Influence of surface charge decay on cavity PD frequency at DC voltage

In this study, two types of samples, i.e. a disc-shaped cavity embedded within solid dielectrics and the other on an electrode surface, were used to investigate partial discharge (PD) behaviours at DC voltage. It has been found that the discharge frequency of the sample with one metallic surface was much larger under a positive voltage than under a negative one, whereas it was not sensitive to voltage polarities for the sample with two insulating surfaces. In order to explain experimental results, a simulation model based on continuity equations was established to obtain PD sequences at DC voltage, in which surface charge decay and discharge time lag were taken into account. Simulation results showed that positive surface charges dissipated faster than the negative, and the discharge time lag kept almost unchanged at the same voltage amplitude. The discharge time interval consisted of field recovery time and discharge time lag, and the former was determined by surface charge decay rate. In terms of these, the effect of surface charge decay on discharge frequency was discussed. The research is helpful to clarify PD mechanism at DC voltage.

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