Single Sheet Tester Research Articles

Improved estimation of iron losses for non-sinusoidal voltages

PurposeThe electrical machines connected to modern electric power grids are non-sinusoidal excited, and their augmented losses, including iron losses, limit their working characteristics. This paper aims to propose a prediction method for iron losses in non-oriented grains (NO) FeSi sheets under non-sinusoidal voltage, involving an inverse classical Preisach hysteresis model and the time-integration of each loss component.Design/methodology/approachThe magnetic history management in inverse Preisach model is optimized and a numerical Everett function is identified from measured symmetrical hysteresis cycles. The experimental data for sinusoidal waveforms obtained by a single sheet tester were also used to identify the parameters involved in Bertotti’ losses separation method. The non-sinusoidal magnetic induction waveform, corresponding to a measured voltage in an industrial electrical grid, was the input for Preisach model, the output magnetic field being accurately computed. The hysteresis, classical and excess losses are calculated by time-integration and the total losses are compared with those obtained for sinusoidal excitation.FindingsThe proposed method allows to estimate the iron losses for non-sinusoidal magnetic induction, using carefully identified parameters of FeSi NO sheets, using experimental data from sinusoidal regimes.Originality/valueThe method accuracy is assured by using a numerical Everett function, a variable Preisach grid step (adapted for the high non-linearity of FeSi sheets) and high-order fitting polynomials for the microscopic parameters involved in the excess loss estimation. The procedure allows a better design of magnetic cores and an improved estimation of the electric machine derating for non-sinusoidal voltages.

Effect of multi-axial stress on iron losses of electrical steel sheets

The effect of multi-axial stress on the iron losses of a non-oriented electrical steel sheet under alternating magnetization is analyzed. Multi-axial magneto-mechanical measurements on a M400-50A grade non-oriented electrical steel sheet are performed by using a custom made single sheet tester device. The measured losses are separated into hysteresis, classical and excess loss components by using statistical loss theory, and the effect of various stress configurations on the hysteresis and the excess loss components is analyzed. By utilizing the statistical loss theory, an equivalent stress model and a magneto-elastic invariant based model are derived. These models can be used to predict the iron loss evolution under multi-axial stress even if only uniaxial stress dependent measurements are available. The accuracy of both models to predict the multi-axial stress dependent iron losses is found to be satisfactory when they are identified only from uniaxial stress dependent measurements. The invariant based model is shown to be slightly more accurate for the studied material.

Influence of Grain Size and Blanking Clearance on Magnetic Properties Deterioration of Non-Oriented Electrical Steel

In motor manufacturing, blanking process of non-oriented electrical steel inevitably induces plastic deformation and residual stress near the blanked edge and thus leads to the deterioration of magnetic properties. However, as for the newly developed non-oriented electrical steel, the scale of grain size is close to both blanking clearance and thickness. Grain size integrated with blanking clearance thus significantly affects the blanked edge quality. In order to reveal the effects of grain size and blanking clearance on magnetic properties deterioration, systematic blanking tests have been conducted using various non-oriented electrical steel sheets (same chemical composition, three thicknesses, and three grain sizes) in a considered clearance range. The blanked edges are characterized by means of optical microscopy, scanning electron microscopy, and micro-hardness tests. Magnetic domain structures are also observed by magnetic force microscopy. The iron losses are measured by single sheet tester method. The burnished ratio decided by clearance and grain size can be taken as the indicator to assess the deterioration of magnetic properties. The blanked edge with larger burnished ratio leads to lower increase of micro-hardness, less degradation of domain structure, and less deterioration of iron loss. In this paper, about 5.8% iron loss can be reduced by optimization of blanking clearance, which is quite pronounced for energy saving. In further study, an approximate linear function of the ratio of optimum clearance to gain size with $D^{-1/2}$ is empirically proposed to demonstrate the grain size dependence on optimum clearance determination. This paper thus provides an in-depth understanding and guidance for reducing the deterioration of magnetic properties caused by the blanking process.

Theoretical Basis for Physically Correct Measurement and Interpretation of Magnetic Energy Losses

This paper discusses fundamental physical mechanisms that are responsible for specific errors of standardized methods of magnetic loss measurements on laminated soft magnetic materials. It is shown that the Poyntings theorem offers an exact distinction between localized loss portions on the one hand and total losses on the other hand. Further, a clear distinction is suggested between mechanisms of hysteresis and eddy currents. The correct applicability of experimental measurements proves to be restricted to cases where the Poynting vector is restricted to normal off-plane components. This represents the only case where total losses can be determined on the basis of surface field and cross-sectional averaged induction. As a consequence, physically “correct” loss measurements are to be restricted to sample regions that exhibit mere axial magnetization, in exact ways. This is attainable with a single sheet tester, the homogeneously magnetized region of which is equipped with an induction coil and a large-area tangential field coil, in consistent ways.

