Analysis of Moisture Aggregation State in Transformer Oil-Paper Insulation Using Improved Davidson-Cole Dielectric Model

To evaluate the moisture content, different characteristic parameters can be used to characterize the FDS of oil-paper insulation. However, the shape of the FDS spectra is affected by the presence of different moisture aggregation states within the oil-paper insulation, which in turn affects the assessment of the degree of moisture exposure. We have prepared oil-paper insulation samples with different moisture aggregation states and analyzed the effects of moisture content m.c. and moisture inhomogeneity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$n$</tex> on the dielectric properties of the samples in this study. It was found that the tantδ-f curves would show loss peaks with different polarization processes for different moisture aggregations, and the positions of the loss peaks would vary with the moisture aggregation states. Using the Davidson-Cole model to extract the characteristic covariates of the tantδ-f curves, the results show that the β loss peak associated with interfacial polarization changes with the increase of moisture content m.c., and moisture inhomogeneity n. After that, the relaxation time τβ of the β loss peak and the relationship between m.c. and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$n$</tex> were fitted and found to exhibit exponential and polynomial function relationships, respectively, which can be regarded as a characteristic parameter for assessing the moisture content of oil-paper insulation.