Jan Subocz

Assessment of water content in an impregnated pressboard based on DC conductivity measurements theoretical assumptions

The paper presents results of investigations of the effect of moisture content and temperature on DC conductivity of the impregnated pressboard. It has been found that the conductivity of the impregnated pressboard is a function of activation energy, moisture content and temperature. It has been found that moisture content ranging from 1.4% to 6.4% do not cause any changes in the conductivity activation energy whose value is ΔWav = (0.853±0.071) eV. On the other hand water content strongly influences the value of DC conductivity. It has been also found that the conductivity is determined by electron hopping between the closest located potential wells formed by water molecules in the oil-impregnated cellulose structure. For the experimentally obtained dependences of conductivity vs. moisture content and temperature theoretical ones have been determined to describe the experimental results. Based on the research results, a localization radius of the water molecule valence electron that coincides with the O2- ion radius has been determined. The obtained results concerning DC conductivity vs. moisture level and temperature dependence of an electric insulation pressboard can make a basis for the identification of the amount of moisture accumulated in solid elements of a power transformer paper-oil insulation.

An analysis of AC conductivity in moist oil-impregnated insulation pressboard

The paper presents research results of testing AC conductivity in a moist oilimpregnated electric insulation pressboard, depending on the moisture content level and temperature of the samples. A new method has been elaborated for converting experimentally obtained dependences from frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 /dpl deg/C). Activation energy values have been determined for the conduction and relaxation time. It has been found the conductivity is realized by electron tunnelling between potential well formed by water molecules contained in the structure of moist cellulose.

Analysis of AC conductivity in wet oil impregnated insulating paper

In paragraph are presented the results of research based on the AC conductivity of the wet oil-impregnated insulating paper, depending on the moisture content and temperature of the samples. This is a new experimental method, which converts the results from the FDS to the reference temperature of 293.15 K (20 ° C). Takes account of the activation energy for conduction and relaxation time.

Electrically and Thermally Conductive Low Density Polyethylene-Based Nanocomposites Reinforced by MWCNT or Hybrid MWCNT/Graphene Nanoplatelets with Improved Thermo-Oxidative Stability

In this paper, the electrical and thermal conductivity and morphological behavior of low density polyethylene (LDPE)/multi-walled carbon nanotubes (MWCNTs) + graphene nanoplatelets (GNPs) hybrid nanocomposites (HNCs) have been studied. The distribution of MWCNTs and the hybrid of MWCNTs/GNPs within the polymer matrix has been investigated with scanning electron microscopy (SEM). The results showed that the thermal and electrical conductivity of the LDPE-based nanocomposites increased along with the increasing content of carbon nanofillers. However, one could observe greater improvement in the thermal and electrical conductivity when only MWCNTs have been incorporated. Moreover, the improvement in tensile properties and thermal stability has been observed when carbon nanofillers have been mixed with LDPE. At the same time, the increasing content of MWCNTs and MWCNTs/GNPs caused an increase in the melt viscosity with only little effect on phase transition temperatures.

The influence of temperature on the AC conductivity of a composite pressboard-synthetic ester-water nanoparticles

This paper presents the results of the AC conductivity of electrical pressboard production company Weidman with a water content from 0,6% to 7% by weight, impregnated with MIDEL 7131 synthetic ester. Frequency and temperature dependencies of the AC conductivity were determined. The Arrhenius plots were developed for the whole range of measurement frequencies, from which the activation energies of the AC conductivity were determined. It was found that changes in AC conductivity can be described by means of two activation energies. Each of these activation energies decreases with the increase of the measurement frequency. This may mean, in our view, that these differences are due to changes the environment occurring water nanoparticles. Some of the nanoparticles be are located in the environment cellulose material, while the other part - in the environment the MIDEL 7131 ester.

Moisture level content analysis in oil impregnated pressboard used in power transformers

The article presents the results of research based on the DC electrical conductivity of wet paper depending on the moisture content and temperature of the samples. The change of moisture content does not change the activation energy of conductivity. The conductivity is performed by the hopping mechanism between the nearest possible holes which are formed in the material with nanodrops of water by the plotting of theoretical dependence that accurately describes the dependence of the conductivity of the water content and temperature. Medium size of nanodrops was about 1.5 nm, and the composition contains about 220 molecules of water.