A quantitative calculation method of frequency domain dielectric spectroscopy of moisture-containing oil-paper insulation

Abstract

In order to apply frequency domain dielectric spectroscopy(FDS) techniques in non-destructive evaluation of transformer oil-paper insulation and insulation pressboard moisture content, based on the XY equivalent model of transformer, the FDS quantitative calculation formula of oil-paper insulation was derived theoretically in this paper. Firstly, XY equivalent model without moisture was composed of dry oil impregnated pressboard (OIP) and dry transformer oil, the FDS quantitative calculation formula of the dry XY equivalent model was derived based on characteristics of composite dielectric. Then according to the characteristics of mixture of moisture and OIP, the concept of the parallel factor was used in this paper, and the dielectric constant of OIP with moisture was derived. Furthermore, combined with the formula obtained from the first stage, the formula of the FDS of the XY equivalent model with moisture was derived. To verify the correctness of the above theoretical derivation, the XY equivalent models with different moisture content were prepared in laboratory, and the moisture content and the frequency domain dielectric spectroscopy of the above samples were tested respectively by Karl Fisher titration method and IDAX-300. The results of moisture content test were substituted into the above formula to calculate the FDS of the XY equivalent model. It can be found a good fit when compared with the measured FDS, therefore the correctness of the theoretical derivation was verified.