Electrode conditioning mechanism based on pre-breakdown current under non-uniform electric field in vacuum

Electrode conditioning in vacuum is very important technique for improvement of the insulation performance of vacuum circuit breakers (VCBs). This paper discusses the spark conditioning mechanism through the measurement and analysis of the pre-breakdown current under non-uniform field. From F-N plots, we made sure that the pre-breakdown current was based on field emission mechanism. We quantitatively evaluated the variation of pre-breakdown current in the conditioning process. As a result, field enhancement factor beta decreased as the conditioning proceeded and reached the final value. In addition, in case of non-uniform field, we found that beta on rod electrode surface after conditioning was distributed according to the electric field distribution on the surface.