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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]

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]

• 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]

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]