Grain-oriented Steel Sheets Research Articles

Static and dynamic energy losses along different directions in GO steel sheets

Grain-oriented (GO) Fe-Si sheets are often preferred to non-oriented steels in large rotating machines, where the material response along directions different from the rolling one (RD) matters, both in terms of magnetisation curve and energy losses. The experiments show that the material properties depend in a complex fashion on the angle θ made by the applied field with respect to RD in the lamination plane, an effect that can be quantitatively interpreted in terms of evolution of the domain wall processes. It was shown that the pre-emptive knowledge of the material behaviour along RD (θ=0°) and the transverse direction TD (θ=90°) allows one to predict, under quasi-static excitation, the normal magnetisation curve, the hysteresis loop shape, and the energy loss dependence on θ in high-permeability GO sheets. The evolution of the quasi-static magnetic properties with θ has an obvious counterpart in the dynamic behaviour. In the present work we have therefore investigated, from the experimental and theoretical viewpoint, the behaviour of the magnetic energy loss W(f,Jp) versus frequency 1Hz⩽f⩽200Hz and peak polarisation (0.15T⩽Jp⩽1.6T) in high-permeability 0.29 mm thick GO Epstein samples, cut at 15° steps between RD and TD. We show that the predicting method developed for the quasi-static loss can be made general through loss decomposition and applied, in particular, to the determination of the excess loss term. This leads to a general description of W(f,Jp) as a function of the sheet cutting angle, without using arbitrary parameters.

The use of segmented-shifted grain-oriented sheets in magnetic circuits of small AC motors

AbstractIn order to increase energy efficiency of AC rotating machines, one possibility is the use of Grain-Oriented steel sheets to build stator magnetic circuits in order to reduce iron losses. After presenting the general concept considering a non-segmented-shifted sheets prototype recently developed in our laboratory, a segmented structure is introduced. Experimental comparisons between these structures are performed using static machines. The main results are analysed using Finite Element modelling that leads to extract the particular physical concepts which govern these associations.

Pragmatic Modeling of Dynamic Magnetization and Iron Loss in Grain-Oriented Steel Sheets

This paper presents the extension of two 1-D lamination models with magnetic hysteresis to reproduce dynamic hysteresis loops and power loss in grain-oriented (GO) electrical steels. For this purpose, the concept of magnetic viscosity is introduced in the model equations. The applicability and accuracy are demonstrated by means of two GO steels of different thicknesses at magnetizing frequencies up to 1000 Hz. Advantages and limits of the classical approach with and without viscosity and comparisons to measured data are discussed in detail.

Characterizing Grain-Oriented Silicon Steel Sheet Using Automated High-Resolution Laue X-ray Diffraction

Controlling texture in grain-oriented (GO) silicon steel sheet is critical for optimization of its magnetization performance. A new automated laboratory system, based on X-ray Laue diffraction, is introduced as a rapid method for large scale grain orientation mapping and texture measurement in these materials. Wide area grain orientation maps are demonstrated for both macroetched and coated GO steel sheets. The large secondary grains contain uniform lattice rotations, the origins of which are discussed.

A Description for the Anisotropy of Magnetic Properties of Grain-Oriented Steels

A methodology to evaluate the anisotropy of magnetic properties of grain-oriented steel sheets is presented. The approach is based on the orientation distribution function (ODF) theory. The existence of sheet symmetry and orthorhombic symmetry of body-centered cubic iron crystal is discussed with ODF. As a result, in order to characterize the magnetic properties, it is sufficient to carry out measurements for three directions, since the evaluated property is directly related to the magnetocrystalline anisotropy. The presented approach may be a useful tool for the designers of magnetic circuits in electrical machines.

