Correlation between Polarization-depolarization Current and Interface Barrier in Oil-paper Insulation

Mineral oil and kraft paper have been widely utilized as insulating materials for quite a long time and commonly adopted in transformers. In previous research, the connection of interface barrier between oil and oil-immersed paper and its correlation with the aging states were discovered, revealing that the interface barrier rises and the dissipation of interface charges slows down with aging. In this paper, a further study in the current behaviors influenced by the interface charges is stepped out, as well as a set of automatic current measuring system is built up. For the intention of exploring the relation between the external current change and the interface barrier variation in the samples with two layers of oil and oil-paper under DC voltage, a polarization and depolarization current test and a bipolar carrier transport simulation have been introduced. A series of current measurements have been implemented using the plate specimen of different aging states. Moreover, Space charge effects on the external current has been studied through simulation of space charge transport in two layers of oil and oil-paper specimen. The fluctuation of polarization current shows the influence of dielectric polarization, transporting of carriers and oil/paper interface block effect of carriers. By contrast, the depolarization current has an overt connection to the interface barrier, with less variation with the external voltage. This study shows a potential to use the de-polarization current for the diagnosis of aging state of oil-paper insulation.