Search

The effect of plastic strain on magnetic behaviour was studied earlier by many authors. These studies mainly focused on plastic straining obtained by tensile testing and on magnetic measurement along the tensile axis. We present in this paper some new results showing the influence of a plastic shear strain obtained thanks to a torsion test on the magnetic behaviour of a pure iron. These results highlight the dominant role of the cumulative plastic strain on the magnetic behaviour. • A pure iron is subjected to plastic shear strain obtained from a torsion test. • Plastic shear strain leads to a degradation of magnetic properties similar qualitatively to plastic tensile strain. • Magnetic behaviour depends only on the cumulative plastic strain. • A two-phase model shows that residual stresses, even though existing, have no effect on magnetic behaviour. [ABSTRACT FROM AUTHOR]

• Broadband investigation (1 Hz-10kHz) on the loss properties and domain dynamics on HGO Fe-Si. Role of the sheet thickness (conventional 0.29 mm vs. novel 0.18 mm thick laminations). • Fluxmetric measurements of hysteresis loops and losses are associated with dynamic high-speed Kerr imaging of the domain structure. • Modeling of loss versus frequency made by keeping into account deep skin effect. • The dynamic response of the array of 180° dws is treated starting from the concept of dw bowing. The dw configuration along the magnetization cycle and its evolution with frequency are obtained by numerical modeling. The magnetic properties of high-permeability grain-oriented (HGO) Fe-Si sheets have been investigated in the frequency range 1 Hz-10 kHz, with attention devoted to the role of thickness on the behavior of the magnetic losses and the phenomenology of skin effect. The study is focused on the wideband response of 0.174 mm and 0.289 mm thick sheets, comparatively tested at peak polarization values ranging between 0.25 T and 1.7 T. The experiments associate fluxmetric measurements with direct Kerr observations of the dynamics of the domain walls. A picture of the magnetization process comes to light, where the dynamics of the flux reversal takes hold under increasing frequencies through the motion of increasingly bowed 180° walls, eventually merging at the sheet surface for a fraction of the semi-period. This effect can be consistently predicted, starting from the Kerr-based knowledge of the equilibrium wall spacing, by the numerical modeling of the motion of an extended array of 180° domain walls, subjected to the balanced action of the applied and eddy current fields, and the elastic reaction of the bowed walls. This model can be incorporated into the general concept of loss separation, by calculating the classical loss component through the solution of the Maxwell's diffusion equation under a magnetic constitutive law identified with the normal DC curve. The numerical domain wall model and the loss decomposition consistently predict that the excess loss component, playing a major role in these grain-oriented materials at power frequencies, tends to disappear in the upper induction-frequency corner. [ABSTRACT FROM AUTHOR]

Abstract: We propose a simplified dynamic hysteresis model for the prediction of magnetization behavior of electrical steel up to high frequencies, taking into account the skin effect. This model has the advantage of predicting the hysteresis loop and loss behavior versus frequency with the same accuracy provided by the Dynamic Preisach Model with a largely reduced computational burden. It is here compared to experimental results obtained in Fe-Si laminations under sinusoidal flux up to 2kHz. [Copyright &y& Elsevier]

