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

Perfluoroisobutyronitrile (C₄F₇N) gas mixture is considered one of the most promising alternative gases for SF₆ due to its excellent environmental protection and insulation performance. At present, the Shanghai region of China has adopted 8.5% C₄F₇N-86% CO₂-5.5% O₂ 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 C₄F₇N/CO₂/O₂ gas mixture under discharge faults mainly include CO, CF₄, C₃F₈, C₄F₈, C₃F₆, and CF₃CN. According to the decomposition path of the C₄F₇N gas mixture, this paper selected three primary decomposition products (CO, CF₄, C₃F₈) and one secondary decomposition product (C₄F₈) for the correlation characterization of discharge types, and proposed the ratios of c(CO)/c(CF₄) and c(C₄F₈)/c(C₃F₈) as the characteristic quantities to characterize the different discharge types. Finally, in order to accurately identify the C₄F₇N/CO₂/O₂ 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 (CF₄) and c (C₄F₈)/c (C₃F₈) can be used as the identification criterion for typical discharge fault types.