Improved DGA Pentagon Model for Identifying Discharge and Thermal Faults of Three Element Mixed Oil-paper Insulation Used in Power Transformer

Three-element mixed insulation oil, as a new type of environmental protection insulation oil, is made up of mineral oil, soybean oil and palm oil fatty acid ester (PFAE). Nowadays, 10 kV and 35 kV transformers with mixed insulation oil have been connected to the network. However, the criterion for fault determination of mixed insulation oil transformer has not been established. In current work, the gas generation characteristics of three-element mixed oil-paper insulation system in overheating and partial discharge faults were studied. The results show that H2, CH4 and C${}_{2}\mathrm{H}_{6}$ are the main characteristic gases of overheating failure of mixed oil-paper insulation system. H2, C${}_{2}\mathrm{H}_{2}$ and C${}_{2}\mathrm{H}_{6}$ are mainly produced during partial discharge of mixed insulation oil. H2, C${}_{2}\mathrm{H}_{4}$ and C${}_{2}\mathrm{H}_{2}$ are the main characteristic gases of power frequency breakdown fault of mixed insulation oil, while $\mathrm{H}_{2}, \mathrm{C}_{2}\mathrm{H}_{6}$ and C2H2 are the main characteristic gases of power frequency breakdown fault of mixed insulation oil immersed paper. $\mathrm{H}_{2}, \mathrm{C}_{2}\mathrm{H}_{4}$ and C2H2 are the main characteristic gases in the surface flashover discharge fault of the mixed oil-paper insulation system. $\mathrm{H}_{2}, \mathrm{C}_{2}\mathrm{H}_{4}$ and C2H2 are the main characteristic gases of lightning shock breakdown of mixed oil and oil-impregnated paper. Based on dissolved gas analysis (DGA), Duval pentagon fault diagnostic methods of three-element mixed insulation oil was proposed. This paper is beneficial to the further application and popularization of three-element mixed insulation oil.