Single Sheet Tester Research Articles

Measurement Technique of Magnetic Properties for Evaluation of Power Magnetic Materials

In recent years, the precise magnetic properties of electrical steel sheet are needed to develop high efficiency electromagnetic devices. An IEC standard single sheet tester is often used for the magnetic property measurement, especially for commercial transactions. But it is not accurate, so is not proper for the material evaluation based on its precise properties data. Therefore, we developed the measurement technique for the precise magnetic properties of electrical steel sheet. In this paper, two single sheet testers are shown. One is according to IEC standard (IEC-SST), and the other, the Stress load type-Single Sheet Tester (S-SST) is originally designed with our measurement technique for the precise magnetic properties. The key technology for evaluation of electrical steel sheet is proposed, using the S-SST and the IEC-SST. In particular, magnetic field strength distribution in measurement area inside exciting coil and solution of H coil specification difference are studied. And the magnetic properties of the S-SST and the IEC-SST are compared.

Magnetostriction of Transformer Core Steel Considering Rotational Magnetization

As it is well known, the power loss of transformer core steel depends on a series of parameters which vary in the final core in complex ways. The aim of the present study was to investigate the corresponding dependencies for the second key characteristic, i.e., magnetostriction (MS), as the most significant source of no-load noise. The MS-performance of core material was investigated by means of a rotational single sheet tester (RSST). Compared to loss, the peak-to-peak MS in rolling direction (RD; as the direction of strongest strain) shows similar increases with increases of both induction and axis ratio a. On the other hand, the shape of induction pattern B (t) proves to be rather insignificant, MS being similar for elliptic and rhombic magnetization. While increased dynamics of the pattern yields rising eddy current loss, MS remains unaffected. However, the harmonics show increases as being of relevance for audible noise. While mechanical tension in RD yields slight decreases of MS for alternating magnetization, MS for rotational magnetization increases for both tension and compression. As in the case of loss, MS shows significant increases for DC-bias which correlates with reports of increased noise. The study also included local measurements on a 2-limb, 1-phase model core and on a 3-limb, 3-phase core. MS remains in the order of 0.5 ppm for the 1-phase core, except from its corners. On the other hand, T-joint regions of the 3-phase core show values up to the order of 6 ppm, in accordance to RSST-results. Moderate DC magnetization, as being possible in practice as a long term phenomenon, yields distinct increase of MS intensity and MS harmonics with strong regional differences.

Vector magnetic property of electrical steel sheet and its influence on distributions of magnetic field and iron loss for electrical machines

Purpose – The purpose of this paper is to present the vector magnetic properties of the electrical steel sheet and investigate its influences on the magnetic field and iron loss distributions for the electrical machines. Design/methodology/approach – The vector magnetic property of the electrical steel sheet is measured by using a two-dimensional single sheet tester and modelled through an E&S vector hysteresis model to be applied to finite element analysis. Findings – The magnetic field and iron loss distributions are calculated by finite element analysis combined with the E&S vector hysteresis model for the three-phase transformer and induction motor models. Originality/value – The influences of the vector magnetic property on the electrical machines are verified by comparing with the numerical results from a scalar magnetic property.

Directional Properties of Cold Rolled Non-oriented Electrical Steel Sheets

Applications of cold rolled non-oriented (CRNO) electrical steels demand uniform magnetic property in all directions. The objective of the present study was to investigate the magnetic properties of CRNO steel in different directions. Four different sets of samples were made from CRNO steel sheets—(1) samples along the rolling direction, (2) samples at 30° to the rolling direction, (3) samples at 60° to the rolling direction and (4) samples at 90° to the rolling direction. The textural and magnetic properties were investigated using standard techniques. X-ray diffraction and electron backscattered diffraction were used for bulk- and micro-texture measurements respectively. Single sheet tester was used for core loss and magnetic permeability measurements. The results showed different textural and magnetic properties in all the CRNO samples. However, the properties were always better in rolling direction where the texture was more.

