Investigations on the impact of moisture and aging on the charge de-trapping characteristics of ester oil-impregnated pressboard using PDC measurements

With intrusion of moisture and aging, the dielectric characteristics of oil-paper insulation undergo deterioration. Some of the important specifications for assessing the insulation health of oil paper include space charge accumulation and charge trapping characteristics in the insulation. Both criteria are significantly affected by the deterioration of the insulation. In this study, the effect of these two crucial factors on the charge trapping characteristics of natural ester impregnated pressboard insulation have been examined using Isothermal Relaxation Current (IRC) and Polarization-Depolarization Current (PDC) analysis. To accomplish this, both polarization-depolarization current (PDC) measurements and IRC measurements were conducted on carefully prepared ester oil-impregnated pressboard specimens with varying aging conditions and moisture contents. The findings outlined in this study underscore that aging and moisture notably affect charge trapping characteristics, however in a quite different manner.