tower panel face 1 (respectively face 2) of the section being considered; φ is the angle between wind direction and the longitudinal axis of the lattice cross-arm. Figure 4.2 illustrates the definitions of lattice tower panel face, effective area, angle of wind direction and solidity ratio, χ. For lattice cross-arms, the wind force can be estimated as follows: where Q Wtc = q p (h) G tc A tc (sinφ + 0,4 cosφ) q p (h) is the peak wind pressure given in 4.3.4; h G tc C tc A tc φ is the reference height above ground to be considered for the lattice cross-arm; is the structural factor for lattice cross-arms. The recommended value is 1, but another value may be specified in the NNAs; is the drag factor for the lattice cross-arm face in a wind perpendicular to the longitudinal axis of the cross-arm; is the effective area of the elements of the lattice cross-arm face exposed to the wind; is the angle between wind direction and the longitudinal axis of the lattice cross-arm. Figure 4.2 illustrates the definitions of lattice cross-arm panel face, effective area, angle of wind direction and solidity ratio, χ.

66 EN : Figure 4.2 Definitions of tower panel face, cross-arm and solidity ratio, χ The drag factor, C t1 (respectively C t2 and C tc ) is determined according to the solidity ratio, χ defined in Figure 4.2 and given by the following expression from EN : Values of the drag factor are given in Figure 4.3. C t1 (respectively C t2 and C tc ) = 3,96 (1 1,5 χ + χ²) C t1 C t2 χ Solidity ratio Figure 4.3 Drag factor for a rectangular tower composed of flat sided members

67 EN : Method 2 For each member of the tower, the wind force is perpendicular to the member axis and in the plane formed by this axis and the wind velocity direction. Wind force is given by the expression: where Q Wm = q p (h) G m C m A m cos 2 φ m q p (h) is the peak wind pressure given in 4.3.4; h G m is the reference height above ground to be considered for each individual tower member; is the structural factor for each tower member. The recommended conservative value is 1, but another value may be specified in the NNAs; G m may be calculated as follows if the recommended conservative value of 1 is not required: G m = 1+ 6 Iv ( h) B² 1+ 7 I ( h) v with: B² = 1 3 H 1 + t 2 L ( h) H t is the total height of the tower; L (h) is defined in Those formulae are based on EN :2005, Annex C and give values of G m smaller than 0,9. C m is the drag factor for each tower member. The recommended conservative value is 1,6 for an angle member but another value may be specified in the NNAs; 1,6 is a conservative value, especially for the upper part of the tower where the sheltering effect of windward frames (cross-arms) on leeward frames may not be neglected; A m φ m is the effective area of the tower member being considered and is equal to its length multiplied by its width; is the angle between the wind direction and the normal axis plane of the tower member being considered. Different expressions for the wind forces on tower members may be specified in the NNA.

68 EN : Wind forces on poles Wind forces on poles (steel, concrete, wood, etc.) result from wind forces on the conductors and the insulators, as well as wind pressure on the pole itself. The reference height to take into account to evaluate wind forces on poles can be determined by one of the two following methods: Method 1: the pole is divided into sections and the reference height of each section is the height above ground of the geometrical centre of the section being considered; Method 2: the pole is considered as a vertical structure and the reference height is a percentage of the total height of the pole. The recommended value is 60% but another value may be specified in the NNAs. The method to be used shall be specified in the NNAs. Wind force on the pole itself perpendicular to the wind direction, can be determined by expression: where Q Wpol = q p (h) G pol C pol A pol q p (h) is the peak wind pressure given in 4.3.4; h G pol C pol A pol is the reference height above ground of the pole; is the structural factor for the pole. The recommended value is 1, but another value may be specified in the NNAs; is the drag factor for the pole; is the projected area of the pole, or section of the pole, on a vertical plan perpendicular to the wind direction. The following are representative drag factors, C pol, based on EN and taking into account an end-effect factor, (Ψ λ ) equals to 0,9 for a slenderness, (λ) equals to 60. steel, concrete, composite or glulam wood poles with: sharp edge cross section 1,8 hexagonal (six-sided) cross section 1,4 octagonal or decagonal (eight or ten-sided) cross section 1,2 dodecagonal (twelve-sided) cross section 1,0 hex-decagonal (sixteen-sided) cross section 0,7 circular cross section 0,7 wood poles (naturally grown timber) with circular cross-section 0,9 double and A-shaped wood poles with circular cross-section (naturally grown timber) in the plane of the pole, that part of the pole exposed to the wind 0,9 in the plane of the pole, leeward pole of the structure for a < 2 d m 0 for 2 d m a 6 d m 0,35 for a > 6 d m 0,7 perpendicular to the plane of the pole for a < 2 d m 0,9 where a d m is the spacing of the two poles at half structure height; is the average of the mean diameters from two separate poles.

69 EN :2012 Other values may be specified in the NNAs. For a greater degree of accuracy, particularly for rectangular profile poles, reference shall be made to EN Ice loads General This subclause gives rules for establishing forces on conductors from ice loads, Q I. As far as applicable, they can also be used for guy wires, etc. There are two main types of atmospheric ice depending on the process of formation: precipitation ice, which can be wet snow or glaze ice; in-cloud ice, which can be soft or hard rime. NOTE 1 Detailed descriptions of the meteorological conditions regarding ice loads are given in IEC and ISO In areas where both types can occur, it is often difficult to distinguish between them. This is particularly the case in mountainous regions, where the most serious icing events often are a combination of the two types. For the two main types mentioned above, the statistical methods, which are described in this clause, may be used independently. When determining the design values of ice actions, the influence of the terrain shall also be considered when necessary. It is not possible to provide simple and general rules for the terrain effects, but guidance on the influence of local topography for the two main types of atmospheric icing, as well as the influence on the height above terrain, can be found in the IEC or ISO standards mentioned above. If there are differing climatic and atmospheric conditions along the overhead line, it shall be divided into zones. In most countries, statistical ice data is often poor. Therefore, ice loads often have to be specified based directly on experience or on long-term applications with positive results. Annex B gives guidelines for the statistical evaluation of ice load data for determination of the extreme ice load. IEC and ISO give guidelines for collecting statistical ice data. It may be practical to use the ice classes (IC) of ISO to define the characteristic values of ice loads. With regard to wet snow, the thickness of icing may be considered the same on conductors and earthwires unless service experience indicates otherwise. Ice loads on other components can be derived from the loadings on conductors, but are not treated especially in this standard. NOTE 2 ISO gives guidelines for evaluating these loads Ice forces on conductors Ice loads on conductors cause vertical forces as well as increased tensions in the conductors. From the two adjacent spans, the vertical ice force on a support from each sub-conductor is: where Q I = I (L w1 + L w2 ) I L w1 and L w2 is the ice load per length of the conductor (N/m); are the weight spans of the two adjacent spans. The weight lengths of two adjacent spans, L w1 and L w2 depend on the sag of the ice covered conductor and the horizontal and vertical distances between their attachment points.

70 EN : Combined wind and ice loads Combined probabilities Only combined wind and ice loads on conductors are considered in this standard. Wind loads on ice covered supports and insulators may be treated similarly when appropriate drag factors are used. NOTE ISO gives guidelines for evaluating those loads. The effect of wind force on an ice covered conductor is determined by three variables: the wind velocity during the period of time that the conductor is ice covered; the mass of the ice layer; the shape of the ice layer, i.e. the equivalent diameter and the relevant drag factor. In this standard a simplified method is used to determine this effect, taking into account two main combinations: an extreme (or low probability) ice load, I T combined with a high probability wind velocity, V IH (described in ); a nominal (or high probability) ice load, I 3 combined with a low probability wind velocity, V IL (described in ). Load combinations and combination factors are given in the NNA, which may include lower wind velocities in accordance with the experience in each country. In respect of lines exceeding nominal system voltage AC 1 kv up to and including AC 45 kv, all scenarios of combined wind and ice loads shall be considered, unless otherwise specified in the NNA. The wind velocity according to the different combinations occurs in each case simultaneously with the vertical load due to actual ice load. Flowchart 4.2 summarises the structure of Subclause 4.6 on combined wind and ice loads.

71 EN :2012 B.4 Basic ice load, I b 4.6 Combined wind and ice loads 4.3 Basic wind velocity V b,0 B.3 Extreme ice load per length, I 50 B.2 Extreme wind velocity, V Extreme ice load, I T = γ I I Combination 1 of wind and ice loads High probability wind velocity, V IH = V 3 B I or V 50 Ψ W Nominal ice load, I 3 = Ψ I I Combination 2 of wind and ice loads Low probability wind velocity, V IL = V T B I = V 50 B I γ W Equivalent diameter of ice covered conductor, D Conductor diameter, d Mean wind velocity associated with icing, V Ih Ice density, ρ I Air density, ρ Mean wind pressure, q Ih Ice type Turbulence intensity, I v Peak wind pressure, q Ip Drag factor according to the ice type, C Ic Structural factor, G c Angle of wind direction, φ Line angle, θ Sag of the ice covered conductors Level difference between the attachment points Weight spans of two adjacent spans, L w1, L w2 Span lengths of two adjacent spans, L 1, L Vertical force on support due to ice covered conductors, Q I = I (L w1 + L w2) Horizontal force on support due to wind on ice covered conductors, Q WIc = q Ip G c C Ic D L(φ, θ) Flowchart 4.2 Structure of Subclause 4.6 on combined wind and ice loads Drag factors and ice densities Table 4.5 gives indicative values for the density of various ice types appropriate to a range of drag factor values. Alternatively, values may be defined in the NNAs. NOTE The values of Table 4.5 are well correlated to the simplified design methods proposed by this standard. If required, ISO gives guidelines to determine more precise values.

72 EN : Table 4.5 Drag factors C Ic and ice density ρ I (kg/m 3 ) for various ice types Ice type Wet snow Glaze ice Soft rime ice Hard rime ice C Ic 1,0 1,0 1,2 1,1 ρ I Mean wind pressure and peak wind pressure The mean wind pressure, q Ih (h) (in N/m²), associated with icing is calculated as in 4.3.3: where q Ih (h) = ½ ρ V² Ih (h) ρ is the air density in kg/m 3 (see 4.3.3); V Ih (h) is the mean wind velocity at a reference height, h above ground according to the actual combination as specified in The peak wind pressure, q Ip (h) at a height h above ground is calculated as in 4.3.4: where q Ip (h) = [ I v (h) ] q Ih (h) q Ih (h) is the mean wind pressure (see above); I v (h) is the turbulence intensity (see 4.3.4) Equivalent diameter D of ice covered conductor Even if the shape of the ice deposit is rather irregular, it is assumed in this standard as an equivalent cylindrical shape with diameter, D: D = d I 9,81 π ρ I where d I ρ I is the conductor diameter (m); is the ice load per length of the conductor (N/m) according to the actual combination as specified in 4.6.1; is the ice density according to type of ice deposit (kg/m³) and drag factor (see Table 4.5) Wind forces on support for ice covered conductors The wind force on ice covered conductors is analogous to that detailed in and is expressed: - in the direction of the cross-arm: Q WIc_V = q Ip (h) G c C Ic D L ± cos 2 θ1 θ1 L2 φ + cos θ2 2 cos φ cos θ - perpendicular to the cross-arm: Q WIc_U = q Ip (h) G c C Ic D L ± cos 2 θ1 θ1 L2 φ + sin θ2 cos φ 2 2 sin θ

73 EN :2012 where q Ip (h) is the peak wind pressure given in 4.6.3; h is the reference height to be used for the conductor; G c is the structural factor for the conductor (see ); C Ic is the drag factor for ice-covered conductors given in 4.6.2; D is the equivalent diameter of ice-covered conductor given in 4.6.4; L 1, L 2 φ θ 1, θ 2 are the lengths of the two adjacent spans; is the angle between wind direction and the longitudinal axis of the cross-arm defined in Figure 4.1.a; (θ 1 + θ 2 ) / 2 = θ is the angle of line direction change defined in Figure 4.1.a. NOTE For load combinations with nominal wind velocities, the values used for G c are conservative. For the calculation of the conductor tension, a reduction in the effect of the wind pressure due to the section length may be taken into account if the terrain conditions and the conductor height above ground remain the same. In such a case, a span factor based on the section length of the line can be applied Combination of wind velocities and ice loads Extreme ice load I T combined with a high probability wind velocity V IH The extreme (or low probability) ice load, I T with a theoretical return period of T years is defined in B.3 or is found as: where I T = γ I I 50 γ I is the partial factor for ice loads. Associated with icing, the high probability wind velocity, V IH is equal to V 3 with a theoretical return period of T = 3 years as given in B.2 and is further multiplied with a reduction factor, B I : or is found as: V IH = V 3 B I where V IH = V 50 Ψ W Ψ W is the combination factor for wind loads. Ψ W includes the effect of the reduction factor, B I. The reduction factor, B I depends on the type of ice. For wet snow, B I is equal to 0,7 and for in-cloud icing is equal to 0,85. Accordingly, a representative value of the combination factor for wind action, Ψ W, equal to 0,4 has been entered in Table Nominal ice load I 3 combined with a low probability wind velocity V IL The nominal (or high probability) ice load, I 3 with a theoretical return period of 3 years is defined in B.3 or is found as: where I 3 = Ψ I I 50 Ψ I is the combination factor for ice loads.

74 EN : Associated with icing, the low probability wind velocity, V IL is determined as the extreme wind velocity, V T with return period, T years given in B.2, and is further multiplied by the reduction factor, B I given in above, or is found as: where V IL = V T B I = (V 50 γ W ) B I γ W is the partial factor for wind loads. NOTE 1 The values of combination factors are well correlated to the simplified design methods proposed by this standard. NOTE 2 ISO gives guidelines for an alternative method with a reduction factor k to be applied to the wind load. NOTE 3 A further simplification can be made by countries which have experience that one or two of the above mentioned combinations are never critical. In some countries it can also be necessary to investigate the possibility of high probability wind velocity, V IH and nominal ice load, I 3 combined with extreme values of the drag factor and low ice densities. The design approach which uses a three year return period load for one meteorological parameter associated with another extreme parameter presupposes that the ice and wind phenomena are occurring independently. If available statistics show otherwise in a given region, modified combination factors, based on statistics, should be used even if they are lower than specified. 4.7 Temperature effects For overhead lines exceeding a nominal system voltage of AC 45 kv, temperature effects in five different design situations may generally apply as described below. They will depend on other climatic actions that may be present: a) a minimum temperature to be considered with no other climatic action, if this is relevant; b) a normal ambient reference temperature assumed for the extreme wind velocity condition; c) a nominal wind velocity combined with a minimum temperature condition to be considered, if relevant; d) a temperature to be assumed with icing. For both of the main types of icing (precipitation icing and in cloud icing) a temperature of 0 C may be used, unless otherwise specified. A lower temperature should be taken into account in regions where the temperature often drops significantly after a snowfall; e) a temperature to be used for the combination of wind and ice. It is expected that lower minimum temperatures will be applicable for the longer return periods, T indicated in Table 3.1. The relevant temperatures and associated design situations are given in the NNAs. 4.8 Security loads General Security loads in this standard are specified to give minimum requirements on the torsional and longitudinal resistance of the supports by defining failure containment loads. The loads considered are one-sided release of static tension in a conductor and conventional unbalanced overloads, respectively. National requirements and calculation rules may be defined in NNAs or Project Specification. Security loads need not be taken into account in lines with nominal system voltages of AC 45 kv and below unless specified in NNA or Project Specification. NOTE The guying effect of the conductors and earth-wires (compact line) can be taken into account, when calculating the effects of the security loads Torsional loads At any one earth wire or phase attachment point, the relevant residual static load, if any, resulting from the release of the tension of a phase conductor or sub-conductor or of an earth wire in an adjacent span shall be applied. Tension release in several sub-conductors or conductors may be considered in the same load case (up to all conductors) for more stringent conditions.

75 EN :2012 Loads and conductor tensions may be calculated at the normal ambient reference temperature without any wind load or ice load and are the applicable design values. This also applies to all unreleased earth wires or phase conductors. More severe climatic conditions may be specified in the NNAs or Project Specification Longitudinal loads Longitudinal loads shall be applied simultaneously at all attachment points. The loads on the support shall be equal to the unbalanced loads - produced by the tension of conductors in all spans in one direction from the support - when a fictitious overload equal to the selfweight of the conductors (affected by a factor, if required) is considered in all spans in the other direction. Alternatively, the loads may be determined as one-sided release of tension in the conductors. Loads and conductor tensions are calculated at the normal ambient reference temperature without any wind load and are final design values. More severe climatic conditions may be specified in the NNAs or Project Specification. NOTE The load transferred to the support from the conductor will depend on the degree of freedom at the conductor attachment point. For conductors supported by suspension insulator sets of typical length the differential loads will normally be small due to the swing of the string Mechanical conditions of application The security loads resulting from and 4.8.3, for suspension supports, may be calculated taking into account the relaxation of the load resulting from any swing of the insulator sets and the elastic deflection or rotation of the support. The calculation may normally be carried out for the ruling span of the line section. The security load values (resulting from and 4.8.3) may also be limited by devices designed for this purpose (slipping clamps, for instance). Alternatively, the security load may be determined as a fraction of the conductor tension, as follows: A K = β T 0 where A K β T 0 is the characteristic residual conductor tension; is the reduction factor for the conductor tension; is the initial horizontal tension in the conductor. Different β-factors may be chosen to cover the different relevant conditions in and A partial factor may be applied on the characteristic residual conductor tension. 4.9 Safety Loads Construction and maintenance loads The supports shall be able to withstand all construction and maintenance loads, Q P, which are likely to be imposed on them with an adequate margin of safety, taking into account working procedures, temporary guying, lifting arrangement, etc. Overstressing of the support shall be prevented by specifying allowable procedures and/or load capacities. National requirements may be defined in the NNAs Loads related to the weight of linesmen The characteristic erection and maintenance load on cross-arms shall not be less than 1,0 kn acting together with the permanent loads and, other imposed loads, if relevant. In the case of lattice steel structures, these forces shall act at the individual most unfavourable node of the lower chords of one cross-arm face, and in all other cases in the axis of the cross-arms at the attachment point of the conductors.

76 EN : Where walkways or working platforms are installed, they shall be designed for the maximum loads. Requirements may be given in the NNAs or in the Project Specification. For all members, which can be climbed and are inclined with an angle less than 30 to the horizontal, a characteristic load of 1,0 kn acting vertically in the centre of the member shall be assumed without any other loads. Additional requirements or precautions shall be added in case pre-assembling on the ground takes place. Steps (of any kind) shall be rated for a concentrated characteristic load of 1,0 kn acting vertically at a structurally unfavourable position Forces due to short-circuit currents Consideration shall be given to the effects of the forces imposed on those overhead lines forming part of a transmission system with very high short circuit characteristics. Information on this subject is given in Annex C.2.2. National requirements for forces due to short-circuit currents shall be defined in the NNAs or Project Specification, as necessary Other special forces Avalanches, creeping snow When overhead lines are to be routed in or through mountainous regions where they may be exposed to avalanches or creeping snow, consideration shall be given to the possible additional loads which may act on the supports, foundations and /or conductors. Some information on this subject is given in Annex C.2.3. National requirements shall be defined in the NNAs or Project Specification, as necessary Earthquakes When overhead lines are to be constructed in seismically active regions, consideration shall be given to forces on lines due to earthquakes and/or seismic tremors. Some information on this subject is given in Annex C.2.4. National requirements shall be defined in the NNAs or Project Specification, as necessary Load cases General For overhead lines exceeding a nominal system voltage AC 45 kv, the following subclauses shall apply. For overhead lines exceeding a nominal system voltage AC 1 kv up to and including AC 45 kv, specific regulations shall be specified in the NNAs. For the design of conductors, equipment and supports including foundations in the ultimate limit state the load case giving the maximum loading effect in each individual member shall be considered. In cases where an external load component decreases the stress in a particular member or crosssection, a special load case shall be considered where the load component causing the decrease shall be set to the minimum credible value whilst the other load components remain unchanged. An example of the effect mentioned above occurs in the gantry of a horizontal configuration support. The ice load on the middle conductor causes a decrease in the stress in the middle of the gantry, and a load case with minimum ice load in the centre shall be considered. Another example is a guyed support where an eccentricity at the ends of pinned masts is introduced to reduce the bending effects due to wind load on the mast. A loading condition with minimum wind load on the mast should be considered. Conductor tensions shall be determined according to the loads acting on the conductor in the defined load case. The components of the conductor tension at the attachment points of the support, including the effect of vertical and horizontal angles, shall be taken into account. If initially the circuits on a multi circuit support or the sub-conductors of bundles will only be partially installed this condition should be considered in the design. NOTE The conductor tension can normally be calculated using the ruling span concept, provided that the conductor is suspended by insulator sets allowing the necessary deflections in the longitudinal direction of the line. For reasonably flat terrains, the ruling span, L R is determined by the expression:

77 EN :2012 where L n L R = is the horizontal length of individual span n of the line section. For lines where the elevations of span ends are unequal, the ruling span, L R is more correctly determined by the expression: where C n LR = 3 n L L 4 Ln Cn Cn is the chord length of individual span n of the line section. Loads on the supports shall be properly selected taking into account defined capacities and intended purpose. Generally, a distinction is made between suspension supports and tension supports. Also a combination of these support types, for example a junction-support, may apply. Requirements in the NNAs may refer to the above-mentioned support types, as applicable. Further, special supports may be required, for example high crossing supports, for which specific requirements in the Project Specification shall be defined Standard load cases For control of adequate reliability and functions under service conditions of the overhead line, load cases, including the standard load cases specified in Table 4.6 and options given below shall be defined in the NNAs. Load case Load as per subclause Table 4.6 Standard load cases (Normative) Conditions 1a 4.4 Wind loads See (a) 2a 2b 2c 2d 4.5 Uniform ice loads on all spans Uniform ice loads, transversal bending Unbalanced ice loads, longitudinal bending. Unbalanced ice loads, torsional bending Combined wind and ice loads See (e) n Remark If relevant, see (b) See (c) If relevant, see (d) Minimum temperature with/without wind loads If relevant 5a 5b 6a 6b Security loads, torsional loads Security loads, longitudinal loads Safety loads, construction and maintenance loads Safety loads, loads due to the weight of linesmen Reduced partial material factors may apply as given in Clauses 7 and 8. In all load cases, the vertical component of the permanent actions as given in 4.2 shall be included. Where permanent actions reduce the effects of other actions such as uplift on a foundation, the minimum value of the permanent action shall be applied, for example minimum allowed ratio of weight-to-wind span. If applicable and stated in the Project Specification, load cases involving short circuit loads or other special loads in accordance with 4.10 and 4.11, respectively, should be investigated. Items (a) to (e) apply as given in Table 4.6:

78 EN : a) A wind direction normal to the line should be considered and at all other angles which may be critical for the design. Wind load on all spans in one direction from the support resulting in longitudinal loads may be considered in the design of the relevant supports, where this condition is not adequately addressed by other defined load cases. (optional) b) In load case 2b, a reduced ice load equal to the extreme ice load multiplied by a reduction factor α on all the conductors on all the cross-arms on one side only of the support should be investigated. This load case is illustrated in Figure 4.4. Where this load condition can be ignored α is defined as 1. (optional) c) In load case 2c, the extreme ice load on all the conductors in one direction only from all the cross-arms of the support should be multiplied by a reduction factor α 1 and in the other direction by a reduction factor α 2. This load case is illustrated in Figure 4.5. (optional) d) In load case 2d, the extreme ice load on all the conductors on all the cross-arms on one side only of the support and in one direction of the line only should be multiplied by a reduction factor α 3. For all the remaining conductors, the characteristic ice load should be multiplied by a reduction factor α 4, thus providing the maximum torsion. This load case is illustrated in Figure 4.6. The number of unbalanced conductors may otherwise be specified in the NNAs. Where this load condition can be ignored or is otherwise taken care of in the NNA by other defined load cases, α 3 and α 4 are defined as 1. (optional) e) Where site conditions require it, combined unbalanced wind and ice loads may be considered in the design of the relevant supports, providing this condition is not adequately addressed by other defined load cases. The ice load and/or the wind load should be applied on all the conductors in one direction only from all the cross-arms of the support resulting in longitudinal loads. (optional) NNAs shall specify if the optional load cases have to be applied. A non-uniform ice load generally applies in up to 3 consecutive spans. However, in the NNAs reduced ice loads on all spans to one side of the support may be required. If not specified in the NNAs, the reduction factors applied to the ice load per conductor length (I) mentioned above may be taken as follows: α = 0,5; α 1 = 0,3; α 2 = 0,7; α 3 = 0,3; α 4 = 0,7 When assessing longitudinal loads on tension tower cross-arms, a designer will additionally need to be aware of the applied out of balance load which may be apparent where adjacent equivalent spans are significantly different. See also of this standard regarding sag-tension calculations.

79 EN :2012 Figure 4.4 Transversal bending Figure 4.5 Longitudinal bending Figure 4.6 Torsional bending

80 EN : Partial factors for actions Recommended values of partial factors, γ and combination factors, Ψ for the actions defined respectively in and are given in Table 4.7. Modified factors may appear in the NNAs. With respect to security load partial factors for overhead lines exceeding AC 1 kv up to and including AC 45 kv, these are only applicable when specified in the NNAs. Table 4.7 Partial factors γ and combination factors Ψ for actions in the ultimate limit state Action Variable actions (Climatic loads): Extreme wind load Nominal wind load Extreme ice load Nominal ice load Symbol γ W Ψ W γ I Ψ I Reliability level ,0 0,4 1,0 0,35 Permanent actions: Self-weight γ G 1,0 Security loads (Accidental actions): Torsional loads due to conductor tension Longitudinal loads due to conductor tension Safety loads Construction and maintenance loads a γ P 1,5 γ A1 γ A2 1,2 0,4 1,25 0,35 1,0 1,0 1,4 0,4 1,5 0,35 The partial factors on actions mentioned above should be considered in conjunction with the partial factors on material properties, which are defined in other clauses of this standard. a The combination value of wind and ice actions may be taken as the actual forces likely to occur during construction and maintenance. Frequently, the effects of wind and ice actions may be neglected.

81 EN : Electrical requirements 5.1 Introduction The purpose of this clause is to give guidance on the calculation of electrical clearances phase to phase and phase to earth to withstand electrical stresses on overhead lines. The selection of the insulation withstand level to achieve specific line performance criteria is dealt with in Clause 10. Internal clearances shall assure that the probability of flashovers at top of support and in mid span is kept to an acceptably low level. External clearances to crossing or adjacent objects shall guarantee the safety of the general public. Internal and external clearances shall be coordinated such that flashovers will occur within the overhead line and not to persons or objects in proximity to a line. To achieve the design targets the required clearances should be derived from the electrical characteristics of the transmission system by distinguishing power frequency and impulse surge voltages. Meteorological data on wind velocity and ice weight or thickness are used to determine the positions of conductors and insulator sets. This clause indicates how minimum air clearances may be determined in distinctive and successive steps. Reference is made to: the theoretical method described in and detailed in Annex E with general formulae and application examples; the empirical European method presented in The numerical values of minimum air clearances given in Tables 5.3 to 5.6 in this Clause 5 apply only to standard reference conditions regarding gap configurations and altitudes. Annex E allows adjustment to those values for differing conditions. Subclause 5.2 deals with normal and short-circuit currents. Subclause 5.3 introduces the principles of insulation coordination. Subclause 5.4 defines the electrical stresses of the system such as power frequency and impulse surge voltages. Subclause 5.5 deals with minimum air clearances phase to phase and phase to earth to withstand electrical stresses. Subclause 5.6 deals with the load cases for the calculation of electrical clearances. Subclause 5.7 summarises how wind load cases and the electrical stresses can be combined. Subclause 5.8 includes Tables 5.8 and 5.9 for the determination of internal clearances at the top of a support and at mid span. (Annex F gives an empirical method for calculating mid span clearances.) Subclause 5.9 includes Tables 5.10 to 5.15 for the determination of external clearances assuring safety of the general public. Finally subclauses 5.10 and 5.11 deal with corona effects and electric and magnetic fields. These subclauses are valid for all self-supporting and guyed structures of overhead lines and all line configurations (vertical, horizontal, trianglular). The clearances relate to lines which use bare conductors, covered conductors or overhead insulated cables. Flowchart 5.1 summarises the structure of Clause 5. Clearance distances during live working are not considered in this standard. The clearances for live working are considered and recommended by IEC TC 78 and CENELEC TC 78. No design guidance is provided for the following issues: differential sags caused by differential ice loading;

82 EN : Ice drop; Galloping. 5.2 Currents 5.3 Insulation coordination Annex E 5.4 Highest system voltage Transient overvoltages Nominal system voltage (Table 5.1) 5.5 Minimum air clearances Definitions (Table 5.2) Theoretical method ( 5.5.2) Empirical method ( 5.5.3) Table 5.3 to 5.5 Table Load cases 5.7 Combination wind load cases / electrical stresses (Table 5.7) 5.8 Internal clearances (at support top and at mid span) - Tables 5.8 and External clearances (safety distances) - Tables 5.10 to Currents Normal current Figure 5.1 Structure of Clause 5 on the Electrical Requirements The normal current is dependent on the magnitude of the transmitted power and on the operating voltage. The cross-section of the phase conductors shall be chosen such that the maximum design temperature for the conducting material is not exceeded under specified conditions which shall be defined in the NNAs or the Project Specification Short-circuit current The overhead line shall be designed and erected to withstand without damage the mechanical and thermal effects due to the short-circuit currents as specified in the Project Specification. The short-circuit current can be: three-phase; phase-to-phase; single phase to earth; two phases to earth.

83 EN :2012 Typical values of the duration of the short circuit for design purposes are: earth and phase conductors 0,5 s; accessories 1,0 s. However, it is important to take into account the actual duration which is dependent on the tripping time of the protection system for the overhead line. Sometimes therefore, the duration can be longer or shorter than the above typical values. Methods for the calculation of the short-circuit currents in three phase a.c. systems are given in EN and methods for calculation of the effects of short-circuit current are given in EN Alternatively, methods for calculation may be specified in the NNAs or the Project Specification. 5.3 Insulation co-ordination The principles and rules of insulation co-ordination are described in EN and EN The procedure for insulation co-ordination includes selection of a set of standard withstand voltages which characterise the insulation. In the case of an overhead line, the procedure is composed of the following steps as given in the calculation formulae of Annex E.3: determination of the representative voltages and overvoltages, U rp (described in E.2.2); determination of the co-ordination withstand voltages, U cw (described in E.2.3); determination of the required withstand voltages for an air gap, U rw (described in E.2.4); determination of the corresponding clearance distance of the air gap, d (described in E.2.5); Annex E is not applicable for lines with nominal system voltages, U n up to and including AC 45 kv. 5.4 Classification of voltages and overvoltages General The electric system is usually characterised by a nominal system voltage. The system voltage is the rms phase-to-phase power frequency voltage of the electric system. The voltages and overvoltages stressing the insulation in service are classified as follows: power frequency voltages (given in 5.4.2); temporary overvoltages (given in 5.4.3); transient overvoltages or impulse voltages. Power frequency voltages are continuous whilst overvoltages are temporary or transient. The transient overvoltages are classified as follows: slow-front overvoltages (given in 5.4.4); fast-front overvoltages (given in 5.4.5) Representative power frequency voltages The representative continuous power frequency voltage is considered as constant and equal to the highest system voltage (U s ), the highest value of operating voltage which occurs under normal operating conditions at any time and any point in the system. [IEV ] (phase-to-phase voltage). The highest voltage for equipment (U m ) is used for the insulation level of insulators and other equipment connected to the overhead line. It defines amongst others the voltage level with which the line components are tested. Note that the highest voltage for equipment is not less than the highest system voltage. Table 5.1 gives nominal system voltages, U n, the corresponding highest system voltages, U s and the highest voltages for equipment, U m.

