A Comparison of SF6 Decomposition Characteristics under Corona with Point-to-plane Electrode Defect and Spark with Floating Potential Defect

Corona and spark are two typical discharge types in gas-insulated switchgear (GIS). Studies on the SF6 decomposition characteristics under corona and spark are significant for the safe operation of the GIS. In this paper, the discharge energy/charge and SF6 decomposition products under ac corona with point-to-plane electrode defect and spark with floating potential defect were investigated under different electrode dimensions, applied voltages, SF6 gas pressures, adsorbents and moisture contents. The upper limit of the formation rates, feature extraction, and the amount of wear of the GIS were also discussed. The results show that the influences of gas pressure and moisture content on the discharge energy and SF6 decomposition products under two different defects are distinguishable. In addition, the concentration ratios of (SOF2+SO2)/(SO2F2) under corona and spark lie in the ranges, 0-1, and 1-5, respectively. The formation rates of SF6 decomposition products calculated from experimental results under corona discharge lie in the range, 0.1-5 mu moles/J. However, the formation rates under spark are usually in the range, 0.02-0.04 mu moles/J, which are far lower than that under corona. Theoretically the upper limit of the formation rates under corona and spark are estimated to be in the ranges, 67-540 mu moles/J, and 188-376 nmoles/J respectively. Besides, the concentration ratios and formation rates can be used to distinguish the discharge types and the amount of wear of the GIS can be estimated.