Application of Dielectric Spectroscopy Measurements for Estimating Moisture Content in Power Transformers

Application of Dielectric Spectroscopy Measurements for Estimating Moisture Content in Power Transformers

Frequency Domain Spectroscopy (FDS) measurements were performed on pressboard samples containing different moisture contents and on insulation system of power transformers. The results were used for evaluating sensitivity of the so-called X - Y model, which is applied for estimating moisture content in transformer insulation using the results of FDS measurements. Based on the observations of this analysis a simplified model, called X model, was introduced in which the presence of spacers in transformer insulation has been neglected. Finally, reliability of the X model was assessed by comparing estimates of moisture contents based on FDS measurements on field installed power transformers with moisture contents obtained from chemical analyses of their oil samples.