Search results

The purpose of this paper is to investigate the effect of Mg²⁺substitution on the magnetic and electrical properties of Li_0.35−x Mg_2x Zn_0.3 Fe_2.35−xO₄ thick films synthesized with polyvinyl alcohol (PVA) matrix.

The nanoferrites Li_0.35−x Mg_2x Zn_0.3 Fe_2.35−xO₄ (x=0, 0.07, 0.14, 0.21, 0.28 and 0.35) were synthesized by chemical technique using aqueous solution of PVA (the matrix) and thick films were fabricated by screen printing technique. The DC magnetic hysteresis measurements, AC magnetic susceptibility and DC electrical resistivity were measured as a function of temperature.

The lattice parameter of thick film Li_0.35−x Mg_2x Zn_0.3 Fe_2.35−xO₄ (x=0, 0.07, 0.14, 0.21, 0.28 and 0.35) increases with the substitution of Mg²⁺ions for Li¹⁺and Fe³⁺. The surface morphology of the thick films showed the grain size increasing with Mg²⁺substitution till x=0.21 and then decreasing for the higher concentrations of magnesium. The magnetic moment n_B (μ_B) computed from the M_s obtained by extrapolation of the magnetization curve showed a gradual decrease with the composition till x=0.21, beyond which a sudden decrease was observed. The resistivity of the films at room temperature had variation with composition x, similar to that of magnetic moment. The activation energies ΔE_F and ΔE_P were found to vary with composition x of the ferrite system.

The paper reports, for the first time, the magnetic and electrical properties of fritless Li_0.35−xMg_2xZn_0.3Fe_2.35−xO₄ thick films using PVA polymer matrix. Up to x=0.21 (Mg²⁺), grain size increases and Curie temperature decreases beyond which reverse effect takes place.

The paper presents a method of creating electrical equivalent diagrams of magnetic circuits. The method is based on bond‐graph techniques, using flux derivative as flow variable. Couplings between magnetic and electric part of the system are represented by gyrators. Simple models of magnetic branches, including non‐linear effects due to saturation, hysteresis and eddy currents, are presented. These models can be easily combined into magnetic circuit models, which can be transformed into dual electric equivalent circuit. Various equivalent circuits of transformers are discussed. The proposed models are simple and particularly useful for system‐level simulation of power electronic and motion control systems with magnetic elements. These models can be easily developed if needed. Theoretical considerations are illustrated by examples of digital simulation and experimental results.

The purpose of this paper is to investigate the added value of using temperature-dependent electric and magnetic properties in high-temperature electromagnetic simulations.

In this work, the electromagnetic properties of Domex 420, SSAB, have been characterized as a function of the temperature, from room temperature to 900°C. The measurement of the electric and magnetic properties was performed inside a vacuum furnace at a number of discrete temperature steps, with particularly small intervals around the Curie temperature. A simple transient multi-physics model was used to investigate the impact of the measured properties in three different representations.

In certain intervals, a simplified approximation of the properties produces accurate results, while fully parametric representation is beneficial when heating above the Curie temperature.

Temperature-dependent electromagnetic properties are rarely found, especially in an easy-to-use form. Using parameterized temperature-dependent approximation of key properties shows noteworthy differences in the outcome of high-temperature electromagnetic modeling.

This paper aims to give a perspective about the variety of techniques which are available and are being further developed in the area of coupled field formulations, with selective bibliography and practical examples, to help postgraduate students, researchers and designers working in design or analysis of electrical machinery.

This paper reviews the recent trends in coupled field formulations. The use of these formulations for designing and non‐destructive testing of electrical machinery is described, followed by their classifications, solutions and applications. Their advantages and shortcomings are discussed.

The paper gives an overview of research, development and applications of coupled field formulations for electrical machinery based on more than 160 references. All landmark papers are classified. Practical engineering case studies are given which illustrate wide applicability of coupled field formulations.

Problems which continue to pose challenges to researchers are enumerated and the advantages of using the coupled‐field formulation are pointed out.

This paper gives a detailed description of the application of the coupled field formulation method to the analysis of problems that are present in different electrical machines. Examples of analysis of generators and transformers with this formulation are presented. The application examples give guidelines for its use in other analyses.

