Assessment on the Application Feasibility of C4F7N/CO2 for Eco-Friendly Gas Insulated Transformer

Sulfur hexafluoride (SF6) gas insulated transformers (GIT) have been widely used in power transmission and distribution systems due to the advantages of being incombustible, explosion-proof, and maintenance-free. However, SF6 is listed as the strongest greenhouse gas with a global warming potential (GWP) of 23 500. Recently, perfluoroisobutyronitrile (C4F7N) gas mixture has attracted wide attention as eco-friendly gas insulating medium. Herein, we evaluated the application feasibility of C4F7N/CO2 gas mixture for GIT considering the insulation, thermal conductivity, and materials compatibility. The ac breakdown, partial discharge (PD), heat dissipation, and gas compatibility with typical materials in GIT were systematically investigated. We found that a 15% C4F7N/85% CO2 gas mixture demonstrated superior dielectric strength and self-recovery performance. The metal protrusion and PET surface PD caused the decomposition of C4F7N to mainly produce CF4, C2F6, and C3F8. The thermal conductivity of C4F7N/CO2 is lower than that of SF6, resulting in an average temperature rise of 63.7–86.9 K under 100% load. Besides, the gas is compatible with most typical materials used in GIT. This work can provide guidance for the development of C4F7N/CO2 gas mixture-based GIT.