Decomposition characteristics of SF6 under creeping discharge on solid insulator

The decomposition compound analysis of SF₆ in GIS is an effective method to diagnose the partial discharge (PD) caused by the insulation defect. Creeping discharge on solid insulator is a major kind of fault in gas insulated switchgear. It is significant to develop the research on the decomposition characteristics of SF₆ under creeping discharge on solid insulator. SF₆ decomposition was investigated with the GIS-defect-simulating apparatus, where partial discharge energy and charge were monitored by the on-line insulation diagnosis system PD check combining with pulse current method. The gas sample was measured by the Gas Chromatography (GC), and the SF₆ decomposition characteristics under different applied voltage, gas pressure and moisture contents (adsorbent) were analyzed. The results show that the typical decomposition products are CO₂, CF₄, SOF₂ and SO₂F₂. Meantime, increasing the applied voltage will increase the discharge energy and charge, so as to increase the yield of decomposition products. But the discharge energy decreases with the increased pressure of SF₆, thereby decreasing the yield of decomposition products. In addition, the increase of moisture content (200 μL/L - 1500 μL/L) has inhibition effect on the yields of CF₄. The adsorbents 5A, KDHF-03, and F-03 limit the yield of CO₂, SOF₂ and SO₂F₂ apparently, while they show no adsorption to CF₄. Finally we discuss the relationship between the discharge energy and SF₆ decomposition products and feature extraction under creeping discharge on solid insulator. The concentration ratios of (SOF₂+SO₂)/(SO₂F₂) and (SOF₂+SO₂+SO₂F₂)/(CF₄+CO₂) lie in the ranges, 2 - 6, and 0.75 - 2.75 respectively.