Wound core and transformer

Abstract

The coiled core (10) is constructed by winding an orientation-oriented electromagnetic steel sheet (11) along the rolling direction. In the coiled core (10), in the section parallel to the rolling direction in the bent portion of the corner (12) of the coiled core (10), the width of the sheared region in the area from the center of the thickness of the orientation-oriented electromagnetic steel sheet (11) to the outer periphery of the coiled core (10) is more than 100 μm and less than 400 μm.

Description

Technical Field

[0001] This disclosure relates to wound iron cores and transformers. Background Technology

[0002] Transformer cores are broadly classified into wound cores and stacked cores. Regardless of the type, most transformers use oriented electromagnetic steel sheets as the raw material.

[0003] There are two types of coiled iron cores. In this specification, one type will be referred to as "Tranco core" or "Tranco", and the other type will be referred to as "Unicore".

[0004] Figure 1 Two types are illustrated schematically. For example, patent document 1 describes Tranco. Tranco is a coiled iron core formed by winding an oriented electromagnetic steel sheet into a cake-like shape along the rolling direction and then pressing it from four directions to form a quadrilateral shape with rounded corners.

[0005] For example, Patent Document 2 describes Unicore. Unicore is a coiled iron core formed by stacking steel plates with pre-bent sections at corresponding corner positions along the thickness direction.

[0006] Compared to Tranco, Unicore does not require pressure forming, thus allowing for the use of smaller equipment in its manufacturing. Furthermore, since the strain introduced into the steel sheet during Unicore manufacturing is concentrated only at the bending points, stress-relieving annealing equipment is unnecessary. Due to these industrial advantages, Unicore's applications continue to expand.

[0007] In recent years, from the perspective of energy conservation and environmental constraints, there has been a strong demand to reduce energy losses in transformers and to reduce noise during transformer operation. To improve transformer efficiency, the properties of grain-oriented electromagnetic steel sheets, used as core materials, are being continuously enhanced.

[0008] It is known that when a transformer is manufactured using oriented electromagnetic steel sheet as the core blank, the transformer's iron loss increases compared to the iron loss of the electromagnetic steel sheet used as the blank. This increase is known to be the building factor. The building factor is defined as the transformer's iron loss divided by the iron loss of the blank electromagnetic steel sheet.

[0009] Therefore, in order to improve the efficiency of transformers, in addition to improving the characteristics of the electromagnetic steel sheet in the billet, improving the process coefficient is also an important R&D factor.

[0010] To improve process efficiency, various methods have been investigated. For example, Patent Document 3 proposes a strain-based magnetic domain refinement process for oriented electromagnetic steel sheets near the joint. Magnetic domain refinement is a technique that forms magnetic discontinuities in the rolling direction through thermal strain. By forming such magnetic discontinuities, the magnetic domain refinement technique can refine the magnetic domains of the oriented electromagnetic steel sheet and improve iron loss.

[0011] In addition, for example, Patent Document 4 proposes to tilt the joint in the winding direction in order to improve the iron loss caused by magnetic flux crossing.

[0012] Furthermore, in Unicore, the bending process introduces significant strain at the corners, which increases the process coefficient. For example, Patent Document 5 proposes a method to improve magnetic degradation caused by corner strain by performing magnetic domain refinement treatment by adding grooves to the bent portion of the corner.

[0013] Patent Document 1: Japanese Patent Application Publication No. 2016-146441

[0014] Patent Document 2: Japanese Patent Application Publication No. 2005-286169

[0015] Patent Document 3: Japanese Patent Application Publication No. 2020-96100

[0016] Patent Document 4: Japanese Patent Application Publication No. 2005-150507

[0017] Patent Document 5: Japanese Patent Application Publication No. 2021-163942 Summary of the Invention

[0018] The methods disclosed in Patent Documents 3-5 are all effective as methods for improving process efficiency. However, the methods disclosed in Patent Documents 3-5 are based on the premise of additional processing during the design of the iron core. Therefore, problems arise such as increased manufacturing time and increased manufacturing costs due to the need to change the shearing direction during manufacturing.

[0019] The purpose of this disclosure is to provide a wound core and transformer that can improve the process coefficient by suppressing the increase in manufacturing time and manufacturing costs.

[0020] [1] A type of coiled iron core is constructed by winding an orientation-oriented electromagnetic steel sheet along the rolling direction.

