Dielectric recovery of copper chromium vacuum interrupter contacts after short circuit interruption

The recovery of a vacuum interrupter gap after short circuit interruption was measured by application of an overshooting transient recovery voltage (TRV) several tens of microseconds after current zero. Copper chromium contact materials were employed varying in composition (25% and 50% chromium content), gas content and production method. The gap failure was either pure dielectric or it was dominated by a significant post arc current. Correlation between these post arc current facilitated failures, the ultimately dielectric recovery and the erosion rate of the material was found. Strong indication is given that all these effects are dominated by the metal vapor pressure rise given by the constricted rotating arc. A significant influence of the material properties can be drawn from these experiments, allowing a good estimation on the capability for short circuit current interruption, thus providing a useful tool for material development