The coupled‐field formulation is used in the analysis of rotational machines and transformers where reference data are available and comparisons with other methods are performed and the advantages are justified. This paper serves as a guide for the ongoing research on coupled problems in electrical machinery.

This paper aims to present the proposition of a new experimental method for obtaining very crucial data of the structural steel that is used in the tank of oil filled power transformers, namely, the volumetric losses and the magnetic permeability, both in function of the density of magnetic flux. Although these data are not usually available, they are fundamental for helping the transformer designer in avoiding the occurrence of hot spots in the transformer tank. The adoption of a conventional Epstein frame has restrictions because of the incompatibility between it and the samples of the steel.

The basis of the proposition is the same as that of the Epstein frame, with significant attention paid to the additional losses in the winding that creates the magnetic flux to the samples in the core. These losses can be significant and are created by the harmonics of current along the windings and are summed to the ohmic losses. For separating these winding losses from the magnetic losses, each sample is made as being the core of a toroidal 1:1 transformer. Thus, two tests with two identic of these toroidal transformers are necessary.

The proposed methodology is simple, because it is very similar to the classical tests of transformers (no-load and short-circuit tests). The process of separation of losses requires only a numerical fitting of curves for adjusting the winding losses as a function of the current amplitude, and the obtained results are coherent with the expected behavior of the magnetic losses and the magnetic permeability of a structural steel.

The method gives very approximate results in comparison to those obtained using the Epstein frame. The influences of the temperature and/or of the skin effect have not been evaluated.

Practical, real and thus confident data of structural steel, such as the magnetic permeability and the volumetric losses (hysteresis and Foucault), become available for the transformer designer to take actions for not only reducing the tank losses but also for avoiding the occurrence of hot spots through computer simulation.

The proposition is very new, as it allows to test steel samples with a size that does not fit to a usual Epstein frame. It takes into account the real influence of harmonic of currents in the losses along the winding of a classical Epstein frame, which has not been so far mentioned. It allows obtaining data of structural steel that had not been considered important until now.

The purpose of this paper is to derive the geometry‐based equations for inductances which are used in circuit theory analysis of synchronous reluctance motor (SRM). Transient and steady state performance analyze of SRM by using the 2D time‐stepping finite‐element method (FEM).

The analytical approach is used to obtain the equations which describe geometry dependent magnetizing inductances of SRM. Transient and steady state performance of the SRM is analyzed by using the 2D time‐stepping FEM. The external electric circuit connected with the finite‐element model of the SRM geometry allows the study of almost any of the electric and magnetic properties of the machine. Presented SRM model is also connected to the external mechanical loads (friction, rotor inertia and load torque). The use of different materials for the magnetic‐pole part of the rotor and for flux barriers was analyzed. The flux barriers in the first SRM rotor were filled with a pure massive electrically conductive ferromagnetic with a proper B‐H curve, whereas the rotor magnetic segments were made of non‐conductive electric steel described with its B‐H curve. The conductive barriers with their end rings form a squirrel cage and allow SRM to start on‐line. The flux barriers of the second SRM rotor were made of aluminum but between the second and third flux barrier a massive electrically‐conductive ferromagnetic was inserted which during starting‐up acted as a part of the squirrel cage. All of the flux barriers of the third SRM rotor were made of electrically‐conductive aluminum with iron parts axially laminated. The finite‐element SRM models coupled with an electric circuit is also used to evaluate the motor performance at various asynchronous speeds.

Analytical geometry‐dependant equations for the d‐ and q‐axis SRM inductances are derived. On the basis of the proposed 2D time‐stepping finite‐element analysis, the start‐up performance for the SRM rotor design using different materials is established. The torque distribution as a function of time at any of the observed asynchronous speeds is not smooth and uniform. It consists of the stator‐to‐rotor tooth pulsating torque, and the synchronous and asynchronous component.

The main disadvantage of analytical geometry‐dependant equations for the d‐ and q‐axis SRM inductances is the linearization of any of the ferromagnetic parts.

On the basis of the proposed 2D time‐stepping finite‐element analysis, the start‐up performance, asynchronous run and synchronous torque characteristics for the SRM rotor design using different materials are established.

The value of the paper is the closed view about happenings in rotor flux barriers of SRM, mostly regarding the time distribution of induced currents in the rotor flux barriers. On the base of 2D time‐stepping FEM, the use of different materials for the magnetic‐pole part of the rotor and for flux barriers was analyzed.

