Research Of Discharge Phenomena Of SF₆ In Short Gap Under Nanosecond Impulse Based On PIC-MCC

Because of the excellent insulating properties and extinction arc performance,SF6 has been became the most widely used gas dielectric in the field of electrical equipment insulation.At present,analysis on insulating performance of the SF6 almost always carries out under the DC,AC and the standard lightning wave.However,the research results of the SF6,applied the non-standard impulse voltage,in specially,nanosecond impulse exciting under extreme conditions is rarely reported.With the discovery of VFTO generated in GIS,discharge phenomenon and mechanism of SF6 under the nanosecond impulse has been paid great an attention.Therefore,the investigation on the discharge characteristic of the under the nanosecond impulse with the short gap is provided with practical significance and academic value.In order to find the characteristics of particles production,multiplication,attachment,adhesion and migration in SF6 during the discharge process under nanosecond impulse,the PIC(Particle-In-Cell)model combined with Monte Carlo(Monte Carlo)law has been used,and also the physical model of the plate-plate structure in the short gap is established,then according to the law of conservation of mass,momentum and energy conservation of physics laws,the mathematical model for simulating analysis had been given to characterized the short gap SF6 nanosecond impulse discharge process,at the same time,the appropriate analytical methods are adopted for theoretical research.The results show that,when a wave head time 6ns,the amplitude of 54kV nanosecond impulse voltage applied under the condition of atmospheric pressure in the 5mm gap,the electron density is decreased before the voltage reaches the SF6 critical breakdown voltage,as the nanosecond impulse voltage rises to critical breakdown voltage,the electron density increases.The streamer forms gradually at 8.6ns when electron density accumulated into 1018 magnitude.Changing the rising time to 2ns,since the electron density is not reached to the threshold value of streamer formed before the impulse voltage drops to the critical breakdown voltage,streamer can not be formed.Changing the rising time to 10ns,the electron density accumulates slowly because the voltage rising time is long,the streamer forms at 12ns.Applying a wave head time 6ns,the amplitude of 54kV voltage nanosecond impulse to the same gap,the initial seed electron density affects the location and time of streamer appearing,with the initial seed electron density increasing,the streamer formation time is decreased,which is formed a position closed to the cathode.With the initial seed electrons from the cathode distance increasing,the position of streamer formation is far away from the cathode.The electrons in the gap will produce the reverse streamer,when the initial position of the seed electrons is much closer to the anode.Analyzing the SF6 discharge process nanosecond impulse,not only understanding the discharge process under these conditions,and also in-depth understanding the mechanism of gas discharge,and providing reference for researching nanosecond impulse SF6 gas insulation properties.