Abstract
The paper presents results of testing permittivity of an oil-impregnated electric pressboard containing water nanoparticles depending on AC frequency, moisture content level and the temperature of samples. A new method has been developed for converting experimentally obtained frequency dependences of permittivity determined with the frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 °C) using exponential dependence of the relaxation time versus temperature. Activation energy of the permittivity relaxation time has been determined for a moist oil-impregnated electric insulation pressboard. It has been established that variations of the moisture content level in a composite of cellulose, mineral oil, and water nanoparticles do not cause any changes in the relaxation time activation energy value, neither in energy states of electrons in potential wells nor in the structure of water nanoparticles. It has been also found that the conversion of experimentally obtained permittivity versus frequency dependences determined with the FDS method to the reference temperature of 293 K (20 °C) eliminates temperature dependences that occur in characteristics based directly on measurement results. Once the relative permittivity is converted to the reference temperature it is only its dependence on the moisture content level that remains.
Highlights
For about 100 years, cellulose in the form of paper and pressboard impregnated with insulating oil has been used as a basic insulation material for high voltage power transformers
An analysis of the relative permittivity dependences on frequency obtained for a composite of cellulose, mineral oil, and water nanoparticles, measured at different temperatures, has shown that increase of the temperature not changes the shape of the waveform but only causes a shift to higher frequency value
That the content variations moisture in a composite of cellulose, mineral oil, and water nanoparticles do not affect values of the relaxation time activation energy, the electron energy states in potential wells nor the structure of water nanoparticles
Summary
Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions. This article is published with open access at Springerlink.com
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