Single Sheet Tester Research Articles

Unreliable determination of vector B in 2-D SST

Rotations of vector B in a square rotational single sheet tester and a round rotational single sheet tester were compared. Two pairs of B coils (45° displaced) were used to control and verify the rotation of vector B at different coil diameters. It was clarified that two sinusoidal induced voltages in B coils do not ensure the rotational flux condition in the area inside the B coils in the sample, especially in a larger measuring region.

WITHDRAWN: Two-dimensional field model for single-sheet tester

WITHDRAWN: Two-dimensional field model for single-sheet tester

Magnetic properties and loss separation in iron powder soft magnetic composite materials

New developments in powder metallurgical composites make soft magnetic composite (SMC) material interesting for application in electrical machines, when combined with new machine design rules and new production techniques. In order to establish these design rules, one must pay attention to electromagnetic loss characteristics of SMC material. In this work, five different series of iron based SMCs are produced and studied: (1) Pure iron powder with resin; (2) sintered iron based powders; (3) pure iron powder with additions of Zn-st and carbon; (4) iron based powder alloys (Fe,Nb,Si); (5) commercially available iron powder “Somaloy.” The specimens were shaped as rectangular rods and characterized on a miniature single sheet tester which was calibrated to Epstein. The measured energy losses are analyzed following the loss separation theory of Bertotti, in which the total energy loss is decomposed into hysteresis loss, classical Foucault loss, and an excess loss component.

Controlled circular magnetization of electrical steel in Rotational Single Sheet Testers

A new waveform control algorithm for Rotational Single Sheet Testers (RSST) is presented. The new algorithm achieves circular magnetization for high induction levels even in samples of grain-oriented silicon steel sheets. The algorithm is based on the circuit model of the system and takes the coupling between the two phases of the RSST into account. Identification of the parameters of the measurement setup with the Least Squares (LS) method avoids preliminary measurements on the sample and the setup. The performance of the algorithm is illustrated by measurements on a grain-oriented sample. The algorithm is universally applicable and allows fully automated measurements.

The measurement of magnetic properties of electrical sheet steel – survey on methods and situation of standards

A brief review of the different requirements for magnetic measurement techniques for material research, modelling of material properties and grading of the electrical sheet steel for trade purposes is presented. In relation to the main application of laminated electrical steel, this paper deals with AC measurement techniques. Two standard methods, Epstein frame and Single Sheet Tester (SST), producing different results, are used in parallel. This dilemma was analysed in detail. The study leads to a possible solution of the problem, i.e. the possibility of converting the results of one of the two methods into the results of the other in order to satisfy the users of the Epstein method and, at the same time, to improve the acceptance of the more economical SST method.

Effect of grain diameter on iron loss properties of non-oriented silicon steel sheets

The iron loss properties of the non-oriented silicon steel sheets as a function thickness, silicon contents, cutting angle and grain diameter were measured by single-sheet tester (SST). The specimens were excited by sinusoidal waveform (50 Hz), fundamental waveform (50 Hz) with a single high-order harmonic component and PWM waveform. The averaging loss of three directions is defined as ( L+2× C+ T)/4 (called as A3D loss). The increase ratio of non-sinusoidal waveform exciting condition’s A3D loss against the sinusoidal waveform one was different despite the equal levels of the A3D loss under sinusoidal waveform exciting condition. This is because it depends on a difference of iron loss constitution.

Comparison between the H-coil method and the magnetizing current method for the single sheet tester

In order to clarify the difference between the magnetizing current method and the H-coil method quantitatively, a special single-sheet tester which can separate the iron loss produced in the yokes is designed. The results measured show that 1.7–3.9% of power loss difference in the two methods is mainly due to the iron loss in the yokes.

Accurate field strength measurement in rotational single sheet testers

The accuracy of the field strength measurement in rotational single sheet testers (RSST) has been investigated by means of both finite element calculations and measurements on the built set-up. Shielding laminations should be used above and underneath the actual sample in order to obtain a two-dimensional and homogeneous magnetization and to measure the field strength accurately.

Application of neural networks for the prediction of multidirectional magnetostriction

This paper describes attempts to use artificial neural networks (ANNs) for the prediction of magnetostriction (MS) characteristics of transformer core materials. In this first approach, the ANNs were trained with data from a rotational single-sheet tester to predict MS in rolling direction (r.d.) as a function of material grade, amplitude and shape of multidirectional magnetisation as well as the level of additional mechanical stress. It is shown that ANNs are able to forecast the corresponding relative MS changes in an approximate way.

Waveform control algorithm for rotational single sheet testers using system identification techniques

In rotational single sheet testers (RSST), the magnetic properties of electrical steel sheet are measured for well-defined one- or two-dimensional induction waveforms over a large frequency range (1–200 Hz). For this task, a new iterative waveform control algorithm is presented. It is based on the recursive least squares system identification technique. The modeling of the setup as well as the principles and implementation details of the algorithm are discussed. Simulation and measurement results for alternating sinusoidal magnetization of the sample are presented. The main advantage of the proposed method is that it does not require preliminary information concerning the properties of the tested material or the measurement setup. The method is therefore ideally suited for use in a fully automated measurement system. Furthermore, especially for low frequencies (1–10 Hz) the proposed algorithm exhibits faster convergence compared to previously described methods.

