Decomposition Characteristics and Marker Products of C3F7CN/EP Insulation System with Long-term Surface Discharge

Abstract C3F7CN has the potential to replace SF6 in gas insulated equipment due to its excellent insulation properties and low GWP. In order to apply better use of C3F7CN gas in the future, it is of great significance to study the reaction products of C3F7CN and epoxy resin (EP) with discharge failure conditions for online monitoring and insulation evaluation. In this paper, the experiments of gas-solid interface discharge for 300 hours were carried out. The gas decomposition products were tested by GC-MS, the elements and chemical bonds on the surface of EP before and after discharge were tested by FTIR and XPS. The results showed that the number of gas decomposition products increased with the increase of discharge time. The products mainly included saturated carbon-fluorine gas CF4, C3F8, and C6F14, unsaturated carbon-fluorine gas C3F6, C4F6, and C4F8, nitrile gas CF3CN, ester gas C12F7H17O2, among which C12F7H17O2 was the marker product of C3F7CN/EP. And the relative contents of CF4 and C3F8 increased linearly with the increase of discharge time. The growth rates of C4F10, C4F8, C3F6 and C6F14 increased firstly and then decreased. After discharging on the gas-solid insulating surface, F and N elements in the gas appeared on the EP surface in the form of C-F bond and C≡N bond. Further analysis of the products, a mathematical model for the variation of product formation rate with discharge time was proposed. Finally, it was proposed that C12F7H17O2 was a marker product for diagnosing discharge decomposition of C3F7CN/EP resin insulation system.