Wound cores and transformers

Abstract

Wound core 10 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 bent portions of corner portions 12, wound core 10 has a KR defined as KR=Kin / Kout of 1.05 or more and 1.6 or less, where Kout is the average KAM value in a region from the center of thickness of grain-oriented electromagnetic steel sheet 11 to the outer periphery of wound core 10, and Kin is the average KAM value in a region from the center of thickness of grain-oriented electromagnetic steel sheet 11 to the inner periphery of wound core 10.

Description

[Technical field]

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

[0002] Transformer cores are broadly divided into wound cores and stacked cores. In both types of cores, grain-oriented electrical steel sheets are often used as the material.

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

[0004] The two types are shown diagrammatically 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 shape, and then applying pressure forming from all four 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, on which bending work has been applied in advance at locations corresponding to corner portions to form bent portions, are laminated in the plate 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, Unicore does not require annealing equipment for removing strain. Because Unicore has such industrial advantages, its use is progressing.

[0007] In recent years, from the viewpoint of energy conservation and environmental regulations, there has been a strong demand for reducing energy loss in transformers and reducing noise during operation of transformers. To increase 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] It is known that when a transformer is manufactured using grain-oriented electrical steel as the core material, the iron loss of the transformer increases more than the iron loss of the electrical steel sheet used as the 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, in addition to improving the properties of the electromagnetic steel sheet material, improving the building factor is an important development element.

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

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

[0012] In addition, in the case of Unicore, bending creates large distortion in the corners, which increases the building factor. For example, Patent Document 5 proposes a method of improving the magnetic degradation caused by distortion in the corners by adding grooves to the bent corners to perform magnetic domain refinement. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2016-146441 A [Patent Document 2] JP 2005-286169 A [Patent Document 3] JP 2020-96100 A [Patent Document 4] JP 2005-150507 A [Patent Document 5] JP 2021-163942 A Summary of the Invention [Problem to be solved by the invention]

[0014] The methods disclosed in Patent Documents 3 to 5 are all effective as methods for improving the building factor. However, the methods disclosed in Patent Documents 3 to 5 are proposals that assume additional processing is performed when designing the iron core. This causes 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. [Means for solving the problem]

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

[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 discontinuity in 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-legged wound core in which a plurality of single-phase wound cores are arranged, The gap length in the rolling direction of each layer of the discontinuous portion of the grain-oriented electrical steel sheet, which is obtained by observing the discontinuous portion of the grain-oriented electrical steel sheet from the side in the lamination direction and the rolling direction of the grain-oriented electrical 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 wr=w max / w min The ratio wr between the maximum and minimum values ​​defined by is 100 or less, The wound core according to any one of [1] to [4] above, wherein the gap length is a length of the discontinuous portion of 0.1 mm or more.

[0022] [7] The wound core is a three-phase, three-legged wound core consisting of an inner core and an outer core, The gap length in the rolling direction of each layer of the discontinuous portion of the grain-oriented electrical steel sheet, which is obtained by observing the discontinuous portion of the grain-oriented electrical steel sheet from the side in the lamination direction and the rolling direction of the grain-oriented electrical 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 wr=w max / w min The wound core according to any one of [1] to [4] above, wherein a ratio wr of the maximum value to the minimum value defined by is 500 or less. Effect of the Invention

[0023] According to the wound core and transformer according to the present disclosure, the building factor can be improved by suppressing increases in manufacturing man-hours and manufacturing costs. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a diagram showing two types of wound cores. [Diagram 2] FIG. 2 is a diagram showing the composition of the steel slab when the experiment was conducted. [Diagram 3] FIG. 13 is a diagram showing measurement results of the relationship between building factor and KR. [Figure 4] FIG. 13 is a diagram showing the measurement results of the relationship between noise and KR. [Diagram 5] FIG. 2 is a diagram illustrating a schematic configuration of a wound core according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a diagram illustrating a schematic configuration of a transformer according to an embodiment of the present disclosure. [Figure 7] FIG. 4 is a diagram showing an example of a configuration of a bending portion. [Figure 8] FIG. 2 is a diagram showing the composition of a steel slab in an embodiment. [Figure 9] FIG. 2 is a schematic diagram showing a three-phase, three-legged wound core. [Figure 10] FIG. 2 is a diagram illustrating a gap length w. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] (Experimental Results) First, 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 a steel slab 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 stacking thickness of 30 mm, long side of 300 mm, and short side of 150 mm. In this way, a single-phase unicore was manufactured. At this time, the part corresponding to the short side was sheared to form a shape called a cut core. At this time, three types of cores were manufactured, one bent at 90 degrees once, one bent at 45 degrees twice, and one bent at 30 degrees three times. At this time, the bending angle θ of each was θ±1 degree. At the time of manufacturing each core, the film thickness of the tensile coating was changed between the outer periphery and the inner periphery of the steel sheet. At the time of manufacturing the core, no strain relief annealing (SRA) was performed on any of the cores.

