Comparison of dielectric breakdown properties for different carbon-fluoride insulating gases as SF6 alternatives

As a widely used insulating medium, sulfur hexafluoride (SF6) is a greenhouse gas with very high global warming potential (GWP). Some carbon-fluoride gases have potential to replace SF6 in insulating applications. In order to reveal their different dielectric performance, this paper is devoted to a comparative study of dielectric breakdown properties for SF6 and four carbon-fluoride insulating gases i.e. CF3I, C2F6, C3F8, and c-C4F8 mixed with CO2, N2, and CF4 based on the numerical solution of Boltzmann equation. The electron energy distribution function (EEDF), reduced ionization coefficients α/N, reduced electron attachment coefficients η/N, and reduced critical electric field strength (E/N)cr are compared for various gas mixtures. Generally c-C4F8 presents the largest dielectric strength among the four carbon-fluoride insulating gases whichever buffer gas is mixed, while C2F6 presents the lowest dielectric strength. In terms of (E/N)cr and GWP, CF3I is a good eco-friendly insulating medium. However, with the addition of buffer gases, the (E/N)cr of CF3I mixtures declines more quickly than other mixtures. It is also found that the mixing of CF4 makes insulating mixtures depend more linearly on the proportions of buffer gas than CO2 and N2.