Discharge fault type identification of C₄F₇N/CO₂/O₂ mixed insulating gas for engineering based on product components

Abstract Perfluoroisobutyronitrile (C 4 F 7 N) gas mixture is considered one of the most promising alternative gases for SF 6 due to its excellent environmental protection and insulation performance. At present, the Shanghai region of China has adopted 8.5% C 4 F 7 N-86% CO 2 -5.5% O 2 proportion gas mixture as the insulation medium for 126 kV gas insulated switchgear and has put it into practical engineering application. This paper conducted decomposition experiments on the proportion gas mixture under spark discharge, suspension discharge, and corona discharge conditions, respectively. The composition analysis of the decomposition products was carried out using a gas chromatography mass spectrometry and a gas chromatography-pulsed discharge helium ionization detector, which got decomposition products of the C 4 F 7 N/CO 2 /O 2 gas mixture under discharge faults mainly include CO, CF 4 , C 3 F 8 , C 4 F 8 , C 3 F 6 , and CF 3 CN. According to the decomposition path of the C 4 F 7 N gas mixture, this paper selected three primary decomposition products (CO, CF 4 , C 3 F 8 ) and one secondary decomposition product (C 4 F 8 ) for the correlation characterization of discharge types, and proposed the ratios of c(CO)/c(CF 4 ) and c(C 4 F 8 )/c(C 3 F 8 ) as the characteristic quantities to characterize the different discharge types. Finally, in order to accurately identify the C 4 F 7 N/CO 2 /O 2 gas mixture discharge type, this paper chose the decision tree algorithm to build a identification tree. The final identification result indicates that the ratio of c (CO)/c (CF 4 ) and c (C 4 F 8 )/c (C 3 F 8 ) can be used as the identification criterion for typical discharge fault types.