[0021] In the curved portion at the corner of the aforementioned coiled iron core, on a cross section parallel to the rolling direction, in the region extending from the center of the thickness of the aforementioned oriented electromagnetic steel sheet to the outer periphery of the aforementioned coiled iron core, the width of the shearing region is 100 μm or more and 400 μm or less.

[0022] [2] According to the coiled iron core described in [1] above, the width of the sheared region is more than 150 μm and less than 350 μm.

[0023] [3] The coiled iron core according to [1] or [2] above, wherein the corner portion has a bent portion.

[0024] [4] A transformer comprising a wound iron core and a coil as described in any one of [1] to [3] above.

[0025] According to the coiled iron core and transformer disclosed herein, the process coefficient can be improved by controlling the increase in manufacturing time and manufacturing costs. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating two types of coiled iron cores.

[0027] Figure 2 It is a diagram showing the composition of the steel billet used in the experiment.

[0028] Figure 3 This is a graph showing the measurement results of the relationship between the process coefficient and the width of the shearing zone.

[0029] Figure 4 This is a graph showing the measurement results of the relationship between noise and the width of the sheared region.

[0030] Figure 5 This is a schematic diagram illustrating the structure of a wound core according to one embodiment of the present disclosure.

[0031] Figure 6 This is a schematic diagram illustrating the configuration of a transformer according to one embodiment of the present disclosure.

[0032] Figure 7 This is a diagram illustrating an example of the structure of a curved section.

[0033] Figure 8 This is a schematic diagram of the Kr distribution.

[0034] Figure 9 This is a diagram of the corner.

[0035] Figure 10 This is a diagram showing the composition of the steel billet in the embodiment.

[0036] Figure 11A This is a table showing the relationship between the width of the shearing region and the process coefficient in the embodiments.

[0037] Figure 11B This is a table showing the relationship between the width of the shearing region and the process coefficient in the embodiments. Detailed Implementation

[0038] (Experimental Results)

[0039] First, experimental results will be explained to illustrate the concept that led to the embodiments of this disclosure.

[0040] Figure 2 The composition of the steel billet used in the experiment is shown. In the experiment, a steel billet with… Figure 2 The test material was an orientation-oriented electromagnetic steel sheet and strip manufactured from a billet with the composition shown in the figure through a conventional manufacturing process.

[0041] Oriented electromagnetic steel sheets and strips are cut into 100mm wide pieces and wound into a shape with a stack thickness of 30mm, a long side of 300mm, and a short side of 150mm. This manufactures a single-phase Unicore. The portion corresponding to the short side is then cut to form a so-called cut core shape. Furthermore, three types of cores are manufactured with bends of 90 degrees (one bend), 45 degrees (two bends), and 30 degrees (three bends). Each bending angle θ is set to θ±1 degrees. All cores are manufactured without stress-relief annealing (SRA).

[0042] Iron loss was measured using single-plate specimens cut from the test material steel strip, according to the single-plate magnetic determination method specified in JIS C2556. Simultaneously, the iron loss characteristics (transformer iron loss) of each manufactured wound-core transformer were measured at a magnetic flux density of 1.7T in the core column section at a frequency of 50Hz.

[0043] As mentioned above, the iron loss characteristics at a magnetic flux density of 1.7T and a frequency of 50Hz in the core column section were determined by measuring the no-load loss using a wattmeter.

[0044] The process factor (BF) of each transformer is calculated based on the ratio of transformer iron loss to single-plate iron loss as determined by this method.

[0045] Then, each model transformer was energized in a soundproof room under the conditions of maximum magnetic flux density Bm = 1.7T and frequency 50Hz, and the noise level was measured using a noise meter: dBA (transformer noise).

[0046] Samples are cut from the corners of the iron core after various measurements are completed, and the samples are embedded in a carbon mold. Then, a section parallel to the rolling direction is ground, and EBSD (Electron BackScatter Diffraction) measurements are performed.

[0047] The KAM (Karnel Average Misorientation) value is calculated based on the results obtained. Additionally, within the region from the center of the steel plate thickness to the outer periphery of the coiled core, the width of the shear zone, formed by multiple points extending through the plate thickness direction and arranged along the rolling direction, is calculated. The ratio of the KAM value Kp at each of these points to the average KAM value Kave of the total plate thickness section of the bent portion, Kr = Kp / Kave, is greater than 1.0.

[0048] Figure 3 The results of the measurement show the relationship between the process coefficient and the width of the shear zone. Figure 4 The results of the measurement show the relationship between noise and the width of the sheared region.