磁気的性質を利用したSM490鋼の残留ひずみの測定法に関する研究

In order to establish a nondestructive method of estimating residual strains induced in structural components for buildings, the magnetization properties of stress-imposed SM490A steel were measured, using a tensile tester equipped with a single sheet tester. In this measurement, the correlation between the magnetization properties such as the coercive force and the permeability and the mechanical properties such as the stress and the strain was discussed. In order to confirm the degree of deterioration, the magnetization properties were estimated compared with the dislocation density. The magnetization properties were measured when repeated stress was loaded to simulate the stress applied by the earthquake and the wind. Monotonic decrease and increase as functions of the tensile strain are observed in the permeability and the coercive force, respectively. These findings suggest that changes in the permeability and the coercive force with strains can be used for nondestructive estimation of deterioration of structural materials.

単板磁気試験器を用いた偏磁気特性の測定

A common method for the measurement of dc-biased magnetic properties is the use of ring specimens. Although ring specimens are popular for measuring magnetic properties, it takes a long time to prepare the windings. It is therefore difficult to compare various kinds of specimens in a short period. This problem can be solved by using a single-sheet tester (SST). This paper presents an improved measurement system for dc-biased magnetic properties and some measured results for grain-oriented silicon steel sheets of different rolling direction.

Field homogeneity in a two-phase rotational single sheet tester with square samples

Finite element method (FEM) calculations have been used to determine the geometry and field homogeneity in a two-phase rotational field single sheet tester with square samples. Mounting shielding laminations above and underneath the actual sample improves the field homogeneity. Chamfering the yoke also enhances field distribution, but this effect turns out to be less important than shielding the sample.

Inter-comparison of single sheet testers for amorphous alloys by round robin measurements

An international round robin supported by the Japanese Government has been started in order to establish the IEC standard of measuring the magnetic characteristics of amorphous magnetic materials. Several kinds of single sheet testers are produced and automatic measuring systems are prepared at 6 countries. Power loss and exciting VA are measured and the accuracies are compared.

Single sheet tester having open magnetic path for measurement of magnetostriction of electrical steel sheet

A single sheet tester having closed magnetic path (a closed type of SST) has a problem that measurement accuracy of magnetostriction is considerably affected by electromagnetic force between specimen and yoke. Therefore, an open type has been developed. In order to get uniform flux distribution in a sufficiently large region, a compensating magnetizing winding is installed, and a method of waveform control is investigated, in which applied voltages to main and compensating windings are adjusted individually. The effectiveness of the newly developed open type is demonstrated by measuring magnetostrictions of thin amorphous sheet as well as highly grain-oriented silicon steel sheet.

Improvements of single sheet testers for measurement of 2-D magnetic properties up to high flux density

Due to structural limitation, the currently proposed apparatus based on a single sheet tester (SST) cannot measure magnetic properties along arbitrary directions (so-called 2-D magnetic properties) of silicon steel at high flux densities. In this paper, significant improvements are carried out on magnetizing windings and auxiliary yokes of a double excitation type of SST. Furthermore, crosswise overlapped H-coils are introduced so that even an ordinary single-excitation type of SST can be applicable to the measurements of 2-D properties. It is demonstrated that 2-D magnetization property up to 1.9 T can be measured by using the newly developed SST's.

引張荷重負荷時の磁化特性に着目した構造材の劣化評価

In order to establish a nondestructive method of estimating residual strains induced in structural components for buildings, the magnetization properties of stress-imposed SS400 steel were measured, using a tensile tester equipped with a single sheet tester. In the elastic region, the permeability increases with increasing tensile stress and reaches a peak at the beginning of the plastic deformation, whereas the coercive force decreases with increasing stress. In the plastic region, as the applied stress increases, the permeability decreases, while the coercive force increases. Monotonic decrease and increase as functions of the tensile strain are observed in the permeability and the coercive force, respectively. These findings suggest that changes in the permeability and the coercive force with strains can be used for nondestructive estimation of deterioration of structural materials.

単板磁気試験器を用いたディジタル磁気特性測定システムにおける波形制御法

単板磁気試験器を用いたディジタル磁気特性測定システムにおける波形制御法

Measuring system for magnetostriction of silicon steel sheet under AC excitation using optical methods

A measuring system for magnetostriction of silicon steel sheet using optical methods and a single sheet tester has been developed to establish a standard test method for IEC and JIS. Various factors affecting measurement accuracy and reproducibility of the developed system are examined. Two optical instruments, such as a laser Doppler vibrometer and a heterodyne displacement meter, are compared. 3-D characteristics of magnetostriction under ac excitation in the rolling direction are measured up to 2.0 T.

The single sheet tester. Its acceptance, reproducibility, and application issues on grain-oriented steel

Different systematic error characterictics of the Epstein and the Single Sheet Tester (SST) method (accordin to IEC publ. 404-3 (1992)) cause differences of up to 10% between the specific total power loss values provided by th two methods, resulting in inconsistent values of core loss building factors in transformers. In addition, the older SST version, SST(1982), being calibrated to the Epstein tester which uses annealed samples, has been found to yiel questionable results for some materials.Moreover, the calibration to the Epstein tester tends to decrease th reproducibility. This unclear situation made ABB initiate an international Round-Robin Test of correspondin measurements of grain-oriented materials including the comparison of SST(92) and SST(82). The results of this stud are presented in this paper along with the presentation of the application issues. The results underline the need for further activities in this field. These activities should aim at arriving at the mo reproducible and reasonably simple method which delivers power loss values acceptable to manufacturers an consumers. The paper concludes with suggestions for future work.