84 EN : Table 5.1 Nominal system voltages and corresponding highest system voltages and highest voltage for equipment in accordance with EN Nominal system voltage U n (kv) Highest system voltage U s (kv) Highest voltage for equipment (min. value) U m (kv) NOTE 3 3,6 3,6 6 7,2 7, ,5 17, ,5 40, ,5 72, ,5 72, or 362 or or 362 or or 525 or or 525 or or or or or 1200 Nominal system voltages over 230 kv are defined by national standards Representative temporary overvoltages Temporary overvoltages are oscillatory overvoltages at power frequency at a given location, of relatively long duration, and which are undamped or weakly damped [IEV ]. They usually originate from faults, switching operations (i.e. load rejection), resonance conditions, non-linearities (ferro-resonance) or by a combination of these. The representative temporary overvoltage is a oneminute duration voltage at power frequency, but is generally not considered for the determination of electrical clearances of a line Representative slow-front overvoltages Slow-front overvoltages can originate from faults, switching operations or distant direct lightning strokes to overhead lines. Slow-front overvoltages of importance for overhead lines are earth fault overvoltages, energisation and re-energisation overvoltages. The representative voltage stress is characterised by: the standard switching impulse wave shape (250/2 500 µs),

85 EN :2012 a representative amplitude which can be either an assumed maximum overvoltage or deduced from a probability distribution of the overvoltage amplitudes Representative fast-front overvoltages Fast-front overvoltages of importance for overhead lines are mainly lightning overvoltages due to direct strokes to the phase conductors or backflashovers or, in the lower system voltage range (< 245 kv), voltages induced by lightning strokes to earth close to the line. The representative voltage stress is characterised by the standard lightning impulse wave shape (1,2/50 µs). The representative amplitude is either given as an assumed maximum or by a probability distribution of peak values. For the purpose of determining air clearances the representative overvoltage to be considered is that which can propagate beyond a few towers from the point of the lightning strike. The lightning performance of overhead lines can be described by the shielding failure flashover rate, R sf, and by the backflashover rate, R b. It is fixed by operational considerations and depends on the insulation strength of the line and on the following parameters: the lightning ground flash density; the height of the overhead line; the conductor configuration; the protection by earth wire(s); the tower earthing; the installation of surge arresters on the overhead line. Acceptable levels of shielding failure flashover rates and back flashover rates may be defined in the Project Specification. NOTE Guidance for the calculation of shielding failure flashover (R sf) rates and backflashover rates (R b) are given in the CIGRE Technical Brochure nº 63 "Guide to procedures for estimating the lightning performance of transmission lines : Section 4 deals with R sf and section 6 with R b. 5.5 Minimum air clearance distances to avoid flashover General Four types of minimum air clearances are considered in the present standard. They are summarised in Table 5.2. Table 5.2 Minimum air clearances Minimum air clearances Minimum air clearance required to prevent a disruptive discharge between phase conductors and phase conductors objects at earth potential during fast- or slow-front overvoltages D el D pp at power frequency voltage D 50Hz_p_e D 50Hz_p_p D el may be either: an internal clearance when considering conductor to tower structure or earth wire clearances or an external clearance when considering conductor to obstacle clearances. D pp, D 50Hz_p_e and D 50Hz_p_p are only internal clearances. Nevertheless, clearance D pp may also be external if clearances to other power lines or telecommunication lines are considered (see 5.9.6). For derivation of D el and D pp, it is recommended to use one of the following methods: Theoretical method described in and detailed in Annex E;

86 EN : Empirical method based on experience in Europe, described in Annex E is not applicable for lines with nominal system voltages up to and including AC 45 kv Application of the theoretical method in Annex E Annex E gives a theoretical method to determine for each type of transient overvoltage (fast-front and slow-front) and for the power frequency voltage the minimum air clearance necessary to provide the required withstand voltage for certain air gap configurations and a given range of altitudes. Temporary overvoltages are not considered. When applying the theoretical method, one can either use the Tables 5.3, 5.4 or 5.5 for standard reference conditions (for gap configurations and altitude), or the general formulae in Table E.5 of Annex E for conditions outside the standard conditions. Numerical applications of the formulae in Table E.5 of Annex E are given respectively in Table 5.3 and Table 5.4 for the general case of conductor to earth distances, D el with a gap factor, K g = 1,3 and phase conductor distances, D pp with a gap factor, K g = 1,6 necessary to withstand respectively fastfront overvoltages due to lightning and slow-front overvoltages due to switching. The numerical application of the formulae in Table E.5 of Annex E is given in Table 5.5 for the general case of conductor to earth distances, D 50Hz_p_e with a gap factor, K g = 1,45 and phase conductor distances, D 50Hz_p_p with a gap factor, K g = 1,6 necessary to withstand power frequency voltages. NOTE The gap factor, K g used to calculate the values within Tables 5.3, 5.4 and 5.5 are in each case K g_sf.. The value of K g_sf can be reviewed in Annex E. Annex E.5, gives examples of calculation of D el, D pp and D 50Hz, for different highest system voltages. These examples cover most of the cases which may occur in practice. There are many possible arcing distances. The corresponding withstand voltages are not the same as the standard impulse voltages given for equipment in EN According to the different possible shapes of insulators and arcing devices, the insulation level of the line needed for this application can result in many values, even outside the list of standard impulse withstand voltages given for equipment in EN All these minimum air clearances are solely based on insulation co-ordination requirements. Other requirements may result in substantially larger clearances. Other values shall be specified in the NNAs together with an explanation of their derivation.

87 EN :2012 Table 5.3 Minimum air clearances D el and D pp to withstand lightning overvoltages Representative lightning withstand voltage U 90%_ff_is of the line insulator strings (kv) D el (m) K g = 1,3 k a (1 000 m) D pp (m) K g =1,6 k a (1 000 m) 250 0,48 0, ,58 0, ,67 0, ,77 0, ,85 0, ,95 1, ,04 1, ,14 1, ,23 1, ,33 1, ,41 1, ,50 1, ,60 1, ,69 1, ,78 2, ,88 2, ,97 2, ,05 2, ,14 2, ,23 2, ,33 2, ,42 2, ,51 2, ,61 2, ,70 3, ,79 3, ,89 3, ,98 3, ,07 3, ,17 3, ,26 3, ,35 3, ,45 3, ,54 3, ,63 4, ,72 4, ,82 4, ,91 4, ,00 4,48 This table gives numerical values of clearances at m of altitude. If the altitude is consistently lower or higher than m, the clearance distances may be corrected using the atmospheric factor k a given in Table E.3.

88 EN : Table 5.4 Minimum air clearances D el and D pp to withstand switching overvoltages Representative switching overvoltage U 2%_sf (kv) D el (m) K g = 1,3 k a (1 000 m) D pp (m) K g = 1,6 k a (1 000 m) 400 0,88 1, ,01 1, ,14 1, ,29 1, ,44 1, ,59 1, ,73 2, ,90 2, ,07 2, ,25 2, ,44 2, ,64 3, ,84 3, ,02 3, ,24 3, ,47 4, ,71 4, ,96 4, ,22 5, ,49 5, ,77 5, ,06 6, ,37 6, ,69 7, ,02 7, ,37 8, ,73 8, ,11 9, ,50 9,70 This table gives numerical values of clearances at m of altitude. If the altitude is consistently lower or higher than m, the clearance distances may be corrected using the atmospheric factor k a given in Table E.3.

89 EN :2012 Table 5.5 Minimum air clearances necessary to withstand the power frequency voltage (to be used in extreme wind conditions) Highest system voltage U s (kv) D 50Hz_p_e (m) K g = 1,45 conductor-structure D 50Hz_p_p (m) K g = 1,60 conductor to conductor 52 0,11 0,17 72,5 0,15 0, ,19 0, ,23 0, ,27 0, ,31 0, ,43 0, ,51 0, ,70 1, ,86 1, ,28 2, Empirical method based on European experience The values given in Table 5.6 are based on an analysis of commonly used European values for the specification of external clearances, which have been proved to be sufficient to achieve safety for the general public. When using these values it shall be verified that the calculated distance to a person or an object is greater than 110 % of a som (the minimum discharge gap between live parts and earthed parts) at the moment that an overvoltage occurs. In most of the cases, probability considerations achieve this. The NNAs may define this in more detail.

90 EN : Table 5.6 Minimum air clearances D el and D pp Highest system voltage U s (kv) D el (m) D pp (m) 3,6 0,08 0,10 7,2 0,09 0, ,12 0,15 17,5 0,16 0, ,22 0, ,35 0, ,60* 0,70 72,5 0,70 0, ,90 1, ,00 1, ,20 1, ,30 1, ,70 2, ,10 2, ,80 3, ,50 4, ,90 5,60 * A value of D el = 0,48 m is given within EN D 50_Hz_p_p and D 50_Hz_p_e may be defined in NNA. 5.6 Load cases for calculation of clearances Load conditions For the determination of the electrical clearances the following load conditions need to be considered: Maximum conductor temperature (given in 5.6.2); Wind loads (given in 5.6.3); Ice loads (given in 5.6.4); Combined wind and ice loads (given in 5.6.5). At angle suspension tower with short spans, minimum conductor temperature should also be a load condition to be considered Maximum conductor temperature All internal and external vertical clearances shall be based on the maximum continuous service temperature of the conductors specified in the NNAs or in the Project Specification (see also Clause 9 on conductors). Countries may wish to consider short duration higher temperature loading and reduced clearances in these cases. Requirements should be given in NNAs or the Project Specification Wind loads for determination of electric clearances Wind load cases Three wind load cases are to be considered:

91 EN :2012 still air; nominal wind load for a 10 minutes mean wind velocity, with a 3 year return period; extreme wind load for a 10 minutes mean wind velocity, with the reference 50 year return period. Nominal and extreme wind loads on conductors and insulators sets for a 10 minutes mean wind velocity are given in Because a mean wind velocity has to be considered, q h is used instead of q p with G x = 1 in the formulae in National requirements shall be defined in the NNAs. Under wind loading the temperature of a conductor will decrease. The reduction of temperature is dependent on electrical loading, wind velocity, wind direction, ambient temperature, etc. The designer may take these parameters into account when calculating the actual position of the conductor. Under still air conditions (maximum temperature or ice without wind), the internal clearances shall be greater than D el or D pp. Nominal and extreme wind loads are considered in the following subclauses. In general the extreme wind load is not considered for the external clearances Nominal wind loads for determination of internal and external clearances Under nominal wind conditions internal clearances may be reduced because there is only a low probability that there will be an overvoltage under these conditions. The extent to which the internal clearances should be reduced has to be determined by the National Committee and reflects the required probability of flashover of the line. National requirements shall be defined by the NNAs. For the derivation of wind load for this condition, a three-year return period shall be employed with the wind velocity averaged over a 10 minute period Extreme wind loads for determination of internal clearances Under extreme wind conditions, in which simultaneous occurrence of a transient overvoltage is considered to be acceptably small, internal clearances shall withstand the highest system voltage phase-to-earth in directly-earthed neutral systems with earth fault factor of 1,3 and below. For higher earth fault factors and especially in isolated and resonant-earthed-neutral systems consideration of transient overvoltages may be necessary. For the derivation of wind load for this condition, a reference 50-year return period shall be employed with the wind velocity averaged over a 10 minutes period Ice loads for determination of electric clearances One ice load case is to be considered: extreme ice load for the reference 50 year return period. Extreme ice loads on conductors are given in Annex B.3 as well as in National requirements shall be defined by NNAs Combined wind and ice loads In some countries combined wind and ice loads should be considered. The methods of calculation of those load cases shall be defined in NNAs. It is also accepted that to produce economical designs of transmission networks the designer has to optimise the design for a foreseeable range of climatic conditions such as wind velocities and ice loading. Exceptional meteorological events occur, and in these circumstances it is considered acceptable that the clearances in this clause should not be applied. In these exceptional conditions safety of persons is paramount and alternative means should be sought to ensure this. It is considered that exceptional in this context is once in more than 50 years. 5.7 Coordination of conductor positions and electrical stresses This subclause summarises how the power frequency and impulse surge voltages from Subclauses 5.4 and 5.5 can be combined with the wind load cases from Subclause 5.6. Two cases are considered in Table 5.7.

92 EN : Case A - In still air or under nominal wind velocity, there should be adequate clearance to withstand the lightning or switching surge impulse voltages with a probability of more than 90 %. Case B - Under extreme wind velocity, the clearances should be adequate to withstand the power frequency voltage only. The probability of flashovers depends on the probability of occurrence of the corresponding wind velocity. Generally this Case B is not considered for external clearances. Table 5.7 Coordination of conductor positions and electrical stresses Conductor and insulator positions Electrical stresses of the air gap Lightning / switching impulse voltage Power frequency voltage Small or zero swing angle Still air or nominal wind velocity with T = 3 years Large swing angle (only for internal clearances) Extreme wind velocity with T = 50 years Probability High Low Low Case A Not considered High Covered by cases A & B Case B Nominal ice load can also be considered as Case A noted above. Other approaches to determine the conductor and insulator set positions may be stipulated in the NNA. NOTE 1 Swing angles due to wind load on conductors and insulator sets depend on the ratio of wind span to weight span. Cigré Technical Brochure n 348 Tower top geometry and mid span clearances quote appropriate formulae and meteorological conditions (temperature, wind, ice) to determine swing angles of insulator sets at top of support and of conductor at mid span, to associate them with corresponding internal electrical clearances. NOTE 2 According to Cigré Technical Brochure n 348 Tower top geometry and mid span clearances the mean swing angle of an insulator set under a given wind action can be reliably calculated based on Formula (2.14) using a mean wind velocity averaged over 5 minutes to 10 minutes with 5 minutes being a conservative value. The mean swing angle of a conductor is given by Formula (2.15). 5.8 Internal clearances within the span and at the top of support Internal clearances include phase to phase and phase to earth distances. For internal clearances, distinction is made between: Clearance between phase conductors; Clearance between the phase conductor and the earth wire or the earthed parts of the support. The internal clearances are checked: At the top of support; In the span, especially at mid span. Minimum clearances within the span and at the top of the support for overhead lines with nominal system voltage exceeding AC 45 kv are specified in Table 5.8. For overhead lines with nominal system voltage exceeding AC 1 kv up to and including AC 45 kv, the minimum internal clearances are given in Table 5.9. The minimum internal clearances are determined from a technical point of view. It is accepted that National Statutes may use differing values (both higher and lower) and these shall be specified in the NNAs. As an alternative, Annex F describes an empirical method for calculating the mid span clearances in still air which takes account of swing angles. The minimum internal clearances given in Table 5.8 are solely for the purpose of designing an acceptable clearance with respect to withstand overvoltages. (It is accepted in EN and EN that the economic design of a power network will have a limited number of flashovers across some of the critical internal clearances, such as those between the conductors and the

93 EN :2012 support). For internal clearances, it is permitted to use lower values than D el and D pp because this affects only the electrical reliability of the network. There is only a low probability that there will be an overvoltage under these conditions and the occurrence of a flashover would not result in danger to persons or properties. The internal clearances k 1 D el and k 1 D pp are defined in the NNAs. For overhead lines with nominal system voltage exceeding AC 1 kv up to and including AC 45 kv (in respect of bare and covered conductor overhead lines and overhead insulated cable systems), the electrical clearance to be used shall be the distance at which the electrical circuit considered withstands the lightning overvoltage. In these cases, the minimum clearances shall, however, only be applied for the specification of the internal clearances of overhead line components. Other methods may be defined in the NNAs to calculate the clearances in the span.

94 EN : Load Case Table 5.8 Minimum internal clearances within the span and at the top of support (for lines with nominal system voltage > 45 kv) Phase conductor - phase conductor Clearance cases: within the span and at the top of support Within the span At the top of support Phase conductor - earth-wire Between phases and/or circuits Between phase conductors and earthed parts Remarks Maximum conductor temperature D pp D el D pp D el Load conditions in still air Extreme ice load D pp D el D pp D el Load conditions in still air Nominal wind load k 1 D pp k 1 D el k 1 D pp k 1 D el k 1 shall be defined in NNAs. Extreme wind load D 50 Hz_p_p D 50_Hz_p_e D 50_Hz_p_p D 50_Hz_p_e If the attachment of the earth wire at the support is higher than that of the phase conductor then the earth wire shall not sag below the phase conductor. If lines with similar conductors (same cross-sectional area, material, construction and sag) are to be considered there are approximation methods to calculate the required clearance within the span in still air to ensure that clearances are not infringed in windy conditions (see Annex F.1).

95 EN :2012 Load Case Protection System Maximum conductor temperature Extreme ice load Nominal wind load Extreme wind load Table 5.9 Minimum internal clearances within the span and at top of support (for lines with nominal system voltage > 1 kv and 45 kv) Phase conductor - phase conductor Clearance cases: within the span and at top of support m Within the span At top of support Phase conductor - earth wire Between phases and/or circuits Between phase conductors and earthed parts B C I B C I B C I B C I Remarks D pp 0,25 - D el 0,2 - D pp 0,25 2 d D el 0,2 0,1 Load conditions in still air D pp 0,25 - D el 0,2 - D pp 0,25 2 d D el 0,2 0,1 Load conditions in still air D pp k 1 0,25 k 1 - D el k 1 0,2 k 1 - D pp k 1 0,25 k 1 2 d k 1 D el k 1 0,2 k 1 0,1 k 1 Factor k 1 shall be defined in NNAs D pp k 1 0,07 - D el k D pp k D el k Factor k 1 shall be defined in NNAs Insulated line: Clearance between circuits: d is the diameter of the insulated cable/line. If the attachment of the earth wire at the support is higher than that of the phase conductor then the earth wire shall not sag below the phase conductor. If the covered conductors are not insulated at the support, i.e. by use of penetrating clamps, the minimum clearances given in Table 5.6 shall be applied. If lines with similar conductors (same cross-sectional area, material, construction and sag) are to be considered there are approximation methods to calculate the required clearance within the span in still air to ensure that clearances are not infringed in windy conditions (see F.1). NOTE The coding for column headings above is as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system.

96 EN : External clearances General The purpose of the external clearances is to avoid danger to the general public, persons undertaking work in the vicinity of the power lines and to persons maintaining the power network due to an electrical discharge. The aim of these external clearance values is to ensure that any part of a person, or any object that they can reasonably be expected to be carrying, is avoided from coming closer than the distance, D el from an energised conductor. The following cases are considered: a) Clearances to ground in areas remote from buildings, roads, railways and navigable waterways (Table 5.10); b) Clearances to residential and other buildings, when the line is above or adjacent to the buildings or near antenna or similar structures (see Table 5.11); c) Clearances to line crossing roads, railways and navigable waterways (see Table 5.12); d) Clearances to line adjacent to roads, railways and navigable waterways (see Table 5.13); e) Clearances to line crossing or parallel to other power lines or overhead telecommunication lines (see Table 5.14); f) Clearances to recreational areas, line above and in close proximity (see Table 5.15). For external clearances, D el shall be used. In case e) above, D pp is used. An additional safety clearance is necessary to ground or buildings etc. which is intended to ensure that no person or conductive object enters the electrical distance, D el even when they are undertaking work or leisure activities which can be foreseen as reasonably likely. It is necessary for the designer of the line to confirm that the sum of D el and the safety distance is sufficient to ensure safety for the general public. When the clearance distance is not specified as horizontal or vertical it shall be taken as the smallest distance between the live parts and the object under consideration. The external clearances as given in Tables 5.10 to 5.15 are determined from a technical point of view. It is accepted that National Statutes may use differing values (both higher and lower), and these shall be specified in the NNAs. Higher values for minimum clearances may be given in the Project Specifications. These values will overrule those in this standard and its annexes. The clearances shall be checked according to load conditions in 5.6. With very long insulator strings, the risk of flashover shall always be on the internal distance, a som and not to any external object or person. For overhead lines with nominal system voltage exceeding AC 1 kv up to and including AC 45 kv, the relevant values of D el and D pp shall be independent of line voltage. For these voltages, external clearances to the ground and crossing of obstacles, D el = 0,60 m shall be considered, and D pp = 0,70 m for crossings with other overhead lines. These basic electrical clearances are considered in Tables 5.11 to Due to the increased safety requirements for crossings over buildings, recreational areas, traffic routes and other power lines, consideration should be given to employing multiple insulator strings where there is considered to be the possibility of an insulator string mechanical failure.

97 EN : External clearances to ground in areas remote from buildings, roads, etc. Table 5.10 Minimum external clearances to ground in areas remote from buildings, roads, railways and navigable waterways Clearance to ground in unobstructed countryside m Rockface or steep Normal ground profile slope Load Case (see NOTE 1) Trees which cannot be climbed Protection System Maximum conductor temperature Extreme ice load Nominal wind load Remarks Under the line Trees which can be climbed (see the 'Requirement' sentence below) Clearance to trees m Trees which cannot be climbed Beside the line (horizontal clearance) Trees which can be climbed (see the 'Requirement' sentence below) B C I B C I B C I B C I B C I B C I 5,0 + D el but at least 5,6 5,0 + D el but at least 5,6 5,0 + D el but at least 5,6 5,6 5,6 5,6 5,6 5,6 5,6 2,0 + D el but at least 3,0 2,0 + D el but at least 3,,0 2,0+ D el but at least 3,0 3,0 3,0 3,0 2,5 3,0 2,5 Basic requirement is that a vehicle or person etc. can pass under the line without danger. When that case does not apply (steep slope etc) clearance may be reduced consistent with the requirement that safety of persons shall be ensured. D el but at least 0,5 D el but at least 0,5 D el but at least 0,5 0,5 0,5 0,5 0,5 0,5 0,5 1,5 + D el but at least 2,1 1,5 + D el but at least 2,1 1,5 + D el but at least 2,1 1,5 0,5 1,5 0,5 1,5 0,5 Where trees or ladders are climbed under the line (for example in orchards and hop fields) then a height above the ladder or tree shall be applied so that work close to the line can be done without danger. D el but at least 0,6 D el but at least 0,6 D el but at least 0,6 0,5 0,5 0,5 0,5 0,5 0,5 1,5 + D el but at least 2,1 1,5 + D el but at least 2,1 1,5 + D el but at least 2,1 1,5 1,0 1,5 1,0 1,5 1,0 If the risk of causing an earth fault due to a falling tree is unacceptable, then the height of the trees shall be reduced or their horizontal distance from the line shall be limited. In some countries it is normal practice to overspan forests to avoid lopping and in this case maximum future height of the trees should be allowed for. Requirement: Where appropriate, the Project Specification shall define which trees are climbable by persons. NOTE 1 These clearances are based on a 5 m high vehicle. NOTE 2 The coding for column headings above is as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system. The clearances for C- and I-conductors are only valid for voltage levels > 1 kv and 45 kv.

98 EN : External clearances to residential and other buildings Load Case Protection System Maximum conductor temperature Extreme ice load Nominal wind load Remarks With fire resistant roofs where the slope is greater than 15 to the horizontal Table 5.11 Minimum clearances to residential and other buildings Line above buildings With fire resistant roofs where the slope is less than or equal to 15 to the horizontal Clearance cases: Residential and other buildings m Line adjacent to buildings (Horizontal clearance) With non fire resistant roofs and fire sensitive installations such as fuel stations, etc. Antenna, street lamps, flag poles, advertising signs and similar structures Antennas and lightning protection facilities Street lamps, flag poles, advertising signs and similar structures which can not be stood on B C I B C I B C I B C I B C I B C I 2,0 + D el but at least 3,0 3,0 2,5 2,0 + D el but at least 3,0 2,5 3,0 2,0 + D el but at least 3,0 2,5 3,0 It is considered that it is reasonable for a person to stand on the roof for maintenance and to use a hand tool. In the event of heavy icing it is assumed that no-one will use the roofs under this condition. 4,0 + D el but at least 5,0 4,0 + D el but at least 5,0 4,0 + D el but at least 5,0 4,0 3,0 4,0 3,0 4,0 3,0 It is considered that it is reasonable for a person to stand on the roof for maintenance and to use a small ladder. In the event of heavy icing it is assumed that no-one will use the roofs under this condition. 10,0 + D el but at least 10,6 10,6 10,6 10,0 + D el but at least 10,6 10,6 10,6 10,0 + D el but at least 10,6 10,6 10,6 The clearance shall be sufficient to remove the possibility that induced voltages could lead to ignition. 2,0 + D el but at least 3,0 3,0 3,0 2,0 + D el but at least 3,0 3,0 3,0 2,0 + D el but at least 2,0 2,0 3,0 If this horizontal distance can not be met the vertical clearances in the case of a line above buildings shall be met. 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 The clearance D el shall be maintained even when the structure would fall towards the line conductors, with the conductors at maximum likely temperature and hanging vertically in still air. In some countries it is not permitted to cross over or to be close to buildings and the clearances given in this clause do not apply in those countries. Those countries should define how close power lines can be to buildings in the NNAs. NOTE The coding for column headings above are as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system. The clearances for C- and I-conductors are only valid for voltage levels > 1 kv and 45 kv.

99 EN : External clearances to crossing traffic routes Load Case Protection System Maximum conductor temperature Extreme ice load Nominal wind load Special load case -1 Special load case -2 Special load case -3 To road surface or top of rail level (if no electric traction system is used) (see the 'Requirement' sentence below) Table 5.12 Minimum clearances to line crossing roads, railways and navigable waterways To components of electric traction systems of railways, trolley bus lines or rope ways Clearance cases: Line crossing roads, railways and navigable waterways m To pulling ropes of rope ways To an agreed gauge of a clear height of a recognised navigable waterway To fixed points of a ropeway or fixed components of an electric traction system of a railway To towers or supporting and pulling ropes of a ropeway installation To rope way installations in the case of undercrossing B C I B C I B C I B C I B C I B C I B C I 6,0 + D el but at least 6,6 6,0 + D el but at least 6,6 6,0 + D el but at least 6,6 6,6 6,6 6,6 6,6 6,6 6, ,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2, ,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 2,0 + D el but at least 2,6 2,0 + D el but at least 2, D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 4,0 4,0 4,0 4,0 4,0 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 + D el but at least 2,6 2,0 2,0 2,0 2,0 2,0 2,0 2,0 2, ,0 2, ,0 + D el but at least 2,6 For minor roads, as defined in NNAs, clearance Remarks Horizontal clearance. Horizontal clearance. can be reduced by 1 m. Special load case 1 is the swinging of the over crossing conductors due to varying wind loads at a temperature defined in NNAs and simultaneously loading of the undercrossing conductor of the traction system at its minimum sag. Special load case 2 is the swinging of the over crossing conductors due to varying wind loads at a temperature defined in NNAs and maximum tensile force in the pulling rope increased by 25 %. In evaluating horizontal clearances the following load cases shall be considered: - swinging of the conductor due to wind towards fixed components of the ropeway installation; - swinging ropes of the ropeway installation at maximum swing angle of 45 towards parts of the overhead line. Special load case 3 is the minimum sag of the undercrossing conductor and maximum sag of the pulling rope. In addition the height of the cabin shall be considered. Requirement: For clearances from the rail level, the clearance should be fixed with respect to the gauge of the train rather than the top of the rail level. In the case of crossing a railway without electric traction system, clearances should be agreed by the railway authorities when conversion to an overhead traction system is planned. NOTE The coding for column headings above is as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system. The clearances for C- and I-conductors are only valid for voltage levels > 1 kv and 45 kv. 2,0 2,0

100 EN : External clearances to adjacent traffic routes Table 5.13 Minimum clearances to line adjacent to roads, railways and navigable waterways Load case Protection System Horizontal clearance to loading gauge or the components of an electric traction system wire installation of a railway or trolley bus line Clearance cases: Line adjacent to roads, railways and navigable waterways m Horizontal clearance to components of a ropeway installation Horizontal clearance to outer edge of a carriageway (incl. hard shoulder) of a motorway, highway, country road or of a waterway Horizontal clearance between nearest part of the overhead line and the outer edge of the nearest track of a railway B C I B C I B C I B C I Maximum conductor temperature Extreme ice load Nominal wind load 0,5 + D el but at least 1,5 0,5 + D el but at least 1,5 0,5 + D el but at least 1,5 1,5 1,5 1,5 1,5 1,5 1,5 Special load case Remarks 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 4,0 4,0 4,0 4,0 4,0 0,5 + D el but at least 1,5 0,5 + D el but at least 1,5 0,5 + D el but at least 1,5 1,5 1,5 1,5 1,5 1,5 1,5 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 + D el but at least 4,6 4,0 4,0 4,0 4,0 4,0 4,0 4, If this horizontal clearance cannot be met, clearances for crossing of railway installations as given in Table 5.12 shall be met. If conversion to electric traction system is planned 15 m. Special load case 4: Additionally it should be assumed that the supporting and pulling ropes of a rope way installation swing through an angle of 45 towards the overhead line. NOTE The coding for column headings above is as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system. The clearances for C- and I-conductors are only valid for voltage levels > 1 kv and 45 kv.

101 EN : External clearances to other power lines or overhead telecommunication lines Table 5.14 Minimum clearances to other power lines or overhead telecommunication lines Load Case Vertical clearance between lowest conductor of the upper circuit and live parts or earthed components of the lower line Crossing of lines m Horizontal clearance between the vertical axis of the swung conductor and components of telecommunication lines Parallel lines on common structures m Clearance between conductors of lines of separate utilities Parallel or converging lines on separate structures m Protection System B C I B C I B C I (See NOTE 1) B C I Maximum conductor temperature Extreme ice load Nominal wind load Remarks D pp but at least 1,0 a 1,0 1, D pp but at least 0,7 a 0,5 2 d D pp but at least 1,0 a 1,0 1,0 D pp D pp D pp but at least 1,0 1, but at least 0,5 2 d but at least 1,0 1,0 1,0 a 0,7 a 1,0 a D pp D pp D pp but at least 1,0 1,0 2,0 2,0 2,0 but at least 0,5 2 d but at least 1,0 1,0 1,0 a 0,7 a 1,0 a Special care shall be taken with respect to crossing of lines and parallel lines. The clearance shall be greater than 1,1 times the arcing distance a som (defined as the straight line distance between live and earthed parts) of the insulator string. If this horizontal clearance can If circuits of separate utilities are placed Consideration should be given to not be met, the vertical on common structures, the possibility of conductor swing on either of the clearances between lowest influencing each other shall be circuits on the two lines conductor of the upper circuit and minimised; i.e. consideration should be live parts or earthed components given to the use of rotating crossarms, of the lower line shall be met. consequences of broken insulators, induction and maintenance. a D pp is the greater of the values of D pp for the two lines. NOTE 1 Insulated line: d is the diameter of the insulated cable/line. NOTE 2 The coding for column headings above is as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system. The clearances for C- and I-conductors are only valid for voltage levels > 1 kv and 45 kv.

102 EN : External clearances to recreational areas (playgrounds, sports areas, etc.) Table 5.15 Minimum clearances to recreational areas Load Case Protection System To general sports areas To highest level of swimming pools Line above m To agreed gauge of sailing facilities To permanently installed sports facilities, such as starting and winning post installations, camping installations as well as structures which can be erected or climbed on Line in close proximity m Horizontal clearance to all recreational installations B C I B C I B C I B C I B C I Maximum conductor temperature Extreme ice load Nominal wind load Remarks 7,0 + D el but at least 7,6 7,6 7,0 7,0 + D el but at least 7,6 7,0 7,6 7,0 + D el but at least 7,6 7,0 7,6 In the case of a sport with throwing of implements or shooting, it shall be ensured that an approach to the conductor less than 2,0 m + D el is avoided. 8,0 + D el but at least 8,6 8,6 8,0 8,0 + D el but at least 8,6 8,0 8,6 8,0 + D el but at least 8,6 8,0 8,6 In case of a diving board, it shall be ensured that an approach of anyone closer than D el is avoided. 1,0 + D el but at least 1,6 1,0 + D el but at least 1,6 1,0 + D el but at least 1,6 1,6 1,0 1,6 1,0 1,6 1,0 Maximum high water level to be considered or highest transport position on shore facilities. 3,0 + D el but at least 3,6 3,0 + D el but at least 3,6 3,0 + D el but at least 3,6 3,6 3,0 3,6 3,0 3,6 3,0 3,0 + D el but at least 3,6 3,6 3,0 3,0 + D el but at least 3,6 3,0 3,6 3,0 + D el but at least 3,6 3,0 3,6 If this horizontal clearance is not met, then the vertical clearances for the line above condition shall be met. In some countries it is not permitted to cross over or run close to recreational areas and the clearances given in this clause do not apply to these countries. Those countries should define how close power lines could be to recreational areas in the NNAs. NOTE The coding for column headings above is as follows: B = Bare conductors; C = Covered conductors; and I = Insulated cable system. The clearances for C- and I-conductors are only valid for voltage levels > 1 kv and 45 kv.

