Investigation of SF₆ arc characteristics under shock condition in a supersonic nozzle with hollow contact

Arc-shock interaction and its influence on steady and dynamic characteristics of SF₆ arcs in a supersonic nozzle with hollow contact, which is representative of switching arcs in a gas blast high-voltage circuit breaker, are computationally investigated using the magneto-hydro- dynamic theory with fixed inlet stagnation pressures and at five different exit pressure to inlet stagnation pressure ratios (referred to as pressure ratios). The significant quantity in determining the thermal interruption capability of a circuit breaker, i.e., the critical rate of rise of recovery voltage, was predicted and compared with available test results. The deterioration of thermal interruption capability of a supersonic nozzle under shock conditions, which was observed in previous tests is verified and discussed by current arc model. It was found that the close coupling between the shock and the surrounding gas flow can greatly influence the aerodynamic and electrical behavior of a nozzle arc and hence the thermal recovery behavior of current interruption. Additionally, the velocity deceleration caused by the shocks and the enhanced turbulent cooling brought by the sucked gas and arc interaction both pay a significant role in the determination of thermal interruption capability.