Calculation of sparking potentials in industrially important insulating electronegative gases

Abstract

A method for predicting the breakdown potentials in electronegative gases used for high-voltage insulation is proposed and described in detail. The method employs the Maxwellian electron-energy distribution function and the fundamental physical and data of the swarm properties of the gas, such as the ionization, attachment and momentum transfer cross sections, and the ionization and detachment energies. In some of the complex electronegative gases the fundamental data have not yet been reported due to either the inherent difficulty in measuring them or because their industrial importance became apparent only recently. Alternative approximate formulas for the relevant basic data of these gases are proposed, from which the breakdown voltage can be calculated without resorting to empirical methods. The approximations used are justified. The method is extended to calculate the breakdown voltage in a binary mixture of SF6 with CC2F2, C–C4F8, CBrCF2, and C4F6 for varying mixture ratios in the range 0–100† of the admixture. Reasonable agreement has been obtained with the measured values.