Chemical kinetic model of SF6/O2/H2O decomposition products under 50 Hz ac corona discharges

Abstract

Partial discharge (corona discharge) is generated in the gas-insulated switchgear (GIS) before faults occur due to insulation defects. The GIS is usually filled with compressed SF6 for electric insulation. When partial discharge occurs, a portion of SF6 will decompose and oxidize in the presence of oxygen and water vapor to form various stable gaseous by-products, including SO2F2, SOF2, SOF4, SO2, S2F10, S2OF10, S2O2F10, SF4, HF and so on. In order to analyze the discharge mechanism, two zone chemical kinetic models are coupled to interpret the chemical process of point-to-plane 50 Hz ac corona discharge. In the plasma region, the electron impact dissociation reactions, electron-impact ionization reactions, electron-impact attachment reactions, radical-radical reactions, and ion-radical reactions are considered. SF6 decomposes into various low fluorine sulfides, which continue to react with the radicals O or OH, produced from the dissociation of H2O and O2. The electron energy is the function of electric field at 300K. In addition, the stable fragments from SF6 decomposition in the plasma region, like SF2 and SF4, diffuse into the main gas volume and react with water or oxygen to produce the feature by-products SO2F2, SOF2 and SOF4. With comparing the variation rules of these decomposition byproducts with time from simulation and the experimental results, the model is verified to be reliable and reasonable. And also, the physicochemical process of SF6 decomposition mechanism under corona discharge can be captured.