Simulation of the influences of the pressure ratio and Cu Vapour on SF ₆ arc characteristics

The inlet and outlet pressure of the SF₆ high voltage circuit-breaker nozzle are of importance in determining the thermal interruption capability of a breaker. Besides, electrode evaporation is inevitable during the arcing process, which may affect the SF₆ arc behaviour significantly. In this study a numerical investigation on the arc characteristics of a supersonic nozzle is carried out, by considering the influence of the pressure ratio between the inlet and outlet, and the Cu vapour. It is demonstrated that a lower inlet pressure may result in a higher arc temperature, a lower arc voltage and a smaller mach number, and Cu vapour from electrode evaporation may cool the arc significantly.