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Simulation of cavity PD sequences at DC voltage by considering surface charge decay

In this paper, the dynamic distribution of surface charges during partial discharge (PD) sequences was obtained at both polarities of direct current (DC) voltage, as well as at different levels of voltage. It is found that the decay rate of positive charges was higher than that of negative ones, and PD would take place with the existence of residual surface charges. Moreover, the curves to describe surface charges decaying discipline were obtained. Based on these, a simulation model about PD sequence at DC voltage was constructed by considering surface charge decay and discharge time lag. With the help of simulation model, microscopic physical processes, i.e. streamer development and surface charge accumulation, were obtained, as well as macroscopic parameters i.e. discharge current and discharge time. The accumulation of surface charges took a much shorter time at negative voltage than at the positive. Besides, discharge time interval at positive voltage was smaller than that at negative one, and it diminished as voltage increased, which were in accordance with the experimental results. In terms of the evolution of electric field within cavity, the effects of surface charge decay and discharge time lag on discharge time interval and PD magnitude were discussed. The exhaustive physical model is significant to clarify PD mechanism at DC voltage.