Simulation Of Streamer Discharge Mechanisms In SF₆/N₂ Gas Mixtures

SF₆ gas is an important insulated medium and is widely used in electric power industry for gas-insulated equipment. However, SF₆ is a greenhouse gas and is used under limitations since the Kyoto Protocol was signed in 1997. The research of the substitute for SF₆ has become a focus for scientists and electrical equipment manufacturers. The purpose of this paper is to simulate the gas discharge process of SF₆/N2 gas mixtures, which is the most promising substitute for SF₆, and the research can help to understand the discharge mechanisms for such gaseous dielectric.Continuity equations for electrons, positive ions, and negative ions are used to establish a discharge model in gas mixtures with different content of SF₆. The electric field distortion caused by space-charged field is settled by coupling Poisson's equation to the continuity equations. A flux-corrected transport (FCT) technique is used to solve the continuity equations and the simulation of two-dimensional discharge process in SF₆ is realized, which includes ionization, attachment, recombination, diffusion and photoionization processes.The anode- and cathode-directed streamers in different gas mixtures are simulated and the simulation results are analyzed. The results show that a cathode-directed streamer can be observed if the initial streamer is an anode-directed streamer. Gap breakdown time of an anode-directed initial streamer is less than a cathode-directed initial streamer. The dielectric strength of a high SF₆ content gas mixture is higher than a low one. Photoionization can accelerate the gas discharge process and the SF₆ content is lower, the acceleration is stronger.The simulation result can describe the streamer discharge process and different particles distribution in SF₆/N2 gas mixtures accurately. The densities of different particles and the electric field intensity can be calculated quantitatively.