Thermophysical and radiation properties of high-temperature C₄F₈-CO₂ mixtures to replace SF₆ in high-voltage circuit breakers Available to Purchase

C₄F₈-CO₂ mixtures are one of the potential substitutes to SF₆ in high-voltage circuit breakers. However, the arc quenching ability of C₄F₈-CO₂ mixtures is still unknown. In order to provide the necessary basic data for the further investigation of arc quenching performance, the compositions, thermodynamic properties, transport coefficients, and net emission coefficients (NEC) of various C₄F₈-CO₂ mixtures are calculated at temperatures of 300–30 000 K in this work. The thermodynamic properties are presented as the product of mass density and specific heat, i.e., ρC_p. The transport coefficients include electrical conductivity, viscosity, and thermal conductivity. The atomic and molecular radiation are both taken into account in the calculation of NEC. The comparison of the properties between SF₆ and C₄F₈-CO₂ mixtures is also discussed to find their differences. The results of compositions show that C₄F₈-CO₂ mixtures have a distinctive advantage over other alternative gases e.g., CF₃I and C₃F₈, because the dissociative product (i.e., C₄F₆) of C₄F₈ at low temperatures has a very high dielectric strength. This is good for an arc quenching medium to endure the arc recovery phase. Compared with SF₆, C₄F₈-CO₂ mixtures present lower ρC_p at temperatures below 2800 K and larger thermal conductivity above 2800 K. Based on the position of peaks in thermal conductivity, we predict that the cooling of C₄F₈-CO₂ arc will be slowed down at higher temperatures than that of SF₆ arc. It is also found that the mixing of CO₂ shows slight effects on the electrical conductivity and NEC of C₄F₈-CO₂ mixtures.