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Broadband Dieletric Properties of Impregnated Transformer Paper Insulation at Various Moisture Contents
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2011 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The actual life of a transformer is determined by ageing of the cellulosic insulation such as transformer paper. The presence of moisture in the insulation system decreases the electrical strength of paper and accelerates the aging. It is an efficient way to monitor the moisture content in paper insulation by measuring the dielectric constant of the paper. The moisture dependent permittivity of impregnated transformer paper below 1 MHz has been widely investigated. High frequency (> 1 MHz) dielectric spectroscopy is under requirement since the loss peak information is missing. The impregnated paper is kept in desiccators with saturated salt solutions to get the samples with moisture content from 1 % to 5.5 %. Then they are placed in a coaxial line and the scattering parameters are obtained by modern Vector Network Analyzer. Full wave analysis is utilized to calculate the permittivity from the obtained S-parameters due to its high accuracy. The magnitude of the dielectric spectroscopy below 100 Hz is very dependent on the moisture content while there is a horizontal shift of curves towards higher frequencies depending on the water content over a wide frequency range. The loss peaks appear between 1 MHz and 1 GHz for the impregnated paper with moisture level less than 5.5 %. Due to the limited system accuracy, there is a blank frequency band from 1 MHz to 100 MHz.

Place, publisher, year, edition, pages
2011. , 95 p.
EES Examensarbete / Master Thesis, XR-EE-ETK 2011:004
Keyword [en]
broadband dielectric spectroscopy, transformer paper, Karl Fischer titration
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-91922OAI: diva2:511555
Educational program
Master of Science - Electric Power Engineering
Available from: 2012-03-22 Created: 2012-03-22 Last updated: 2012-03-22Bibliographically approved

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