Calculation and characteristic analysis of thermodynamic properties and dielectric breakdown properties of CO₂ and its mixture with O₂

CO₂ is a potential alternative to SF₆ as insulation gas. Obtaining the critical breakdown field strengths of CO₂ and CO₂/O₂ gas mixture is essential for studying the insulation and arc performance of gases. Hence, we derived the chemical compositions of CO₂ and CO₂/O₂ gas mixture plasma in equilibrium state, as well as the thermodynamic properties of 90%CO₂-10%O₂ (in volume fraction) gas mixture, under various pressures. By solving the two-term Boltzmann equation, we obtained the converted critical breakdown field strengths of CO₂/O₂ gas mixtures of various proportions under the conditions of 300~3500 K and 0.4 MPa. The results show that when the gas temperature is below 2 000 K, (E/N)_cr of 50%CO₂-50%O₂ is far higher than that of 90%CO₂-10%O₂. However, (E/N)_cr of 50%CO₂- 50%O₂ gas is hardly affected by the gas temperature, and when the gas temperature exceeds 2 000 K, (E/N)_cr of 90%CO₂-10%O₂ increases significantly with the temperature.