Abstract
Due to the greenhouse effect of SF6, the research on alternative insulation gases is currently a hot topic in high voltage engineering. The refrigerant gas such as HFC-227ea with low GWP has stable chemical properties, and high dielectric strength because of a large number of fluorine atoms. However, it is necessary to add buffer gases for relatively high liquefaction temperature(−16.7°C) of HFC-227ea. In this article, the dielectric strengths of HFC-227ea and its gas mixtures under different gas pressure, mixture composition and ratio are investigated under DC and AC electric fields. At atmospheric pressure, the results show that the breakdown voltage of HFC-227ea mixed with N2 or CO2 could only account for 60% of SF6 gas. When HFC-227ea is mixed with HFC-125, which has similar chemical composition and structure, their dielectric strength can reach at least 80% of SF6 gas and the gas mixture shows good synergistic effect. At higher gas pressure, the HFC-227ea/HFC-125 gas mixture at pressure of 0.8 MPa and low HFC-227ea content has the best insulating performance and it is suitable for a lower operating temperature, demonstrating the potential of substituting SF6 for gas insulated electrical equipment.
Highlights
SF6, with its excellent dielectric properties, is widely applied as an insulation gas in long-distance and large-capacity electric power transmission equipment, especially gas insulated switchgear (GIS) and gas insulated transmission line (GIL) [1]
The results show that under certain conditions, the gas mixtures of C5F10O, O2 and CO2 can achieve dielectric strength similar to that of SF6, while the current interruption performance is worse than that of SF6 [12], [26] GIS using C5F10O/air as insulation gas has been put into trial operation in a substation in Zurich, Switzerland [27]
The dielectric strength of pure HFC-227ea is 150% of SF6 and its mixture with CO2 and N2 could reach about 83% and 80% of SF6, respectively
Summary
SF6, with its excellent dielectric properties, is widely applied as an insulation gas in long-distance and large-capacity electric power transmission equipment, especially gas insulated switchgear (GIS) and gas insulated transmission line (GIL) [1]. The effects of gas composition, mixing ratio, pressure and applied voltages on the insulation performance of the novel alternative gases are systematically studied. When HFC-227ea is mixed with CO2, N2 and other conventional buffer gases, the dielectric strengths of HFC-227ea gas mixtures are only 60∼70% of SF6.
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