Investigation on Pressure Build-Up and Blowing Processes by Multipoint Pressure Measurement and Fluid Analysis for Self-Blast-Type High-Voltage Circuit Breaker

In high-voltage gas circuit breakers, processes to blow high-pressure and low-temperature gas into an arc are important for efficient fault current interruption. Self-blast-type gas circuit breakers obtain a high pressure by using arc energy to blow the high-pressure gas into the arc. In order to understand the self-blast phenomenon, we carried out multipoint pressure measurements to investigate the pressure build-up mechanism and blowing processes quantitatively. Because the pressure in the nozzle throat was particularly high around the arc area, the nozzle throat with a narrow cross-sectional area and high-current density works as a pressure source at a high-current condition. Blowing gas from a thermal puffer chamber becomes dominant when interrupting current decreases, and then a switch is made to the blowing process a few milliseconds before current zero. The pressure ratio between the thermal puffer chamber and nozzle throat agreed well with the pressure ratio calculated from the sound speed condition thereafter around current zero. Therefore, we confirmed the formation of sound speed flow in the nozzle throat, and supersonic flow was established in the nozzle diverging section. It was possible to use the pressure distribution and influence of pin position around current zero in the nozzle diverging section to evaluate gas flow by a theoretical calculation, and the pressure measurement found the influence of stagnation flow by pin contact. The influence of pin contact could be evaluated from the comparison of measurement and gas flow analyses, and it was confirmed that the evaluation of gas flow and interrupter design was possible.