The effect of discharge area variation on stochastic characters of PD magnitude

Surface charges generated by previous discharges at the solid-gas interface in a void can affect the characteristics of subsequent ones. In this paper, the effect of discharge area variation on the stochastic characters of partial discharge (PD) magnitude was investigated by changing the void size. It is found that the uniformity of PD magnitude increased when void diameter was reduced. In order to clarify this, the corresponding discharge area variation was obtained by Pockels effect of Bismuth Silicon Oxide (BSO) crystal. As void diameter became smaller, due to the limitation of cavity walls, the fluctuation of discharge area became weaker, and hence the uniformity of PD magnitude increased. Besides, the result that the fluctuation of PD magnitude decreased when PD void height became larger was obtained. Considering the safety of BSO crystal, surface charge distribution was not measured by experiment for this case. Instead, a simulation model was constructed to obtain it. As a result, discharge area became larger when void height increased. According to this, it is inferred that the expanding of discharge area may be affected by cavity walls in the experiment. Therefore, the changing tendency of the uniformity of PD magnitude with the void height can be explained when the void area remained unchanged. These results suggest that the variation of discharge area can affect the stochastic character of PD magnitude and further investigation is needed to clarify the PD mechanism.