Study of a circuit-breaker arc with self-generated flow. II. The flow phase

For pt.I see ibid., vol.16, no.6, p.606-14 (1988). The experimental results presented concern the variations of the mean electric field and gas mass flow during this phase. The most important part consists of a modeling of the evolution of the interruption arc during the decrease of the current from 1000 A to 0. In this modeling, based on the conservation equations of mass and energy, the boundary conditions are determined by an approximate separate modeling of the arc whereas turbulence is treated through Prandtl´s approximation. This theoretical study has been developed in the case of SF/sub 6/ and nitrogen. The computed values of the electric field and temperature show that the arc has a quasi-stationary behaviour as long as the current intensity is greater than a few tens of amperes, for a decay rate of 1.35 A/ mu s. The energy losses are governed by radiation at high current and by turbulence conduction at low current. The most important results concern the conductance, whose evolution time constant, immediately prior to current zero, is 3.5 mu s in SF/sub 6/ and 15 mu s in nitrogen. The difference is essentially due to variations with temperature of thermal conductivity and specific heat in two gases.<>