WOUND IRON CORES AND TRANSFORMERS

Abstract

A wound iron core (10) is configured by winding a grain-oriented electrical steel sheet (11) in the rolling direction. In a cross-section parallel to the rolling direction in a folded portion of a corner (12) of the wound iron core (10), Kout is an average of a KAM value in a region from the center of the thickness of the grain-oriented electrical steel sheet (11) to an outer peripheral side of the wound iron core (10), Kin is an average of the KAM value in a region from the center of the thickness of the grain-oriented electrical steel sheet (11) to an inner peripheral side of the wound iron core (10), and KR, defined as KR = Kin / Kout, is 1.05 or more and 1.6 or less.

Description

Wound cores and transformers

[0001] The present disclosure relates to wound cores and transformers.

[0002] Transformer cores are broadly divided into wound cores and stacked cores. Both types of cores often use grain-oriented electromagnetic steel sheets as their material.

[0003] There are two known types of wound cores. In this specification, one is referred to as a "Trancocore" or "Tranco" and the other is referred to as a "Unicore".

[0004] Two types are shown schematically in Figure 1. TRANCO is described, for example, in Patent Document 1. TRANCO is a wound core made by winding grain-oriented electromagnetic steel sheet in the rolling direction to form a Baumkuchen-like shape, and then press-forming it from all sides to form a square shape with arc-shaped corners.

[0005] The Unicore is described, for example, in Patent Document 2. The Unicore is a wound core in which steel plates, each having a bent portion formed by bending the corner portions in advance, are laminated in the thickness direction.

[0006] Compared to Tranco, Unicore does not require pressure forming, so the equipment required for manufacturing can be relatively small. Also, since the strain introduced into the steel plate during manufacturing is concentrated only in the areas where bending is performed, annealing equipment for strain relief is not required. Because Unicore has these industrial advantages, its use is increasing.

[0007] In recent years, there has been a strong demand for reducing energy loss in transformers and reducing noise during operation in order to comply with energy conservation and environmental regulations. To improve the efficiency of transformers, efforts are being made to improve the properties of grain-oriented electrical steel sheets, which are used as iron core materials.

[0008] When a transformer is manufactured using grain-oriented electrical steel as the core material, it is known that the iron loss of the transformer increases compared to the iron loss of the electrical steel sheet used as the core material. This increase ratio is known as the building factor. The building factor is defined as the iron loss of the transformer divided by the iron loss of the electrical steel sheet used as the core material.

[0009] Therefore, in order to improve the efficiency of transformers, it is important to improve the building factor in addition to improving the properties of the electromagnetic steel sheet used as the material.

[0010] Various methods have been investigated to improve the building factor. For example, Patent Document 3 proposes applying a magnetic domain refining process to grain-oriented electrical steel sheets near the joints by strain. The magnetic domain refining technology is a technology that forms magnetic discontinuities in the rolling direction by thermally strained parts. By forming such magnetic discontinuities, the magnetic domain refining technology can refine the magnetic domains of the grain-oriented electrical steel sheets and improve iron loss.

[0011] Furthermore, for example, Patent Document 4 proposes tilting the joint with respect to the winding direction in order to improve iron loss due to magnetic flux transfer.

[0012] Furthermore, in the case of Unicore, bending causes large distortions in the corners, which increases the building factor. For example, Patent Document 5 proposes a method for improving magnetic degradation caused by distortions in the corners by applying magnetic domain refining treatment using additional grooves in the bent corners.

[0013] JP 2016-146441 A JP 2005-286169 A JP 2020-96100 A JP 2005-150507 A JP 2021-163942 A

[0014] The methods disclosed in Patent Documents 3 to 5 are all effective methods for improving the building factor. However, the methods disclosed in Patent Documents 3 to 5 are proposals that assume additional processing is performed during the design of the iron core. This results in problems such as an increase in manufacturing man-hours and an increase in manufacturing costs due to the need to change the shear direction during manufacturing.

