Overhead lines. 110 kv wood tower with guy wires

Transcription

1 Overhead lines a) ja b) 0 kv wood poles c) free standing 0 kv metal tower with I-strings d) free standing 440 kv metal tower with V-strings e) 400 kv metal tower with guy wires 0 kv wood tower with guy wires

2 Rated data of OH line conductors resistance W/km nominal load carrying capacity A s thermal withstand current ka The corresponding maximum temperatures : I nim I s - copper 70 C 70 C - aluminum 80 C 0 C - aluminum alloy 80 C 60 C - Al steel reinforced 80 C 60 C Thermal time constant t : J - ( t) ( e t / t J0 + - ) ( J - J0) J(t) temperature rise at time t J J 0 steady state temperature rise (constant load) temperature rise in the beginning t time constant - overhead lines t 7 min - underground cables t 5 60 min J J t 0

3 Temperature rise by short circuit current Temperature rise J ( C) : J p mc t I r mc t () p heating power (per km) I current r resistance (per km) m conductor mass (per km) c heat capacity of the material Example: 5.5 aluminum alloy : Solving I from Eq. () : Þ Þ I I s» Jmc rt,568 0,9 ka ,67 7 A C kg/km Ws/ C kg W / km s W VA A W V/A Temperature rise for different currents and different times: r 0,67 W/km (80 C) m 45 kg/km c 90 Ws/ C kg J allowed 80 C J J I r t mc : I r t mc I I t t I s?

4 Example: DT in a MV OH-line during a short circuit fault t 0 t t t t 4 t 5 fault RC RC RC 0,5 0,5 0,5 0 0,5 0 0,5 Data : I s,9 ka I k,0 ka thermal s withstand current fault current t 4 min time constant T max 80 C max operation temperature T maxs 60 C max I s temperature T 0 50 C T a 0 C initial conductor temperature ambient temperature One 0,5 s fault current pulse causes the temperature rise of J : J J s Þ J Dt R I s R I k s 0,96 J s 0,5,0,0,9 0,96 0,96 (60-80) C»,7 C Temperature at time t (t -t 0 << t ; all the heat in conductor) : T 0 T + J 50 +,7 C 97,4 C Cooling in the period t -t : T T a + (T - T ) (- e ,4 (- e a -/ 4 ) C ) -(t -t )/ t 50,5 C Heating by re-closing at time t : T T + J 74, C Cooling in the period t -t 4 : T 4 T a + (T - T ) (- e , (- e a -/ 4 ) ) -(t -t ) / t» 4 4, C Heating by re-closing at time t 5 : T 4 5 T + J 65 C

5 Example: DT in a MV OH-line during a short circuit fault 00 T/ C The run of temperature ~ time : t t t t t 4 t 5

6 Capacitances in the chain of isolators Overhead line isolators a) pin type, b) suspension type, c) long rod type, d) multi-material-type, e) and the cross-section: fiber glass rod, silicon plating, silicon discs, 4,5,6 junctions, 7 terminal piece, 8 filling piece

7 400 kv chain of suspension insulators. insulator, 8 upper arcing horn, 9 lower arcing horn, armor rod, 5 suspending clamp

8 Overhead lines with covered conductors Types of OH lines with covered conductors: a) SAX-line (Nokia), b) SAMI-line (Sekko). support, spacer suspender, spacer. narrower right of way needed contact of two phases Þ no disturbance a leaning tree causes fault only after days power arc not able to move - risk of a broken conductor - clamps as arcing horns detection of a broken conductor not easy After a possible fault the line must be checked in case a conductor has been broken!

