Measurement of Magnetic Properties of Grain-Oriented Electrical Steel Sheet Using 2D Single Sheet Tester

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Yuki MORI, Daisuke MIYAGI, Masanori NAKANO, Norio TAKAHASHI Okaama Universit Measurement of Magnetic Properties of Grain-Oriented Electrical Steel Sheet Using D Single Sheet Tester Abstract.

1 Yuki MORI, Daisuke MIYAGI, Masanori NAKANO, Norio TAKAHASHI Okaama Universit Measurement of Magnetic Properties of Grain-Oriented Electrical Steel Sheet Using D Single Sheet Tester Abstract. We have alread reported the accurac of measurement of D magnetic properties of non-oriented electrical steel sheet using a novel SST. In this paper, magnetic properties under alternating and rotating magnetic flu of grain-oriented sheet are measured. The accurac of measurement in the case of grain-oriented sheet is eamined b comparing the measured results using D-SST with those using an ordinar SST under alternating flu ecitation. The effect of positioning error of orthogonal B and H coils on measurement accurac is also discussed. Strescenie. Oceniono dokładność badania blach orientowanej pr wkorstaniu testera D SST. W celu ocen niepewności wniki porównano reultatami otrmanmi pr wkorstaniu konwencjonalnego testera SST. Predskutowano problem błędu pocjonowania cujników. (Pomiar właściwości magnetcnch blach orientowanej pr użciu testera D SST) Kewords: grain-oriented electrical steel sheet, alternating magnetic flu, rotating magnetic flu, two-dimensional magnetic properties. Słowa klucowe: blacha orientowana, tester SST. Introduction Recentl, a miniature and efficient magnetic device is required. When it is miniaturied, the magnetic flu densit of the magnetic circuit becomes high. Therefore, a precise measurement at high flu densit of electrical steel sheet that is a main material of magnetic device is important. Generall, the magnetic properties are measured b using a single sheet tester (SST), but it can onl measure magnetic properties in one direction. In order to anale magnetic characteristics of magnetic devices, it is necessar to accuratel measure magnetic properties of electrical steel sheet in arbitrar directions []. We have alread developed a novel D-SST and reported the accurac of measurement of D magnetic properties of non-oriented electrical steel sheet []. In this paper, magnetic properties of grain-oriented electrical steel sheet under alternating magnetic flu and rotating magnetic flu are measured using our sstem. The accurac of measurement is also eamined. D-SST ( dimensional single sheet tester) Fig. shows the measuring equipment. The eciting coils for rolling direction () are covered b those for transverse direction (TD). The dimension of a square specimen used for measurement is mm mm. Two kinds of specimens, grain-oriented electrical sheet, G, and highl grain-oriented one, P, are measured. The flu densit under alternating and rotating flu ecitation is increased until.8t. B eciting the specimen in the diagonal direction, the uniformit of magnetic field distribution near the center is improved []. It is verified that the magnetic field is uniform within % deviation in mm mm area at the center of specimen. The flu densit in the specimen is measured using the so-called modified probe method []. Pin holes are made in the insulating coating on the specimen b a needle with mm distance. Then, the electricall conductive adhesive is put with lead-out wires into the pin holes as shown in Fig.. The lead-out wires are twisted in order to avoid inductive pick up. The same lead-out wires are put on other side. Both lead-out wires form a B-coil. The orthogonal H coils is made of mm thick plate. Each H coil has turns and has been wound with.mm polester copper wire. Two H coils [] are installed on the specimen, as shown in Fig.. Investigation of measurement accurac of D-SST In order to eamine the accurac of D-SST in measuring magnetic properties of grain-oriented electrical steel sheet, the measured results using D-SST and the ordinar mm width SST are compared. Magnetic properties are measured b using D-SST under alternating magnetic flu ecitation. Magnetic properties in the rolling direction (, B =deg.) and transverse direction (TD, B =9deg.) are measured. Rectangular specimens (mm mm) which are parallel to and TD directions are prepared for mm width SST. The specimen is processed b wire cut. The H-coils method is used in mm width SST. The frequenc was H and H, and the edd current loss (W e ) and the hsteresis loss (W h ) are separated b the two frequenc method using the measured results at H and H. Fig.. D-SST. B-coil (a) upper view (b) side view Fig.. B-coils and those setting position. (a) upper view H-coil specimen supporting jig B-coil (b) side view Fig.. H-coils and those setting position. electricall conductive adhesive specimen supporting jig PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN -9, R. 8 No 9b/

