Investigating the Formation of Trace Metal Contamination in Insulating Oil: from Electrical Erosion and Chemical Corrosion Perspectives

The presence of trace metal in transformer oil significantly affects its insulating properties, posing potential risks to the safe operation of transformers. Therefore, understanding the intrinsic mechanisms behind the formation of the trace copper within transformers is of critical importance. In this study, we investigated the two primary forms of trace copper in transformer oil—suspended particulate and soluble ionic states—and conducted detailed experimental analyses to elucidate their formation mechanisms. Through electrical arcing experiments, we examined the behavior of metal contacts in insulating oil, identifying the transfer of surface material during arc interruption as a crucial pathway for the generation of suspended metallic particulates. Additionally, we explored the impact of electrical arcing on the damage mechanisms of the contacts and the resulting microstructural characteristics of the ablated surfaces. Corrosion tests were employed to study the formation mechanisms of metal ions, with both macroscopic and microscopic analyses performed on different corrosion morphologies. Our findings suggest the presence of copper corrosion products and their soluble forms, specifically identifying copper-oleate as a major component, which demonstrates high solubility and diffusion capacity in the oil.