Evolution of PD properties till breakdown in silicon nitride substrate molded with resin

This paper deals with evolution of partial discharge (PD) occurrence phase and charge (φ-q) characteristics of 0.32 mm thick Si3N4 substrate molded with resin by applying ac 9 kVrms at 60 Hz until breakdown to quantitatively evaluate the degradation degree as well as the lifetime. Experimental results revealed that all specimens broke down just after PD magnitude suddenly increased. This means difficulty to expect the lifetime from only the PD magnitude. On the other hands, it was also found that φ-q characteristics changed continuously until breakdown. Namely, the shape of φ-q characteristics exhibited a rabbit-like pattern a few minutes before breakdown. In addition, the skewness of the pattern of PD distribution was analyzed in the positive and negative phases separately. As a result, the positive and negative skewness has increased three to four times with approaching to the breakdown. Thus, the present research indicates that a statistical parameter skewness of PD occurrence distribution can provide a possibility for expecting the lifetime of Si3N4 insulation substrate molded with resin.