2 Measured results of B =deg., 9deg. of G are shown in Fig.. The whole iron loss (W), the edd current loss (W e ) and the hsteresis loss (W h ) measured using D-SST are almost agree with those of mm width SST. But, there is some discrepanc in W e and W h at B =9deg. between D-SST and mm width SST. This ma be due to the fact that the effect of stress, which is remained in the specimen, cannot be neglected [], because the width (=mm) of specimen is not sufficientl large. Therefore, it is considered that the accurac of D-SST is similar to that of mm width SST. In order to eamin the effect of grain on the measured iron losses in three kinds of small areas (mm mm), namel, area A (center of mm mm specimen), area B (-mm apart from the center in the longitudinal direction), area C (+mm apart from the center), the iron losses are measured using mm width SST. The H coils with mm mm and mm mm measurement areas is used. The B coil with mm width, prepared using the modified probe, is put on the specimen in each area. The measured iron losses are shown in Table. The discrepanc between measurements is within %. Therefore, it can be understood that magnetic properties of the grain-oriented electrical steel sheet can be measured in the measurement area of mm mm, because the grain sie is of the order of mm. Iron loss [W/kg] Iron loss [W /kg]... W (D-SST) W (D-SST) W h (D-SST) W h (D-SST) W e (D-SST) W e (D-SST).. (a) =deg. W (D-SST) W (D-SST) Wh(D-SST) W h(d-sst) We(D-SST) We(D-SST).. (b) =9deg. Fig.. Comparison of iron loss of D-SST and D-SST (H, G). Table. Iron loss measured at various areas (H, G). iron loss [W/kg] area A area B area C Magnetic properties under alternating magnetic flu The magnetic properties of the grain-oriented electrical steel sheet (grade: G) in each direction (ero to 9 deg. with deg. step from the rolling direction) is measured under an alternating flu ecitation. The measurement frequenc is H. Fig. shows the measured B m -H b curve, angle HB and iron loss W. H b is the magnetic field strength when the magnetic flu densit becomes a maimum. B m is the maimum flu densit. HB is the phase angle of H waveform which is measured from the B waveform. The magnetic field strength H b becomes the largest when B is equal to around deg. and deg. for the same flu densit as shown in Fig. (a). This ma be due to the fact that the structure of magnetic domain changes around those direction B. Main magnetiation process at low magnetic flu densit is due to the moving of the magnetic domain wall. Then, the magnetic field strength H b at low flu densit become a maimum at 9 deg. due to the uniaial magnetic anisotrop. On the contrar, the magnetiation process at high magnetic flu densit is changed due to the rotation of magnetic domain. The magnetic anisotrop induced at the grain boundar influences at high magnetic flu densit []. H vector is usuall eceeds B vector. This means that HB is usuall positive. However, HB is positive, for eample, in the cases of B = and 8deg. at high flu densit as shown in Fig.(b). The iron loss becomes the largest at around B =deg. at high magnetic flu densit as shown in Fig. (c) θ HB [deg.] H b [A/m] (a) B m -H b curve.. (b) B m - HB curve deg. deg. deg. deg. deg. deg. deg. deg. 8deg. 9deg... (c) W -B m curve deg. deg. deg. deg. deg. deg. deg. deg. 8deg. 9deg. deg. deg. deg. deg. deg. deg. deg. deg. 8deg. 9deg. Fig.. Magnetic properties in arbitrar directions (H, G). 8 PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN -9, R. 8 No 9b/

