Variation of surface charge distribution in PD sequences

Partial discharge (PD) occurring in gas void introduced during the manufacturing process of insulating constructions forms a serious threat to the life of insulation, hence it´s necessary to clarify its mechanism. In our paper, the surface charge measurement system based on Pockels effect was constructed to detect the residual surface charge distribution after PD occurred in a cylindrical void enveloped by PE. The real discharge current (ns level) of the PD sequences was obtained simultaneously. Depending on the combined measurement system, the current wave of a PD and corresponding discharge area were clearly observed. During continuous discharge sequences, PDs tended to take place at the sites having heterocharges at dielectric surface after voltage polarity reversed. Sometimes, the pulse current waveforms of more than two discharges showed overlapped. This phenomenon could be easily observed at initial discharges after voltage was applied. This may be due to the discharge time lag and photoionization effect. Besides, there were no discharges observed at the decreasing part of applied voltage though some area without surface charges existing.