Comparative Analysis of Distribution Transformers with Varying Ratings and Insulation States via Frequency Domain Spectroscopy and Capacitance Ratio

This paper presents a comparative analysis of distribution transformers with varying power ratings and insulation conditions using Frequency Domain Spectroscopy (FDS). The investigation was conducted both by comparing transformers with different performance ratings (from 100 to 1000 kVA) and insulation quality at a constant ambient temperature, and by evaluating insulation properties of a transformer across varying temperatures. The FDS method allows for separate assessments of oil quality and moisture content in solid insulation. An advantage of using capacitance measured by FDS for insulation assessment is its relatively lower sensitivity to temperature variations compared to the loss factor, a finding confirmed by temperature-effect analyses. However, assessing transformer insulation via capacitance measurements is influenced by the insulation’s geometric configuration, which depends on the transformer type and power rating. Therefore, when comparing the quality of insulating parts of transformers with different powers, it is recommended to compare the capacitance ratio depending on low frequencies against the capacitance at 50 Hz.