Insulation Characteristics of c-C₄ F₈-N ₂ and CF₃ I-N₂ Mixtures as Possible Substitutes for SF₆

c-C4F8and CF3I and their mixtures have garnered much attention as possible substitutes for SF6due to their excellent electrical strength and minimal impact on the environment. Taking into account the limitations of saturated vapor pressure on the mixed ratio, the insulation performances of c-C4F8-N2and CF3I-N2mixtures are numerically investigated and compared in this paper. The saturated vapor pressures of c-C4F8-N2and CF3I-N2mixtures are determined by combining the Antoine equation and the basic law of vapor liquid equilibrium. Then, the critical electric-field strengths of these mixtures are calculated by Boltzmann analysis. By analyzing the saturated vapor pressure characteristic and critical electric-field strength, it is found that the CF3I-N2mixture shows greater potential than the c-C4-F8-N2mixture as an insulating medium, from the view of electrical strength. Under a gas temperature of -10°C, the CF3I-N2mixture at CF3I concentrations of 20% and 30% can be used under 0.79 MPa and 0.53 MPa, and the electrical strength of the CF3I-N2mixtures can approach 1.02 and 0.75 times that of pure SF6 at 0.5 MPa, respectively.