Dielectric Properties of Fluoronitriles/CO2 and SF6/N2 Mixtures as a Possible SF6-Substitute Gas

Perfluoronitriles (PFN) and their mixtures have garnered much attention as a great potential SF6-substitute gas, owing to their excellent dielectric strengths and minimal impacts on the environment. The dielectric properties of C4-PFN/CO2 and SF6/N-2 mixtures are investigated and compared by experiments and calculations, with taking into account the limitations of saturated vapor pressure on the mixed ratio at certain ambient temperatures. The saturated vapor pressures of these two mixtures are determined by combining the Antoine Equation and the basic law of vapor liquid equilibrium. Then, the 50% breakdown voltages V-50% of the C4-PFN/CO2 and SF6/N-2 mixtures are determined by tests with up-and-down method, and the values of E/p are deduced. Finally, the dielectric properties of these two mixtures are analyzed by combining the saturated vapor pressure characteristics and the breakdown electric field strengths. The results show that a proper choice of the mixed ratio and gas pressure of the C4-PFN/CO2 mixture can provide a stronger DS than the SF6/N-2 mixture and pure SF6. This indicates a great potential of the C4-PFN/CO2 mixture as a SF6-substitute gas for high voltage apparatus.