3 Magnetic properties under rotating magnetic flu It is confirmed that the measured magnetic properties under rotating magnetic flu ecitation have errors due to the angle error between two orthogonal coils of B and H coils []. Therefore, the measured result of rotational iron loss under clockwise (CW) ecitation is different from that under counter clockwise (CCW) ecitation especiall at high flu densit. The iron loss can be obtained as an average of the losses under CW rotating flu and that under CCW rotating flu. Because, the rotational iron loss under CW ecitation should be equal to that under CCW ecitation. In order to check the angle error b of two orthogonal coils used for B coil shown in Fig., the coordinates of pin holes made on the surface of the specimen are measured using a microscope. The measured angle of B coil was b =.deg. The magnetic flu densit in TD direction is calibrated as B TD b using (). BTD sin b () B' TD cos b where: B magnetic flu densit measured b the B coil for, B TD magnetic flu densit measured b the B coil for TD, B TD calibrated magnetic flu densit in TD direction. In the control of flu densit waveform, the calibrated B TD is used. Fig. shows the measured iron loss under circular rotating magnetic flu ecitation ( =) before and after calibration. is the ais ratio (=B min /B ma ). The definition of B ma and B min is shown in Fig.8. is the inclination angle. The frequenc is H. The iron loss under CW ecitation is different from that under CCW ecitation especiall at more than.t. The difference between CW and CCW ecitations is reduced at more than.t b the calibration. The figure denotes that even if the angle error is ver small ( b =.deg.), the measured iron loss under CW and CCW ecitation is influenced b the error at high magnetic flu densit. The average value of CW and CCW ecitation before calibration is almost agree with that after calibration. In order to eamine the reproducibilit of measurement, the specimen is taken off from the equipment and it was again put on for measurement. Fig.9 is shown results of No. and No. measurements. The difference between No. and No. measurements is due to the change of relative position of B coil and H coil after putting on the specimen in D-SST. It is impossible to remove the change of relative position perfectl. But the reproducibilit can be guaranteed in the rotational iron loss b adopting the average of CW and CCW measurement. As a result, it is not eas to accuratel measure magnetic properties under rotating magnetic flu, because a small error between B and H coils influences measured result under CW and CCW ecitation at high magnetic flu densit. B coil () flaw Fig.. Error of orthogonal B-coils. B coil (TD) θ b - - CW (before) CCW(before) average(before) CW (after) CCW(after) average(after).. Fig.. Iron losses under rotating magnetic flu before and after calibration of B-coils (H, G, =). Fig.8. Ellipticall rotating magnetic flu. W [W/kg] TD θ B ma CW(No.) CCW(No.) average(no.) CW(No.) CCW(No.) average(no.).. Fig.9. Iron losses under rotating magnetic flu at No. and No. measurements (H, G, =). Bmin Magnetic properties under ellipticall rotating magnetic flu The effects of ais ratio, inclination angle on iron losses under ellipticall rotating magnetic flu ecitation are eamined. Fig. shows measured results at H. The iron loss W is obtained as an average of the losses under CW and CCW ecitation. The iron loss W is increased with the ais ratio at low magnetic flu densit. When is near to unit, the iron loss is decreased at high magnetic flu densit. This is, because the hsteresis loss is decreased under rotating flu at high flu densit. When is large, the flu densit, when the iron loss begins to decrease, is reduced. The bigger the inclination angle, the smaller the difference in the iron loss b the ais ratio at low magnetic flu densit. The iron loss at = does not change even if the inclination angle is changed, because it is a circle. In the case of =deg.(eas magnetiation), the bigger the ais ratio, the bigger the iron loss as shown Fig. (a). This is, PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN -9, R. 8 No 9b/ 9

