Calculation of the insulation properties of different CF₃I-N₂ and CF₃I-CO₂ mixtures at 300 K

We investigated the insulation properties of different CF₃I-N₂ and CF₃I-CO₂ mixtures for further analyzing the possibility of applying these mixtures as substitutes for SF₆ in high voltage apparatuses. Firstly, we calculated the reduced ionization coefficient α/N, the reduced attachment coefficient η/N and the reduced effective ionization coefficient (α-η)/N of the mixtures, where α, η and N are ionization coefficient, attachment coefficient and particle number density respectively. The results were compared with experimental values from references, which verified the method and parameters adopted in the calculation. Then in the same way, we obtained the α/N, η/N and (α-η)/N of different CF₃I-N₂ and CF₃I-CO₂ mixtures. Finally, setting (α-η)/N=0, we calculated the reduced critical electric field intensity (E/N)cr of different the mixtures. The results indicate that the (E/N)cr of pure CF₃I is 439×10^-17 V·cm², which is much higher than that of SF₆, 366×10^-17 V·cm²; when CF₃I-N₂ mixture has x(CF₃I), mole fraction of CF₃I, higher than 65%, its (E/N)cr is higher than that of SF₆-N₂; similarly, CF₃I-N₂ mixture with x(CF₃I)> 70% and CF₃I-CO₂ mixture with x(CF₃I)> 40% have higher (E/N)cr than pure SF₆ and SF₆-CO₂ mixture, respectively.