Electrical Steel Sheets Research Articles

A simplified magnetostrictive model under rotational magnetization in an electrical steel sheet taking the pinning hysteresis effect into account

A large number of experimental observations show that under two-dimensional (2-D) rotational magnetization, there is a complicated relationship between the magnetostrictive strain and magnetic flux density. In this paper, the magnetostrictive characteristics in a non-oriented electrical steel sheet under 2-D magnetization are measured and modelled based on the experimental system developed by the laboratory. The in-plane magnetostrictive strain tensor under the 2-D magnetization is expressed as nonlinear superposition of dynamic magnetostrictive strain in the rolling direction (RD) and transverse direction (TD), respectively. The magnetostriction’s first derivative with respect to magnetization depicts the pinning effect and the interaction among magnetic domains which result in the hysteresis behaviour. And based on the particle swarm optimization (PSO), the model parameters are identified. The validity of the proposed model is verified by comparing the calculation results with the experimental ones. Studies have shown that the magnetostrictive properties in an electrical steel sheet have strong hysteresis behaviour under the 2-D magnetization, and the model proposed here can well characterize these characteristics.

CMT and GTA welding on microstructural characteristics and magnetic performance of thin CRNO electrical steel sheets

The Cold-Rolled Non-Oriented (CRNO) electrical steel of M − 45 grade are widely employed in medium capacity rotating electrical systems and small motors. The present work is based on the investigations performed on the CRNO electrical steel core samples welded on 6 sides around the outer periphery using Cold Metal Transfer (CMT) and Gas Tungsten Arc Welding (GTAW) process. The welded toroidal core samples were investigated for analyzing the alterations in magnetic properties and core losses by varying the magnetic flux density. In addition, the microstructure, residual stress and microhardness evaluation of the weld samples were also performed. The investigation on magnetic property revealed an considerable increase in core losses (W/Kg) affecting the magnetic performance, with coarse sized grains, drastic variations in hardness and residual stress in the weld affected region of the GTAW welded samples were noticed, in comparison to the CMT welded sample.

Effects of processing routes on recrystallization texture development and magnetic properties of 0.10 mm ultrathin non-oriented electrical steel sheets for high-frequency application

Fabricating ultrathin non-oriented electrical steels (NOES) sheets has been a challenge because the severe plastic deformation inevitably results in undesirable texture such as intensive γ-fiber (<111>//ND). In the present work, both one-stage rolling route with severe plastic deformation and two-stage rolling route combining different rolling process and the intermediate annealing were used to prepare 0.10 mm-thick 3.1Si-0.8Al NOES. A rare phenomenon was found that severe plastic deformation in one-stage rolling route split the orientations of α (<110>//RD) grains through deformation banding and caused lattice curvature, exhibiting the similar microstructure characteristic and stored energy distribution as the deformed γ-grains. As a result, dominant α*-fiber ({1 1 h} <1 2 1/h>) and relatively soft α-fiber textures besides sharp γ-fiber recrystallization texture were formed, which seriously deteriorated the magnetic induction and led to high magnetic anisotropy. By comparison, the two-stage rolling route favored the development of shear bands and increased the final grain size. As the second rolling reduction decreased, detrimental γ- and α*‐fiber recrystallization textures were significantly weakened, whereas λ-fiber (<001>//ND) and {117}<291> recrystallization textures were enhanced. Besides, the final grain size was gradually increased. Therefore, the magnetic induction was continuously improved and the core loss was gradually decreased. Another new finding was that magnetic anisotropy was simultaneously improved as a result of the occurrence of {117}<291> texture and the weakening of α*-fiber texture. The recrystallization mechanism of specific texture components was investigated in detail.

