Evaluation of Electric-Thermal Performance of High-Power Contact Systems With the Voltage-Temperature Relation

Researchers and engineers use the voltage-temperature (V-T) relation to calculate the maximum temperature of electric contacts from contact voltage drop and thus evaluate their performance. However, researchers found deviations from the V-T relation for large contact systems when heat dissipation to the environment becomes significant. We investigated the applicability of the V-T relation to high-power contact systems with spring-loaded contact elements. Such connections with rated normal currents of several kiloamperes and short-time withstand currents of several tens of kiloamperes are used in high-voltage switchgear. We loaded a connector cooled by a potent variable water cooling system with continuous ac up to 6.7 kA to create a multitude of thermally symmetric and asymmetric steady-state operating points. However, temperature differences in the contact system remained below 20 K. Temperature differences calculated with the V-T relation were 23% higher than the measured values, but nevertheless deliver an assessment of the maximum contact system temperature valid for engineering purposes. In the case of a 1-s, 20-kA short-circuit current, a transient temperature rise occurs in the contact system. We numerically calculated the development of the spatial temperature distribution over time and found significant differences to the electric-thermal steady state. While contacts react very quickly and even oscillate with twice the line frequency on ac load, the contact element and conductor continuously heat up and do not reach the steady state.