Validity of the voltage-temperature relation for contact elements in high power applications

With the voltage-temperature (V-T) relation, established by Kohlrausch in 1900, the electric potential distribution in an arbitrarily shaped, thermally insulated, current carrying conductor can be used to calculate the associated temperature distribution. An important application is the determination of the maximum temperature in electric contacts. However, researchers found deviations from the V-T relation for large contact systems when heat dissipation to the environment via radiation and convection becomes significant. The present investigation aims to verify the applicability of the V-T relation to typical spring-loaded contact elements for high power applications as for instance plug-in connections in highvoltage switchgear. A connector with a variable cooling system was continuously loaded with currents up to 6.7 kA to create a multitude of thermally symmetric and asymmetric steady-state operating points. Contact element temperatures were measured and compared to calculations with the V-T relation. When the load current varies over time, the spatially distributed heat capacity of the contact element and the adjacent conductors is charged or discharged to reach the electric-thermal steady-state for which the V-T relation applies. The transient temperature distribution may differ significantly, which is demonstrated by numerical calculations.