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.

Modifying of the dielectric properties of adsorbed water in the force field of a solid surface

The results of thermodynamic and acoustoelectric studies of changes in the dielectric properties of adsorbed water under the influence of a solid surface force field are presented. It is noted that the dielectric properties of adsorbed water depend not only on the characteristic size of the system, but also on the interaction energy with the solid surface. Near the hydrophilic solid surface, the density of adsorbed water is increased and the mobility of molecules is reduced. The opposite effect occurs for hydrophobic surfaces. The frequency dependences of the dielectric properties of adsorbed water, as in the case of water in the solid and liquid phase, can be characterized using Debye relaxation theory. It is shown that a significant increase in the orientational dielectric relaxation time in adsorbed water can be explained by taking into account the energy of interfacial boundaries.

Microstructures and Electrical Conduction Behaviors of Gd/Cr Codoped Bi3TiNbO9 Aurivillius Phase Ceramic

In this work, a kind of Gd/Cr codoped Bi3TiNbO9 Aurivillius phase ceramic with the formula of Bi2.8Gd0.2TiNbO9 + 0.2 wt% Cr2O3 (abbreviated as BGTN−0.2Cr) was prepared by a conventional solid-state reaction route. Microstructures and electrical conduction behaviors of the ceramic were investigated. XRD and SEM detection found that the BGTN−0.2Cr ceramic was crystallized in a pure Bi3TiNbO9 phase and composed of plate-like grains. A uniform element distribution involving Bi, Gd, Ti, Nb, Cr, and O was identified in the ceramic by EDS. Because of the frequency dependence of the conductivity between 300 and 650 °C, the electrical conduction mechanisms of the BGTN−0.2Cr ceramic were attributed to the jump of the charge carriers. Based on the correlated barrier hopping (CBH) model, the maximum barrier height WM, dc conduction activation energy Ec, and hopping conduction activation energy Ep were calculated with values of 0.63 eV, 1.09 eV, and 0.73 eV, respectively. Impedance spectrum analysis revealed that the contribution of grains to the conductance increased with rise in temperature; at high temperatures, the conductance behavior of grains deviated from the Debye relaxation model more than that of grain boundaries. Calculation of electrical modulus further suggested that the degree of interaction between charge carriers β tended to grow larger with rising temperature. In view of the approximate relaxation activation energy (~1 eV) calculated from Z’’ and M’’ peaks, the dielectric relaxation process of the BGTN−0.2Cr ceramic was suggested to be dominated by the thermally activated motion of oxygen vacancies as defect charge carriers. Finally, a high piezoelectricity of d33 = 18 pC/N as well as a high resistivity of ρdc = 1.52 × 105 Ω cm at 600 °C provided the BGTN−0.2Cr ceramic with promising applications in the piezoelectric sensors with operating temperature above 600 °C.

Configurational Entropy Relaxation of Silica Glass—Molecular Dynamics Simulations

Vitreous silica was modelled using molecular dynamics (MD). The glass structure was transferred into an undirected graph and decomposed into disjoint structural units that were ideally mixed to calculate the configurational entropy. The Debye relaxation model was suggested to simulate the evolution of entropy during the cooling of the system. It was found that the relaxation of the configurational entropy of MD corresponds to the effective cooling rate of 6.3 × 106 Ks−1 and its extrapolation to 0.33 Ks−1 mimics the glass transition with Tg; close to the experimental value. Debye relaxation correctly describes the observed MD evolution of configurational entropy and explains the existence of freezing-in temperature and the shape of the curve in the transition region.

Localized Deep and Shallow Traps of α-Peaks from Thermally Stimulated Current (TSC) Measurement on Thermoplastic Polymers

In this paper, trap levels around the glass transition temperature (Tg) of polymers have been characterized using Thermally Stimulated Current (TSC) technique. Deconvolution on α-peaks of the Tg for PE (-104 °C), plasticized PVC (-35 °C), PMMA (90 °C) and PET (96 °C) were carried out based on the first-order kinetic theory for non-Debye relaxation. Using temperature, T from TSC experimental data, we have successfully separated the α-peaks of the thermoplastic polymers. It is found that the complex curve of α-peaks can composed of four (4) to eight (8) sub peaks. Dominant sub peaks were identified at Tmax = -105 °C, -34 °C, 89 °C and 92 °C for PE, pPVC, PMMA and PET, respectively. These peaks show activation energy, Ea of shallow and deep trap centers ranged from 0.3 eV to 4.6 Ev where they represent the depolarization of localized dipoles and space charges relaxations in the polymers.

Growth, Structural, NLO and Impedance Properties of Cu2+ doped Lithium Sulphate Monohydrate Single Crystals

Single crystals of 2.5 mole% of Cu 2+ doped Lithium sulphate monohydrate (LSMH) have been grown using slow evaporation technique at room temperature. Powder X-ray diffraction (PXRD) analysis ensures that the crystal belongs to monoclinic crystal system. The variation of relative dielectric constant, dielectric loss and tangent loss with frequency have been discussed. The conductivity and dielectric relaxation mechanism involved in the grown crystals have been carried out by using complex impedance spectroscopy in the temperature range (343K and 353K) and in the frequency range from 20Hz to 2MHz. The frequency dependent ac conductivity obeys the Jonscher’s power law. The imaginary part Mʺ of electrical modulus of grown crystals shows the formation of asymmetric dispersion peak and indicating non- Debye relaxation behaviour. Morphology properties of the grown crystals have been studied using atomic force microscopy and hence the roughness of the grown crystals has been calculated. The NLO property and LDT values of the grown crystals are analysed using Nd:YAG laser operating at 1064 nm and 532 nm respectively.

Reversible Electroporation Study of Realistic Normal and Cancerous Cervical Cells Model Using Avalanche Transistor Based Nanopulse Generator

In this paper, we study the reversible electroporation process on the normal and cancerous cervical cell.The 2D contour of the cervical cells is extracted using image processing techniques from the Pap smear image. The conductivity change in the cancer cell model has been used to differentiate the effects of the high-frequency electric field on normal and cancerous cells. The cells modulate themselves when this high-frequency pulse is applied based on the Debye relaxation relation. In order to computationally visualize the effects of the electroporation on the cell membrane Smoluchowski equation calculates the number of pores generated and Maxwell equations are used to determine the Transmembrane potential generated on the membrane of the cervical cell. The results produced demonstrates that this mathematical model perfectly describes the numerical tool to study the normal cells and cancerous cells under the electric field. The electric field is provided with the help of a realistic pulse generator which is designed on the principle of Marx circuit and avalanche transistor-based operations to produce a Gaussian pulse. The paper here use strength duration curve to differentiate the electric field and time in nanoseconds required to electroporate normal and cancerous cells.

Non-Debye Relaxations: Two Types of Memories and Their Stieltjes Character

In this paper, we show that spectral functions relevant for commonly used models of the non-Debye relaxation are related to the Stieltjes functions supported on the positive semi-axis. Using only this property, it can be shown that the response and relaxation functions are non-negative. They are connected to each other and obey the time evolution provided by integral equations involving the memory function M(t), which is the Stieltjes function as well. This fact is also due to the Stieltjes character of the spectral function. Stochastic processes-based approach to the relaxation phenomena gives the possibility to identify the memory function M(t) with the Laplace (Lévy) exponent of some infinitely divisible stochastic processes and to introduce its partner memory k(t). Both memories are related by the Sonine equation and lead to equivalent evolution equations which may be freely interchanged in dependence of our knowledge on memories governing the process.