In search for performance indicators of short-circuit current interruption in vacuum

Abstract

Current interruption in vacuum is characterized by a very rapid transition from an almost perfectly conducting arc plasma state to a very good insulating state. During the transition, the recovery process determines the success of the interruption. The aim of this contribution is to derive characteristics from measurements of the initial ("current zero") stage of this recovery process, having the potential to indicate the quality of the interruption. In the case of vacuum, a large number of measurements has been performed giving detailed information on the recovery process during the decay period of the post-arc plasma. The best-known indicator is the post-arc current, drawn from the decaying residual plasma by the transient recovery voltage. It turned out from measurement statistics, that post-arc current quantities (duration, peak value, charge) alone are not suitable as performance indicators. In addition, the role of conductivity (evolution) is examined, also showing not a very strong relationship with performance. It must be concluded that current-zero performance indicators for vacuum interruption are more difficult to define than for SF6 interruption. This suggests that vacuum interruption success is strongly related to di-electrical stesses, that are still relatively mild in the current zero period of a few microseconds duration.