Distinct Representations of Hot Gas Dielectric Strength and Their Impact

Abstract

The common practice of assuming constant pressure in the dielectric strength estimation of hot gases is compared with that assuming constant number density. The dielectric strengths of dissociated gaseous He- H2-N2 mixture and $\mathbf{SF}_{\mathbf{6}}$ are estimated at various temperatures. The compositions of the dissociated gas species at temperatures as high as 5,000 K are obtained by minimizing the Gibbs free energy assuming local chemical equilibrium. The calculated mole fractions of the dissociated gas species and electron-scattering cross section data are used for calculating the density-reduced critical electric field that represents the dielectric strength of the gas mixtures. Through this study, it is shown that the dielectric strength of hot gases depends significantly on the two assumptions, and the assumption of constant pressure results in the underestimation of dielectric strength at high temperatures compared to the assumption of constant number density.