Analysis of the insulation characteristics of CF₃I mixtures with CF₄, CO₂, N₂, O₂and air

Abstract

This paper investigates the insulation characteristics of CF3I mixtures with CF4, CO2, N2, O2 and air by Boltzmann equation analysis (with mole percentages), neglecting the influence of electron-vibrational superelastic collisions. The critical reduced electric field strength (E/N)cr of a electronegative gas can be considered as the value for which the reduced effective ionization coefficient (α − η)/N = 0. First, the reduced ionization coefficient α/N, reduced attachment coefficient η/N and (α–η)/N of CF3I mixtures with CF4, CO2, N2, O2 and air are calculated. Then the (E/N)cr of those mixtures are determined. The results indicate that CF3I–N2 and CF3I–air have a superior insulation performance than the other three mixtures. Further, the (E/N)cr of CF3I–N2 and CF3I–air are obviously higher than that of SF6–N2 at the CF3I concentration higher than 65%, and even higher than that of pure SF6 at the CF3I concentration higher than 70%. In addition, the calculated results of CF3I and CF3I–N2 are compared with the experiment values from other literature for confirming the validity of present calculation method and parameters.