Abstract
CF3I-N2 mixtures have garnered much attention as potential SF6-substitutes due to their excellent dielectric strengths, and the dielectric strength of SF6-N2 mixtures has a good synergy effect. This paper attempts to propose an approach of adding a small amount of SF6 to improve the dielectric strength of the CF3I-N2 mixture, by making an all-around consideration of dielectric strength, impact on the environment and the limitations of engineering pressure and the lowest ambient temperature. The influences of adding different amounts of SF6 on the electron energy distribution function, the reduced ionization, attachment and effective ionization coefficients, the critical reduced electric field strength and critical electron temperature of ternary SF6-CF3I-N2 mixtures are investigated by Boltzmann analysis. Then the relations of the critical electric fiend strength, mixed ratio and saturated vapor pressure of the ternary SF6-CF3I-N2 mixture are built and analyzed. The results demonstrate that an effective improvement of its dielectric strength can be obtained by adding a small amount of SF6 into the CF3I-N2 mixture, and that a proper choice of the mixed ratio and the gas pressure of the ternary SF6-CF3I-N2 mixture can provide a comparable dielectric strength to pure SF6.
Highlights
Owing to its excellent comprehensive properties, sulfur hexafluoride (SF6) has been considered the most preferred gaseous dielectric or interrupting medium for high-voltage apparatus
Trifluoromethane (CF3I) has approximately 1.21 time the dielectric strength (DS) of SF6 under a uniform electric field, and its global warming potential (GWP) is only about 0.45.6–9 But the boiling point of completely replace SF6 was aroused.3–5Trifluoromethane (CF3I) is very high, about −22.5 ○C at atmospheric pressure, causing that pure CF3I cannot be used for high-voltage apparatus
The critical reduced electric field strength (E/N)cr of CF3I mixtures, c-C4F8 mixtures with CF4, CO2, N2, O2 and air were calculated and compared firstly,11 and found that the (E/N)cr of CF3I-N2 and c-C4F8-N2 were higher than the other CF3I mixtures and c-C4F8 mixtures obviously; by taking into account the limitations of saturated vapor pressure on the mixed ratio, the insulation performances of c-C4F8-N2 and CF3IN2 mixtures were investigated and compared,12,13 and found that the CF3I-N2 mixture shows greater potential than the c-C4F8-N2 mixture as an insulating medium, from the view of DS
Summary
Owing to its excellent comprehensive properties, sulfur hexafluoride (SF6) has been considered the most preferred gaseous dielectric or interrupting medium for high-voltage apparatus. Trifluoromethane (CF3I) has approximately 1.21 time the dielectric strength (DS) of SF6 under a uniform electric field, and its GWP is only about 0.45.6–9 But the boiling point of CF3I is very high, about −22.5 ○C at atmospheric pressure, causing that pure CF3I cannot be used for high-voltage apparatus.. The critical reduced electric field strength (E/N)cr of CF3I mixtures, c-C4F8 mixtures with CF4, CO2, N2, O2 and air were calculated and compared firstly, and found that the (E/N)cr of CF3I-N2 and c-C4F8-N2 were higher than the other CF3I mixtures and c-C4F8 mixtures obviously; by taking into account the limitations of saturated vapor pressure on the mixed ratio, the insulation performances of c-C4F8-N2 and CF3IN2 mixtures were investigated and compared, and found that the CF3I-N2 mixture shows greater potential than the c-C4F8-N2 mixture as an insulating medium, from the view of DS. Where E is the electric field strength and N is the number density of particles
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