[0028] Using single sheet samples cut from the test steel strip, the iron loss was measured by the single sheet magnetic measurement method specified in JIS C2556. In addition to this measurement, the 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 leg part 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 iron core legs and a frequency of 50 Hz as described above were measured by measuring the 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 maximum magnetic flux density Bm=1.7T and frequency of 50Hz, and the noise level: dBA (transformer noise) was measured using a sound level meter.

[0032] After various measurements were completed, a sample was cut out from the 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 Back Scatter Diffraction) measurements.

[0033] From the results obtained in this way, a KAM (Kernel Average Misorientation) map was calculated. The average KAM value in the region from the center of the steel sheet thickness to the outer periphery of the wound core was defined as Kоut, and the average KAM value in the region from the center of the steel sheet thickness to the inner periphery of the wound core was defined as Kin, and the ratio of Kin to Kоut, KR = Kin / Kоut, 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] Referring to Figure 3, a significant improvement in the building factor (BF) can be seen in the region where KR is between 1.05 and 1.6. This is thought to be because the higher the KR, i.e., the higher the residual compressive stress acting on the inner circumference of the steel sheet, the more the springback of the steel sheet is suppressed and the closer it is to a square shape, reducing the effect of external stress when formed into a wound core.

[0036] 3 and 4, it can be seen that when KR exceeds 1.6, the building factor (BF) and noise tend to deteriorate. This is thought to be because the residual stress in the steel plate becomes excessive, causing excessive distortion in the steel plate, which deteriorates the 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 a wound core having discontinuous parts of magnetic steel sheets, in a wound core where the KR is not taken into consideration, the discontinuous parts of the magnetic steel sheets of a certain layer are subjected to stresses that push them apart from the innermost steel sheets due to springback. As a result, the inventors discovered that the gap length w in the rolling direction of the discontinuous parts increases with an increase in the number of laminated steel sheets, deteriorating the characteristics of the transformer. The inventors discovered that by adjusting the shear length of the magnetic steel sheets in the circumferential direction to be longer than the geometric theoretical value in addition to adjusting the KR, the gap length expansion can be kept within a certain range, and a wound core with even better characteristics can be obtained. Figure 10 shows a schematic diagram of the gap length w.

[0039] Here, the gap length of the joint can be measured using the following method. The side of the wound core, i.e. the surface consisting of the steel sheet lamination direction and the rolling direction of the steel sheet, is photographed with a digital camera along with a scale such as a ruler, and its length is measured. For measurement purposes, a length of less than 0.1 mm will result in large errors, so a value of 0.1 mm or more is used as the gap length. Also, any discontinuity of less than 0.1 mm is determined to mean that there is no gap.

[0040] For the gap length w of each layer obtained in this way, the maximum 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, in the case of a single-phase wound core or a three-phase five-legged wound core, wr must be 100 or less, and in the case of a three-phase three-legged wound core, wr must be 500 or less. More preferably, in the case of a single-phase or three-phase five-legged wound core, wr must be 60 or less, and in the case of a three-phase three-legged wound core, wr must be 300 or less. Note that a "single-phase wound core" is a wound core having a configuration as shown in Figure 1. A "three-phase five-legged wound core" is a wound core having 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 diagrammatically 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 illustrating a schematic configuration of a wound core 10 according to an embodiment of the present disclosure.

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

[0044] The wound core 10 can be used as a component of a transformer. Fig. 6 shows a schematic 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 composition of the slab for the grain-oriented electrical steel sheet 11 may be 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 contain appropriate amounts of Al and N, and when, for example, when an MnS·MnSe-based inhibitor is used, it is sufficient to contain 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: 0.010~0.065% by mass, N:0.0050~0.0120% by mass, S:0.005~0.030% by mass Se:0.005~0.030% by mass

[0048] The grain-oriented electrical steel sheet 11 may be one that does not use an inhibitor and limits the contents of Al, N, S, and Se. In this case, it is preferable to suppress the contents of Al, N, S, and Se as follows. Al: less than 0.010% by mass, N: less than 0.0050% by mass, S: Less than 0.0050% by mass Se: less than 0.0050% by mass

[0049] Representative basic components and optional added 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 mass%, it becomes difficult to decarburize to 50 mass ppm or less, at which magnetic aging does not occur during the manufacturing process. Therefore, it is preferable that the C content be 0.08 mass% or less. In addition, since secondary recrystallization occurs even in steel materials that do not contain C, no lower limit is set for the C content.