Induction machine magnetic noise: Impact of a new stator magnetic circuit design

The main topic of this paper is to examine the impact on induction machine magnetic noise of a new stator magnetic circuit design. This new design was developed in order to increase AC machine energetic performance by assembling non-segmented shifted grain-oriented steel sheets which make it possible to reduce iron losses. Experimental results on induction machine efficiency increase are presented and justified using reluctance network simulations. An analysis, finally, shows and explains how this structure behaves considering acoustic magnetic noise in a Pulse Width Modulation supply case.

Texture measurement of grain-oriented electrical steels after secondary recrystallization

The measurement of the final Goss texture sharpness in grain-oriented electrical steels is a challenging task due to the immense grain size ranging from millimeters to centimeters. Although, it is widely claimed in the literature that the orientation deviations from the ideal Goss orientation lie in the range of about 7° for conventional grain-oriented steel and in the range of about 3° for high permeability grades, no precise investigation with an appropriate statistical relevance is known to the authors. In this work, X-ray diffraction and large-area EBSD-based orientation microscopy (EBSD: electron backscatter diffraction) were used for texture analysis and orientation determination in order to estimate the Goss orientation spread of different grades of grain-oriented steel. Two production routes for grain-oriented steel sheets are compared, the conventional route and a low heating route with lower inhibitor strength. The results of the texture measurement demonstrate that both routes deliver comparable values of orientation deviations. Furthermore, it can be shown that small differences of the magnetic properties can be correlated with the texture sharpness of the material.

回転磁束下における二方向性けい素鋼板の磁気特性

回転磁束下における二方向性けい素鋼板の磁気特性

Localized distribution of two-dimensional magnetic properties and magnetic domain observation

This paper describes the localized distribution of the two-dimensional magnetic properties, which means the relationship between field strength H -vector and magnetic flux density B -vector measured by two-dimensional special sensor on a grain-oriented steel sheet. These results are compared with the magnetic domain structure.

Rotational Iron Losses and Their Estimation in Electrical Steel Sheets

The rotational iron loss, WR (BL BC), of electrical steel sheets at two-dimensional flux densities BL and BC were compared with the sum of the alternating iron losses WL (BL) and WC (BC) at BL and BC, respectively. In the case of BL+BC<2T, K nearly equals l, where K is the ratio of WR (BL, BC) to WL (BL)+ WC (BC). For BL+BC>2 T, K<1, the value of K is almost independent of the grade of a non-oriented steel sheet. K is higher in a grain-oriented steel sheet than in a non-oriented steel sheet, and is highest in a doubly grain-oriented steel sheet. The rotational iron losses can be approximately estimated from the alternating iron losses and the constant K. In a non-oriented steel sheet, which is polycrystalline, if BL+BC is low, it is assumed that each crystal grain is mainly magnetized along the easy axis, even if the exciting field is rotational, and that the rotational iron loss is almost equal to the sum of the alternating iron losses in two directions.

Ultrathick glassless high-permeability, grain-oriented silicon steel sheets with high workability

A high-permeability, grain-oriented silicon steel sheet of ultrathick gauge 0.50 nm with better punchability, realized by the formation of an extremely thin glass film formed in the surface region, has been developed. The new product has almost the same core loss as conventional grain-oriented steel sheet of 0.35 mm gauge, when used in the iron cores of large rotary machines.

けい素鋼板の回転磁界下でのバルクハウゼンノイズ

Barkhausen noise (BN) was measured in grain-oriented steel sheets and non-oriented steel sheets. We studied the difference in the BN under an alternating field and a rotating field with changing magnetic flux density B. One of the crucial problems of electromagnetic machines in the occurrence of magnetic losses in the rotating field in three- or poly-phase transformers. In a non-destructive inspection, the BN is measured as one of the parameters for investigating the progress of the fatigue. If we can determine magnetic domain wall displacements from the BN without observing the inside of the specimen, it may be possible to guess the relationship between the eddy current and the magnetic domain wall displacements. Understanding the relationship between the BN and the domain wall displacements is also useful for a destructive inspection, because the relative permeability measured in metal materials changes in proportion to the progress of the fatigue.