103 5.10 Corona effect Radio noise General EN :2012 Radio noise from high voltage overhead power lines can be generated over a wide band of frequencies by: corona discharges in the air at the surfaces of conductors and fittings; discharges and sparking at highly electrically stressed areas of insulators; sparking at loose or imperfect contacts. There are two basic methods to predict the radio noise of a high-voltage line: comparative and analytical. NOTE These methods are described and compared in CISPR/TR 18-3 and CIGRÉ Working Group (1974) Document Interferences produced by corona effect of electrical systems Design influences The most important design influence on the corona-generated radio noise levels produced by any high-voltage line is the electric field very close to the conductors. This field is influenced by voltage, number of conductors per phase bundle, size of conductors, phase spacing, and to a lesser extent, line configuration, line phasing, line height, and line proximity to other lines or wires. Radio noise levels are also influenced by the local earth conductivity and the relative smoothness of conductor and hardware surfaces. Generally, corona generated radio-noise levels become a significant design concern only for lines operating at voltages of 230 kv or above. For these high voltages, noise-level prediction methods assume that line hardware is designed or shielded so that only the corona on conductors will be responsible for observed radio noise levels, and that conductors are installed taking care not to damage their surface. In the first few months of energised operation, conductor surfaces are not yet weathered, and radio noise levels can be a few decibels above ultimate expectations. A practical design of overhead lines and associated equipment in order to keep the various types of radio noise within acceptable levels is described in CISPR/TR Noise limits The degree of annoyance caused by radio noise is determined by the so-called "signal-to-noise ratio" at the receiving installation. When establishing limits for the emission of radio noise, the radio and television signal strengths to be protected have to be determined. Maximum permissible levels of radio noise may be given by national or local authorities and incorporated in NNAs or the Project Specification. Methods for derivation of limits of radio noise from overhead power lines and high-voltage equipment in order to safeguard radio and television reception are given in CISPR/TR Audible noise General Corona on high-voltage power lines can, in some circumstances, produce audible noise. Such noise is more likely to occur in foul weather and fog; in fair weather it arises mainly where lines are subject to special kinds of pollution. The principal source of foul weather acoustic noise is from water droplets. Whether hanging from a wet line, arriving at the line as rain drops, or streaming from the line, water can give rise to various types of discharge. Rime ice on conductors may also give rise to noise. Both comparative and analytical methods exist which predict A-weighted levels of audible noise for proposed high-voltage lines. The methods currently available are described and compared in an IEEE Subcommittee report (1982) A comparison of methods for calculating audible noise of high voltage transmission lines and in CIGRÉ Working Group Interferences produced by corona effect of electrical systems (1974).

104 EN : Design influences The most important design influence on the audible noise levels produced by a high-voltage line is the electric field generated very close to the conductors (surface electric gradient). This field is influenced by voltage, number of conductors per phase bundle, size of conductors, phase spacing, and to a lesser extent, line configuration, line phasing, line height, and line proximity to other lines or wires. Audible noise levels are further influenced by the relative smoothness of conductor and hardware surfaces and contamination due to hydrophobic materials. In general, audible noise levels become a significant design concern only for lines operating at voltages of 400 kv or above. For these high voltages, noise-level prediction methods assume that line hardware is designed or shielded so that only the corona on conductors will be responsible for observed audible noise levels in wet weather, and that conductors are installed taking care not to damage their surfaces. As with radio noise, audible noise levels may be a little above ultimate expectation during an initial weathering period Noise limit Maximum permissible levels of audible noise may be given by national or local authorities and specified in NNAs or the Project Specification, preferably as a weighted noise level in db above the background noise level at a specified distance from the line Corona loss The corona loss is the power lost due to corona emission. On overhead power lines, corona loss is expressed in watts per metre (W/m) or kilowatts per kilometre (kw/km). The power loss due to corona is typically less than a few kilowatts/kilometre in fair weather but, it can amount to tens of kilowatts/kilometre during heavy rain and up to one hundred kilowatts/kilometre during frost. The magnitude of fair-weather corona loss is insignificant in comparison with foul-weather loss (maximum corona loss). However, fair weather losses occur for a large percentage of time and affect the value of the total energy consumed by the line (yearly average corona loss). In some countries corona loss can be higher in winter. Maximum permissible values of corona loss may be defined in the NNAs or Project Specification in terms of fair weather and foul weather losses in kw/km/year Electric and magnetic fields Electric and magnetic fields under a line The design of transmission lines can be influenced to a great extent by the necessity to limit electric and magnetic fields produced by energised conductors. Basic parameters and methods for the evaluation of power frequency electric and magnetic fields are the following: Electric fields can be determined by using different analytical and numerical methods, or from reduced-scale models. The choice of the most suitable method depends on the complexity of the problem to be solved and on the required degree of accuracy. The method of equivalent charges is applicable when the problem is to calculate the electric field near the ground under overhead lines. The validity of the above two-dimensional assumptions shall be duly evaluated in the presence of three-dimensional effects (i.e. sag of conductors, proximity to towers, irregular ground levels, changes in line direction). If necessary, correction factors may be applied or fully dimensioned calculations made. Magnetic field calculation may call for different methods depending: on the problem to be solved; on the nature of the materials surrounding the conductors; and on the required degree of accuracy. However, for many purposes, it is adequate to apply the fundamental Ampere s law, which gives the intensity of magnetic field produced by each current carrying conductor.

105 EN :2012 Reference levels for electric and magnetic fields are given in the European Council Recommendation 1999/519/EC. NOTE For 50 Hz, those levels are respectively 5 kv/m and 100 µt. Details about the way magnetic fields should be calculated can be found in the Cigré Technical Brochure n 320 "Characterisation of ELF magnetic fields". Different reference levels may be specified in the NNAs Electric and magnetic field induction Electro-magnetic fields near an overhead line may induce currents in and voltages on adjacent conductive objects. Induction effects shall be considered in the case of long metal structures (e.g. communication installations, fences, lines or pipes) or bulky objects (e.g. conductive roofs, tanks or large vehicles) in proximity to power lines. Electricity companies shall be able to take any measures to prevent/remove potentially dangerous, or simply annoying, induction effects. Suitable procedures shall be agreed by the parties concerned in this respect. Prevention measures range from optimisation of the sources by proper arrangement of the circuits to adequate shielding (screens are acknowledged as very efficient against electric fields, while it is generally recognised that there is no adequate and practical way to shield against magnetic fields on a large scale). Most of the effects relate to the induction of voltages on metallic structures or objects which are not in good electrical connection to the general mass of earth. In these cases, each conductive part shall be connected to earth. Long metal structures which are electrically connected to the general mass of earth at one or a few places and which run parallel to electric power lines, shall be connected to earth at appropriate intervals and/or installed with insulating elements to reduce loop sizes and hence induction Interference with telecommunication circuits For interference calculations in telecommunication circuits and suggested measures to be taken to eliminate the effects or reduce them to acceptable levels, reference should be made to relevant International and National Standards and/or to qualified Codes of Practice (i.e. ITU Directives (CCITT) Vol VI Danger, damage and disturbance, 2008) and/or to particular agreements between the parties concerned. Attention should also be paid to the possibility of induced voltages that can represent danger to persons.

106 EN : Earthing systems 6.1 Introduction Purpose The purpose of this Clause 6 and the Annexes G and H is to give guidance on the criteria for the design, installation and testing of earthing systems. Depending on the design of the overhead line, type of supports and local conditions, earthing systems may become necessary. Supports of conducting material are in principle earthed by their footings, but additional measures for earthing may be required. For towers within or adjacent to substations, reference should be made to EN for the design and installation of earthing systems. Supports of non-conducting material need not be earthed. NOTE EN does not apply to overhead lines between separate installations (e.g. substations). Earthing systems shall be designed to ensure the safety of the public by keeping step and touch voltages caused by fault currents to acceptable levels. They are constituted of earth electrodes with or without earthing or bonding conductors. Clause 6 deals with the three requirements for the design of those earthing systems. Annex G provides the corresponding calculation methods for designing the earthing systems. Annex H summarises the guidelines for installation of earthing systems (H.3) and testing by measurements of resistance and impedance to earth (H.4). In the case of power lines containing earth wires along the whole length, earthing impedance shall be determined including the effect of earth wires and the neighbouring supports (H.4.4) Requirements for dimensioning of earthing systems The design of earthing systems at power frequency shall meet at least the following 3 requirements: a) to ensure mechanical strength and corrosion resistance by observing minimum dimensions; b) to withstand, from a thermal point of view, the highest fault current as determined by calculation;. c) to ensure personal safety with regard to step and touch voltages appearing during an earth fault. Moreover damage to property and equipment shall be avoided. Parameters relevant to earthing system dimensioning are thus: value and duration of fault current (given in 6.3.2); characteristics for soil resistivity (given in H.2.1). Subclauses 6.2 to 6.4 deal with the three design requirements of earthing systems: 6.2 with regard to corrosion and mechanical strength (Annex G.2 for the minimum dimensions); 6.3 with regard to thermal strength (Annex G.3 for the calculation method of the fault current); 6.4 with regard to human safety (Annex G.4 for the calculation method of the touch voltage). Finally Subclause 6.5 provides some guidelines regarding site inspection and documentation of earthing system. When an overhead line is constructed with two or more different voltage levels, the three requirements for the earthing system shall be met for each voltage level. Simultaneous faults in different voltage circuits need not be considered.

107 6.1.3 Earthing measures against lightning effects EN :2012 The footing resistance values have an influence on the back-flashover rate of the line and therefore affect the lightning performance of the line (see 5.4.4). However, it is not within the scope of this standard to specify the lightning performance, because that is matter of optimisation in individual projects. Maximum or reference resistance values shall be specified in the NNAs or Project Specification Transferred potentials The transfer of potential may occur due to metallic pipes and fences, low voltage cables etc., and general guidelines are difficult to provide especially because circumstances vary from one case to another. Guidelines on individual cases shall be determined by the utility. Proposals from IEC TC 64 also give guidance. Rules for telecommunication systems on, or in the vicinity of, high voltage earthing systems are outside the scope of this standard. When considering transferred potentials due to telecommunication systems, existing international documents (i.e. ITU [CCITT] directives) shall be taken into account. 6.2 Ratings with regard to corrosion and mechanical strength Earth electrodes The earth electrodes, being directly in contact with the soil, shall be of materials capable of withstanding corrosion (chemical or biological attack, oxidation, formation of an electrolytic couple, electrolysis, etc.). They shall resist the mechanical influences during their installation as well as those occurring during normal service. Mechanical strength and corrosion considerations dictate the minimum dimensions for earth electrodes given in G.2. If a different material, for example stainless steel, is used, this material and its dimensions shall meet the requirements a) and b) in NOTE It is acceptable to use steel reinforcing bars embedded in concrete foundations and steel piles as a part of the earthing system Earthing and bonding conductors For mechanical and electrical reasons, the minimum cross-section of earthing and bonding conductors shall be: copper 16 mm²; aluminium 35 mm²; steel 50 mm². Composite conductors can also be used for earthing provided that their resistance is equivalent to the examples given. For aluminium conductors corrosion effects shall be considered. Earthing and bonding conductors made of steel require protection against corrosion. 6.3 Dimensioning with regard to thermal strength General Because fault current levels are governed by the electrical system rather than the overhead line the values shall be provided by the network utility. In some cases, steady-state zero-sequence currents should be taken into account for the dimensioning of the relevant earthing system. For design purposes, the currents used to calculate the conductor size should take into account the possibility of future growth. The fault current is often subdivided in the earth electrode system; it is, therefore, possible to dimension each electrode for only a fraction of the fault current.

108 EN : The final temperatures involved in the design, and to which reference is made in the following Subclause 6.3.2, shall be chosen in order to avoid reduction of the material strength and to avoid damage to the surrounding materials, for example concrete or insulating materials. No permissible temperature rise of the soil surrounding the earth electrodes is given in this standard because experience shows that soil temperature rise is usually not significant Current rating calculation The calculation of the cross-section of the earth electrodes and earthing conductors depends on the value and duration of the fault current as given in G.3. The fault current parameters are mainly dependent on the method of earthing the neutral of the system. There is a discrimination between fault duration lower than 5 s (adiabatic temperature rise), and greater than 5 s. The final temperature shall be chosen with regard to the material and the surroundings. Nevertheless, the minimum dimensions in 6.2 shall be observed. 6.4 Dimensioning with regard to human safety Permissible values for touch voltages Risk of harm exists depending on the magnitude of current passing through the human body and IEC/TS gives guidance on the effects of this current due to its magnitude and duration. In practice, it is more convenient to refer to touch voltages. Touch voltage limits are given in Figure 6.1 based on the calculations given in G.4.1. The curve U D1 represents the value of voltage that can appear across the human body, bare hand to bare feet. No additional resistances have been considered in that curve. Nevertheless, it is permitted to use the curves, U D2 to U D4 based on the calculations given in G.4.2, to take account of additional resistances such as footwear or protective high resistivity materials. Every earth fault will be disconnected automatically due to substation protection or by hand. Thus indefinitely applied touch voltages do not appear as a consequence of earth faults. For step voltages this standard does not define permissible values. NOTE Permissible values of step voltages are somewhat greater than the permissible touch voltages; therefore, if an earthing system satisfies the touch voltage requirements, then it can be assumed that in most cases dangerous step voltages will not occur. For the relevant fault duration the correct operation of protection and interrupting devices shall be taken into account. Methods of calculation and values of touch voltage shall be specified in the NNAs or the Project Specification Touch voltage limits at different locations Figure 6.1 shows touch voltage limits, U D1 (voltage differences) which can appear across the human body at different typical locations. The curves, U D2, U D3 and U D4 illustrate the effects of progressively increased additional resistances. If specified in the NNA, Figure 6.1 may be replaced with Figure B.2 from EN 50522:2010.

109 EN : V U D4 U D3 U D2 Voltage difference UD U D1 10 0,01 0,1 1 s 10 Duration of the fault current t F Figure 6.1 Examples of touch voltage limits (voltage difference U D ) as a function of the duration of the fault current t F The voltage difference, U D, acting as a source voltage in the touching circuit with a value that guarantees the safety of a person when there are additional resistances, R a, see G.4.2. The curves in Figure 6.1 are: - Curve U D1 : R a = 0 Ω (example 1); - Curve U D2 : R a = Ω, R a1 = Ω, ρ E = 500 Ω m (example 2); - Curve U D3 : R a = Ω, R a1 = Ω, ρ E = Ω m (example 3); - Curve U D4 : R a = Ω, R a1 = Ω, ρ E = Ω m (example 4). Description of typical locations corresponding to the above mentioned examples 1 to 4 and curves, U D1 to U D4 in Figure 6.1. Example 1 - Curve U D1. Locations such as play grounds, swimming pools, camping areas, recreational areas and similar locations where people may gather with bare feet. No additional resistance other than the body resistance is considered. Example 2 - Curve U D2. Locations where it can be reasonably assumed that people are wearing shoes such as pavements of public roads, parking places etc. The additional resistance of Ω is considered. Example 3 - Curve U D3. Locations where it can be reasonably assumed that people are wearing shoes and the soil resistivity is high e.g Ω m. The additional resistance to be taken into account is Ω. Example 4 - Curve U D4.

110 EN : Locations where it can be reasonably assumed that people are wearing shoes and the soil resistivity is very high e.g Ω m. The additional resistance to be taken into account is Ω. A touch voltage of 80 V may be accepted for periods longer than 10 s Basic design of earthing systems with regard to permissible touch voltage Application of the requirements a) and b) in will give the basic design of the earthing system. This design shall be checked with respect to the danger of excessive touch voltages, and can then be considered as a type design for similar situations. The block diagram of Figure 6.2 shows a general approach to the design of an earthing system with regard to permissible touch voltage. Numbers between parentheses are explained after the Figure. All the following explanatory remarks are related to Figure 6.2.

111 EN :2012 Figure 6.2 Design of earthing systems with regard to permissible touch voltage 1) For wood or other non conductive poles or towers without any conducting parts to earth, earth faults are not possible in practice and there are no requirements for earthing. 2) Towers at locations which are freely accessible to people and where people can be expected to be either for a relatively long time (some hours per day) during some weeks, or for a short time but very frequently (many times a day) for example close to residential areas or play grounds, are included and shall be reviewed in more detail. Locations which are only occasionally occupied such as forests, open country sides etc. are not included.

112 EN : ) In those locations where towers are not freely accessible or where access by people will be rare, and where the line is provided with automatic disconnection for protection, the touch voltages need not be considered. If it can be assumed that access by people will be rare, then the probability of this access and the incidence of a simultaneous automatically cleared fault can be considered negligible and thus the earthing design can be considered satisfactory. 4) See H.4.4 regarding the determination of the earth potential rise. 5) If earth potential rise is lower than 2U D related to appropriate circumstances curves, U D2, U D3 or U D4 of Figure 6.1 then the design can be considered acceptable. The touch voltage under most of these circumstances is only a fraction of earth potential rise, which is explained in detail in G.4.1. In areas with unpredictable soil conditions the voltage difference U D shall be proved, generally by measurements. 6) See G.4.1 regarding the determination of touch voltages. 7) See Figure 6.1, curve U D1, which is the same as U TP, permissible touch voltage. 8) If the condition given in previous remark (7) is not satisfied, then remedial measures to reduce the touch voltage shall be taken. These measures may be specified in the NNAs. NOTE These measures can be for example: buried potential grading rings, insulation of the tower, increase of the resistance of the upper soil layer, etc. Transferred potentials, if they occur shall always be checked by a separate calculation (see 6.1.4) Measures in systems with isolated neutral or resonant earthing In systems with isolated neutral or with resonant earthing, where touch voltages are higher than the permissible value, one of the following measures may be taken in order to make sure that a long lasting earth fault at the tower is unlikely to occur or the duration of the earth fault is limited to a short duration: using long rod insulators or solid core insulators; using insulators of which the insulation performance may be seen by visual inspection (for instance cap and pin insulators of glass); using an earth fault detection tool and disconnecting the line, if an earth fault occurs. 6.5 Site inspection and documentation of earthing systems For overhead lines with a nominal system voltage exceeding AC 45 kv, a site plan of the earthing system shall be provided which shows the components and position of the earth electrodes, their branching points and the depth of burial. For lines with nominal system voltage exceeding AC 1 kv up to and including AC 45 kv, a site plan may be provided. Where identical earthing systems are installed, a generic site plan is recommended. If specific measures are needed to achieve permissible touch voltages, they shall be included in the site plan and shall be described in the Project Specification.

113 EN : Supports 7.1 Initial design considerations Introduction The purpose of this clause is to provide guidance on the structural design of supports. Subclause 7.2 deals with the materials of supports. Subclauses 7.3 to 7.8 deal respectively with lattice steel towers (7.3 and Annex J), steel poles (7.4 and Annex K), wood poles (7.5), concrete poles (7.6), guyed structures (7.7) and other structures (7.8). Generally, the following items are considered for each support type: basis of design, materials, durability, structural design, ultimate limit states, serviceability limit states, resistance of connections and design assisted by testing. Subclauses 7.9 to 7.12 deal respectively with corrosion protection and finishes (7.9), maintenance facilities (7.10), loading tests (7.11) and assembly and erection (7.12). In order to properly and efficiently design the structures, it is recommended to provide the information specified in Annex L. Unless otherwise specified, durability shall comply with the specific requirements of the parent structural Eurocodes: EN , EN and EN Some numerical values identified by in the NNAs or the Project Specification. boxed values in the following subclauses may be amended If a defined life-time is required, a reference time-period specifying environmental conditions, environmental requirements, maintenance management strategy, performance criteria, shall be specified in the NNAs and/or in a Project Specification prior to an order Structural design resistance of a pole Structural design resistance (R d ) of a pole (see 3.7.4) due to bending is the overall load applied horizontally to the top of the pole as detailed by the pole supplier for a given foundation depth, with any vertical load ignored Buckling Resistance For self-supporting structures, except lattice steel towers, where vertical loads are high and/ or soil conditions are poor and/ or a high slenderness ratio is apparent, the buckling resistance of the structure shall be considered. 7.2 Materials Steel materials, bolts, nuts and washers, welding consumables For requirements and properties for structural steel, see EN For requirements and properties for bolts, nuts, washers and welding consumables, see EN Cold formed steel For requirements and properties for cold-formed steel, see EN Requirements for steel grades subject to galvanising Except where otherwise specified, when steels are to be galvanised, in order to avoid dull dark grey and excessively thick coating which may result in an increased risk of coating damage, it is recommended that the maximum silicon (Si) and phosphorus (P) contents meet the requirements of EN ISO 1461: C Holding-down bolts Unless stated to the contrary in a Project Specification, the material toughness (steel grade) of holding-down bolts shall be calculated, but the test temperature shall not be greater than 0 C. Anchor bolt nuts shall be compatible with the anchor bolt strength.

114 EN : Concrete and reinforcing steel Concrete and reinforcing steel shall be specified in conformity with the requirements of EN Wood Wood poles shall be specified in conformity with the requirements of EN Guy materials The guy material properties, including the characteristic strength, shall be taken from the relevant standards. The characteristic strength of the guy fittings and insulators shall be at least that of the guy itself Other materials For all other materials, the material characteristics shall be in accordance with the performance requirements of the finished product and shall also meet the functional requirements regarding both strength and serviceability (deformation, durability and aesthetics). Account shall be also taken of the Project Specification and NNAs. 7.3 Lattice steel towers General Subclause 7.3 refers to self-supporting lattice towers predominantly made of angle members with bolted connections. For the design of other types of lattice towers, which are not covered in this standard, the requirements of all the clauses except Clause 2 of EN :2006, shall be complied with. NOTE 1 Clause 2 of EN :2006 refers to basis of design and it is replaced by The requirements of all the clauses but Clause 2 of EN :2006 may also be complied with as an alternative method for the design of lattice towers made of angle members. That choice should be specified in the NNAs. The general requirements of the relevant parts of EN 1993 shall be complied with, except where otherwise specified below. Unless otherwise specified in the NNAs, it is not necessary to consider seismic effects or fire resistance. NOTE 2 For more information about seismic effects on overhead line towers, cf. Annex F of EN : Basis of design Rules given in Clause 3 "Basis of design" are applicable. Members on which it is possible for a man to stand shall be designed to resist a load specified in Materials Materials shall comply with Durability See requirements of Structural analysis a) Method of analysis The internal forces and moments in a statically indeterminate structure shall be determined using elastic global analysis. Gross cross-sectional properties (see ) may be used in the analysis. Lattice steel towers are usually considered as pin jointed truss structures.

115 EN :2012 If the continuity of a member is considered, the consequent secondary bending stresses may generally be neglected. Approximate calculation of member loads by considering tower panels as two-dimensional trusses is acceptable providing the equilibrium conditions are satisfied. It shall be verified that bracing systems have adequate stiffness to prevent local instability of any parts. b) Effects of deformations The internal forces and moments may generally be determined using either: 1) First order theory, using the initial geometry of the structure, or 2) Second order theory, taking into account the influence of the deformation of the structure. Normally, first order theory is used for the global analysis of self-supporting lattice towers. c) Elastic global analysis Elastic global analysis shall be based on the assumption that the stress-strain behaviour of the material is linear, irrespective of the stress level. The assumption may be maintained for both first-order and second-order elastic analysis. Three types of members are considered: main legs and chords, bracings and secondary members (often referred to as redundant members). The secondary (redundant) members may be considered not to be loaded directly by external actions, and assure the local stability of members carrying loads. In the global analysis network the secondary members can normally be neglected. Bending moments due to normal eccentricities are treated in the selection of buckling cases in Bending moments caused by wind loads on individual member are generally negligible, but they may need to be considered in the design of slender bracings or horizontal edge members. Bending moments caused by normal eccentricities in the connections of the diagonals at the leg members are generally negligible, providing that the detail design of the joint is undertaken in order to minimise these effects. NOTE Ultimate limit states General More information about structural analysis can be found in the CIGRE Technical Brochure n 387 "Influence of the hyperstatic modelling on the behaviour of transmission line lattice structures". The partial material factors, γ M as defined in should be applied to the various characteristic values of resistance in as follows: Resistance of cross-section areas to yield strength whatever the class is: γ M0 Resistance of members to buckling: γ M1 Resistance of cross-section areas in tension to fracture: γ M2 Resistance of bolted connections to fracture: γ M2 Resistance of other types of connections: see EN The following numerical values are recommended for lattice towers: γ M0 = 1,00 γ M1 = 1,00 γ M2 = 1,25

116 EN : The NNA's shall indicate which approach shall be employed relevant to subclauses of 7.3.6, where EN 1993 and Annex J are given as alternatives. If no indication is given in NNA, then EN 1993 shall be used instead of Annex J Resistance of cross section areas Classification of cross section areas shall be made according to 5.5 of EN :2005. NOTE 1 Angles are considered to be class 3 or 4 according to 5.5 of EN :2005. The gross cross section areas shall be calculated according to of EN :2005. The net area of cross section areas shall be calculated according to of EN :2005. For hot rolled angles, the effective cross section properties shall be based on the effective widths of the compression legs. The effective widths are determined by applying a reduction factor, ρ, which is determined as follows: ρ = 1 if λ 0, 748 p λp 0,188 ρ = 1if λ p > 0, 748 λ ² with p λ p ( h 2t) / t = or 28,4ε k σ λ p ( b 2t) / t = 28,4ε k σ k σ = 0,43 ε = 235 f y with f y in N/mm² and, b, h and t defined as in Figure 7.1 Figure 7.1 Angle section dimensions NOTE 2 In the case of angles connected by one leg, the reduction factor, ρ, only applies to the connected leg. NOTE 3 This follows the procedure relating to Formulae (4.3) of EN :2005, completed by Notes 1 to 3 of of EN :2006. For cold-formed angles, see EN Tension, bending and compression resistance of members The following design resistance shall be taken into account: 1) Tension resistance shall be calculated according to Formula (6.7) of of EN :2005. For angles connected through one leg, tension resistance should be calculated using one of the following two procedures: a) The method according to the provisions of of EN :2005, b) The method according to the provisions of Annex J.3.

117 EN :2012 2) Compression resistance shall be calculated according to of EN : ) Bending moment resistance shall be calculated according to of EN : ) Bending moment and axial force resistance shall be calculated according to Formula (6.44) of (2) of EN :2005 with the shifts of the relevant centroidal axis, e Ny and e Nz being equal to zero Buckling resistance of members in compression Compression members in lattice towers shall be designed using one of the following two procedures: a) The method according to the provisions of Annex G and Annex H of EN :2005. b) The method according to the provisions of Annex J.4. This method can be used only if fullscale tests are performed according to The torsional and/or flexural-torsional mode should also be checked as follows: Torsional and/or flexural-torsional buckling of equal legged angles is covered by the use of the effective cross section properties in accordance with , For hot rolled unequal legged angles and all other cross sections, see of EN :2005, For cold formed thin gauge members see of EN : Buckling resistance of members in bending Buckling resistance of members in bending should be calculated according to of EN : Serviceability limit states It is normally unnecessary to consider deflection or vibration of a lattice tower, unless specified in the Project Specification. The serviceability limits states are related to the tower geometry, and shall be defined in compliance with the required electrical clearances (to ground and to structure) as given in Clause 5 "Electrical requirements" Resistance of connections The provisions for connections given in EN should be applied. Bolted connections in lattice towers shall be designed using one of the following two procedures: a) The method according to the provisions of Clause 3 of EN :2005, b) The method according to the provisions of Annex J Design assisted by testing Experimental verification by a full-scale test may be required to validate the calculated resistance of either a complete tower or part of it. The full-scale test shall be carried out, according to the provisions given in EN 60652, to determine the load resistance, F test,r. The minimum test load shall be determined from: where F test,r > 1,05 F R,d F R,d is the design load for the ultimate limit state. When the test has been continued up to failure, the results may be used for analysis by recalculating the design strength with the actual characteristics of the specific element that led to damage Fatigue Unless otherwise specified, it is not necessary to consider fatigue.

118 EN : Steel poles General The requirements of EN shall be complied with, except where otherwise specified below. In all the following subclauses except 7.4.8, reference is made to the corresponding chapters of EN in brackets Basis of design (EN :2005 Chapter 2) 1) The rules given in Clause 3 Basis of design are applicable, although traditional design methods are equally acceptable, if stated in the NNA. 2) Unless otherwise specified, it is not necessary to consider seismic effects, fatigue or fire resistance. 3) If a dynamic analysis is required, it shall be undertaken whilst taking into account the different factors influencing the behaviour of the pole such as conductors, dampers and foundations. Dynamic effects, where appropriate, may be considered by applying dynamic factors to the loading, and adopting a quasi-static design approach Materials (EN :2005 Chapter 3) 1) Materials shall comply with ) The grades of structural steel subjected to loads shall reflect the manufacturing process and the minimum service temperature, but in general a Charpy V-notch energy of 40 J at 20 C for steel thicknesses greater than 6 mm is recommended for steel poles or tubular welded structures Durability (EN :2005 Chapter 4) See Structural analysis (EN :2005 Chapter 5) 1) The internal forces and moments in any transverse section of the structure shall be determined using elastic global analysis. 2) The second order theory, taking into account the influence of the deformation of the structure, shall be used for the global analysis of steel poles. 3) Global elastic analysis shall be based on the assumption that the stress-strain behaviour of the material is linear, irrespective of the stress level. 4) The design assumptions for the connections shall satisfy the requirements specified in ) For steel poles, only class 3 and class 4 cross sections, according to the definition given in EN , shall be considered and the analysis limited to elastic behaviour Ultimate limit states (EN :2005 Chapter 6) General 1) Steel poles and components shall be so proportioned that the basic design requirements for ultimate design state given in Clause 3 Basis of design are satisfied. 2) The partial material factors, γ M shall be taken as follows: a. Resistance of cross section areas γ M1 = 1,00 b. Resistance of net section area at bolts holes γ M2 = 1,25 c. Resistance of connections see 7.4.8

119 EN :2012 3) It is recommended that the deflection under a second order analysis at the ultimate limit state does not exceed 8 % of the height of the pole above ground level Resistance of cross section areas 1) The resistance of cross section areas of steel poles shall be determined in accordance with the requirements of Annex K. 2) The effective cross section area shall take into account the local buckling, according to Annex K. 3) Vertical reinforcing stiffeners around openings shall be designed to resist buckling in order to satisfy the general requirements of EN , including the connections (welds, bolts, etc.) Serviceability limit states (EN :2005 Chapter 7) 1) Appropriate limiting values of deformations and deflections shall be agreed between the client and the designer. 2) The serviceability limits for steel poles are related to the pole geometry and shall be defined in compliance with the required electrical clearances (to ground and to structure) as given in Clause 5 Electrical Requirements Resistance of connections Basis 1) All connections shall have a design resistance such that the structure remains effective, and that the basic design requirements given in Clause 3 Basis of design are satisfied. 2) The partial material factors, γ M shall be taken as follows: a. resistance of bolted connections: bolts in shear or bearing γ Mbs = 1,25 bolts in tension γ Mbt = 1,25 b. resistance of welded connections γ Mw = 1, Bolts (other than holding-down bolts) 1) The design resistance of bolts in shear, bearing or tension shall be designed using one of the following two procedures: a. The method according to the provisions of Clause 3 of EN :2005; b. The method according to the provisions of J.5. 2) The design resistance of preloaded high strength bolts is given in of EN : Slip joint connections Slip joint connections need not be justified by calculation if the following requirements are observed: 1) When modelling the pole considering a global elastic analysis, only the nominal inside male section in the splice area shall be considered for resistance. 2) The connections are defined, on drawings, with a nominal lap at least equal to 1,5 times the maximum average diameter across angles of the female section. 3) The assembly is carried out on site. To take into account variations in thickness due to the galvanising and dimensional variations of the polygonal section, the minimum effective length of jointing shall be greater than 1,35 times the maximum average diameter across the angles of the female section.

120 EN : ) However, the sum of the slip tolerances at each joint shall comply with the pole length tolerance defined in the NNAs or in the Project Specification. 5) The jointing force shall exceed the maximum factored design vertical compressive force at joint level. 6) When necessary, anchoring devices on either sides of the slip joint shall be provided on the pole in order to ensure on the site a proper splicing using hydraulic jacks or pulling devices according to the supplier recommendations Flanged bolted connections 1) Preloaded high strength bolts of property classes 8.8, 10.9 or similar shall be used. 2) It is recommended that the centre distance between bolts shall be less than 5 times the diameter of the bolts. 3) The stress in the bolts shall be calculated taking due consideration of the eccentricity of the loading transmitted through the connection as specified in EN ) The design resistance of bolts in shear, bearing and tension are given in Welded connections 1) The design resistances of fillet welds and butt welds are given in 4.3.2, and of EN : ) Welding operations shall be in accordance with EN ) Connections made by welding shall generally conform to the relevant requirements for materials and execution specified in Chapter 4 of EN : ) Complete penetration longitudinal welds shall be used in the splice area of the female section. In other areas, partial penetration longitudinal welds with a minimum of 60 % may be used if they comply with the strength requirements Direct embedding into the concrete 1) Pole-to-foundation connection shall be made preferably by direct embedding of the bottom part of the steel pole into the concrete. 2) The length of the section of the pole embedded into the concrete shall be determined using a linear loads distribution in conformity with requirements of EN ) Due consideration shall be given to the buckling of the steel section if the part of pole embedded is not filled with concrete Base plate and holding-down bolts 1) The base plate and the holding-down bolts shall be adequate to take the applied loads developed at the joint between the structure and the foundation or supporting structure. 2) The design of the anchorage length of bolts into concrete is given in Annex K. 3) The holding-down bolts shall be checked for shear and axial load. Due care shall be taken for possible bending moment due to lateral displacement of the bolts while there is no grouting. 4) An appropriate grouting material, correctly applied, shall be inserted between the base plate and the top of the foundation concrete to ensure the transfer of the shear load. In its absence, the method of load transfer by the holding-down bolts shall be verified. Satisfactory means of drainage and/or ventilation shall be provided to prevent accumulation of water inside poles.