Investigation of the compaction process of electrical machines magnetic circuits and its detrimental effect on magnetic performances

The manufacturing processes of electrical machines may lead to significant degradation of the magnetic properties of their magnetic core (stator, rotor) performances and, as a consequence, to a decrease of their energy efficiency. While the effects of some processes (cutting, welding …) are widely discussed in the literature, this is not the case with the compaction process although it is systematically used to maintain the assembly of electrical steel sheets that compose the magnetic circuits. In addition to the conventional one, a specific compaction process exists for high-power electrical machines. After an introduction, the paper firstly deals with the two studied processes (conventional, specific). Then, an experimental mock-up to study the impact of the two configurations on the magnetic properties (iron losses, normal magnetization curve) is presented. This mock-up is the first, in the literature, that allows to study the effect of a controlled compaction mechanical stress on magnetic properties. Obtained results in both configurations highlight a magneto-mechanical effect that is not reported in the literature where these effects are commonly considered following in-plane mechanical stresses. This paper presents a magneto-mechanical model, taking into account the compaction stress effect, as well as a modelling protocol to model the effect of 3D mechanical stress on magnetic properties, which has never been done in the literature.

Influence of working pressure on laser beam welding in vacuum of electrical steel sheets

In a recent research project of RWTH Aachen University it is shown, that laser beam spot welding is advantageous over line welds with respect to the magnetic properties of an iron core and can therefore increase the efficiency of electric motors. In this case laser beam welding in vacuum is used to join these iron cores. A pulsed laser beam process was used to generate individual weld spots. The influences of a reduced working pressure on the welding result in the range of 1 mbar–1000 mbar occurring in this process are presented in this paper.

Temperature Rise Calculation of Magnetic Core Considering the Temperature Effect of Magnetic Properties in an Electrical Steel Sheet

The magnetic properties of electrical steel sheets are affected by magnetization patterns, working temperature, and external pressure. In order to study the temperature effect of electrical steel sheets on the temperature rise of a transformer core, in this paper, based on the magnetic property test system of an electrical steel sheet, the permeability and loss of a 50AW600 grain non-oriented electrical steel sheet and a 30ZH120 grain oriented electrical steel sheet under different temperatures and excited frequencies were measured, and the influence of temperature on the properties of the material was analyzed. A magneto-thermal iterative coupling method considering the temperature effects of magnetic properties in the electrical steel sheet was investigated. Based on the above measurement data and iterative coupling method, the temperature distribution of the core of a 500-kV power transformer was simulated and analyzed, and compared with the simulation results of the traditional coupling method without considering the temperature effect of the electrical steel sheet. Magneto-thermal coupling simulation under no-load operation is a symmetrical problem. It was found that the temperature of the hottest spot of the transformer core calculated by the magneto-thermal iteration method proposed in this paper was significantly reduced, the temperature of the hottest spot on the core column was about 45 °C, and the temperature of the hottest spot on the upper and lower yoke was about 39 °C, which provides an effective simulation method for accurately calculating the temperature rise distribution of electrical products such as transformers.

Modeling of the Stress–Strain of the Suspensions of the Stators of High-Power Turbogenerators

In the submitted scientific work, the existing types of stator fastening design of turbogenerators and the main causes of the stressed state of the stator suspensions are considered. A detailed calculation of the complex stressed state of the turbogenerator stator suspension was carried out for a number of electrical sheet steels, taking into consideration the unevenness of the heat distribution along the horizontal axis of the unit. It is proposed that the calculation of the mechanical stress is carried out by means of the mechanical and thermal calculation, coordinated with the electrical one. The possibility of replacing steel 38Х2Н2ВА with steel 34CrNiMo6 and 40NiCrMo7 is indicated, subject to compliance with GOST 8479-70 for the same strength group.

Temperature-dependent modelling of magnetic ageing of FeSi electrical steels

This paper deals with the temperature-dependent modelling of iron losses in the context of magnetic ageing of electricals steel used in high power electrical machines. First, two electrical steel sheet grades were heat treated at three temperatures in order to study the ageing effect evolution as a function of temperature. Results show a significant increase in iron losses for both steel grades. Then, considering the link between the macroscopic magnetic properties evolution (effect) and the microscopic precipitation (cause), the Johnson – Mehl – Avrami – Kolmogorov (JMAK) law describing the kinetics of precipitation was applied to model the time evolution of magnetic ageing. By coupling this model with the Arrhenius’ law, a model is developed to be able to predict the ageing for several temperature levels.

