P. Żukowski

Formation of water nanodrops in cellulose impregnated with insulating oil

This article presents results on the DC conductivity of moist pressboard impregnated with insulating oil and its dependence on the moisture and temperature of the samples. The transfer of charges was found to take place because of electron hopping between potential wells produced by water nanodrops. The average dimension of the nanodrops was around 2.32xa0nm, forming approximately 220 water molecules.

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.

Permittivity of a composite of cellulose, mineral oil, and water nanoparticles: theoretical assumptions

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 293xa0K (20xa0°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 293xa0K (20xa0°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.

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

The paper presents an analysis of test results by Frequency Domain Spectroscopy (FDS) of the loss tangent (tgδ) 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 tgδ 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 tgδ 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 293xa0K (20xa0°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 293xa0K (20xa0°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.

Low-Temperature DC Carrier Transport in (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x Nanocomposites Manufactured by Sputtering in Pure Ar Gas Atmosphere

This presented work investigates the structure and temperature relationship/dependence of the DC conductivity in the (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x nanocomposites deposited in Ar atmosphere with composition ( u2009at.%) and temperature ( u2009K). It is shown that VRH displayed crossover from Mott-like to Shklovskii-Efros regimes which occurred at temperatures of 100–120u2009K. It is also noted that the observed shift of the percolation threshold to higher concentrations of metallic fraction can be attributed to the disordering of the metallic nanoparticles due to the incorporation of the residual oxygen in the vacuum chamber during the deposition procedure.

Electric properties of composite ZnO-based ceramics doped with Fe

This work is focused on the analysis of phase structure and temperature dependences of electric resistivity ρ(Т) in ZnO-based composite ceramics (ZnO)90(FexOy)10, doped with Fe by the addition of 10 wt.% of one of the iron oxides FexOy. Streszczenie. Praca koncentruje się na analizie struktury fazowej oraz zależności temperaturowych rezystywności elektrycznej ρ(Т) kompozytów ceramicznych (ZnO)90(FexOy)10 opartych o ZnO, domieszkowanych Fe poprzez dodanie 10% wag. jednego z tlenków żelaza FexOy. (Własności elektryczne ceramiki kompozytowej na bazie ZnO domieszkowanej Fe)

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.

Determination of nanocapillaries radii statistical distribution in electrotechnical pressboard

The article presents research on the percolation time of oil through the electrotechnical pressboard, which results in determining the statistical distribution of capillary radii, involved in the process of impregnation of paper-oil insulation. On the basis of the conducted research, a positive effect of pressboard calendering on its operation was detected.

Modeling of dielectric to metal conduction transition in nanocomposites by using high voltage discharge

Paper presents method of the percolation phenomenon visualization through modeling metal-dielectric type nanocomposite. Model was based on high voltage discharge in air between metallic discs modeling the metallic phase. A research station for visualization and simultaneous registration of percolation process was developed and built. Models have been executed in 2 dimension plane of randomly arranged metallic discs. The quantity of metal rings models different value of metal nanoparticles concentration. For different concentration of nanoparticles relationship of discharge voltage to metal concentration was determined.

Visualization of the percolation phenomenon in two-dimensional arrangement of metallic spherical particles

The paper presented the method of visualization the phenomenon of percolation in the model of nanocomposite type metaldielectric, based on the occurrence of high voltage jumps in the air between metallic discs modeling the metallic nanoparticles. A research station for visualization and registration of the percolation process was developed and built. The models were made from metallic discs, randomly arranged on a plane for different values of „nanoparticles” concentration. The dependence of the jump voltage from the concentration was established. Visual images of percolation for different „nanoparticles” concentration were registered.