Local Non-contact Evaluation of the ac Magnetic Hysteresis Parameters of Electrical Steels by the Barkhausen Noise Technique

The potential of the magnetic Barkhausen noise method for local repeatable testing of the magnetic hysteresis properties of electrical steels was investigated. Strips of non-oriented and grain-oriented electrical steels were magnetized by a single yoke through 0–10 mm air gaps. The measurements were performed at standard ac conditions: 50 Hz sine induction waveform with different amplitudes. A vertically mounted array of three Hall sensors was used for the direct measurement of the surface magnetic field. The Barkhausen noise was detected locally by a surface-mounted pancake coil. The simultaneous measurement of the actual sample field makes it possible to stabilize a recently introduced parameter, called Barkhausen noise coercivity. This parameter demonstrates strong linear correlations to the hysteresis coercive force and to the hysteresis losses measured by the standard single sheet tester.

Multiobjective Cuckoo Search Algorithm Based on Duffing's Oscillator Applied to Jiles-Atherton Vector Hysteresis Parameters Estimation

The parameter identification of hysteresis models is a fundamental task for correct hysteretic material simulation. In vector models, as the Jiles-Atherton (J-A) vector model, the parameter determination increases in complexity since one must solve a nonlinear system with a relative large number of variables. In these cases, fitting methods one of the most attractive solution. In this study, an improved multiobjective cuckoo search (IMCS) is introduced for the J-A parameters determination. The proposed IMCS based on the Duffing's oscillator to step size tuning is verified using data from a rotational single sheet tester in two-dimensional version. Numerical comparisons of IMCS with results using a multiobjective cuckoo search demonstrated that the performance of the IMCS is promising in parameters estimation. Furthermore, the proposed IMCS method can be easily extended to solve a wide range of multiobjective optimization problems.

Development of Single Sheet Tester under Stress towards Reduction of Building Factor

In recent years, the precise magnetic properties of electrical steel sheet are needed to develop high efficiency electromagnetic devices. An IEC standard single sheet tester is often used for magnetic property measurement, especially for commercial transactions. But it is not proper for the material evaluation based on its precise properties data. Therefore, we developed measurement techniques for the precise magnetic properties of electrical steel sheet. In this paper, the key technology for evaluation of electrical steel sheet is proposed. The single sheet tester based on evaluation measurement technique is useful for adequate choice of electrical steel sheet for high efficiency electrical devices and evaluation of high performance power magnetic materials, etc.

Controllable Magnetic Hysteresis Measurement of Electrical Steels in a Single-Yoke Open Configuration

A newly developed measurement system was comprehensively tested for the industrially attractive case of an open magnetic circuit. Series of industrial electrical steels were magnetized by a single yoke through a gap of several millimeters. According to standards, the magnetic induction waveform was adjusted to a 50-Hz sine curve using a digital feedback procedure. The magnetic surface fields above the sample were measured directly by a vertically mounted array of three Hall sensors. The actual magnetic field was determined by a linear extrapolation of the measured field profile to the sample face. It was experimentally shown that control of the induction waveform and simultaneous direct determination of the sample field make the hysteresis loop measurements independent of the yoke-sample gap. In addition, the obtained physically correct data show good linear correlations with the corresponding standard values measured by a single sheet tester. These outcomes are important for revision of the principles of industrial testing and further development of the measurement standards.

전기강판의 벡터 자기특성을 고려한 전기기기의 손실특성 해석

This paper presents vector magnetic properties of an electrical steel sheet (ESS) employed for electric machine and iron loss analysis considering the vector magnetic properties of the ESS. The vector magnetic properties of the ESS are measured by using a two-dimensional single sheet tester and modeled by an E&S vector hysteresis model to be applied to finite element method. The finite element analysis considering the vector magnetic properties is applied to iron loss analysis of a three-phase induction motor model, and the influences of the vector magnetic properties on the iron loss distribution are verified by comparing with numerical results from a typical B-H curve model.

Modeling of Two-Dimensional Magnetic Properties Based on One-Dimensional Magnetic Measurements

This paper proposes a modeling method of two-dimensional (2D) magnetic properties based on magnetic energy obtained from several one-dimensional (1D) magnetic properties with different inclination angles from rolling direction. We compare the measurement results of non-oriented electrical steel sheets by 2D and 1D single sheet testers (SSTs) and confirm that almost the same magnetic properties can be obtained from each tester. Based on several 1D magnetic properties measured by the 1D-SST, we evaluate a magnetic energy by using a Fourier series expansion. By differentiating the estimated magnetic energy, we can obtain the perpendicular components of magnetic field with respect to the magnetic flux density which cannot be measured by the 1D-SST. In order to confirm the validity of the proposed method, we compare the estimated 2D magnetic properties with measured ones. Finally, the calculation procedure of the Jacobian matrix is presented and the proposed method is applied to the finite element analysis.

