Corrosion mechanism for local enrichment of acids and copper ions in copper-insulating paper contacts leading to the acceleration of copper sulfide formation induced by dibenzyl disulfide

Abstract

Numerous failures of high-voltage transformers occur because of sulfur corrosion in oil-impregnated paper insulation containing dibenzyl disulfide (DBDS). This study determines the effects of DBDS, the copper-insulating paper contact, the insulating paper and the atmosphere on copper sulfide formation. Accelerated thermal aging experiments were conducted for mineral oil that contained DBDS and insulation windings under atmospheric (nitrogen/air) conditions. The corrosive sulfur deposits were quantified using SEM/EDX, ICP-AES and precipitation methods. Oil acidity was measured and analyzed. The study proposes a corrosion mechanism for local enrichment of acids and copper ions in copper-insulating paper contacts leading to the acceleration of sulfur corrosion.