Magnetic Properties Of Electrical Steels Research Articles

Magnetic Properties of Fe-Si Electrical Steel after Laser Scribing

Improvement of magnetic properties of electrical steel can be achieved by reduction the size of magnetic domains. The application of local stresses through laser scribing leads to reduced core losses. In order to determine the effect of laser refinement conditions of magnetic domains on the properties of the soft magnetic material, four samples with a thickness 0.23 mm were refined. The refinement of each sample was carried out using different line energies of the laser beam. Estimation of the magnetic domain size was performed using the Jeffries method, the magnetic viewer was used to reveal the domain structure. The measurement of the magnetic properties was performed at a frequency of 50 Hz and an induction of 1.5 T. The analyzed results presented in this work indicate impact of laser refining on magnetic properties of grain oriented electrical steel depending on used laser beam energy.

Measurement of magnetic properties of grain-oriented electrical steel considering multi-physics factors influence

The magnetic properties of electrical steel sheets are strongly affected by the Multi-Physics Factors (MPF), such as bending stress, working temperature, and magnetization patterns. To investigate the complex magnetic properties of the material under MPF magnetizing conditions, a magnetic property measurement system is first developed, considering the effect of bending stress, temperature loading, and non-sinusoidal magnetization waveforms. Then, the magnetic and the loss properties of Grain-Oriented (GO) electrical steels under MPF magnetizing conditions are measured and discussed. Obtained results showed that bending stress and non-sinusoidal magnetization waveforms are positively correlated with the loss properties of electrical steel sheets, and elevated temperatures can mitigate the effects of bending stress and harmonics on magnetic properties and losses.

Microstructure and magnetic domain structure of additively manufactured Fe–Si soft magnetic alloys with 3 and 9 wt.-% Si

Electrical steels are numerously used in engineering applications. Nowadays, future challenges related to climate change and e-mobility push the boundaries to higher efficiency also in electrical parts. A promising material group to reduce electrical losses are electrical steels with high silicon contents. However, such steels are difficult to process with conventional methods and, thus, additive manufacturing came into focus in recent years. The present study investigates the processability, crack sensitivity, microstructure evolution and magnetic domain structures of laser powder bed fused Fe–Si alloys with 3 and 9 wt.-% Si. It is shown that specimens, which are built using appropriate process parameters, are dense and free of cracks. Still, Fe–9Si is characterized by a higher crack susceptibility at low temperatures of the build platform. A checkerboard like microstructure with elongated grains alongside build direction evolved. Global magnetic properties from ring core measurements showed lower losses for the Fe–9Si ring. Moreover, it was found that the magnetic domain structures are directly influenced by the crystallographic orientations present in the specimen volumes. The findings elaborated will contribute to advanced possibilities in tailoring the magnetic properties of electrical steels for an increase of the efficiency of envisaged applications.

Effect of Cutting Process on the Magnetic Properties of Electrical Steels with Different Si Contents

Effect of Cutting Process on the Magnetic Properties of Electrical Steels with Different Si Contents

Investigative study on the properties of magnetic materials for electrical machines

<p><span>The paper attempts to investigate the properties of the magnetic materials used in the construction of rotating electric machines, with a view to arrive at the appropriate choice for the induction motors in particular. Measurement of magnetic properties for rotating electrical machines are more important to both machine designer and operator. This paper discusses the influence of magnetic properties of electrical steel on performance of electrical machine. Here properties like BH curve, core loss, permeability and other vital parameters are measured using 400×400 Epstein tester over wide range flux density and frequency up to 50 Hz and 400 Hz. The results measured in terms of the core loss, BH curve and permeability showcase the benefits to decide on the suitability of the material for use in practice.</span></p>

A new approach to measure fundamental microstructural influences on the magnetic properties of electrical steel using a miniaturized single sheet tester

Magnetic properties of electrical steel are usually measured on Single Sheet Testers, Epstein frames or ring cores. Due to the geometric dimensions and measurement principles of these standardized setups, the fundamental microstructural influences on the magnetic behavior, e.g., deformation structures, crystal orientation or grain boundaries, are difficult to separate and quantify. In this paper, a miniaturized Single Sheet Tester is presented that allows the characterization of industrial steel sheets as well as from in size limited single, bi- and oligocrystals starting from samples with dimensions of 10 × 22 mm. Thereby, the measurement of global magnetic properties is coupled with microstructural analysis methods to allow the investigation of micro scale magnetic effects. An effect of grain orientation, grain boundaries and deformation structures has already been identified with the presented experimental setup. In addition, a correction function is introduced to allow quantitative comparisons between differently sized Single Sheet Testers. This approach is not limited to the presented Single Sheet Tester geometry, but can also be used to compare the results of Single Sheet Testers of various sizes. The results of the miniaturized Single Sheet Tester were validated on five industrial electrical steel grades. Furthermore, first results of differently oriented single crystals as well as measurements on grain-oriented electrical steel are shown to prove the additional value of the miniaturized Single Sheet Tester geometry.

