Numerical Calculation and Experimental Study on the Insulation Characteristics of SF6-N2 and SF6-CF4 Gas Mixtures

This paper presents a numerical model for simulating the breakdown performance of SF6-N-2 and SF6-CF4 mixtures gas. Firstly, the ionization and attachment coefficients of mixtures were obtained by solving Boltzmann equation at different mixing ratio and 300K. All these parameters were applied on the fluid model to investigate the mechanism of electron number density varies along with time and space by finite element method-flux corrected transport (FEM-FCT) way. The breakdown voltages were obtained by cyclic iteration to solve the gas discharge process at different voltages, and the synergistic effects were finally studied. The results show that the plasma conduction channel was formed when the discharge gap had been completely broken down, and its peak value could reach 10(17) level. The calculation and experimental results show that the breakdown voltage of SF6-N-2 and SF6-CF4 mixtures gas increase linearly with pressure. But the insulating strength of SF6-N-2 is stronger than that of SF6-CF4 mixture in uniform electric field. Under the same pressure, the synergistic coefficients of SF6-N-2 and SF6-CF4 gas mixtures, which contain 20%SF6 gas, are the smallest, but the synergistic effect of SF6-N-2 mixture is stronger than that of SF6-CF4 mixture. This model simulation results of the breakdown voltages and synergistic coefficients show good agreement with measurements.