Summary of research on corrosive sulfur in oil-paper insulation system

Oil-paper insulation plays an important role in the internal insulation of power transformers. Aging of transformer insulation is a gradual procedure which can eventually threaten the safe operation of power transformers. During long-term operation of power transformers, oil-paper insulation is exposed to multiple stresses, including electrical, thermal, mechanical factors and so on. Lot of vigor is given to maintenance of the health of transformers in transmission system. Usually the reliability of power transformer is very high and is expected to have a long service life. But according to the recent report and observations, many transformers and reactors have failed prematurely due to the resultant formation of copper sulfide in the windings, which has attracted wide attention. In the past decade, considerable amount of work has been carried out to understand the long term effects of corrosive sulfur in mineral insulating oils, which has been recognized as the culprit of failure of some shunt reactors and power transformers. However, the problem of copper corrosion is very complex because of the complicated existence of sulfur element in transformers. Depending on oil, there are many different sulfur compounds present in oil. Other components of transformer, like pressboard, paper, glue, gasket, contaminated oil deliver hose etc are all potential sources of sulfur of one form or the other, either independently or due their interaction with oil. It is not one single corrosive sulfur compound that is responsible for all corrosive sulfur issues. Therefore the main sources, detection method, corrosive mechanism, damage and suppression measures are still the puzzled research focus. This paper present a comparatively detailed summary of research status about this phenomenon, and some useful research proposals and findings are introduced as well.