The minimum concentration of 1,2,3-benzotriazol to suppress sulfur corrosion of copper windings by DBDS in mineral transformer oils

The incubation criterion of the 62535 standard procedure of the International Electrochemical Commission (IEC) was modified to obtain the depletion profiles for different concentrations of each of 1,2,3-benzotriazol (BTA) and dibenzyl disulfide (DBDS) when both are present in a mineral oil matrix. Measurements on BTA concentrations ranging from 0 to of 70 mg L^-1 show that its depletion profile after incubation for 72 h, at room temperature, and at 150°C in the presence and absence of a copper strip, is the same irrespective of the DBDS concentration. Similar measurements on DBDS at concentrations ranging from 10 to 300 mg L^-1 show that identical depletion profiles are obtained as long as the BTA concentration is maintained in excess of 5 mg L^-1. The results show that a minimum BTA concentration of 5 mg L^-1 is needed to make the copper windings in contact with the mineral oil passive and in turn suppress their sulfur corrosion by DBDS.