121 7.4.9 Design assisted by testing EN :2012 Experimental verification by a full-scale test may be required to validate the calculated resistance of either a complete steel pole or a part of the structure. The full-scale test shall be carried out to determine the load resistance, F test, R. At least one test shall be carried out on a specimen nominally identical with the series manufacture. The minimum test load shall be determined from: where F test, R > 1,05 F R, d F R, d is the design load for the ultimate limit state. Alternatively, when the test has been continued up to failure, the results may be used for analysis by recalculating the design strength with the actual characteristics of the specific element that led to damage. 7.5 Wood poles General The requirements of the standard EN Structural timber - Wood Poles for overhead lines shall be complied with. However, as an alternative to 7.5.5, EN shall be used, if so specified in NNA. When using EN , the recommended value for parameter K mod, which is directly connected to the strength of wood, is 1,0 if not specified in the NNA or in the National Annex NA EN Basis of design 1) The rules given in Clause 3 Basis of design are applicable. 2) Unless otherwise specified, it is not necessary to consider seismic effects, fatigue design or design and construction for fire resistance Materials 1) Materials shall comply with ) The shape and dimensions shall comply with EN ) Sawn or laminated and glued timber is not covered in this standard. For these materials EN shall be used Durability See requirements of Ultimate limit states Basis 1) Wood poles and components shall be so proportioned that the basic design requirements for ultimate design state given in Clause 3 Basis of design are satisfied. 2) The partial material factors γ M shall be taken as follows: Resistance of wood pole cross sections and elements: - in normal load conditions γ M1 = 1,40 - in accidental conditions γ M1 = 1,10 - under bolted connections γ Mb = 1,25 At permanently loaded wood parts (i.e. top cantilever of a guyed angle support) a reduction of the resistance may be required. Further information shall be given in NNA s for such use Calculation of internal forces and moments 1) The internal forces and moments in any transverse section of the structure shall be determined normally using linear elastic global analysis.

122 EN : ) If the flexibility of the structure makes it necessary, the second order theory (P-Delta effect), taking into account the influence of the deformation of the structure, shall be used for the global analysis. Alternatively, higher partial material factors shall be employed for linear analyses. Further requirements shall be given in NNA or Project Specification. 3) Global elastic analysis shall be based on the assumption that the stress-strain behaviour of the material is linear, irrespective of the stress level. 4) In guyed wood structures, the simultaneous compression and bending of the pole(s) shall be considered. The measured or maximum allowable initial out of straightness shall also be considered. 5) Measured values (if available) of the pole dimensions may also be used instead of the standard table values given in different NNAs. See the definition of allowable value for the out of straightness in EN ) The taper (i.e. the uniform change of diameter over the length) of the wood pole shall be taken into account. Further information (values of taper etc.) shall be available in NNA, Project Specification or pole supplier's catalogues Resistance of wood elements The resistance of wood poles against tension, compression and bending shall be determined so, that in any cross section of the pole the following formula are satisfied: σ d f d where f d = f k / γ M1 σ d f d f k is the calculated stress (design value); is the design strength; is the characteristic strength (given in NNA or by pole supplier) complying with EN 14229; γ M1 is the partial material factor for wood (see ). The value of the characteristic strength, f k shall comply with the climatic conditions prevailing at the location where the trees were grown. Modulus of elasticity, E will be given in the NNA or by the pole supplier. NOTE According to EN the characteristic strength is based on 5 % exclusion limit and is calculated from: f k = k m (f m,05) f m,05 = f m - 1,65 f s where f m f s f m,05 m(f m,05) Decay conditions k is the mean value of a normally distributed test sample; is the standard deviation of a test sample; is the 5 % exclusion limit value of a test sample; is the mean of f m,05 values of different test samples; is the reduction factor depending on the size (= number of tests) of the smallest sample. The value of k varies from 0,9 to 1,0. Minimum size of a sample is 50. Wood poles, being natural products, are more prone to decay than most overhead line components. It is recommended that design of wood poles should take account of the very probable loss of strength that will occur over the service of life of the pole. This may be done be specifying larger poles than required by the initial strength requirements, or by increasing the partial factor.

123 7.5.6 Serviceability limit states EN :2012 1) Serviceability limit states for wood poles are deformations or deflections, which may affect the appearance or the effective use of the structure. 2) The serviceability limits are related to the tower geometry and shall be defined in compliance with the required electrical clearances (to ground and to structure) as given in Clause 5 Electrical requirements. 3) Options for serviceability limits may be given in NNA or Project Specification Resistance of connections 1) All connections shall have a design resistance such that the structure remains effective, and that the basic design requirements given in Clause 3 Basis of design are satisfied. EN shall be used in the design of connections, when applicable. 2) The design resistance of bolts in shear or tension is given in Annex J.5. 3) When applicable, EN shall be used for calculating the shear capacity in connections between wood parts and in connections between a wood part and a steel part Design assisted by testing Experimental verification by a full-scale test may be required to validate the calculated resistance of either a complete wood pole or a part of the structure. The full-scale test shall be carried out to determine the load resistance, F test,r. At least one test shall be carried out on a specimen representative of the bulk supply material. The minimum test load shall be determined from: where F test,r > 1,25 F R,d F R,d is the design load for the ultimate limit state. Alternatively, when the test has been continued up to failure, the results may be used for analysis by recalculating the design strength with the actual characteristics of the specific element that led to damage. Any such test item shall be scrapped and not used for normal service conditions since there is the possibility of wood fibres having ruptured during the test. 7.6 Concrete poles General The requirements of EN shall be complied with, except where otherwise specified in EN Dimensioning and construction of the poles shall be in accordance with EN This latter document is completed by the following clauses Basis of design General rules 1) The rules given in Clause 3 Basis of design are applicable, although traditional design methods are equally acceptable, if stated in the NNA. 2) Unless otherwise specified, it is not necessary to consider seismic effects, fatigue or fire resistance Design load The horizontal design load is the load applied horizontally to a conventional section at a specified distance d from the top of the pole, and generally d = 0,25 m. The value of this design load is such that its effect in terms of moment at the base of the pole is equivalent to the effect of the design live loads.

124 EN : Lateral reinforcement In order to control longitudinal cracking from several potential sources, lateral reinforcement is used. This reinforcement consists of lateral ties or spirals. Potential sources of cracking may include the transversal forces, the concrete shrinkage, the thermal effects and the wedging effects due to prestressing loads near the ends of the pole Materials Materials shall comply with 7.2 and with EN Ultimate limit states 1) Concrete poles and components shall be so proportioned that the basic design requirements for ultimate design state given in Clause 3 Basis of design are satisfied. 2) The partial factor for the following actions shall be taken as follows: prestressing force γ Pt = 0,90 or 1,20 * (* depending whether the action is favourable or not for the calculated effect) 3) The partial material factors γ M shall be taken as follows: concrete γ MC = 1,50 steel (ordinary or prestressed) γ MS = 1,15 As far as elements subjected to quality control are concerned, lower values of γ MC and γ MS may be taken Serviceability limit states 1) The partial factor for the following actions shall be taken as follows: prestressing force : γ Pt = 1,00 2) The design values are defined as follows: maximum deflection (where H is the total pole length) = 0,025 H maximum width of cracks, in case of reinforced concrete = 0,3 mm Tensile stresses in the concrete of prestressed concrete poles are not permitted under permanent working loads as well as under loads less than or equal to 40 % of maximum working loads Design assisted by testing Experimental verification by a full-scale test may be required to validate the calculated resistance of either a complete concrete pole or a part of the structure. The full-scale test shall be carried out to determine the load resistance, F test, R. At least one test shall be carried out on a specimen nominally identical with the series manufacture. The minimum test load shall be determined from: where F test, R > 1,30 F R, d F R, d is the design load for the ultimate limit state. Alternatively, when the test has been continued up to failure, the results may be used for analysis by recalculating the design strength with the actual characteristics of the specific element that led to damage.

125 EN :2012 In addition, the maximum deflection at serviceability limit states and the residual deflexion after releasing the load shall comply with the following criteria: maximum deflection after permanent loading for 15 min at serviceability limit state (where, H is the total pole length) = 0,0125 H; maximum residual deflection = 0,003 H. 7.7 Guyed structures General A guyed support can be a lattice steel structure or a pole of tubular steel, concrete or wood with guys of galvanised extra high strength steel wire strands. Various types of configurations exist such as V- tower, portal, column, catenary, double guyed timber leg structures, multi-level guyed tubular leg structures, etc. The requirements of parent Eurocodes shall be complied with, except where otherwise specified below Basis of design 1) The rules given in Clause 3 Basis of design are applicable. 2) Unless otherwise specified, it is not necessary to consider seismic effects, fatigue design or design and construction for fire resistance Materials Materials shall comply with 7.2 and documents relative to parent single supports. For guys the requirements of the standard EN Design of steel structures with tension components shall be complied with, when applicable for transmission line support structures. It gives design rules and dimensional requirements also to guy fittings, saddles and thimbles Ultimate limit states Basis 1) Guyed structures and their components shall be so proportioned that the basic design requirements for ultimate design state given in Clause 3 Basis of design are satisfied. 2) The partial material factor, γ M shall be taken as specified in the parent support, and in addition: - resistance of guys and guy fittings to characteristic strength γ M2 = 1,40 - resistance of guy insulators to characteristic strength γ M2 = 2,00 3) The guyed structure shall generally be analysed using the second order theory. Embedded guyed supports with pre tensioned guys and other simple structures are often stiff enough to allow the use of the first order theory. In single-guyed supports (one guy level only) the linear elastic analysis can be applied, if the global stability of the legs will be verified in separate analyses, where the geometric non-linearity (PD-effect) is taken into account. 4) The analysis shall be based on the assumption that the stress-strain behaviour of the material is linear. 5) The final design resistance of the guy will be reduced from the theoretical value after the assembly and erection due to the bending of the guy around a saddle, thimble, wedge clamp or pin-bolt. This shall be taken into account in the design. See details in EN and EN (all parts). The characteristic strength of the guy shall be the nominal value for ultimate breaking strength specified in appropriate standards, such as EN (all parts), or it can be taken from the manufacturer's specifications, which shall be based on laboratory tests. The final design resistance of the guy assembly shall be calculated from the formula: F d,g = F ke,g / γ M2 where F d,g F ke,g = K e F k,g is the design resistance of guy assembly;

126 EN : F ke,g F k,g γ M2 is the reduced characteristic resistance of the guy; is the characteristic resistance of the guy; is the partial material factor of the guy; K e is the loss factor depending on the end fitting type (see Table 7.1). The value of the loss factor, K e can be proven by laboratory tests or calculations based on the methods in EN In the absence of tests or calculations, the value of the loss factor, K e can be taken from Table 7.1. Other values and options may be specified in the NNA. Table 7.1 Loss factor, K e for the resistance of guy assembly Termination type K e Remarks Metal filled socket 1,00 Resin filled socket 1,00 Helical terminator 1,00 Swaged socket 0,90 Ferrule secured eye 0,90 Wedge clamp 0,80 Type and size according to manufacturer s instructions Thimble and saddle 0,80 Type and size according to manufacturer s instructions U-bolt 0,80 Type and size according to manufacturer s instructions Other 0,50-0,70 Pin bolt etc, depends on the bend radius (see calculation rules in EN ) Calculation of internal forces and moments A latticed column (leg or cross-arm) shall be analysed for bending and buckling using a 3-dimensional beam or pin ended member model or using a simplified 3-dimensional beam model where the axial and bending stiffness shall be calculated from the main member properties while the torsional stiffness shall be derived from the bracing member properties. Torsional-flexural buckling of cold-formed profiles shall be checked. Local buckling of main legs and bracing members shall be taken into account. The use of horizontal diagonal bracings inside a square lattice tower body shall be used to prevent the possible distortion of the cross section. Shear force distribution shall be taken into consideration when calculating member forces at both ends of a hinged latticed column. To consider imperfections in the column, an additional force acting transverse to the column may be added. A value of 1,5 % of the axial force is recommended. In multi-guyed steel supports, the analysis model shall also take into account the large displacements and changing locations of the load points. An incremental second order, finite element method (FEM) analysis is recommended. Care should be taken, when selecting the guy sizes and specifying the initial guy tensions. Guyed poles shall be designed for bending and buckling. For tubular steel poles the local buckling shall be analysed according to Second order analysis In the second order analysis the following aspects shall be taken into account: An initial out of straightness shall be assumed for sections hinged at both ends (tower legs). A normal design value is L/600 for steel sections and L/150 for timber sections, where L is the length of the leg. Smaller values (not less than L/1000) may be used, if these are based on measurements. The out of straightness shall be applied in the most unfavourable direction considering the response or stress

127 EN :2012 concerned. Embedded guyed supports shall be analysed using an initial out of straightness or inclination. The slackening of one or more guys as a result of the load distribution in the different load cases applied shall be taken into consideration. An eccentricity tolerance of 20 mm (in addition to the design eccentricity value) at the ends of a hinged lattice leg shall be applied when calculating bending stresses in the compression leg. The tolerance shall act in the most unfavourable direction considering the response or stress concerned. A smaller value may be used, if this is based on measurements. If an end eccentricity at the ends of hinged lattice legs is used to compensate for the bending effects of the wind load on the leg, an additional special load case shall be checked as follows: extreme gust wind load on the conductors and extreme 10 min mean wind load on the support Maximum slendernesses Maximum slendernesses of structural elements in guyed supports are listed below. The values for legs concern also each span of the leg, if the support contains more than one guy level. For tapered tubular or wood legs the average diameter shall be used for slenderness verification. Lattice steel leg (overall slenderness) 150 Tubular steel leg 150 Wood leg 250 Horizontal beam between legs 250 (in multi-guyed portal supports) Serviceability limit states The serviceability limits are related to the tower geometry and shall be defined in compliance with the required electrical clearances (to ground and to structure) as given in Clause 5 Electrical Requirements Design details for guys The design of the guys shall be based on the tested values of the parameters given in the relevant standards or by the manufacturer. The effective modulus of elasticity of the guy determined from standard, manufacturer or test shall be used in the analysis. The methods and design parameters of EN shall be used, when applicable. Galvanised steel wire strands or steel ropes with steel core shall be used for the guys. To withstand high fault current in the guy, the steel wires can be complemented with aluminium wires, type AL1/STYZ. The guys shall be equipped with devices for retightening. The connection between the guy rope and the anchor device shall be accessible. The connections and tightening devices shall be secured against loosening in service. In the attachment of the guy thimbles, wedge clamps or other relevant equivalent fittings, reliable and documented type tests shall be used. These shall have a reasonable bending radius (proven by tests), if the guy wire will be bent. However, rope clamps are not accepted. See requirements and details in EN Additional information may be given in NNA and Project Specification. The guys used in structures such as V-tower, portal, catenary and double-guyed timber leg tower are generally pretensioned to a small force after the erection of the structure. The effect of this force, usually not greater than 20 kn, may be neglected in the calculations. The guys used in other structures are generally pretensioned to a specified value in order to reduce the deformation at extreme loads. The pretensioning stress shall be specified as a percentage of the breaking or maximum stress. The angle towers shall be vertical after the stringing of the conductors at the reference condition temperature.

128 EN : In order to minimise the possibility of guy vibrations the pretension should be normally less than 15 % of the breaking load of the guy. In angle towers higher values may be needed. At guyed towers, where tubular sections are used as legs, crossarms or horizontals, special attention shall be paid to preventing possible vibration, galloping and fluttering phenomena in the tubular elements. Where cast steel sockets or cast wedge sockets are used in the guy terminations, freedom from defects in the casting should be ensured by an acceptable non-destructive test or manufacturer's certificate. The actual out of straightness of the tower leg shall be checked by inspection before erection and shall comply with the design value. The possible pre-tensioning of the guys shall be checked and maintained during periodical inspections. For a multi-level guyed support, instructions for the erection work are needed because the structure is sensitive to the pre-tensioning of the guys. Due care shall be taken for protection of the guy in populated areas from possible flashover. In some cases, insulation of the guy may be necessary / recommended. Also, guys that may become slack or made loose by the wind, maintenance or other event shall be considered with respect to electrical safety. All guys that are anchored in the ground shall be equipped with some means of making the guy as visible as possible. Due care shall be taken for the protection of the guy from possible exposure to voltage. All guys for wood poles and poles of materials with insulating properties located at a distance less than 0,5 m +D el from live parts, shall be equipped with a sufficiently designed insulator unless the guy is electrically bonded to earth at the ground end or structure end. The earthing shall be such that in the event of failure of the guy, no part shall become live and remain as an electrical risk to the public. If needed, the earthing shall be undertaken at both ends. For all other guyed poles, the guys shall be included in the support earthing system. They shall be equipped with a guy insulator, if specified in the Project Specification. The distance between the lower part of the guy insulator and ground shall normally be at least 3,5 m + D el. This distance shall be at least 3,0 m + D el to take account of a guy that has become slackened or loosened at the lower end. Additional guidance may be given in NNA. 7.8 Other structures Other structures shall be designed in accordance with the requirements of the parent Eurocodes: EN and EN The analysis and the design of other specific structures not covered by the above subclauses shall be agreed between the client and the designer/manufacturer prior to the commencement of the contract. 7.9 Corrosion protection and finishes General The supports shall be protected against corrosion in order to fulfil their intended working life according to Clause 3 Basis of design, taking into account the intended maintenance regime. The following subclauses include minimum requirements, but enhanced requirements, including compliance with local environmental regulations, may be included in the NNAs or the Project Specification Galvanising Unless otherwise stated in the Project Specification, after completion of all fabrication procedures, all steel material shall be hot-dip galvanised and tested in accordance with EN ISO The coating mass (unless otherwise stated) shall be in accordance with the requirements of EN ISO All steel materials prior to galvanising shall be free from any substance or impurities, which may adversely affect the quality of finish. The preparation for galvanising and the galvanising itself shall

129 EN :2012 not adversely affect the mechanical properties of the coated material. All bolts, screwed rods and nuts, including the male threaded portions, shall be hot-dip galvanised (see EN ISO 1461:2009 C.2.2) Metal spraying Unless otherwise stated in the Project Specification, when pieces are too large or difficult to galvanise, they shall be protected against corrosion by thermal spraying a zinc coating over the base metal, performed according to EN ISO and in accordance with EN ISO Zinc deposit thickness shall be not less than 80 µm. When this system is used, the inside surface of hollow sections shall also be protected Paint over galvanising in plant (Duplex system) When a paint coating is to be applied in plant after hot-dip galvanising of steel structures, this coating shall be done as soon as possible. The coating material shall be lead-free according to national general employee protection regulations. Recommended materials, giving an excellent adherence to new galvanised steel, shall preferably be mono-component materials in a base of vinyl or acrylic copolymers in aqueous dispersion. Usually single layer coatings are applied with dried out thickness of 70 µm to ensure proper protection. If required by the technical chart of the coating material supplier, the galvanised steel parts shall be shot blasted before coating. As a blasting material, corundum or granules of high grade steel with a size of 0,25 mm to 0,50 mm shall be used for best results. The blasting pressure and distance are determined so that the maximum thickness of zinc blasted away is 10 µm. The zinc surface of all parts, which are to be coated, shall be dust-free, oil-free and free from all foreign substances as well as free from all zinc corrosive products. These parts shall be coated immediately after surface treatment. Surface preparation and actual painting shall be carried out indoors. After coating, the part number on each construction part shall remain legible for proper erection work. Connecting parts like gusset-plates need not be coated. The drying out of coated construction parts shall be carried out sufficiently in the plant, so that no damage to the coated surfaces can arise through transport. In order to avoid transport damage, pieces of double-sided aluminium-coated cardboard or equivalent material shall be inserted between each individual section. The bundle weight of the coated construction parts shall be assessed such that those elements, which are on the bottom, do not suffer damage due to pressure. After assembling of supports, all minor uncoated parts (bolts, nuts, gusset-plates, etc.) or parts with damage to the coating shall be coated on site Decorative finishes For daytime aircraft warning systems, attention is drawn to the fact that the paint system used shall be compatible with the underlying surface finish. Due reference to International Civil Aviation Organisation (ICAO) Regulations - annex 14 Chapter 6 or local regulations shall be included in the NNAs or the Project Specification Use of weather-resistant steels The use of weather resistance steels requires special design considerations and full-scale test experience. They shall be used with caution in areas where limited corrosion occurs since some corrosion is necessary to provide the weathering layer Protection of wood poles Wood poles shall be protected from deterioration by impregnation with salt or creosote, or other approved preservative agents against rotting, birds and insects. This protection increases the design service life of the wood. Particular attention shall be given to augured holes and scarfings, whether they are made before or after impregnation of preservative.

130 EN : Maintenance facilities Climbing Facilities to allow safe access to structures by authorised personnel shall be as stated in the Project Specification and/or in the NNAs. Where appropriate, this shall include access for live line maintenance. Access to pole cross-arms shall be made preferably by a lightweight, removable device, designed to support the required loads. The design of structures shall take into account the requirements of safe climbing procedures. Each NC shall record in the NNAs the safe method of access to the pole support. Account shall be taken of the requirements to prevent unauthorised access to supports as specified in Maintainability In addition to climbing attachments, the provision of other attachments/holes for installation of maintenance equipment shall be as stated in the Project Specification and/or in the NNAs Safety requirements The requirements and methods of providing for the following shall be as stated in the Project Specification and/or in the NNAs and shall take into account relevant national (and international) legal obligations such as: provision of safety information for the general public (e.g. warning signs, telephone number for emergency contact); prevention of unauthorised climbing; provision of aids to authorised personnel to enable them to correctly identify energised and de-energised conductors (e.g. circuit identification markings); provision for bonding of earth wire and earthing of the support Loading tests Loading tests on overhead lines supports shall be carried out in accordance with EN Assembly and erection The workmanship for assembly and erection shall be in conformity with the minimum requirements of EN , EN , EN and EN

131 EN : Foundations 8.1 Introduction Foundations fulfil the task of transferring the structural loads from the support to the subsoil, as well as protecting the support against critical movements of the subsoil. The general requirements of EN :2004 (Sections 1 to 5) and EN :2007 should be considered. The following subclauses give complementary details for the specific purpose of the foundations of overhead lines. Subclause 8.2 introduces the basis of geotechnical design (section 2 of EN :2004). Sample calculation models are given in Annex M. Subclause 8.3 deals with soil investigation and geotechnical data (section 3 of EN :2004 and EN :2007). Subclauses 8.4 and 8.5 refer to supervision of construction, monitoring and maintenance (section 4 of EN :2004) as well as fill, dewatering, ground improvement and reinforcement (section 5 of EN :2004). Detailed specifications and additional requirements to those detailed in this clause shall be specified in the NNAs or Project Specification. Foundations for supports may take the form of single foundations or separate footings for each leg. The loading on single footings is predominantly in the form of an overturning moment, which is usually resisted by lateral soil pressure, together with additional shear and vertical forces resisted by upwards soil pressure. Common types of single foundations are monoblock footings, pad or raft footings, grillage footings, caisson or pier foundations, and single pile or pile group foundations. When separate footings are provided for each leg the predominant loadings are vertical downward and uplift forces. Uplift is usually resisted by dead weight of the foundation bulk, earth surcharges and/or shear forces in the soil. This also applies to guy foundations. Compression loads are countered by the soil resistance. Common types of separate footing foundations are (stepped) block footings with or without undercut ( pad and chimney, spread footings), auger bored footings with or without expanded base, pier or caisson foundations, grillage foundations and vertical or raked pile foundations. 8.2 Basis of geotechnical design (EN :2004 Section 2) General Foundations for supports shall be considered as foundations of Geotechnical Category 1 or 2 (see Subclause 2.1 of EN :2004). Foundations for overhead lines not exceeding AC 45 kv may be considered as foundations of Geotechnical Category 1 whereas foundations for overhead lines exceeding AC 45 kv should be considered as foundations of Geotechnical Category Geotechnical design by calculation The calculation model may consist of any of the following: an analytical model; a semi-empirical model; a numerical model. The models to be used to determine the foundation resistance are those given in the appropriate code of practice, as given in EN , or in the NNAs, or in the relevant literature, or those which have been used with satisfactory practical experience.

132 EN : Sample analytical models for uplift resistance calculation are given in Annex M.2 for: concrete stepped block footings with undercut; concrete stepped block footings without undercut. Sample semi-empirical models for resistance estimation are given in Annex M.3 for: monoblock foundations, slab foundations; grillage-type slab foundations; single-pile foundations; separate stepped block foundations ( pad and chimney ); auger-bored and excavated foundations; separate grillage foundations; pile foundations. It shall be verified that the ultimate limit states are not exceeded: internal failure or excessive deformation of the structure or structural elements, including footings, piles or basement walls, in which the strength of structural materials is significant in providing resistance (STR); failure or excessive deformation of the ground, in which the strength of soil or rock is significant in providing resistance (GEO). NOTE 1 Limit state GEO is often critical to the sizing of structural elements involved in foundations or retaining structures and sometimes to the strength of structural elements. When considering a limit state of rupture or excessive deformation of a structural element or section of the ground (STR and GEO), it shall be verified that: E d R d E d is the total design effect of actions on foundations resulting from all the actions on the supports as defined in Clause 4 and from the supports themselves. Partial factors for actions, which depend on the reliability level, are already included in the calculation of the actions on the supports. R d is the design resistance of foundations. Partial factors may be applied either: to resistances (R): R d = R{X k } / γ R (EN Design Approach 2) to ground properties (X): R d = R{X k / γ M } (EN Design Approach 3) The set of partial factors to be applied to the main ground properties (or soil parameters) in Design Approach 3 is given in the following Table 8.1: Table 8.1 Partial factors for soil parameters (according to Annex A of EN :2004) Soil parameters Symbol Value Angle of shearing resistance* γ φ' 1,25 Effective cohesion γ c' 1,25 Undrained shear strength γ cu 1,4 Unconfined strength γ qu 1,4 Weight density γ γ 1 * : This factor is applied to tan φ' Partial factors γ R to be applied to resistances could be:

133 EN :2012 found in Annex A of EN :2004 (if it is relevant), determined by test or by calculation. In the former case, the determination of γ R could be undertaken according to Annex D of EN 1990:2002 (Design assisted by testing). NOTE 2 Annex M.3 gives partial factors, γ R for some semi-empirical models for resistance. The choice of the Design Approach and the values of partial factors shall be specified in NNAs or Project Specification. EN Design Approach 1 may also be specified in NNAs or Project Specification. In that case, the set of partial factors for actions that shall be used is given in EN :2004, Annex A. In foundation design, limiting values for the foundation movements should be specified in NNAs or Project Specification. As guidance, limit movement values given in IEC or in Annex H of EN :2004 may be adopted Design by prescriptive measures The foundation of self-supporting wood poles in medium or good soils can be constructed according to the sample rule: Self supporting wood poles shall be erected using direct embedment in the ground. The depth shall be at least 1/7 of the pole length and not less than 1,5 m. The excavation shall be filled with gravel and stones, which shall be carefully compressed to ensure the lateral rigidity of the embedment. Concrete may be used if there is no risk of standing water. Good quality backfill or concrete may be required in poor soils Load tests and tests on experimental models Details concerning the preparation of the tests, testing arrangement, test procedure and evaluation are given in EN Soil investigation and geotechnical data (EN :2004 Section 3) Prior to determination of the type of foundation, and its form and dimensions, the structure of soil below the surface down to a depth of at least the effective width of the foundation, and in the case of a piled foundation, greater than the pile tip depth, shall be known in sufficient detail. Natural risks shall also be considered in the choice of the type of foundation. Geotechnical investigations shall be planned, taking into account the type of foundation and the required parameters for the design of the foundation. The soil investigations shall be carried out to such a depth that all layers, which significantly influence the foundation strength, are included. When determining the extent and depth of soil investigations, information already available concerning the pattern, uniformity and characteristics of the individual layers should be taken into consideration. Where justified, further soil investigation may be omitted. Annex M.1 gives complementary information about geotechnical parameters of soils and rocks. 8.4 Supervision of construction, monitoring and maintenance (EN :2004 Section 4) Prior to the start of the construction, a plan of contingency actions should be devised which may be adopted if excavations reveal soil characteristics or behaviour outside acceptable limits. 8.5 Fill, dewatering, ground improvement and reinforcement (EN :2004 Section 5) If backfill is used, its compaction shall be undertaken carefully in order to achieve soil characteristics as close as possible to those of the undisturbed soil. 8.6 Interactions between support foundations and soil Special attention shall be paid to the interaction of:

134 EN : loads deriving from the support; loads resulting from active soil pressures and the permanent weight of foundation and soil; buoyancy effects of ground water on soil and foundation. These, together with the reaction forces of the soil strata, shall be taken into account in the calculation of the support foundations. Also, the limit state criteria for: acceptable/unacceptable settlement of the foundation, including uneven settlement; imposed deformations on the support or support members; inclinations of the support (especially angle and dead-end supports), shall be defined and taken into consideration.

135 EN : Conductors and earth-wires 9.1 Introduction This clause gives the requirements for conductors and earth wires (ground wires) with or without telecommunication circuits which are attached to overhead line supports. Conductors and earth wires shall be designed, selected and tested to meet the electrical, mechanical and telecommunications requirements as defined by the line design parameters. Consideration shall also be given to the necessary protection against fatigue due to vibration. Design life may be subject to agreement between the supplier and the purchaser. Lines strung with covered conductors (in accordance with EN ) and overhead, insulated cable systems with nominal system voltage exceeding AC 1 kv up to and including AC 45 kv shall be designed according to this standard. In the following subclauses the term "conductor" should be taken to include "earth wires" and where appropriate, conductors and earth wires with telecommunication circuits. NOTE This standard does not apply to wrapped cables or all dielectric self supporting (ADSS) telecommunication cables. Similarly it does not include metal clad telecommunication cables which are not used as earth wires. 9.2 Aluminium based conductors Characteristics and dimensions Conductors shall be manufactured from round or shaped wires of aluminium or aluminium alloy and can contain zinc coated steel wires or aluminium clad steel wires for strengthening. Earth wires shall be designed to the same standards as phase conductors. Homogeneous round or formed wire conductors, both all aluminium (AL1) and all aluminium alloy (ALx), and composite round or formed wire conductors, aluminium or aluminium alloy conductor steel reinforced (AL1/STyz or ALx/STyz), aluminium or aluminium alloy conductor aluminium clad steel reinforced (AL1/yzSA or ALx/yzSA) and aluminium conductors aluminium alloy reinforced (AL1/ALx) shall be designed according to EN 50182, EN or EN as appropriate. For conductors with cross-sectional aluminium area in excess of 50 mm² it is recommended that the diameter of the outer layer round wires shall not be less than 2,33 mm. Material specifications for wire used in these conductors shall be according to EN 50183, EN 50189, EN 60889, EN and EN and the design arrangements shall be specified in the Project Specification or agreed by the purchaser with the supplier. For some projects types of conductors or materials not included in existing EN standards may be used in overhead line construction. In such cases, and in the absence of definitive standards, the Project Specification should specify all the required characteristics together with the relevant methods of test, making reference as appropriate to EN standards. When materials are used which differ from those in the referenced standards their characteristics and their suitability for each individual application should be verified as specified in this standard or in the Project Specification. The design of a conductor, including its construction and the characteristics of the materials, shall take into consideration the effect of permanent elongation (long term creep) on the conductor sag. NOTE Guidance on the methods of design calculation, including an assessment of conductor creep and other characteristics, can be found in IEC and in EN Electrical requirements The resistivity of the aluminium or aluminium alloy wire shall be selected from the values in EN 50183, EN 60889, EN and EN The DC resistance of the conductor at 20 C shall be calculated according to the principles of EN The resistances of a preferred range of round wire conductors are given in EN For conductors with different wire sections the conductor resistance shall be calculated using the resistivity of the wire, the cross-sectional area and stranding parameters of the conductor.

