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Magnetics, IEEE Transactions on

Issue 2 • Date Mar 1992

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Displaying Results 1 - 25 of 202
  • A general method for electric and magnetic coupled problem in 2D and magnetodynamic domain

    Page(s): 1291 - 1294
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    The authors present a novel formulation which allows the inclusion of the circuit equations in the finite element analysis in two dimensions. Two types of magnetic conductors are considered: massive conductors which can develop eddy currents and `fine wire' without eddy current. Kirchhoff's voltage and current equations have been established for these conductors in accordance with magnetic equations. Furthermore, these conductors have been integrated into an external electric network. This formulation allows the solution of two-dimensional magnetic problems with all kinds of electric connections between conductors, which consist of impedances (R, L, and C) fed by sinusoidal sources. The modeling of an asynchronous machine with a squirrel cage (with simulation of end rings) is given to illustrate one application of the formulation View full abstract»

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  • A non-linear coupled 3D model for magnetic field and electric circuit equations

    Page(s): 1295 - 1298
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    The authors propose a 3-D numerical model in which the magnetic field and electric circuit equations in the absence of eddy currents are solved simultaneously. To consider the magnetic equations, use is made of a magnetic vector potential formulation with the gauge condition (A.w=0) which makes it possible to reduce the number of unknowns. To take into account the magnetic and electric nonlinearities, the Newton-Raphson algorithm has been used. Two applications have been considered: an iron core coil fed by sinusoidal voltage through a diode and a current transformer. For the latter example the results obtained from the simulation are compared with experimental ones View full abstract»

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  • Three-dimensional model of one- and three-phase transformer for leakage field calculation

    Page(s): 1344 - 1347
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    A simplified model of a small one- and three-phase transformer for simulation of the space-distribution of the leakage field outside the magnetic core is presented. The transformer windings with rectangular cross-section are enclosed in a parallelepiped area of calculation. The authors use the finite difference method with procedures based on the fast Fourier transform. For numerical calculation, the program package FISHPAK for an IBM PC is adopted. The model may be used for simulation of the leakage field taking into account magnetic screens in which the eddy-current reaction is omitted View full abstract»

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  • A method for circuit connections in time-dependent eddy current problems

    Page(s): 1299 - 1302
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    The authors consider eddy current diffusion problems in which the electromagnetic field is computed in 2-D but external circuit connections, between the conductors with eddy currents are taken into account. The approach combines conventional circuit analysis techniques with the integro-differential finite element formulation of the transient eddy current problem. Conductors with eddy currents are treated as circuit elements with terminal voltages implicitly defined by the field equations. A numerical example is presented to illustrate the proposed formulation View full abstract»

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  • Eddy-current imaging of buried cracks, by inverting field data

    Page(s): 1336 - 1339
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    A novel method for imaging flaws, based on the inversion of eddy-current data, has been demonstrated. A thin subsurface slot was manufactured in an aluminum plate. Oscillating current was injected into the plate, and the magnetic field was sampled with a Hall transducer scanned over the blind face. An integral operator defines an analytical relationship between the distribution of electric dipoles excited on the slot faces and the scattered field. The relationship was inverted using singular value decomposition to obtain the dipole density as a representation of the slot in the form of an image. Enhanced spatial information on the flow may be obtained by performing the inversion at several individual frequencies, and constructing a composite image View full abstract»

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  • Boundary element analysis of 3-D magnetostatic problems using scalar potentials

    Page(s): 1099 - 1102
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    A boundary element formulation for 3-D nonlinear magnetostatic field problems using the total scalar potential and its normal derivative as unknowns is described. The boundary integral equation is derived from a differential equation for the total scalar potential where a nonlinear operator term can be separated from a linear term. The nonlinear term leads to a volume integral which can be treated as a known forcing function within an iterative solution process. An additional forcing term results from the magnetic excitation coil system. It is shown that the line integral of the magnetic source field which can be defined outside of the current-carrying regions as a gradient of a scalar potential acts as an excitation term. The proposed method is applied to a test problem where an iron cube immersed in the magnetic field of a cylindrical coil is investigated. The numerical results for different saturation stages are compared with finite element method (FEM) calculations. The comparison with FEM calculations shows a good agreement only in highly saturated iron parts View full abstract»

