In recent years, the gas mixture of perfluoroisobutyronitrile (C4F7N) has attracted extensive attention as a potential substitute for the strong greenhouse gas SF6 in gas insulation equipment. On this basis, the possibility of C4F7N/CO2/O2 mixture gas replacing SF6 at medium pressure was studied. The insulation properties such as AC breakdown and partial discharge are systematically studied. It is found that the mixture of 15% C4F7N/81% CO2 /4% O2 has the best dielectric strength and self-recovery performance. Metal protrusion and insulator pollution caused by PD lead to the decomposition of C4F7N, resulting in by-products CF4, CO, C2F6, C3F8, and COF2.

C4F7N/CO2/O2;insulation properties