Account Eddy Currents Research Articles

Simulation of Magnetic Measurements on the T-15MD Tokamak Taking into Account Eddy Currents in the Vacuum Chamber

Simulation of Magnetic Measurements on the T-15MD Tokamak Taking into Account Eddy Currents in the Vacuum Chamber

Equivalent Scheme of the Fuel Cell Taking into Account the Influence of Eddy Currents and A Practical Way to Determine Its Parameters

The aim of this work is to develop a dynamic equivalent scheme of the fuel cell, taking into account eddy currents in the conductive parts of the structure, to offer a practical way to determine the parameters of this circuit and also to show the adequacy of the scheme and parameters by numerical simulation and comparison with experiment. Fuel cells, as a rule, are connected to the voltage converters, which create a high-frequency component of the main fuel cell current and eddy currents in the conductive parts. The problem is that the effect of these currents on the characteristics of the fuel cell-based power plants has not been studied. To determine the parameters of the proposed equivalent scheme, we use experiments and calculations of transient modes of the fuel cell. The main result of the work is the possibility and feasibility of calculating circuits with fuel cells, taking into account the influence of eddy currents. This effect depends both on the design of the fuel cell and on the parameters of the circuit to which it is connected. From this it follows that, in general, it is necessary to take into account the influence of eddy currents of the fuel cell. The refusal of this accounting is possible, but in each specific case it must be justified.

Numerical modelling of magnetic characteristics of ferrite core taking account of both eddy current and displacement current

In the magnetic field analysis of magnetic devices using a ferrite core, such as a pulse transformer, the frequency-domain analysis is often carried out using the measured complex permeability under different frequency range. However, the nonlinear magnetic characteristics cannot be considered in the frequency-domain analysis because of the harmonics caused by it cannot be represented. The nonlinear magnetic characteristics can be considered in the time-domain analysis, but suitable constant conductivity and permittivity taking account of the microstructure of ferrite core, which can represent the measured complex permeability under different frequencies, needs to be investigated for the time-domain analysis. In this paper, the effective permeability of a toroidal ferrite core is tried to be demonstrated by using the linear ac steady state magnetic field analysis taking account eddy currents and displacement currents. It is shown that the measured permeability can be realized roughly by using the modified constant conductivity and permittivity. The nonlinear time-domain magnetic field analysis can be carried out using the modified constant conductivity and permittivity obtained from this paper.

Electromechanical Numerical Analysis of an Air-Core Pulsed Alternator via Equivalent Network Formulation

In this paper, the numerical analysis on an air-core pulsed alternator is presented. Since compulsators are characterized by very fast electromechanical transients, their accurate analysis requires strong coupling between the equations governing the electrical and the mechanical behaviors. The device is investigated by using a dedicated numerical code capable to take into account eddy currents, compensating windings, as well as the excitation/control circuits. Furthermore, the code is capable of modeling centrifugal forces and vibrations acting on the shaft due to electric and mechanical unbalances or to misalignments of the shaft from its centered position. This makes the code a very powerful tool during the design phase. Examples of application of the code to machines with nonuniform compensating shield and with shorted compensating windings are shown.

Technique of the Choice of Parameters of Regulators of the Electromagnetic Bearing Taking Into Account Eddy Currents

Technique of the Choice of Parameters of Regulators of the Electromagnetic Bearing Taking Into Account Eddy Currents

Eddy currents: A misleading contribution when measuring magnetoelectric voltage coefficients of thin film devices

Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) magnetoelectric (ME) thin films were deposited on Pt/TiO2/SiO2/Si substrate. The ME voltage coefficient αHME was determined at room temperature using a lock-in amplifier and by applying to the sample an alternating magnetic field of a few mT. Surprisingly, very similar responses were obtained from a simple commercial capacitor set in series with a small loop of wire. This allowed us first to accurately model and reproduce the frequency response of the ferroelectric PZT layer alone. We also observed that, at low frequency, the voltage across the ferroelectric capacitor and the current in the circuit did not decrease significantly when diminishing then removing, the area of the conductive loop. One major conclusion is that eddy currents in the lead wires, rather than the classical electromotive force across conductive loops, contribute significantly to the total voltage response, at least for thin film ME devices. A model taking into account eddy currents was then developed for the extraction of the true αHME. A large αHME of 4.6 V/cm.Oe was thus obtained for the Terfenol-D/Pt/PZT thin film device, without DC magnetic field.

