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

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.