[0051] Si:2.0~8.0% by mass Silicon is an element that is effective in increasing the electrical resistance of steel and improving core loss. If the Si content is less than 2.0 mass%, the above-mentioned improving effect is not fully exhibited. On the other hand, if the Si content exceeds 8.0 mass%, the workability and threading property are significantly deteriorated, and the magnetic flux density is also reduced. Therefore, the Si content is preferably in the range of 2.0 to 8.0 mass%.

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

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

[0054] Ni is an element effective for improving the hot-rolled sheet structure and enhancing magnetic properties. If the Ni content is less than 0.03 mass%, the 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] In addition, Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties. If the content of any of the elements is less than the above lower limit, the effect of improving the magnetic properties is insufficient. If the content of any of the elements is more than the above upper limit, the growth of secondary recrystallized grains is suppressed, and the magnetic properties deteriorate. Therefore, it is preferable that the contents of Sn, Sb, Cu, P, Mo, and Cr are each within the above content range.

[0056] The slab for the grain-oriented electrical steel sheet 11 contains Fe and unavoidable 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 composition is hot-rolled and then hot-rolled annealed. The slab is then cold-rolled once or twice. Then, a steel strip of the final thickness is produced.

[0058] The steel strip of the final thickness is then subjected to decarburization annealing and coated with an annealing separator. 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] Corner portion 12 of wound core 10 has a bent portion. Wound core 10 is bent 90 degrees at corner portion 12 by being deformed and bent at the bent portion. Corner portion 12 has at least one bent portion. For example, when corner portion 12 has one bent portion, it is bent 90 degrees at the bent portion. Also, for example, when corner portion 12 has two bent portions, it is bent 45 degrees at one bent portion. Also, for example, when corner portion 12 has three bent portions, it is bent 30 degrees at one bent portion.

[0061] A restoring force called springback acts on the bent parts of the corners 12. As a result, the grain-oriented electromagnetic steel sheets 11 constituting the wound core 10 have residual stress that causes 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 in a state where they are subjected to stress that presses them toward the inner periphery of the wound core 10. This stress contributes to the iron loss and noise of 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 parts of the corners 12.

[0062] The bent portion will be described with reference to Fig. 7. In the grain-oriented electrical steel sheet 11, a tangent line is drawn as a half line from the flat surfaces (the outer peripheral surface layer of the steel sheet 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 having 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 called tangent points O1 and O2. The points of contact between the tangent and the inner peripheral surface layer of the steel sheet are called tangent points I1 and I2. In this case, the area surrounded by the four tangent points O1, O2, I1, and I2 is the bent part.

[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 cut surface is a cross section parallel to the rolling direction of the grain-oriented electromagnetic steel sheet 11. Next, the cut surface is subjected to distortion-free polishing.

[0065] Next, the crystal orientation misorientation of the distortion-free polished surface is analyzed by EBSD (Electron Back Scatter Diffraction) to calculate the KAM (Kernel Average Misorientation) value. At this time, the orientation misorientation is defined as the orientation 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 sheet thickness of the grain-oriented electromagnetic steel sheet 11 as the boundary. Then, the average KAM value in the region from the center of the sheet 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 KAM value in the region from the center of the sheet 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] The method for controlling the KR value is not particularly limited, but for example, the KR value can be effectively controlled by manufacturing wound core 10 using a tensile coating with different thicknesses or compositions on the inner and outer peripheral surfaces of corner portion 12 of grain-oriented electromagnetic steel sheet 11 used in the pieces of wound core 10, with the tension on the outer peripheral side being higher than that on the inner peripheral side.

[0069] It is believed that in the bent portion of the corner portion 12 of the wound core 10 configured in this way, stronger compressive stress is generated in the inner peripheral portion, thereby increasing Kin. However, the present invention is not limited to such a manufacturing method, and as long as the KR of the bent portion 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 this embodiment, other than the steps and manufacturing conditions described above, a known manufacturing method for the grain-oriented electrical steel sheet 11 can be used as appropriate.

[0071] As explained in the above experimental results 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. It is even more preferable that the KR value be 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 adjustment amount of the shear length of the steel sheet cannot be generally defined because it depends largely on the magnitude of the residual stress caused by the springback of the iron core, but for example, the following adjustment methods are effective.

[0073] When manufacturing the Unicore, electromagnetic steel sheets are sent out one layer at a time from the bending machine, and workers stack them as needed. At this time, the discontinuous parts of the electromagnetic steel sheets of the core are photographed with a camera from the side of the core, and the gap length is measured. Next, if the gap length exceeds 50 times the minimum value up to that layer, this is fed back to the feed amount of the next steel sheet, and it is extended by 50 times the minimum value. In this way, it is possible to adjust the gap length. Other methods that are possible include a method of extending each layer at a fixed rate (fixed extension) and a method of increasing the amount of extension for each fixed number of layers (step extension).

