The Prediction of the Dielectric Breakdown Properties of 6% C4F7N–94% CO2 Mixtures at 300–4000 K and 0.1–3.2 MPa

SF6 is a greenhouse gas, therefore, we need to find a SF6 substitute environment gases as an insulation and arc-quenching medium is an urgent for electrical engineer. C4F7N is a promising environmentally friendly insulating gas, while its boil temperature is high, therefore, CO2 was added as a buffer gas. The dielectric strength of 6% C4F7N–94% CO2 mixtures were evaluated at different pressure and temperature 0.1–3.2 MPa, and 300–4000 K. Firstly, the equilibrium compositions of 6% C4F7N–94% CO2 mixtures at different gas pressures and temperatures up to 4000 K were calculated by the method of minimizing the Gibbs free energy. By Boltzmann equation analysis, the electron energy distribution function was obtained by the composition data. Finally, the critical reduced electric field ((E/N)cr) of hot 6% C4F7N–94% CO2 mixtures was determined, at which the rate of ionization is equal to attachment. The results show that in the gas temperature has an influence on 6% C4F7N–94% CO2 mixing. The overall trend was that it first decreased with the increase of temperature, then rised, and finally falld. Further, the effect of barometric pressure on the (E/N)cr was also evident after 2000 K. The calculated results provided basic data for the post-arc breakdown of 6% C4F7N–94% CO2, and have guiding significance for the engineering application of 6% C4F7N–94% CO2.