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

Abstract

The hysteresis properties of electrical steel sheet (ESS) is very helpful to develop new type electrical machines and improve their performance. Therefore, two-dimensional steel sheet tester (SST) is required to measure the hysteresis properties of ESS. This paper introduces a kind of square type SST, but this SST can only measure the non-oriented and grain-oriented ESS because the size of the specimen is not large enough. To measure highly grain-oriented ESS, a new round type SST which is designed to have broader region of uniform field and allows a larger specimen is proposed in this paper. Meanwhile, magnetostriction properties also can be measured by this round type SST.

Keywords

Electrical steel sheet single sheet tester hysteresis property magnetostriction

1. Introduction

In order to satisfy the need to develop new type electrical machines and improve their performance, various magnetic materials have been employed as the cores of these devices. Typically, highly grain-oriented (HGO) and grain-oriented (GO) silicon electrical steel sheet (ESS) are used in transformer core and non-oriented (NO) ESS is used for rotating electrical machines. Meanwhile, the magnetic properties of these magnetic materials used have a strong impact on the performance of these devices, such as iron loss, vibration and noise. Therefore, the magnetic properties of these ESSs should be carefully characterized.

In order to measure rotating two-dimensional (2-D) magnetic properties, a lot of different 2-D Steel sheet testers (SSTs) were built up in various laboratories [1, 2, 3, 4, 5, 6, 7, 8]. Most of them use the square type SST with square specimen [2, 3, 4, 5]. The square type SST has some disadvantages, therefore some different tester such as round type SST has been developed [6, 7, 8]. However, all of the above 2-D SST cannot use for HGO ESS measurement if feedback method is selected to control the applied current. The iteration process cannot converge because the size of the specimen is not enough. In this paper, a new round type 2-D SST which is designed to have broader specimen size and region of homogeneous magnetic field is proposed to measure HGO ESS and it will be compared with traditional square type SST.

2. Measurement

Square type SST is a traditional measurement device which is proposed by Enokizono [2]. In this paper, a Square type SST is proposed as shown in Fig. 1, has its specimen of 80 $\times$ 80 mm, H-coil of 20 $\times$ 20 mm with 150 turns, and B-coil of one turn. The exciting coils consist of two pair of orthogonal coils with 300 turns per pair to generate the rotating magnetic fields. Compared with traditional device (i.e., rectangular type SST), two upper and lower electrical shields which are made of NO ESS are fixed at the positions of 2 mm apart from the specimen respectively to isolate jumping-flux and apply a uniform magnetic field on the specimen as shown in Fig. 1b.

Figure 1.

Photo of square type SST.

Figure 2.

Measured data for NO ESS using square type SST.

Figure 3.

Photo of round type SST.

In this system a feedback method is selected to control the applied current of the exciting coils, as in a typical SST, in order to ensure that the exact magnetic field applied on the specimen. The convergence process is as follows:

Step 1:

Output the target magnetic field on the specimen though the exciting voltage applied on the exciting coils;

Step 2:

Measure the induced voltage from the B-coils;

Step 3:

Compare the measured induced voltage and the target applied voltage and calculate the error. Then the applied voltage will be modified by following equation:

$\mbox{V}_{c}^{i+1}=V_{c}^{i}-\frac{V_{c}^{i}}{E_{b}}\cdot k(E_{b}^{i}-E_{bt})$ (1)

where $k$ is the feedback coefficient, and it will decide the speed of convergence. $V^{i}_{c}$ is the applied voltage at i-th convergence loop, and $E^{i}_{b}$ is the induced voltage from B-coils. $E_{bt}$ is the target applied voltage. Then the modified voltage will applied on the exciting coils and go to step 2. Until the error is small enough, this process will be stopped. After this feedback control method, the target rotating magnetic field will be applied on the specimen.

Figure 2 shows the applied rotating magnetic field and the corresponding magnetic field strength of a NO ESS 35PN440 measured by using SST. From the results, exactly circle magnetic fields are applied on the specimen.

A HGO-ESS has magnetic domains which are in general bigger in size and higher in degree of alignment than those of NO and GO ones, and accordingly requires wider region of uniform magnetic field than other ESS. According to our experience, using the conventional square type SST, B-waveform control using Eq. (1) is very difficult, and sinusoidal B-waveform could not be obtained. We think it is because the width of the B-coil in conventional Square type SST is not enough wide to measure the magnetic flux density in average sense.

In order to measure the magnetic property of HGO, a new round-type 2-D SST which is designed in this paper to have broader region of uniform field and allows a larger specimen than the square-type SSTs [1, 2, 3, 4, 5, 6, 7, 8] is shown in the Fig. 3 which has its specimen of diameter 162.5 mm, H-coil region of 40 $\times$ 40 mm with 130 turns, and B-coil of one turn. The system, to remove the jumping-flux and apply uniform magnetic field on the specimen, has upper and lower magnetic shielding plates made of NO ESS at the positions of 2 mm apart from the specimen, respectively. In the system, the $B$ -coils threaded through small holes at the center of the specimen, and the $H$ -coil is located at the surface of the specimen. The three-axial strain gauge is attached to the central part of the specimen to measure the mechanical strain. The specifications of the rectangular and round-type SSTs are compared in Table 1. The convergence situation is compared in Table 2.

Table 1

Specifications of the developed R-2D-SST system

Item	Proposed	Conventional
Type	Runo d	Rectangle
Specimen	Circular $d=$ 162.5 mm	Rectangular 80 $\times$ 80 mm ${}^{2}$
B-coil width	40 mm	20 mm
H-coil region	40 $\times$ 40 mm ${}^{2}$	20 $\times$ 20 mm ${}^{2}$
Shield	Upper and lower	Upper and lower

Table 2

Convergence situation comparison

Item	Round type SST	Rectangle style SST
Non- oriented	Convergence	Convergence
Grain-oriented	Convergence	Convergence
Highly grain-oriented	Convergence	Non-convergence

In addition, the magnetostriction properties of HGO are also important because it will generate noise and vibration of transforms. Therefore, three-axial strain gauge is attached on the specimen as shown in Fig. 3c to measure the magnetostriction properties. The detail configuration has shown in [9]. Figures 4 and 5 show the measured magnetic hysteresis properties and magnetostriction butterfly loops under elliptic magnetic field. From the results, the target ellipse rotating magnet fields are exactly applied on the HGO specimen by the B-waveform feedback control method.

Figure 4.

Measurement hysteresis properties of HGO ESS under ellipse magnetic fields when $\alpha=$ 0.3, $\varphi=$ 50 ${}^{\circ}$ .

Figure 5.

Butterfly loops of normal strain ( $\varepsilon_{x}$ and $\varepsilon_{y}$ ) of the HGO-ESS under elliptic magnetic fields when $\alpha=$ 0.3, $\varphi=$ 50 ${}^{\circ}$ .

3. Conclusion

In this paper, two kinds of 2-D steel sheet testers, Square type and round type SST, are explained. For highly grain-oriented ESS, voltage control feedback method cannot converge if the traditional Square type SST is used. Therefore, a round type SST which allows a larger specimen is proposed to measure its magnetic properties and magnetostriction properties of HGO-ESS. The measured results are presented in this paper.

Footnotes

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (2017R1D1A3B03034633).

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