Particle Condensation in Two-Temperature (2T) Arc Plasmas of Various SF6 Replacements

Abstract

Fluorinated gases, e.g., CF₃I, C₃F₈, C₄F₈, C₄F₇N, and C₅F₁₀O, show potential to replace SF₆ in power industry due to their high dielectric strength and low global warming potential . However, particle condensation from arc plasmas of these compounds may reduce dielectric performance. We perform a systematic investigation of particle condensation in two-temperature (2T) arc plasmas of various SF₆ replacements mixed with CO₂, N₂, and O₂, by the Gibbs free energy minimization and entropy maximization methods. The influences of buffer gases, non-equilibrium degree, and gas pressure on particle condensation are discussed in various cases. The results indicate that O₂ is necessary to prevent graphite formation in carbon–fluorine gaseous arcs, and specific mixing ratios of CO₂ and N₂ are required to avoid graphite and iodine crystals in CF₃I arc plasmas. The relationship between condensation temperature and non-equilibrium degree is complex, with peaks and valleys observed for graphite and iodine crystal condensation temperatures. Moreover, different calculation methods (Gibbs free energy minimization versus entropy maximization) show varying sensitivity of condensation temperatures to pressure changes. All the above findings highlight the importance of considering non-equilibrium effects and multiple condensed species in evaluating arc plasma compositions of SF₆ replacements.