Corrosive Sulfur Induced Failures in Oil-Filled Electrical Power Transformers and Shunt Reactors

Abstract

The nature and causes of corrosive sulfur induced failures are examined in oil-filled transformers and shunt reactors. Copper sulfide, which is formed when the corrosive sulfur in a mineral oil reacts with the copper conductors, is likely to diffuse into the paper tapes insulating the conductors. Since copper sulfide is partially conducting, the dielectric losses of the contaminated oil-impregnated-paper tapes are markedly increased; paper tapes in close proximity to the copper conductors are found to attain tan delta values > 1.0 even at room temperature. It is highly likely that thermal instabilities develop at those sites at operating temperatures, leading to increased loss currents and, ultimately, short circuits between the turns. This sequence of events is substantiated by evidence from the field, which indicates large areas of thermally degraded insulations and charred breakdown regions along the coils, the extent of which becomes more pronounced at higher operating temperatures (toward the top of the windings)

Space Charge Behavior in Paper Insulation Induced by Copper Sulfide in High-Voltage Direct Current Power Transformers

“…Unfortunately, researchers have recently faced a new problem, namely, corrosive sulfur in insulating oil. Corrosive sulfur can form the semi-conductor substance copper sulfide, which will be deposited on the paper surface [5,6]. Insulating resistance and dielectric property of oil-paper insulation have decreased because of emergence of this substance.…”

Characterization of Performance of Paper-Oil Insulation System in the Presence of DBDS

“…In the previous two decades, the systematic studies carried out throughout the world on transformer oil and oil immersed equipments and their breakdown have had clearly and conclusively proved that sulphur present in transformer oil and its reaction with copper conductors leads to the formation of copper and cupric sulphide [1][2][3][4][5][6]. The semi conducting copper sulfide which is formed on the copper conductor of windings, starts migrating towards inner papers layers [7,8].…”

Static secondary ion mass spectrometry investigation of corrosion inhibitor Irgamet ® 39 on copper surfaces treated in power transformer insulating oil

“…In fact, previous studies have shown how certain organic compounds containing sulphur (e.g. dibenzyl disulphide, DBDS) [11] are able to chemically attack copper surfaces immersed in insulating mineral oil causing metal displacement, promoted by oxygen, together with the formation of corrosive by-products such as copper sulphides (Cu x S) [12][13][14][15]. Copper sulphides, being ionic compounds, can interfere with the insulation system (solid and liquid components) reducing its reliability; this can result in catastrophic failure of high voltage assets, power distribution disruption and, ultimately, reputational and financial losses [16][17][18].…”