[0074] Thus, the wound core 10 according to the present embodiment has a configuration in which the grain-oriented electromagnetic steel sheet 11 is wound in the rolling direction, and in a cross section parallel to the rolling direction at the bent portion of the corner portion 12 of the wound core 10, when the average value of the KAM value in the region from the center of the thickness of the grain-oriented electromagnetic steel sheet 11 to the outer periphery of the wound core 10 is Kоut, and the average value of the KAM value in the region from the center of the thickness of the grain-oriented electromagnetic steel sheet 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 value of KR at the bent portion of the corner portion 12 in such an appropriate range, the wound core 10 according to the present embodiment can realize a reduction in the building factor due to magnetic flux transfer in the lamination direction and a reduction in noise. Furthermore, by keeping the expansion of the discontinuous portion of the electromagnetic steel sheet due to springback within a certain range, it is possible to obtain even better transformer characteristics. In this case, the wound core 10 according to the present embodiment can be manufactured with a small number of manufacturing steps. 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] (Example) Next, the contents of the present disclosure will be specifically described based on examples. The following examples are intended to illustrate preferred examples of the present disclosure, and are not intended to limit the scope of the present disclosure. The present disclosure may be modified within the scope of the present disclosure, and such modifications 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 using a general manufacturing process. Steel strip B is a grain-oriented electrical steel sheet that has been subjected to electrolytic etching on the surface of the steel strip 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 finished annealing. Steel strip C is a grain-oriented electrical steel sheet in which part of steel strip A has been irradiated with a laser. Steel strip D is a grain-oriented electrical steel sheet in which part of steel strip A has been irradiated with an electron beam.

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

[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 core loss of each test piece was measured by the single sheet magnetic measurement method described in JIS C2556.

[0080] After that, each steel strip was 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 annealed to relieve distortion were also produced. For steel strips C and D, only Unicores were produced because the magnetic domain refining effect produced by the laser and electron beam disappears when annealed to relieve distortion.

[0081] These cores were manufactured in two shapes: a non-cut type that does not have 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 ones in which the gap length was adjusted by a feedback method.

[0082] For each manufactured transformer, the iron loss characteristics were measured when the magnetic flux density in the iron core legs was 1.7 T at a frequency of 50 Hz. The no-load loss was measured using a wattmeter to determine the iron loss characteristics under the conditions of a magnetic flux density of 1.7 T and a frequency of 50 Hz. At the same time, this 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) was measured using a sound level meter.

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

[0084] [Table 1]

[0085] [Table 2]

[0086] [Table 3]

[0087] [Table 4]

[0088] [Table 5]

[0089] With reference to Tables 1 to 5, it can be confirmed that a good transformer satisfying low iron loss and low noise can be obtained under the conditions that satisfy the configuration of this embodiment. It can also be confirmed that Unicore has a higher BF improvement effect than Tranco. In particular, when KR is 1.1 or more and 1.5 or less, the improvement in transformer characteristics is remarkable. Also, cut cores can obtain better characteristics than non-cut cores. Also, Unicore can obtain better characteristics than Tranco. Furthermore, it was confirmed that better characteristics can be obtained by adjusting the gap length and setting the ratio wr of the maximum value to the minimum value of the gap length w of the discontinuous parts of all grain-oriented electromagnetic steel sheets that make up the wound core to 100 or less for single-phase / three-phase five-legged and 500 or less for three-phase three-legged.

[0090] The present disclosure is not limited to the above-described embodiments. For example, multiple blocks shown in the block diagram may be integrated, or one block may be divided. Instead of executing multiple steps shown in the flowchart 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 necessary. Other modifications are possible without departing from the spirit of the present disclosure. [Explanation of symbols]

[0091] 1. Transformer 10 Wound core 11 Grain-oriented electrical steel sheet 12 Corner section 20 Coil

Claims

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

2. 2. The wound core of claim 1, wherein said KR is greater than or equal to 1.1 and less than or equal to 1.

5.

3. The wound core of claim 1 , wherein the corner portion has a bend.

4. 2. The wound core according to claim 1, wherein the grain-oriented electrical steel sheet has one discontinuity in a magnetic path direction.

5. A transformer comprising the 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 a plurality of single-phase wound cores are arranged, The gap length in the rolling direction of each layer of the discontinuous portion, which is obtained by observing the discontinuous portion of the grain-oriented electrical steel sheet from the side in the lamination direction of the grain-oriented electrical steel sheet and the rolling direction of the grain-oriented electrical 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 wr = w ｍａｘ / w ｍｉｎ The ratio wr between the maximum value and the minimum value defined by is 100 or less, 5. The wound core according to claim 4, wherein 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-legged wound core formed by combining an inner core and an outer core, The gap length in the rolling direction of each layer of the discontinuous portion, which is obtained by observing the discontinuous portion of the grain-oriented electrical steel sheet from the side in the lamination direction of the grain-oriented electrical steel sheet and the rolling direction of the grain-oriented electrical 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 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:

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