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.