Influence of microwater on the decomposition of SF6/N2 gas mixture insulating media in overheating faults

Currently, China is using the SF6/N2 gas mixture to gradually replace SF6 in GIS and other equipment. However, gas-insulated equipment will inevitably have local overheating faults. The SF6/N2 gas mixture will decompose to some extent at high temperatures. Impurities such as moisture in the equipment can affect this decomposition process. At present, there are fewer studies on the moisture content of the superheated decomposition of the SF6/N2 gas mixture. Therefore, this paper carries out the SF6/N2 mixed gas superheat decomposition experiment on the constructed superheat decomposition simulation experiment platform. By changing the content of trace water, the influence of trace water on the decomposition of the SF6/N2 mixed gas insulation medium with superheat failure was initially investigated. It is found that trace H2O will promote the generation of SF6 characteristic decomposition products, especially for the generation of SO2F2. The generation of SO2 in the product is the largest, and its generation process needs the full participation of H2O. In addition, the addition of trace water will also improve the yield of nitrogen-containing products NO and NO2, and under the experimental conditions of this paper, by adding the microwater, the yield reaches 100–300 µl/l. The reaction mechanism of H2O decomposition and combining with N atoms to generate NO and NO2 at high temperatures was analyzed in this paper. The thermodynamic properties of the main reaction paths and the equilibrium constants were calculated based on the density functional theory, which provided theoretical references for the further study of the mechanism of SF6/N2 superheated decomposition.