Experimental study on pulse characteristics of negative corona discharge in SF₆/N₂ gas mixtures under DC voltages

Corona discharge, an inevitable phenomenon, may lead to insulation degradation, threatening the safe and reliable operation of gas-insulated power equipment. The pulse stage is a complex but usual discharge process in corona discharge. In this paper, we investigate the pulse characteristics of negative corona discharge in a needle-to-plane electrode configuration in SF6/N-2 gas mixtures under DC voltages. With an increase in mean current, a stage transition phenomenon from the Townsend stage through the pulse stage to the breakdown stage is observed. The variation in pulse amplitude and pulse time characteristics at the pulse stage is analyzed. In addition, the effects of gas pressure, gap spacing, and N-2 content on onset voltage and pulse characteristic parameters, including pulse time parameters and the pulse repetition rate, at the pulse stage are presented. The results show that the current pulses mainly exhibit an irregular distribution of small amplitude. The pulse time parameters are not affected by gas pressure, gap spacing, or N-2 content at pressures higher than 0.1 MPa. The pulse repetition rate decreases with an increase in gas pressure and N-2 content but is only weakly affected by gap spacing, ranging from 1 kHz to dozens of kHz.