Evidence for changing PD properties at short voltage rise times

The increased use of power electronic components in power systems makes it important to understand how rapidly rising voltages affect insulation systems. One vital aspect of this challenge is to measure partial discharges, PDs, which are considered as being a sign of weakness and can affect the life of insulation considerably. In this paper we report on continuation of our earlier investigations on the different behavior of PDs when voltages characterized by different rise times are applied. Significant differences in PD characteristics are found, which indicate that the effect on the insulation system is dependent on the voltage wave shape. Applying square-like voltages to a cavity with dielectric insulated electrodes significantly affects the discharge amplitude, its rise time, the inception voltage and the distribution shape. The investigation shows that PD amplitude increases while PD rise time decreases for shorter voltage rise times, being indications of a possible change in the discharge mechanism. This in turn can lead to faster deterioration and reduction of service life and may therefore need to be considered when designing insulation systems exposed to fast transients.