We describe a 3-D analytical model based on formal resolution of Maxwell's equations of a permanent-magnet linear actuator, with circular-shaped magnets. We present all details of the 3-D analytical calculation for the no-load flux and then compare results obtained by this model to those obtained by 3-D finite-element analysis. The comparisons show a good agreement between the two models and so validate our analytical model. Unlike 3-D finite-element analyses, which are time consuming, the analytical models that we present in this paper are suitable for an optimization process of such a structure. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method for the calculation of the electromagnetic field in the airgap of a permanent-magnet synchronous machine is developed, so as to compute the torque of the machine. Such a work is applicable to different machine topologies (even for salient rotor ones), when a two dimensional approximation of the structure is possible. This analytical model can be useful in an optimization task. In the first part, the analytical method of the field computation is explained in detail, both for the magnet's field, and for the armature reaction field. The results are compared to finite elements analysis. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of loss evaluation in Soft Magnetic Composites (SMCs), focusing on the classical loss component. It is known that eddy currents can flow in these granular materials at two different scales, that of the single particle (microscopic eddy currents) and that of the specimen cross-section (macroscopic eddy currents), the latter ensuing from imperfect insulation between particles. It is often argued that this macroscopic loss component can be calculated considering an equivalent homogeneous material of same bulk resistivity. This assumption has not found so far clear and general experimental validation. In this paper, we discuss energy loss experiments in two different SMC materials, obtained using different binder types, and we verify that a classical macroscopic loss component, the sole size-dependent term, can be separately identified. It is also put in evidence that, depending on the material, the measured sample resistivity and the equivalent resistivity entering the calculation of the macroscopic eddy currents may not be the same. A corrective coefficient is, therefore, introduced and experimentally identified. This coefficient appears to depend on the material type only. An efficient way to calculate the macroscopic classical loss in these materials is thus provided. [ABSTRACT FROM AUTHOR]

We present novel results on magnetic losses in soft magnetic composites (SMCs) excited with rotating field. Soft composites are very promising in electrical engineering applications, where new topologies of electrical machines with two- and three-dimensional induction loci are increasingly found. An experimental characterization of industrial SMC products has, therefore, been carried out, up to the kilohertz range, under alternating and circular flux loci, making use of a specifically designed and optimized loss measuring setup. The obtained results have been analyzed for all kinds of excitation, according to the loss separation concept, with the emphasis being placed on the relationship between the rotational and the alternating loss components. In particular, it is found that the ratio between the rotational and the alternating losses is, for any given peak induction, independent of frequency. [ABSTRACT FROM AUTHOR]

We report and discuss significant results on the magnetic losses and their frequency dependence insoft magnetic composites. Two types of bonded Fe-based materials have been characterized atdifferent inductions from dc to 10 kHz and analyzed by extending the concept of loss separation and the related statistical theory to the case of heterogeneous materials. Starting from the experimental evidence of eddy current confinement inside the individual particles, the classical losscomponent is calculated for given particle size distribution. Taking then into account thecontribution of the experimentally determined quasistatic (hysteresis) loss, the excess losscomponent is obtained and quantitatively assessed. Its behavior shows that the dynamichomogenization of the magnetization process with frequency, a landmark feature of magnetic laminations, is restrained in these materials. This results into a partial offset of the loss advantage offered by the eddy current confinement. [ABSTRACT FROM AUTHOR]

We investigate in theory and experiment the frequency dependence of magnetic losses in Grain-Oriented 0.29 mm thick high-permeability steel sheets up to 10 kHz. Such an unusually broad frequency range, while responding to increasing trends towards high-frequency regimes in applications, is conducive to a complex evolution of the magnetization process, as imposed by increasing frequencies to a non-linear high-permeability saturable material. We show that the concept of loss decomposition, supported by observations of the domain wall dynamics through Kerr experiments, is effective in the assessment of the broadband frequency dependence of the energy loss. By calculating, in particular, the instantaneous and time averaged macroscopic induction profiles across the sheet thickness through the Maxwell's diffusion equation, the classical loss component Wclass, versus frequency f and peak polarization Jp, is obtained. A simplified theoretical approach is pursued in this case by identifying the normal magnetization curve with the magnetic constitutive equation of the material. While the hysteresis loss Whyst is shown to invariably increase with frequency, the excess loss Wexc, the quantity directly associated with the eddy currents circulating around the moving domain walls, tends to vanish upon increasing both frequency and induction values. The Kerr experiments actually show that, while the oscillating 180° domain walls can adjust to the depth of the induction profile by bowing at low Jp values, the magnetization reversal at high inductions and high frequencies occurs by inward motion of symmetric fronts originating at the sheet surface, according to a classical framework. [ABSTRACT FROM AUTHOR]