Waveform Conditioning Problems of Nanocrystalline Alloys Under One/Two-Dimensional High-Frequency Magnetization

The problem of waveform distortion in high-frequency magnetization of nanocrystalline alloys has been discussed and analyzed in this paper. By measuring the sample in a rotational single sheet tester, the distortion caused by the dc bias field is largely reduced. A robust control algorithm based on model-free control is developed to keep the magnetic flux density sinusoidal when the materials are magnetized to saturated at high frequencies. Finally, the vector magnetic properties of nanocrystalline alloys are measured after adjusting the waveforms. The losses from 2 to 10 kHz in the casting direction and the transverse direction are calculated and compared.

Core Loss Calculation Based on Finite-Element Method With Jiles–Atherton Dynamic Hysteresis Model

For accurate computation of core losses, the Jiles–Atherton ( $J$ – $A$ ) dynamic hysteresis model accounting for hysteresis, eddy current and excess losses is incorporated into the finite-element method (FEM). The $J$ – $A$ dynamic hysteresis model is constructed by combining the traditional $J$ – $A$ hysteresis model with the models of instantaneous eddy current and excess losses. The $J$ – $A$ model parameters and dynamic loss coefficients are determined by fitting the models to the measurement data of a single sheet tester (SST 500) and Epstein frame tester. To find the robust best fit, the particle swarm optimization algorithm is employed. By using the proposed $J$ – $A$ dynamic hysteresis model and FEM, the magnetic characteristics of a magnetic core is simulated and the core loss distribution within the core obtained. The calculated and measured results are compared to show the accuracy and effectiveness of the proposed model.

Influence of Shielding on the Magnetic Field Measurement by Direct H-Coil Method in a Double-Yoked SST

This paper aims at describing the influence of shielding on the magnetizing magnetic field measured with an H-coil system, used in a double-yoked single-sheet tester. By the mean of a positioning system especially conceived for the purpose of this paper, the magnetic field is measured at different distances from the laminated sheet. The evolution of this field along the perpendicular line thus defined shows a distinctive behavior, whether the measure is realized in the presence of a magnetic shield or not. A description of the obtained experimental results is made, and a comparison with numerical models is realized. Finally, an explanation over the observed phenomena based on physical principles of electromagnetism is proposed.

Rotating magnetizations in electrical machines: Measurements and modeling

This paper studies the magnetization process in electrical steel sheets for rotational magnetizations as they occur in the magnetic circuit of electrical machines. A four-pole rotational single sheet tester is used to generate the rotating magnetic flux inside the sample. A field-oriented control scheme is implemented to improve the control performance. The magnetization process of different non-oriented materials is analyzed and compared.

Characterisation of soft magnetic materials by measurement: Evaluation of uncertainties up to 1.8 T and 9 kHz

Magnetic measurements are indispensable for the characterization of soft magnetic material used e.g. in electrical machines. Characteristic values are used as quality control during production and for the parametrization of material models. Uncertainties and errors in the measurements are reflected directly in the parameters of the material models. This can result in over-dimensioning and inaccuracies in simulations for the design of electrical machines. Therefore, existing influencing factors in the characterization of soft magnetic materials are named and their resulting uncertainties contributions studied. The analysis of the resulting uncertainty contributions can serve the operator as additional selection criteria for different measuring sensors. The investigation is performed for measurements within and outside the currently prescribed standard, using a Single sheet tester and its impact on the identification of iron loss parameter is studied.

Distribution of magnetic field strength inside exciting coil of single sheet tester

The double H-coil method was proposed to detect magnetic field strength on the surface of a specimen more accurately than the single H-coil method. In this paper, the distribution of magnetic field strength inside exciting coil of a single sheet tester (SST) is measured simultaneously by the single H-coil method using four separated H-coils. They are placed at different distances from the surface of the specimen and thereby enable us to evaluate the influence of the position of the H-coil on the measurement accuracy of magnetic properties. As a result, it was revealed that the magnetic field strength and specific total loss increase linearly as the distance of the H-coil from the surface of the specimen increases. However the increasing rate of the specific total loss is smaller than that of the magnetic field strength and within the range of required measurement reproducibility.

Performance Factor Comparison of Nanocrystalline, Amorphous, and Crystalline Soft Magnetic Materials for Medium-Frequency Applications

The efficiency of electromagnetic devices is influenced by the losses of the applied soft magnetic material. Different structured materials are available. Choosing the most appropriate material for a medium-frequency application is not intuitive. Electromagnetic circuits of power transformers or electric motors are usually made of conventional silicon–iron sheets. Higher power densities can be achieved by an increased operational frequency, but the loss density increases with higher frequencies as well. Amorphous and nanocrystalline materials benefit from reduced eddy current losses at higher frequencies. In this paper, a performance factor is evaluated to determine the suitability of each material in a frequency range up to 10 kHz. The geometric parameters of electromagnetic designs depend on the applied material. A performance factor may help to identify the most appropriate material at a specific frequency. The final application is a medium-frequency transformer. The losses of the magnetic materials are measured by using standardized measurement equipment such as single sheet tester or Epstein frame. A semi-physical iron-loss model is used to describe the measured losses. These results are used to determine the performance factor.

