Modelling of Transient Heating and Softening Behaviour of Contact Points During Current Pulses and Short Circuits

In this paper, electrical connectors for high power applications such as gas-insulated switchgear or charging stations are investigated. Recent findings show that the contact points in these connectors are heated up rapidly during current pulses and thus, they soften and their contact resistance drops instantly. The contact points are a major source of power losses in the electrical connector. Therefore, a precise estimation of the drop in contact resistance is needed for an accurate estimation of the maximum temperature during a short circuit. In this paper, a new multiphysics calculation model is presented which aims at a better understanding of these transient processes. For this calculation, the influence of contact temperature, contact hardness and contact force on the contact resistance is evaluated. The contact hardness is highly temperature-sensitive. Therefore, pulse current tests were done to evaluate the contact hardness depending on temperature. The contact force is given by design but can be reduced by high current pulses. For the contact points, this blow-off force is estimated analytically. With these data, the effective contact resistance for every moment of a short circuit is calculated with a transient electric-thermal FEM model. Finally, the calculations are compared to results of short circuit tests.