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  • Factors influencing the need for upwinding in two-dimensional field calculation

    Page(s): 1611 - 1614
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    Numerical simulations have been conducted in an attempt to clarify some of the findings of previous work on the necessity of upwinding in the finite element analysis of electromagnetic problems that involve relative motion. The results presented demonstrate that, besides the Peclet number, the stability of the finite element solution also depends on the boundary conditions of the problem and the magnetic characteristics of the moving conductor. When the moving conductor is nonferromagnetic and a periodic boundary condition is imposed, a Galerkin method can model the problem successfully. Whenever numerical oscillation is exhibited, the upwind finite element scheme can be used to solve the problem. In a 3-D model where the biconjugate gradient solver is the most economical, and often the only, choice of solver to use, upwinding may be necessary to ensure convergence View full abstract»

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  • Three-dimensional eddy current analysis by the finite element method with integral equations using T

    Page(s): 1150 - 1153
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    The finite-element method with integral equations is used to calculate the current vector potential defined in conductors and the total scalar potential in magnetic bodies. The eddy current and the magnetization can be obtained from the potentials T-Ω. After that, the magnetic field at an arbitrary point can be calculated by the integral equations. Results of standard models specified by the IEE of Japan for magnetostatic and eddy current analysis suggest the validity of the method View full abstract»

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  • Some applications of the boundary element method to high-voltage discharge devices

    Page(s): 1501 - 1504
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    An extensive boundary element method code has been developed to calculate Laplacian field distributions in axially symmetric, multielectrode, multidielectric systems and extended to cases where space charges produced by the developing discharge are sufficiently large to distort the applied field. Experience with using these codes to evaluate surface fields and to model discharge development is reported View full abstract»

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  • Coupling of a nonlinear diffusive electromagnetic system to a linear electric circuit

    Page(s): 1307 - 1310
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    A composite electromagnetic system that includes a nonhysteretic ferromagnetic conducting body and a linear resonant circuit fed by a sinusoidal voltage source is studied. The diffusion of the magnetic field in the iron core inductor is described by means of a finite-dimensional nonlinear dynamic system obtained by applying the Galerkin method. These equations are coupled with the circuit ones. This physical system might exhibit different nonlinear phenomena: multiple periodic oscillations and even apparently completely disordered aperiodic chaotic motions. Multiple harmonic and subharmonic oscillations are investigated by computer-aided analysis using a static method View full abstract»

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  • Solutions of three-dimensional multiply connected and open boundary problems by BEM in three-phase combination transformers

    Page(s): 1340 - 1343
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    A boundary element method (BEM) in terms of magnetic vector potential and electric scalar potential is successfully applied to three-dimensional, multiply connected, and open boundary problems caused by the heavy current of leads in a three-phase combination transformer. The quasi-frontal method is employed for the solution of the set of equations with asymmetric and full coefficient matrix. At most a quarter of the whole matrix needs to be stored. The numerical results are compared with experimental values and show very good agreement. Corrective measures for reducing the losses and preventing the box from locally overheating are presented View full abstract»

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  • Calculating stray losses in power transformers using surface impedance with finite elements

    Page(s): 1355 - 1358
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    The authors describe the results obtained from a rarely published method of calculating eddy losses in thick conducting materials. The surface impedance formulation is used in a finite element software package which is applied in turn to the design of large power transformers. The transformer and model details are discussed, as are the excellent results obtained by employing these techniques. The authors then discuss the further application of these methods and their implications for transformer design. The transformer tank wall and fittings can be modeled accurately with surface elements, removing the need for complex layers of brick elements to account for skin effects, and this in turn reduces the complexity and size of the models. This method thus yields the advantages of reduced complexity, which is especially important in the analysis of very large devices such as three-phase transformers View full abstract»

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  • Linear finite element method in axisymmetric magnetostatic problems