Vector Magnetic Hysteresis Measurement of Nonoriented Electrical Steel Sheets Under Unidirectional Compressive Stress Applied by Piezoelectric Actuators

This paper presents the vector magnetic hysteresis measurement of nonoriented electrical steel sheets under unidirectional compressive stress applied by piezoelectric actuators. We used a round rotational single sheet tester system to measure the vector magnetic hysteresis, where a stator of an induction motor was used to magnetically excite a sample in the in-plane orthogonal directions. To apply stress to the sample, we used commercial film-type piezoelectric actuators, which were directly glued on both surfaces of the sample. The experimental results showed that the compressive stress in the sample was proportional to the dc voltage applied to the actuators and that the loci of the magnetic field in the stress application direction were extended when increasing the compressive stress.

Implementation of the Single Hysteron Model in a Finite-Element Scheme

The single hysteron model is identified to reconstruct the magnetization processes of a grain-oriented electrical steel and it is implemented in a finite-element scheme. The model involves the Zeeman energy and the anisotropy energy of the material and an interaction field to take into account others terms, such as the magnetoelastic energy, the exchange energy, inclusions, and crystallographic discontinuities. The interaction field is evaluated experimentally using a round rotational single sheet tester, where a disk sample of the material is excited for several rotational magnetization processes. Details about the finite-element scheme, the computational time, and the memory allocations involved in the simulations are presented and discussed.

Investigation of a measurement method of 2-D magnetic properties by means of 1-D single sheet tester

Although two-dimensional (2-D) magnetic properties can be measured by using a 2-D single sheet tester (SST), the construction of the reliable 2-D SST is considerably difficult. By contrast, the flux density and magnetic field parallel to the excitation direction can be measured in a normal one-dime nsional (1-D) SST. If the average flux density points toward the excitation direction in a specimen with any inclination angle from its rolling direction, the magnetic energy can be defined and therefore 2-D magnetic properties can be calculated by means of an energy-based modelling method. However, the direction of the flux density and magnetic field in the 1-D SST has not been deeply discussed when a specimen with any inclination angle is measured. In this paper, the behavior of the flux density and the magnetic field strength is examined by using 1-D SST. The direction of the flux density is measured by using a pair of cross B-coils. The direction of the magnetic field strength is measured by using a pair of cross H-coils. The effect of the specimen width on the distribution of flux density is also investigated by using a magnetic field analysis. As a result, when a pair of cross H-coils is adopted to a specimen with appropriate aspect ratio, 2-D magnetic properties can be measured by means of the 1-D SST.

An anisotropic magnetostriction model based on BP neural network combining Levenberg-Marquardt algorithm and particle swarm optimization

In this paper, the dynamic magnetostriction of the electrical steel sheet is measured by a triaxial strain gauge based on a single-sheet tester under the alternating magnetic flux condition. The anisotropic magnetostriction property is analyzed, and an improved back propagation neural network assis ted model is applied to model the anisotropic principal strain of magnetostriction along different excitation directions. To keep the evaluation cost at an acceptable level, the Levenberg-Marquardt algorithm combined with particle swarm optimization is developed. Finally, the proposed model is verified by comparing the measured magnetostriction and computed one.

Measurement and modeling of magnetostriction characteristics of highly Grain-oriented electrical steel sheet by using round-type two-dimensional single sheet tester

Measurement and modeling of magnetostriction characteristics of highly Grain-oriented electrical steel sheet by using round-type two-dimensional single sheet tester

Comparison of two-dimensional single sheet testers for the measurements of vector hysteresis and magnetostriction characteristics

Comparison of two-dimensional single sheet testers for the measurements of vector hysteresis and magnetostriction characteristics

Measurement and analysis of effect of the stress on magnetostriction of electrical steel under harmonic fields

A magnetostriction single-sheet tester with an air compressor was developed and the magnetostriction in an electrical steel sheet was measured by a triaxial strain gauge under applied stresses externally and higher harmonic of field. The magnetostriction property’s sensitivity on the applied stress was described. This investigation also tried to understand the relationship between the presence of higher harmonics in the magnetization waveform and those in the magnetostriction waveform under a certain stress. The study results for the magnetostriction under stresses and harmonics show that the appearance of harmonic of magnetic field cannot be ignored, which aggravates the principal strain harmonics.

Representation of microstructural features and magnetic anisotropy of electrical steels in an energy-based vector hysteresis model

This paper demonstrates how the statistical distribution of pinning fields in a ferromagnetic material can be identified systematically from standard magnetic measurements, Epstein frame or Single Sheet Tester (SST). The correlation between the pinning field distribution and microstructural parameters of the material is then analyzed.

Dynamic extension of vector Preisach model

The objective of the present paper is to generalize the vector Preisach hysteresis model to take dynamic effects into account. A comprehensive analysis of the vector behavior has been performed by a single sheet tester with a specimen of round shape. The locus of the magnetic flux density vector has been controlled by a digital measurement set up at different frequency. An inverse vector Preisach hysteresis model has been built up by viscous-type scalar models and an identification procedure has been developed to follow the measured data. Finally, the model has been inserted into a finite element procedure through the fixed point technique to simulate electrical engineering problems.