Punching effects on local magnetic properties near the edge of nonoriented electrical steels

PurposeThe purpose of this study is to investigate the effect of punching on the local magnetic properties of the nonoriented electrical steel sheet.Design/methodology/approachA microcomposite B–H sensor consisting of a pair of B probes with a spacing of 2 mm and a 1.8 × 1.8 mm2 H coil is designed. The region and degree of local magnetic properties degradation caused by punching can be quantitatively analyzed by flexibly moving the composite B–H sensor. The influence and physical mechanism of punching on the hysteresis loss, eddy current loss and excess loss are analyzed based on the Bertotti loss separation theory.FindingsThis study investigates the deterioration effect of the punched nonoriented electrical steel. The permeability near the edge decreases, and the core loss as well as the microhardness increases. The region of magnetic property deterioration is dependent on the area of work hardening.Originality/valueThe microcomposite B–H sensor can be used to measure the magnetic properties near the edge of electrical steel sheets under different processing conditions. This study provides the possibility of precise magnetic property model of the motor core after punching, especially valuable for motors without annealing process.

An Improved Model for Anomalous Loss Utilizing Loss Separation and Comparison With ANN Model in Electrical Steel Sheet

This article investigates the behavior of anomalous magnetic field in electrical steel sheet (ESS). For this, anomalous magnetic field is extracted from measured magnetic field by excluding static hysteresis and eddy current fields. To overcome the shortcomings of the Bertotti’s and artificial neural network (ANN) models for anomalous magnetic field and loss, an improved model is proposed by introducing a new parameter, time shifting, to modify the phase of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B$ </tex-math></inline-formula> -waveform. Through comparisons of Bertotti’s model, ANN model, and experimental measurements over non-oriented, highly grain-oriented, and domain-refined highly grain-oriented ESSs, the proposed model is validated.

Modeling of Magnetic Anisotropy in Electrical Steel Sheet by Means of Cumulative Distribution Functions of Gaussians

This article proposes a methodology for modeling magnetic anisotropy in ferromagnetic materials. This approach was initially used to represent the isothermal remanent magnetization (IRM) acquired by natural mineral assemblages and based on the use of the cumulative distribution function (CDF) of a probability density function (PDF). For the purpose of this work, the anisotropy of electrical steel sheets is modeled by means of CDFs of Gaussians. The methodology is validated by comparisons between numerical and experimental data obtained from an Epstein frame and a Rotational Single Sheet Tester. The outcomes of the study are twofold: first, the parameters defining the CDF follow a polynomial trendline, and second, they can easily be calculated from a limited amount of experimental data which is a key point from an engineering point of view.

Loss Parameter Identification After Cutting for Different Non-Oriented Electrical Steel Grades

The magnetic properties of nonoriented (NO) electrical steel sheet are sensitive to industrial cutting processes. Decreased operation point efficiency and an increase in local iron loss in the magnetic circuit of an electrical machine are the consequences. During the design of electrical machines, the cut-edge effect and its consequences can only be considered and assessed, if the effect is locally modeled. In fact, the cut-edge effect is often neglected as standardized magnetic characterization is performed, where the sheet material is measured on an Epstein frame or single sheet tester (SST) and gentle sample preparation is specified. In order to parameterize a local material model, a large number of samples and their detailed magnetic characterization at various magnetizing frequencies are necessary. In this article, the loss parameters of nine different industrial NO electrical steels are identified and analyzed in order to study the course of the parameters and possible interrelation with material properties. The sheet thickness, alloying content of silicon and aluminum, and grain sizes are considered as they are the dominant influences on the iron loss from the material side. The presented results help to increase the understanding of the cut-edge effect and its consequences on the iron loss modeling. Furthermore, they help to identify possibilities to decrease the measurement effort significantly.

