Dynamic behavior of surface charge distribution during partial discharge sequences

A surface charge measurement system based on Pockels effect was constructed to detect the variation of residual surface charge distribution in partial discharge (PD) sequences. The current form (ns level) of the PD sequence was measured simultaneously. By using this system, it is found that surface charge distribution caused by PDs appeared as several isolated charges spots similar to that in dielectric barrier discharges (DBD). The result also agrees with the previous models, suggesting that charge distribution is not uniform and that it plays an important role in the stochastic behavior of PDs. As the applied voltage increased, the number of charge spots increased and the hetero-discharge occurred. Besides, a charge ring along the void edge was observed after aging due to PD. An approximate linear relationship existed between PD magnitude and the corresponding accumulated surface charges. In the PD sequence, the discharges tended to take place at the sites having heterocharges at dielectric surface after voltage polarity reversed. Moreover, there were no homodischarges observed at the decreasing part of applied voltage even at the area without surface charges existing. This could not be explained by the accumulation of surface charges. It was also observed that more than one charge spot in one PD could occur. This was named simultaneous discharge in our paper, and may be attributed to the effects of photoionization and time lag.