Two-temperature thermodynamic and transport properties of C₄F₇N–CO₂–O₂ mixture as an arc-extinguishing gas

Abstract Given the significant greenhouse effect of SF 6 , the C 4 F 7 N–CO 2 –O 2 mixture has been identified as one of the most promising eco-friendly arc-extinguishing gases. Switching arcs typically exhibit pronounced non-local thermodynamic equilibrium (NLTE) phenomena in the peripheral regions and at the current zero-crossing point, thereby influencing the thermophysical properties of the plasma. To investigate the impact of NLTE conditions, the thermodynamic properties and transport coefficients of two-temperature (2-T) C 4 F 7 N–CO 2 –O 2 plasma were calculated under the local chemical equilibrium assumption. The results indicate that NLTE conditions significantly affect the properties of the mixture by altering its composition and particle energy, often having a more substantial impact than pressure variations. The generation of CO plays a critical role in shaping the thermodynamic and transport parameters of the plasma due to its molecular stability, particularly under non-equilibrium states. To maximise the arc-extinguishing performance of the gas, recommended oxygen mixing ratios are proposed. The results provide fundamental data for 2-T magnetohydrodynamic modelling of C 4 F 7 N gas mixtures in arc simulations.