Characterization of partial discharges in solid insulators under DC voltage using physical cavity properties

Presently, the Partial Discharge (PD) process at DC voltage is not as well known as for AC voltage. In this paper, the characterization of PD activity under DC voltage is studied in order to be used as a future tool for the diagnostic of insulators. The PD is associated with a bipolar charge deployment inside the cavity of the insulating material. PD characterization was usually investigated based on PD magnitude and the time interval between PDs. In this study the analysis of PD pulses pattern is focused especially on the time constant of charge decay τ within the cavity. The relationship between τand the parameters of the cavity is established using a theoretical model. To validate this approach, measurements were performed on samples with an artificial cavity containing air or oil and compared with samples without any artificial cavity. The experimental results, in accordance with theoretical statements, show a strong relationship between τ, geometrical and electrical parameters of the cavity within the solid insulation.