[0015] An object of the present disclosure is to provide a wound core and a transformer that can improve the building factor by suppressing increases in the number of manufacturing steps and manufacturing costs.

[0016] [1] A wound core having a configuration in which grain-oriented electromagnetic steel sheets are wound in the rolling direction, wherein, in a cross section parallel to the rolling direction at a bent portion of a corner of the wound core, KR, defined as KR = Kin / Kout, is 1.05 or more and 1.6 or less, where Kout is the average KAM value within a region from the center of thickness of the grain-oriented electromagnetic steel sheets to the outer periphery of the wound core, and Kin is the average KAM value within a region from the center of thickness of the grain-oriented electromagnetic steel sheets to the inner periphery of the wound core.

[0017] [2] The wound core according to [1] above, wherein the KR is 1.1 or more and 1.5 or less.

[0018] [3] The wound core according to [1] or [2] above, wherein the corner portion has a bent portion.

[0019] [4] A wound core according to any one of [1] to [3] above, having at least one discontinuous portion of the grain-oriented electrical steel sheet in the magnetic path direction.

[0020] [5] A transformer comprising the wound core according to any one of [1] to [4] above and a coil.

[0021] [6] The wound core is a single-phase wound core or a three-phase five-leg wound core made up of a plurality of single-phase wound cores arranged side by side, and the gap length in the rolling direction of each layer of the discontinuous portion, obtained by observing the discontinuous portion of the grain-oriented electromagnetic steel sheet from the side in the lamination direction and the rolling direction of the grain-oriented electromagnetic steel sheet, is defined as w, and the maximum value of the gap length is w ｍａｘ The minimum gap length is w ｍｉｎ When this is done, wr = w ｍａｘ / w ｍｉｎ is 100 or less, and the gap length is the length of the discontinuous portion that is 0.1 mm or more.

[0022] [7] The wound core is a three-phase, three-legged wound core consisting of a combination of an inner core and an outer core, and the gap length in the rolling direction of each layer of the discontinuous portion, obtained by observing the discontinuous portion of the grain-oriented electromagnetic steel sheet from the side in the lamination direction and the rolling direction of the grain-oriented electromagnetic steel sheet, is defined as w, and the maximum value of the gap length is w ｍａｘ The minimum gap length is w ｍｉｎ When this is done, wr = w ｍａｘ / w ｍｉｎ The wound core according to any one of the above [1] to [4], wherein a ratio wr of the maximum value to the minimum value defined by

[0023] The wound core and transformer according to the present disclosure can improve the building factor by suppressing increases in manufacturing steps and manufacturing costs.

[0024] FIG. 1 is a diagram schematically showing two types of wound cores. FIG. 2 is a diagram showing the component composition of a steel slab when an experiment was conducted. FIG. 3 is a diagram showing the measurement results of the relationship between building factor and KR. FIG. 4 is a diagram showing the measurement results of the relationship between noise and KR. FIG. 5 is a diagram schematically showing the configuration of a wound core according to an embodiment of the present disclosure. FIG. 6 is a diagram schematically showing the configuration of a transformer according to an embodiment of the present disclosure. FIG. 7 is a diagram showing an example of the configuration of a bent portion. FIG. 8 is a diagram showing the component composition of a steel slab in an example. FIG. 9 is a diagram schematically showing a three-phase three-limbed wound core. FIG. 10 is a diagram schematically showing the gap length w.

[0025] (Experimental Results) First, the experimental results that led to the conception of the embodiments of the present disclosure will be described.

[0026] The chemical composition of the steel slab used in the experiment is shown in Figure 2. In the experiment, grain-oriented electrical steel strips manufactured by a general manufacturing process using steel slabs having the chemical composition shown in Figure 2 were used as test materials.

[0027] The grain-oriented electrical steel strip was slit to a sheet width of 100 mm and wound to a shape with a stack thickness of 30 mm, long sides of 300 mm, and short sides of 150 mm. In this way, single-phase Unicores were manufactured. The portions corresponding to the short sides were sheared to form a shape called a cut core. Three types of cores were manufactured: one 90-degree bend, two 45-degree bends, and three 30-degree bends. The bending angle θ for each was θ±1°. The thickness of the tensile coating was varied between the outer and inner peripheral portions of the steel sheet. None of the cores were manufactured under stress relief annealing (SRA).

