Structure improvement of a 126 kV vacuum circuit breaker using electromagnetic-thermal field coupling simulation

Overheating limits the development of high voltage vacuum circuit breakers (HVVCB) toward large current and compact size. In this paper, an electromagnetic-thermal simulation model is proposed to investigate the thermal characteristics of a 126 kV/40 kA HVVCB. This model is first validated using experimental data. Then it is used to evaluate the thermal performance of the HVVCB with the 2/3 coil-type and horseshoe-type electrodes, respectively. The comparison results showed that the resistance and temperature of the horseshoe-type electrode are much lower than those of the 2/3 coil-type electrodes. The temperature rise in the HVVCB with the horse-type electrodes is also much lower than that in the HVVCB with the 2/3 coil-type electrode. Based on the analysis, a new structure of the HVVCB is proposed by replacing the spring finger connection between the static conductive rod and its conductive support with a fixed connection. The temperature distribution in the new structure and conventional structure is analyzed and compared. The results showed that the temperature reduction at the upper end of the connection is about 23 °C and at the contact surfaces of the two electrodes is about 20 °C in the HVVCB at a current of 2500 A.