[0049] Reference Figure 3 If the width of the sheared region increases, the process coefficient improves. In particular, a significant improvement is observed when the width of the sheared region exceeds 100 μm. This is attributed to the orientation difference between adjacent measurement points in KAM; therefore, in sheared regions with a larger Kr, the magnetization direction changes slightly, creating magnetic discontinuities and thus exhibiting a magnetic domain refinement effect.

[0050] Reference Figure 4 It can be seen that the transformer noise tends to increase with the width of the sheared region. In particular, if the width of the sheared region reaches 400 μm or more, the noise increases significantly. This is attributed to the increased strain within the steel plate and the resulting deterioration of its magnetostrictive properties.

[0051] These results show that a coiled iron core with good properties can be obtained by making the width of the shearing region 100 μm or more and 400 μm or less. Furthermore, it is more preferable to make the width of the shearing region 150 μm or more and 350 μm or less, resulting in a coiled iron core with even better properties.

[0052] (This implementation method)

[0053] Next, the embodiments of the wound core involved in this disclosure will be described with reference to the accompanying drawings.

[0054] Figure 5 This is a schematic diagram illustrating the structure of the wound core 10 according to one embodiment of the present disclosure.

[0055] The coiled core 10 is constructed by winding an oriented electromagnetic steel sheet 11 along the rolling direction. The coiled core 10 has corner portions 12-1 to 12-4. Hereinafter, unless there is a specific distinction between corner portions 12-1 to 12-4, it will sometimes be simply referred to as "corner portion 12". Figure 5This illustrates the case where the coiled core 10 is of the Unicore type. When the coiled core 10 is of the Unicore type, the corner 12 has the following characteristics: Figure 1 The bent section shown.

[0056] The coiled iron core 10 can be used as a component of a transformer. Figure 6 The diagram schematically illustrates the configuration of a transformer 1 according to one embodiment of this disclosure. The transformer 1 includes a wound core 10, coils 20-1 and 20-2. (As...) Figure 2 As shown, coils 20-1 and 20-2 are wound on the coiled iron core 10.

[0057] Figure 5 The oriented electromagnetic steel sheet 11 shown can be made from a slab as a steel billet. The composition of the slab used for the oriented electromagnetic steel sheet 11 only needs to be able to produce secondary recrystallization.

[0058] In the case of using inhibitors in the oriented electromagnetic steel sheet 11, for example, if AlN-based inhibitors are used, Al and N can be contained in appropriate amounts; and if MnS-MnSe-based inhibitors are used, Mn and Se and / or S can be contained in appropriate amounts. Alternatively, two inhibitors can be used together.

[0059] The preferred contents of Al, N, S and Se when using two inhibitors together are as follows.

[0060] Al: 0.010–0.065% by mass

[0061] N: 0.0050~0.0120% by mass

[0062] S: 0.005~0.030% by mass

[0063] Se: 0.005~0.030 (mass).

[0064] Furthermore, the orientation-oriented electromagnetic steel sheet 11 can be an orientation-oriented electromagnetic steel sheet that limits the content of Al, N, S, and Se and does not use inhibitors. In this case, the content of Al, N, S, and Se is preferably controlled as follows.

[0065] Al: less than 0.010% by mass

[0066] N: less than 0.0050% by mass

[0067] S: less than 0.0050% by mass

[0068] Se: less than 0.0050% of mass.

[0069] The following details the representative basic components and any added components of the steel billet (slab) used for oriented electromagnetic steel sheet 11.

[0070] C: less than 0.08% by mass

[0071] Carbon (C) is added to improve the microstructure of hot-rolled steel sheets. If the C content exceeds 0.08% by mass, it becomes difficult to achieve decarburization to below 50 ppm by mass, which prevents magnetic aging during the manufacturing process. Therefore, the C content is preferably below 0.08% by mass. Furthermore, since secondary recrystallization occurs even in C-free steel billets, a lower limit for the C content is not specifically set.

[0072] Si: 2.0–8.0% by mass

[0073] Si is an element that effectively increases the resistivity of steel and improves iron loss. If the Si content is less than 2.0% by mass, the aforementioned improvement effect is not fully realized. On the other hand, if the Si content exceeds 8.0% by mass, in addition to significant deterioration in processability and permeability, magnetic flux density also decreases. Therefore, the Si content is preferably in the range of 2.0 to 8.0% by mass.

