Measurement of hot gas exhaust characteristics in SF<inf>6</inf> circuit breaker with small model interrupter

Abstract

High-voltage circuit breakers have continuously been developed to reduce their size and operating energy. In the current interruption process, hot gas is generated and exhausted out of the conducting exhaust tube. The hot gas causes electrical breakdown at the exit of the exhaust tube. The hot gas characteristics in the exhaust tube were measured to clarify the dielectric strength. Two measurement methods, the small gap discharge method and the extra-fine thermocouple, were used to estimate the temperature of the hot gas. In the small gap discharge method, the temperature was deduced from the breakdown voltage at the small gap by referencing the critical electric field strength. The critical electric field strength is the electric field strength where ionization coefficient is equal to electron attachment one. An extra-fine thermocouple with a 25 micron tip was also used to measure the temperature on a trial basis. The response speed of the thermocouple was slower than that of transient change of temperature in the interruption process. First-order response lag was compensated by de-convolution with fast Fourier transform (FFT). As a result, the peak value of the temperature in the conducting exhaust tube agreed well with the results estimated by the other method.