Recent advances of lab-based diffraction contrast tomography – reconstruction speed benchmark testing and validations

Lab-based diffraction contrast tomography (DCT) enables the user to reconstruct 3D grain maps of polycrystalline materials non-destructively. For each grain, the morphology and crystallographic orientation, as well as derived properties such as grain boundaries, can be determined. Through two application examples this paper demonstrates the data acquisition and reconstruction speed of the current implementation and validates the resulting grain maps. Firstly, for a conventional Laue focusing scan of an AlCu sample comprising 340 grains, major performance enhancements of the reconstruction algorithm have reduced the reconstruction time from half a day to half an hour. The second example highlights an advanced scan with projection geometry of an oriented electrical steel sheet containing 7,800 grains. While the data collection time is around a day for each of the data sets, the boosted reconstruction of the advanced acquisition data takes half a day and gives the full grain map without the need for stitching. After the major algorithm speed enhancements, grain map qualities are comparable with misorientations below 0.02° and grain boundary distances less than a voxel for both samples.

Evaluation of magnetic properties of two kinds of permendurs by vector magnetic measurement

Vector magnetic properties of various electrical steel sheets have been investigated by using a vector magnetic property measurement apparatus to select a magnetic material suitable as a motor core material. However, a magnetic material with a higher saturation magnetization than an electrical steel sheet is useful for increasing torque of a motor. Therefore, a permendur with higher saturation magnetization than an electrical steel sheet is selected as a measurement sample. It is known that a permendur does not have magnetic anisotropy. In this paper, vector magnetic properties of two kinds of permendurs made by VACUUMSCHMELZE (VAC) and Hitachi Metals are measured. Moreover, maximum magnetic field intensities and core losses of two kinds of permendurs to an inclination angle of magnetic flux density vector locus from rolling direction are evaluated for investigation of those magnetic anisotropies. As a result, differences of vector magnetic properties of two kinds of permendurs are revealed.

Using grain oriented electrical steel sheets for electric motor in automotive application: Tooth segmentation

Grain Oriented Electrical Steel (GOES) have better performance in terms of permeability and iron losses compared to conventional Fe-Si 3% Non-Oriented Grains Electrical Steel (NOES), particularly when it is magnetized in the rolling direction. This paper presents a concentrated winding radial flux permanent magnets synchronous machine (PMSM) equipped with teeth made of GOES sheet. The goal is to assess the suitability of the use of GOES sheets to improve the efficiency of electric motors. This work is based on the comparison of the performances (Joule losses, iron losses, losses in the permanent magnets and efficiency) of two iso-geometric motors: a reference motor made of NOES sheets and a motor with GOES sheet teeth, at iso-torque and over the operating range (at constant torque and flux weakening). The comparison is made using a finite element software application considering the magnetic anisotropy of the GOES sheets.

Study on the influence of ultra-thin non-oriented silicon steel sheet on the performance of ultra-high-speed permanent magnet motor

The ultra-high-speed permanent magnet motor has the characteristics of high-power density, small size, and high speed, but there are problems with it, such as generation of local excessive heat and obvious vibration and noise. In order to reduce the loss and improve the efficiency of the motor, in this study, ultra-thin silicon steel sheets are used as the material of the iron core of the motor, and two non-oriented silicon steel sheets with different thicknesses—0.05 and 0.15 mm—were selected. First, we use the Epstein square ring electrical steel sheet magnetic properties test to determine the magnetic properties and the loss properties of the two ultra-thin non-oriented silicon steel sheets under working conditions. Then, we use electromagnetic simulation software to calculate the magnetic performance and the temperature rise performance of two kinds of motors with different materials. Finally, through the test of the prototype, we know the difference in the influence of the two kinds of silicon steel sheets on the performance of air compressors. We hope the outcome of the study will provide technical support for optimizing the design of ultra-high-speed permanent magnet motors for air compressors.

