Breakdown Characteristics of C4F7N/CO2/O2 Gas Mixtures with Low Content of C4F7N

Perfluoroisobutyronitrile (C4F7N) gas mixture is a promising SF6 alternative characterized by its low global warming potential (GWP), high insulation strength, and short atmospheric lifetime. Considering the persistent environmental pollution and bioaccumulation risks associated with per- and polyfluoroalkyl substances (PFAS), regulatory measures have been implemented across regions to control PFAS and F-gases. Therefore, investigating the insulating performance of C4F7N gas mixtures with low concentration is essential. In this study, the influence of oxygen content and gas pressure on the insulation performance of C4F7N/CO2/O2 gas mixtures with low content of C4F7N were investigated. The results show that, compared with C4F7N mixture without O2, increasing oxygen content at 0.1 MPa reduced the insulating strength of the gas mixture, with the smallest reduction of 0.33% observed at an O2 concent of 4%. At 0.2 MPa, adding 4%–8% oxygen decreased the insulation strength, while an O2 content of 12% enhances it by 7.36%. At pressures between 0.3 and 0.4 MPa, higher oxygen concentrations were found to enhance the insulation performance., with the maximum increases of 9.35% and 8.20% occurring at 8% O2(0.3 MPa) and 12% O2(0.4 MPa), respectively.