Influence of aging degree on polarization and depolarization currents of oil-paper insulation

The oil-immersed power transformer is the core equipment for energy transmission and distribution power system. Assessing the condition of Oil-paper insulation system accurately is tremendously significant. Polarization and depolarization current measurement (PDC), which is based on the dielectric response, is currently widely used for condition assessment of transformer insulation as non-destructive testing methods. This paper based on the equivalent model of Oil-paper Insulation structure-X model, the characteristic parameters extracting for dielectric in time domain was worked out. Then an accelerated aging experiment at 130°C was done. Polarization and depolarization current were measured under different aging degrees. Characteristic parameters of them were also calculated, to investigate the influence of aging degree on polarization and depolarization current. Experimental results show that, polarization and depolarization current values and the corresponding characteristic parameters would changed regularly with aging degree. In guarantee under the condition of water content is consistent, the polarization and depolarization currents can be used to assess the aging state of transformer oil-paper insulation.