Study on temperature-rise of a 72.5kV vacuum circuit breaker for the higher rated current

In the development of ultra high-voltage (UHV) vacuum circuit breakers (VCB), higher current-rating and improved thermal performance become more and more important to provide safe function and reliability in spite of scale-down and increasing performance demanded of modern devices. Due to the high complexity of heat generation and loss processes, it is not easy to predict temperature-rise of the breaker under various load conditions. In order to prevent the abnormal temperature-rise inside of the breaker the designer should pay attention to heat transfer mechanism of the breaker. Related international standards including IEC and ANSI limit that the temperature-rise of the various parts of the switchgear should not exceed its specified values. Therefore, the thermal analysis on vacuum breakers should be carried out. In this study, systematic approaches have been undertaken using combination of experiments, numerical analysis, and thermal network finite difference analysis technique to understand the heat transfer mechanism of a 72.5kV vacuum circuit breaker with various design alternatives. It was found that the temperature-rise of the vacuum circuit breaker through numerical analysis and the error was less than 10% with both two methods, CFD and TNA.