Behavior of inhomogeneous high-temperature SF6 gas in a gas circuit breaker

The purpose of the present paper is to show the dielectric characteristics of inhomogeneous hot SF6 gas in a gas circuit breaker (GCB) experimentally. High-temperature and low-density SF6 gas generated by a heavy current interruption is distributed inhomogeneously in the grounded tank, and can strongly threaten the dielectric capability of the GCB. Few studies, however, have been carried out on the dielectric characteristics of the inhomogeneous hot gas. Using small gap discharges, the hot gas behavior of a GCB model, having breakdown or no breakdown, was investigated. The temperature of the hot gas flowing through the, exhaust tube was estimated from the sparking voltage of the small gap installed in the exhaust tube. It was also found that there was very little or no effect on breakdown voltages of the cool gas in the breakdown paths. This suggests that the breakdown voltage of inhomogeneous hot gas could be obtained as the applied voltage at which the electrical field strength equals E-crit of local hot gas at the location concerned.