Polarization and Depolarization Current Analysis of Thermally aged Oil Impregnated Kraft Paper

Condition monitoring of transformer has become a major look-out for utilities all over the world owing to the substantial amount of reliability assurance. Non-destructive methods of insulation assessment have gained popularity in recent times as it does not harm the transformer insulation. The oil impregnated paper insulation in a transformer is largely affected by the operating temperature and consequently aging occurs which degrades the insulation, thus increasing the risk of transformer failure. The objective of this paper is to quantify the effect of thermal aging on the physical condition of the aforementioned insulation. This is achieved by means of polarization and depolarization current (PDC) analysis which parameterizes the insulation system of the transformer. The values of such parameters were manifested by the PDC testing technique using the DIRANA instrument. It is observed that thermal aging significantly affects the PDC parameters.