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Purpose The theoretical method of converting the magnetic circuit into an electric circuit is mature, but the way to determine the inductances in the electric circuit is not reliable, especially for the core working in saturation status, and it is impossible to determine the inductances by the transformer terminal measurements, as the measurement information is not enough to determine a number of inductances. This paper aims to propose an approach of calculating the reluctances.Design/methodology/approach In this paper, an approach of calculating the reluctances is proposed based on the numerical simulation of magnetic field in transformer with different values of current excitation. The reluctance of a core segment or air region as a branch of magnetic circuit is obtained by the magnetic energy and magnetic flux. By this way, all the reluctances as function of flux can be determined, and then the inductances can be determined. The reluctances and equivalent electric circuit of three-phase integrative transformer is determined, and its validation is proved in the paper.Findings The single phase example shows that the proposed method has a good performances on analysis of the inrush current in deep saturation. The peak value of the inrush current derived from the proposed approach matches well with the results obtained by coupled circuit-FEM analysis, and the difference is about 4.8 per cent. For studies on dual models of single phase transformers, the leakage inductances have important effects on the peak value of the inrush current. The reluctances of three-phase transformer are calculated, and the equivalent circuit simulation results are slightly smaller than the coupled circuit-FEM simulation results.Originality/value Approach of calculating the reluctances based on the numerical simulation of magnetic field in transformer is proposed. The magnetic core and air space are divided into several segments, and the reluctance for each segment is calculated based on the energy in the region and the flux of the cross-sectional area. By applying various excitation currents, all the reluctances as function of flux can be determined, and then all the non-linear inductances including the non-linear leakage inductances are obtained. The proposed approach is reliable to determine a number of inductances in the dual electric circuit, especially for deep saturation status. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to study the influence of supply voltage variations on the external magnetic field emitted by grid-powered induction machines (IMs).Design/methodology/approach Two models are developed in the paper to analyse, for different supply voltage values, the influence of the variations of the magnetizing voltage for which there is a link with the tangential component of the external flux. The first is an analytical model based on the IM single-phase-equivalent circuit with variable magnetizing reactance to take into account the saturation of the magnetic circuit. The second is a numerical finite element simulation to model the same phenomenon. Results of both models are analysed with experimental measures of the external flux.Findings The study shows that the amplitude of the external field strongly depends on supply voltage values.Research limitations/implications The investigation is mainly focused on the tangential component of the external magnetic field which is of high importance concerning the applicability of non-invasive methods of diagnosis, as electromagnetic torque estimation developed by the authors or internal fault determination.Originality/value The originality of the paper concerns the characterization of the external flux with the supply voltage for IMs. It is shown that the magnetic circuit radiates external flux differently with the load and with the supply voltage. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to analyze the conical-shaped compensator applied to infrared (IR) thermometry for planar materials.Design/methodology/approach The compensator for the IR thermometry system has been analyzed by means of numerical simulations performed in a commercial finite element analysis tool. Afterwards, the characteristics of a final system have been proposed. The simulation results have been validated by means of experimental measurements performed in a prototype of the proposed system.Findings The proposed conical shape geometry of the compensator is suitable to reduce the errors associated with the temperature estimation by IR thermometry when emissivity of the material is not known with adequate accuracy.Practical implications This work proposed an arrangement of conical-shaped compensator to increase the precision in the IR radiation thermometry of planar materials.Originality/value In this paper, the conical shape geometry is proposed instead of the classical semi-spherical geometry for the compensator of an IR radiation thermometry system with the purpose of reducing the thickness of the complete system. This new proposal can be advantageous when geometrical constraints are imposed. [ABSTRACT FROM AUTHOR]