136 EN : The current carrying capacity (ampacity) and the performance under short circuit conditions, particularly the effect on strength, shall be verified against the requirements of the Project Specification. Consideration shall also be given to the predicted radio noise level and audible noise level of conductors for higher voltage systems against the requirements of the Project Specification (see and ) Conductor service temperatures and grease characteristics The maximum service temperatures of aluminium based conductors under different operating conditions shall be specified either in the NNAs or in the Project Specification. This shall give some or all of the requirements under the following conditions: maximum service temperature at normal line loading; maximum short duration temperature for specified times at different line loading(s) above the normal level; maximum temperature due to a specified power system fault. NOTE 1 The use of certain special alloys generally permits the use of higher service temperatures. Information on the calculation of temperature rise due to short circuit currents is given in EN and in CIGRE Technical Brochure n 207 "Thermal behavior of overhead conductors". Alternatively and with suitable precautions the actual temperature rise due to short circuit currents may be measured during a test. The Project Specification shall specify the characteristics of the conductor grease to allow for the maximum conductor temperature during normal service and during short duration overloads following a power system fault. Greases containing soap additives and soap free greases are available. These two types of greases possess different performance characteristics, the most important of which are the oil separation point and the drop point. In the case of soap free greases the drop point may not necessarily exceed 100 C. NOTE 2 Further information concerning greases and their application is given in EN Mechanical requirements The rated tensile strengths of aluminium based conductors, calculated in accordance with EN shall be sufficient to meet the loading requirements determined from Clause 4 in conjunction with the partial factors for conductors given in When considered necessary, the maximum permissible tensile load in the conductor shall be specified either in the NNAs or in the Project Specification Corrosion protection The purchaser and supplier shall agree the requirement for corrosion protection of conductors, which may include grease and/or zinc coating or aluminium cladding of steel wires. Grease, when used, shall comply with the requirements of EN The Project Specification shall specify the type and required amount of grease to be applied during stranding of the conductor. Normally, this shall be selected from one of the cases defined in Annex C of EN For voltages in excess of 100 kv, grease shall not be applied to the outer layer of wires of the conductor. The properties of the grease shall not allow its migration to the conductor surface during its service life. The requirements for coating or cladding of steel wires with zinc or aluminium shall be specified in the Project Specification by reference to EN or EN 61232, as appropriate Test requirements The test requirements for aluminium based conductors shall be as specified in EN The Project Specification may also specify requirements for a conductor creep test, or an elastic modulus test.

137 9.3 Steel based conductors Characteristics and dimensions EN :2012 Information relevant to constructional methods is given in EN Material specifications are given in EN for zinc coated steel wire and EN for aluminium clad steel wire. NOTE see also Electrical requirements The resistivity of zinc coated steel wires is given for calculation purposes in EN and specified for aluminium clad steel wires in EN The DC conductor resistance at 20 C shall be calculated according to the principles of EN NOTE Cf. also in relation to current rating, short circuit performance and radio noise level when relevant to the conductor design Conductor service temperatures and grease characteristics The maximum service temperatures of steel based conductors under different operating conditions shall be specified either in the NNAs or in the Project Specification. This shall give some or all of the requirements under the following conditions: maximum service temperature at normal line loading; maximum short duration temperature for specified times at different line loading(s) above the normal level; maximum temperature due to a specified power system fault. The Project Specification shall specify the characteristics of conductor grease taking into account the service temperatures. NOTE Cf. also Mechanical requirements The rated tensile strength of steel based conductors, calculated in accordance with the principles given in EN 50182, or the relevant national standards, shall be sufficient to meet the loading requirements determined from Clause 4 in conjunction with the partial factors for conductors given in When considered necessary, the maximum permissable tensile load in the conductor shall be specified either in the NNAs or in the Project Specification Corrosion protection The purchaser and supplier shall agree the requirement for corrosion protection of steel based conductors which may include grease and/or zinc coating or aluminium cladding. The requirements for coating or cladding of steel wires with zinc or aluminium shall be specified in the Project Specification by reference to EN or EN as appropriate. Grease, when used, shall comply with the requirements of EN The Project Specification shall specify the type and required amount of grease to be applied during stranding of the conductor. Normally this shall be selected from one of the cases defined in Annex C of EN 50182:2001. For voltages in excess of 100 kv grease shall not be applied to the outer layer of wires of the conductor and the properties of the grease shall not allow its migration to the conductor surface during its service life Test requirements Steel based conductors shall be tested according to the relevant requirements of EN and of EN and EN Copper based conductors Conductors are generally constructed from round wires of copper or copper alloy according to relevant National Standards in the absence of any existing International Standards. Where appropriate, requirements shall be specified in the Project Specification.

138 EN : Conductors and ground wires containing optical fibre telecommunication circuits Characteristics and dimensions The design characteristics of OPCON's and OPGW's with optical telecommunication fibres shall be specified in the Project Specification. NOTE Electrical, mechanical and physical requirements and test methods for OPGW are given in EN All aspects of OPCON's and OPGW's are currently being studied by a Joint Working Group of CLC/TC 7 and CLC/TC 86 - Optical cables to be used on electrical power lines. Reference should be made to EN , EN and EN for optical cables and EN for conductor requirements Electrical requirements The DC resistance at 20 C of an OPCON or OPGW shall be calculated using the resistivity of the individual aluminium, aluminium alloy, zinc coated steel or aluminium clad steel wires together with the appropriate stranding constant and the resistivity of other aluminium components of the conductor according to the requirements of Annex A of EN :2003 and/or the principles of EN Reference shall be made in the Project Specification to the current carrying capacity and short circuit conditions, and, if appropriate, radio noise level Conductor service temperatures The maximum service temperatures of OPCON's and OPGW's shall be specified either in the NNAs or in the Project Specification. This shall give the maximum continuous temperature and the maximum short duration temperatures for specified times. NOTE Cf. also Mechanical requirements The rated tensile strengths of OPCON's and OPGW s calculated according to the Project Specification, shall be sufficient to meet the loading requirements determined from Clause 4 in conjunction with the partial factors for conductors given in When considered necessary, the maximum permissible tensile load in the conductor shall be specified either in the NNAs or in the Project Specification Corrosion protection The Project Specification shall specify or the purchaser shall agree with the supplier the requirement for corrosion protection of OPCON's and OPGW's, which may be grease and/or aluminium cladding or zinc coating of steel strands Test requirements The test requirements for OPCON's and OPGW's shall be as specified in EN and in the Project Specification. 9.6 General requirements Avoidance of damage The Project Specification shall specify the packaging and marking requirements for delivery of the conductor in accordance with EN The manufacturer shall also specify the minimum diameter to be used for the conductor stringing equipment (e.g. tensioner/puller bull wheels, running blocks etc) and any special stringing procedures or precautions required to avoid conductor damage and/or birdcaging. The purchaser shall also ensure that requirements for conductor fittings e.g. selection, positioning and installation are adequately specified to avoid the risk of birdcaging Partial factor for conductors The partial factor applied to the rated tensile strength for all types of conductors shall have a minimum value of:

139 EN :2012 γ M = 1,25 A different value for the partial factor may be specified in the NNAs Minimum cross-sections Due to the risk of fatigue failure, it is recommended that solid single wire conductors, or conductors having a cross-sectional area of 25 mm² or less, should not be used unless a satisfactory service performance history indicates that such conductor sizes are suitable Sag - tension calculations Once an overhead line is constructed, the phase conductors may be subject to extreme events (high temperatures during periods of high electrical loading, etc.). Under all foreseeable conditions, the conductors shall not break nor sag such that minimum electrical clearances are compromised. To assure that these conditions are met over the life of the line, the designer shall specify initial measured (i.e. stringing) sags, and determine the sag in those conditions with sag-tension calculations. Conductor shall be designed to resist the tensions occurring due to climatic loadings at the specified Reliability Level. The conductors shall also not fail due to fatigue under persistent wind-induced vibration motions nor sag such that minimum electrical clearances are compromised. NOTE Further detailed discussion regarding the development and application of sag/ tension calculations can be found in Sag Tension calculation methods for overhead lines CIGRE Technical Brochure No. 324, and CIGRE Electra Journal, June 2007, No Test reports and certificates The results of all type tests shall be reported in certificates issued by the supplier or a qualified organisation. These shall be valid without time limit provided that there is no change in materials, construction, method of manufacture or manufacturer of the conductor. The results of sample tests shall be reported in a certificate issued by the supplier for each lot delivered. 9.8 Selection, delivery and installation of conductors Information relating to the selection, delivery and installation of conductors is given in Annex N.

140 EN : Insulators 10.1 Introduction The insulator designs include string insulator units of the cap and pin and long rod types, line post insulators, pin type insulators and stay wire insulators. These may be manufactured using ceramic material or glass, or produced from composite material. On some overhead lines, combinations of these insulators may be used. NOTE All these types of insulators are covered by EN and/or IEC Publications except stay wire insulators. Insulators shall be designed, selected and tested to meet the electrical and mechanical requirements as determined by the design parameters of the overhead line. Design life may be subject to agreement between the supplier and the purchaser. Insulators shall be resistant to the influence of all outdoor climatic conditions including solar radiation. They shall be resistant to atmospheric pollutants and be capable of satisfactory performance when subjected to the pollution conditions specified in the Project Specification. Insulators shall be designed for ease of maintenance including, when specified, maintenance under live line conditions Standard electrical requirements The design of insulators shall be such that the required electrical withstand voltages (see subclause 5.3) as specified in the NNAs or Project Specification are achieved. These requirements are summarised in Table RIV requirements and corona extinction voltage All types of insulators for overhead lines shall, under test conditions, only produce levels of radio interference consistent with the overall level specified for the installation. The visible corona extinction voltage shall, when applicable, be specified. Further information on corona effect, including radio interference, is given in Clause 5. When type tests are required they are normally performed on complete insulator sets or on line post insulators. The purchaser shall specify the applied voltage and the corresponding maximum radio interference voltage and if required the minimum visible corona extinction voltage. Tests shall be carried out in accordance with the requirements of EN When type and/or sample tests are required on string insulator units they shall be carried out in accordance with EN

141 EN :2012 Table 10.1 Standard electrical requirements Voltage range 1 kv < U s 245 kv U s > 245 kv Insulator type Insulator sets Insulator sets Cap and pin a Long rod a Composite b Line post a Cap and pin a Long rod a Composite b a b c Wet power frequency withstand voltage Dry lightning impulse withstand voltage Wet switching impulse withstand voltage Puncture withstand voltage (single unit) Tests carried out to EN and EN X X - X X X - - Tests carried out to EN (applicable to composite insulator units only), and EN as appropriate. For those line post insulators which are not puncture proof. X X - - X X - X c - X X X - X X - - X X Pollution performance requirements When required by the Project Specification insulators shall comply with the specified pollution performance requirements. Guidance on the design and selection of ceramic and glass insulators for use in polluted conditions is given in IEC/TS In the case of insulators of ceramic material or glass, the purchaser shall specify the pollution performance requirements for insulator sets and line post insulators in accordance with one of the procedures described in EN 60507, or, alternatively, specify the minimum creepage distances, both total and protected. The protected creepage distance, when required, shall be specified and measured using a 90 angle to the axis of the insulator. NOTE A pollution performance test for composite insulators is currently being studied by IEC TC 36 and CIGRE Power arc requirements When required by the Project Specification insulator sets, line post and pin type insulators of all types shall comply with the specified power arc requirements. The purchaser shall state whether a power arc test is required. Information on power arc tests is given in EN The purchaser and supplier shall agree the relevant procedure for a test Audible noise requirements When required by the Project Specification all types of overhead line insulators shall be designed so that they comply with the audible noise requirements specified for the installation. Further information concerning audible corona noise is given in subclause Mechanical requirements Insulators shall comply with the specified mechanical design requirements. The partial factor for all types of insulators, including stay wire insulators, shall be specified in the NNAs or in the Project Specification. The partial material factor shall be applied to the specified mechanical or electro-mechanical failing load according to EN or EN The relevant acceptance criteria shall be used for type and sample tests. If the partial material factor of insulators is not specified in the NNA, the partial material factor for hardware, specified in subclause 11.6, shall be considered

142 EN : Durability requirements General requirements for durability of insulators The durability of an insulator is influenced by the design, the choice of materials and the manufacturing procedures. All materials used in the construction of insulators for overhead lines shall be inherently resistant to atmospheric corrosion which can affect their performance. An indication of the durability of string insulator units of ceramic material or glass can be obtained from the thermal-mechanical test as specified in EN In special cases, it may be necessary to consider fatigue characteristics by means of suitable tests specified in the Project Specification or agreed between the purchaser and the supplier. NOTE Background information concerning the thermal-mechanical test is given in IEC/TR Protection against vandalism Special precautions may be necessary to combat the effects of vandalism. When specified in the Project Specification, the supplier shall offer methods to improve the performance and to meet the relevant requirements. NOTE Information relating to impact testing of string insulator units of the cap and pin type is given in ANSI C29.1: American National Standard for electrical power insulators Test methods and ANSI C29.2: American National Standard for electrical power insulators Wet process Porcelain and Toughened Glass Suspension Type Protection of ferrous materials All ferrous materials, other than stainless steels, used in overhead line insulators shall be protected against corrosion due to atmospheric conditions. The usual form of protection shall be hot dip galvanising which shall meet the test requirements specified in EN For installation in especially severe conditions, either an increased thickness of zinc may be specified in the Project Specification, or other methods agreed between the purchaser and the supplier. In these cases the methods of test to demonstrate the enhanced corrosion resistance shall also be agreed. Reference may also be made to EN ISO Additional corrosion protection When specified in the Project Specification or recommended by the supplier and agreed by the purchaser, the pins of cap and pin type string insulator units shall be fitted with zinc sleeves for additional corrosion protection. The purchaser and supplier shall agree the specification for the sleeve which shall include details of the mass, shape, zinc purity and degree of bonding. NOTE Suitable test methods are given in EN Material selection and specification Materials used in the manufacture of overhead line insulators shall be selected having regard to the relevant electrical, mechanical and durability requirements. The manufacturer shall ensure that the specification and quality control of materials is sufficient to ensure continuous achievement of the specified characteristics and performance requirements. Locking devices used in the assembly of insulators shall comply with the requirements of EN When selecting the grade of malleable cast iron, including spheroidal graphite iron, consideration should be given to the requirements for strength and ductility and, if appropriate, low temperature performance and hot dip galvanising requirements Characteristics and dimensions of insulators The characteristics and dimensions of insulators used for overhead line construction shall wherever possible, comply with the dimensional requirements of the following EN and IEC Publications: string insulator units: EN and EN 60433; line post insulators: IEC 60720; composite insulators: EN and EN

143 EN :2012 Compliance with the above Publications also requires compliance with HD 474, EN and IEC Approved types of insulators with dimensional characteristics differing from those specified in the above standards may be included in the Project Specification. All tests and physical characteristics, other than dimensional matters, should comply with the relevant standards. There are no EN or IEC standards for the dimensions of pin type or stay wire insulators. The requirements should be given in the NNAs or the Project Specification Type test requirements Standard type tests When required, type tests on string insulator units, line post insulators, and pin type insulators of ceramic material or glass shall be carried out in accordance with EN Unless otherwise specified in the Project Specification, or agreed by the purchaser with the supplier, the acceptance criteria for the electrical, mechanical and other characteristics shall be as given in EN Design and type tests on composite tension and suspension insulators shall be carried out in accordance with EN Type tests on composite line post insulators shall be carried out in accordance with EN Unless otherwise specified in the Project Specification or agreed by the purchaser with the supplier, the acceptance criteria for all characteristics shall be as given in EN or EN as appropriate. Type tests on insulator strings and sets shall be carried out in accordance with EN The acceptance criteria shall be as given in EN Type tests on stay wire insulators shall be carried out in accordance with the principles of EN Optional type tests When specified in the Project Specification or by agreement between the purchaser and supplier, additional type tests may be specified. Suitable standard specifications exist to cover: radio interference test: EN 60437, EN , and CISPR/TR 18-2; pollution performance test: EN 60507; power arc performance test: EN 61467; impulse voltage puncture test: EN 61211; zinc sleeve test: EN 61325; residual strength test: IEC The performance requirements shall be specified in the Project Specification or agreed by the purchaser with the supplier before the commencement of each test. If other type tests which are not included in existing national or international standards are required by the purchaser, the details of the test procedures and the acceptance criteria shall be specified in the Project Specification or agreed with the supplier at the time of placing the order Sample test requirements The specified sample tests shall be carried out on samples taken at random from each lot of insulators offered for delivery. The tests shall be in accordance with the relevant standard for: string insulator units, line post insulators, and pin insulators of ceramic material or glass: EN , composite tension and suspension insulators: EN 61109, composite line post insulators: EN 61952, stay wire insulators: EN Unless otherwise specified in the Project Specification or agreed by the purchaser with the supplier at the time of placing the order, the acceptance criteria for all characteristics shall be as given in EN or EN as appropriate.

144 EN : When specified in the Project Specification or agreed by the purchaser with the supplier, other sample tests may be specified. Examples of these tests are: radio interference test on single string insulator units of the cap and pin type: EN 60437; zinc sleeve test, where applicable, on pins from cap and pin insulator units: EN Routine test requirements Routine tests as specified in the relevant standard shall be carried out by the supplier on every unit in a lot offered for delivery. The tests shall be in accordance with the relevant standard: string insulator units, line post insulators and pin type insulators of ceramic or glass: EN ; composite tension and suspension insulators: EN 61109; stay wire insulators (visual inspection test only): EN If conditions of service require any alternative routine tests then the details shall be specified in the Project Specification or agreed by the purchaser with the supplier at the time of placing the order Summary of test requirements Annex P summarises all the tests relevant to insulators in porcelain and glass insulating materials. It does not include composite tension and suspension and line post insulators for which the relevant tests are fully detailed in EN and EN Test reports and certificates The results of all type tests shall be reported in certificates issued by the supplier or a qualified organisation. These shall be valid with the conditions and for the periods specified in EN , EN or EN as appropriate. The results of sample tests shall be reported in a certificate issued by the supplier for each lot delivered. The supplier shall certify that all units in each lot delivered have passed the specified routine tests. Any other requirements for certification shall be specified by the purchaser in the Project Specification Selection, delivery and installation of insulators Information relating to the selection, delivery and installation of insulators is given in Annex Q.

145 EN : Hardware 11.1 Introduction Overhead line fittings shall be designed, manufactured and erected in such a way as to meet the overall requirements for the operation, maintenance and environmental impact as determined by the design parameters of the line, on the basis of information contained elsewhere in this standard. Design life may be subject to agreement between the supplier and the purchaser. Overhead line fittings shall be tested in accordance with the requirements of EN 61284, EN and/or EN Any alternative or additional parameters shall be defined in the Project Specification Electrical requirements Requirements applicable to all fittings The design of all fittings shall be such that they are compatible with the specified electrical requirements (see Clause 5) for the overhead line. Arcing devices are not normally designed to reduce the electric field intensity at the line end on overhead lines with nominal system voltages below AC 45 kv. Grading rings or similar devices shall be used where necessary to reduce the electric field intensity at the line end of insulator sets, including the compression terminations of composite insulators. Grading rings or stress control devices are not normally required on string insulator sets for use on overhead lines at or below AC 45 kv Requirements applicable to current carrying fittings Conductor fittings intended to carry the operating current of the conductor shall not, when subjected to the maximum continuous current in the conductor or to short circuit currents, exhibit corresponding temperature rises greater than those of the associated conductor. Also the voltage drop across current carrying conductor fittings shall not be greater than the voltage drop across an equivalent length of conductor. The methods of test and the acceptance criteria shall be in accordance with EN RIV requirements and corona extinction voltage Fittings, including spacers and vibration dampers, for overhead lines shall be designed such that under test conditions the levels of radio interference are consistent with the overall level specified for the installation. The visible corona extinction voltage shall, when applicable, be specified in the Project Specification. Further information on corona effect, including radio interference, is given in 5.9 and the method of test is specified in EN Magnetic characteristics The choice of materials and/or the design of fittings attached to the conductor shall, where appropriate, be such that magnetic losses are acceptably low. The method of test and the acceptance criteria shall, unless otherwise specified in the Project Specification, be in accordance with EN Short circuit current and power arc requirements Fittings shall, when required, comply with the specified short circuit current or power arc requirements. In particular insulator set fittings shall be such that if a short circuit current or power arc test is required they retain, unless otherwise specified in the Project Specification, at least 80 % of their specified mechanical failing load on completion of the test. Arcing horns shall be capable of safely carrying the anticipated fault level current for the anticipated duration of the fault without adverse effect on the safety aspects of overhead line maintenance. Power arc tests on fittings shall be carried out in conjunction with insulator tests (see 10.5) but when agreed between the purchaser and supplier short circuit current follow through tests may be carried out on assemblies of fittings only.

146 EN : Mechanical requirements The design of overhead line fittings shall be such that the specified mechanical design requirements are achieved. The partial factor applied to the specified minimum failure load as defined in EN for all types of line fittings shall have a minimum value of: γ M = 1,6 A higher value of the partial factor may be specified in the NNA. For all fittings upon which a man may stand, the fittings shall withstand a concentrated characteristic load of 1,5 kn Durability requirements All materials used in the construction of overhead line fittings shall be inherently resistant to atmospheric corrosion which may affect their performance. The choice of materials and/or the design of fittings shall be such that bimetallic corrosion of fittings or conductor is minimised. All ferrous materials, other than stainless steels, used in the construction of fittings shall be protected against atmospheric corrosion by hot dip galvanising or other methods specified in the Project Specification, or agreed by the purchaser with the supplier. Reference may also be made to EN ISO Fittings subjected to articulation or wear shall be designed, including material selection, and manufactured to ensure maximum wear resistant properties Material selection and specification Materials used in the manufacture of overhead line fittings shall be selected having regard to their relevant characteristics. The manufacturer shall ensure that the specification and quality control of materials is sufficient to ensure continuous achievement of the specified characteristics and performance requirements. Locking devices used in the assembly of fittings with socket connectors should comply with the requirements of EN When selecting metals or alloys for line fittings the possible effects of low temperature should, where relevant, be considered. When selecting non-metallic materials their possible reaction to temperature extremes, UV radiation, ozone and atmospheric pollution should be considered Characteristics and dimensions of fittings The mechanical characteristics of insulator set fittings shall comply with the mechanical strength requirements, where appropriate, of EN and EN or EN The coupling dimensions of insulator set fittings shall comply with HD 474 or IEC Accessories for the attachment of conductors on line post and pin type insulators, shall be designed such that they can carry the transverse forces due to the conductor tensile forces resulting from the forces on the conductors according to Clause 4 of this Standard. In addition, they shall reliably support the conductor in the case of unbalanced tensile forces. This latter requirement does not apply to those accessories that are designed to allow the conductor to slide through. If a continuous conductor (main cable) is connected to an auxiliary cable attached to a second line post or pin type insulator to the side of the main insulator, then the connections of the two conductors shall be designed to carry the maximum tensile force occurring under the conditions specified for the line Type test requirements Standard type tests When required type tests on overhead line fittings shall be carried out in accordance with the requirements of EN 61284, EN and/or EN Unless otherwise specified by the purchaser in the Project Specification, the acceptance criteria for mechanical and other characteristics shall be as given in these standards.

147 Optional type tests EN :2012 When specified in the Project Specification or by agreement between the purchaser and supplier, tests may be carried out to confirm the performance of insulator set fittings under power arc conditions. Information relating to such tests is given in EN Sample test requirements The specified sample tests shall be carried out on samples taken at random from each lot of fittings offered for delivery. The tests shall be carried out in accordance with the requirements of EN 61284, EN and/or EN Unless otherwise specified in the Project Specification or agreed by the purchaser with the supplier at the time of placing the order the acceptance criteria for all characteristics shall be as given in these standards Routine test requirements Routine tests, as specified in the relevant standard, shall be undertaken by the supplier on every fitting in a lot offered for delivery. The tests shall be in accordance with the requirements of EN 61284, EN and/or EN EN 61284, EN and EN include examples of non-destructive tests. The extent to which these tests are selected and applied should be agreed between the manufacturer and purchaser and included in the Project Specification Test reports and certificates The results of all type tests shall be reported in certificates issued by the supplier or a qualified organisation. These shall be valid without time limit provided that there is no change in the design or material of the fitting. The results of sample tests shall be reported in a certificate issued by the supplier for each lot delivered. The supplier shall certify that all fittings in each lot delivered have passed the specified routine tests Selection, delivery and installation of fittings Information relating to the selection, delivery and installation of fittings is given in Annex R.

148 EN : Quality assurance, checks and taking-over 12.1 Quality assurance During the design, manufacture and construction the quality assurance arrangements shall conform to the relevant requirements of EN ISO 9001 as appropriate. The systems and procedures, which the designer and/or installation contractor will use to ensure that the project works comply with the project requirements, shall be defined in the designer's and/or installation contractor's quality plan for the project works. Each quality plan shall set out activities in a logical sequence and shall take into account the following: an outline of the proposed work and programme sequence. the structure of the organisation for the contract, both at the head office and at any other centres responsible for part of the work. the duties and responsibilities assigned to staff ensuring quality of the work. hold and notification points. submission of engineering documents required by the Project Specification. the inspection of materials and components on receipt. reference to the quality assurance procedures appropriate to each activity. inspection during manufacture/construction. final inspection and testing. The quality assurance plan is part of the execution plan of a project or a project phase Checks and taking-over Prior to taking over a new overhead line from a Contractor, a number of appropriate measures and checks on the line shall be specified before it will be put into service. It is up to the Engineer in Charge to define, in agreement with the Purchaser, the exact measures to be taken, by whom it will be done, and in which way it will be reported and/or documented. It is recommended to check the complete line, section by section, component by component, and in the different construction steps, for instance the foundations and stub installation before starting the tower erection, and so on. A standard format with checklists can usefully help the documentation of the various stages of construction of the line and/or the final state of the line. This format can be established on the basis of the requirements of the general specifications. It allows the comparison of the inspection results of different inspectors on different line components of the same type. It shall be specified that the Contractor will guarantee the conformity of the construction of the overhead line to the general and special specifications as well as to the design drawings by appropriate quality assurance checks.

149 A.1 Recommended design criteria EN :2012 Annex A (informative) Strength coordination In order to decide on an appropriate strength coordination, the following criteria are recommended: a) the component with lowest level of reliability should be chosen so as to introduce the least secondary load effect (dynamic or static) on other components, in order to minimise cascading failure; b) repair time and costs following a failure should be kept to a minimum; c) the component with the lowest reliability ideally has a ratio of the damage limit (corresponding to the serviceability state) to the failure limit (corresponding to the ultimate limit state) close to 1,0; it may be difficult to coordinate the strength of components when the least reliable component has a very large strength dispersion; d) a low cost component in series with a high cost component should be designed to be at least as strong and reliable as the major component if the consequences of failure are as severe as for the failure of that major component. An exception to this criterion is when a component is purposely designed to act as a load limiting device. In such a case its strength should be well coordinated with the component it is intended to protect. If line components such as suspension supports, tension supports, conductors, foundations and hardware are analysed using the above criteria, it is found that conductors should not be the weakest component because of a), b) and c); hardware because of d); tension supports because of a) and b); and foundations because of b) and c). A.2 Proposed strength coordination An appropriate coordination of strength applying the criteria recommended in A.1 above is given in Table A.1. It appears from Table A.1 that suspension supports are the component with the lowest reliability and would fail first when the line is subjected to loads exceeding design values. Table A.1 Typical coordination of strength Major component Coordination within major components* To fail first Suspension support Support, foundations, hardware Not to fail first with 90 % confidence Tension support Section support Dead-end support Conductors Support, foundations, hardware Conductors, insulators, hardware NOTE The above strength coordination can be applied to most overhead lines. However, there will be some situations where different criteria can be used and thus lead to another sequence of failure. * Within each major component the underlined component is the weakest at the 90 % confidence level.

150 EN : In order to develop factors for multiplication of the partial factors as stated in this standard, leading to the target strength coordination, two methods can be considered: NOTE for the component with the lowest target reliability, design loads should be used in conjunction with the partial factors for actions given in this standard. The next components with higher target reliabilities should then be designed with a lower exclusion limit (percentage factor 5-10 lower), corresponding to the same design values of actions. partial factors for material properties should be established in such a way that the target strength coordination between two components will be reached with a high level of confidence (approx. 80 % to 90 %). Due to the random distribution of material properties, it is theoretically impossible to guarantee with 100 % confidence level that the sequence of failure will be met in all cases.

151 EN :2012 Annex B (informative) Conversion of wind velocities and ice loads B.1 Definition of symbols used in this annex B Symbol C T C 1, C 2 I B I T I m I max I mm I 3 I 50 K sp n n Q WT T V T V 3 V 50 v I v W γ I, γ W Ψ I, Ψ W Signification Conversion factor Gumbel law parameters Basic ice load per length Ice load with return period, T Yearly maximum ice load Maximum ice load observed over several years Mean value of yearly maximum ice loads Nominal ice load with return period of 3 years Extreme ice load with reference return period of 50 years Shape parameter Exponent in C T formula Number of years of observation Wind load with return period, T Return period Wind velocity with return period T years Nominal wind velocity with return period of 3 years Extreme wind velocity with reference return period of 50 years Coefficient of variation for yearly maximum ice loads Coefficient of variation of extreme wind velocity Partial factor for ice and wind action Combination factor for ice and wind action B.2 Evaluation of extreme wind velocity data Extreme wind velocity, V T is equal to the wind velocity with a return period, T which corresponds to the reliability level that is chosen for the overhead line. Conversion of the extreme velocity, V 50, associated with a reference 50 year return period, into another wind velocity, V T associated with another return period T can be made using the conversion factor, C T (probability factor, C prob in EN ) given by expression: C T = V T / V 50 = K 1 1 K sp sp ln ( ln ( 1 1/ T )) ln ( ln ( 1 1/ 50 )) n where T is the return period (in years) associated to V T ; K sp n is the shape parameter; is the exponent. Recommended value is 1 but another value may be specified in the NNAs.

152 EN : This expression of C T comes from a Gumbel distribution such as described in Annex D, applied to the wind velocity. NOTE 1 In EN , the recommended value for n is 0,5 because the wind pressure (and not the wind velocity) is assumed to follow a Gumbel distribution. The value of K sp can be determined according to: the coefficient of variation of the extreme wind velocity, v W ; the length of the measuring series (in years); the C 1 and C 2 parameters of that distribution depending on the length of the measuring series, with the expression: K sp = C v W 1 C2 v W For 30 years of extreme wind observation, values of C 1 and C 2 can be determined according to Table D.1 of Annex D: C 1 = 1,1124 and C 2 = 0,5362. NOTE 2 In EN , the number of years of observation is assumed to be very large. In so doing C 1 = π / 6 and C 2 = 0,57722 (Euler constant). With a coefficient of variation v W equal to 0,12 over 30 years of extreme wind observation, K sp is 0,114. NOTE 3 A representative coefficient of variation v W for the wind pressure in Europe is supposed to be 0,24. Such a coefficient of variation, associated to a very large number of years of observation, leads to the recommended value of EN for K sp (K sp = 0,2). EN National Annexes or NNAs may specify others values more applicable to local meteorological data. With T = 3 years, C T can convert the extreme wind velocity, V 50 into nominal wind velocity, V 3. All C T values for 3, 50, 150 and 500 years in Table B.1 are obtained with K sp = 0,114. Others values more applicable to local meteorological data may be specified in the NNAs. C² T can be used directly to determine partial factors linked to their reliability level, because wind load, Q WT is proportional to wind velocity, V T squared. C² T in Table B.1 represents the theoretical value of the partial factors for wind action, γ W : Q WT = γ W Q W50 In the case of a three year return period the combination factor for wind action, Ψ W, is used: Q W3 = Ψ W Q W50 Table B.1 Conversion factors for different return period of the wind velocity Reliability level Return period T [years] Conversion factor C T = V T/V 50 C² T Partial factor (Table 4.7) Combination factor (Table 4.7) Nominal wind 3 0,76 0,58-0,4 1 (reference) 50 1,00 1, ,09 1,18 1, ,18 1,40 1,4 - B.3 Evaluation of extreme ice load data Extreme ice load I T is equal to the ice load with a return period T which corresponds to the reliability level selected for the overhead line.

