Correlation analysis between SF6 decomposed components and negative DC partial discharge strength initiated by needle‐plate defect

Abstract

To obtain and understand the decomposition characteristics and decomposition process of SF6 gas under different negative DC voltages, a physical model of the needle‐plate defect is used to conduct decomposition experiments of SF6 gas. Experimental results show that, under different negative DC voltages, the partial discharge (PD) caused by the needle‐plate defect decomposes SF6 gas and generates five stable decomposed components, namely CF4, CO2, SO2F2, SOF2, and SO2. The concentration and effective formation rates (RRMS) of these five components can be associated with the mean discharge magnitude per second (Qsec), and the effective concentration ratios (CRRMS) of CF4/CO2 and SO2F2/(SOF2 + SO2) correlate well with Qsec. The concentration, RRMS, and CRRMS of SF6 decomposed components can be used as characteristic quantities of the PD strength under a negative DC voltage. Based on these characteristic quantities, we establish two evaluation tables to assess the PD magnitude under negative DC voltage. That is, the range of PD magnitude in the gas chamber can be deduced by the RRMS and CRRMS of SF6 decomposed components. These tables provide a practical method for assessing the insulation status of the gas‐insulated equipment under a negative DC voltage. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.