Measurement and Analysis of Corona Current Pulses in Needle-Plate Air Gap Under Negative Switching Impulse Voltages

With the development of offshore wind power, the insulation reliability of converter equipment has been paid more attention. The metal protrusion of converter equipment will lead to corona discharge or even breakdown under negative switching impulse (SI) voltages. The study of corona current pulses under negative SI voltages will be helpful to the monitoring and location of insulation defects in converter equipment. In this article, the corona current pulses of needle-plate gap in air under negative SI voltages were investigated by experiments and theoretical calculations. The first current pulse has a large crest value and mostly occurs at the wavefront of negative SI voltages. The subsequent current pulses have a small crest value and mostly occur at the wave tail of negative SI voltages. The voltage-time delay of corona current pulses under negative SI voltages were obtained by experiment, and the effect of wavefront time and voltage amplitude on the average discharge voltage and average time delay of current pulses were analyzed. The average time delay of the first current pulse decreases and the average discharge voltage of the first current pulse increases as the amplitude of negative SI voltages increase. The calculation model of theoretical time delay of the first current pulse was established, and the theoretical voltage-time delay curves of the first current pulse were calculated. The influence of particle volume fraction and air humidity on the voltage-time delay of the first current pulse were investigated by theoretical calculations. The theoretical discharge voltage and theoretical time delay of the first current pulse increase slightly as the air humidity increases and decrease as the particle volume fraction increases.