Insulation Characteristics of c-C 4 F 8-N 2 and CF 3 I-N 2 Mixtures as Possible Substitutes for SF 6

c-C 4 F 8 and CF 3 I and their mixtures have garnered much attention as possible substitutes for SF 6 due 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-C 4 F 8 -N 2 and CF 3 I-N 2 mixtures are numerically investigated and compared in this paper. The saturated vapor pressures of c-C 4 F 8 -N 2 and CF 3 I-N 2 mixtures 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 CF 3 I-N 2 mixture shows greater potential than the c-C 4 -F 8 -N 2 mixture as an insulating medium, from the view of electrical strength. Under a gas temperature of -10°C, the CF 3 I-N 2 mixture at CF 3 I concentrations of 20% and 30% can be used under 0.79 MPa and 0.53 MPa, and the electrical strength of the CF 3 I-N 2 mixtures can approach 1.02 and 0.75 times that of pure SF6 at 0.5 MPa, respectively.