Purpose Surface heat treatment by induction heating (10-100 kHz) requires precise prediction and control of the depth of the induced phase transformation. This paper aims at identifying common issues with the measurement and modeling of magnetic properties used in induction heating simulations, and it proposes ways to improve the situation.Design/methodology/approach In particular, it is demonstrated how intrinsic magnetic properties (i.e. the B-H curve) of a sample can change during the magnetic characterization process itself, due to involuntary annealing of the sample. Then, for a B-H curve that is supposed perfectly known, a comparison is performed between multiple models, each one representing the magnetic properties of steel in time-harmonic (TH) finite element method simulations. Finally, a new model called “power-equivalent model” is proposed. This model provides the best possible accuracy for a known nonlinear and hysteretic B-H curve used in TH simulations.Findings By carefully following the guidelines identified in this paper, reduction of errors in the range of 5-10 per cent can be achieved, both at the experimental and modeling levels. The new “power-equivalent model” proposed is also expected to be more generic than existing models.Originality/value This paper highlights common pitfalls in the measurement and modeling of magnetic properties, and suggests ways to improve the situation. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to present application of electromagnetic field (EMF) modeling in the educational process of electrical engineering study. Special attention has been paid to determination of specific parameters and characteristics as a function of device design. The aim is to introduce to the students the great opportunities for study and optimization of system behavior, based on the modeling of EMF distribution.Design/methodology/approach Illustrative examples have been considered, in which the students have to model the EMF distribution in relatively simple devices, using both analytical field determination and finite element method (FEM) analysis. The task includes also the determination of capacitances, inductances, magnetic fluxes, energies and forces. The problem has to be solved for different values of geometry parameters and material properties of the device. Thus, students can examine specific relation between field distribution and changes of the design.Findings The modeling of EMF distribution for different geometry and material properties allows determination of key factors, significantly influencing the behavior and processes in the studied device, which is the basic element in the computer-aided design systems and it can be used in subsequent system optimization.Practical implications The wide possibilities and advantages of the FEM simulations have been demonstrated in the modeling of EMF distribution and obtaining of device parameters. It enables students to significantly improve their knowledge in EMF theory and helps the future engineers to estimate the great advantages and possibilities for optimal device designing, which offer them the numerical simulation of electromagnetic processes.Originality/value This work illustrates possibilities, advantages and many years of author’s experience in application of EMF modeling in the teaching process in the study of electrical engineering specialties. The work problems presented have been solved analytically and on the basis of computer FEM simulations, which allows comparison of the opportunities and necessary efforts, offered by both kinds of methods. [ABSTRACT FROM AUTHOR]

Purpose Induction machines for traction applications are operated at working points of high ferromagnetic saturation. Depending on the working point, a broad spectrum of harmonic frequencies appears in the magnetic flux density of induction machines. Detailed loss analysis therefore requires local and temporal highly resolved nonlinear field computation. This loss analysis can be performed in the post processing of nonlinear transient finite element simulations of the magnetic circuit. However, it takes a large number of transient simulation time steps to build up the rotor flux of the machine.Design/methodology/approach In this paper, hybrid simulation approaches that couple static FEA, transient FEA and analytic formulations to significantly decrease the number of simulation time steps to calculate the magnetic field in steady state are discussed, analyzed and compared.Findings The proposed hybrid simulation approaches drastically decrease the simulation time by shortening the transient build-up of the rotor flux. Depending on the maximum error of the rotor flux linkage amplitude compared to the steady state value, a reduction of simulation time steps in the range of 55.5 to 98 per cent is found.Originality/value The presented hybrid simulation approaches allow efficient performing of the transient FE magnetic field simulations of induction machines operated as traction drives. [ABSTRACT FROM AUTHOR]

Purpose Multiphysics problems are solved either with monolithic or segregated approaches. For accomplishing contrary discretisation requirements of the physics, disparate meshes are essential. This paper is comparing experimental results of different interpolation methods for a segregated coupling with monolithic approaches, implemented using a global and a local nearest neighbour method. The results show the significant influence of discretisation for multiphysics simulation.Design/methodology/approach Applying disparate meshes to the monolithic as well as the segregated calculation of finite element problems and evaluating the related numerical error is content of the contribution. This is done by an experimental evaluation of a source and a material coupling applied to a multiphysics problem. After an introduction to the topic, the evaluated multiphysics model is described based on two bidirectional coupled problems and its finite element