The Influence of Sample Configuration on PD Frequency at DC Voltage

In this paper, the discharge frequency was measured for two types of cylindrical cavities at DC voltage. One was surrounded by polyethylene (PE), while the upper surface of the other was metallic. It is found that the partial discharge (PD) frequency was independent on voltage polarity for the former sample, while for the latter one the discharge frequency in the case with positive voltage application was larger than that with negative voltage. In order to explain experimental results, a PD simulation model was constructed based on surface charge decay. In terms of it, the dynamic distributions of surface charges during PD sequences were obtained, which took place in the two types of cavities. In the cavity with one metallic surface, positive charges landed on the lower surface of the cavity when the positive voltage was applied, and the polarity of surface charges would be reversed if the voltage polarity varied. Due to the slower decay rate of negative surface charges, discharge frequency in the case with positive voltage was higher than that with negative voltage application. However, as for the cavity embedded in the solid insulation, there was no such law because positive and negative charges always accumulated on both surfaces regardless of voltage polarity.