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

SF₆ decomposition 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 CF₄ as 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 SO₂F₂ and SOF₂ owing 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 SO₂F₂ and SOF₂ is positively related with H₂O. Whereas H₂O has no evident influence on CO₂, it can consume intermediate by-products CF₂ and CF₃ which restrain CF₄ generation. 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 SF₆ insulated equipment based on SF₆ decomposition characteristics.