[0074] Mn: 0.005~1.0% by mass

[0075] Mn is an element required to improve hot workability. If the Mn content is less than 0.005% by mass, it is difficult to fully obtain the 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.

[0076] In addition to the basic components described above, the slab for the oriented electromagnetic steel sheet 11 may appropriately contain one or more of the following additives. The following additives are known to be effective in improving magnetic properties.

[0077] Ni: 0.03–1.50% by mass

[0078] Sn: 0.01–1.50% by mass

[0079] Sb: 0.005~1.50% by mass

[0080] Cu: 0.03–3.0% by mass

[0081] P: 0.03–0.50% by mass

[0082] Mo: 0.005–0.10% by mass

[0083] Cr: 0.03–1.50 by mass.

[0084] Ni is an effective element for improving the microstructure of hot-rolled steel sheets to enhance their magnetic properties. If the Ni content is less than 0.03% by mass, its contribution to improving magnetic properties is small. On the other hand, if the Ni content exceeds 1.50% by mass, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, the Ni content is preferably in the range of 0.03% to 1.50% by mass.

[0085] In addition, Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties. However, if the content of any element is below the lower limit mentioned above, the effect of improving magnetic properties is insufficient. Furthermore, if the content of any element exceeds the upper limit mentioned above, the magnetic properties deteriorate due to suppressed secondary recrystallization grain growth. Therefore, the contents of Sn, Sb, Cu, P, Mo, and Cr are preferably within the ranges mentioned above.

[0086] The slab used for the oriented electromagnetic steel sheet 11 contains, as other than the components mentioned above, Fe and unavoidable impurities.

[0087] After hot rolling the steel billet (slab) of the orientation-oriented electromagnetic steel sheet 11 composed of the above-mentioned composition system, hot-rolled sheet annealing is performed. Then, the slab is cold-rolled once or twice. Then, it becomes a steel strip with the final sheet thickness.

[0088] Next, the steel strip of the final thickness undergoes decarburization annealing and is coated with an annealing separating agent. Then, the steel strip of the final thickness is wound into a coil. Next, the steel strip of the final thickness undergoes final annealing for secondary recrystallization. Then, the final annealed steel strip undergoes planarization annealing to form a tension film, thus producing the steel strip for the product sheet.

[0089] In the process following planarization annealing for manufacturing the oriented electromagnetic steel sheet 11, a magnetic domain refinement process may also be included, which forms thermal strain by irradiating the surface of the oriented electromagnetic steel sheet 11 with an energy beam. Additionally, in the process following cold rolling for manufacturing the oriented electromagnetic steel sheet 11, a magnetic domain refinement process may also be included, which forms grooves by electrolytic etching or laser irradiation of the oriented electromagnetic steel sheet 11.

[0090] Next, the calculation methods for the KAM and Kr values ​​in this embodiment will be explained.

[0091] The corner 12 of the coiled iron core 10 has a bent portion. The coiled iron core 10 is bent at a 90-degree angle at the corner 12 by deformation at the bent portion. The corner 12 has at least one bent portion. For example, when the corner 12 has one bent portion, it is bent at a 90-degree angle. Alternatively, for example, when the corner 12 has two bent portions, one bent portion is bent at a 45-degree angle. Alternatively, for example, when the corner 12 has three bent portions, one bent portion is bent at a 30-degree angle.

[0092] Reference Figure 7 An example of the structure of the curved portion is shown, and the curved portion is explained. The curved portion of corner 12 is... Figure 7 The region marked as the bend F.

[0093] like Figure 7 As shown, a tangent is drawn in a semi-straight line from the flat surfaces (outer and inner circumferential surfaces of the steel plate) of the regions (flat portions) without curvature existing on both sides of the rolling direction to the regions with curvature in the corner 12. Figure 7 In this context, the tangents drawn from the outer periphery of the oriented electromagnetic steel plate 11, i.e., the outer periphery of the steel plate, are marked as tangent L1 and tangent L2. Additionally, in... Figure 7 In the diagram, the tangent lines drawn from the inner circumference surface of the oriented electromagnetic steel plate 11, i.e., the inner circumference surface of the steel plate, are marked as tangent line L3 and tangent line L4.

[0094] like Figure 7 As shown, the points of tangency between tangents L1 and L2 and the outer surface of the steel plate are designated as tangent points O1 and O2, respectively. Similarly, the points of tangency between tangents L3 and L4 and the inner surface of the steel plate are designated as tangent points I1 and I2, respectively. The region enclosed by these four tangent points O1, O2, I1, and I2 is the curved portion F.

