Time variation of partial discharge current waveforms with degradation of insulators

The presence of partial discharges is one of the most prominent indicators of defects and ongoing degradation processes in electrical insulation systems. Lately ns order partial discharge signal measurements has become of major interest, because the waveforms of partial discharges are changed with the degradation of the dielectric materials. In our studies, it became clear that sometimes the reversed polarity current with applied voltages has been detected right after the same polarity current. In this paper, we investigated the time variation of partial discharge current waveforms incorporated with degradation of insulator. From the experimental results, following conclusions are obtained. The negative current with the reversed polarity to the applied voltage was observed right after the positive impulse PD current. Initially, the negative current increased with aging time. After the PD changed to swarming pulsive microdischarges, however, the negative PD current was not observed.