representation. Afterwards, the considered methods for approximating the coupling are introduced. Then, the evaluated methods are described and the experimental results are discussed. A summary concludes this work.Findings An experimental evaluation of the numerical errors for different multiphysics coupling methods using disparate meshes is presented based on a bidirectional electro-thermal simulation. Different methods approximating the coupling values are introduced and challenges of applying these methods are given. It is also shown, that the approximation of the coupling integrals is expensive. Arguments for applying the different methods to the monolithic and the segregated solution strategies are given and applied on the example. The significant influence of the mesh density within the coupled meshes is shown. Since the projection and the interpolation methods do influence the result, a careful decision is advised.Originality/value In this contribution, existing coupling methods are described, applied and compared on their application for coupling disparate meshes within a multiphysics simulation. Knowing their performance is relevant when deciding for a monolithic or a segregated calculation approach with respect to physics dependent contrary discretisation requirements. To the authors’ knowledge, it is the first time these methods are compared with a focus on an application in multiphysics simulations and experimental results are discussed. [ABSTRACT FROM AUTHOR]

Purpose – This paper aims to focus on the hybrid numerical method for effective design of silicon micromotor. Design/methodology/approach – In this work, the authors introduced finite element methods combined with LUA and Matlab. The paper focuses on analysis of electrostatic micromotor and uses computer simulation procedure leading to new structure design. Findings – This strategy enables changing of all parameters of the micromotors MEMS. Moreover, this strategy allows for taking advantage of FEM, namely possibility of calculations of complicated geometries (different electromagnetic devices too) without additional operations. Originality/value – A novel strategy in computer modeling of micromotor MEMS, based on the fast and very efficient hybrid method for analysis and design, is proposed. [ABSTRACT FROM AUTHOR]

Purpose – The paper seeks to present a methodology of computer simulation of 3D transient electromagnetic fields, losses and forces due to negative sequence currents in fragments of large synchronous turbogenerator rotors. The methodology allows for the preparation of initial data for further computations of thermal and mechanical behaviour of rotors. Design/methodology/approach – The governing equations for 3D negative sequence transient electromagnetic fields with the Coulomb gauge using magnetic vector potential and scalar electric potential A, V – A are solved by the nodal finite element method in a Cartesian coordinate system moving synchronously with the rotor. Findings – The presented methodology of 3D transient electromagnetic phenomena computation seems to be effective because the electromagnetic field in the rotor of a synchronous generator is generally three dimensional, and therefore 2D field-computation approaches and software are not able to simulate intrinsically 3D electromagnetic processes in turbogenerator rotors. Research limitations/implications – Currently it is difficult to carry out accurate numerical simulation of 3D transient electromagnetic fields and therefore losses and forces within the whole structure of the rotor because of the resulting huge computational expenses. This paper is devoted to the finite element analysis of electromagnetic fields, losses and forces in separate structural parts of the rotor. As an example of practical utilization of the developed technique, the computer simulation of electromagnetic phenomena in junctions of nonmagnetic rotor slot wedges of a 300 MVA class synchronous turbogenerator is carried out. Practical implications – The methodology can successfully be used during the design process of modern large synchronous turbogenerators. Originality/value – This paper presents numerical analysis of intrinsically 3D transient electromagnetic phenomena in large turbogenerator rotors. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to present a simulation concept and an experimental verification of a novel sensor design for the shaft position measurement based on the eddy current principle and the phase-shift measurement. The simulation method for the sensor characteristic determination is presented. Possible application of a new sensor type is theoretically presented, verified in simulation and compared with experimental results.Design/methodology/approach Sensor is based on the injection-locking phenomenon between coupled oscillators. Only one sensor per axis is used for position measurement. A pair of the sensing and reference oscillators in the sensor is electrically coupled via the coupling resistor. A change in the inductance for the eddy current sensor is simulated in the finite element method (FEM) software Flux and behavior of the sensor circuit is simulated in the SPICE simulator software LTSpice program. Finally, the simulation results are compared with the measurements conducted on the laboratory test rig.Findings A novelty in this approach is the usage of only one sensor per axis compared to the well-known differential measurement of the position that uses the opposite pair of the sensing oscillators in the same axis. A methodology for the sensor characteristic determination is presented and experimentally verified.Originality/value A new variation of a coupled-oscillator eddy current sensor design is introduced. A simulation approach for the characteristic determination of the sensors based on the weakly coupled oscillators and the injection-locking mechanism is presented. [ABSTRACT FROM AUTHOR]

