A first-principles study of the formation and regulation of the electric double layers at Cu (0 0 1)/mineral oil interfaces

Abstract

Copper-mineral oil interfaces are key components of oil-impregnated power transformers and are commonly believed to be one of their weak points. The formation of an electric double layer (EDL) at this interface as a result of charge accumulation and transfer is crucial to its insulating properties, but a molecular-level understanding of this phenomenon remains unclear. To understand this fundamental aspect, we have investigated the effect of different EDLs on the electric potential and interfacial potential barrier between copper and mineral oil by using first principle calculations. Based on the calculations, the EDL is shown to reduce the interfacial potential barrier and enhance the diffusion of oil molecules at the interface when the copper side is negatively charged and the mineral oil side is positively charged. In contrast, when the copper side is positively charged and the mineral oil side is negatively charged, the corresponding EDL can increase the interfacial potential barrier and reduce the diffusion of oil molecules at this interface. Our findings shed light on the relationship between the structure of EDLs and their electrical properties in oil-impregnated power transformers.