Analysis of insulating materials of power oil transformer by method FDS

Faculty of Electrical Engineering and Information Technology, University of Zilina, Univerzitna 1, 01026 Zilina, Slovakia

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Published online: 11 June 2026

Abstract

This work presents an in-depth study of the evaluation of oil paper as an insulating material of a transformer using the frequency dielectric spectroscopy (FDS) method. The research focuses on comparing power oil transformers with different ratings and insulation properties under the same internal temperature conditions. The FDS method was used to determine the characteristics of the capacitance and dissipation factor, which allows a comprehensive analysis of the dielectric response. However, the analysis revealed a significant limitation in the influence of the geometric configuration of the insulation system, which introduces a dependence on the transformer type and rated power. By analyzing the ratio of the capacitance at a given frequency to the reference value at 50 Hz, it is possible to significantly suppress the influence of the transformer geometry, but it has a limited ability to distinguish differences in paper moisture. The analysis of the dissipation factor showed the disadvantages of accurately determining the moisture content in the paper above a frequency of 0.02 Hz at low temperatures and good oil condition.