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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 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 – 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]