Experimental Investigations on Low-Energy Discharge in ${\rm SF}_{6}$ Under Low-Moisture Conditions

The detection of gas decomposition products is widely used to diagnose the inner condition of SF₆-insulated electrical equipment for its anti-interference ability and high sensitivity. A discharge chamber with Teflon coating inside was designed, with adjustable defect parameters and the volume nearly the same as real ones in gas-insulated switchgear. With the assistance of newly developed dual gas chromatography detection system, this paper investigated the influences of relatively low moisture on the discharge characteristics and gas decomposition under corona and mild spark in SF₆. Considering notable hydrolysis reactions in the main gas volume and on the vessel walls, SO₂F₂, SO₂, and S₂OF₁₀ were selected as typical gas decomposition products. The average discharge capacity and its fluctuation were found to decrease with the increase of moisture content within research scope, which is related to the electronegativity of water molecule. The concentration of typical decomposition products under various moisture conditions was observed in detail. The results show that in mild spark, O atom in S₂OF₁₀ mainly originated from oxygen rather than water vapor in SF₆. To diagnose internal insulation condition by only monitoring, the magnitude of discharge capacity is proved unreliable. A new parameter, the concentration ratio of SO₂/S₂OF₁₀, was proposed to group moisture content and discharge types.