Partial discharge deterioration and through-hole formation in polypropylene for power capacitors: Effects of PD magnitude and accumulated PD charge

The authors have been investigating the deterioration characteristics of polypropylene (PP) films due to partial discharge (PD) in a closed void as a basic study of longterm deterioration of power capacitors. We reported that (1) the number of PD pulses decreased with time and then fluctuated, (2) through holes were observed only after the inception of fluctuation, and so on. In this work, we focused on the effect of PD magnitude on the degradation and through hole formation by dividing the range of PD magnitude into 10 bands each of which was with the width of 200 pC. As a result, the number of small PD pulses showed a temporal change similar to that of entire PD pulses without discriminating the magnitude, while the number of large PD pulses typically increased with time and then suddenly dropped to almost zero at the inception of the fluctuation. This and the tendency of the cumulative PD charge as a measure of cumulative damage suggested that the large PD pulses were related to through hole formation.