Experimental investigation of the dielectric recovery strength between the separating contacts of vacuum circuit breakers

An experimental investigation has been carried out to examine the dielectric recovery strength of two commercial vacuum circuit breakers rated 15 kV and 7.2 kV, respectively, using the substitute method of Rabus. The two breakers exhibited different characteristics when tested up to 45 kV; continuous repetitive breakdowns occurred with the 7.2 kV device but not with the 15 kV interrupter, reflecting the influence of different contact materials. Variability in the initial rate of rise of dielectric strength was observed for both breakers. Tests indicated that the dielectric characteristic of vacuum breakers may depend upon the repetition rate of the probing voltage. It is concluded that, when evaluating a breaker by this method for a particular application, the recovery voltage should follow as closely as possible the voltage to be expected in service