A measuring setup for testing the mechanical stress dependence of magnetic properties of electrical steels

Measurements of mechanical stress dependence of magnetic properties of electrical steels are significant from both theoretical and application points of view. The paper presents a novel measuring setup for testing the magnetoelastic properties of electrical transformer sheets made of grain-oriented and non-grain-oriented steel. The proposed method takes into consideration the angle between the easy electrical steel magnetization axis and the mechanical stress direction. Due to the innovative 3D self-adjustment mechanism of the yoke position, measurements may be taken for different magnetization strengths and angles. The paper also presents detailed uncertainty analyses and examples of results of magnetoelastic measurements for grain-oriented electrical steel M120-27s. The presented results validate the method and confirm its usability for further detailed studies of mechanical stress dependence of magnetic properties of electrical steels.

Impact of Manufacturing Stresses On Multiple-Rib Synchronous Reluctance Motor Performance

The effects of manufacturing stresses on the overall magnetic properties of electrical steel core applied in the stator and transversally-laminated rotor of Synchronous Reluctance motors are studied. In addition, it is investigated how the -manufacturing-degraded electrical steel core affects the electromagnetic performance of two different Synchronous Reluctance motors. The traditional transversally-laminated rotor of this kind of a machine requires the adoption of mechanical elements (inner and tangential ribs) to maintain its mechanical integrity. Especially, for high-speed applications, the number of rotor ribs must be increased to make the rotor withstand higher centrifugal forces. Lamination manufacturing typically affects the magnetic properties of electrical steel by reducing its permeability at the machined edge. This machining effect is greater when the overall core layer area surrounded by the machined edges is small i.e., the machined surface area ratio to the total core area is high. Considering this, the degradation of the core magnetic properties in the ribs could improve the performance of the machine, and this effect would be more visible when the machine is designed with a higher number of narrow ribs with the adoption of Topology Optimization. The paper aims to propose some guidelines for the simulation of these effects starting from the measurements on defined core samples and then based on the measured results the simulation model should be updated accordingly. The samples are manufactured from several assembled sheets in order to modify the width of the cut area while maintaining the same external geometry.

Study of magnetic properties of electrical steels with different Si content considering the effect of temperature

Electrical steel cores in electric motors are often operated under variable temperature conditions, and the temperature has a large impact on the magnetic properties of electrical steel. Different Silicon content also makes electrical steel have different performance characteristics. Therefore, in this paper, an environmentally adjustable electrical steel magnetic property testing system is built to investigate the magnetic property variation of non-oriented electrical steel sheets with different Si contents at different temperatures. Through the experiments in this paper, it is found that the trend of magnetic properties of electrical steels tends to flatten out with increasing Si content under the influence of temperature. In particular, the loss of 6.5% Si shows a trend of first decreasing and then increasing with the increase of temperature. The internal grain structure of electrical steel can explain this phenomenon very well. The larger the grain size, the less the magnetic properties of electrical steel are affected by temperature. In order to further analyze the variation phenomenon of electrical steel loss, the loss separation calculation was carried out for 5 more electrical steels with different Si content in this paper. The reason for this phenomenon was finally explained by a special preparation process of 6.5% Si.

Non-Destructive Electromagnetic Evaluation of Material Degradation Due to Steel Cutting in a Fully Stacked Electrical Machine

Although it is well known that the magnetic properties of electrical steel can be deeply affected by the cutting process, it is still not clear how to accurately evaluate these effects on a prototyped machine on its final shape, especially at a high frequency or a high power rating. This research provides a more practical method for accurate measurement of magnetic losses in electrical steel with consideration of material degradation effects due to the cutting process. Unlike other similar studies, these investigations are conducted not only on a few laminations but also on a complete electrical machine core. For a fair comparison between both cases, backlack bonding is used for lamination stacking since it is the most non-damaging joining technique. Two different test setups are used to measure the steel performance at a wide range of frequency and input power. Furthermore, a full axial length stator of a switched reluctance machine (SRM) is used as a case study to identify the magnetic properties of NO20 electrical steel. Additionally, by comparing the results obtained from the individual laminations and the assembled stator, the extra losses due to the cutting process and material degradation are extracted accurately.

