Journal
IET SCIENCE MEASUREMENT & TECHNOLOGY
Volume 8, Issue 6, Pages 588-594Publisher
INST ENGINEERING TECHNOLOGY-IET
DOI: 10.1049/iet-smt.2013.0262
Keywords
moisture; discharges (electric); minerals; transformer oil; electric breakdown; permittivity; electrical resistivity; solubility; water; on-load operating transformer; oil resistivity; water solubility; resistivity; dissipation factor; dielectric constant; breakdown voltage; transformer mineral oils; physicochemical properties; naphthenic mineral oil properties; electrical discharges; moisture
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The physicochemical properties of three transformer mineral oils of different levels of degradation, resulting from exposure to moisture and electrical discharges, are investigated. The first oil is new and untreated whereas the second is taken from a transformer after one year of normal operation; and the third oil is extracted from a 15-year-old operating transformer. The considered parameters are breakdown voltage, dielectric constant epsilon(r), dissipation factor (tan ) and resistivity. Isothermal charging currents have also been measured under dc for long application times. It is shown that the physicochemical characteristics present major differences depending on the considered oil sample. An easy method enabling to determine the water solubility in oil is proposed; this method is based on the measurement of oil resistivity. To validate a part of the results obtained in laboratory, measurements on an on-load operating transformer have also been achieved. These show that the properties of oils with dissolved water in laboratory are similar to those of oils with really dissolved water inside operating transformers.
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