[0028] Using single sheet samples cut from the test steel strip, iron loss was measured by the single sheet magnetic measurement method specified in JIS C 2556. In addition to this measurement, iron loss characteristics (transformer iron loss) were also measured for each of the manufactured wound core transformers when the magnetic flux density in the core legs was 1.7 T at a frequency of 50 Hz.

[0029] The iron loss characteristics at a magnetic flux density of 1.7 T in the core leg portion and a frequency of 50 Hz as described above were measured by measuring no-load loss using a wattmeter.

[0030] The building factor (BF) of each transformer was calculated from the ratio of the transformer iron loss measured in this way to the single-plate iron loss.

[0031] Furthermore, each model transformer was excited in a soundproof room under the conditions of a maximum magnetic flux density Bm=1.7 T and a frequency of 50 Hz, and the noise level: dBA (transformer noise) was measured using a sound level meter.

[0032] After the various measurements were completed, a sample was cut out from a corner of the core and embedded in a carbon mold. The cross section parallel to the rolling direction was then polished and subjected to EBSD (Electron Backscatter Diffraction) measurement.

[0033] A Kernel Average Misorientation (KAM) map was calculated from the results obtained in this manner. The average value of the KAM values ​​in the region from the center of the steel sheet thickness to the outer periphery of the wound core was designated Kout, and the average value of the KAM values ​​in the region from the center of the steel sheet thickness to the inner periphery of the wound core was designated Kin, and the ratio of Kin to Kout, KR = Kin / Kout, was calculated.

[0034] Figure 3 shows the measurement results of the relationship between building factor and KR. Figure 4 shows the measurement results of the relationship between noise and KR.

[0035] 3, a significant improvement in the building factor (BF) can be seen in the region where KR is 1.05 or more and 1.6 or less. This is thought to be because the higher the KR, i.e., the higher the residual compressive stress acting on the inner periphery of the steel sheet, the more suppressed the springback of the steel sheet and the closer it is to a rectangular shape, thereby reducing the influence of external stress when formed into a wound core.

[0036] 3 and 4, it can be seen that the building factor (BF) and noise tend to deteriorate when KR exceeds 1.6. This is thought to be because excessive residual stress in the steel sheet causes excessive strain to remain in the steel sheet, resulting in deterioration of iron loss and magnetostriction.

[0037] These results show that a wound core with good characteristics can be obtained by setting KR to 1.05 or more and 1.6 or less, and more preferably, by setting KR to 1.1 or more and 1.5 or less, a wound core with even better characteristics can be obtained.

[0038] Furthermore, in wound cores with discontinuities in electrical steel sheets, if the KR is not taken into account, springback stress acts on the discontinuities in a certain layer of electrical steel sheets, pushing them apart from the innermost steel sheets. Therefore, the inventors discovered that the gap length (w) in the rolling direction of the discontinuities increases with the number of laminated steel sheets, degrading the transformer's performance. Therefore, the inventors discovered that by adjusting the shear length of the electrical steel sheets in the circumferential direction longer than the geometrically theoretical value in addition to adjusting the KR, the gap length can be kept within a certain range, resulting in a wound core with even better performance. Figure 10 shows a schematic diagram of the gap length (w).

[0039] The gap length of the joint can be measured using the following method. The side surface of the wound core, i.e., the surface consisting of the steel sheet lamination direction and the rolling direction of the steel sheets, is photographed with a digital camera along with a scale such as a ruler, and its length is measured. Due to measurement considerations, a length of less than 0.1 mm results in a large error, so a value of 0.1 mm or more is adopted as the gap length. Furthermore, a discontinuous portion of less than 0.1 mm is determined to have no gap.

