Dynamic Evolution of Copper Impurities in Transformer Oil under Thermal Induction and Their Effects on Performance

In recent years, the copper impurity-induced insulation failure in transformer oil has attracted wide attention from foreign and domestic researchers and engineers. In this paper, a 10-week accelerated aging study of oil-paper insulation at $120^{\circ}\mathrm{C}$ was conducted to regularly test and analyze the key performance parameters (acid value, micro water, dielectric loss factor, breakdown voltage) of transformer oil and their change patterns under different aging times. The influence of copper ions on the transformer oil’ performance was studied, and the ExpDecl model was used for curve fitting. The results showed that with the increase of aging time, the content of copper impurities, acid value, micro water content, and dielectric loss factor of transformer oil showed significant increasing trends, while the breakdown voltage showed a significant decreasing trend. The trend of copper ion content exhibited the most significant positive correlation with the dielectric loss factor. Monitoring the copper ion content and key performance parameters of transformer oil is of great significance for understanding the operational status of transformers and implementing effective prevention and control measures.