[0095] When calculating the KAM and Kr values, a portion of the oriented electromagnetic steel sheet 11 is taken from the bent portion of the corner 12 of the coiled core 10, with the section in the rolling direction as the cutting surface. Then, stress-free grinding is performed on the cutting surface.

[0096] Next, the crystal orientation difference of the polished surface after strain-free polishing was analyzed by EBSD (Electron BackScatter Diffraction) to calculate the KAM (Karnel Average Misorientation) value. Here, the orientation difference is the difference between a given measurement point and its third adjacent point.

[0097] Furthermore, in the region from the center of the thickness of the oriented electromagnetic steel plate 11 to the outer periphery of the coiled iron core 10, the ratio of the KAM value Kp at each point to the average KAM value Kave of the total thickness section of the bent portion is defined as Kr (=Kp / Kave).

[0098] In this embodiment, the width of the sheared region is measured using a Kr distribution map that distributes the aforementioned Kr values ​​across the entire observation surface. It should be noted that in this embodiment, the "sheared region" refers to the overall region formed by multiple points with Kr values ​​greater than 1.0 penetrating the thickness of the oriented electromagnetic steel sheet 11, arranged along the rolling direction as shear bands.

[0099] Figure 8The diagram shows a schematic of the Kr distribution. Figure 8 The diagram shows the distribution of Kr in the outer half of the observation area of ​​the oriented electromagnetic steel sheet 11, from the center of the sheet thickness (1 / 2 sheet thickness) to the outer periphery of the coiled core 10 (outer periphery of the steel sheet), in the field of view of the section parallel to the rolling direction in the curved portion of the corner 12.

[0100] exist Figure 8 In this context, the region marked as the cutoff region is the cutoff region as defined above. For example... Figure 8 As shown, in this embodiment, the length of the shearing region in the rolling direction at 1 / 4 plate thickness is referred to as the "width of the shearing region".

[0101] For reference Figure 3 and Figure 4 As explained in the above experimental results, the width of the shearing region is preferably 100 μm or more and 400 μm or less. This results in a wound core 10 with excellent properties. Furthermore, the width of the shearing region is more preferably 150 μm or more and 350 μm or less. This results in a wound core 10 with even better properties.

[0102] Figure 9 This is a schematic diagram of the corner 12 of the coiled iron core 10.

[0103] When manufacturing the coiled iron core 10, if the bending angle (bending angle) formed by the extension lines of the long and short sides adjacent to the corner 12 and the inner circumferential direction of the coiled iron core 10 is less than 90 degrees, and then the core is bent back to form a quadrilateral shape, the width of the sheared area can be made to the width described above, easily achieving a significant effect. Alternatively, when manufacturing the coiled iron core 10, by using a tension film of the orientation-type electromagnetic steel plate 11 used for the coiled iron core blank with different film thicknesses or coating types on the inner and outer circumferential sides of the corner 12, and with the tension on the inner circumferential side being higher than that on the outer circumferential side, the width of the sheared area can also be made to the width described above, easily achieving a significant effect.

[0104] It is speculated that this is because when the coiled iron core 10 is made by combining the various coiled iron core blanks, the bending angle is opened to 90 degrees, and compressive stress is generated on the outer periphery of the thickness of each steel plate due to the tension difference between the inside and outside, thereby forming a shearing region with the width of the shearing region as described above.

[0105] However, the method of manufacturing the coiled iron core 10 having the width of the sheared region as described above is not limited to this manufacturing method. Other manufacturing methods can also achieve the width of the sheared region as described above. If the sheared region of the corner 12 has the width described above, the coiled iron core 10 can obtain an improvement in process coefficient due to the magnetic domain refinement effect.

[0106] Thus, the coiled iron core 10 according to this embodiment is configured to be formed by winding an orientation-oriented electromagnetic steel sheet 11 along the rolling direction. In the curved portion of the corner 12 of the coiled iron core 10, on a cross section parallel to the rolling direction, the width of the shearing region in the area from the center of the thickness of the orientation-oriented electromagnetic steel sheet 11 to the outer periphery of the coiled iron core 10 is 100 μm or more and 400 μm or less. By setting the width of the shearing region within such a range, the KAM value of the cross section parallel to the rolling direction can be rationalized in the coiled iron core 10 according to this embodiment. Therefore, the coiled iron core 10 according to this embodiment can improve the process coefficient, thereby improving the iron loss of the coiled iron core 10. Furthermore, the coiled iron core 10 according to this embodiment can be manufactured with fewer manufacturing steps, thus reducing manufacturing time and costs.

