Analysis of the temperature-frequency effect on dielectric losses in a grain medium

The aim of the study is to determine the influence of the thermal effect on dielectric losses in grain mass subject to bruising during drying and storage on the example of wheat across a wide external electric field frequency range. The study of the electrophysical characteristics of a dispersed medium comprising mechanically activated wheat grains takes into account the effect of the degree of breakage on the dielectric parameters of the studied medium. The studies were carried out on experimental samples having different degrees of mechanical activation of particles, which ranged in size from from 50 to 1000 μm. Variations in the dielectric loss tangent were studied using the dielectric method across a wide temperature-frequency range. Studies of variations in dielectric properties were carried out for wheat sam-ples subjected to grinding according to the mechanical activation method at temperatures varying from 20°C to 255°C with a constant heating rate of 0.7 deg / min. During the course of the experiment, the frequency of the external electric field was varied from 25 Hz to 1∙106 Hz. Dielectric constant and dielectric loss tangent calculations were carried out using data on electrical capacity and conductivity obtained using an E7-20 immittance meter and a measuring cell in the form of a flat capacitor. An analysis of variations in these dielectric characteristics was also performed. The obtained stable correlation of the dielectric loss tangent with the frequency of external electric impact and the degree of heating of the samples was most pronounced for finely dispersed samples (particle size 50 μm). Variations in dielectric characteristics are most significant when the frequency decreases to 100 Hz and below. The study of variations in the main dielectric parameters can be used to prevent self-heating and ignition of the grain mass during storage, as well as for selecting the most efficient energy-saving drying mode.

Dielectric Properties of Electrical Insulating Liquids for High Voltage Electric Devices in a Time-Varying Electric Field

The motivation to improve components in electric power equipment brings new proposals from world-renowned scientists to strengthen them in operation. An essential part of every electric power equipment is its insulation system, which must have the best possible parameters. The current problem with mineral oil replacement is investigating and testing other alternative electrical insulating liquids. In this paper, we present a comparison of mineral and hydrocarbon oil (liquefied gas) in terms of conductivity and relaxation mechanisms in the complex plane of the Cole-Cole diagram and dielectric losses. We perform the comparison using the method of dielectric relaxation spectroscopy in the frequency domain at different intensities of the time-varying electric field 0.5 kV/m, 5 kV/m, and 50 kV/m. With the increasing intensity of the time-varying electric field, there is a better approximation of the Debye behavior in all captured polarization processes of the investigated oils. By comparing the distribution of relaxation times, mineral oil shows closer characteristics to Debye relaxation. From the point of view of dielectric losses at the main frequency, hydrocarbon oil achieves better dielectric properties at all applied intensities of the time-varying electric field, which is very important for practical use.

Analysis of XLPE cable parameters subject to thermo aging

Modern marine vessels use electrically driven rudders; cruise liners, gas carriers, tankers are equipped with Azipod systems manufactured by the Swedish-Swiss company ABB. Gondola-type propellers make it possible to break ice when the vessel is moving astern, therefore such vessels are used for work on the Northern Sea Route, in particular, when working on the Yamal LNG project. The 22MW Azipod propulsion system rotates 360° and enables difficult maneuvering without the assistance of tugs. When operating such propellers, powerful diesel generators are installed on the ship. For the transmission of electricity, ship cables are used, which are subject to increased requirements that meet the standard of the International Electrotechnical Commission. Modern marine vessels are equipped with XLPE or EPDM insulated cable lines; industrial production of these cables is carried out in the Russian Federation. In the course of the study, a method for auditing the state of insulation has been considered based on an assessment of the change in the tangent of the angle of dielectric losses in the process of thermal aging of the cable of the PvBPng(A)-HF brand. Measurements of the tangent of the dielectric losses' angle have been carried out with a Tangens-2000 insulation parameter meter.

Study of Dielectric, Polarization Properties of Cyclopentanol and Their Solutions in Cyclopentane by a New Variation Method

Results of calculating the theoretical principles of the variational method for measuring the dielectric parameters of polar liquids: cyclopentanol and its solutions in cyclopentane have been shown in the paper. Their dielectric constant ξ' and dielectric losses ξ'' are calculated. Solutions to the equations were found and a graphical solution method and an automated method for calculating ξ' and ξ'' were developed on the basis of this method. Comparison with the results of other methods revealed that these indicators are at the same time minimal within 1.5–2.0%.

