Trend of Sulfur Hexafluoride (SF6) Gas Mixtures and Other Alternatives as Insulation Gas: an Overview

Research works are actively ongoing to seek a solution for reducing the usage of sulfur hexafluoride (SF6) as a gas insulator in high-voltage equipment since it was listed as one of the greenhouse gases under the Kyoto Protocol. However, manufacturers still in favor of using SF6 due to its excellent insulation and arc-quenching properties. One way to reduce SF6 usage is to mix it with other gases or replace it with alternative gas mixtures. The research status of SF6 gas mixtures and other potential substitutes is summarized in this paper. Electrical insulation properties, physical and chemical mechanisms, and environmental considerations, along with the scope and limitations of such mixtures were analyzed. The development prospects of SF6 gas mixtures were forecasted based on their best mixture ratio. Hybrid insulation gases consisting of three compounds (two electronegative gases with one buffer gas) have shown to be an ideal compromise in terms of cost, distinguished low environmental impact, and high dielectric strength. Trifluoroiodomethane (CF3I) offers great advantages among other dielectric gases, since it exerts minimal greenhouse effects, and has a considerable liquefaction temperature and higher dielectric strength. Therefore, the application of CF3I for reducing the usage of SF6 in gas mixtures was highlighted. The fundamental knowledge on the breakdown strength of the gas mixtures and their behavior under different electric fields need to be analyzed before any recommendations can be made.