Effect of Temperature on Condition Assessment of Oil-Paper Insulation using Polarization-Depolarization Current

Polarization Depolarization Current method of dielectric testing is popularly used by the utilities for condition assessment of the insulation of power transformers. Test temperature is an important factor that affects the polarization depolarization current data measured. In this work the effect of test temperature in condition assessment of cellulosic part of oil-paper insulation using polarization depolarization current method has been investigated. Polarization and depolarization current of experimental samples, emulating oil-paper insulation of power transformers, at different test temperatures were measured. The cellulosic moisture content was estimated for the samples at different temperatures using the farthest zero of the transfer function of the Maxwell's model derived from the polarization depolarization current data. The error in the calculated paper moisture content is determined from comparison with the moisture content calculated from the minimum tan delta of the frequency domain spectroscopy data of the test samples maintained at different test temperature. Results obtained clearly show that the error in the moisture content calculated from the polarization depolarization current data increases with the increase in temperature.