9 Conductor resistance R r l A ; r r 0,05W 0,079 W mm m mm m (Al) (Cu) Example: 0 mm copper, DC-resistance R ,079 W/km» 0,5 W/km By AC the resistance is increased due to the skin effect and in cables also due to the proximity effect Þ additional resistance DR, about % for OH lines % for cables Resistance is given at +0 C. Temperature dependence : a 0,009 / C (Cu) a 0,0040 / C (Al) Total resistance : [ + a ( J - 0 C) ](R + R) R 0 D

10 Capacitances of an OH-line r conductor radius h geometric mean height h h h h a, A : geometric mean distances a a a a ; A A A A C k C k C k C 0 C 0 C 0 Positive sequence capacitance C C 0 + C k pe0 c ha ln ra a a a Zero sequence capacitance C 0 pe0 c h æ A ö ln ç r è r ø h h h A A A e 0 vacuum permittivity 8, F/m

11 Example : 0 kv line with conductors in the same plane r 0,007 m h 0 m» a,,,,8 m» A 0,0 0,0 0, 0,06 h, m, m 0 m Positive sequence capacitance: c» pe0 ha ln ra 0,5 0 - ln F m - p 8,84 0 0,8 0, nf 0,5 km F/m Zero sequence capacitance : pe0 p 8,84 0 c h æ A ö 0 æ ln ç ln ç r è a ø 0,007 è - F nf» 4,7 0 4,7 m km - 0,06,8 ö ø F m

12 OH-line inductance L m 0 m0 p é ê + ln ë4 4p 0-7 d ù r ú û H/m d r d If the distances between the phases are not equal: d eq d d d r d r Example: a 0 kv line with horizontal arrangement:, m, m 50 mm Þ r» 7 mm d,,,»,9 m L m0 p 4p 0 p é d ê + ln ë4 r -7 æ ç è 4 eq + ù ú û ln,9 0,007 ö ø H/m X 0»,mH/km wl -7 pf L» 0,5 W/km (0,5 + 5,9) H/m p 50, 0 - W/km

13 The inductance of a multi-conductor line L m é 0 ê p ë4n d e de de d e + d ln r n number of sub-conductors d e equivalent distance between the phases and r e equivalent radius of one phase conductors e aa e e ù ú û a e ab a e ab e an b n b n phase phase d r e e n n (r (e e aa' ab e ab' Le an Le an' ) L(e ) L(e na e nb na' e Le nb' n(n-) Le r) nn' )

14 Zero sequence inductance of an OH-line Inductance in a loop of phase conductors and the ground return: m é 0 ê p ë + H ln r en ù ú û L d d H r e en re d d d r r en phase conductors equivalent radius d distance between phases and H equivalent depth of the ground return current H,85 rm wm 0 In Finland the soil resistivity typically is r m 00 Wm 00,85 p 50 4p 0» 4465 m Þ H -7 m

15 Example : a 0 kv line, m, m H r 7 mm (50 ) r m 00 Wm Þ H 4465 m r 0,007,,, en» 0,8m The zero sequence inductance for the three phases is: L a» m0 p é ê + ln ë -7 4p 0 é p ê ë,98 mh/km H r en + ù ú û ln ,8 ù ú û H/m And the zero sequence inductance per phase is: L 0 Þ L X 0 a 5,94 mh/km wl 0 p 50 L 0»,87 W/km

16 Structures of power cables Belt type cable: conductor, conductor insulation, belt insulation, protection screen Single conductor cable: conductor, conductor screen, insulation, core screen, protection screen, (armoring) H-type cable. Composed of single conductor cables with a common protection screen Multi-screen cable. Composed of single conductor cables with a common plastics screen.

17 Cable capacitances. Cables with cylindrical field : C R C C C C C Positive sequence C zero sequence C C T S. Belt type cable : C C C C 0 C 0 C 0 C C 0 C Positive sequence C : C0 C C 0 C C 0 + C Zero sequence C C 0 The usually given rated data for cables includes : operational (pos.seq.) capacitance mf/km (C) charging current A/km (U v wc) earth fault current A/km (U v wc0 ) The data is given in tables according to the type and cross-section

18 The load carrying capacity of power cables The thermal circuit : Heat flow R jv R jv Heat source Thermal resistances : R jv R va R au R um conductor - screen screen - armoring armoring - cable surface cable surface - earth surface conductor R jv R va R au R um metal screen armoring cable surface earth surface Maximum load depends on the allowed insulation temperature : MV-cables normally: (during fault) PVC : 65 C (5) paper: 65 C (50) PE : 65 C (50) PEX : 90 C in air (50) 65 C in soil

19 Power cable load carrying capacity Maximum load currents are given in standard conditions: in soil : cable in 70 cm depth, soil temperature +5 C and soil resistivity Km/W in air : ambient temperature +5 C, free air flow around the cable The differences to the standard conditions are taken into account by correction coefficients k i : impact of adjacent cables effect of burial depth difference in soil thermal resistivity soil ambient temperature The final loading is the product of std-loading and the correction coefficients.

