Abstract
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.
Highlights
The role of grain-oriented (GO) steel sheets in the transmission and conversion of the electrical energy is increasingly challenged by novel applications, such as those enforced by the emerging “smart grid” technologies, the related medium-to-high frequencies conversion devices, and the development of efficient low-noise rotating machines.1,2 Comprehensive knowledge of the material behavior, going beyond the usual assessment and implementation in the machine design of the properties measured along the rolling direction (RD), is appreciated in the engineering practice
The interpretation of the quasi-static and dynamic energy losses in the GO sheets and their dependence on angle θ and sample geometry starts from the determination of the J180(t) and J90(t) behaviors, like the ones observed in Figs. 5, 7, and 8, and their assumed relationship with the known behavior of the losses in the RD and Transverse Direction (TD) strips
We have discussed and assessed the anisotropic behavior of the magnetization process and energy losses in high-permeability grain-oriented Fe–Si sheets. This is done through the combination of magnetic measurements from 1 to 300 Hz, magneto-optical observations, and physical assumptions regarding the dw processes and their dependence on the cutting angle of the tested strip samples
Summary
The role of grain-oriented (GO) steel sheets in the transmission and conversion of the electrical energy is increasingly challenged by novel applications, such as those enforced by the emerging “smart grid” technologies, the related medium-to-high frequencies conversion devices, and the development of efficient low-noise rotating machines. Comprehensive knowledge of the material behavior, going beyond the usual assessment and implementation in the machine design of the properties measured along the rolling direction (RD), is appreciated in the engineering practice. Small and medium power rotating machines with cores built of shifted non-segmented GO sheets are shown to exhibit low reactive power and low loss.9 Faced with these excellent perspectives in applications, the theoretical treatment of the magnetization process and losses and their evolution with the direction of the field in the lamination plane are typically limited to experiments made on conventional Epstein strips cut at different angles with respect to the Rolling Direction (RD).. We identify, for a generic angle θ, the contribution to the magnetization reversal provided by the 180○ dw displacements, occurring within the [001] phases, and by the motion of the 90○ dws, responsible for the growth/shrinkage of the [100] and [010] phases, in balance with the [001] ones This amounts, in practice, to determine the loss components obtained by separate measurements on the RD and TD strips as a function of Jp and f and composing them, by virtue of their geometry-independent character, through a simple set of linear equations. Certain simplifications regarding the actual domain structure and its evolution with Jp, f , and θ are assumed in the model (e.g., single crystal approximation and absence of supplementary flux-closing domains), the identified magnetization mechanisms are shown to provide quantitative interpretation of the anisotropic behavior of the material
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