Emerging Eco-Friendly Alternatives to SF₆ for High Voltage Insulation: A Review

Sulphur hexafluoride (SF₆) has been extensively utilized as an arc-quenching and insulating gas in high-voltage apparatus including gas-insulated switchgear (GIS), circuit breakers, and transformers because of its high dielectric strength and thermal stability. SF₆ is a very powerful greenhouse gas with a very high global warming potential (GWP ≈ 23,500) and atmospheric lifetime (~3200 years), which makes its future use environmentally unsustainable. In turn, studies have focused more intensely on substitute gases with comparable insulation qualities but much lower environmental footprint. Of the likely candidates, hydrofluorocarbons (HFCs) HFC-227ea (C₃HF₇) and HFC-125 (C₂HF₅) have been increasingly receiving attention. The present review offers a thorough appraisal of the physical, chemical, thermal, and environmental properties of HFC-227ea and HFC-125 in comparison with SF₆ and other future alternatives such as C₄F₇N and CO₂. The major performance parameters such as dielectric strength, liquefaction temperature, boiling point, GWP, electrical conductivity at different temperatures, and partial discharge (PD) characteristics are thoroughly examined. The results indicate that HFC-227ea and HFC-125 have good insulation properties with dielectric strength from 0.5 to 0.7 times that of SF₆, no ozone depletion potential (ODP), and significantly lower GWPs (2900 and 3500, respectively). Both gases exhibit minimal conductivity at operational temperatures, satisfactory thermal stability, and good compatibility with PD measurement methods. Although not direct replacements, these gases may serve as viable options for medium-voltage or mixed-gas systems under carefully controlled conditions. The study concludes that HFC-227ea and HFC-125 hold significant potential for contributing to the development of environmentally sustainable high voltage insulation technologies.