(Proceedings on Seminar on Fault-Finding and Life-Assessment of Power Transformers, 25-26 April, 2008, New Delhi, pp 31-42)
Corrosion of copper conductors due to Sulphur in transformer oil is a serious problem affecting both Power and converter transformers. The sulphur components which are of low concentration in fresh transformer oil are converted to reactive and corrosive forms during service conditions. These species react with copper to form copper sulphide which migrate from conductor surface to outer layers of paper and then are carried to other parts of the transformer. Since copper sulphide is conductive, it affects the voltage distribution leading to surface discharges. These discharges eventually damage paper insulation. In this investigation, samples of paper-oil insulation are subjected to thermal/electrical ageing. During ageing, oil parameters like Total sulphur and Mercaptan sulphur are regularly monitored. The discharge characteristics of the insulation system are also studied for understanding the phenomenon of copper corrosion and consequent failure of insulation system.
