Novel Approaches of DGA to Transformers Filled with Natural Ester Based Insulating Oils

Vegetable insulating oils have different chemical compositions as compared to mineral oils, hence, dissolved gas characteristics under thermal and electrical faults have differences, thus fault diagnostic methods based on Dissolved gas analysis (DGA) used for mineral oil-filled transformers cannot be used to investigate vegetable oil-filled transformers. This paper presents experimental results of dissolved gases in the camellia insulating oil under typical thermal and electrical faults in transformers. The thermal fault simulation experiments include low temperature, medium temperature and high temperature, and the electrical fault simulation experiments include partial, breakdown and arc discharges. Experimental results show that except CO and CO2, H2 and C2H6 were main characteristic gases under thermal faults, the percentage contents of H2 decreases while CH4, C2H4 and C2H6 increases with the temperature increase. In addition, H2 and CH4 were main characteristic gases under partial discharge faults, C2H2 was the main characteristic gas under breakdown faults, and C2H2 and C2H4 were main characteristic gases under arc discharge faults. Characteristic parameters were extracted based on DGA, and fault diagnostic methods of camellia insulating oil-filled transformer were proposed, including graphic diagnostic method and none code diagnostic method. Results showed that faults could be effectively analyzed by triangle and pentagon diagnostic methods as well as none code diagnostic method. H2, C2H4, C2H2&H2, CH4, C2H6 Triangle method and none code diagnostic method are better fault diagnostic methods for camellia insulating oil.