AC Breakdown Strength and Its By-Products of Eco-Friendly Perfluoroisobutyronitrile/O2/N2 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.