Effects of antioxidants and acids on copper sulfide generation and migration induced by dibenzyl disulfide in oil‐immersed transformers

This study aims to explore the effect of the antioxidant 2,6-di-tert-butyl-p-cresol (DBPC) and acids on the generation and migration of copper sulfide on insulating windings as a result of the reaction of dibenzyl disulfide (DBDS) and copper in oil-immersed transformers. The heating experiments were conducted by adding different amounts of DBPC and different kinds of acids to the naphthenic mineral oil. The result indicates that acids can accelerate the generation of copper sulfide and that DBPC cannot effectively consume DBDS to reduce the corrosion phenomenon, but rather accelerates the deposition of copper sulfide onto the insulating paper. In particular, when the DBPC concentration is approximately 0.9% (w/w) at 130 °C for ten days, the amount of copper sulfide deposited on the insulating paper reaches its maximum. Moreover, excessive use of the antioxidant DBPC accelerates the aging of insulating oil, on the contrary, which adversely affects the mineral oil. Although the addition of DBPC can improve the antioxygenic property of mineral oil, too much of it is inadvisable because the transformers that contain DBPC and DBDS may be at high risk and suffer from breakdown. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.