[0040] For the gap length w of each layer obtained in this way, the maximum value of the gap length is w ｍａｘ The minimum gap length is w ｍｉｎ Then, wr = w ｍａｘ / w ｍｉｎ With respect to the ratio wr of the maximum value to the minimum value defined by the formula (1), for a single-phase wound core or a three-phase five-legged wound core, wr must be 100 or less, and for a three-phase three-legged wound core, wr must be 500 or less. More preferably, for a single-phase or three-phase five-legged wound core, wr must be 60 or less, and for a three-phase three-legged wound core, wr must be 300 or less. Note that a "single-phase wound core" is a wound core with the configuration shown in Figure 1. A "three-phase five-legged wound core" is a wound core with a configuration in which multiple single-phase wound cores are arranged side by side. A "three-phase three-legged wound core" is a wound core consisting of a combination of an inner core and an outer core, as shown schematically in Figure 9.

[0041] (Present Embodiment) Next, a wound core according to an embodiment of the present disclosure will be described with reference to the drawings.

[0042] FIG. 5 is a diagram schematically illustrating the configuration of a wound core 10 according to an embodiment of the present disclosure.

[0043] The wound core 10 is configured by winding grain-oriented electromagnetic steel sheets 11 in the rolling direction. The wound core 10 has corner portions 12-1 to 12-4. Hereinafter, when there is no need to particularly distinguish between the corner portions 12-1 to 12-4, they may be simply referred to as "corner portions 12." Figure 5 shows a case where the wound core 10 is a Unicore type. When the wound core 10 is a Unicore type, the corner portions 12 have bent portions as shown in Figure 1.

[0044] The wound core 10 can be used as a component of a transformer. Fig. 6 schematically shows the configuration of a transformer 1 according to an embodiment of the present disclosure. The transformer 1 includes the wound core 10, and coils 20-1 and 20-2. The coils 20-1 and 20-2 are wound around the wound core 10, as shown in Fig. 2.

[0045] 5 may be manufactured from a slab, which is a steel material. The slab for the grain-oriented electrical steel sheet 11 may have any composition that allows secondary recrystallization to occur.

[0046] When an inhibitor is used in the grain-oriented electrical steel sheet 11, for example, when an AlN-based inhibitor is used, it is sufficient to add appropriate amounts of Al and N, and when, for example, when an MnS / MnSe-based inhibitor is used, it is sufficient to add appropriate amounts of Mn and Se and / or S. It is also possible to use both inhibitors in combination.

[0047] When both inhibitors are used in combination, the preferred contents of Al, N, S and Se are as follows: Al: 0.010 to 0.065 mass%, N: 0.0050 to 0.0120 mass%, S: 0.005 to 0.030 mass%, Se: 0.005 to 0.030 mass%.

[0048] The grain-oriented electrical steel sheet 11 may be one in which the contents of Al, N, S, and Se are limited and no inhibitor is used. In this case, it is desirable to suppress the contents of Al, N, S, and Se as follows: Al: less than 0.010 mass%, N: less than 0.0050 mass%, S: less than 0.0050 mass%, Se: less than 0.0050 mass%.

[0049] Representative basic components and optional additional components applied to the steel material (slab) for the grain-oriented electrical steel sheet 11 will be specifically described below.

[0050] C: 0.08% by mass or less C is added to improve the hot-rolled sheet structure. If the C content exceeds 0.08% by mass, it becomes difficult to decarburize to 50 ppm by mass or less, at which point magnetic aging does not occur during the manufacturing process. Therefore, the C content is preferably 0.08% by mass or less. Furthermore, since secondary recrystallization occurs even in steel materials that do not contain C, no lower limit for the C content is set.

[0051] Si: 2.0 to 8.0 mass% Si is an element effective in increasing the electrical resistance of steel and improving iron loss. If the Si content is less than 2.0 mass%, the above-mentioned improvement effect is not fully exerted. On the other hand, if the Si content exceeds 8.0 mass%, not only will workability and threadability be significantly deteriorated, but magnetic flux density will also decrease. Therefore, the Si content is preferably in the range of 2.0 to 8.0 mass%.

