Study on Electron Swarm Parameters and Insulation Properties of C₄F₇N-CO₂-O₂ Mixture

In recent years, new environmentally friendly gases represented by perfluoronitrile (C4F7N) have attracted great attention with their extremely low GWP and high insulation strength, and have been applied in engineering. Manufacturers started to use mixtures of C4F7N with CO₂ and O₂, or with air, as insulating and switching media in medium and high-voltage gas-insulated substations. However, the lack of relevant electron swarm parameters, makes it difficult to further study the microscopic discharge mechanism. This study measured the electron drift velocity, density-normalized effective ionization coefficient, and density-normalized longitudinal diffusion coefficient of C₄F₇N-CO₂-O₂ mixtures at different mixing ratios by pulsed Townsend technique. We discuss the effect of C₄F₇N-CO₂-O₂ rationing on electron swarm parameters and density-reduced critical electric field strength (E/N)_cr and evaluate the synergistic effects of the gas mixtures. The C4F7N content of the mixture varies between 5% 20%. At a constant ratio of C4F7N, combined with the actual project needs, the ratio of CO₂:O₂ is set as 1:0, 20:1, 15:1, 10:1, and 5:1. Our measurements provide fundamental data for modeling the discharge of C₄F₇N-CO₂-O₂ mixtures.