Purpose |!|#8211; The purpose of this paper is to present the basic ideas of magnetic nanoparticles|!|#39; usage in the breast cancer treatment, which is called magnetic fluid hyperthermia. The proposed approach offers a relatively simple methodology of energy deposition, allowing an adequate temperature control at the target tissue, in this case a cancerous one. By means of a numerical method the authors aim to investigate two heating effects caused by varying magnetic fields, i.e. to compare the power density heating effects of eddy currents and magnetic nanoparticles. Design/methodology/approach |!|#8211; In order to numerically investigate the combination of the overheating effect of magnetic nanoparticles and eddy currents, the Finite Element Method solver based on FEniCS project has been prepared. To include the magnetic fluid in the model it has been assumed that power losses in the magnetic nanoparticles are completely converted into heat, according to experimentally developed formula. That formula can be interpreted as the hysteresis losses with regard to the volume of magnetic fluid. Finally, the total power density has been calculated as the product of the sum of power density from eddy currents and hysteresis losses. That methodology has been applied to calculate the effectiveness of magnetic fluid hyperthermia with regard to the female breast phantom. Findings |!|#8211; The paper presents the methodology which can be used in magnetic fluid hyperthermia therapy planning and Computer Aid Diagnosis (CAD). Furthermore, it is shown how to overcome one of the most serious engineering challenges connected with hyperthermia, i.e. achieving adequate temperature in deep tumors without overheating the body surface. Practical implications |!|#8211; The obtained results connected with the assessment of eddy currents effect suggest that during hyperthermia treatment the configuration which consists of an exciting coil and human body, plays a curial role. Moreover, the authors believe that these results will help to predict the skin surface overheating that accompanies deep heating. The presented methodology can be used by engineers in the development of Computer Aid Diagnosis systems. Originality/value |!|#8211; In a given patient|!|#39;s situation a number of choices must be made to determine the parameters of the hyperthermia treatment. These include the need of multiple-point temperature measurements for accurate and thorough monitoring. Treatment planning will require accurate characterization of the applicator deposition pattern and the tissue parameters, as well as the numerical techniques to predict the resultant heating pattern. The presented paper shows how to overcome these problems from the numerical point of view at least. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to investigate and explain the unexpected current flow patterns and twisting equipotential surfaces observed in strongly anisotropic materials. Design/methodology/approach - Potential distributions and current flow paths in highly anisotropic composite materials were studied via numerical simulation and experimentally. Simplified composite panels with two plyes were analysed using a finite-element model; the predictions were then confirmed experimentally. Findings - The unexpected twisting equipotential surfaces and current flow patterns were found to be consistent with minimising of Joule heat release in the material. Numerical modelling suggests that the twisted profiles of the potential are highly sensitive to the anisotropic electrical conductivity. Originality/value - This paper discusses the reverse current flows witnessed in a two-layer anisotropic system. Such behaviour has never been predicted or observed experimentally before. The reported results will be of interest to anyone who is considering using anisotropic materials such as carbon fibre composites which might experience applied potential difference, such as lightning strikes. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to elaborate a method of computer analysis of high-speed motor with specific parameters and verifying the obtained results, i.e. computer models by experimental (laboratory) tests. Design/methodology/approach - In order to determine motor properties from the viewpoint of energy conversion, a model using FEM was worked out with the help of Maxwell software. To determine static and dynamic properties of both motor and drive, Matlab/Simulink models were used; one of these models was a built-in (library) model, the other one was proposed by the authors. Findings - The new analysis method and model of high-speed motor have been carried out. Research limitations/implications - The permanent magnet brushless direct current high-speed motor was the subject of the research. In the first part of the research, the properties of the motor were determined by using finite element method. Practical implications - The laboratory prototype can be a starting point in establishing the production of the high-speed motors with rotational speed in the range of 50,000-100,000?rpm. Social implications - At this moment, there are several possible application of the high-speed motor and it should be expected that other new applications can appear in near future after the start of the production. Originality/value - The paper shows that the computer-based analysis method determines the motor properties accurately. It is also pointed out that a motor with half-open slots has advantageous properties. The new simulation model of high-speed motor has been carried out. This model allows taking into account some imperfections caused by slots and rectangular cross-section magnets. [ABSTRACT FROM AUTHOR]

