The depletion of dibenzyl disulfide from a mineral transformer insulating oil

This study examines the kinetics of the net depletion of dibenzyl disulfide (DBDS) from its solution in mineral insulating oil due to copper corrosion at elevated temperatures in power transformers. The concentration of DBDS is determined using liquid-liquid extraction followed by GC detection. Measurements, at 24 h intervals, up to 168 h, show that the depletion of DBDS from its solutions in mineral insulating oil at 150 °C and initial concentrations of 3.00, 6.00, 9.00, 12.00 and 15.00 mg L^-1 is very slight compared to identical measurements in the presence of copper strips in the mineral oil. The analysis of the kinetic data reflects the complexity of the corrosion process and its occurrence at a concentration as low as 1 mg L^-1 which is much lower than what has been previously believed. Measurements on solutions at initial DBDS concentrations of 150 mg L^-1 indicate that even when the insulation oil matrix is in contact with copper strips the corrosion does not occur to any measurable extent below 100 °C and starts to speed up appreciably only beyond 125 °C. From data at 100, 125 and 150 °C an energy of activation equal to 123 kJ mol^-1 is estimated.