Simulation Of Charge Accumulation And Flashover On The Surface Of Insulator In SF₆/N₂ Gas Mixtures Using Particle-in-cell Method

SF₆ gas is widely used in electric power industry for gas-insulated equipment as an important quenching and insulated medium because of its excellent chemical and physical characteristics. However, SF₆ is one of the six greenhouse gas listed in the Kyoto Protocol and its application should be limited. Therefore, in recent years the research on the substitute for SF₆ has become a pressing need that should be resolved for scientists and the electricity sectors. As an ideal substitute gas, SF₆/N₂ gas mixtures have good prospects for development with its insulation characteristics close to the pure SF₆ gas. The main work of this paper is to simulate the insulator surface discharge in SF₆/N₂ gas mixtures, with a view of more profound understanding of insulation properties of such gas media, and then providing the necessary theoretical support for the insulation design of electrical equipment.In this paper, equations of motion of plasma particles are established to simulate surface discharge in the SF₆/N₂ gas mixtures. The nonlinear process of movement and collision of many particles is solved by coupling the finite element two-dimensional Poisson equation and Monte-Carlo Collision Model. The two-dimensional surface discharge dynamic process in SF₆/N₂ gas mixtures, which includes ionization, attachment, recombination, diffusion and photo-ionization processes, is simulated.Under the same conditions, the development of surface discharge in 10%-90% SF₆/N₂ and 50%-50% SF₆/N₂ gas mixtures are simulated respectively, and simulation results are compared and analyzed. The results showed that: the electronic collapse develop more quickly, electric field breakdown faster, insulation capability fall more in a low SF₆ gas mixture than a high one. Electrons will gradually deposit on the surface of the insulator during the process of moving to positive electrode by the impact of the normal component of the field strength.The simulation results can provide a very good explanation for surface discharge process in SF₆/N₂ gas mixtures, and the simulation is important for theoretical research on the mechanisms of such kind of gas discharge.