RESEARCH OF PHYSICAL PROCESSES IN LAMINATED MAGNETIC CORES OF ELECTRIC MACHINES

The aim of this work is to use fast-moving processes to detect defects in the inter-sheet insulation of laminated magnetic core of electric machines. Violation of the sheet insulation causes increased eddy currents as a result of increased losses and integrated local overheating in the body of the magnetic core. The article develops a mathematical field model of induction distribution in a toroidal toothed magnetic core of an asynchronous motor series 4AA63V4U3 0.37 kW when superimposed on the back of the core of the power winding powered by a high frequency voltage source in the range. An experimental study of losses in the magnetic coret and the distribution of losses on eddy currents and remagnetization (hysteresis).&#x0D; When designing an electric machine, its operating characteristics, optimal operating modes, thermal condition and many other factors are calculated using the nominal values ​​of steel parameters, windings and all materials used in the machine. However, these materials do not always have the stated characteristics and quality. For example, during the manufacture and stamping of electrical steel sheets, it is exposed to a significant level of influence, which in some way affects its characteristics. In addition, even if we assume that during the production of all stages of manufacturing the material came flawlessly, the condition and as a result the parameters of materials and EM in general change during operation as a result of accidents or even simple aging and wear.&#x0D; Therefore, given these facts, it becomes clear that during planned or unplanned repairs it makes sense to check the condition of materials, insulation, as their condition depends on the allowable loads, temperature, etc. In particular, the state of the magnetic circuit largely determines the temperature around the conductors in the grooves and as a result determines how long the winding will actually last in contrast to the specified service life and rated power at which to use this EM.&#x0D; The concept of the state of the magnetic circuit can be divided into the state of electrical steel and the state of its insulation. The first component changes quite poorly during operation and is generally caused by the "aging" of steel if you do not take into account any serious damage as a result of accidents, but it can be damaged during manufacture. But the second component is significantly affected during operation and significantly determines the quality of the magnetic circuit as a whole.

Magnetostrictive hysteretic properties estimation of electrical steel sheet under external stress using improved ADSM model

PurposeThe purpose of this paper is to improve the modeling accuracy of the magnetostrictive hysteretic characteristics by introducing hysteresis energy instead of pinning energy in the assembled domain structure model (ADSM).Design/methodology/approachFirst, the magnetostrictive characteristics and the domain movement process in an electrical steel sheet are measured and observed. The reasons for the influence of stress on magnetostriction are discussed on the mesoscopic level. Second, the ADSM model using the hysteresis energy is investigated to estimate the influence of external stress. Finally, the simulation results of the modified ADSM model are compared with the experimental data under the same calculation conditions.FindingsThe results show that the improved model not only explains the cause of hysteresis clearly from the perspective of the magnetic moment but also improves the modeling ability of magnetostrictive hysteretic.Originality/valueThe magnetostriction in electrical steel lags behind the external magnetic field, and it is significant for reducing core vibration to estimate the magnetostrictive hysteretic property accurately. This paper proposes an effective approach to model the hysteretic characterization of magnetostriction.

Transverse thickness profile control of electrical steel in 6-high cold rolling mills based on the GA-PSO hybrid algorithm

In order to meet the shape control requirements of “dead flat” transverse thickness profile of electrical steel sheet in cold rolling process, the 3D finite element model (FEM) for roll stacks and strip of 6-high tandem cold rolling mills (TCMs) was built with the developed Edge Drop Control Work Rolls for Non-shifting (EDW-N). The efficiency curves of the work roll bending (WRB), the intermediate roll bending (IRB), and the intermediate roll shifting (IRS) in cold rolling process are obtained for transverse thickness profile control performance. The control strategy of multi-stand and multi-variable profile and flatness control actuators, i.e., WRB, IRB, and IRS of stands 1 ~ 5 in 6-high TCMs is proposed based on the GA-PSO hybrid algorithm with better optimization ability. The results show that the control strategy can fully exploit the shape control ability and achieve the high precision control for transverse thickness profile of 6-high TCMs. The industrial application on the production gives remarkable results that the rate of the measured strip crown less than 7 μm increased from 38.58 to 67.74% for electrical steel sheet in the 1420-mm 6-high TCMs. The control strategy has applied to the production successfully.

Texture Adjustment of Hot-Rolled Fe-1.6 wt% Si Non-oriented Electrical Steel Sheet by Annealing Processes

Texture Adjustment of Hot-Rolled Fe-1.6 wt% Si Non-oriented Electrical Steel Sheet by Annealing Processes