INFLUENCE OF SWITCHING ON DIELECTRIC-PROPERTIES OF VACUUM INTERRUPTERS

This paper deals with the influence of switching operations 'closing w ithout current/breaking without current', 'closing without current/bre aking with rated current', and 'closing without current/breaking of ra ted short-circuit current' on vacuum interrupter dielectric strength. Two types of commercially available vacuum interrupter with transverse magnetic field CuCr contacts were tested. Breakdown voltages and emis sion currents, which appear before and after switching operations, wer e determined experimentally. The corresponding characteristics were de termined after conditioning. The voltage shapes dc, lightning impulse voltage (1.2/50 mus), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical cons iderations, it was concluded which physical mechanisms determine the i nfluence of switching operations on the dielectric strength. It was fo und that in interrupters with poor contact material, the dielectric st rength can deteriorate below the limits required by standards.