Half-Order Modeling of Saturated Synchronous Machine

Non-integer-order systems are used to model diffusion in conductive parts of electrical machines as they lead to more compact knowledge models and also to improve their precision. In this paper, a linear half-order impedance model of a ferromagnetic sheet deduced from the diffusion of magnetic field is briefly introduced. Then, from physical considerations and finite-element simulation, the nonlinear half-order impedance model of a ferromagnetic sheet is proposed, taking into account both saturation and diffusion effects. Next, it has been proved that this model can be successfully included in the equivalent circuits of a synchronous machine (SM), taking into account eddy currents in massive parts of the rotor or damper bars and of small-signal saturation. The new SM equivalent circuit is validated by stand-still frequency response tests performed on the solid salient-pole SM of 125 kVA for variable field excitation conditions. An example of the SM transfer function computation in relation to different magnetization levels indicates the usefulness of this modeling approach for robust control issues.

FEM/BEM Hybrid Method for Magnetic Field Evaluation Due to Underground Power Cables

This paper is a contribution to the evaluation of electromagnetic fields due to underground power cables. Open boundary 2-D problems may be treated combining the finite element method (FEM) inside a region surrounded by a regular (cylindrical) fictitious surface with a semi-analytical boundary element method (BEM) to describe the field outside this region. For the outside region, a generalization of Pollaczek's solution is applied, taking into account eddy currents in the soil and the proximity effect between the soil/air plane surface and the cylinder fictitious surface with finite radius. The method is validated by using typical underground power cables where analytical methods may be applied accurately.

Optimal Structure of Magnetic and Conductive Layers of a Magnetically Shielded Room

Although the method of optimal design of magnetically shielded rooms (MSRs) for dc magnetic noise seems to be well established, that for ac magnetic noise at a frequency range from 0.01 to 1 Hz is also required for measurements of extremely weak magnetic fields such as biomagnetic measurements. However, such a method cannot easily be established due to eddy current effects. In order to establish an optimal design method of an MSR for low frequency ac magnetic noise, we have investigated an optimal structure of the magnetic and conductive layers using three-dimensional (3-D) linear magnetic field analysis taking into account eddy currents. We show why a structure which sandwiches the conductive layer between double magnetic layers gives high shielding effect. Moreover, we found that the spacing between the layers does not affect the shielding effect for ac magnetic noise. This is useful knowledge from the standpoint of MSR production

A transformer model based on optimized Cauer circuits

A transformer model is presented where both winding and core were modeled by Cauer circuits in order to take into account eddy currents. The physical property of the magnetic circuit allowed the insertion of a hysteresis model. Thermal effects in the winding insulation were also modeled by a Cauer circuit. The discretization of the circuits was optimized by an iterative method that fits the reluctance of a core part or the impedance of a winding layer to known analytical solutions. This reduced the number of required circuit elements substantially and the accuracy was increased.

Macroscopic fields in thin ferromagnetic sheets taking into account eddy currents and Landau–Lifshitz magnetization

The paper deals with a numerical model for the evaluation of the electromagnetic behavior in thin magnetic sheets. Therefore, we consider Maxwell's equations together with a nonlinear magnetic constitutive law described by the Landau–Lifshitz equation. We present a suitable numerical approximation based upon a finite element-finite difference method. At each time step in the numerical scheme, the magnetization dynamics is calculated analytically by introducing for each finite element node a transformation towards a local coordinate system.

CMS coil thermal shields final design

The Compact Muon Solenoid (CMS) is one of the detectors that is under construction in the framework of the Large Hadron Collider (LHC) project at CERN. The design field of the CMS magnet is 4 T in a 6 m diameter and 12.5 m long bore leading to a stored energy of 2.7 GJ. The coil cryogenic system is designed to cool the thermal shields by helium gas at 60 K and protect the cold mass at 4.5 K from the thermal radiation. The thermal shield design must take into account cryogenics, eddy currents, mechanical and realization considerations. This paper presents a detailed analysis of the eddy currents induced in the thermal shield, using a variational formulation of the problem in terms of the electric vector potential and a finite element method. The thermal and mechanical design are then described.

3-D finite element analysis of a linear induction motor

This paper presents the thrust characteristics analysis of linear induction motors (LIMs) using the 3-D finite element method (3-D FEM) with edge elements taking into account eddy currents. LIMs have advantages of simple structure, easy maintenance, less environmental pollution and so on. Therefore, they are widely used for high speed transport systems in clean rooms and hospitals. However, it is difficult to analyze the thrust characteristics of LIMs numerically because of the three dimensional shape. In this paper, we calculate the thrust of a LIM using the 3-D FEM. It is clarified that the validity of the 3-D FEM by comparison of the calculated and measured results.

