A fast and accurate dielectric response measurement for transformer moisture assessment and remaining life estimation

This paper proposes a fast dielectric response measurement for transformer moisture assessment and remaining life estimation. The dielectric response measurements in the time domain for in-service transformers with various insulation conditions categorized into four levels, i.e., excellent, good, fair, and poor conditions, were investigated. The dielectric response measurements were investigated by polarization and depolarization time for 100, 500, 1000, and 3000 seconds. For the dielectric response of oil-paper insulation of such a transformer, the conductivity of oil in ducts and moisture content in paper can be estimated by using the curve fitting technique in advanced evaluation tool in PDC-Analyzer-1MOD. Besides, significant parameters, i.e., dc resistance, insulation resistance, polarization index, tan δ of oil, complex capacitance, conductivity and interfacial polarization loss factors in the low-frequency range, the paper remaining life time, and bubbling inception temperature were evaluated with a single dielectric response measurement result. To confirm the PDC measurement test results, other insulation test techniques were performed. The dielectric response results obtained from PDC measurement were compared with the results from the other mentioned techniques. It was found that the polarization time for 3000 seconds and depolarization time for 500 seconds is suitable for assessing the moisture content in paper and other dielectric parameters comparatively.