[0052] Mn: 0.005 to 1.0 mass% Mn is an element necessary for improving hot workability. If the Mn content is less than 0.005 mass%, it is difficult to obtain a sufficient effect of improving hot workability. On the other hand, if the Mn content exceeds 1.0 mass%, the magnetic flux density deteriorates. Therefore, the Mn content is preferably in the range of 0.005 to 1.0 mass%.

[0053] In addition to the above basic components, the slab for the grain-oriented electrical steel sheet 11 may contain one or more of the following optional components. The following optional components are known to be effective in improving magnetic properties: Ni: 0.03 to 1.50 mass%, Sn: 0.01 to 1.50 mass%, Sb: 0.005 to 1.50 mass%, Cu: 0.03 to 3.0 mass%, P: 0.03 to 0.50 mass%, Mo: 0.005 to 0.10 mass%, Cr: 0.03 to 1.50 mass%

[0054] Ni is an element effective in improving the hot-rolled sheet structure and enhancing magnetic properties. If the Ni content is less than 0.03 mass%, its contribution to improving magnetic properties is small. On the other hand, if the Ni content exceeds 1.50 mass%, secondary recrystallization becomes unstable and magnetic properties deteriorate. Therefore, the Ni content is preferably in the range of 0.03 to 1.50 mass%.

[0055] Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties. If the content of any of these elements is below the lower limit, the effect of improving magnetic properties is insufficient. If the content of any of these elements exceeds the upper limit, the growth of secondary recrystallized grains is suppressed, resulting in deterioration of magnetic properties. Therefore, it is desirable that the contents of Sn, Sb, Cu, P, Mo, and Cr are each within the range of the content described above.

[0056] The slab for the grain-oriented electrical steel sheet 11 contains Fe and inevitable impurities as components other than those mentioned above.

[0057] The steel material (slab) of the grain-oriented electrical steel sheet 11 having the above-mentioned chemical composition is hot-rolled and then hot-rolled sheet annealed. Subsequently, the slab is cold-rolled once or twice to produce a steel strip with the final thickness.

[0058] The steel strip of the final thickness is then subjected to decarburization annealing and an annealing separator is applied. The steel strip of the final thickness is then wound into a coil. The steel strip of the final thickness is then subjected to final annealing for the purpose of secondary recrystallization. The steel strip after final annealing is then subjected to flattening annealing, a tension coating is formed, and the steel strip of the product plate is produced.

[0059] Next, a method for calculating the KAM value and the KR value in this embodiment will be described.

[0060] The corner portions 12 of the wound core 10 have bent portions. By deforming and bending at the bent portions, the wound core 10 is bent 90 degrees at the corner portions 12. The corner portions 12 have at least one bent portion. For example, if the corner portion 12 has one bent portion, it bends 90 degrees at the bent portion. Also, for example, if the corner portion 12 has two bent portions, it bends 45 degrees at one bent portion. Also, for example, if the corner portion 12 has three bent portions, it bends 30 degrees at one bent portion.

[0061] A restoring force known as springback acts on the bent portions of the corners 12. As a result, residual stress occurs in the grain-oriented electromagnetic steel sheets 11 that make up the wound core 10, causing them to warp toward the outer periphery of the wound core 10. However, because the entire wound core 10 is manufactured to maintain a rectangular shape, the grain-oriented electromagnetic steel sheets 11 are subjected to stress that pushes them toward the inner periphery of the wound core 10. This stress contributes to iron loss and noise in the wound core 10, but the characteristics of the wound core 10 can be improved by optimizing the KAM value of the cross section parallel to the rolling direction at the bent portions of the corners 12.

[0062] The bent portion will be described with reference to Fig. 7. In the grain-oriented electrical steel sheet 11, tangent lines are drawn as half lines from the flat surfaces (the outer peripheral surface layer and the inner peripheral surface layer of the steel sheet) of the regions (flat portions) that do not have a radius of curvature and exist on both sides in the rolling direction, toward the region that has a radius of curvature.

