Property Calculations and Application Study of SF6/CF4 Gas Mixture

Addressing the liquefaction issue of SF6 high-voltage gas circuit breakers in extremely low-temperature environments, this paper investigates SF6/CF4 gas mixture as an alternative solution. Based on the Peng-Robinson (PR) equation, a thermodynamic parameter calculation model was established, and a dedicated program was developed to design multiple gas mixture schemes with reliability assessment according to different circuit breaker rated pressures and molar ratios. The low-temperature stability of the gas mixture was verified through temperature range tests from −40 °C to 25 °C, and T100a short-circuit interruption tests were completed on a 252 kV circuit breaker prototype. Research results demonstrate that the calculation method based on the PR equation accurately predicts the phase change characteristics of the gas mixture, and the designed gas mixture schemes simultaneously satisfy both low-temperature adaptability and interruption performance requirements in engineering applications.