Investigation on Susceptibility of Transformer Oil in Service to Accelerated Thermal Stress on Generation of Key Gases and Fault Diagnosis

The transformer is a vital constituent of the electricity network. Trouble-free operation of the transformer is very essential to maintaining a reliable and uninterrupted power supply. Several electrical and physicochemical diagnostic methods are in practice for condition monitoring of power transformers to keep them in service. Dissolved Gas Analysis (DGA) is considered as the paramount tool for assessing emerging faults in oil-filled transformers. Numerous established methods like Key Gas, Doernenburg Ratio, Rogers Ratio, Nomograph, IEC Ratio, Duval Triangle, Pentagon etc. are available for analyzing and interpreting the gas content of oil to predict the type of plausible fault. Accurate and interference-free measurement of dissolved hydrocarbon gases is essential for application of these interpretation methods. The chemical behavior of oil differs based on the source, refining process, additives, contamination, service condition, service period, and so on. As a result, it is critical to look at the impact of these changes in oil on the formation of dissolved gases. Samples of almost the same age with varying chemical status are selected for the study. The trends in the formation of dissolved gases in transformers under service for a studied period are presented. The accelerated ageing study at 120°C of oil samples in the laboratory with copper and kraft paper is also conducted for comparison with field data. Despite a substantial variation in gas content among field and laboratory aged samples, no significant effect on the interpretation of the incipient fault is observed.