Effects of frequency and applied voltage on electrical treeing discharges

We have investigated, for low density polyethylene, the effects of frequency and applied voltage on electrical treeing discharges. Partial discharge (PD) number increased with frequency. At a constant frequency, PD number and average PD intensity increased linearly with applied voltage for applied voltage above a certain value. In the case of triangular applied voltage, average charge per cycle is the same for both positive and negative PDs. These were explained well by using the two-threshold model.