153 EN :2012 The extreme ice load can be calculated according to the Gumbel distribution for extremes based on the mean value, I mm, the coefficient of variation, v I for yearly maximum ice loads (see B.5.4 and B.5.5) and the number of years with annual maximum values, n. When n < 10, n is set equal to 10. Table B.2 gives factors to convert these to other return periods. For this conversion, v I = 0,7 and n = 10 years are used. Return period, T = 3 years should be used for calculating nominal ice load, I 3 (with a high probability of occurrence) as defined in The conversion factors in Table B.2 represent the theoretical value of the partial factor for ice action, γ I, I T = γ I I 50 and, in the case of a three year return period the combination factor for ice action, Ψ I : I 3 = Ψ I I 50 Others values, more applicable to local meteorological data, may be specified in the NNAs. In cases where there are many winters without icing events being observed, other distributions of extremes should be used. Table B.2 Conversion factors for different return periods for ice load Reliability level Return period T [years] Extreme ratio I T / I mm Conversion factor C T = I T / I 50 Partial factor (Table 4.7) Combination factor (Table 4.7) Nominal ice load 3 1,30 0,37-0,35 1 (reference) 50 3,51 1,00 1, ,33 1,23 1, ,22 1,49 1,5 - B.4 Statistical ice parameters B.4.1 Basic ice load, I B The basic ice load per length, I B, (in N/m) is referred to a conductor of diameter 30 mm in a 100 m long span 10 m above ground, on a site which is representative for the overhead line. When measurements are performed on conductors with other diameters or span lengths, they should be evaluated according to separate specifications. B.4.2 Yearly maximum ice load, I m This is the maximum of the ice load I B in one year. B.4.3 Maximum ice load over several years, I max This is the highest ice load observed over a period of several years, if such information exists (see B.4.2). B.4.4 Mean value, I mm of yearly maximum ice loads This is a calculated or estimated mean value of yearly maximum ice loads, I m (see B.4.2). B.4.5 Coefficient of variation, v I for yearly maximum ice loads This is a calculated, modified or estimated coefficient of variation for yearly maximum ice loads, I m (see B.4.2). B.5 Extreme ice load evaluation based on various data sources B.5.1 Data sources for statistical evaluation The database available for evaluating ice loads varies widely. This standard describes statistical methods based on three types of data:

154 EN : yearly maximum ice load, I m (see B.4.2) recorded for a period of at least 10 years (see B.5.2); only the maximum value, I max (see B.4.3) for ice load over a limited number of years is recorded (i.e. no statistical data) (see B.5.3); yearly maximum ice load, I m calculated by means of meteorological data analyses (icing model) (see B.5.4). Use of data on ice loads collected for only a few years may be misleading if the icing seasons were not representative. If possible, a meteorological evaluation should be performed covering a period of at least years for the area. Unless this is done, misleading conclusions can be drawn from too short periods or non-representative seasons. B.5.2 Yearly maxima ice loads, I m during periods of at least 10 years are available If the calculated coefficient of variation for yearly maximum ice loads, v I, is outside the range given in Table B.3, the nearest limit value should be selected. Table B.3 Coefficient of variations Yearly maximum ice loads I m Number of years of observations n 10 n < n Mean value I mm I mm I mm Coefficient of variation v I 0,5 v I 0,7 v I 0,7 B.5.3 Maximum ice load, I max is known only for a limited number of years The mean value of yearly maximum ice loads, I mm, is calculated as 0,4 I max, and the coefficient of variation, v I as 0,7. Extreme ice load according to B.3 above should be calculated with n = 10 years of observation. B.5.4 Yearly maximum ice load, I m, based on meteorological analyses Values of ice load data for the use of the statistical methods in this standard can be established by means of an icing model. The result from such a model should be used in order to find the mean value, I mm, and coefficient of variation, v I (see B.4.2, B.4.4 and B.4.5). An icing model of this type should analyse meteorological data over a period of 20 years or more. In addition to standard meteorological observation parameters, data which is not included in standard weather observations (liquid water content, droplet sizes, precipitation intensities, etc.) are required. If data which is representative for the location of the overhead line does not exist, a measuring programme can be set up, either to measure the parameters or to measure ice loads directly. In the latter case, these should be made with supplementary meteorological measurements and data collected. A correct calibration of an icing model requires at least 5-10 well-documented icing events. In many locations, there can be several seasons without icing events. The time series for meteorological measurements should be performed for at least two seasons, but preferably for 5 years or more. When a new overhead line is planned in an area where little information about icing exists or the line traverses an especially exposed terrain, a possible measurement programme should be considered as early as possible.

155 EN :2012 Annex C (informative) Application examples of wind loads - Special forces C.1 Application examples of the calculation of wind loads as defined in 4.3 and 4.4 C.1.1 Example 1 : Typical 24 kv wood pole tangent support Description: - 1 circuit - Typical ruling span: 100 m - Conductor: ACSR 99 mm 2 type Pigeon Diameter: 12,8 mm - At +50 C Lowest conductor about 7 m above ground level - At 0 C Catenary constant = 1322 m Data and calculation step by step Figure C.1 - Typical 24 kv wood pole tangent support V b,0 = 25 m s -1 Basic wind velocity ( 4.3.2) z 0 = 0,05 m Roughness length for terrain category II (4.3.2) k r = 0,189 Terrain factor for terrain category II (4.3.2) h = 10 m Reference height above ground (4.3.2) For lines up to AC 45 kv, h may be taken as 10 m regardless of the actual height provided that the structure height is a maximum of 20 m. c o = 1 Terrain topography factor (4.3.2)

156 EN : c dir = 1 Wind direction factor (4.3.2) V h (h) = V b,0 c dir c o k r ln (h / z 0 ) = 25 m s -1 Mean wind velocity (4.3.2) ρ = 1,225 kg m -3 Air density (4.3.3) q h (h) = ½ ρ V² h (h) = 383 Pa Mean wind pressure (4.3.3) I v (h) = 1 / [ c 0 ln (h / z 0 ) ] = 0,189 Turbulence intensity (4.3.4) q p (h) = [ I v (h) ] q h (h) = 890 Pa Peak pressure (4.3.4) L 1 = 120 m Adjacent span length before the pole ( ) L 2 = 80 m Adjacent span length after the pole ( ) L m = (L 1 + L 2 ) / 2 = 100 m Mean span ( ) L(h) = h ,67+ 0,05Ln( z0 ) = 63,1 m Turbulence length scale ( ) B² = L m 2 L ( h) + = 0,296 Background factor ( ) k p = 3 Peak factor ( ) R² = 0 Resonance factor ( ) G c = 1+ 2 k p Iv ( h) B² + R² = 0,696 Structural factor ( ) 1+ 7 I ( h) v NOTE The value given in Table 4.4.c is 0,70 for z 0 = 0,05 m, L m = 100 m and h = 10 m. φ = 0 Angle of incidence ( ) C c = 1 Conductor drag factor ( Method 1) d = 12,8 mm (0,0128 m) Conductor diameter ( ) Q Wc_V = q p (h) G c C c d cos²φ ( L 1 + L 2 ) / 2 = 793 N Wind force on the support ( ) from each conductor d ins = 150 mm h ins = 305 mm Insulator diameter Insulator height A ins = 0,046 m² Insulator area (d ins x h ins ) (4.4.2) C ins = 1,2 Insulator drag factor (4.4.2) G ins = 1 Insulator structural factor (4.4.2) Q Wins = q p (h) G ins C ins A ins = 49 N Wind force on the support (4.4.2) from each insulator d topole = 15 cm d groundpole = 25 cm H pole = 10 m Pole top diameter Pole diameter at ground level Height of pole above ground level

157 EN :2012 A pol = 2 m² Projected area of pole (H pole (d toppole + d groundpole ) / 2) (4.4.4) G pol = 1 Structural factor for poles (4.4.4) C pol = 0,9 Drag factor for wood poles (4.4.4) Q Wp = q p (h) G pol C pol A pol = 1602 N Wind force on the support at (4.4.4) the centre of gravity of the pole C.1.2 Example 2 : Typical 225 kv suspension lattice tower Description: - 2 circuits - Typical ruling span: 400 m - Conductor: AAAC 570 mm 2 (ASTER) Diameter: 31,05 mm - Earth wire: AACSR 147,6 mm² Diameter: 15,6 mm - At +75 C Lowest conductor about 8 m above ground level - At 15 C Catenary constant = 2000 m Figure C.2 - Typical 225 kv suspension lattice tower

158 EN : Data and calculation step by step V b,0 = 24 m s -1 Basic wind velocity ( 4.3.2) z 0 = 0,05 m Roughness length for terrain category II (4.3.2) k r = 0,189 Terrain factor for terrain category II (4.3.2) c o = 1 Terrain topography factor (4.3.2) c dir = 1 Wind direction factor (4.3.2) h = 33 m Reference height above ground (method 8) ( ) [31,05 (23,7 + 31,2 + 38,7) + 15,6 (43,7)] / [3 x 31, ,6] V h (h) = V b,0 c dir c o k r ln (h / z 0 ) = 29,5 m s -1 Mean wind velocity (4.3.2) ρ = 1,25 kg m -3 Air density (conservative value from EN ) (4.3.3) q h (h) = ½ ρ V² h (h) = 544 Pa Mean wind pressure (4.3.3) I v (h) = 1 / [ c 0 ln (h / z 0 ) ] = 0,154 Turbulence intensity (4.3.4) q p (h) = [ I v (h) ] q h (h) = 1130 Pa Peak pressure (4.3.4) L m = 400 m Mean span ( ) L(h) = 300. h 200 0,67+ 0,05.Ln(z 0 ) = 117,5 m Turbulence length scale ( ) B² = 1 3 Lm 1+ 2 L(h) = 0,164 Background factor ( ) k p = 3 Peak factor ( ) R² = 0 Resonance factor ( ) G c = k.I (h). B² + R² p v I (h) v = 0,661 Structural factor ( ) NOTE The value given in Table 4.4.c is 0,66 for z 0 = 0,05 m, L m = 400 m and h = 30 m or 35 m. φ = 0 Angle of incidence ( ) C c = 1 Conductor and earth wire drag factor ( Method 1) d = 31,05 mm (0,03105 m) Conductor diameter ( ) Q Wc_V = q p (h) G c C c d cos² φ L m = 9277 N Wind force on the support ( ) from each conductor d = 15,6 mm (0,0156 m) Earth wire diameter ( ) Q Wc_V = q p (h). G c. C c. d.cos² φ L m = 4661 N Wind force on the support ( ) from each earth wire Calculation of wind force on a member (angle) of that tower H t = 44,7 m Total height of the tower ( )

159 EN :2012 h = 27 m Reference height (60% of H t ) ( ) V h (h) = V b,0 c dir c o k r ln (h / z 0 ) = 28,5 m s -1 Mean wind velocity (4.3.2) ρ = 1,25 kg m -3 Air density (conservative value from EN ) (4.3.3) q h (h) = ½ ρ V² h (h) = 508 Pa Mean wind pressure (4.3.3) I v (h) = 1 / [ c 0 ln (h / z 0 ) ] = 0,159 Turbulence intensity (4.3.4) q p (h) = [ I v (h) ] q h (h) = 1073 Pa Peak pressure (4.3.4) C m = 1,6 Drag factor for an angle ( ) G m = 1 Structural factor for an angle ( ) Q Wm = [q p (h) G m C m ] A m cos²φ m Wind force on each angle ( ) Q Wm = 1717 (Pa) A m cos²φ m (function of A m and cos²φ m ) C.2 Special forces C.2.1 Definition of symbols used in this annex C.2 Symbol Signification I SC2φ I SC3φ 2 phase short circuit current 3 phase short circuit current C.2.2 Forces due to short-circuit currents The main concern during a short circuit is with uncontrolled swinging of conductors leading to possible conductor clash and resulting in permanent circuit isolation following circuit breaker operation at that time. Short circuit conditions may also cause mechanical problems (on supports), but these are less important than those due to conductor swinging. A possible solution to the swinging conductor problem, lies in the use of interphase spacers which reduce the movements by holding the conductors apart from each other (suppressing the conductor whipping). The calculation requires software capable of simulating the forces and movements of conductors during, and after, the short circuit. A mechanical analysis of overhead lines under short circuit loads may be performed, if identified in the Project Specification. The following should be considered. A short circuit level should be specified with reference to the levels specified for switchgear rating. For information, the short circuit level (short circuit 3 phase current, I SC3φ ) in a substation may exceed the following specified levels: 1) 40 ka for 420 kv highest system voltage; 2) 31,5 ka for 245 kv highest system voltage; 3) 20 ka for lower voltages. The short circuit current used for checking is the maximum level allowed by substation equipment (even if it is not attained in the present stage of development of the transmission system) in order to facilitate further evolution of the system. The supports close to the substation should be checked taking into account the reduction of the short circuit current due to line impedance. The support check ceases where the short circuit current decreases to less than the above specified levels.

160 EN : This rule should be applied to check 5 to 10 spans from the substation. Usually, only 1 span is affected by excessive swinging and 1 or 2 supports adjacent to the substation are subjected to mechanical overloads from short circuits. Only the 2 phase short circuit current, I SC2φ, should be checked as the most restrictive. As an approximation: I SC2φ = I SC3φ The reduction of short circuit current with time should also be taken into account according to the electrical characteristics of the system. The fault time should be considered in accordance with the type of protection relays used and the possibility of covering breaker failure or not (breaker tripping time without failure usually estimated at 80 to 200 ms assuming solid state relaying). C.2.3 Avalanches, creeping snow In addition to the effects of direct avalanches, the effects of avalanches from the opposite slope of the valley on overhead lines should not be neglected. This can influence conductors and fittings (especially in case of powdery avalanches), supports and foundations. Creeping snow is to be considered with regard to additional loadings on foundations and lower parts of supports (especially bracing members). Principles for the calculation of loadings caused by avalanches or creeping snow cannot be fully defined and should be specified in the NNAs or Project Specification. The coincident temperature with avalanches may be in the range from 20 C to + 10 C. Appropriate loading assumptions may help to reduce the risk of failures of supports: for example, in the event of rupture of all conductors and ground wires on one side of the support, the tensions of conductors and ground wires on the remaining side should be taken equal to their breaking strengths. Values for pressure of creeping snow on protection devices can be found in the Project Specification. Protection measures should be taken with regard to neighbouring buildings as well as to structures on the opposite slope of the same valley which can be influenced by deviated avalanches or snow. C.2.4 Earthquakes Since wind loadings are usually more onerous for lattice type overhead line towers, seismic loads which may lead to additional loading forces may be expected only in very active seismic zones. These considerations may include the natural period of vibration of the structure, the site structure resonance factor (depending on the soil conditions), and the height, weight and mass distribution of the support structure. Since the frequency of the support is higher than that of the conductors, the dynamic load from the conductors will not be significant. Conversly, no important effects from the support relative to conductors should be expected. Ground acceleration due to earthquakes may influence the design of rigid and heavy concrete structures. Effects on the equipment (fittings, insulators, etc.) due to earthquakes are not considered in this annex.

161 EN :2012 Annex D (informative) Statistical data for the Gumbel distribution of extremes D.1 Definition of symbols used in this annex Symbol C 1, C 2 G G 1 i K K conv n v x i x z i Signification Parameters depending on the length of the measuring series Complementary probability, or the risk of the extreme value, x i exceeding the chosen value, x in an arbitrary year Gumbel cumulative distribution for extremes Symbol to indicate arbitrary year in a series Factor dependent on the return period, T, number of years, n and coefficient of variation, v Conversion factor for different return periods Number of years Coefficient of variation Extreme value for a variable, x in an arbitrary year Mean value of a variable, x Constant calculated for an arbitrary year, i in a series of n years z Mean value of z i and equal to C 2 σ Standard deviation of z z i and equal to C 1 y, α, µ, σ Factors used in the calculation of Gumbel distribution D.2 The Gumbel distribution Although there are several functions which represent extreme distributions, this annex is based on the Gumbel distribution (Fisher Tipett or Gumbel, type II). The cumulative distribution can be written G e y( x) 1 ( x) = e (D.1) which gives the probability that the extreme value x i for an arbitrary year is less than any chosen value x. In this formula y = α ( x µ) (D.2) C1 α σ = (D.3) C x α 2 µ = (D.4) where x is the mean value of n yearly extremes x i and σ, the standard deviation or the square root of the variance

162 EN : x = 1 n n x i i = 1 (D.5) n σ = ( x i x) (D.6) n i = 1 v σ = (D.7) x Rather than the standard deviation itself, the per unit value, v is more useful in the following. This is also called coefficient of variation. C 1 and C 2 in Formulae (D.3) and (D.4) are parameters depending on the length of the measuring series as given by n. They are given in Table D.1. The complementary probability, or the risk of the extreme value, x i exceeding the chosen value, x in an arbitrary year is: G ( x ) = 1 G 1 ( x ) (D.8) The return period, T is the inverse value of G(x), here written as T(x) to underline its dependence on the chosen value x: 1 T ( x) = (D.9) G( x) Combining Formulae (D.1), (D.8) and (D.9) gives 1 T or = 1 e e y (D.10) y 1 = ln ( ln (1 )) (D.11) T It is seen that there is a unique connection between the return period, T and the parameter, y independent of x and σ. This is shown in Table D.2.

163 EN :2012 Table D.1 Values of parameters C 1 and C 2 Length of measuring series n Parameters Years C 1 C , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,577 2 Table D.2 Corresponding values of return period, T, risk of exceedence, G and parameter, y Return period T Years Risk of exceedence G Parameter y , , , , , , , ,213 6

164 EN : Formula (D.2) can be written: y x µ + α = (D.12) and, using (D.4) and (D.3) x = σ x C C ( 2 1 y) (D.13) Observing Formula (D.7) and rearranging since y is always > C 2 : y C2 x = x (1 + v ) (D.14) C Formula (D.14) can be written 1 x = K x (D.15) where K, a function of v, of T (since y is given by T) and of n (since C 1 and C 2 are given by n) is given by: K ( T, v, n) y C 2 = 1+ v (D.16) C1 Table D.3 gives some K values for return periods T (years), periods of measurement, n (years) and coefficients of variation, v, which might be practical. Very often it is necessary to convert a given climatic value with a return period of 50 years to a value with 3, 150 or 500 years. Such conversion factors can be calculated using the same formulae as above. Such a factor would be: K ( T, v, n) K conv ( T, v, n) = (D.17) K (50, v, n) which is also a function of the return period, coefficient of variation and length of measuring series, n. Table D.4 shows conversion factors from extremes with a return period of 50 years to extremes with return periods of 3, 150 and 500 years, depending on the measured values of the coefficient of variation and length of the measured series. D.3 Example of using C 1 and C 2 An example of using C 1 and C 2 may be useful. Wind velocities have been measured for a period of 35 years. The mean value of the yearly extremes is found to be 33 m/s and the coefficient of variation, v = 0,12. If the return period T = 50 years is chosen, Table D.2 gives y = 3,9019. Further, Table D.1 gives C 1 = 1,1285 and C 2 = 0,5403 for n = 35. Formula (D.14) then gives a design wind velocity: x 3,9019 0,5403 = 33 (1 + 0,12 ) = 44,8 1,1285 (m/s) The so-called ideal Gumbel distribution with C 1 = 1,282 5 and C 2 = 0,577 2 (based on an infinite measuring period) would give: 3,9019 0,5772 x = 33 (1 + 0,12 ) = 43,3 1,2825 (m/s)

165 EN :2012 The more realistic distribution gives a design value 3,5% above that given by the ideal one. D.4 Calculation of C 1 and C 2 With a period of measurement of n years, n z-values can be calculated numbered from 1 to n: i z i = ln ( ln ) (D.18) n + 1 where i takes on values from 1 to n. A mean of these z values is found z = 1 n n z i i = 1 (D.19) The parameter C 2 is simply equal to this mean value: C 2 = z (D.20) The variance of the z i values is then found: n σ = ( z z) (D.21) z n i = 1 i where, σ z is the standard deviation of z i. The parameter, C 1 is simply equal to this standard deviation: C1 = σ z (D.22) With some rearrangement the variance can be expressed as follows n σ z = zi z (D.23) n i = 1 This makes calculation easier, since the summation can be carried out before z is known. An example shows how C 1 and C 2 are calculated for n = 10.

166 EN : Table D.3 Factors for calculating design values based on the mean values of yearly extremes Return period T Period of measurements n Coefficient of variation v Years Years 0,10 0,12 0,14 0,16 0,18 0,20 0,30 0,40 0,50 0,60 0, ,04 1,04 1,04 1,03 1,03 1,03 1,03 1,03 1,05 1,05 1,04 1,04 1,04 1,04 1,04 1,03 1,06 1,05 1,05 1,05 1,05 1,04 1,04 1,04 1,07 1,06 1,06 1,05 1,05 1,05 1,05 1,04 1,08 1,07 1,06 1,06 1,06 1,06 1,06 1,05 1,09 1,08 1,07 1,07 1,07 1,06 1,06 1,05 1,13 1,11 1,11 1,10 1,10 1,10 1,09 1,08 1,17 1,15 1,14 1,14 1,13 1,13 1,13 1,10 1,21 1,19 1,18 1,17 1,16 1,16 1,16 1,13 1,26 1,23 1,21 1,20 1,20 1,19 1,19 1,15 1,30 1,27 1,24 1,23 1,23 1,22 1,22 1, ,36 1,33 1,32 1,31 1,30 1,30 1,29 1,26 1,43 1,40 1,38 1,37 1,36 1,36 1,35 1,31 1,50 1,46 1,45 1,43 1,42 1,42 1,41 1,36 1,57 1,53 1,51 1,49 1,48 1,48 1,47 1,42 1,65 1,60 1,57 1,56 1,54 1,54 1,53 1,47 1,72 1,66 1,64 1,62 1,61 1,60 1,59 1,52 2,08 2,00 1,95 1,93 1,91 1,89 1,88 1,78 2,43 2,33 2,27 2,24 2,21 2,19 2,18 2,04 2,79 2,66 2,59 2,54 2,51 2,49 2,47 2,30 3,15 2,99 2,91 2,85 2,82 2,79 2,77 2,56 3,51 3,32 3,23 3,16 3,12 3,09 3,06 2, ,48 1,44 1,42 1,41 1,40 1,40 1,39 1,35 1,57 1,53 1,51 1,49 1,48 1,48 1,47 1,42 1,67 1,62 1,59 1,57 1,56 1,55 1,55 1,48 1,76 1,70 1,67 1,66 1,64 1,63 1,63 1,55 1,86 1,79 1,76 1,74 1,72 1,71 1,70 1,62 1,95 1,88 1,84 1,82 1,80 1,79 1,78 1,69 2,43 2,32 2,27 2,23 2,21 2,19 2,17 2,04 2,90 2,76 2,69 2,64 2,61 2,58 2,56 2,38 3,38 3,20 3,11 3,05 3,01 2,98 2,96 2,73 3,85 3,64 3,53 3,46 3,41 3,38 3,35 3,08 4,33 4,08 3,95 3,87 3,81 3,77 3,74 3, ,60 1,56 1,54 1,52 1,51 1,50 1,50 1,44 1,72 1,67 1,64 1,62 1,61 1,60 1,60 1,53 1,84 1,78 1,75 1,73 1,71 1,70 1,70 1,62 1,96 1,89 1,86 1,83 1,82 1,80 1,79 1,70 2,08 2,01 1,96 1,94 1,92 1,90 1,89 1,79 2,20 2,12 2,07 2,04 2,02 2,01 1,99 1,88 2,81 2,68 2,61 2,56 2,53 2,51 2,49 2,32 3,41 3,23 3,14 3,08 3,04 3,01 2,99 2,76 4,01 3,79 3,68 3,60 3,55 3,51 3,48 3,20 4,61 4,35 4,21 4,12 4,06 4,02 3,98 3,64 5,22 4,91 4,75 4,64 4,57 4,52 4,48 4,08

167 EN :2012 Table D.4 - Conversion factors for calculating design values based on the corresponding values with 50 years return period Return period T Period of measurements n Coefficient of variation v Years Years 0,10 0,12 0,14 0,16 0,18 0,20 0,30 0,40 0,50 0,60 0, ,77 0,78 0,79 0,74 0,75 0,75 0,71 0,72 0,73 0,68 0,69 0,70 0,65 0,67 0,68 0,63 0,65 0,65 0,54 0,56 0,57 0,48 0,50 0,50 0,43 0,45 0,46 0,40 0,41 0,42 0,37 0,38 0, ,79 0,76 0,73 0,71 0,68 0,66 0,57 0,51 0,46 0,42 0, ,79 0,76 0,73 0,71 0,69 0,66 0,58 0,51 0,46 0,43 0, ,80 0,80 0,81 0,77 0,77 0,79 0,74 0,74 0,76 0,71 0,71 0,74 0,69 0,69 0,71 0,67 0,67 0,69 0,58 0,58 0,60 0,51 0,52 0,54 0,47 0,47 0,49 0,43 0,43 0,45 0,40 0,40 0,42 50 All 1,00 1,00 1,00 1,00 1,00 1,00 1,00 1,00 1,00 1,00 1, ,09 1,08 1,08 1,10 1,09 1,09 1,11 1,10 1,10 1,12 1,11 1,11 1,13 1,12 1,12 1,14 1,13 1,13 1,17 1,16 1,16 1,19 1,19 1,18 1,21 1,20 1,20 1,22 1,22 1,21 1,23 1,23 1, ,08 1,09 1,10 1,11 1,12 1,13 1,16 1,18 1,20 1,21 1, ,08 1,09 1,10 1,11 1,12 1,12 1,16 1,18 1,20 1,21 1, ,08 1,07 1,07 1,09 1,09 1,08 1,10 1,10 1,09 1,11 1,11 1,10 1,11 1,11 1,11 1,12 1,12 1,11 1,16 1,15 1,15 1,18 1,18 1,17 1,20 1,20 1,19 1,21 1,21 1,20 1,22 1,22 1, ,18 1,17 1,17 1,20 1,19 1,19 1,23 1,22 1,21 1,25 1,24 1,23 1,27 1,26 1,25 1,28 1,27 1,27 1,35 1,34 1,33 1,40 1,39 1,38 1,44 1,43 1,42 1,46 1,45 1,45 1,49 1,48 1, ,16 1,19 1,21 1,23 1,25 1,26 1,33 1,38 1,42 1,45 1, ,16 1,18 1,20 1,22 1,24 1,26 1,33 1,38 1,41 1,44 1, ,16 1,16 1,14 1,18 1,18 1,17 1,20 1,20 1,19 1,22 1,22 1,20 1,24 1,24 1,22 1,26 1,26 1,24 1,32 1,32 1,30 1,37 1,37 1,35 1,41 1,41 1,39 1,44 1,44 1,42 1,46 1,46 1,45 The first sum in Table D.5 gives: z 1 10 z i i = 1 = 10 = 0,49521 and then successively σ 2 z σ z 1 10 = z 10 i = 1 = 0, i z 2 = 1, ,24523 = 0,90179 C1 = σ z = and C 2 = z = 0,9496 0,4952

168 EN : It can be shown that if n, then C 1 π / 6 = 1, and C 2 0, The latter is called Euler's constant. Table D.5 Calculation and summation of z and z² i z z , , , , , , , , , , , , , , , , , , , ,525 4 Σ 4, ,470 2

169 EN :2012 Annex E (normative) Theoretical method for calculating minimum air clearances E.1 Definition of symbols used in this annex NOTE Symbol This annex is not applicable for lines with nominal system voltages up to and including AC 45 kv. Signification D el D pp D 50Hz_p_e D 50Hz_p_p d d is K cs K g K g_ff K g_ff_is K g_pf K g_sf K z K z_ff K z_pf K z_sf k a N U 2 %_sf U e2 %_sf U p2 %_sf U 100 % U 50 % U 50rp U 50rp_sf U 50rp_ff U 50rp_50Hz U 90 % Minimum air clearance required to prevent a disruptive discharge between phase conductors and objects at earth potential during fast-front or slow-front overvoltages Minimum air clearance required to prevent a disruptive discharge between phase conductors during fast-front or slow-front overvoltages Minimum air clearance required to prevent a disruptive discharge at power frequency voltage between a phase conductor and objects at earth potential Minimum air clearance required to prevent a disruptive discharge at power frequency voltage between phase conductors Clearance distance of the gap Clearance distance between the extremities of the insulator string Statistical coordination factor Gap factor Gap factor of the air gap for fast-front overvoltages Gap factor of the insulator strings for fast-front overvoltages Gap factor of the air gap for power frequency voltages Gap factor of the air gap for slow-front overvoltages Deviation factor Deviation factor of the air gap withstand voltage distribution for fast-front overvoltages Deviation factor of the air gap withstand voltage distribution for power frequency voltages Deviation factor of the air gap withstand voltage distribution for slow-front overvoltages Atmospheric factor Number of standard deviations corresponding to U rw 2 % slow-front overvoltage stressing the air gap 2 % slow-front overvoltage phase to earth 2 % slow-front overvoltage phase to phase 100 % withstand voltage of the air gap 50 % withstand voltage of the air gap 50 % withstand voltage of a rod-plane gap 50 % withstand voltage of a rod-plane gap for slow-front overvoltages 50 % withstand voltage of a rod-plane gap for fast-front overvoltages 50 % withstand voltage of a rod-plane gap for power frequency voltages 90 % withstand voltage of the air gap

170 EN : U 90 %_ff_is U cw U n U rp U rw U s Z z 90 % withstand voltage of insulator strings installed on a line for fast-front overvoltages Co-ordination withstand voltage Nominal system voltage Representative voltage or overvoltage Required withstand voltage of the air gap Highest system voltage Standard deviation Coefficient of variation E.2 Insulation co-ordination E.2.1 Development of theoretical formulae for calculating electrical distances The theoretical method given in E.2 is that used to derive the minimum air clearance distance Tables 5.3 to 5.5 containing D el, D pp, D 50Hz_p_e, D 50Hz_p_p in The calculation formulae are summarised in E.3 (Table E.5) and some application examples are given in E.4. Flowchart E.1 shows the structure of this Annex E. This theoretical method is based upon the work of ENV supported by information from EN , EN and CIGRÉ Report 72 Guidelines for the evaluation of the dielectric strength of external insulation. The values of the atmospheric factor are taken from EN If specified in the NNA the different stages of insulation coordination described in Annex E may be replaced with the methodology and terminology given in EN NOTE EN considers the altitude correction factor K a. The inverse of this factor 1/K a corresponds to the atmospheric factor k a of EN The altitude correction factor in EN is different for power frequency voltages, slow-front and fast-front overvoltages.

171 EN :2012 E.2 Insulation co-ordination Fast-front overvoltages Slow-front overvoltages Power frequency voltages 90 % lightning withstand voltage of insulator strings installed on a line, U 90 %_ff_is Statistical co-ordination factor and 2 % overvoltage stressing the air gap, K cs U e2 %_sf Highest system voltage, U S E.2.2 Representative voltages and overvoltages, U rp (Table E.1) E.2.3 Co-ordination withstand voltage, U cw U rp E.2.4 Required withstand voltage of the air gap, U rw = U cw / k a Atmospheric factor, k a (Table E.2) 50 % withstand voltage, U 50 % = U rw / K z E Deviation factor, K z (Table E.3) 50 % withstand voltage of a rod-plane gap U 50rp = U 50 % / K g E Gap factor, K g (Table E.4) E.2.5 Clearance distance of the air gap, d f (d) = U 50rp = U rw / (K z K g ) E Formulae, f (d) E.3 Formulae for calculation minimum air clearances D el, D pp, D 50Hz_p_e, D 50Hz_p_p (Table E.5) E.4 Examples of calculation Flowchart E.1 Structure of Annex E on the theoretical method to derive the minimum air clearance distances E.2.2 Representative voltages and overvoltages U rp Fast-front overvoltages caused by lightning shall be considered for the calculation of clearances in systems in Range I (U S above 1 kv to 245 kv included) and II (U S above 245 kv) of EN Slow-front overvoltages caused by switching shall be considered for the calculation of clearances in systems in Range II (U S above 245 kv) of EN

172 EN : The representative voltages and overvoltages, U rp to be taken into account are as follows (Table E.1): Fast-front overvoltages For the purpose of determining air clearances the representative overvoltage, U rp to be considered is that which can propagate beyond a few towers from the point of the lightning strike. For phase to earth clearances it shall be taken as U 90 %_ff_is the 90 % lightning withstand voltage of the insulator strings installed on the line. For phase to phase clearances it shall be taken as 1,20 U 90 %_ff_is. Slow-front overvoltages A simplified statistical method for slow-front overvoltages suitable for the insulation co-ordination of overhead lines can be used if it is assumed that the distribution of overvoltage and insulation strength can be defined by a point on each of these curves. The overvoltage distribution is identified by the statistical overvoltage stressing the air gap, U 2 %_sf, which is the overvoltage having a 2 % probability of being exceeded. The insulation strength is identified by the statistical withstand voltage, which is the voltage at which the insulation exhibits a 90 % probability of withstand. The representative overvoltage, U rp is obtained by multiplying the statistical overvoltage by a statistical co-ordination factor, K cs : phase to earth K cs U e2 %_sf ; phase to phase K cs U p2 %_sf = 1,4 K cs U e2 %_sf. The probability of failure is related to the statistical co-ordination factor, K cs. For the purpose of determining electrical clearance distances, K cs may be taken equal to 1,05 which corresponds to a probability of failure of the order of 1,0 x Power frequency voltages For purposes of insulation design and co-ordination, the representative continuous voltage shall be considered as constant and equal to the highest system voltage, U S : 2 3 U s phase to earth (peak value); 2 U s phase to phase (peak value). Table E.1 Representative voltages and overvoltages Representative voltage or overvoltage U rp Phase to earth Phase to phase Fast-front overvoltages (lightning) U 90 %_ff_is 1,2 U 90 %_ff_is Slow-front overvoltages (switching) K cs U e2 %_sf 1,4 K cs U e2 %_sf Power frequency voltages 2 Us 3 2 U s U 90 %_ff_is is the maximum of the 90 % fast-front overvoltages of the insulator strings on the line (*); U e2 %_sf is the 2 % slow-front overvoltage phase to earth stressing the air gap (i.e. slow-front overvoltage having a probability of 2 % of being exceeded); is the highest system voltage (kv rms). U s (*) The value, U 90 %_ff_is may not be known by some utilities. In this case, U 90 %_ff_is can be derived from the values of the clearance distance of the insulator strings and of their gap factors.

