Analysis of conditioning and damaging process in vacuum based on breakdown probability distribution

For the enhancement of insulation strength in vacuum, spark conditioning is an important and effective method. In order to enhance the insulation performance of vacuum circuit breakers, we have to clarify the conditioning effect and improve a conditioning procedure. In this paper, we discuss the conditioning process of Cu and stainless steel rod electrodes based on breakdown (BD) probability distribution. We applied a negative impulse voltage to a rod-plane electrode configuration. We adopted two procedures for the voltage application, i.e. up-down and 3 times methods. For the Cu rod with the up-down method, BD voltage increased by the conditioning effect, however, the minimum BD voltage did not increase or even decreased due to the damaging effect by BD. A moderate conditioning procedure, e.g. 3 times method, could increase the minimum BD voltage as well as the stabilization of insulation strength. The Weibull analysis of the development of a BD probability distribution has enabled us to discriminate the conditioning and damaging effects. Based on these results, we can discuss a suitable conditioning procedure.