Thrust Analysis of Permanent Magnet Linear Synchronous Motor Using 3-D Finite Element Method

Permanent magnet linear synchronous motors are widely used in the linear drive systems. For the optimum design of linear motors, it is necessary to obtain the thrust characteristics accurately. In this paper, we calculate the thrust characteristics of a Surface Permanent Magnet Linear Synchronous Motor (SPM-LSM) using the 3-D finite element method taking into account eddy currents in the cores, and the results are compared with the 2-D calculated and the measured ones. Consequently, it is clarified that the 3-D finite element analysis is very useful to obtain the thrust characteristics of the SPM-LSM.

Principle of a multi-load/single converter system for low power induction heating

The induction heating appliances used for cooking generally include two or four inductors and in the most common solution, a converter is connected to each inductor. The main aim of this paper is to suggest a way of building a multi-load/single converter system, based on the use of a series-resonant ZVS inverter supplying several resonant loads. The principle can be probably extended to different applications (DC-to-DC converters, high power induction heating applications) but their study has been restricted to a low power induction heating context. In order to make this study, suitable models for the loaded inductors had to be found. Therefore, in the first part of this document, a number of different electrical inductor models, from the basic L-R equivalent circuit to a representation taking into account eddy currents effects, are presented. The second part describes the multi-load operating principle with respecting ZVS conditions, by the analysis of an R-L inductor model. Finally, the third part completes this work with simulations, including a more realistic model of the inductors and the associated experimental validation. These emphasize the interest of this original system that is currently being evaluated for an industrial application.

Dynamic analysis of linear actuator taking into account eddy currents using finite element method and 3-D mesh coupling method

The dynamic analysis of a linear actuator, taking into account eddy currents using the finite element method (FEM) and a 3-D mesh coupling method, is presented. The finite element mesh is constructed using the 3-D mesh coupling method at each position of the actuator. After the mesh coupling, the magnetic field analysis is performed. Since the mesh of the actuator, which has conductivity, is not changed by the mesh coupling, the transient FEM is directly applicable to the problem. Computed results confirm the efficiency of this method.

Ultrafast laser diagnostics and modeling for high-speed recording heads

A comparison of experiment and modeling in high-speed recording heads is given from study of the dependence of flux rise times on yoke lengths. A brief overview is given of optical methods for characterizing the response of devices and materials for high data rate recording. Several abilities of the technique and, in particular, measurements of current and flux rise times on high-speed writers are presented. A micromagnetic model that takes into account gyromagnetic effects and eddy currents gives calculations that agree well with experimental data. Flux rise times are found to decrease with shorter yoke lengths for both unlaminated and laminated heads for a current rise time of 0.8 ns.

Magnetic field analysis of coupling transformers for electric vehicle using 3-D finite element method

The 3-D analysis is useful for the optimum design of high frequency coupling transformers which have complex structures. It is difficult to predict the current distributions taking into account eddy currents in sheet coils. In this paper, the current density vector analysis and the magnetic field analysis taking into account eddy currents in the spiral sheet coils are coupled. The exciting current characteristics and copper loss are calculated by our method. It is shown that the load characteristics can be accurately calculated by comparison with measurements. The copper loss distributions taking into account eddy currents in the coils are also shown quantitatively.

Numerical analysis of axial magnetic field acting on the arc in vacuum circuit breakers by 3-D finite element method taking into account eddy currents

It is necessary for the optimum design of vacuum circuit breakers with axial magnetic field electrodes to analyze the residual magnetic field between the contacts in vacuum chambers at the instant when the arc current becomes zero. The residual magnetic field is generated by the eddy currents flowing in the electrodes. In this paper, the residual magnetic field is obtained by using a 3-D finite element analysis taking into account eddy currents. It is shown that the eddy currents are greatly influenced by the configuration of the electrodes, for example the number of slits in the contacts.

Numerical analysis of electromagnetic forces in low voltage AC circuit breakers using 3-D finite element method taking into account eddy currents

It is necessary for the optimum design of low voltage circuit breakers to analyze electromagnetic forces acting on the contact systems when the circuit breakers interrupt fault currents. In this paper, the forces which are known as the magnetic blowout force acting on the arc and the electromagnetic repulsion force acting on the moving contact arm are obtained by using the 3-D finite element analysis taking into account eddy currents. It is shown that our 3-D analysis is capable of evaluating a new design of contact systems in low voltage ac switching devices.