Influence of switching on dielectric properties of vacuuminterrupters

This paper deals with the influence of switching operations `closing without current/breaking without current', `closing without current/breaking with rated current', and `closing without current/breaking of rated 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 emission currents, which appear before and after switching operations, were determined experimentally. The corresponding characteristics were determined after conditioning. The voltage shapes, dc, lightning impulse voltage (1.2/50 μs), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical considerations, it was concluded which physical mechanisms determine the influence of switching operations on the dielectric strength. It was found that in interrupters with poor contact material, the dielectric strength can deteriorate below the limits required by standards