AC Breakdown Strength and Its By-Products of Eco-Friendly Perfluoroisobutyronitrile/O 2 /N 2 Gas Mixture at High Pressure for HV Equipment

Eco-friendly C4F7N (Perfluoroisobutyronitrile)/N2 gas mixture is now recognized as a potential alternative gas insulating medium to the most greenhouse gas SF6 used in the power industry. In order to reduce the carbon generated during the discharge process, O2 can be used as an additional gas of C4F7N-N2 gas mixture to improve its electrical endurance. This paper investigates the AC breakdown strength and the change rule of by-products content of C4F7N/O2/N2 gas mixture used in high-voltage gas insulating equipment (HV-GIE) for the first time. We find that adding 4-10% oxygen into the C4F7N-N2 gas mixture at 0.6 MPa can significantly enhance the insulating self-recovery characteristic and reduce the breakdown voltage dispersity of the gas mixture. The insulation strength of C4F7N/O2/N2 gas mixture with 6% oxygen can reach 60% of SF6 at 0.6 MPa. The addition of 2-8% oxygen can inhibit the generation of characteristic by-products at high pressure. Considering the insulation performance and the impact of by-products on personnel safety, adding 6% oxygen into the C4F7N-N2 gas mixture for HV equipment application is appropriate.