Modelling Dynamic Losses Under Rotational Magnetic Flux

The flux density waveform in the stator of a rotational electrical machine or three-phase transformer is typically bidirectional in many regions of the core. However, rotational magnetic flux can be observed in some parts of their magnetic circuits. The iron core under rotational flux presents magnetic losses, usually, greater than the alternating ones, for a same flux magnitude. The magnetic behavior of materials under rotating flux is extremely complex and can not be represented with hysteresis or conventional magnetic losses models. The vector hysteresis model of Jiles-Atherton has been shown effective in modeling rotating flux for isotropic and anisotropic materials. It is observed that the rotational losses increase with the increase of excitation frequencies. In this work, the iron losses behavior is investigated under rotational flux by combining the Jiles-Atherton vector hysteresis, eddy currents and excess losses models. Experimental curves are obtained from a rotational single sheet tester and the losses components are analyzed.

Phase Correction for High Precision Measurement of Iron Loss using H-coil Method

SUMMARY The accurate magnetic properties of electrical steel sheets are important for the development of high-efficiency electromagnetic devices. In particular, the H-coil method is a useful technique for accurately measuring magnetic field strength in a single sheet tester. Therefore, we developed a tester for magnetic field properties using the H-coil method, referred to as the stress load type single sheet tester (S-SST), and a problem was found in iron loss measurement at a high flux density of 1.6 T or more. In this paper, it is shown that the cause of this problem is the phase difference between the induced voltage in the H-coil and the B-coil. Because the phase difference makes the B–H loop slightly twisted near the tip point, the iron losses are evaluated low. Thus, we propose a method of determining the phase correction values. These values are measured in the absence of a specimen in the S-SST measurement system, and the phase correction method for induced voltage in a coil is investigated. Finally, ideal results for the correction of iron loss in nonoriented electrical steel sheets are shown. The proposed method is effective for the calibration of a single sheet tester using the H-coil method.

Rotational Magnetization in Transformer Cores—A Review

Usually, rotational magnetization (RM) is associated with rotating machine cores. However, in more restricted ways, it also arises in three-phase transformer cores. Modern designs of T-joint yield detours of flux, as a source of RM in the T-joint, the middle limb ends, as well as in the yokes. Simulation of RM is possible by means of so-called rotational single sheet testers which should consider the large grains of highly grain oriented materials. Their high effective anisotropy yields induction patterns of rhombic or lancet-like type with maximum values of axis ratio a up to 0.5, and very high angular velocity round the materials hard directions. Compared to elliptic RM-as arising in non-oriented materials-the corresponding losses are lower due to restricted induction in the hard direction. But they show strong increase with (i) rising a and (ii) rising angular velocity of the induction vector. The magnetostrictive strain shows a pronounced (negative) maximum in the rolling direction with values up to 10 ppm, the transverse direction and normal direction exhibiting positive maxima of lower extent. With respect to industrial relevance, significant RM effects are restricted to the vicinities of T-joints. They represent the location of maximum core loss and also of maximum magnetostrictive strain as a source of audible core noise.

Development of the 2-D Single-Sheet Tester Using Diagonal Exciting Coil and the Measurement of Magnetic Properties of Grain-Oriented Electrical Steel Sheet

In order to analyze magnetic characteristics of magnetic devices, it is necessary to accurately measure magnetic properties of an electrical steel sheet in arbitrary directions. In this paper, we developed a 2-D-single-sheet tester (SST) using diagonal exiting coils in order to improve the measurement accuracy under high flux condition. The measurement region of flux density B and magnetic-field strength H is examined for the accurate measurement. The magnetic properties of grain-oriented electrical steel sheet under alternating magnetic flux and rotating magnetic flux are measured using our system. The accuracy of measurement in the case of grain-oriented sheet is examined by comparing the measured results using 2-D-SST with those by using an ordinary SST under alternating flux excitation. The effect of positioning error of orthogonal B and H coils on measurement accuracy is also discussed.

