Insulating oil is the "blood" of the transformer, which plays the role of insulation protection and heat dissipation, and can effectively ensure the safe and stable operation of the transformer. At present, as a liquid insulating dielectric material with excellent comprehensive performance, synthetic ester insulating oil has been used more and more widely. Transformers will experience electrical faults and thermal faults during operation, resulting in dissolved gas in the oil. Dissolved Gas-in-oil Analysis (DGA) can diagnose transformer faults by analyzing the type, content and proportion of dissolved gas in the oil, which can effectively guarantee the operational stability of the transformer. In order to ensure the safe and reliable operation of the transformer, combined with domestic and foreign literature and relevant research results of the research group, the characteristics of dissolved gas in synthetic ester insulating oil under the electrical fault and thermal fault simulation test are summarized, and the current fault diagonsis methods applied to synthetic ester insulating oil are analyzed and summarized, which could provide theoretical reference value and engineering guiding significance for improved disgnosed methods applied to synthetic ester insulating oil and the operation of synthetic ester insulating oil transformers.

synthetic ester insulating oil, electrical fault, thermal fault, dissolved gas-in-oil analysis, fault diagnosis