MEDIUM AND LOW VOLTAGE Part 1 SWITCHGEAR: design concepts, testing, standards and safety of persons and installations Presented by: Sergio Feitoza Costa COGNITOR Consultancy, R&D & training Ltd www.cognitor.com.br sergiofeitoza@cognitor.com.br
Contact data: Sergio Feitoza Costa Cognitor Consultancy, R&D and Training Phone : ( 55) (21 ) 2465 Skipe sergiofeitoza1 ( may speak in English, Portuguese, Spanish or French) E-mail: sergiofeitoza@cognitor.com.br Site: http://www.cognitor.com.br Author previous experience : Test engineer and manager of Brazilian high power, high voltage and other laboratories Chairman IEC -International Electro technical Commission TC 32 - Fuses ( 1990-1994 ) Member WG A3.24 CIGRE International: Simulation... Tools. Member WG IEC SC 17 C / WG31: Guidance for the extension of validity of type tests of ac metal-enclosed switchgear and controlgear Services and simulation software development and training for substations and equipment design. Design of testing laboratories
Switchgear TEMPERATURE RISE Supportability of materials, overloads, ageing and loss of life. Design issues that affect temperature rise test results.
ELECTRIC CONTACT : the main source of Joule effect Temperature rise near the electrical contact
TEMPERATURE RISE TEST Fundaments of the values of temperature rise specified in the IEC standards Limits showed in the relevant technical standard; If they are exceeded premature ageing or even destruction of parts may occur. Temperature rise depend on the circulating electric current, the materials involved, and the contact resistances, the ambient air temperature, the air velocity and the geometry of conductors and compartment components. There is an omission in IEC standards for switchgear when they request to measure only the total resistance per phase before the temperature rise test. To enable a test to be reproducible it is necessary to know at least the total resistance per phase AND the contact resistances of the main circuit breaker or switch. As the standard do not emphasize what shall be identified, most test reports issued by laboratories are poor from the point of view of photos and drawings not permitting a reliable comparison between the equipment which was tested and the equipment which is commercialized.
TEMPERATURE RISE TEST Fundaments of the values of temperature rise specified in the IEC standards If certain limits specified in the technical standards are exceeded parts may have accelerated aging or even destroyed in a small time
Estimating the contact resistance R c 0 2.. a.. a 2 ( geometry ) Constriction resistance Resistance due to the oxide layer in the interface of the contacts 0 = surface resistivity (function of the ( layer thickness of the oxide = material resistivity a = radius of each small virtual contact n = number of virtual contacts
R c Contact resistance 0 2.. a.. a 2 Force = 100 N resistance Constriction = material resistivity a = radius of each small virtual contact n = number of virtual contacts Surface resistance 0 = surface resistivity a 100 85x10 8 18..(0.45).(5.5 x10 ) 6 m = 1.78 x 10-8.m 0 = 5 x 10-12.m 2 R c = 6 + 12 = 18
Contact resistance for relatively clean surfaces R c = K 1 * F -0.6 + K 2 σ* 0 * F -1 Copper contact silver plated with force 100 N oxidized R c = 88 *10-6 * 100-0.6 + 225 *10 6 * 5 *10-12 * 100-1 R c = ( 5,55 + 11,2 ) * 10-6 = 16,7 µω
TEMPERATURE RISE SIMIULATION GEOMETRY AND MORE INPUT DATA
TEMPERATURE RISE SIMIULATION MORE INPUT DATA
TEMPERATURE RISE SIMIULATION WITH SERGIO S SOFTWARE The values in the vertical axis are the temperature rise above the external air in each point of the central phase (conductors # 4, # 5 and # 6 represent (phaseperresistanceµω the circuit breaker with 60 The yellow numbers are the numbers of the conductors showed in the figure before as the consductors were aligned side by side
The effect of the contact resistance and why the standards should request their measurement and not only the total resistance per phase Total resistance per phase (circuit breaker + busbar + connections) = 72 Circuit breaker resistance per phase = 18 APPROVED The numbers in yellow are the number of the conductors in the figure
The effect of the contact resistance and why the standards should request their measurement and not only the total resistance per phase Total resistance per phase (circuit breaker + busbar + connections) = 72 Circuit breaker resistance per phase = 30 NOT APPROVED
TEMPERATURE RISE CALCULATION (CONCEPTS)
ELEVAÇÃO DE TEMPERATURA (fundamentos)
TEMPERATURE RISE (CONCEPT USED IN THE SOFTWARE)
TEMPERATURE RISE (CONCEPT USED IN THE SOFTWARE)
TEMPERATURE RISE (CONCEPT USED IN THE SOFTWARE)
TEMPERATURE RISE CALCULATION ΔT s Over the temperature of the surrounding air Te Joule effect Sun light if applicable Eddy currents and similar + W edy Lateral area Radiation losses Convection losses Eddy currents= W eddy = K 1 * B 2 * ω 2 * e 2 volume*ρ* enclosure K 1 = adjustment B = magnetic field ω= 2*π*f e = plate thickness ρ = plate resistivity
Atention: this is not suficient to design switchgear
TEMPERATURE RISE TEST SIMULATION Bus way of an existing offshore platform 15 kv 3200 A Installation with a high short circuit level 50 KA rms x 125 kacr Bars in the horizontal position are favorable for the electrodynamical forces but an expensive solution for temperature rise
Assessing the aging Influence of the temperature (T e1 e T e2 ) and temperature rise (ΔT i1 ΔTand i2 ) in the aging 1 hour of operation in the condition 1 = K x 1 hour of operation in the condition 2 e and i are functions of T i
SHORT-TIME WITHSTAND CURRENT and PEAK WITHSTAND CURRENT (testing and simulations) Electrodynamical forces, mechanical stresses and supportability of conductors and insulators.
Neighbor conductors Current in conductor #1 produce magnetic field B1 Field B1 interact with current I2 in conductor # 2 producing a force Force bend the conductor and is transmited to the insulators
Equation for the forces distribution
Forces Stresses
INTERNAL ARC TEST Intended to offer a tested level of protection to persons in the vicinity of switchgear in the event of an internal arc. Applicable to high, medium and low voltage equipment. Medium voltage: type test defined in the IEC 62271-200.: classification (IAC, Internal Arc Classification) taking into account the types of accessibility (front, rear and sides) and the effects of the ejected gasses and particles. Fuerzas electrodinámicas y tensiones mecánicas en una celda Low voltage: not a type test but the users request
Internal arc test simulation CRITERIA Overpressure Gasses speed Current Arc voltage