[0063] As shown in Fig. 7, the points of contact between the tangent and the outer peripheral surface layer of the steel sheet are designated as tangent points O1 and O2. The points of contact between the tangent and the inner peripheral surface layer of the steel sheet are designated as tangent points I1 and I2. In this case, the area surrounded by the four tangent points O1, O2, I1, and I2 is the bent portion.

[0064] When calculating the KAM value and the KR value, a portion of the grain-oriented electromagnetic steel sheet 11 is taken from the bent portion of the corner portion 12 of the wound core 10 so that the cross section parallel to the rolling direction of the grain-oriented electromagnetic steel sheet 11 is the cut surface. Subsequently, the cut surface is subjected to distortion-free polishing.

[0065] Next, the crystal orientation misorientation of the strain-free polished surface is analyzed by EBSD (Electron Backscatter Diffraction) to calculate the KAM (Kernel Average Misorientation) value, where the misorientation is defined as the misorientation between a certain measurement point and its third adjacent point.

[0066] After calculating the KAM value from each measurement point in this manner, the region is divided into an inner periphery side and an outer periphery side, with half the thickness of the grain-oriented electromagnetic steel sheet 11 as the boundary. Then, the average value of the KAM values ​​in the region from the center of the thickness of the grain-oriented electromagnetic steel sheet 11 to the outer periphery side of the wound core 10 is calculated as Kout. Also, the average value of the KAM values ​​in the region from the center of the thickness of the grain-oriented electromagnetic steel sheet 11 to the inner periphery side of the wound core 10 is calculated as Kin. Then, KR, defined as KR = Kin / Kout, is calculated.

[0067] In this case, the bending portion for which the average value of the KAM value is calculated is the area surrounded by the four tangent points O1, O2, I1, and I2 shown in Figure 7, and is shown in Figure 7 as the "averaging target range."

[0068] There are no particular limitations on the method for controlling the KR value, but for example, when manufacturing the wound core 10, the film thickness or composition of the tension coating is made different on the inner and outer surfaces of the corner portions 12 of the grain-oriented electromagnetic steel sheets 11 used in the pieces of the wound core 10, and the tension on the outer side is made higher than that on the inner side, thereby enabling effective control.

[0069] It is believed that in the bent portions of the corner portions 12 of the wound core 10 configured in this manner, stronger compressive stress occurs in the inner peripheral portion, thereby increasing K. However, the present invention is not limited to such a manufacturing method, and as long as the KR of the bent portions is within the range of this embodiment, it is possible to obtain an improvement in the building factor due to the magnetic domain refinement effect.

[0070] In addition, in this embodiment, for the steps and manufacturing conditions other than those described above, a known manufacturing method for the grain-oriented electrical steel sheet 11 can be used as appropriate.

[0071] As explained in the experimental results above with reference to Figures 3 and 4, the KR value is preferably 1.05 or more and 1.6 or less. This makes it possible to obtain a wound core 10 with good characteristics. Furthermore, the KR value is more preferably 1.1 or more and 1.5 or less. This makes it possible to obtain a wound core 10 with even better characteristics.

[0072] In addition to adjusting the KR, it is desirable to keep the expansion of the gap length of the discontinuous part of the electromagnetic steel sheet in the wound core within a certain range by adjusting the shear length of the electromagnetic steel sheet in the circumferential direction longer than the geometric theoretical value. The amount of adjustment of the shear length of the steel sheet cannot be generally defined because it depends largely on the magnitude of the residual stress due to springback in the iron core, but the following adjustment methods, for example, are effective.

[0073] During the manufacturing of the Unicore, electromagnetic steel sheets are fed out one layer at a time from the bending machine, and workers stack them as needed. At this time, the discontinuous portions of the electromagnetic steel sheets in the core are photographed with a camera from the side of the core, and the gap length is measured. If the gap length exceeds 50 times the minimum value up to that layer, this is fed back to the feed rate of the next steel sheet, and the sheet is stretched by 50 times the minimum value. This makes it possible to adjust the gap length. Other methods available include stretching each layer at a fixed rate (fixed stretching) and increasing the stretch amount every certain number of layers (stepwise stretching).

