Numerical Analysis On Discharge Process Of SF₆/N₂/CO₂ Mixture Gases

SF6 gas as insulating dielectrics is widely used in power system and electrical equipment,because of its high dielectric strength,excellent arc extinguishing and cooling and incombustible,etc.However,SF6 is a greenhouse gas,the pollution of SF6 about environment can not be ignored.Currently,in order to reduce the use of SF6,on the insulation properties of SF6 gas mixture conducted extensive research and found that SF6/N2/CO2 may become an alternative gas of SF6,the study of its discharge characteristic is also of concern.In this paper,the discharge processes of different ratios of SF6/N2/CO2 and 50%/49%/l%SF6/N2/CO2 gas mixtures under 0.2-0.6MPa are analyzed.The tempo-spatial evolution of positive ions,negative ions,and electrons in the discharge process is described by two-dimensional continuity equations,and coupled with the Poisson’s equation described the space field strength,and considered fully the effects of ionization,recombination,electron diffusion,attachment,and photoionization.the continuity equations was solved by the flux corrected transport technique method(FCT),the finite difference method and the iterative symmetric successive over-relaxation(SOR)method was used to solve the coupling Poisson’s equation.By studying and analyzing the discharge process of different ratios of SF6/N2)/CO2 gas mixtures,the effects of the ratio are trend to increase gradually in the phase of the electron avalanche and streamer.The discharge characteristics of five different ratios of the gas mixtures are analyzed,because of the decreasing N2.and increasing CO2,mixtures complete the discharge process takes more time with the same voltage,the breakdown time is 8.5、8.7、9.0、9.2 and 9.5ns.The discharge processes of 50%/49%/1%SF6/N2/CO2 gas mixtures under 0.2-0.6MPa are calculated and the results are analyzed.The tempo-spatial transformation of charged particle densities and electric field distribution are investigated.The discharge processes of different pressures are similar.The dielectric strength become stroner with the increase of pressure.Increasing the applied voltage to achieve the numerical analysis on the discharge process.With 0.1 MPa as the increase step,the voltage increase part is 5.4kV、1.8kV、1.0kV、0.2kV、0.2kV.The growth trend is similar to the trend of breakdown voltage.Under the same applied voltage,the discharge speed is significantly among the different pressures,and the speed under 0.1 MPa significantly faster than the others.The results of this paper can describe the discharge mechanism of different ratios of SF6/N2/CO2 gas mixtures and 50%/49%/1%SF6/N2/CO2 under 0.2-0.6MPa,deeply understand the discharge processes,have a better understanding of the impact of the ratio and pressure on discharge characteristics.Contribute to provide a theoretical basis for more rational use of SF6/N2/CO2,full use the insulating properties of the gas dielectric.