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

Abstract

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 SF6–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).