20 The effect of adjacent cables in the soil to the ampacity of cables number of adjacent cables correction factor when the free distance between cables is a) 0 mm 0,79 0,69 0,6 0,58 0,55 0,50 0,46 The effect of burial depth in soil depth rated voltage in soil 0,6/ kv 6/0 40/69 m kv 0,5 0,7,0,0 0,7 0,9 0,97 0,99 0,9, 0,95 0,98,, 0,9 0,96,,5 0,9 0,95 b) 70 mm 0,85 0,75 0,68 0,64 0,60 0,56 0,5 c) 50 mm 0,87 0,79 0,75 0,7 0,69 0,66 0,64 The effect of soil thermal resistivity Soil thermal resistivity Km/W 0,7,0,,5,0,5,0 0,6/ kv up to 5 mm, 0,94 0,87 0,78 0,7 0, mm, 0,9 0,86 0,76 0,70 0, mm,4 0,9 0,85 0,75 0,69 0,6 6/0 kv up to 5 mm,09 0,95 0,88 0,80 0,74 0, mm, 0,94 0,87 0,78 0,7 0, mm, 0,9 0,86 0,77 0,70 0,65 /0 kv up to 5 mm,08 0,96 0,90 0,8 0,75 0, mm,0 0,95 0,89 0,79 0,7 0, mm, 0,94 0,88 0,78 0,7 0,66 8/0-4,6/60 kv up to 95 mm,08 0,95 0,90 0,8 0,76 0, mm,09 0,95 0,89 0,80 0,74 0,69

21 Examples of the soil thermal resistivities Dry sand (water content 0 %),0 Km/W Dry gravel and clay,5 " Half dry gravel and sand (water content 0 %), " Half dry clay and wet gravel,0 " Wet clay and sand (water content 5 %) 0,7 " The effect of soil ambient temperature Soil temperature C C conductor temp.,06,0,0 0,96 0,9 0,89 80 C ",07,04,0 0,96 0,9 0,88 70 C ",09,04,0 0,95 0,90 0,85 65 C ",0,05,0 0,95 0,89 0,84

22 Example: Three cables APAKM 85 0,6/,0 kv with 7 cm distances in soil: in 90 cm depth half dry gravel soil soil temperature +0 C std-loading 50 A / cable Correction coefficients : cables Þ k 0,75 90 cm Þ k 0,97 soil resistivity Þ k 0,9 soil temperature Þ k,04 Þ Maximum allowed load current is I n» k k k k A A

23 Power line electrical fields and health risks WHO v. -8 : safe limit is 0 kv/m exception : users of artificial pacemaker (heart) 0 kv lines: maximum value in practice about kv/m 400 kv double lines ~0 kv/m, can be reduced by a proper phase location. EU Comission recommendation 59 year 999: -5 kv/m for longer duration -5 kv/m temporarily Electrical field strength at the earth level in the vicinity of power lines. ) 4) 400 kv, lowest conductors 0 m from earth 5), 6) 0 kv, lowest conductors 8 m from earth ), 5) phase conductors located symmetrically ) phase order reversed in the other pole ) phase order reversed in other sub-conductor 4) poles with guy wires, d distance from center

24 Magnetic fields and health risks WHO v. -8 : safe limit 0, mt risk of cancer when 0, mt? compare with the earth magnetic field~0 mt under an overhead line max value 0 40 mt - at 0 m distance attenuated to 0 % - at 00 m distance 0, mt - Buildings do not attenuate! EU Comission recommendation ut for longer time -500 ut temporarily Magnetic fields of overhead lines at the earth surface level ), ) 400 kv, 000 A / circuit ) 0 kv, 000 A ) double lone ), ) towers, d distance from the center