Development of Quantitative Evaluation of Copper Sulfide Deposition on Insulating Paper

We have developed a new heating test to investigate the influence of dissolved copper and oxygen on the 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 deposition on the insulating paper originated from the dissolved copper (copper complex compound) in the insulating oil. 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.