Influence of trace water on decomposition mechanism of c-C4F8 as environmental friendly insulating gas at high temperature

Abstract

Fluorocarbon gas has excellent environmental characteristics and insulation properties and has the potential of replacing SF6 for medium-voltage electrical equipment. While c-C4F8 will decompose under discharge or overheating faults conditions. At present, studies on the decomposition characteristics of c-C4F8 have made some achievements, but little attention has been paid to the influence of temperature and trace water. In this paper, the interaction between OH· and H· produced by H2O and c-C4F8 is analyzed based on the density functional theory (DFT) and plasma discharge decomposition experiment. The decomposition path, reaction enthalpy and activation energy, and the impact of temperature on the reaction path is discussed. It is found that the decomposition of c-C4F8 requires an endothermic heat of about 420 kJ/mol, and the decomposition of c-C4F8 to C2F4 is more likely to occur at high temperature. The H· and OH· generated by trace water will promote the decomposition of c-C4F8, which produces HF and low fluoride particles. The main decomposition products of c-C4F8 in the trace water environment are C2F4, CF4, CF3OH, CF3H, C2F6, CF2O and HF. Among them, CF2O and HF are toxic and corrosive substances, which pose a threat to the safety of operation and maintenance personnel. Relevant research results not only reveal the decomposition mechanism of c-C4F8, but also provide guidance for the application of c-C4F8 gas mixture.