Dielectric losses in the composite cellulose–mineral oil–water nanoparticles: theoretical assumptions

Abstract

The paper presents an analysis of test results by Frequency Domain Spectroscopy (FDS) of the loss tangent (tgd) in electrotechnical pressboard impregnated with insulating oil and containing nanoparticles of water depending on the frequency of alternating current, sample temperature and degree of moisture. We found tgd reduction in areas of low and ultra-low frequency. It is associated with relaxation due to the hopping conductivity (tunnelling) of electrons between moisture nanoparticles occurring in the cellulose impregnated with insulating oil. In frequency areas close to the local minimum of tgd and higher, relaxation does not depend on the moisture content and is associated with other polar molecules which are part of the cellulose. We developed a new method converting experimental frequency dependence of the loss angle tangent, measured by the FDS method to the reference temperature of 293 K (20°C), using the exponential dependence of the relaxation time on the temperature, was developed. The activation energy of the relaxation time was determined based on the loss angle tangent of moist electrotechnical pressboard impregnated with insulating oil. It was found that the variation in moisture content in the composite cellulose-mineral oil-water nanoparticles do not cause changes in the activation energy of the relaxation time. The conversion of experimental frequency dependence of the loss angle tangent determined by the FDS method to the reference temperature of 293 K (20°C) eliminates the temperature dependence in the areas of ultra-low and low frequencies occurring in the runs made directly on the basis of the measurement results. After calculating the frequency dependence of the loss angle tangent to the reference temperature, all that remains is its dependence on the moisture content.

Precise Measurements of the Temperature Influence on the Complex Permittivity of Power Transformers Moistened Paper-Oil Insulation

“…For the analysis of the obtained results, the model of alternating and direct current hopping conductivity was used, which was developed on the basis of the quantum mechanical electron tunneling phenomenon. The results of the direct and alternating current conductivity tests of the composite of cellulose, insulating liquid and water nanoparticles perfectly agree with this model [49,52,[58][59][60][61].…”

Cellulose Ester Insulation of Power Transformers: Researching the Influence of Moisture on the Phase Shift Angle and Admittance

“…In [23][24][25][26][27], the quantum mechanical phenomenon of electron tunneling between potential wells produced by water nanoparticles was used to analyze the dependence of AC conductivity, dielectric permittivity, and the loss tangent of cellulose composites, insulating oil and water nanoparticles on temperature, frequency, and moisture content. The results obtained during the analysis made it possible to develop methods that converted the above-mentioned parameters obtained at any temperature that ranged from 10-80 • C.…”

Precise Measurements of the Temperature-Frequency Dependence of the Conductivity of Cellulose—Insulating Oil—Water Nanoparticles Composite

“…As established in papers [25,29,37,44,45], the relaxation time value should depend on the distance between the nearest potential wells, generated by the nanodrops of water. In this work a relaxation time formula was derived for the conductivity of electron tunneling:…”