Approach to Decaying Process of Arc Conductance after Current Zero on the basis of Thermodynamic and Transport Properties of High Temperature Gases

The decaying aspect of the conductance of an arc after a current zero for SF6, N2, O2, air, c-C4F8, CO2, H2, He and Ar was studied on the basis of thermodynamic and transport properties of high temperature gases: a mass density ρ, an enthalpy h, an enthalpy h300 at 300 K, a specific heat CP, and a thermal conductivity κ and an electrical conductivity σ. Theoretical calculation revealed two principal phenomena as follows:(1) for the case in presence of gas flow, the conductances for SF6, c-C4 F8, O2, CO2, H2, He and Ar decay rapidly just around a current zero and (2) the conductances for H2 and He in no axial gas-flow decrease in an almost similar aspect to that for the case in presence of the gas flow. To explain the phenomenon (2), a thermal diffusivity α expressed as α = κ /(ρ CP) was calculated. The H2 and He proved to have very much higher α than the others. This higher α of the H2 and He was found to result in the more rapid reduction in the conductance through a thermal conduction mechanism. To interpret the phenomenon (1), β expressed as β =(h-h300)/(ρCP) was calculated. The SF6, c-C4 F8, O2, CO2 and Ar were found to have higher β than N2 and air. This higher β of SF6, c-C4F8, O2, CO2 and Ar proved to cause the more rapid diminution in the conductance through convection mechanism.