173 EN :2012 U 90 %_ff_is = K z_ff K g_ff_is 530 d is where: K z_ff is the deviation factor (K z = 0,961); K g_ff_is d is is the gap factor of the insulator strings for fast-front overvoltages; is the clearance distance between the extremities of the insulator string. E.2.3 Co-ordination withstand voltage U cw The co-ordination withstand voltage, U cw to be used shall be taken as higher than or equal to the representative overvoltage, U rp : U cw U rp E.2.4 Required withstand voltage of the air gap, U rw The required withstand voltage of the air gap, U rw, is determined from the co-ordination withstand voltage taking into account a correction factor associated with atmospheric conditions. The dielectric strength of the line insulation is affected by the altitude above sea level. This effect, which varies to some extent with the air gap length, is accounted for by an atmospheric factor, k a depending on the value of the co-ordination withstand voltage considered. U rw = U cw / k a The atmospheric factor, k a is generally valid for altitudes up to m. All the values of k a are indicated in Table E.2. k a has different values for fast-front and slow-front overvoltages and for power frequency voltages, as well as for their phase to earth and phase to phase clearances. The relationship between the required withstand voltage and the clearance distance of the air gap is described in E.2.5. Table E.2 Atmospheric factor, k a depending on the co-ordination withstand voltages considered Atmospheric factor, k a Altitude (m) up to 200 kv from 201 kv to 400 kv from 401 kv to 700 kv from 701 kv to kv above kv 0 1,000 1,000 1,000 1,000 1, ,994 0,995 0,997 0,998 0, ,982 0,985 0,990 0,993 0, ,970 0,975 0,982 0,987 0, ,938 0,946 0,959 0,970 0, ,904 0,915 0,934 0,948 0, ,870 0,883 0,906 0,923 0, ,834 0,849 0,875 0,896 0, ,798 0,815 0,844 0,867 0,885 If specified in the NNA, ka may be taken as 1,0 for fast-front overvoltages. NOTE The k a values have been taken from the document EN

174 EN : E.2.5 Relationship with the clearance distance of the air gap E Statistical approach The ability of self-restoring insulation to withstand dielectric stresses caused by the application of an impulse of given shape can be described in statistical terms. For a given insulation and for impulses of given shape and various peak values voltages, a discharge probability, P can be associated with every possible value of the voltage. The function, P is normally given by a mathematical function which is fully described by the parameters, U 50 %, Z and N. EN recommends the use of a modified Weibull distribution function whose parameters are determined in such a way as to correspond to a Gaussian function for the 50 % and 16 % probability of flashover and to truncate the distribution at U 50 % - 3 Z. The required withstand voltage of the air gap, U rw, may then be expressed as a function of the 50 % withstand voltage of the air gap, U 50 % : where U rw = U 90 % = U 50 % - N Z U 90 % U 50 % Z N is the 90 % withstand voltage of the air gap; is the 50 % withstand voltage of the air gap; is the standard deviation; is the number of standard deviations corresponding to U rw. Transient overvoltages For the transient electrical stresses (fast-front and slow-front overvoltages), the required statistical withstand voltage, U rw, is the 90 % withstand voltage of the air gap, U 90 %. As a function of the 50 % withstand voltage of the air gap, U 50 %, it is defined in terms of the following relationship: Power frequency voltages U rw = U 90 % = U 50 % - 1,3 Z For the power frequency voltages, the required withstand voltage of the air gap, U rw, considered is deterministic: U rw = U 100 % = U 50 % - 3 Z E Deviation factors The standard deviation, Z can be expressed in terms of the 50 % withstand voltage, U 50 % : Z = z U 50 % The following coefficients of variation, z and standard deviations, Z are usually considered: for fast-front overvoltages: z = 0,03 and Z = 0,03 U 50 % ; for slow-front overvolages: z = 0,06 and Z = 0,06 U 50 % ; for power frequency voltages: z = 0,03 and Z = 0,03 U 50 %. The effect of atmospheric conditions is taken into account in the above values of conventional deviations. The required withstand voltage of the air gap, U rw, may then be expressed using a deviation factor K z. U rw = K z U 50 %

175 The resulting deviation factors, K z are given in Table E.3: EN :2012 Table E.3 Deviation factors K z Type of voltage stress Required withstand voltage of the air gap U rw Standard deviation Z Deviation factor K z Fast-front overvoltage U rw = U 90 % = U 50 % - 1,3 Z 0,03 U 50 % K z_ff = 0,961 Slow-front overvoltage U rw = U 90 % = U 50 % - 1,3 Z 0,06 U 50 % K z_sf = 0,922 Power frequency U rw = U 100 % = U 50 % - 3 Z 0,03 U 50 % K z_pf = 0,910 E Gap factors In general, the configuration of the air gap has an effect on its dielectric strength. For a given configuration, the 50 % withstand voltage of the air gap, U 50 %, can be expressed as a function of the 50 % withstand voltage of a rod-plane gap, U 50rp : where U 50 % = K g U 50rp K g is the gap factor. For each type of voltage stress, the gap factor can be expressed in terms of the gap factor for slowfront overvoltages, K g_sf : slow-front overvoltages : K g_sf ; fast-front overvoltages : K g_ff = 0,74 + 0,26 K g_sf ; power frequency voltages : K g_pf = 1,35 K g_sf - 0,35 K 2 g_sf. The required withstand voltage of the air gap, U rw, may then be expressed using the gap factor, K g. U rw = K z K g U 50rp The values of gap factors, K g_sf to be used for slow-front overvoltages depends on the configuration. Four configuration types are considered in Table E.4. The gap factors in Table E.4 are typical values only. In practice, other values supported by experiments may be used. Typical gap factor values can be obtained from EN :1997, Annex G.

176 EN : Table E.4 Gap factors for slow-front overvoltages Nature of air clearance Configuration Gap factor for slow-front overvoltages K g_sf = K g External clearances Internal clearances Conductor - obstacle (safety clearances). conductor-window e.g. air gap configuration between a conductor inside a tower window and the tower structure vertical string or V string inside the window conductor-structure e.g. air gap clearance between a conductor, connected to a free swinging insulator string at the extremity of a crossarm, and the tower structure. vertical string at the extremity of a cross-arm V strings 1,30 1,25 1,45 conductor-conductor. 1,60 E Insulation response to overvoltages EN gives formulae describing the response of a rod-plane gap to overvoltages in which the 50 % withstand voltage of the rod plane gap, U 50rp, is given depending on the clearance distance of the air gap, d: U 50rp = f (d) Consequently the required withstand voltage of the air gap, U rw, can be expressed depending on the clearance distance of the air gap, d: Fast-front overvoltages U rw = K z K g f (d) For standard lightning impulses applied to rod-plane gaps of up to 10 m, the positive polarity breakdown strength is given by: U 50rp_ff = 530 d [kv crest]; d (m) Slow-front overvoltages Under slow-front overvoltages, a given self-restoring insulation exhibits an appreciably lower withstand voltage than under fast-front surges of the same polarity. In practice, for rod-plane gaps of up to 25 m, the positive-polarity for critical peak time is given by: U 50rp_sf = ln (0,46 d + 1) [kv crest]; d (m) Power frequency voltages The 50 % breakdown voltage for a rod-plane gap can be approximated to by the following formula: U = ln (1 0,55 d ) [kv crest]; d (m) 50rp_50Hz + 1,2

177 E.3 Calculation formulae for the minimum air clearances EN :2012 For each type of voltage stress, the co-ordination withstand voltage of the air gap, U cw, (given in E.2.3) shall be higher than, or equal to, the representative overvoltage, U rp (given in E.2.2) so that the failure rate is acceptable. Considering the atmospheric factor, k a to be taken into account for the correction of the co-ordination, the required withstand voltage of the air gap, U cw, (given in E.2.4) and the formulation describing the relationship with the clearance distance of the air gap, d (given in E.2.5) is as follows: U cw U rp U rw = U cw / k a f (d) = U rw / (K z K g ) The calculation formulae given in Table E.5, for the minimum air clearances to be used, may be deduced from these expressions.

178 EN : Table E.5 Formulae for the calculation of the minimum air clearances, D el, D pp, D 50Hz_p_e, D 50Hz_p_p Phase to earth Phase to phase For fastfront overvoltag D el U90%_ff_is D el = = 530 k K K a z_ff d is is the clearance distance between the extremities of the insulator string; K g_ff is the lightning impulse gap factor of the air gap, expressed in terms of switching impulse gap factor, K g, K g_ff = 0,74 + 0,26 K g_sf ; K g_ff_is is the lightning impulse gap factor of the insulator string; K z_ff is the deviation factor of the air gap withstand voltage distribution for fast-front overvoltages, K z_ff = 0,961; k a is the atmospheric factor according to Table E.2; U 90 %_ff_is is the maximum of the 90 % lightning impulse withstand voltages of the insulator strings on the line. g_ff 1 k a K K g_ff_is g_ff d is D = pp 530 D pp 1,2 k U a 90%_ff_is K z_ff K g_ff D el D pp For slowfront overvolta K cs Ue2%_sf 1,4 K cs Ue2%_sf D el = 2,174 ( exp ( ) 1) D pp = 2,174 ( exp ( ) 1 ) 1080 k K K 1080 k K K a z_sf g_sf a z_sf g_sf K cs is the co-ordination statistical factor; K g_sf is the switching impulse gap factor of the air gap, K g_sf = K g, according to Table E.4; K z_sf is the deviation factor of the air gap withstand voltage distribution for slow-front overvoltages, K z_sf = 0,922; k a is the atmospheric factor according to Table E.2; is the 2 % slow-front overvoltage phase to earth stressing the air gap (i.e. slow-front overvoltage having a probability of 2 % of being exceeded). U e2 %_sf D 50Hz_p_e D 50Hz_p_p For power frequency voltages s 0,83 D 50Hz_p _ e = 1,642 ( exp ( ) 1) K a K z_pf K g_pf U s 0,83 D 50Hz_p _ p = 1,642 ( exp ( ) 1) 750 k a K z_pf K g_pf K g_pf is the power frequency gap factor of the air gap, expressed in terms of switching impulse gap factor, K g, K g_pf = 1,35 K g_sf - 0,35 K 2 g_sf ; K z_pf is the deviation factor of the air gap withstand voltage distribution for power frequency voltages, K z_pf = 0,91; k a is the atmospheric factor according to Table E.2; is the highest system voltage (kv rms). U s U

179 EN :2012 E.4 Examples of calculation of D el, D pp and D 50 Hz for different U S voltages (informative) E.4.1 Range I: 90 kv system equipped with insulator strings composed of 6 units The following example illustrates the calculation of the minimum air clearance distances for a 90 kv system, equipped with insulator strings composed of 6 units, for lines at a height of m above sea level. The highest system voltage is U s = 100 kv. For this highest system voltage, there is no need to consider any slow-front overvoltage. For the purpose of this example, it is considered that when insulator strings composed of 6 units are used, the value of fast-front overvoltage to be taken into account is: phase to earth : U 90 %_ff_is = 385 kv. According to the above mentioned overvoltage and to Table E.2, the atmospheric factors to be used at a height of m above sea level are then: fast-front overvoltages: phase to earth k a = 0,946; phase to phase k a = 0,959. power frequency voltages: phase to earth and phase to phase k a = 0,938. The deviation factors to be considered are the following: fast-front overvoltages K z_ff = 0,961; power frequency voltages K z_pf = 0,910. For the four air gap configurations taken into account in the present standard, the gap factors (K g_sf ) defined in Table E.4, for slow-front overvoltages are the following: conductor-obstacle 1,30; conductor-window 1,25; conductor-structure 1,45; conductor-conductor 1,60. The values of the minimum air clearance distances are then calculated using the formulae defined in Table E.5. Conductor - conductor configuration (K g_sf = 1,60): for fast-front overvoltages D 1,2x385 = 0,82 m pp 530x0,959x0,961x(0,74 + 0,26x1,60) = for power frequency voltages 100 D = 1,642 ( exp ( ) 1) _p_p 750x0,938x0,910x 1,35x1,60 0,83 50Hz = 2 ( 0,35x1,60 ) 0,30 m

180 EN : Table E.6 Minimum air clearance distances - 90 kv system equipped with insulator strings composed of 6 units cond a - obstacle (K g_sf = 1,30) cond a - window (K g_sf = 1,25) cond a - structure (K g_sf = 1,45) cond a - cond (K g_sf = 1,60) D el and D pp D el = 0,74 m D el = 0,75 m D el = 0,71 m D pp = 0,82 m D 50Hz - D 50Hz_p_e = 0,21 m D 50Hz_p_e = 0,19 m D 50Hz_p_p = 0,30 m a cond: conductor. E.4.2 Range I: 90 kv system equipped with insulator strings composed of 9 units The following example illustrates the calculation of the minimum air clearance distances for a 90 kv system, equipped with insulator strings composed of 9 units, for lines at a height of m above sea level. The highest system voltage is the same as in the previous example. The minimum air clearances necessary to withstand the power frequency voltage are then the same. The 90 % withstand voltage for fast-front overvoltages of the line insulation is much higher when the insulator strings are composed of 9 units than when they only have 6 units. For the purpose of this example, it is considered that when insulator strings composed of 9 units are used, the value of fast-front overvoltage to be taken into account is: phase to earth : U 90 %_ff_is = 557 kv. According to the above mentioned overvoltage, the atmospheric factor to be used at a height of m above sea level is then: phase to earth and phase to phase: k a = 0,959. For the other factors being the same as in the previous example, the values of the minimum air clearance distances are then calculated using the formulae defined in E.3, Table E.5: Conductor - window configuration (K g_sf = 1,25): for fast-front overvoltages D 557 el = 1,07 m 530x0,959x0,961x(0,74 + 0,26x1,25) = For the conductor-structure and conductor-obstacle configurations, the calculation is the same except for the value of the gap factor. The minimum air clearance distances are given in Table E.7. Conductor - conductor configuration (K g_sf = 1,60): for fast-front overvoltages D 1,2x557 pp = 1,18 m 530x0,959x0,961x(0,74 + 0,26x1,60) = Table E.7 Minimum air clearance distances - 90 kv system equipped with insulator strings composed of 9 units cond a - window (K g_sf = 1,25) cond a - structure (K g_sf = 1,45) cond a - obstacle (K g_sf = 1,30) cond a - cond (K g_sf = 1,60) D el and D pp D el = 1,07 m D el = 1,02 m D el = 1,06 m D pp = 1,18 m a cond: conductor

181 EN :2012 The clearances values obtained in these two examples show that for a given nominal system voltage, the minimum air clearance distances may be very different from one network to another depending on the line insulation. This justifies that Table 5.3 gives a clearance value for each standard lightning impulse withstand voltage. Care should then be taken using Table 5.6 which gives a unique typical clearance value depending on the highest system voltage. E.4.3 Range II : 400 kv system The following example illustrates the calculation of the minimum air clearance distances for a 400 kv system at a height of m above sea level. The highest system voltage is U s = 420 kv. For the purpose of this example, it is considered that when insulator strings composed of 19 units are used, the value of fast-front overvoltage to be taken into account is: phase to earth : U 90 %_ff_is = kv. For the purpose of this example, it is considered that the value of slow-front overvoltage to be taken into account is: phase to earth : K cs U 2 %_sf = 1,05 x = kv; phase to phase : 1,40 K cs U 2 %_sf = 1,40 x 1,05 x = kv. According to the above mentioned overvoltage, the atmospheric factors to be used at a height of m above sea level are then: slow- and fast-front overvoltages: phase to earth and phase to phase k a = 0,978. power frequency voltages: phase to earth k a = 0,946; phase to phase k a = 0,959. The deviation factors to be considered are the following: fast-front overvoltages K z_ff = 0,961; slow-front overvoltages K z_sf = 0,922; power frequency voltages K z_pf = 0,910. The values of the minimum air clearance distances are then calculated using the formulae defined in Table E.5. Conductor - window configuration (K g_sf = 1,25) : for fast-front overvoltages D 1550 el = 2,92 m 530x0,978x0,961x(0,74 + 0,26x1,25) = for slow-front overvoltages 1,05x1050 D el = 2,174 ( exp ( ) -1) = 3,20 m 1080x0,978x0,922x1,25 for power frequency voltages 420 0,83 D50Hz_p_e = 1,642 ( exp ( ) -1) = 0, x 3x0,946x0,910x 1,35x1,25 0,35x1,25 m For the conductor-structure and conductor-obstacle configurations, the calculation is the same except for the value of the gap factor. The minimum air clearance distances values are given in Table E.8.

182 EN : Conductor - conductor configuration (K g_sf = 1,60): for fast-front overvoltages D 1,2x1550 pp = 3,23 m 530x0,978x0,961x(0,74 + 0,26x1,60) = for slow-front overvoltages 1,4x1,05x1050 D pp = 2,174 ( exp ( ) -1) = 3, x0,978x0,922x1,60 m for power frequency voltages 420 0,83 D50Hz_p_p = 1,642 ( exp ( ) - 1) = 1,17 m 750x0,959x0,910x 1,35x1,60 2 ( 0,35x1,60 ) The largest clearances are given by slow-front overvoltages except for the internal clearance distance D el, which with K g_sf = 1,45, is given by fast-front overvoltage. Table E.8 Minimum air clearance distances kv system cond a window (K g_sf = 1,25) cond a - structure (K g_sf = 1,45) cond a - obstacle (K g_sf = 1,30) cond a - cond (K g_sf = 1,60) Fast-front: D el and D pp D el = 2,92 m D el = 2,78 m D el = 2,89 m D pp = 3,23 m Slow-front : D el and D pp D el = 3,20 m D el = 2,57 m D el = 3,02 m D pp = 3,68 m D 50Hz D 50Hz_p_e = 0,75 m D 50Hz_p_e = 0,70 m - D 50Hz_p_p = 1,17 m a cond: conductor

183 EN :2012 Annex F (informative) Empirical method for calculating mid span clearances F.1 Empirical method for the determination of clearances within the span The following calculation method determines the minimum clearances at mid span in still air, taking account of the swing angle of the conductor under design wind conditions. The empirical method detailed below shall be followed whenever an alternative spacing calculation method is not detailed in the NNAs. In the case of design wind load conditions, the minimum clearances required between phase conductors, or between a phase conductor and earthed metal are related to the values of the minimum air clearances, D pp and D el respectively as indicated in Table 5.6. These values are then multiplied by the factor k 1, which in this calculation, is equal to 0,75 or as specified in the NNA. Under certain extreme wind conditions, reference shall be made to the NNAs. When this spacing calculation method is employed, the minimum clearance, c of the conductors at mid-span in still air shall be at least: c k f + lk + k1 D pp = in m but not less than k in the case of phase conductor to phase conductor; c = k f + lk + k1 D el in m but not less than k in the case of phase conductor to earth wire, where f l k k is the sag in m of the conductor at a temperature of +40 C; is the length in m of that part of any insulator set swinging perpendicular to the line direction; is the coefficient according to Table F.1; D pp is the minimum air clearance (phase to phase) in m according to Table 5.6; D el is the minimum air clearance (phase to earth) in m according to Table 5.6. Where circuits with differing operational voltages run in parallel on the same structures, then the most unfavourable value of D pp or D el shall be used. The swing angle referred to in Table F.1 is obtained from the ratio of the horizontal wind force, Q Wc acting on the conductor according to and the vertical dead weight of the conductor, G K based on the weight span. The swing angle ϕ is calculated by: ϕ = arctan (Q Wc / G K ) where in the expression of Q Wc, the peak wind pressure, q p (h) may be replaced with the mean wind pressure, q h (h), in accordance with The wind forces for the determination of the electrical clearances are employed with a wind velocity averaged over a 10 minutes period, with a conservative value of G x = 1. The extreme wind velocity at 40 C shall be defined in the NNAs. Otherwise the nominal wind velocity shall be applied. For covered conductor systems, the conductor clearance within the span shall be one-third of that distance calculated for an equivalent bare conductor line.

184 EN : to 30 > 30 to 80 >80 to 90 Figure F.1 Position of conductor 2 relative to vertical axis through conductor 1 Table F.1 Values of coefficient k Coefficient k Angle between conductors 1 and 2 corresponding to Figure F.1 0 to 30 > 30 to 80 > 80 to 90 Range of swing angle of conductor 65,1 0,95 0,75 0,70 55,1 to 65,0 0,85 0,70 0,65 40,1 to 55,0 0,75 0,65 0,62 40,0 0,70 0,62 0,60 F.2 Approximate method for conductors with different cross-sections, materials or sags In the case of conductors with different cross-sections, materials or sags in different phases the higher factor, k from Table F.1 and the higher sag shall be used for determining the clearances according to F.1. In addition to the clearances for conductors in still air, the clearances between swung conductors shall also be investigated in this case. It shall be proven that whilst dynamic wind pressures differing by 40% are acting on the individual conductors, a clearance not less than k 1 D pp or k 1 D el is maintained. F.3 Contribution of the insulator set to the determination of clearances at supports When evaluating clearances at the support according to 5.8, the swing angle of the insulator set shall be considered, which results from the ratio of the wind force acting on the conductor and insulator set, to the dead weight of the conductor and the insulator set. The wind force on the conductor shall be calculated according to assuming cos 2 φ = 1, and the wind force on the insulator set according to Thereby, the peak wind pressure may be replaced with the mean wind pressure according to F.1. In case of angle suspension supports, the resultant of the conductor tensile forces under wind force and at +5 C shall be considered, in addition to the wind force on the conductor.

185 EN :2012 The kinematic function of the insulator sets should be studied and assessed independently of the verification of the necessary electrical clearances. The dead weight of the conductor should be determined based on the weight span at the suspension point at +5 C. Additional permanent vertical forces, such as insulator dead weights may also be considered.

186 EN : Annex G (normative) Calculation methods for earthing systems G.1 Definition of symbols used in this annex Symbol A G I I B I d K R a R a1 R a2 s t F U D U T U Tp Z B β θ i θ F ρ E Signification Cross-section area of the earthing conductor or earth electrode Short-circuit current density for earthing conductor Conductor current (rms value) Current flowing through the body Continuous current in an earthing conductor Constant which depends on the material of the current-carrying component Additional electrical resistance Resistance, for example, of the footwear Resistance to earth of the standing point Circumference of a rectangular profile conductor Duration of the fault current Voltage difference acting as a source voltage in the touching circuit with a limited value that guarantees the safety of a person when using additional known resistances (i.e. footwear, standing surface insulating material) Touch voltage Permissible touch voltage, i.e. the voltage across the human body Total human body impedance Reciprocal of the temperature coefficient of resistance of the current-carrying component at 0 C Initial temperature of the earth electrode Final temperature of the earth electrode Resistivity of the ground near the surface

187 EN :2012 G.2 Minimum dimensions of earth electrodes Table G.1 Minimum dimensions of earth electrode materials ensuring mechanical strength and corrosion resistance Minimum size Material Type of earth electrode Core Coating / sheath Diametesectioness Cross- Thick- Single Average value values (mm) (mm 2 ) (mm) (µm) (µm) Steel Copper hot-galvanised Strip b Profile (inc. plates) Pipe Round bar for earth rod Round bar for surface earth electrode with lead sheath a Round wire for surface earth with extruded copper sheath with electrolytic copper sheath bare Round bar for earth rod Round bar for earth rod 14, Strip Round wire for surface earth - 25 c Stranded cable 1,8 d 25 c Pipe tinned Stranded cable 1,8 d 25 c galvanised Strip b with lead sheath a Stranded cable 1,8 d 25 c Round wire - 25 c a b c d Not suitable for direct embedding in concrete Strip, rolled or cut with rounded edges. In conditions where experience shows that the risk of corrosion and mechanical damage is extremely low, 16 mm 2 may be used. Diameter of single wire. G.3 Current rating calculation For fault currents which are interrupted in less than 5 seconds the cross-section of the earth electrode or earthing conductor shall be calculated from the following formula (see IEC 60724): A = I K t F θf + β ln θ + β i where A is the cross-section area in mm 2 ; I is the conductor current in A (rms value); t F is the duration of the fault current in s;

188 EN : K β θ i θ f is a constant in As 1/2 /mm 2 which depends on the material of the current-carrying component. Table G.2 provides values for the most common materials; is the reciprocal in C of the temperature coefficient of resistance of the current-carrying component at 0 C (see Table G.2); is the initial temperature in C. Values may be taken from IEC If no value is laid down in the Project Specification or NNAs, 20 C as ambient ground temperature at a depth of 1 m shall be adopted; is the final temperature in C. Table G.2 Material constants Material β in C K in As 1/2 /mm 2 Copper Aluminium Steel 234,5 228,0 202, For common conditions where the earthing conductor is in air and the earth electrode is in soil the short-circuit current density, G may be taken from Figure G.1 for an initial temperature of 20 C and final temperatures up to 300 C. For fault currents flowing for a longer time (as in systems with isolated neutral or with resonant earthing), the recommended cross-sections are shown in Figure G.2. If a final temperature other than 300 C is selected (see Figure G.1, curves 1, 3 and 4), the current may be calculated with a factor selected from Table G.3. For example, lower final temperatures are recommended for insulated conductors and conductors embedded in concrete. Table G.3 Factors for conversion of continuous current from 300 C final temperature to another final temperature Final temperature C Conversion factor 1,20 1,10 1,00 0,90 0,80 0,70 0,60

189 EN : A / m m G , 02 0, 04 0, 06 0, 08 0, 1 0, 2 0, 4 0, 6 0, s 1 0 t F 1 Copper, bare or zinc-coated 2 Copper, tin-coated or with lead sheath 3 Aluminium only earthing conductors 4 Galvanised steel Curves 1, 3 and 4 apply to a final temperature of 300 C, curve 2 applies to a final temperature of 150 C. Table G.3 contains factors for conversion of short circuit current density relative to other final temperatures. Figure G.1 Short circuit current density G for earthing conductors and earth electrodes dependent on the duration of the fault current, t F

190 EN : A: cross sectional area of circular conductor. A mm 2 A I d mm 2. mm20000 A. s A s: product of cross sectional area and circumference of a rectangular conductor 1 Copper, bare or zinc-coated 2 Copper, tin-coated or with lead sheath 3 Aluminium 4 Galvanised steel Curves 1, 3 and 4 apply to a final temperature of 300 C, curve 2 applies to a final temperature of 150 C. Table G.3 contains factors for conversion to other final temperatures. Figure G.2 Continuous current, I d for earthing conductors of circular and rectangular cross section G.4 Touch voltage and body current G.4.1 Equivalence between touch voltage and body current For the calculation of permissible values of touch voltages for high voltage installations the following assumptions are made: NOTE current path of one hand to feet; 50 % probability factor for body impedance; 5 % probability of ventricular fibrillation; no additional resistances. These assumptions lead to a touch voltage curve with an estimated acceptable risk, taking into account the rare occurrence of earth faults in high voltage systems and the small probability of persons being present at the same time.

191 EN :2012 Assuming that the basis of body current calculation is IEC/TS :2005, Revision 2 of Clause 2, and taking into account as permissible limit of current the curve, c 2 of Figure 5 (probability of ventricular fibrillation less than 5 %, left hand to feet current path), the following table results: Table G.4 Permissible body current I B depending on its duration, t F Fault duration, t F s 0,05 0,10 0,20 0,50 1,00 2,00 5,00 10,00 Body current, I B ma In order to obtain the relevant permissible touch voltage, it is necessary to determine the total human body impedance. This impedance depends on touch voltages and on the current path; values for a hand to hand or hand to foot current path are indicated in IEC/TS , from which the following Table G.5 is drawn (probability of 50 % that body impedances are less than or equal to the given value). Table G.5 Total human body impedance, Z B related to the touch voltage, U T for a current path hand to hand or hand to foot Touch voltage, U T V Total human body impedance, Z B Ω Taking into account a hand to feet current path a correction factor 0,75 for the body impedance is to be applied. By joining the two tables considering this correction factor, it is possible, by means of an iterative process, to calculate a touch voltage limit, U Tp for each value of the fault duration, t F. If specified in the NNA, Table G.6 may be replaced with Table B.3 from EN 50522:2010.

192 EN : Table G.6 Fault duration related to touch voltage, U Tp Fault duration, t F s 0,05 0,10 0,20 0,50 1,00 2,00 5,00 10,00 Permissible touch voltage, U Tp V G.4.2 Calculation taking into account additional resistances I B R a U D Z B U Tp where is the permissible touch voltage, the voltage across the human body; is the body impedance; is the current flowing through the body; is the voltage difference acting as a source voltage in the touching circuit with a limited value that guarantees the safety of a person when using additional known resistances (i.e. footwear, standing surface insulating material ); R a is the additional resistance (R a = R a1 + R a2 ); R a1 is, for example, the resistance of the footwear; is the resistance to earth of the standing point. U Tp Z B I B U D R a2 Figure G.3 Equivalent circuit for touch voltage and body current calculation Table G.7 Values for calculation Type of contact Left hand - Both feet Probability factor for the value of Z B not to be exceeded 50 % Curve I B = f (t) c 2 in Figure 14 of IEC/TS :2005 Circuit impedance Z B (50 %) + R a Additional resistance R a = R a1 + R a2 = R a1 + 1,5 ρ E (*) (*) ρ E is the resistivity of the ground near the surface (Ω m) (see H.2.1)

193 EN :2012 Calculation method: t F Fault duration. U Tp = f (t F ) Z B = f (U Tp ) I B = U Tp / Z B According to Table G.4 and Table G.6 using interpolation or directly from curve, U D1 in Figure 6.1 According to Table G.4 and Table G.6 using interpolation. Per definition. U D (t F ) = U Tp (t F ) + (R a1 + R a2 ) I B = U Tp (t F ) + R a U Tp (t F ) / Z B = U Tp (t F ) (1 + R a / Z B ) The diagram in Figure 6.1 shows curves U D = f (t F ) for 4 values of R a : R a = 0 Ω; R a = Ω, R a1 = Ω, ρ E = 500 Ω m; R a = Ω, R a1 = Ω, ρ E = Ω m; R a = Ω, R a1 = Ω, ρ E = Ω m.

194 EN : Annex H (informative) Installation and measurements of earthing systems H.1 Definition of symbols used in this annex Symbol D d I 0 I E I EW Signification Diameter of the ring earth electrode Diameter of the stranded earth electrode or half width of an earth strip / Diameter of the earth rod Zero sequence current during fault Current to earth during fault Current in the earth wire (in balanced stage) I m L R E R t r U E U em Z E Z EW-E Z ML-EW Measured test current Length of the earth strip/length of the earth rod Resistance to earth Tower footing resistance Reduction factor of earth wires Earth potential rise Measured voltage between the earthing system and a probe in the area of the reference earth Impedance to earth Self impedance of the earth wire Mutual impedance between phase conductors and earth wire Z S Earth wire impedance of one span ρ E Soil resistivity 3 I o Sum of zero sequence currents H.2 Basis for the verification H.2.1 Soil resistivity The soil resistivity ρ E varies considerably at different locations according to the type of soil, grain size, density and moisture (see Table H.1).

195 EN :2012 Table H.1 Soil resistivities for alternating frequency currents (ranges of values, which were frequently measured) Type of soil Marshy soil Loam, clay, humus Sand Gravel Weathered rock Sandstone Granite Soil resistivity ρ E Ω m 5 to to to to mostly below to up to Moraine up to Changes of moisture can cause temporary variations of the soil resistivity for a depth of some metres. Furthermore, it has to be considered that the soil resistivity can change considerably with the depth because of distinctly different layers of soil which are usually present. H.2.2 Resistance to earth The resistance to earth, R E of an earth electrode depends on the soil resistivity, ρ E as well as on the dimensions and the arrangement of the earth electrode. It depends mainly on the length of the earth electrode and less on the cross-section. Figures H.1 and H.2 shows the values of the resistance to earth for surface earth electrodes or earth rods, respectively, relative to the total length. In the case of very long surface earth electrodes (for example cables with earth electrode effect) the resistance to earth decreases with the length, but approaches a final value. Foundation earth electrodes may be regarded as earth electrodes buried in the surrounding soil. The resistance to earth, R E of a meshed earth electrode is approximately: where R E = ρe 2 D D is the diameter in m of a circle with the same area as the meshed earth electrode; ρ E is the soil resistivity in Ω m.