    Page(s): 1107 - 1110
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    If there is a long iron cylinder on the axis of rotational symmetry, the FEM (finite element method) with linear shape function for the computation of the angular component of the vector potential yields an incorrect solution. Based on a suitable weight factor in the expression for the z component of the flux density, new formulas for the coefficients of the linear equations have been derived, which give correct answers View full abstract»

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  • Comparison of coordinate systems for eddy current analysis in moving conductors

    Page(s): 1186 - 1189
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    The moving and fixed coordinate systems for eddy current analysis with moving conductors are examined and compared. It is shown that the moving coordinate system is superior for transient analysis from the standpoints of accuracy, computer storage, and CPU time. In DC steady state analysis of large Peclet number, spurious oscillations occur when using the fixed coordinate system with the ordinary Galerkin finite element method. The solution using the moving coordinate system, however, can be obtained stably View full abstract»

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  • Prediction of thrust forces in tubular induction machines

    Page(s): 1375 - 1377
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    Standstill forces on tubular induction machines are calculated by two methods: a simple one-dimensional technique and a two-dimensional axisymmetric finite element analysis. The end effect force produced by the finite length of the machine is calculated. The work is confirmed by tests taken on a practical machine View full abstract»

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  • Modelling voltage forced coils using the reduced scalar potential method

    Page(s): 1615 - 1618
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    The disadvantage of modeling voltage forced coils using the magnetic vector potential is that the structure of this coil must be meshed, and the coil region must be modeled using three variables per node. A scheme based on the method of modeling current sources using a reduced scalar potential is presented. The current becomes an unknown, and an expression for the terminal voltage is derived. This technique removes the difficulties of meshing the source coils. The scheme has been incorporated into the finite element package MEGA and has been used to model actuators under voltage forced conditions with saturating iron components and eddy currents View full abstract»

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  • Numerical calculation of the non-linear dynamic process in electromagnetic devices

    Page(s): 1252 - 1254
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    A direct coupling model is developed that can be used in analyzing the two-dimensional nonlinear transient magnetic field in electromagnetic devices excited by a voltage source. The relevant numerical method is presented for calculation of the dynamic characteristic of the devices. In the method, mechanical movement, eddy currents, exciting electric circuit, and the nonlinear problem of the magnetic material are taken into account. The direct coupling method is used for solving the transient magnetic field. The numerical technique that modifies the nonsymmetric coefficient matrix to a symmetric and banded one with edges has considerably reduced the computer memory capacity needed and the CPU time. An example of an application is given for a brake electromagnet system View full abstract»

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  • An economic solution for 3D coupled electromagnetic and thermal eddy current problems

    Page(s): 1267 - 1270
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    A technique for the analysis of 3-D coupled electromagnetic and thermal problems is presented that makes use of the surface impedance technique for modeling solid, eddy-current-carrying conductors to substantially reduce the problem size. In particular cases, the electromagnetic and thermal problems can then be posed in separate domains, linked by their common surface. The application of this method to the calculation of the rotor surface temperature of a solid pole synchronous generator under negative-sequence fault conditions showed satisfactory agreement with test measurements View full abstract»

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  • Application of eddy current formulations to magnetic resonance imaging

    Page(s): 1517 - 1520
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    The calculation of 3-D radio-frequency (RF) fields with the aid of an eddy current formulation based on finite elements is described. It is shown that the displacement current density in the first Maxwell equation can be taken into account by making the conductivity a complex quantity. The validity of this formulation has been verified by calculating a conducting sphere influenced by a homogeneous time-harmonic RF field. The numerical results are compared with an analytical solution. The formulation described has been applied to calculate a 3-D phantom with regions of different conducting materials. For this phantom, measured results obtained by magnetic resonance imaging are compared View full abstract»

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  • The modelling of segmented laminations in three dimensional eddy current calculations

