Impact of Through Fault Current on Insulating Oil Characteristics and Dissolved Gas Content in Power Transformers

Faults in the 20 kV distribution network on the low-voltage side of power transformers still frequently occur, allowing Through Fault Currents (TFC) to flow through the transformer windings. This results in the transformer being subjected to significant electrical stress in the form of high current surges. The resulting temperature rise within the windings and transformer core can alter the condition of the insulating oil and potentially trigger the generation of dissolved gases (DGA). By comparing the percentage of TFC with the changes observed in the transformer oil, the impact of the TFC on the condition of the insulating oil can be determined. This serves as a predictive approach to transformer condition monitoring, enabling better analysis, evaluation, and maintenance strategies. The study will investigate and use data from power transformers that have a history of disturbances in the 20 kV distribution network. The cumulative and average percentages of TFC were calculated during the periods between the oil testing intervals. These percentages were analyzed using statistical methods to evaluate changes in the condition of the insulating oil before and after exposure to TFC events. Support Vector Regression (SVR) was used and compared with Multivariate Linear Regression (MLR). The SVR method demonstrated a better ability to capture the relationship between the percentages of TFC and the changes in oil condition, achieving smaller error values. The results indicate that TFC leads to an increase in the concentration of nearly all DGA components and changes in oil characteristics, accompanied by an overall decline in oil quality.