Investigations over new types of materials as a potential power source for different types of devices were raised dramatically in the last few years. It is connected especially with global needs and that most of the devices in our world need electricity to work. In this paper, an investigation on magnetoelectric effect in the magnetostrictive-piezoelectric composite material is presented.

An author's research setup for investigation of magnetoelectric effect in the developed novel material was prepared. The new composite material was made of magnetostrictive particles of Terfenol-D and lead zirconium titanate (PZT) material.

Obtained results show that changes in an electric voltage output from the prepared material are highly dependent on the changes in external magnetic field. It was found out that rate of changes of magnetic field around composite material is one of the most important factors which has influence on the magnetoelectric effect. Taking into account the obtained results, it was proven that prepared hybrid material shows magnetoelectric effect in the case of work in alternating magnetic field.

This phenomenon might be used in a field of energy harvesting as potential power source for devices with low power consumption. Moreover, this new material gives an opportunity to be used as an additional gauge for determination of deformation or crack propagation in the samples during fatigue tests.

The purpose of this paper is to investigate in detail the effects of acid treatment on multi‐walled carbon nanotubes (MWNTs), which could find a variety of applications in coatings and composites.

A number of analytical techniques, including Fourier transform infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and scanning electron microscopy (SEM), were employed to assess the effects of acid treatment on MWNTs.

It was found that desirable modifications to MWNTs occurred after acid treatment. Thus, carboxylic acid groups were introducing on to the surface of MWNTs. It was also found that both chemical and physical properties of MWNTs could be modified/altered.

The investigation established a method to modify MWNTs via acid treatment and the effects of such a treatment on MWNTs in detail. The modified MWNTs can be used for various applications and further modifications. The acid treated and the further modified MWNTs can be dispersed into polymers to prepare polymer/MWNTs composite materials and composite surface coatings. Some properties of the resulting composites were improved by the dispersed MWNTs, giving excellent mechanical, electrical, thermal and magnetic properties.

The finding on the effects of acid treatment on MWNTs, supported by detailed FT‐IR, XPS, Raman and SEM data, would be of interest to the field. The modification technique provided a route to further modification of carbon nanotubes. The acid treated and the further modified MWNTs are useful for preparation of polymer/MWNTs composite materials and composites surface coatings with improved mechanical, electrical, thermal and magnetic properties.

The purpose of this paper is to examine scaling algorithms in the description and modelling of power loss in soft magnetic composites (SMCs).

Three scaling algorithms are examined to determine the most appropriate description of power loss in magnetic composites. The scaling coefficients are estimated in such a way that all measurement data should be collapsed onto a single curve, given in the scaled coordinates. The coefficient estimation is based on a non-linear optimization using the generalized reduced gradient method. The obtained formulae are then used in the power loss modelling.

It is revealed that only two-component formulae are suitable for the scaling analysis of power loss because these allow obtaining of the collapse of measurement data.

This study considers just one type of SMC (Somaloy 700). Further research will be devoted to the verification of the scaling approach to the power loss modelling for other types of magnetic composites.

The power loss is a basic property of soft magnetic materials, which determines their practical applications. The scaling approach to the power loss modelling gives quite simple models that require a reduced number of measurement data to estimate coefficients.

The scaling algorithms can be a useful tool in the analysis and designing of magnetic circuits made of SMCs.

The paper presents a methodology in which the slotted regions of electrical machines are replaced by homogeneous regions with anisotropic magnetic permeability. The resulting FEM model is then built and solved in an easy way, because a simplified structure is analyzed, with fixed geometrical characteristics and electrical and magnetic properties depending on the original geometry. The methodology is therefore useful for estimating the machine performances as a function of slot and winding parameters and can be conveniently used at the initial step of the design to perform parametrical analyses and optimizations with uncomplicated procedures for the generation of the FEM model. In order to test the reliability of the method, the FEM results obtained with both the actual configuration and the “smoothed” one must be compared. In the example of application, the proposed methodology is applied to a linear brushless DC motor. The dependence of the accuracy and convergence speed on different “smoothing” strategies is first discussed. Then the obtained results are compared with the ones related to the original slotted configuration. Finally, the correspondence of some important electromagnetic quantities (flux lines distribution, air‐gap flux density and electromagnetic force) is analyzed.