Solution of Jiles–Atherton vector hysteresis parameters estimation by modified Differential Evolution approaches

Differential Evolution (DE) is a simple and efficient stochastic global optimization algorithm of evolutionary computation field, which involves the evolution of a population of solutions using operators such as mutation, crossover, and selection. The basic idea of DE is to adapt the search during the evolutionary process. At the start of the evolution, the perturbations are large since parent populations are far away from each other. As the evolutionary process matures, the population converges to a small region and the perturbations adaptively become small. DE approaches have been successfully applied to solve a wide range of optimization problems. In this paper, the parameters set of the Jiles–Atherton vector hysteresis model is obtained with an approach based on modified Differential Evolution (MDE) approaches using generation-varying control parameters based on generation of random numbers with uniform distribution. Several evaluated MDE approaches perform better than the classical DE methods and a genetic algorithm approach in terms of the quality and stability of the final solutions in optimization of vector Jiles–Atherton vector hysteresis model from a workbench containing a rotational single sheet tester.

The influence of assist gas on magnetic properties of electrotechnical steel sheets cut with laser

The paper presents the influence of assist gas (air and nitrogen) during laser cutting on magnetization, magnetic permeability and loss characteristics of non-oriented electrical steels. The research was made on an non-oriented M330-50A grade electrical steels by means of single sheet tester. In order to enhance the effect of cutting and the same degradation zone on magnetic properties, strips with different width were achieved. Measurements results indicate that application of air as assist gas has more destructive effect on magnetic properties of electrical steels than nitrogen one.

Novel measurement method of DC magnetic properties having freedom of specimen shape

The dc B–H curve or hysteresis loop of a magnetic material is necessary even in dynamic field analysis. Conventional methods for measuring magnetic properties require special shape specimens like a plate or a rod of specified dimensions. In this paper, we developed a novel technique for measuring the dc magnetic properties of specimens with various shapes using an electromagnet and a special probe having two Hall elements with very small active area. It is also shown that the magnetic field is not uniform near the specimen, and the magnetic field strength H on the surface of the specimen can be obtained by extrapolation. In addition, the dc excitation due to the earth’s magnetic field can be avoided by setting small gaps between the specimen and pole pieces. The magnetic properties of an electrical steel sheet and a cylindrical specimen of a soft magnetic composite can be measured using the proposed technique. It is shown that the measured result using the proposed system is almost the same in comparison to a single sheet tester.

Vector Preisach hysteresis modeling: Measurement, identification and application

The paper presents a Preisach model to simulate the vector hysteresis properties of ferromagnetic materials. The vector behavior has been studied using a single sheet tester with a disk-shaped specimen at low frequency. The locus of the magnetic flux density vector has been controlled by a digital measurement system. An inverse vector Preisach hysteresis model has been developed and identified by applying the measured data. Finally, the inverse model has been inserted into a finite element procedure through the fixed point technique and the reduced magnetic scalar potential formulation to simulate the measurement system. The applicability of the measurement system as well as the developed model has been proven by comparing measured and simulated results.

Simulation of uniaxial anisotropy by vector Preisach model

The paper presents a rotational single sheet tester, which can be used to measure vector hysteresis characteristics using specimen with round shape. The measured hysteresis characteristics in the two orthogonal directions present the uniaxial anisotropy of the material under test, which has been handled by the Fourier expansion of the measured Everett functions. The Fourier coefficients of the unknown vector Everett function have been identified by the modification of a previously implemented algorithm. In the identification task linearly and circularly polarized measured data have been taken into account. Comparisons between measured and simulated data show acceptable results.

Influence of Compressive Stress on Magnetic Properties of Laminated Electrical Steel Sheets

In a practical motor, the compressive stress of more than 100 MPa is sometimes impressed by a shrink fitting etc, as a result, the magnetic properties of iron core deteriorate. Therefore, it is necessary to measure magnetic properties under the compressive stress. However, the measurement under the compressive stress of more than 100 MPa is difficult if a single sheet tester is used, because of the buckling of a single sheet specimen. Then, we measured the magnetic properties under the compressive stress up to 150 MPa without buckling by using a laminated specimen. It is shown that the permeability rapidly decreases even by small stress in both cases of rolling and transverse directions. The iron loss is increased by the stress, but it almost does not increase when the stress is larger than about 50 MPa. Furthermore, the permeability and iron losses of the rolling direction and transverse direction become the same values, and the anisotropy disappears when the stress is larger than about 50 MPa.