Measurement of dielectric response of transformer moisture content

Abstract

Over a transformer's operational lifetime, the moisture content of its insulation pressboard increases because of the ageing of its internal insulation. Thus, this moisture content becomes an important index for judging the ageing of this insulation. In this study, to analyse the moisture content of a transformer's insulation pressboard using the dielectric response insulation technique, the XY-equivalent model analysis method for classical transformers is combined with a dielectric-constant algorithm for mixed media. In addition, a new method for calculating the moisture content of a pressboard is obtained via cyclic iterative comparison calculations based on the dielectric response translation formula, the temperature, and the material activation energy. The XY-equivalent models of transformers with various proportions are derived under laboratory conditions. The moisture contents of the transformers’ insulating pressboards are obtained under the corresponding dielectric loss factor curves by using the proposed moisture content calculation method, which provides a result that is within 4.83% of that provided by the IDAX-300 moisture content analysis algorithm, thus demonstrating its validity.