Partial discharge measurement and analysis under lightning impulse superimposed DC voltage in SF6 gas

Abstract The presence of lightning impulses (LIs) on the DC waveform can seriously influence the insulation performance of a GIL system. The waveshape can be a superposition of the DC and impulse waveform. In this study, the behaviour of partial discharge (PD) on an epoxy surface is investigated under DC and LI superimposed voltage in SF6. The lightning impulses with different polarities are superimposed on the epoxy surface under both positive and negative DC voltages, respectively. Positive lightning impulses are superimposed on a negative DC voltage with a 90% of the partial discharge inception voltage (PDIV) magnitude. The number and amplitude of the PDs are used to evaluate the insulation performance. The experimental results show that the LI with a different polarity applied to DC can excite the PDs on the epoxy surface. The excitation effect of positive LI superimposed on negative DC is more significant. According to the impulse amplitude and PD characteristics, the influence of superimposed LI on PD excitation can be divided into three stages. As the superimposed LI increases, the amplitude of the excited PD increases gradually, while the PD number first increases and then decreases. This study is expected to provide reference for manufacture and protection of power equipment.