4 because the flu densit B TD in TD direction is increased with the ais ratio. In the case of =deg.(almost difficult magnetiation), the bigger the ais ratio, the bigger the iron loss W below.t. But, the smaller the ais ratio, the bigger the iron loss W above.t as shown in Fig. (b). This is, because the iron loss W under circular rotating flu ( =) is smaller than that under alternating flu ( =) in the direction of difficult magnetiation. α =(alternating) α =. α =. α =. α =.. (a) =deg. are also measured. The discrepanc of iron losses between measured results at each area was less than %. Therefore, it should be regarded that the measured result of P in Fig. is an eample of magnetic properties at a special part (mm mm) of specimen, because the grain sie of the highl grain-oriented steel sheet is the order of mm. More larger measurement area (uniform magnetic field area) is necessar in order to measure general magnetic properties of highl grain-oriented steel sheet. The tendenc of results is almost similar to that of G H b [T] (a) B m -H b curve deg. deg. deg. deg. deg. deg. deg. deg. 8deg. 9deg. W [W/kg] 8 α =(alternating) α =. α =. α =. α =.. HB [deg.] deg. deg. deg. deg. deg. deg. deg. deg. 8deg. 9deg. (b) =deg. α =(alternating) α =. α =. α =. α =.. deg. deg. deg. deg. deg. deg. deg. deg. 8deg. 9deg. (b) B m - HB curve (c) =9deg. Fig.. Effect of ais ratio and inclination angle of rotational magnetic flu on resuls of iron losses. Measurement of magnetic properties of highl grain-oriented steel sheet Fig. shows the measured B m -H b curve, angle HB and iron loss W of the highl grain-oriented steel sheet (grade: P) in each direction (ero to 9 deg. with deg. step from the rolling direction under alternating magnetic flu ecitation). The measurement frequenc is H. The iron losses of P in areas A, B and C like the case of Table.. (c) W -B m curve Fig.. Magnetic properties in arbitrar directions (H, P). Fig. shows the measured iron loss W under circular rotating magnetic flu ecitation ( =). The measured result using the D-SST is a part (mm mm) of specimen. PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN -9, R. 8 No 9b/

5 CW CCW average.. Fig.. Iron losses under rotating magnetic flu (H, P, =). Summar The obtained results can be summaried as follows: () The accurac of D-SST in the measurement of grain-oriented electrical steel sheet is eamined b comparing with the measured iron losses using mm width SST. It is also shown that the magnetic properties of the grain-oriented silicon steel sheet like G can be measured in the area of mm mm. () The behaviour of magnetic properties of the grain-oriented electrical steel sheet in each direction (ero to 9deg. with deg. step from the rolling direction) under alternating flu ecitation is clarified. () A small error between B and H coils influences measured results of iron loss under CW and CCW ecitation at high magnetic flu densit. The average value of the iron losses under CW and CCW rotating magnetic flu ecitation before calibration is almost agree with that after calibration. () In the case of = deg. (eas magnetiation), the bigger the ais ratio, the bigger the iron loss W under ellipticall rotating magnetic flu. On the other hand, in the case of = deg. (almost difficult magnetiation), the smaller the ais ratio, the bigger the iron loss W above.t. () An eample of magnetic properties of highl grain-oriented steel sheet under alternating flu and rotating flu ( =) ecitation is shown. REFERENCES [] Enokiono M., Suuki T., Sievert J., Xu J., Rotational Power Loss of Silicon Steel Sheet, IEEE Trans. Magn., Vol. (99) No., - [] Miagi D., Yunoki Y., Nakano M., Takahashi N., Stud on Measurement Method of Dimensional Magnetic Properties of Electrical Steel using Diagonal Eiting Coil, Electrical Review (9) R.8 nr, - [] Nakata T., Fujiwara K., Nakano M., Kaada T., Effects of the Construction of Yokes on the Accurac of a Single Sheet Tester, Anales de Fisica, Serie B, Vol.8 (99), 9-9 [] Nakata T., Kawase Y., Nakano M., Improvement of Measuring Accurac of Magnetic Field Strength, IEEE Trans. Magn., Vol. (98) No., 9-98 [] Nakaoka M., Takahashi N., Kawabe M., Nakano M., Fujiwara K., Investigation of Method for Measuring Magnetic Properties Affected b Shearing Strain using Single Sheet Tester, Journal of the Japan Societ of Applied Electromagnetics and Mechanics, Vol. () No., -8 (in Japanese) [] Kaido C., Takeawa M., Yamasaki J., Fujikura M., Mogi H., Investigation of the Direction Dependence of the Magnetic Properties of Non-oriented Electrical Steel Sheets, Journal of the Magnetics Societ of Japan, Vol. (8), No., -9 (in Japanese) [] Todaka T., Maeda Y., Enokiono M., Counterclockwise (CCW/CCW) Rotational Losses under High Magnetic Field, Electrical Review (9) R.8 nr, - Authors: Mr. Yuki Mori, Dr. Daisuke Miagi, Mr. Masanori Nakano, Prof. Norio Takahashi, Dept. Electrical and Electronic Eng. Okaama Univ., Okaama -8, Japan, mori@dlab.elec.okaama-u.ac.jp, norio@elec.okaama-u.ac.jp. PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN -9, R. 8 No 9b/

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