Quasi 3-D magnetic field computation for the layer structure of transformer cores

The heterogeneous layer structure of overlapping zones in stacked transformer cores made of anisotropic grain-oriented steel sheets, and the presence of air gaps in this region bring about a 3-D magnetic flux distribution, the computation of which under is extremely complicated. This paper presents a calculation method enabling, with simplifying assumptions, to reduce the problem to a 2-D one and solve it with regard to most objectives.

A two-dimensional model describing the magnetic behaviour of textured steel sheet

Grain-oriented steel sheet is modelled assuming 180° domain walls and a perfect texture. Equilibrium calculations are performed taking into account domain wall displacements and coherent rotations of the polarization. The equilibria calculated turn unstable at certain conditions leading to jumps of the total polarization.

Magnetic field computation in a transformer core with an automatic adaptive mesh generator

This paper presents an automatic adaptive mesh generator in two and three dimensions for the study of a three-phase, three-limbed transformer core. The transformer core is laminated with grain-oriented steel sheets. A homogenization model for the iron-air lamination is investigated for the three-dimensional analysis and an elliptic model is applied to represent the crystals’ anisotropy in two and three dimensions. A scalar potential analysis for nonlinear anisotropic problems has been performed. Because of the geometry of the transformer and its mesh, numerical difficulties may appear, and a poor convergence of the solution could be obtained. In order to improve the solution, an adaptive mesh refinement procedure is used.

Rotational power loss of silicon steel sheet

Rotational power losses have been measured on nonoriented grain-oriented silicon steel sheets under different rotational flux conditions. Several methods have been proposed for this purpose. Among these, a method based on the measurement of the field quantities B/sub x/, B/sub y/, H/sub x/, and H/sub y/ seems to be the most convenient as far as the preparation of the test specimen is concerned. In this method, the rotational power loss P/sub r/ is measured as the torque loss generated from the angle of lag between the H-vector and the B-vector caused by the rotating field. The effect of the axis ratio of the rotational flux components and of the inclination angle of field strength relative to the rolling direction of a sample sheet on the rotational power loss was investigated with the method. This loss was compared with the conventional loss, which was shown as the sum of loss P/sub t/ in the x and y directions. Although in the nonoriented steel sheet P/sub t/ (conventional rotational loss) is larger than P/sub r/, in the grain-oriented steel sheet P/sub t/ is smaller than P/sub r/. When the field strength was applied in the nonoriented sheet at a 45 degrees angle from the rolling direction of the sheet, the rotational power loss reached minimum values. >

A mechanism of deformation and recrystallization texture changes in grain-oriented silicon steel sheets

Deformation and recrystallization textures as well as orientation dependence of lattice strain energy in two kinds of the grain-oriented silicon steel sheets with MnS and MnS+AlN precipitates as inhibitors have been investigated by means of x-ray diffraction techniques. Orientation relations corresponding to the textural changes that occurred during primary recrystallization have also been calculated. According to a model of the textural changes concurrently controlled by the stored energy differences and the orientation differences, the textural changes and mathematical relations have been deduced. A qualitative coincidence between the theoretical analysis and experimental results indicated that the mechanism of deformation and recrystallization texture changes in the grain-oriented steel sheets is mainly a preferred growth process controlled in common by the stored energy difference and the orientation difference.

Losses of Grain-Oriented Three Percent Si-Fe with Very High Permeability

Iron losses in 3 percent Si grain-oriented steel sheets with high magnetic flux densities, prepared by secondary recrystallization, are studied. Low iron losses, as measured in the rolling direction with a 1 kg/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> tension applied, were obtained for several samples. Losses of samples on which glass films were deposited were larger than for laser-irradiated samples, probably due to the contribution of the glass film-iron interface to irreversible magnetization. Observations of magnetic domains in each phase under AC excitation indicated a lower domain density, a higher active magnetic wall number, and more uniform wall movement, than commercial samples.