Influence of the antioxidant on the long-term ageing characteristics of oil-paper insulation and the deposition and migration of copper sulphide in oil-immersed transformers

This paper investigated the influence of 2, 6-di-tert-butyl-p-cresol (DBPC) on the long-term ageing characteristics of oil-paper insulation and the deposition and migration of copper sulphide induced by the reaction of copper and dibenzyl disulphide (DBDS) in oil-immersed transformers. A thermal ageing experiment at 130 degrees C were designed and conducted by adding different concentrations of DBPC to the naphthenic mineral oil and after the experiments a set of characteristic parameters were tested. The result indicates that the excessive concentration (0.6%) of DBPC will slightly increase the ageing of insulating oil and increase the carboxyl group in the mineral oil, affecting the reaction of DBDS and copper, and the insulating paper wrapped on the copper strip was also aged seriously accordingly. Meanwhile, the deposition of copper sulphide on the insulating paper is found to be slightly increased with the increase of the concentration of DBPC. When insulating oil contains DBPC and DBDS, due to migration of DBDS-Cu and DBPC-Cu in oil, the copper ions in the oil would be fluctuating at a certain period of time. Although the addition of a small concentration of DBPC can improve the antioxygenic property of the insulting oil to some extent, the transformers that contain excessive concentration of DBPC may be more harmful than beneficial.