SF6 gas decomposition analysis under point-to-plane 50 Hz AC corona discharge

As one of the most commonly used insulating mediums, in electrical discharge, sulfur hexafluoride (SF6) will decompose in the presence of water vapor and oxygen, producing various gaseous by-products. It is shown that the concentrations and production rates of SF6 gaseous decomposition by-products heavily depend on electrical field to gas density ratio (E/N) under corona discharge. Regarding the difficulty in measuring E and N, applied voltage and the SF6 pressure, are proposed in this paper to describe E and N, respectively. Several experiments of 50-Hz AC discharges were carried out under different applied voltages and different SF6pressures using point-to-plane electrodes. The concentrations of SF6gaseous by-products were measured by a gas chromatograph-mass spectrometer system (GS/MS). Experimental data show that the concentrations of SF6gaseous by-products increase while the ratio (SOF2+SO2)/SO2F2decreases, with increasing applied voltage. The concentrations decrease with increasing pressure of SF6. The formation mechanisms of SF6 gaseous by-products with the variations of applied voltage and the SF6pressure are discussed, such as SO2F2, SOF2+SO2, CF4, and CO2and so on. An experimental expression is derived which connects the SF6pressure with the concentration of the decomposition by-products.