[0074] As described above, the wound core 10 according to this embodiment has a configuration in which grain-oriented electromagnetic steel sheets 11 are wound in the rolling direction. In a cross section parallel to the rolling direction at the bent corners 12 of the wound core 10, the average KAM value in the region from the center of the thickness of the grain-oriented electromagnetic steel sheets 11 to the outer periphery of the wound core 10 is Kout, and the average KAM value in the region from the center of the thickness of the grain-oriented electromagnetic steel sheets 11 to the inner periphery of the wound core 10 is Kin. KR, defined as KR = Kin / Kout, is 1.05 or more and 1.6 or less. By setting the KR value at the bent corners 12 within this appropriate range, the wound core 10 according to this embodiment can reduce the building factor due to magnetic flux transfer in the lamination direction and reduce noise. Furthermore, by keeping the expansion of discontinuities in the electromagnetic steel sheets due to springback within a certain range, even better transformer characteristics can be achieved. The wound core 10 according to this embodiment can be manufactured with fewer manufacturing processes. Therefore, the wound core 10 according to this embodiment can improve the building factor by suppressing increases in the number of manufacturing steps and manufacturing costs.

[0075] (Examples) Next, the contents of the present disclosure will be specifically described based on examples. The following examples show preferred examples of the present disclosure, and are not intended to limit the scope of the present disclosure. Modifications can be made within the scope that conforms to the spirit of the present disclosure, and such embodiments are also included in the technical scope of the present disclosure.

[0076] 8 is a diagram showing the chemical composition of a steel slab in the example. Using such a steel slab, steel strips A, B, C, and D were produced.

[0077] Steel strip A is a grain-oriented electrical steel sheet manufactured by a general manufacturing process. Steel strip B is a grain-oriented electrical steel sheet obtained by electrolytic etching the steel strip surface after the cold rolling process to periodically form linear grooves 15 μm deep and 40 μm wide at 5 mm intervals in a direction perpendicular to the rolling direction, and then performing a finish annealing process. Steel strip C is a grain-oriented electrical steel sheet obtained by irradiating a portion of steel strip A with a laser. Steel strip D is a grain-oriented electrical steel sheet obtained by irradiating a portion of steel strip A with an electron beam.

[0078] These steel strips A, B, C, and D were used as test materials. In this case, the type of tension coating was the same, and grain-oriented electrical steel strips were manufactured by varying the coating thickness in the range of 1 to 5 μm on the outer and inner peripheral parts of the wound core.

[0079] Test pieces (samples) measuring 100 mm wide x 280 mm long were cut out from the steel strips of test material produced as described above, and the iron loss of each test piece was measured by the single sheet magnetic measurement method described in JIS C2556.

[0080] Each steel strip was then wound in the rolling direction to produce a single-phase wound core model transformer (core weight 25 kg) and a three-phase wound core model transformer (core weight 50 kg). For steel strips A and B, both Tranco and Unicore models were produced. For Unicore, cores that had been subjected to stress relief annealing were also produced. For steel strips C and D, only Unicore was produced because the magnetic domain refining effect produced by the laser and electron beam is lost by stress relief annealing.

[0081] These cores were manufactured in two shapes: a non-cut type that has no discontinuities in the grain-oriented electrical steel sheet, called air gaps, in the magnetic path direction, and a cut type that has air gaps every other turn in the magnetic path direction. For those with air gaps, we also manufactured cores in which the gap length was adjusted using a feedback method.

[0082] For each manufactured transformer, the iron loss characteristics were measured when the magnetic flux density in the core legs was 1.7 T at a frequency of 50 Hz. The iron loss characteristics under the conditions of a magnetic flux density of 1.7 T and a frequency of 50 Hz were measured by measuring the no-load loss using a wattmeter. At the same time, this model transformer was excited in a soundproof room under conditions of a maximum magnetic flux density Bm = 1.7 T and a frequency of 50 Hz, and the noise level (dBA) was measured using a sound level meter.

