Heat transfer in a high-voltage vacuum circuit breaker

Abstract

Thermal performance is one of the key issues of the high-voltage vacuum circuit breaker (HV VCB). However, temperature rise of a HV VCB cannot be estimated easily. This article studied heat transfer of a 126-kV/2500-A single break VCB. A three-dimensional electro-thermal coupling model of the VCB was built, where the power loss was calculated by the electro-magnetic field analysis, and was then used as the input data to predict the temperature rise for the thermal analysis. The heat transfer coefficients on the boundaries were numerically calculated by a commercial software. The electrical contact resistance as well as the thermal contact resistance was taken into account in the electro-thermal coupling model. The simulated results were validated experimentally. The results showed that power losses of conductors enveloped in the vacuum interrupter took up 63.3 per cent of the total power loss of the VCB. Thermal resistances of conducting rods were the highest. The second highest was thermal resistance of a pair of main contacts. The thermal contact resistance significantly affected temperature at two conductors where there is a contact guaranteed by springs. However, temperature of the conductors exposed in the air was only affected by the natural convection and radiation.