Role of dissolved copper and oxygen on copper sulfide generation in insulating oil

We have developed a new heating test to investigate the influence of dissolved copper (DBDS-Cu complex) and oxygen on copper sulfide generation in alkyl benzene insulating oil with dibenzyl disulfide (DBDS) added. The weight of the deposited and dissolved copper was systematically studied in atmospheres of nitrogen and artificial air. The copper sulfide was deposited on the insulating paper using the heating test by separating the insulating paper from the copper strips in the insulating oil. It was found that dissolved copper (DBDS-Cu complex) has influence to the copper sulfide generation on the insulating paper. The weight of the copper deposited on the insulating paper was increased by the existence of oxygen. The acceleration effect on copper sulfide deposition on insulating paper was clarified for the first time by strictly controlling the experimental atmosphere. Moreover, the influence of the existence of oxygen was investigated individually on insulating oil and insulating paper. The oxidation of both alkyl benzene and insulating paper was found to accelerate copper sulfide generation.