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Title DC and AC Tests of Moisture Electrical Pressboard Impregnated with Mineral Oil or Synthetic Ester—Determination of Water Status in Power Transformer Insulation
Authors Zukowski, P.
Rogalski, P.
Kołtunowicz, T.N.
Kierczynski, K.
Zenker, M.
Pohrebniak, Oleksandr Dmytrovych  
Kucera, M.
ORCID http://orcid.org/0000-0002-9218-6492
Keywords transformer diagnostics
FDS method
insulation of transformers
moisture
mineral oil
ester
pressboard
Type Article
Date of Issue 2022
URI https://essuir.sumdu.edu.ua/handle/123456789/87760
Publisher MDPI
License Creative Commons Attribution 4.0 International License
Citation Zukowski, P.; Rogalski, P.; Kołtunowicz, T.N.; Kierczynski, K.; Zenker, M.; Pogrebnjak, A.D.; Kucera, M. DC and AC Tests of Moisture Electrical Pressboard Impregnated with Mineral Oil or Synthetic Ester—Determination of Water Status in Power Transformer Insulation. Energies 2022, 15, 2859. https://doi.org/10.3390/en15082859
Abstract In this study, the conductivity and permittivity of electrical pressboard—insulating liquid—water composites were investigated, and the electrical properties of the composites and water were analysed comparatively. Mineral oil and synthetic ester were used as insulating liquids. It was found that the presence of water caused an increase in the permeability of the composite in the frequency range below 100 Hz. The value of static permittivity determined by water in the content of 5 wt. % was approximately 15. To obtain this value caused by liquid water, its volume should be approximately five (oil) and four times (ester) higher than its actual content, respectively. The determined values of the activation energy of the DC conductivity of the composites were several times higher than the values of the activation energy of the conductivity of the liquid water. The experimental values of the dielectric relaxation times were many orders of magnitude higher than the dielectric relaxation times of water. This means that the experimental results obtained for the dielectric permittivity, the activation energy of conductivity and the dielectric relaxation times for moisture electrical pressboard impregnated by mineral oil or synthetic ester exclude the possibility of the presence of liquid water in the composites. It was found that the conductivity of the composites increased exponentially with increasing water content. Such dependencies are characteristic of hopping conductivity, caused by the quantum phenomenon of electron tunnelling between nanometre-sized potential wells. As the increase in conductivity is determined by the presence of water in the composites, therefore, the nanometre potential wells were single-water molecules or nanodrops.
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