SF₆/N₂ Discharge Phenomenon Under Nanosecond Impulse Voltage Based On PIC-MCC

As SF6 has high dielectric strength and good arc extinction characteristic,it has already widely used in the insulation and arc extinguishing device.However,SF6 can do harm to the atmosphere,it's a greenhouse gas,and most of us use SF6/N2 mixed gas to substitute for SF6 in recent years.As the VFTO appears,it has drawn lots of people to pay attention to the gas discharge course under the nanosecond impulse voltage.As a result,it is necessary to study the gas discharge characteristic in short gap under the nanosecond impulse voltage.It uses the one-dimensional PIC-MCC method to simulate SF6 gas and 50%-50%SF6/N2 mixed gas in the plate electrode model.It takes advantage of finite difference method to solve the Poisson equation,then to describe the act between the charged particle and the electric field by PIC method,to describe the collision between the charged particle and the gas molecule,thereby it combines two methods to investigate the discharge characteristic of the charged particle in the electric field.Having analyzed the discharge course of SF6 and 50%?50%SF6/N2 gas under the nanosecond impulse voltage,the results show that:the discharge course in short gap under the nanosecond can divide into the following phase:the electron avalanche formation and development,the confluence of the electron avalanche,the electron avalanche chain formation and development and the conductive channel formation,there is only electron avalanche development under 1mm gap.we simulate the discharge course of SF6 when the gap ranges from 1mm to 10mm under the nanosecond impulse voltage,the results show that as separation distance increase from 2mm to 10mm,the joined time of electron avalanche shorten from 9ns to 6.2ns,the joined time of electron avalanche and the time of electron avalanche formation will both be brought forward;when the gap is 1mm,there is no electron avalanche confluence and electron avalanche chain formation.Simulating the discharge course of 50%-50%SF6/N2 under different nanosecond impulse voltage,there is no electron avalanche confluence when the voltage amplitude is 43kV,the voltage gradually increases to 50kV,the joined time of electron avalanche shorten from 7ns to 4ns,as the amplitude becomes large,the joined time of electron avalanche and the time of electron avalanche formation will both be brought forward;analyzing the effect of 50%-50%SF6/N2 gas discharge under different nanosecond rising edge time,when the rising edge time increases from 6ns to 20ns,the joined time of electron avalanche increases from 5.3ns to 11.1ns,as the nanosecond rising edge time increases,the joined time of electron avalanche and the time of electron avalanche formation will both be lagged;when the rising edge time is 2ns,there is no electron avalanche confluence and electron avalanche chain formation.In this article,it simulates and analyzes the gas discharge characteristic of SF6 and 50%-50%SF6/N2 under the nanosecond impulse voltage,we have a clear understanding of the gas discharge development rule under the nanosecond impulse voltage,it is better for the application of insulating gas medium in the electric apparatus.