Aging behaviour of dodecylbenzene in the presence of copper and dibenzyl disulfide (DBDS)

Copper sulfide deposition remains a serious issue in high voltage power transformers and can result in equipment failure. In order to understand the chemistry of this process, dodecylbenzene was used as a model oil system. Copper and dibenzyl disulfide (DBDS) were added in controlled amounts and accelerated aging was then performed. It was found that copper sulfide (CuxS) could be formed (i.e. the included copper sheets were blackened) even under non-oxidative conditions but only when DBDS was present in the oil. The reaction was accelerated in the presence of oxygen and competes for available copper with the parallel copper carboxylate producing reaction. The AC breakdown strength was reduced after aging, but exhibited a more catastrophic reduction in oils containing DBDS, confirming the detrimental effects of CuxS on breakdown performanc