Copper catalytic effect on the thermal deterioration and surface morphology performance of transformer oil–paper insulation

Transformer failure caused by copper corrosion in oil–paper insulation has been attracting much attention in recent years. It is necessary to get a better understanding the effect of copper on the degradation rate and the microcosmic performance of the oil–paper insulation. In this way, targeted measures could be taken to prevent harm to the transformer. The catalytic effect of copper on the thermal aging rate and the micro‐/nano‐level morphology of oil–paper insulation aged with and without copper are compared in this paper. The dynamic behavior of copper compounds dissolved in oil and deposited on the insulation paper surface is discussed. Results show that copper plays a catalytic role in the deterioration of oil–paper insulation, and this role becomes obvious in the later stages of aging. Compared to the oil–paper insulation sample aged without copper, in the oil–paper insulation sample aged with copper the oil has higher acidity and higher ultraviolet absorption wavelength. Besides, the degree of polymerization of the paper is lower. Scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) results show that copper is present on the innermost paper surface. SEM and atomic force microscopy clearly show the deposition of copper compounds. Higher deterioration of the paper results in more roughness of the paper surface. The content of copper compounds dissolved in oil was found to be increasing first and then decreasing in the later process of aging. The content of copper compounds deposited on the paper increases significantly when the oil is aged for a long time. The catalytic effect of copper on the thermal aging rate and the surface morphology of oil–paper insulation should be paid more attention even for a noncorrosive oil. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.