Effect of high voltage impulses on partial discharge activity in a cavity embedded in paper insulation

High voltage impulses in electrical power systems are mainly caused by lightning strikes and switching operations. The dielectric properties of a particular insulation at the instant of interaction with a high voltage impulse would determine the level of the degradation of the electrical insulation caused by the high voltage impulse. In this work, the effect of high voltage impulses on the partial discharge (PD) parameters was investigated. The investigation was done in test samples consisting of a cavity deliberately introduced between oil-impregnated papers used in power transformer bushings. The measurement results presented in this paper show that high voltage impulses can have a large impact on the behavior of the PD parameters if the test sample is aged by partial discharges, but a smaller impact when the test sample is unaged.