Pulse-sequence analysis of partial discharges in a void and electrical treeing

Pulse sequence of partial discharge (PD) from a void, electrical treeing and an artificially-simulated tree channel were analyzed. It was found that the residual voltages in a void and a tree channel decreased with the PD magnitude. The magnitude of electrical treeing PD was governed by the instantaneous voltage, while the PD occurrence was strongly affected by the time derivative of the applied voltage. On the other hand, the time lag played an important role in determining the number and the magnitude of void PD. In artificially-simulated tree channel of 10 μm, the PD magnitude increased with phase as in electrical treeing. The average PD number per half cycle was very small and at most 1 PD took place in every half cycle. A “packed-like” behavior of PD occurrence was observed. These were useful to explain electrical treeing PD