Influence regularity of trace H2O on SF6 decomposition characteristics under partial discharge of needle-plate electrode

SF6decomposition characteristics under partial discharge (PD) are not only associated with insulation fault type and its severity but also closely related to the H2O content of in the equipment. This paper studies the decomposition characteristics of mixture gas SF6/H2O with six different gradients of trace H2O under the same PD energy, selects SO2F2, SOF2, CO2, and CF4as the characteristic components, and analyzes the influence regularity of trace H2O on each of the component concentration, effective formation rate and characteristic ratio. Results show that H2O creates favorable conditions for generating SO2F2and SOF2owing to the capacity to capture F atom and inhibit low fluorine sulfides from recombining into SF6. As a result, the concentration and effective formation rate of SO2F2and SOF2is positively related with H2O. Whereas H2O has no evident influence on CO2, it can consume intermediate by-products CF2and CF3which restrain CF4generation. Each characteristic ratio decreases sharply and then becomes stable with increment of H2O. The defined effective characteristic ratio effectively reflects its relationship with H2O, whereas obtained mathematical expression between each effective characteristic ratio and trace H2O lays solid foundation for fault diagnosis of SF6insulated equipment based on SF6decomposition characteristics.