    Page(s): 1122 - 1125
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    A formulation is presented for the inclusion of segmentation effects in a three-dimensional eddy current model of large laminated iron cores. The model has been developed for the study of eddy currents induced in the end laminations of turbogenerator stator cores. It includes magnetic nonlinearity and represents the overlapping pattern which occurs between successive lamination layers by introducing multiple electric vector potentials directed normal to the laminations. Such a formulation has permitted study of the segmentation effect without explicitly modeling each lamination layer, an impractical proposition in terms of the discretization required. Results have demonstrated that the overlapping of successive segment layers has a very substantial influence upon the eddy current distribution in the stator core back. For the open-circuit condition a reduction in total core loss of over 30% is calculated to occur due to the presence of segmentation and third lapping View full abstract»

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  • Automated optimal design techniques for inverse electromagnetic problems

    Page(s): 1549 - 1552
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    Two methods are considered for the solution of automated digital optimal design problems. The computer procedures based on these methods have been implemented and tested. The first method, based on a deterministic approach, considers a quadratic approximation of the cost function. The second, based on a stochastic approach, is derived from the simulated annealing algorithm. Both methods, implemented as computer codes, have been applied to the solution of a test synthesis problem where the magnetic field is generated by discrete coils. The deterministic method is substantially faster, especially when the calculation of the cost function is time consuming. On the other hand, the stochastic method gives good approximation of the global minimum independently of the initial conditions: as far as CPU time is concerned, the method is more expensive, but can be profitably used when the cost function can be calculated quickly and the number of design variables is large View full abstract»

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  • Eddy currents benchmark analysis in ITER

    Page(s): 1505 - 1508
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    The authors present the results of a benchmark analysis among different computational methods used to solve the problem of the eddy current circulation in the conductive structures of a tokamak. The scope of the work, which was carried out in the framework of the ITER (International Thermonuclear Experimental Reactor) conceptual design activities, was to gain knowledge on the approximations due to the geometric descriptions and solution methods in the evaluation of the electromagnetic effects. The benchmark analysis was performed using one simplified axisymmetric model, one 3-D shell finite elements code, and one fully 3-D finite elements code (EC). The results reported include global parameters, such as the total circulating current, ohmic power dissipated, and the forces on the structure or on parts of it, and local values of the current density. The results of the analysis show that there is a significant difference in the results of 3-D shell and fully 3-D codes. The obvious reason is the additional degrees of freedom described in the fully 3-D codes, thus taking into account additional possibilities for the eddy current flow View full abstract»

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  • 3D eddy current computation in the frequency domain regarding the displacement current

    Page(s): 1801 - 1804
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    The application of the FIT (finite integration theory) method to the problem of 3D eddy current computation is presented. Fields are treated in terms of E&oarr; and B&oarr;; the excitation is represented by time harmonic currents. Materials can be anisotropic with real ∈, μ, and κ. The displacement current is taken into account, and thus high-frequency eddy current problems can be treated as well as the case where there are no conductive regions (e.g. air coils). For nonconductive regions the additional condition div D=0 is imposed View full abstract»

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  • Global optimization methods for computational electromagnetics

    Page(s): 1537 - 1540
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    Both higher-order (pseudo)deterministic and zeroth-order probabilistic optimization methods have been analyzed and tested for solving the global optimization problems arising in computational electromagnetics. Previously recommended, but seemingly independent schemes (evolution strategies, simulated annealing, Monte Carlo iteration) have been unified into a robust general method: the global evolution strategy (GES). Regularization techniques, the stability of solutions, and nonlinear phenomena are shown to be topics closely related to global optimization and inverse problems. The speed of convergence is evaluated for different optimization methods. A real-world application (from nuclear magnetic resonance and magnetic resonance imaging) demonstrates the favorable behavior of GES in the context of the finite element method View full abstract»

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  • Edge-element computation of the force field in deformable bodies

    Page(s): 1263 - 1266
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    The author presents an edge-element method (h-formulation) for the computation of force fields in full generality: deformable bodies, nonlinear b-h laws, and the presence of magnets. It gives not only integrated quantities such as resultant or torque, but also local force. The main ingredients are: (1) a Langrangian approach (`co-moving' mesh and Maxwell equations expressed in `material' form); (2) the virtual work principle (force as the derivative of coenergy with respect to configurations), and (3) edge-based degrees of freedom, which can be interpreted as magnetomotive forces along the edges View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology