Research Progress of the Dissolved Gas Analysis in Synthetic Ester Insulating Oil under Electrical Faults

Transformers will be subjected to electrical, thermal, and mechanical stresses during operation, causing decomposition of the insulation materials and consequently generating gas in the oil. Early transformer faults including electrical faults can be detected in time through DGA (Dissolved Gas-in-oil Analysis) which can reflect the state information of insulating oil transformers. Recently, the application of synthetic insulating oil in large power transformers could increase due to excellent fire resistance, environmental protection, strong oxidation stability, etc. Due to the differences in molecular structure between synthetic ester insulating oils and mineral insulating oils as well as natural ester insulating oils, there are differences in the characteristics of dissolved gas in the oil produced under electrical faults, resulting in different limits of dissolved gas in the oil under normal and fault conditions. In order to ensure the safe and reliable operation of synthetic ester insulating transformers, this paper reviews the analysis on faulty gas production of synthetic ester insulating oil and summaries the commonly used diagnostic methods for synthetic insulating oil under electrical faults.