Effects of loading factor in operating time on dielectric characteristics of transformer oil

Aging of transformer occurs as the transformer operates. Dielectric characteristics testing of oil insulation in transformers is needed to estimate the condition of transformers due to aging. Insulating materials in long-term operations will degrade gradually and cause the change of its properties. In this paper, a database of result for dielectric characteristics was analyzed statistically using linear regression method. Specifically the database consists of 219 dielectric characteristics and transformer age in the range of 0–30 years old with rated voltage 150/20kV and 150.70kV. Correlation analysis between dielectric characteristics and transformer age was discussed. Color, IFT (interfacial tension) and acidity were correlated to transformer age with correlation coefficient 0.502, 0.463 and 0.348 respectively. The secondary database consists of trend acidity and color in several years was carried out from operating transformers with the same capacity and rated voltage but various loading factor. The loading factor varies from 9–80% years. Transformer with higher loading factor experiences aging faster than the lower one. Higher loading factor also causes the level of acidity and color increase rapidly.