Research On Discharge Behaviors Of SF₆ And SF₆-N₂ Gases Mixtures

The 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 kind of greenhouse gas,the pollution of SF6 to the environment can't be ignored.Therefore,in order to reduce the use of SF6,the SF6 and N2 gas mixtures as insulating medium obtained preliminary application,and study their discharge characteristics become important.In this dissertation studied the discharge behaviors of SF6 and 50%-50%SF6-N2 mixture gases,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 spatial field,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.The positive and negative streamer under uniform field,and the positive corona discharge under non-uniform field in SF6 and 50%-50%SF6-N2 gas mixtures are studied and the results are analyzed.The tempo-spatial transformation of charged particle densities and electric field distribution are investigated-In parallel-plane electrodes,the change of applied voltage will lead to the change of discharge mode.And understand the different roles of the various physical processes in discharge stages of avalanche,streamer formation and streamer propagation.Compared the discharge characteristics in SF6 and 50%-50%SF6-N2 the results indicated that the gas mixtures have good insulation properties.In the needle-plate electrodes,the SF6 and 50%-50%SF6-N2 gas mixtures are studied under the same applied voltage,results have shown that the speed of corona formation in mixed gas is faster than that in SF6,corona range in the mixed gas is slightly larger than in the SF6,but the difference is not obvious,the formation of local corona discharge near the needle electrode.The results of this dissertation can describe the streamer discharge mechanism of SF6 and 5 0%-50%SF6-N2 gas mixtures,deeply understand the processes of discharge,and also can optimize the gas dielectric applied in electrical equipment,contribute to improve and optimize the insulating structure,full use the insulating properties of the gas dielectric,and improve the level of electrical insulation design.