Dielectric breakdown properties of SF₆-N₂ mixtures at 0.01-1.6 MPa and 300-3000 K

The dielectric breakdown properties of SF₆-N₂ mixtures were investigated at different concentrations of N₂, 0.01-1.6 MPa, and 300-3000 K. The equilibrium compositions of different SF ₆-N₂ mixtures at several gas pressures and temperatures up to 3000 K were first calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. The electron energy distribution function was then obtained using the composition data by Boltzmann equation analysis. It was found that adding N₂ to SF₆ gas can markedly reduce the kinetic energy of electrons at relatively high gas temperatures, which enhances the dielectric field strength. Finally, the critical reduced electric field (E/N)_cr, defined as the value for which ionization is equal to attachment, of hot SF₆-N₂ mixtures was determined. The results indicate that in the gas temperature range around 2000-3000 K, increasing the concentration of N₂ effectively enhances the (E/N)_cr of SF₆-N₂ mixtures, and the (E/N)_cr of SF₆-N₂ mixtures at a wide range of concentrations of N₂ (5, 50, and 95) are all higher than that of pure SF₆ gas. Further, this trend exists at all the gas pressures considered (0.01-1.6 MPa).