A new approach for determination of moisture in paper insulation of in-situ power transformers by combining polarization-depolarization current and return voltage measurement results

Moisture content in an oil-paper insulation system of power transformer accelerates the aging process of cellulose that degrades insulation properties. As a result, dielectric response measurement data is also affected by moisture present in insulation. In time domain these measurements include Return Voltage Measurement and Polarization-Depolarization Current measurement. In addition it is a known fact that power transformer insulation consists of complex structures which is difficult to model in laboratory. Therefore, results obtained from samples prepared under controlled environment may not be applicable to real life power transformer. The present paper discusses a new approach to combine the results obtained from these two methods namely, Return Voltage Measurement and Polarization-Depolarization Current measurement for several power transformers, to find the relation between oil and paper moisture content that is relevant to insitu power transformers.