Examination of magnetic properties of nonoriented electrical steels using ring-type specimens

The Epstein frame test is commonly used for investigating the magnetic properties of electrical steels because of the convenient sample preparation. This test requires the samples to be cut half-parallel and half-perpendicular to the direction of rolling to account for the magnetic anisotropy of the sheet. An alternative method to evaluate the magnetic properties of electrical steels is the ring core test. This test more closely represents the magnetic cores in rotating machinery such as motors and generators because the sample shape for this test resembles the practical rotating applications. The measured results may vary according to the test methods. In this study, the differences between the results of the Epstein frame tests and ring core tests were investigated for the various grades of NO steels. For the magnetic induction measurements, results of the ring core test showed a trend of lower values than in the results of the Epstein frame tests. The core losses measured by the ring core tests are generally greater than those of the Epstein frame tests. The difference in results due to the test methods can be attributed to the anisotropy parameter, A(h), which can be obtained from the crystallographic texture of the sheet sample. The difference becomes significant when an area fraction of the texture component shows a high 1-A(h) value by the Epstein test but a low value by the ring test.

Method to revise a simulation model of single-phase transformer using no-load current waveforms

One of the areas of industrial digitalization is associated with the concept of digital twins, which allows simulating the operation of real devices in various modes. Currently, simulation packages such as MatLab Simulink, or physical field modeling systems, such as ANSYS Maxwell are applied. The problem is that, despite the declared accuracy, practically no model of a technical device can demonstrate a point-to-point correspondence of the simulation results and the experimental results, especially under transient conditions. It is caused by variations of material characteristics and difficulty to consider technological factors. The purpose of this article is to develop a method to revise the simulation model of a single-phase transformer. So, this model can provide 95 % accuracy of the coincidence of the instantaneous values of currents in the windings when simulating the operation of the transformer both in steady state and in transient modes. The authors have used the methods to model electrical circuits, simulation modeling using the MatLab Simulink SimPowerSystem package, experimental methods to record current and voltage oscillograms. The authors have studied the possibility of accurate modeling of transient and steady processes in a single-phase transformer, considering the nonlinearity of the magnetic properties of electrical steel and the mutual influence of magnetic fluxes of windings that close outside the magnetic core. To revise the model, a multichannel high-speed recorder developed by the authors has been used. A technique to revise a simulation model of a single-phase transformer using experimental oscillograms of voltage and no-load current has been developed. Application of the proposed method to revise the transformer magnetization curve using experimental oscillograms of a real transformer, as well as calculating the resistance of the parallel magnetization branch of the equivalent circuit of the transformer based on the oscillogram, makes it possible to obtain an almost point-to-point correspondence of the no-load current curve obtained when modeling with the experimental curve. The proposed technique to develop a simulation model gives more accurate results of modeling transient modes of transformers in comparison with analogues.

Angular magnetic Barkhausen noise of incline- and cross-rolled non-oriented electrical steel sheets

Magnetic Barkhausen noise (MBN) analysis is a relatively new technique used to characterize the magnetic properties of electrical steels. Not only has it been utilized to evaluate the overall core loss of electrical steel sheets, but it has also been employed as a non-destructive testing (NDT) tool to assess the magnetocrystalline anisotropy of ferromagnetic materials. In this study, non-oriented electrical steel sheets produced by inclined and cross rolling were characterized by both MBN and electron backscatter diffraction (EBSD). The angular MBN measured on the surface of the steel sheet was directly compared to the magnetocrystalline anisotropy energy (MAE) calculated from the measured crystallographic texture. The MBN energy corresponding to the saturation-to-remanence part of the hysteresis loop was evaluated, which had been reported to have a close correlation to the MAE in pipeline steels. The results in this study showed that such a relationship did not exist in any of the electrical steel samples examined (including deformed, partially recrystallized, and completely recrystallized), although in some samples the polarities of the MBN and MAE partially coincide. It was shown that the residual stress in the material played an important role in determining the polarities of the angular MBN, which had been ignored in the previous studies when comparing the MBN to the MAE. Possible reasons that caused the discrepancies between the results of this study and those of the previous studies were given.

Effect of industrial impregnation process on the magnetic properties of electrical steels

This paper deals with the experimental investigation of the effect of impregnation process on the normal magnetization curve and iron losses of electrical steels. To address this issue, several laminated toroidal magnetic circuits have been designed to characterize the magnetic properties with the flux metric method. The first configuration considers magnetic circuits wrapped with adhesive tape so that the dielectric resin will be deposited only on the outer surface of the magnetic circuit. In the second configuration, the magnetic circuits are unwrapped, which will allow the resin to diffuse within the inter-laminar spaces of the magnetic circuit. The obtained experimental results show significant effects on the magnetic properties in both cases. However, depending on the considered configuration, the resin diffusion also has an influence on the changes in magnetic properties.

