Pressboard roughness and ageing influence on mineral oil electrification

Probing and Modulation of the Electric Double Layer at the Insulating Oil–Paper Interface

“…Thus, the charge distribution of EDL at the oil–paper interface is formed as shown in Figure , where negative charge gathers on the insulating paper surface at the molecule scale and positive charge diffuses in insulating oil at the macroscopic scale. This is consistent with what researchers observed while exploring the streaming electrification phenomenon in large HV transformers, that is, the insulating oil is positively charged in an oil–paper sample composed of mineral insulating oil and cellulose insulating paper. ,, In the liquid, the local negative potential increases in absolute value as it approaches the interface, which coincides with the measured potential by KPFM, and the lowest potential is at the oil–paper interface.…”

“…This is consistent with what researchers observed while exploring the streaming electrification phenomenon in large HV transformers, that is, the insulating oil is positively charged in an oil−paper sample composed of mineral insulating oil and cellulose insulating paper. 18,48,49 In the liquid, the local negative potential increases in absolute value as it approaches the interface, which coincides with the measured potential by KPFM, and the lowest potential is at the oil−paper interface.…”

“…The basic component of the insulating paper sample used in our work is cellulose, a molecular chain containing multiple hydroxyl and aldehyde groups. The oxygen atoms of hydroxyl and aldehyde groups have strong electronegativity, consequently, it has high affinity for negative charges and tends to attract negative ions in insulating oil. ,, According to Koopmans’ theorem, the electron affinity energy can be approximately represented with the lowest unoccupied molecular orbital energy ( E LOMO ). , The partial density of states (PDOS) of the oil–paper interface structure is calculated by the Perdew–Burke–Ernzerhof (PBE) functional (details are given in the Supporting Information), as shown in Figure a,b, E LOMO of insulating paper is 20% lower than that of insulating oil, which means that insulating paper is more likely to become an electron acceptor in the oil–paper insulation system.…”