Quantum-mechanical model of dielectric losses in nanometer layers of solid dielectrics with hydrogen bonds at ultra-low temperatures

Upon based the finite difference methods construct the solutions for Liouville quantum kinetic equation linearized by the external field, in complex with the stationary Schrodinger equation and the Poisson operator equation, for an ensemble of non-interacting hydrogen ions (protons) migrating in the field of a crystal lattice perturbed by a variable polarizing field. The influence of the phonon subsystem is not taken into account. The equilibrium (non-balanced) proton density matrix is calculated using quantum Boltzmann statistics. The temperature spectra of dielectric losses tangent angle for hydrogen bonded crystals (HBC) in a wide temperature range (50–550 K) are calculated. At the theoretical level detected the effects of nano-crystalline states (1–10 nm) during the polarization of HBC in the region of ultra-low temperatures (4–25 K).

Exploring the characteristics of SnO2 nanoparticles doped organic blend for low cost nanoelectronics applications

The PVA/PVP/SnO2 nanostructure films were fabricated using the casting technique. The structure, dielectric and optical characteristics of PVA/PVP/SnO2 nanostructures were studied for pressure sensors. Results of studying the dielectric characteristics showed that the dielectric constant, dielectric losses and electrical conductivity of blend are enhanced with the rise of SnO2 nanoparticles (NPs) content. The dielectric constant and dielectric losses are reduced, while the conductivity is risen with the increase in frequency. The dielectric constant increases from 2.53 to 7.41, and dielectric losses rise from 0.5 to 2, while the conductivity increases from 2.82·10–11 S/cm up to 1.11·10–10 S/cm. The results of measuring the optical characteristics have indicated that the absorbance rises with increasing the SnO2 NPs content. The energy gap of blend has been reduced from 4.9 down to 4.65 eV with the rise in SnO2 NPs content. The optical constants have been improved with the rise in SnO2 NPs content. Results of studying the pressure sensors have shown that their capacitance grows with the pressure increase.

Determination of the Brewster angle of the wave reflected from a plate with dielectric losses

In free space, the permittivity of materials is usually determined by the value of the Brewster angle using the angular dependences of the amplitude and phase of the wave reflected from the material plate. An expression corresponding to materials without dielectric and magnetic losses is used as a calculation model. Experimental studies of the parameters of the wave reflected from dielectric materials show the discrepancies with theoretical calculations known as deviations from the Fresnel laws. We present the results of determining the Brewster angle of the wave reflected from a plate made of a material with dielectric losses. The angular dependences of the amplitude and phase of the reflected wave were calculated using the numerical solution of the problem of falling at an arbitrary angle of a plane linearly polarized wave with an electric field vector lying in the plane of incidence on a plate of a dielectric material with complex values of the dielectric and magnetic permittivity. They were used to determine the angles corresponding to the minimum reflection coefficient depending on the dielectric losses of the plate material. The differences between the numerical calculations and the data obtained using the Brewster angle formula were noted, which increased with increasing dielectric losses of the material. From the condition that the modulus of the reflected wave amplitude is equal to zero, a different formula for calculating the Brewster angle for a material with losses is analytically obtained. The results of calculations using this formula coincided with the calculations for the reflected wave when solving the classical problem of the inclined incidence of a plane wave on a plate of a dielectric material in the framework of geometric optics. The results obtained can be used to determine the Brewster angle for a wave reflected from a plate with magnetic and dielectric losses.

Influence of Electrochemically Exfoliated Graphite Addition on the Dielectric Properties of Epoxy/Montmorillonite Nanocomposites

The influence of hydrophilic electrochemically exfoliated graphite (EEG) and hydrophobic reduced EEG (rEEG) on the electrical conductivity, dielectric properties, and high-frequency dielectric losses of epoxy-based composites with montmorillonite was described. It was confirmed, that the addition of EEG changes the low-temperature conduction mechanism. The electrical conductivity in composite with EEG and montmorillonite was described by correlated barrier hopping model, whereas for composites with montmorillonite and rEEG two models were used: non-overlapping small polaron tunneling and correlated barrier hopping. The addition of EEG drastically changes the activation energy of charge carriers motions from 2.68 to 0.83 eV, whereas the addition of rEEG only to 2.43 eV. Also composite with EEG was characterized by highest high-frequency dielectric losses.

New sorbents for electrochromatography based on polymer-inorganic dielectric composites

Oligomeric diisocyanate based coatings with different contents of barium titanate (BaTiO3) submicron sized particles as a ferroelectric filler are synthesized on poly(dimethylsiloxane) (PDMS) supports. The study of thus obtained coatings using confocal scanning electron microscopy allowed the characterization of their morphology and features of BaTiO3 particles distribution in the polymer binder, including the determination of threshold filler contents corresponding to the formation of an infinite cluster, matrix-island and chain-like structures as well as the percolation. Dielectric permittivity and dielectric losses of the composites are measured and studied depending on BaTiO3 filler content and relating structural features.