Evaluation of errors of the wattmeter method for determining magnetic losses in transformers

The problem of the influence of the accuracy of dividing magnetic losses into components in transformers on the efficiency of minimizing these losses is considered. Various methods of studying and evaluating the magnetic properties of electrical steels and the power of magnetic losses are described. It is shown that the use of the wattmeter method for determining the components of magnetic losses in a specific transformer, in contrast to the currently used methods for determining the power of specific magnetic losses, does not require special equipment and software. An assessment of two specific errors of the wattmeter method for determining the magnetic losses in the transformer core is carried out. The first error is associated with the errors of the measuring devices (wattmeter and frequency meter), the second – with electrical losses during an idle experiment. The dependences of the errors of these losses on the accuracy class of the devices (wattmeter and cymometer) are obtained. It was found that for a dry single-phase transformer, the error of hysteresis losses is 19 times higher than the accuracy class of devices, and the error of eddy-current losses is 32 times. For low-power transformers (up to 5 kVA), taking into account electrical losses in the no-load experiment underestimates the losses due to hysteresis and overestimates the losses due to eddy currents, the error in determining which can significantly exceed the total error in determining the magnetic losses. It is shown that for transformers with a capacity of over 25 kVA, the error associated with taking into account electrical losses in the no-load test is negligible.

The Influence of Carbonitration on the Magnetic Properties of Electrical Steel

The influence of carbonitration on the magnetic properties, hardness, and wear resistance of unalloyed electrical steel grade 10 895 was investigated. It was found that carbonitration increased the surface hardness from HV = 140 to 580. This is not as important as when applying borides and nickel borides (HV 2015) but is still very significant (4.1-fold), with a 90% increase in the wear resistance being achieved with friction on the Ferodo disk. Due to the improvement of the magnetic properties of steel, the torque of the magnetic clutch MWU increased by 40%.

Modelling and analysis of the effects of cutting of core laminations in electric machines

Experimental measurements of electrical machine performances reveal a significant difference between simulations and measurements. It is known that the manufacturing processes of machines, particularly, the cutting of core laminations adversely affects material properties. The current techniques for considering the effects of cutting lack accuracy, computation efficiency and applicability for finite element (FE) software. This study proposes a method to model the variation in the magnetic properties of electrical steel due to cutting based on a non-equal multi-slice technique. In this work, the method has been validated and implemented on a FE permanent magnet synchronous motor model. Also, the proposed method has been compared with the single-layer method.

Localised Flux Density Distribution around Different Holes on Electrical Steel: Prediction and Calculation

Localised flux density distributions are closely related to the degraded area around a cut edge or hole. Artificial neural networks (ANN) and MATLAB® Curve Fitting ToolboxTM are useful tools in prediction and analytical calculation of magnetic properties of electrical steels. A 4-node input layer, 1-node output layer model with three hidden layers, and full connectivity between nodes was developed by the ANN for prediction of localised flux density distribution. The input parameters were hole size, cutting method, induction frequency and bulk flux density while the output parameter was localised flux density due to the search coil located at the angles 0º, 25º, 45º and 65º corresponding to the centre of hole and rolling direction. The previous data obtained experimentally was used for training the proposed ANN model. Minimum correlation coefficients and RMS error for the localised flux density were found to be 0.99 and 0.09 respectively after the network was trained. The network was tested using untrained data and then minimum correlation coefficient and RMS error for localised flux density were found to be 0.98 and 0.04 respectively due to test results. A simple analytical equation has also been determined to describe the localised flux distributions. The estimation and calculation results obtained from the ANN model and analytical equations are in good agreement with experimental results previously reported. Key words: Electrical steels, flux distribution, neural network. Special Issue of Educational Sciences DOI: 10.7176/JSTR/6-06-02

Формирование магнитных свойств электротехнической стали

Формирование магнитных свойств электротехнической стали

Impact of grain size distribution on the magnetic deterioration due to cutting of electrical steel sheets

Efforts to increase the power density and continuous power of electric machines have intensified the request for tailored non-grain oriented electrical steel grades. Possible measures to optimize electrical steel grades are the use of thinner gauges as well as grades with tailor-made microstructural properties. However, these grades are developed mainly focusing on the magnetic and mechanical properties, neglecting the detrimental and strongly material-dependent processing effect on the magnetic properties of electrical steel, especially the cutting influence. In this paper, the microstructure-dependence of the magnetic material deterioration due to guillotine cutting is studied on ten industrial non-grain oriented electrical steels with thicknesses between 0.1mm and 0.35mm, all of which the chemical composition, grain structure and texture is known. This allows a consideration of the interdependence of material thickness, microstructure, alloy content with the cutting effect. The magnetic deterioration is characterized on a single-sheet-tester with samples in rolling as well as transverse direction. The grain size distribution and homogeneity is evaluated and linked to magnetic-loss and magnetization-curve deterioration by means of statistical methods. As a result sheet-thickness-dependent microstructures are evaluated with respect to their cutting influence.