DIELECTRIC RECOVERY OF COPPER CHROMIUM VACUUM INTERRUPTER CONTACTS AFTER SHORT-CIRCUIT INTERRUPTION

The recovery of a vacuum interrupter gap after short-circuit interrupt ion 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 an d 50% chromium content), gas content, and production method, The gap f ailure was either pure dielectric or it was dominated by a significant postarc current, Therefore, postarc current phenomena were experiment ally investigated focused on the relationship among the postarc curren t, the power frequency current amplitude, and the gap length, It was f ound that two postarc current maxima exist: the first strongly depende nt on the power frequency current, and the second on the held strength , A correlation among postarc current facilitated failures, the ultima tely dielectric recovery, and the erosion rate of the material was fou nd, Strong indication if given that all of these effects are dominated by the metal vapor pressure rise given by the constricted rotating ar e. A significant influence of the material properties can be drawn fro m these experiments, allowing a good estimation of the capability for short-circuit current interruption, thus providing a useful tool for m aterial development.