[0107] (Example)

[0108] The present disclosure will now be described in detail with reference to embodiments. The following embodiments illustrate a preferred example of the present disclosure, but the disclosure is not limited to any of these embodiments. Modifications may be made to implement the disclosure within the scope of its spirit, and such modifications are also included within the technical scope of the present disclosure.

[0109] Figure 10 This is a diagram showing the composition of the steel billet used in the embodiments. Steel strips A, B, C, and D are manufactured using such steel billets.

[0110] Steel strip A is a grain-oriented electromagnetic steel sheet manufactured through conventional manufacturing processes. Steel strip B is a grain-oriented electromagnetic steel sheet produced by electrolytic etching of the surface of a cold-rolled steel strip, forming linear grooves 15 μm deep and 40 μm wide at 5 mm intervals in a direction perpendicular to the rolling direction, followed by final annealing. Steel strip C is a grain-oriented electromagnetic steel sheet produced by irradiating a portion of steel strip A with a laser. Steel strip D is a grain-oriented electromagnetic steel sheet produced by irradiating a portion of steel strip A with an electron beam.

[0111] Steel strips A, B, C, and D were used as test materials. The type of tension film was set to be the same, and the film thickness was varied in the range of 1–5 μm on both the outer and inner periphery of the coiled core to manufacture oriented electromagnetic steel sheets and strips.

[0112] Cut test pieces (samples) with a width of 100 mm and a long side of 280 mm from the steel strip of the test material manufactured above, and measure the iron loss of each test piece according to the single-plate magnetic measurement method described in JIS C2556.

[0113] Then, the steel strips were wound along the rolling direction to manufacture a three-phase wound core model transformer (core weight 50kg). For steel strips A and B, two types, Tranco and Unicore, were manufactured. For the Unicore, a core after stress-relief annealing was also produced. For steel strips C and D, since stress-relief annealing would negate the magnetic domain refinement effect brought about by laser and electron beams, only the Unicore type was manufactured.

[0114] For each manufactured transformer, the iron loss characteristics were measured at a magnetic flux density of 1.7T in the core column at a frequency of 50Hz. The no-load loss was measured using a wattmeter under these conditions of 1.7T magnetic flux density and 50Hz. Simultaneously, the model transformer was energized in a soundproof room at a maximum magnetic flux density Bm = 1.7T and a frequency of 50Hz, and the noise level (dBA) was measured using a noise meter.

[0115] Samples were cut from the corners of the core after various measurements were completed, embedded in a carbon mold, and ground to form a cross-section parallel to the rolling direction for EBSD measurement. Additionally, the KAM value was calculated based on the results, and the width of the shear zone was calculated within the area from the center of the steel plate thickness to the outer periphery of the coiled core. These results are presented below. Figure 11A and Figure 11B .

[0116] Reference Figure 11A and Figure 11B It can be confirmed that, under the conditions of the configuration of this embodiment, a good transformer with low iron loss and low noise can be obtained. Furthermore, it can be confirmed that Unicore has a higher BF improvement effect compared to Tranco. In particular, the improvement in transformer characteristics is significant when the width of the shear region is 150μm or more and 350μm or less.

[0117] This disclosure is not limited to the embodiments described above. For example, multiple blocks shown in the block diagram may be merged, or a block may be split. Instead of executing multiple steps shown in the flowchart sequentially in chronological order, the steps may be executed in parallel or in different orders, depending on the processing capacity of the device executing each step or as needed. Furthermore, modifications may be made without departing from the spirit of this disclosure.

[0118] Symbol Explanation

[0119] 1. Transformer

[0120] 10 coils of iron core

[0121] 11 Oriented Electromagnetic Steel Sheets

[0122] 12 corners

[0123] 20 coils

Claims

1. A type of wound iron core, comprising winding a grain-oriented electromagnetic steel sheet along the rolling direction. In the curved portion at the corner of the coiled core, on a cross section parallel to the rolling direction, within the region from the center of the thickness of the oriented electromagnetic steel sheet to the outer periphery of the coiled core, the width of the sheared region is more than 100 μm and less than 400 μm.

2. The wound core according to claim 1, wherein, The width of the shearing region is greater than 150 μm and less than 350 μm.

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

4. A transformer comprising a wound core and a coil as described in any one of claims 1 to 3.

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