Solid Product Analysis on the Epoxy Resin Surface After Flashovers in C₄F₇N-Based Gas Mixtures Under Negative DC Voltage

The flashover characteristics at the gas-solid interface are crucial for secure and reliable application of insulating gases and must be carefully evaluated when selecting environmentally friendly insulating gas. This study investigates the flashover characteristics of the epoxy resin surface in various gas mixtures, including C4F7N/N2, C4F7N/CO2, and C4F7N/air, with a focus on the analysis of the generation and impact of solid products using macroscopic and microscopic methods. The results show that when N-2 is used as the buffer gas, the deep decomposition of C4F7N generates carbon-based solid particles on the surface of the epoxy resin, forming conductive channel after multiple flashovers and therefore causing surface insulation failure. In case of C4F7N/CO2 and C4F7N/air, the oxygen element can react with the carbon-containing solid products, inhibiting the formation of solid products. Moreover, under high gas pressure (>= 0.3 MPa in this article) and high C4F7N content, the surface of the epoxy resin sample in the C4F7N/air mixture gas environment can form erosion points containing fluorine-containing solid particles, leading to a lower flashover voltage for C4F7N/air than C4F7N/CO2. These findings provide a better understanding of the flashover characteristics of epoxy resin surfaces in different gas mixtures and contribute to the development of effective insulation medium for gas-insulated equipment.