Purpose - In the electromagnetic field simulation of modern servo drives, the computation of higher time and space harmonics is essential to consider appearing torque pulsations, radial forces and ripple torques. The purpose of this paper is to propose a method to cover the effect of saturation on the armature flux density within conformal mapping (CM) by an finite element (FE) re-parameterization. Design/methodology/approach - Field computation by CM techniques is a time-effective method to compute the radial and tangential field components, but it generally neglects the effect of saturation. Findings - This paper presents a method to re-parameterize the CM approach by single FE computations so as to consider saturation in the model over a wide operation range of the electrical drive. Practical implications - The proposed method is applied to a surface permanent magnet synchronous machine, and compared to numerical results obtained by finite element analysis (FEA). Originality/value - The paper shows that an accuracy similar to that of FE simulations can be obtained with still the low-computation time that is the characteristic of analytical models. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to describe research into the problem of creating computer structural models of magnetic microfibres. The main goal of the research is to create the universal generator of computer structural models for whole bundles of magnetic microfibres. Design/methodology/approach - The paper presents the algorithm of magnetic microfibres computer modelling. It covers both finite element method (FEM) and reluctance network method. Because microfibres with ferromagnetic grains have very complicated 3D structure, the quickest possible method was chosen. Findings - The results focus on the methodology presented in the paper which can be implemented in building 3D equivalent B/H curve of the microfibres set by use of field method - combining reluctance network method and FEM. Defining the proper magnetic B/H curves of magnetic fibres will enable the production of smart and resistant clothes. Originality/value - To date there are only measurements characteristics of B/H curve of magnetic microfibres. This paper proposes an innovatory way of determining magnetic microfibres parameters. This universal computer model allows the evaluation of the limiting value of magnetization (magnetic permeability, etc.). [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to present the plan to develop the known algorithm for thermal and electromagnetic coupled problem calculation. This is used for three-phase induction motor (IM) on nominal load. An additional purpose is verification empiric expressions of the heat transfer and equivalent thermal conductivity coefficients for external faces and air zones in analysed motor taken from literature. Design/methodology/approach - The numerical investigations proposed in this paper are based on 3D finite element models for thermal and electromagnetic fields analysis. Electromagnetic analysis includes iron core losses. It gives additional heat sources to thermal analysis. Heat transfer and equivalent thermal conductivity coefficients are assessed applying empiric expressions. Thermal model is experimentally validated. Findings - The results of calculations and experimental test shows that heat transfer coefficient for external zones taken from literature does not guarantee the equal accuracy of the distribution of the temperature in all volume of the machine. Research limitations/implications - Taken from literature, empirical equations do not give correct values of heat transfer coefficient. It states ways to go further in the evaluation of heat transfer coefficients. Originality/value - This paper presents modelling methodology of 3D transient thermal field coupled with electromagnetic field applied in three-phase IM at rated load conditions. [ABSTRACT FROM AUTHOR]

Purpose - This paper aims to present the plan to develop the known algorithm for thermal and electromagnetic coupled problem calculation. This is used for a one-phase induction motor with locked rotor for nominal and lowered voltage excitation values. It also aims to prepare a calculating method for the average heat transfer coefficient for natural convection from the induction motor housing external face. Design/methodology/approach - The numerical investigations proposed are based on 3D finite element models for thermal and electromagnetic fields analysis and 3D volume element model for average heat transfer coefficient calculations. The thermal model is experimentally validated. Findings - The paper provides a numerical method to calculate average heat transfer coefficient for the induction motor housing external faces. This coefficient is shown as a temperature function. Temperature variations in the various parts of the induction motor with locked rotor are calculated. The calculation results are compared with the measurement results. Research limitations/implications - The average heat transfer coefficient is calculated for a limited range of temperature and for the natural convection case. Electromagnetic field analysis does not include losses in the motor core. These losses could be included in the thermal and electromagnetic fields coupled calculation problem as an additional heat source for the thermal field. Originality/value - The paper presents a 3D transient thermal field and electromagnetic field coupled problem and proposes a method for calculating the average heat transfer coefficient of natural convection from the housing external face of the induction motor with a locked rotor. