Prediction of the dielectric strength for c-C4F8 mixtures with CF4, CO2, N2, O2 and air by Boltzmann equation analysis

Abstract

The dielectric strength of c-C4F8, and mixtures of c-C4F8 with CF4, CO2, N2, O2 and air, is studied through solution of the Boltzmann equation. The reduced ionization coefficient α/N and reduced attachment coefficient η/N are calculated, allowing the reduced effective ionization coefficient (α–η)/N and the critical reduced electric field strength (E/N)cr (the reduced electric field for which (α–η)/N = 0), to be determined. A high value of (E/N)cr for an electronegative gas, such as those considered here, indicates good insulating properties. It is found that c-C4F8–N2 and c-C4F8–air have very similar (E/N)cr values, higher than those of the other three mixtures, and superior even to that of pure SF6 for c-C4F8 concentrations above 80%. Comparison of the results obtained for c-C4F8 and c-C4F8–N2 with experimental values from the literature supports the validity of the approach taken here and the parameters used.