CHANGES IN PD PROPERTIES WITH DECREASING VOLTAGE RISE

Paper in proceeding, 2011

The increased use of power electronic components in power systems requires understanding of how rapidly rising voltages affect insulation systems. One important aspect of this challenge is to measure partial discharges, PDs, which are considered as being a sign of insulation weakness and can affect its life considerably. This paper presents a continuation of our earlier investigations on the difference in PD behaviour when voltages characterized by different rise times are applied. The results indicate that the effect on the insulation system is indeed 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. It is further examined how the dimensions of the cavity affect the PD characteristics and the investigation shows that PD amplitude increases while its duration 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 insulation service life. To illustrate the degradation process, microscopic images show how shorter rise times affect differently the cavity surface deterioration, which is consistent with the other observations.