Research on Polarization-Depolarozation Current of Oil-impregnated Paper after Electrical-thermal Aged

The primary insulating material in the converter transformer, oil-impregnated paper, is subject to a complex electric field, mainly including the direct current (DC) stress, the alternating current (AC) stress and relatively minor harmonic stress. In order to investigate the effect of electrical-thermal aging on the oil-paper insulation properties, the breakdown voltage and polarization-depolarization current of oil-impregnated paper samples with different aging conditions were measured respectively. Firstly, the operation electrical field of transformer valve windings was simulated in the PSCAD software, which manifested the proportion of the prominent components-DC stress and AC stress. In terms of the simulation result, the oil-paper sample with different aging hours were prepared by conducting the laboratory accelerated electrical-thermal aging tests. Afterwards, the polarization-depolarization current of samples aged 0 h, 48 h, 72 h, 96 h and 120 h were measured. It showed that electrical-thermal aging caused the deterioration of oil-impregnated paper, resulting in the increase of polarization-depolarization current.