Investigation of factors inducing simultaneous discharges in voids

Simultaneous discharge, characterized by single current pulse corresponding with more than one discharge spots in one PD (partial discharge), was observed in the partial discharge sequences, especially for the first discharge after voltage application. However, its mechanism has not been understood clearly. In this report, we investigated the effects of photoionization and overvoltage on the probability of simultaneous discharges. A combination measurement system was developed to simultaneously observe surface charge and partial discharge in the samples with double-spheres plate electrodes. Focusing on the first discharge, the single square voltage pulse was applied. When two spheres were separated by the glass slide, the simultaneous discharge probability was smaller than the case without glass slide, indicating that photoionization contributed to the simultaneous discharge. Moreover, as the gap distance between two spheres increased, the simultaneous discharge probability diminished, even in the case that the light effect was inhibited by using glass slide. Furthermore, the simultaneous discharge probability became larger as the overvoltage increased, in the both cases with and without glass slide.