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is an accurate computation of eddy currents in laminated media with minimal computer resources. Design/methodology/approach – Modeling each laminate of the laminated core of electrical devices requires prohibitively many finite elements (FEs). To overcome this restriction a higher order multi-scale FE method with the magnetic vector potential A has been developed to cope with 3D problems considering edge effects. Findings – The multi-scale FE approach facilitates an accurate simulation of the eddy current losses with minimal computer resources. Numerical simulations demonstrate a remarkable accuracy and low computational costs. The effect of regularization on the results is shown. Practical implications – The eddy current losses are of great interest in the design of electrical devices with laminated cores. Originality/value – The multi-scale FE approach takes also into account of the edge effects in 3D. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose an efficient numerical simulation tool based on FEM, by which the EMC shielding effect characteristics of power cables can be predicted in the 30-1,000 MHz frequency range, as if it would be measured by the absorbing clamp method. Design/methodology/approach – The simulation method is based on decomposition: a 2D axisymmetric RF FE model is used for describing the whole measurement set-up, while a 3D quasi-static FE model is used for the symmetry cell of the shielding layer in order to capture the effect of its fine geometric details. Findings – Comparison with real measurements shows that the shielding characteristics can be reliably predicted this way, with some deviation in the low end of the frequency range though. Practical implications – This simulation tool can be applied in the design and optimization of braided cable shields to be used in the automotive industry. Originality/value – Two numerical models are coupled by the novel concept of "equivalent shielding layer", which is obtained by homogenization. [ABSTRACT FROM AUTHOR]

Purpose – The paper seeks to present a methodology of computer simulation of coupled magneto-thermo-mechanical processes in various electrical engineering devices. The methodology allows determining their parameters, characteristics and behaviour in various operation regimes. Design/methodology/approach – The mathematical model consisting of three equations describing magnetic field, temperature field and field of mechanical strains and stresses (or thermoelastic displacements) is solved numerically, partially in the hard-coupled formulation. Findings – The methodology seems to be sufficiently robust, reliable and applicable to a wide spectrum of devices. Research limitations/implications – At this stage of research, the hard-coupled formulation of thermo-mechanical (or thermoelastic) problems is still possible only in 2D. Practical implications – The methodology can successfully be used for design of numerous machines, apparatus and devices from the area of low-frequency electrical engineering ranging from small actuators to large synchronous generators. Originality/value – Complete numerical analysis of coupled magneto-thermo-mechanical phenomena in electrical devices. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to present the dependence of the level and harmonic structure of the cogging torque in permanent magnet synchronous motors (PMSM) to interlocks and notches in a stator back iron, which are standard methods for stator lamination stacking in mass-production. Design/methodology/approach - Methods of stacking up the lamination like welding or interlocking are introducing magnetic asymmetries in stator back iron which causes additional harmonic components (AHC). A finite element method and Fast Fourier transform were used to calculate cogging torque harmonic components (HC) with regard to the applied number and positions of interlocks and notches. All simulation results were verified by laboratory tests. Findings - It has been established and proved that technologies for stacking lamination packs cause local saturation peaks in back iron which give rise to additional cogging torque AHC and consequently increase the total cogging torque. It is also shown that the magnetic properties of interlocks cannot be simply considered as air regions but adequate relative permeability of such affected soft magnetic material must be determined to improve the accuracy of FEM calculations. Practical implications - Considering presented results, it is possible to foresee which AHC will include the cogging torque of mass-produced PMSMs due to the stator lamination stacking methods. In this way, the optimal stacking method can be selected in order to minimize the effect of AHC. Originality/value - So far, authors dealing with the cogging torque have not taken into account the influence of the stator lamination stacking method on the level of torque oscillations. [ABSTRACT FROM AUTHOR]