Decay and post-arc phases of a SF6 arc plasma: a thermal and chemical non-equilibrium model

After current zero in a high-voltage SF6 circuit breaker, the recovery volt age heats the remaining electrons, producing departures from thermal equili brium that may modify the electrical conductivity of the medium and thus th e interruption capability of the apparatus. In this study we present a two- temperature hydrodynamic model coupled with a kinetic model, applied to the extinction of a blown SF6 are in a two-dimensional simplified geometry. Th e free decay and the post-are phase with the recovery voltage have been stu died. The kinetic part of the modelling allows us to calculate the evolutio n of the electron number density. A simplified turbulence model has been ad ded to study its influence on the post-are phase. The main results of this study reinforce the conclusions obtained taking in to account only the chemical non-equilibrium: the departures from equilibri um tend to decrease the interruption capability predicted by the model. Thi s effect is due to the weak energy exchange by elastic collisions between t he electrons and the heavy particles, leading to an electron temperature hi gher than the gas temperature which favours the ionization of the medium su bmitted to a recovery voltage.