Comprehensive assessment of the magnetic behavior of grain-oriented steel (GO) Fe–Si sheets, going beyond the conventional characterization at power frequencies along the rolling direction (RD), can be the source of much needed information for the optimal design of transformers and efficient rotating machines. However, the quasi-monocrystal character of the material is conducive, besides an obviously strong anisotropic response, to a dependence of the measured properties on the sample geometry whenever the field is applied along a direction different from the rolling and the transverse (TD) directions. In this work, we show that the energy losses, measured from 1 to 300 Hz on GO sheets cut along directions ranging from 0° to 90° with respect to RD, can be interpreted in terms of linear composition of the same quantities measured along RD and TD. This feature, which applies to both the DC and AC properties, resides on the sample geometry-independent character of the RD and TD magnetization and on the loss separation principle. This amounts to state that, as substantiated by magneto-optical observations, the very same domain wall mechanisms making the magnetization to evolve in the RD and TD sheets, respectively, independently combine and operate in due proportions in all the other cases. By relying on these concepts, which overcome the limitations inherent to the semi-empirical models of the literature, we can consistently describe the magnetic losses as a function of cutting angle and stacking fashion of GO strips at different peak polarization levels and different frequencies. [ABSTRACT FROM AUTHOR]

By means of a newly developed broadband measuring setup we have overcome the usual upper limit for the test frequency, around a few hundred Hz, which is encountered in the two-dimensional characterization of magnetic steel sheets at technical inductions and we have measured the rotational losses in low-carbon steels up to 1 kHz and peak induction 1.7 T. An important piece of information is thus retrieved upon a frequency range useful to predict the performance of high-speed electrical machines. Our experiments, performed on thick (0.640 mm) laminations, have brought to light the emergence of the skin effect under rotational fields. This is revealed by an abrupt deviation of the excess loss component, calculated under the conventional loss separation procedure, from its well-known linear dependence on the square root of the frequency. A simple magnetic constitutive law under rotating induction is proposed and introduced into the electromagnetic diffusion equation, which is solved by finite elements coupled to a non-linear algorithm. The classical rotational eddy current loss, largely prevalent with respect to the hysteresis and excess loss components on approaching the kHz frequencies in low-carbon steels, is then calculated in the presence of skin effect, permitting one to achieve full analysis of the rotational losses and good predicting capability upon a broad range of frequencies and peak inductions. [ABSTRACT FROM AUTHOR]

• New manufacturing procedures can produce optimized non-oriented electrical steels. • Samples of non-oriented 3% silicon steel were submitted to a 2.5% thickness reduction and heat treated. • Under increasing frequencies, the energy loss of the deformed and recovered samples becomes lower. There is increasing interest in the optimization of non-oriented electrical steels for applications under excitation frequencies above 400 Hz. We discuss in this paper the possibility of a new manufacturing procedure, where skin-pass and subsequent heat treatment for recovery are applied as the two last stages of sheet processing. Samples from a commercial non-oriented 3 wt% silicon steel were submitted to 2.5% thickness reduction and were heat treated at temperatures ranging between 600 and 850 °C for 2 h. It is shown that, although the hysteresis loss increases with plastic deformation, the excess loss decreases in such a way that under increasing magnetizing frequencies the total energy loss of the deformed and recovered sample becomes lower than in the starting material. The higher the annealing temperature the lower the frequency at which crossover of the loss curves is observed, as long as full recrystallization does not occur. It is assumed that with the dislocation structures left in the deformed and partially recovered samples one achieves a condition of increased fragmentation of the magnetization process, that is, of increased number of concurring correlation regions (Magnetic Objects). The corresponding decrease of the excess loss component can eventually overcompensate the deterioration of the quasi-static magnetic properties, leading to lower total losses. [ABSTRACT FROM AUTHOR]