The impact of short circuits on contact elements in high power applications

Electrical equipment has to carry the rated normal current and short time withstand current. As shown in previous publications, the voltage-temperature relation allows calculating the temperature of contact elements and connectors for steady- state operating points. In the case of transient electric-thermal load, a finite-element analysis (FEA) is required to calculate the time-dependent distribution of the temperature. This FEA has to be verified for transient load. Therefore a test-environment has been built in which contact elements can be loaded with AC short- circuits. The temperature of the contact system can be measured via infrared thermography during the transient event, so the calculation can be validated quantitatively. Additionally, the benchmark parameters joint resistance and contact force before and after short circuit are discussed. Measurements show that the contact materials soften due to the transient heating. This reduces the electric and thermal contact resistances and affects heat generation as well as heat distribution. Hence, the softening of contact materials was implemented in the FEA. This publication describes the enhanced and validated FEA for transient thermal stress of a high power contact system with contact elements. The performance of the contact elements during and after short circuits are discussed theoretically, via calculation and compared to measurements.