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.