Oil-paper bushing insulation condition assessment based on polarization-depolarization currents

To assess the insulation condition of oil-paper bushing, an assessment method based on polarization and depolarization currents was proposed in this paper. Firstly, the polarization and depolarization current test principle and equipment were introduced and set up to measure the polarization and depolarization currents at pA level. In order to verify the field test effect, the polarization and depolarization currents tests for field bushings were conducted. Three oilpaper bushing with different insulation condition (new, natural aging and moisture containing) were chosen as the test object. The test results indicated that the polarization and depolarization currents showed different character of different bushing insulation conditions. The dielectric loss at low frequency was highly correlated with aging degree and the moisture containing. The DC conductivity was highly correlated with moisture containing but lowly correlated with aging degree.