196 EN : D 600 Ω m R E m 100 Figure H.1 - Resistance to earth R E of surface earth electrodes (made from strip, round material or stranded conductor) for straight or ring arrangement in homogenous soil L D 600 Ω m R E m 100 Figure H.2 - Resistance to earth R E of earth rods, vertically buried in homogeneous soil L

197 EN :2012 Calculated values according to the following formula: R E = (ρ E / 2 π L) ln (4 L / d) where L is the length of the earth rod in m; d is the diameter of the earth rod in m (here 20 mm assumed); ρ E is the soil resistivity in Ω m. H.3 Installation of earth electrodes and earthing conductors H.3.1 Installation of earth electrodes H Earth electrodes An earthing system is generally composed of one or more horizontal, vertical or inclined earth electrodes, buried or driven into the soil by force. It can also consist of the direct embedded tower itself. The use of chemicals to reduce soil resistivity is not recommended, because it increases corrosion, needs periodical maintenance and is not long lasting. However in special circumstances the use of chemicals may be justified. Horizontal earth electrodes shall usually be buried to a depth of 0,5 m to 1 m below ground level. This gives sufficient mechanical protection. It is recommended that the earth electrode is situated below the frost line. In the case of vertically driven rods, the top of each rod will usually be situated below ground level. Vertical or inclined driven rods are particularly advantageous when the soil resistivity decreases with increasing depth. H Horizontal earth electrodes Horizontal earth electrodes are usually laid at the bottom of a trench or a foundation excavation. It is recommended that: they are surrounded with lightly tamped soil, stones or gravel should not be in direct contact with the buried earth electrodes, indigenous soil, which is corrosive to the electrode metal used, should be replaced by a suitable backfill. H Vertical or inclined driven rods Vertical or inclined driven rods are driven into the soil by force and should be separated by a distance not less than the length of the rod. Appropriate tools should be used to avoid any damage to the electrodes whilst they are being driven into the soil. H Jointing the earth electrodes The joints used to connect conductive parts of an earth electrode network (grid) within the network itself, shall have adequate dimensions to ensure an electrical conductance and mechanical and thermal strength equivalent to the electrodes themselves. The earth electrodes shall be resistant to corrosion and should not be liable to contribute to galvanic cells. The joints used to assemble rods shall have the same mechanical strength as the rods themselves and shall resist mechanical stresses during driving. When different metals, which form galvanic cells possibly causing galvanic corrosion, have to be connected, joints shall be protected by durable means against contact with electrolytes in their surroundings.

198 EN : H.3.2 Installation of earthing conductors H General In general the path of the earthing conductors should be as short as possible. H Installing the earthing conductors The following installation methods may be considered: buried earthing conductors: only protection against mechanical damage is required, accessible installed earthing conductors: above the ground the earthing conductors should be installed in such a way that they remain accessible. If there is a risk of mechanical damage, the earthing conductor shall be adequately protected, concrete embedded earthing conductors: earthing conductors may also be embedded in concrete. Easily accessible terminals shall be available at both ends. Special attention shall be taken to avoid corrosion where the bare earthing conductor enters the soil or concrete. H Jointing the earthing conductors The joints shall have good electrical continuity to prevent any unacceptable temperature rise under fault current conditions. Joints shall not become loose and shall be protected against corrosion. When different metals, which form galvanic cells and can cause galvanic corrosion, have to be connected, joints shall be protected by durable means against any contact with electrolytes in their surroundings. Suitable connectors shall be used to connect the earthing conductor to the earth electrode, to the main earth terminal and to any metallic part. It shall be impossible to disassemble joints without tools. H.4 Measurements for and on earthing systems H.4.1 Measurement of soil resistivities Measurements of the soil resistivity, ρ E for the pre-determination of the resistance to earth, R E or the impedance to earth, Z E should be undertaken according to a four probe method (for example Wennermethod), whereby the soil resistivity for different depths can be determined. H.4.2 Measuring touch voltages For touch voltage measurements a current injection method shall be used (see H.4.3). There are two alternative aceptable methods as follows: 1) The touch voltage is determined by assuming the human body resistance as 1 kω. The measuring electrode(s) for simulation of the feet shall have a total area of 400 cm 2 and shall be pressed on the earth with a minimum total force of 500 N. Alternatively, a probe, driven at least 20 cm into the earth, may be used instead of the measuring electrode. For the measurement of the touch voltage in any part of the installation the electrode shall be placed at a distance of 1 m from the exposed part of the installation: for concrete or dried soil it shall be on a wet cloth or water film. A tip-electrode for the simulation of the hand shall be capable of piercing a paint coating (not acting as insulation) reliably. One terminal of the voltmeter is connected to the hand electrode, the other terminal to the foot electrode. It is sufficient to carry out such measurements as a sampling test. NOTE In order to get a quick indication of the upper limit of touch voltages, measurement by a voltmeter with a high internal resistance and a probe driven 10 cm deep is often sufficient. 2) The touch voltage is determined by measuring the driving voltage, U D (Figure G.3) using a high impedance voltmeter and calculating the touch voltage as described in G.4.2. For the measurement of the driving voltage in any part of the installation the electrode shall be placed at a distance of 1 m from the exposed part of the installation. One terminal of the voltmeter is connected to the exposed part and the other terminal to the foot electrode, which will be a probe driven at least 20 cm into earth.

199 EN :2012 H.4.3 Measurement of resistances to earth and impedances to earth The resistances to earth, R E and impedances to earth, Z E can be determined in different ways. Which method is suitable depends on the extent of the earthing system and the degree of interference and disturbance voltages. Attention should be given to the fact that while the measurements and preparations are carried out, even when disconnected, but especially during the measurement on and between earthed parts (for example between tower and detached earth wire), dangerous touch voltages can occur. Examples of suitable methods of measurements and types of instruments are: a) Fall-of-potential method with the earth tester This instrument is used for earth electrodes and earthing systems of small or medium extent, for example single rod earth electrodes, strip earth electrodes, earth electrodes of overhead line towers with detached or attached earth wires, high voltage earthing systems and separation of the low-voltage earthing systems. The frequency of the alternating voltage used shall not exceed 150 Hz. The earth electrode under test, probe and auxiliary electrode shall lie in a straight line as far apart as possible. The distance of the probe from the earth electrode under test shall be at least 2,5 times the maximum extension of the earth electrode under test (in the measuring direction), but not less than 20 m; the distance of the auxiliary electrode shall be at least 4 times, but not less than 40 m. b) High frequency earth tester This instrument facilitates, without removing the earth wire, the measurement of the resistance to earth of a single tower. The frequency of the measuring current shall be so high that the chain impedance of the earth wire and the neighbouring towers becomes high, representing a practically negligible shunt circuit to the earthing of the single overhead line tower. c) Heavy-current injection method This method is used particularly for the measurement of the impedance to earth of large earthing systems, but also if transferred potentials (i.e. metallic pipes) are to be taken into account and therefore greater distances between the earthing system of the relevant tower and the remote earth electrode are necessary. By applying an alternating voltage of approximately system frequency between the earthing system and a remote earth electrode, a test current I m is injected into the earthing system, leading to a measurable potential rise of the earthing system. Earth wires and cable sheaths with earth electrode effect, which are operationally connected to the earthing system, shall not be disconnected for the measurement. The modulus of the impedance to earth, Z E is given by: where Z E = U I m em r U em is the measured voltage between the earthing system and a probe in the area of the reference earth (remote earth) in V; I m is the measured test current in A; r is the reduction factor of earth wires. The reduction factor may be determined by calculation (see H.4.5) or by measurement. For overhead lines without earth wires r = 1.

200 EN : Earth wires of lines which run on separate supports parallel to the test line between earthing system and remote earth electrode, shall be taken into account, if they are connected to the earthing system under test. The distance between the tested earthing system and the remote earth electrode shall, as far as possible be not less than 5 km. The test current should, as far as possible, be sufficiently high such that the measured voltages are greater than possible interference and disturbance voltages. This is generally ensured for test currents above 50 A. The internal resistance of the voltmeter should be at least 10 times the probe resistance to earth. For small earthing systems smaller distances and test currents can be sufficient. Possible interference and disturbance voltages should be taken into account. H.4.4 Determination of the earth potential rise The earth potential rise, U E is given by: where U E =Z E I E I E Z E is the current to earth; is the impedance to earth, for example from the measurement or by calculation. The approximate calculation of Z E taking into account earth wires and effect of the the neighbouring towers can be undertaken using the following formula: where ( Z + Z ( 4 R Z )) Z E = 0,25 + S S t S Z S R t is the earth wire impedance of one span; is the tower footing resistance. The current to earth during fault is given by: I E = r 3 I 0 where r I 0 is the reduction factor of earth wires; is the zero sequence current during fault. The reduction factor may be determined by calculation (see H.4.5) or by measurement. H.4.5 Reduction factor related to earth wires of overhead lines H General Earth wires of overhead lines carry or transmit part of the fault currents of a corresponding circuit. A high voltage earthing system installation will be more efficient during the discharge of an earth fault current. The extent of this efficiency gain is described by the reduction factor, r. For earth wire(s) of a 3-phase overhead line, the reduction factor, r is the ratio of the current to earth to the sum of the zero sequence currents of the 3-phase circuit. where r = I E / 3 I 0 = (3 I 0 I EW ) / 3 I 0 I EW I E is the current in the earth wire (in balanced stage); is the current to earth; 3 I o is the sum of zero sequence currents.

201 EN :2012 For the balanced current distribution of an overhead line, the reduction factor, r of earth wire(s) can be calculated on the basis of the self impedance of the earth wire, Z EW-E and the mutual impedance between phase conductors and earth wire, Z ML-EW : r = (Z EW-E Z ML-EW ) / Z EW-E = 1 - (Z ML-EW / Z EW-E ) The most influential characteristic for Z ML-EW, is the mean distance between phase conductors and earth wire, and for Z EW-E, the resistance of the earth wire. It follows that, the reduction effect of earth wire(s) in respect of the earth current increases (r tending to be small) with lower distance between phase conductors and earth wire and with lower resistance of the earth wire. H Values of reduction factor of overhead lines The values of reduction factors, r vary within the range 0,2 to 1 and are dependent on several parameters, e.g: line geometry, location of earth wire(s) to phase conductors, soil resistivity, number of earth wires and their resistance.

202 EN : Annex J (normative) Angles in lattice steel towers J.1 Definition of symbols used in this annex Symbol A A eff A gv A net A nt A s c d d 0 E e 1 e 2 F F b,rd F t,rd F v,rd f u f ub f y i k L L L eff L th m N Ed N b,rd N d N u,rd n P 1 P 1 Signification Gross cross section area Effective cross section area Gross cross section area for block tearing resistance calculation Net cross section area at holes Net cross section area for block tearing resistance calculation Tensile stress area of bolt Distance between batten plates Bolt diameter Hole diameter Modulus of elasticity End distance from centre of hole to adjacent end in angle Edge distance from centre of hole to adjacent edge in angle Concentrated horizontal load Bearing resistance per bolt Tension resistance per bolt Shear resistance per shear plane Ultimate tensile strength Ultimate tensile strength for bolt Yield strength Radius of gyration about the relevant axis Reduction coefficient Buckling length Member length Effective reduced length Length of horizontal member Number of angles Design value of the compression force Design buckling resistance Compression force Design ultimate resistance Number of bolts Spacing of 2 holes in the direction of load transfer Compressive force

203 EN :2012 P 2 S d S d t V eff,i,rd α η i γ M1 γ M2 γ Mb λ Tensile force Tension force Force in the supporting member (tension or compression) Thickness Block shearing resistance Imperfection factor Reduction factor Partial factor for resistance of member in bending or tension or to buckling Partial factor for resistance of net section at bolt holes Partial factor for resistance of bolted connections Slenderness for the relevant buckling load λ eff Effective non-dimensional slenderness λ λ 1 λ z χ Non-dimensional slenderness Slenderness of one sub-member Slenderness of one full-member Reduction factor for the relevant buckling mode J.2 General The calculation methods for angle members in lattice steel towers with bolted connections proposed in this annex are mainly based on the ECCS Publication: "Recommendations for angles in lattice transmissions towers" (publication n 39: 1985). According to , tension resistance of angles connected through one leg should be calculated using the provisions of EN or Annex J.3. According to , Annex J.4 on buckling resistance of members in compression is applicable only for lattice steel tower designs which are validated by tower tests. For tower designs not validated by tower tests, requirements of EN do apply. According to 7.3.8, bolted connections in lattice steel towers shall be designed using the provisions of Annex J.5 or EN Flowchart J.1 summarises the structure of Annex J.

204 EN : J Angles in lattice steel towers J.3 Tension member J.4 Compression member J.5 Bolted connections Connected through one leg? Full-scale tests acc. to 7.3.9? J.5 Design resistance or EN (see 7.3.8) NO YES NO YES EN (see ) EN (see ) J.3 Design ultimate resistance or EN (see ) J.4.1 Design flexural buckling resistance Flowchart J.1 Structure of Annex J on Angles in Lattice Steel Towers J.3 Tension resistance of angles connected through one leg (see ) A single angle in tension connected by a single row of bolts in one leg, see Figure J.1, may be treated as concentrically loaded over an effective net cross section area, A net for which the design ultimate resistance, N u,rd should be determined as follows: where a) Case of one leg connected with 1 bolt N u,rd = (b 1 d 0 ) t f u / γ M2 b) Case of one leg connected with 2 or more bolts N u,rd = (b 1 d 0 + b 2 /2) t f u / γ M2 b 1, b 2 d 0 t f u are defined as in Figure J.1; is the hole diameter, see Figure J.1; is the thickness; is the ultimate tensile strength; γ M2 is the partial factor for resistance of net section as defined in Flowchart J.2 summarises the structure of this Annex J.3.

205 EN :2012 Figure J.1 Angle with one leg connected J.3 Design ultimate resistance Effective net section area Ultimate tensile strength, f u Partial factor, γ M Flowchart J.2 Structure of Annex J.3 on Tension Members J.4 Buckling resistance of angles in compression (see ) J.4.1 Flexural buckling resistance A compression angle (hot rolled or cold formed angle) should be verified against buckling as follows: N Ed / N b,rd 1 where N Ed N b,rd is the design value of the compression force; is the design buckling resistance of the compression member. The design flexural buckling resistance of a compression member should be taken as: N b,rd = χ A f y / γ M1 N b,rd = χ A eff f y / γ M1 for Class 1, 2 and 3 cross-sections for Class 4 cross-sections where χ A A eff f y γ M1 is the reduction factor for the relevant buckling mode; is the gross cross-section area; is the effective cross-section area; is the yield strength; is the partial factor for resistance of member in bending or tension or to buckling as defined in In determining A and A eff holes for fasteners at the column ends need not to be taken into account. NOTE Angles are considered to be class 3 or 4 according to 5.5 of EN :2005. For axial compression in angles the value of χ should be determined according to: 1 χ = but χ 1 Φ + Φ² 2 λ eff

206 EN : where 2 [ 1+ α ( λ eff 0,2) + λ ] Φ = 0,5 eff λ eff is the effective non-dimensional slenderness as defined in J.4.2.4; α is the imperfection factor, which should be taken as equal to 0,13. The choice of this imperfection factor value corresponds to buckling curve a 0 according to EN The choice of a more conservative value from Table 6.1 of EN :2005 may be specified in the NNA's. Flowchart J.3 summarises the structure of this Annex J.4.1 on the design flexural buckling resistance of a compression member. J.4.1 Design flexural buckling resistance Effective cross section area A eff Yield strength, f y Partial factor, γ M1 Reduction factor for the relevant buckling mode, χ Imperfection factor.a 0 (EN ) or NNA J.4.2 Effective nondimensional slenderness, λ eff Flowchart J.3 Structure of Annex J.4.1 on design flexural buckling resistance of a compression member J.4.2 Effective non-dimensional slenderness for flexural buckling J General λ The effective non-dimensional slenderness, eff, used for the calculation of the design flexural buckling resistance of a compression member in Annex J.4.1, is a linear transformation of the nondimensional slenderness, λ as described in Annex J The non-dimensional slenderness, λ depends on the slenderness ratio, λ as described in Annex J The slenderness, λ is defined in Annex J Flowchart J.4 summarises the structure of Annex J.4.2 on the effective non-dimensional slenderness.

207 EN :2012 J.4.2 Slenderness for flexural buckling J Slenderness, λ J Buckling length for the relevant buckling mode, L Radius of gyration (about the relevant axis), i J Legs and chords J Primary bracing J Compound members J Secondary bracing J Non-dimensional slenderness, λ Yield strength, f y Effective cross section area, A eff J.4.2 Effective nondimensional slenderness, EN Gross cross section area, A Primary bracing? λ eff NO YES J Effective nondimensional slenderness, λ eff Load eccentricity Continuity of member Number of bolts at noncontinuous end Flowchart J.4 Structure of Annex J.4.2 on effective non-dimensional slenderness J Slenderness, λ The slenderness, λ is: with λ = L i

208 EN : L i the buckling length in the buckling plane considered, taken as the distance between centre line intersections; the radius of gyration about the relevant axis, determined using the properties of the gross cross-section. The appropriate slenderness, λ is determined according to the various bracing configurations described in J.4.3 for: Leg members and chords (J.4.3.2); Primary bracing patterns (J.4.3.3); Compound members (J.4.3.4); Secondary (or redundant) bracing members (J.4.4). The recommended maximum slenderness is also given. J Non-dimensional slenderness, λ where λ λ = for Class 3 cross-section λ 1 λ = λ 1 A eff λ for Class 4 cross-section A A A eff λ = π 1 is the gross cross-section area; is the effective cross-section area; E f y with f y E the yield strength; the modulus of elasticity ( N/mm²). J Effective non-dimensional slenderness, λ eff The effective non-dimensional slenderness, λ eff is determined as follows: a) For leg members: λ eff = λ b) For bracing members, 5 cases should be considered. The choice of a case depends for each member on the slenderness, the load eccentricity, the continuity of the member and the number of bolts at the non-continuous end. The choice should be made according to Table J.1. The 5 cases (5 linear transformations) are given in Table J.2.

209 EN :2012 Table J.1 Choice of the buckling case Buckling axis Non-dimensional slenderness condition Load eccentricity condition Member continuity condition Number of bolts at noncontinuous end Case VV YY or ZZ λ 2 λ > 2 λ 2 λ > 2 1 end end ends end 2 bolts 3-1 end 1 bolt 1-0 end 2 bolts 3-0 end 1 bolt 1 1 end end ends end 2 bolts 3-1 end 1 bolt 1-0 end 2 bolts 4-0 end 1 bolt 5 NOTE Member continuity conditions are: 2 ends = the member is continuous at both ends 1 end = the member is continuous at one end only 0 end = single span member Table J.2 Buckling cases Case Linear transformation 1 λ eff = λ 2 λ eff = 0,25 + 0,82 λ 3 λ eff = 0,5 + 0,65 λ 4 λ eff = 0,71 + 0,65 λ 5 λ eff = 0,4 + 0,86 λ J.4.3 Slenderness of members J General There are several different bracing configurations, which are commonly used in lattice towers, and each requires separate consideration.

210 EN : The buckling length of a member and its radius of gyration depend on the type of bracing used to stabilise the member. The appropriate slenderness, λ for the relevant buckling mode should be determined from Annex J to Annex J J Leg members and chords The recommended maximum slenderness for leg members and chords should not exceed 120. The cross section of members usually consists of one profile. For compound members reference should be made to Annex J Several cases need to be considered, as shown in Figure J.2, and the slenderness for angles should be taken as: Leg with symmetrical bracing (a) (b) λ = 1,0 L / i vv Leg with intermediate transverse support (c) λ = 1,0 L / i yy Leg with staggered bracing (d) λ = 1,2 L / i yy 1,0 i vv 1,0 i vv 1,0 i yy 1,2 i yy z z Figure J.2 Symmetrical and staggered bracing to legs J Primary bracing patterns J General The following rules should be used for the typical primary bracing patterns shown in Figure H.1 of EN :2006. Secondary, or redundant, bracings may be used to subdivide the primary bracing or main leg members as shown, for example, in Figures H.1 (IA, IIA, IIIA, IVA) and H.2 of EN :2006. The slenderness, λ for bracing members should be taken as: λ = L i di vv for angles where, L di is specified in Figure H.1 of EN :2006. The slenderness, λ for primary bracing members should generally be not more than 180 and for secondary bracing not more than 250. For multiple lattice bracing (Figure H.1(V) of EN :2006) the overall slenderness should generally be not more than 350.

211 EN :2012 The cross section of bracing members usually consists of one profile. For compound members reference is made to Annex J In case of long members, it may be appropriate to take account of bending stresses induced by wind acting on members, in addition to the axial load. The angle between a main member and a bracing should not be less than 15. J Single lattice (Figure H.1(I) of EN :2006) The provisions given in H.3.2 of EN :2006 should be applied. J Cross bracing (Figure H.1(II) of EN :2006) The provisions given in H.3.3 of EN :2006 should be applied. NOTE The load can be considered as nearly equally split into tension and compression as long as S d / N d > 2/3 with S d = force in the supporting member in tension, N d = force in the compression member. Another, more accurate method may be proposed in the NNAs. J Tension bracing (Figure H.1(VI) of EN :2006) The provisions given in H.3.4 of EN :2006 should be applied. J Cross bracing with redundant members (Figures H.1(IIA and IVA) and H.2(a) of EN :2006) The provisions given in H.3.5 of EN :2006 should be applied. J Discontinuous cross bracing with a continuous horizontal member at centre intersection (Figure H.1(IV) of EN :2006) The provisions given in H.3.6 of EN :2006 should be applied. J Cross bracing with diagonal corner stays (Figure H.2(b) of EN :2006) The provisions given in H.3.7 of EN :2006 should be applied. J K bracing (Figures H.1(III), H.1(IIIA) and H.2.(c) of EN :2006) The provisions given in H.3.8 of EN :2006 should be applied. J Horizontal edge members with horizontal plan bracing The provisions given in H.3.9 of EN :2006 should be applied. The following method may be chosen as an alternative to H.3.9 (5): the horizontal plan bracing needs to be stiff enough to prevent partial buckling. In case of doubt a good practice design rule is as follows: - the horizontal plan bracing, as indicated in Figure J.3, has to resist a concentrated horizontal load F = 1,5 L, in kn, placed in the middle of the horizontal member, where: L = length of the horizontal edge member in m. - the deflection of the horizontal bracing under this load is limited to L / Figure J.3 Typical plan bracing

212 EN : More details about plan bracing design can be found in the CIGRE Technical Brochure n 196 "Diaphragms for lattice steel supports". J Horizontal edge members without horizontal plan bracing The provisions given in H.3.10 of EN :2006 should be applied. For buckling transverse to the frame and when the horizontal member has compression in one half of its length and tension in the other, an effective reduced length, L eff may be used instead of L th to determine λ according to the following formula: with L eff = k x L th L th length of the horizontal member (see Figure H.4(a) of EN :2006). k reduction coefficient depending on the ratio of the compressive force P 1 to the tensile force P 2 as given by the formula: k = 0,085 x ( P 2 /P 1 ) ² - 0,316 x ( P 2 /P 1 ) + 0,730 That formula is consistent with the values of Table G.3 of EN :2006. The rectangular radius of gyration (i yy ) should be used for buckling transverse to the frame over this effective length, L eff. J Cranked K bracing The provisions given in H.3.11 of EN :2006 should be applied. J Portal frame The provisions given in H.3.12 of EN :2006 should be applied. J Multiple lattice bracing (Figure H.1(V) of EN :2006) The provisions given in H.3.13 of EN :2006 should be applied. J Compound members J General Compound members may be built up with two back-to-back angle sections (Figure J.4) or with two, three or four angles in cruciform section (Figure J.5). If welded continuously (Figure J.5.(a)), they may be taken as fully composite. For laced compression members reference should be made to of EN :2006. J Details The slenderness of a sub-member should be, λ 1 50 If batten plates are adopted they should be arranged at least at the third points of the total buckling length and at the ends of the members. If members comprising two angle sections are connected to a common gusset plate, separate batten plates at the ends of the members are not necessary. Every batten plate should be connected to each sub-member by means of bolts or by an equivalent welded seam. At the ends of the members one additional connecting element should be provided for each of these connections. In the case of a cruciform compound member, a minimum of two bolts for each member are required at each batten plate. J Design When the structural design complies with the requirements given previously the members may be calculated according to the following rules:

213 EN :2012 Compound members, which consist of m sub-members and have a material principal axis, yy, may be calculated against buckling transversely to this material axis as a single compression member. As far as buckling transversely to the non-material principal axis, zz, is concerned, the member can be treated as a single compression member with a virtual slenderness of: 2 z λ zi = λ + λ 2 1 m 2 where m λ z is the number of angles; is the slenderness of the full members as defined in J and J respectively; λ 1 is the slenderness of one sub-member and equal to c / i vv ; c is the distance between batten plates according to Figure J.4 and Figure J.5. Figure J.4 Back to back angle section Figure J.5 Cruciform angle sections

214 EN : J.4.4 Secondary (or redundant) bracing members The provisions given in H.4 of EN :2006 should be applied. The angle between the redundant and the main member should be not less than 15.,The percentage p of H.4(2) may be determined according to the alternative following formula: p = ( λ + 32 ) / 60 with 1 p 3,5 J.5 Design resistance of bolted connections (see 7.3.8) J.5.1 General The design resistance for an individual fastener subjected to shear and/or tension is given in Table J.3. Figure J.6 Location of bolts in angle member connected by one leg When filler plate is used for packing, the design shear resistance of bolts should be reduced according to (12) and (13) of EN :2005.

215 EN :2012 Table J.3 Design resistance for individual fasteners subjected to shear and/or tension Shear resistance per shear plane: If the shear plane passes through the unthreaded portion of the bolt: F v,rd = 0,6 f ub A / γ M2 If the shear plane passes through the threaded portion of the bolt: F v,rd = 0,6 f ub A S / γ M2 for classes F v,rd = 0,5 f ub A S / γ M2 for classes Bearing resistance per bolt: F b,rd = α f u d t / γ M2 where α is the smallest value of: η 1 3; η 2 1,20 (e 1 /d 0 ); η 3 1,85 (e 1 /d 0 0,5); η 4 0,96 (P 1 /d 0 0,5); η 5 2,3 (e 2 /d 0 0,5) and η i are reduction factors. The default value for each η i is 1, but a smaller (more conservative) value may be defined in the NNA. The value of α is still valid in the case of bolts layout on two or more rows if P 1, e 1 and e 2 are defined as: P 1 e 1 e 2 is the minimum center-to-center distance between two consecutive holes, on the same row; is the minimum distance of the bolt nearest to the end; is the minimum distance of the bolt nearest to the edge. The design resistance of a group of fasteners may be taken as the sum of the design bearing resistances, F b,rd of the individual fasteners provided that the design shear resistance, F v,rd of each individual fastener is greater than or equal to the design bearing resistance, F b,rd. Otherwise the design resistance of a group of fasteners should be taken as the number of fasteners multiplied by the smallest design resistance of any of the individual fasteners. Tension resistance per bolt: f u f ub A A S d F t,rd = 0,9 f ub A S / γ M2 is the ultimate tensile strength is the ultimate tensile strength for bolt is the gross cross-section area of bolt is the tensile stress area of bolt is the bolt diameter t, d 0, e 1, e 2, P 1 are as defined in Figure J.6 γ M2 is as defined in J.5.2 Block tearing resistance of bolted connections Block tearing consists of failure in shear at the row of 2 or more bolts along the shear face of the hole group accompanied by tensile rupture along the line of bolt holes on the tension face of the bolt group. Figure J.7 shows block tearing for an angle section. For gussets plates with a bolt group subject to concentric loading, the design block shearing resistance V eff,1,rd is given by: V eff,1, Rd = 0,95 fu A γ nt M 2 0,5 f + γ u M 2 A gv For an angle section with a bolt group subject to eccentric loading, the design block shearing resistance V eff,2,rd is given by: V eff,2, Rd = 0,80 fu A γ nt M 2 0,5 f + γ u M 2 A gv The symbols in the above formulae are: f u is the ultimate tensile strength of the plate or the angle section;

216 EN : A nt is the net cross section area subjected to tension. For an angle section with one bolt row, and using the symbols of Figure J.6, the net area subject to tension is to be calculated as follows: A nt = t d ) 2 0 ( e2 A gv is the gross cross section area subjected to shear. For an angle section with one bolt row, and using the symbols of Figure J.6, the gross cross section area subject to shear is to be calculated as follows: where A gv [ e + P ( 1) ] = t n 1 1 n is the number of bolts. Figure J.7 Block tearing of angle sections

217 EN :2012 Annex K (normative) Steel poles K.1 Definition of symbols used in this annex Symbol A A eff A s b b eff d F t,sd f bd f ck f ctm f ctk0,05 f ub f y M sd N sd n t W eff W el M σ com, Ed σ x, Ed γ c γ M1 γ Mb λ p ρ ψ Signification Gross cross section area Effective cross section area Tensile stress area of holding-down bolt Nominal width Effective width Outside diameter ; outside diameter across angles of polygon Design tensile force per bolt for the ultimate limit state Bonding stress of steel into concrete Characteristic strength of concrete in compression Average strength of concrete in tension Characteristic strength of concrete in tension Ultimate tensile strength for holding-down bolt Yield strength Bending moment at cross section Axial force at cross section Number of sides of the polygon Thickness Effective cross section modulus Elastic section modulus Additional moment Maximum calculated compressive stress Actual maximal longitudinal stress Partial factor on bonding Partial factor for resistance Partial factor for resistance of holding-down bolt Plate slenderness Reduction factor Stress ratio K.2 Classification of cross sections (EN : ) Cross sections shall be considered as class 3 if the thinness of the wall allows the calculated stress in the extreme compression fibre of the tube to reach its yield strength. All other sections, in which it is necessary to make explicit allowances for the effects of local buckling when determining their moment resistance or compression resistance, shall be considered as class 4 according to the criteria given in Table K.1.

218 EN : Table K.1 Classification of tubular cross sections in bending Type of section Criteria for class 4 t d/t > 176 ε² d b t for n equal 6 to 18 sides d n sides b/t > 42 ε b where ε = (235/f y ) 0,5 and f y is the nominal value of the yield strength in N/mm 2 K.3 Class 4 cross-sections (EN : and EN :2006 4) The effective cross-section properties of Class 4 cross-sections shall be based on the effective widths (areas in black) of the compression elements as shown in Figure K.1. A eff under axial force W eff under bending moment Figure K.1 - Class 4 effective cross-sections characteristics The effective widths of flat compression internal elements shall be designed using Table 5.2 of EN :2005 and Clause 4 of EN :2006. The stress ratio, ψ used in Table 5.2 of EN and Clause 4 of EN :2006 may be based on the properties of the gross crosssection. However, for greater economy, the plate slenderness, λ p of each element may be determined using the maximum calculated compressive stress, σ com, Ed in that element in place of the yield strength, f y, provided that σ com, Ed is determined using the effective widths, b eff of all the compression elements.

219 EN :2012 This procedure generally requires an iterative calculation in which ψ is determined again at each step from the stresses calculated on the effective cross-section defined at the end of the previous step, including the stresses from the additional moment, M. K.4 Resistance of circular cross sections The resistance of a circular cross section, without opening, under preponderant bending moment is ensured if the actual maximal longitudinal stress, σ x, Ed (including the simultaneous axial force), calculated on the gross section, satisfies the following criteria: σ x ρ f γ, Ed y / M 1 with for class 3 sections : ρ = 1, ε ρ = 0,70 + 1,, with ε = ( 235 / f y ) d / t for class 4 sections : 0 0, 5 Figure K.2 gives directly the reduction factor, ρ as a function of the ratio, d/t. ρ 1 0,99 0,98 0,97 0,96 0,95 0,94 0,93 0,92 0,91 0,90 0,89 0,88 0,87 0,86 0,85 0,84 0,83 Steel S355 Steel S d/t Figure K.2 Reduction factor ρ K.5 Resistance of polygonal cross sections K.5.1 Class 3 cross-sections (EN : ) The resistance of a class 3 polygonal cross section will be satisfactory if the maximum longitudinal stress, σ x, Ed, calculated on the gross section, under preponderant bending moment and simultaneous axial force, satisfies the criterion: σ f γ 1 x, Ed y / M For cross sections without an opening, the above criterion becomes: N A Sd M f Sd y + Wel γ M 1 where

220 EN : A W el is the gross cross-section area; is the elastic section modulus. K.5.2 Class 4 cross-sections (EN : ) Class 4 polygonal cross section, without opening, will be satisfactory if the maximum longitudinal stress, σ x, Ed, calculated on the effective widths of the compression elements, under preponderant bending moment and simultaneous axial force, satisfies the criterion: σ f γ 1 x, Ed y / M For cross sections without an opening, the above criterion becomes: N A Sd eff M f Sd y + Weff γ M 1 where A eff W eff is the effective area of the cross-section when subject to uniform compression; is the effective section modulus of the cross-section when subject only to moment about the relevant axis. NOTE The detailed method for calculation of effective cross-section properties of Class 4 cross-sections is given in of EN :2005. The curves shown in Figures K.3 and K.4 allow a quick determination of A eff and W eff for polygonal cross section, without opening. K.6 Design of holding-down bolts The design of the anchorage length of holding-down bolts into concrete is given in Table K.2. Combined design resistance of bolts in shear and tension or compression is given in EN

221 EN :2012 b t n sides d W el Figure K.3 Class 4 polygonal cross-sections Effective section modulus W eff