[0083] After the various measurements were completed, samples were cut out from the bent corners of the cores and embedded in carbon molds. The cross sections parallel to the rolling direction were polished and subjected to EBSD measurements. The KR values ​​were calculated from the results. The results are shown in Tables 1 to 5 below.

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] Referring to Tables 1 to 5, it can be seen that, under the conditions satisfying the configuration of this embodiment, a good transformer with low iron loss and low noise can be obtained. It can also be seen that Unicore has a greater BF improvement effect than TRANCO. The improvement in transformer characteristics is particularly significant when KR is 1.1 or more and 1.5 or less. Furthermore, cut cores provide better characteristics than non-cut cores. Unicores also provide better characteristics than TRANCOs. Furthermore, it was confirmed that better characteristics can be obtained by adjusting the gap length so that the ratio wr of the maximum to minimum gap lengths w of the discontinuous portions of all grain-oriented electrical steel sheets constituting the wound core is 100 or less for single-phase / three-phase five-legged configurations and 500 or less for three-phase three-legged configurations.

[0090] The present disclosure is not limited to the above-described embodiments. For example, multiple blocks shown in the block diagrams may be integrated, or one block may be divided. Instead of executing multiple steps shown in the flowcharts in chronological order as described, each step may be executed in parallel or in a different order depending on the processing capacity of the device executing each step, or as needed. Other modifications are possible within the scope of the present disclosure.

[0091] REFERENCE SIGNS LIST 1 transformer 10 wound core 11 grain-oriented electromagnetic steel sheet 12 corner portion 20 coil

Claims

1. A wound core having a configuration in which grain-oriented electromagnetic steel sheets are wound in the rolling direction, wherein, in a cross section parallel to the rolling direction at a bent portion of a corner of the wound core, KR, defined as KR = Kin / Kout, is 1.05 or more and 1.6 or less, where Kout is the average KAM value within a region from the center of thickness of the grain-oriented electromagnetic steel sheets to the outer periphery of the wound core, and Kin is the average KAM value within a region from the center of thickness of the grain-oriented electromagnetic steel sheets to the inner periphery of the wound core.

2. A wound core as claimed in claim 1, wherein said KR is greater than or equal to 1.1 and less than or equal to 1.

5.

3. A wound core according to claim 1 or 2, wherein the corner portion has a bent portion.

4. A wound core according to any one of claims 1 to 3, having at least one discontinuity in the grain-oriented electrical steel sheet in the magnetic path direction.

5. A transformer comprising a wound core according to any one of claims 1 to 4 and a coil.

6. The wound core is a single-phase wound core or a three-phase five-legged wound core in which multiple single-phase wound cores are arranged, and the gap length in the rolling direction of each layer of the discontinuous portion, obtained by observing the discontinuous portion of the grain-oriented electromagnetic steel sheet from the side in the lamination direction and the rolling direction of the grain-oriented electromagnetic steel sheet, is w, and the maximum value of the gap length is w ｍａｘ The minimum gap length is w ｍｉｎ Then, wr = w ｍａｘ / w ｍｉｎ 5. The wound core according to claim 4, wherein a ratio wr of a maximum value to a minimum value defined by the formula: is 100 or less, and the gap length is a length of the discontinuous portion that is 0.1 mm or more.

7. The wound core is a three-phase three-leg wound core consisting of an inner core and an outer core, and the gap length in the rolling direction of each layer of the discontinuous portion of the grain-oriented electromagnetic steel sheet, obtained by observing the discontinuous portion of the grain-oriented electromagnetic steel sheet from the side in the lamination direction and the rolling direction of the grain-oriented electromagnetic steel sheet, is w, and the maximum value of the gap length is w ｍａｘ The minimum gap length is w ｍｉｎ Then, wr = w ｍａｘ / w ｍｉｎ 5. The wound core according to claim 4, wherein the ratio wr of the maximum value to the minimum value defined by: