Effects of Oil Temperature, Elemental Sulfur Concentration, and Aging Time on the Corrosion Activity of Transformer Mineral Oil Using Two-Level Factorial Design

The insulation of oil-filled power transformers, shunt reactors, and high voltage bushings may be affected by copper dissolution in the insulating oil and copper deposition on the paper insulation. Dissolved copper increases dielectric losses in the oil while copper deposition can significantly increase the conductivity of the paper insulation. The corrosion activity of transformer insulating oils has been shown to be accelerated by multiple factors such as temperature, oxygen, sulfur groups, passivators, and aging time. To date, there is a lack of studies that systematically design and quantify the effects of corrosion factors on the copper dissolution of transformer insulating oils or copper deposition on the surface of solid insulation (Kraft paper). Therefore, in this study, the effects of corrosion factors on the copper and sulfur deposition on the paper insulation immersed in transformer mineral oil (TMO) were investigated using two-level (2k) factorial design. The factors investigated in this study were: (1) oil temperature, (2) elemental sulfur concentration, and (3) aging time. Based on the results of the two-level factorial design, it is found that the oil temperature has the most significant effect on the surface resistivity, with a percentage contribution of 38.68%. A regression model was also developed in this study, and it is found that the model is adequate to predict the surface resistivity as a function of oil temperature, elemental sulfur concentration, and aging time, where the coefficient of determination (R2) and p-value of the regression model are 0.9694 and 0.0070, respectively.