Investigation of cavity PD physical processes at DC voltage by simulation

Abstract

In order to reveal partial discharge (PD) physical processes at DC voltage, a model with regard to PD taking place within a cavity embedded in polyethylene is established, in which the charge fluid equations and the Poisson equation are employed to simulate streamer propagation and surface charge accumulation processes after it arrives at the gas–solid interface. Meanwhile, parameters such as discharge current and discharge time during a PD sequence are obtained by considering surface charge decay and discharge time lag variation in the discharge time interval. It is found from the simulation results that the electrons generated by the discharge accumulate on the upper surface of the cavity and the time taken to accumulate is less that 1 ns when a positive voltage is applied to the upper electrode. On the contrary, positive ions accumulate on the lower surface, and the time taken is about 90 ns. Besides, the density of positive ions is slightly higher than that of the electrons. During a PD sequence, the decay of surface charges resulting from previous discharge can be considered to be the key factor contributing to the occurrence of subsequent one, and electric field within the cavity mainly depends on negative surface charges just before the subsequent PD takes place, because of the lower decay rate of the negative charges than the positive ones. The discharge time interval can be divided into two parts: discharge time lag and discharge recovery time, which depend on the surface charge decay rate. As surface charge decay rate increases or the discharge time lag decreases, the discharge time interval decreases. Moreover, the discharge current is affected by discharge time lag and the surface charge decay rate. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.