Review of time-domain polarization measurements for assessing insulation condition in aged transformers

This paper presents a review of the time-domain polarization measurement techniques for the condition assessment of aged transformer insulation. The polarization process is first described with appropriate dielectric response theories and then commonly used polarization methods are described with special emphasis on the most widely used "return voltage" (RV) measurement. Most recent emphasis has been directed to techniques of determining moisture content of insulation indirectly by measuring RV parameters. The major difficulty still lies with the accurate interpretation of return voltage results. This paper investigates different thoughts regarding the interpretation of RV results for different moisture and ageing conditions. Other time domain polarization measurement techniques and their results are also presented in this paper.