SF6 decomposition with needle-to-plate defect was investigated with the self-designed GIS-defect-simulating apparatus

where partial discharge current was monitored by the on-line insulation diagnosis system PD check combining with pulse current method.The gas samples were measured by the infrared detection method

and the SF6 decomposition features under different gas pressure and applied voltage were analyzed.The results showed that: The typical decomposition products were SOF4

SO2F2 and CO2

their volume fractions tended to increase with voltage duration;Saturation time of SOF4 was shorter

while SO2F2 showed a near-linear increase within whole voltage duration

and CO2 got a near-linear increase after certain period of voltage application;Similarities were found in the decomposition with different gas pressure

however

under same voltage duration

the concentrations of SOF4 and SO2F2 were higher at lower pressure that that at higher pressure

but the variation was opposite for CO2

which might relate to insulation material involved in reaction;SO2F2 was more sensitive to SF6 decomposition than the other two products.PRPD spectra for different experimental conditions were obviously different in graphic feature.