Three-phase, three-legged wound core and three-phase, three-legged wound core transformer using the same

Abstract

To provide a three-phase tripod-wound core that uses a grain-oriented electromagnetic steel sheet that has been subjected to magnetic domain refining treatment by introducing thermal strain as a core material, and has excellent iron loss reduction effects and noise reduction effects.SOLUTION: A three-phase tripod-wound core consists of two adjacent inner cores 10 and one outer core 12 surrounding the two inner cores 10, made of grain-oriented electromagnetic steel sheets as a raw material. The three-phase tripod wound core has a region formed of a grain-oriented electromagnetic steel sheet that has been subjected to magnetic domain refining treatment by introducing thermal strain and a region formed of a grain-oriented electromagnetic steel sheet that has not been subjected to magnetic domain refining treatment by introducing thermal strain, and has a region 5 formed of the grain-oriented electromagnetic steel sheet that has not been subjected to magnetic domain refining treatment by introducing thermal strain in a region 4 where magnetic flux crossing occurs between the outer core 12 and the inner cores 10 between legs when viewed from the side.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a three-phase, three-legged wound core and a three-phase, three-legged wound core transformer using the same, and in particular to a three-phase, three-legged wound core for a transformer manufactured using grain-oriented electromagnetic steel sheet and a three-phase, three-legged wound core transformer using the above-mentioned wound core. [Background technology]

[0002] The easy axis of magnetization of iron <001> Grain-oriented electrical steel sheets, which have a crystal structure with a highly aligned orientation in the rolling direction of the steel sheet, are used particularly as the iron core material for power transformers. The primary characteristic required of grain-oriented electrical steel sheets is low iron loss, which is the loss caused when excited. One technique for reducing iron loss is magnetic domain refinement. Magnetic domain refinement is a technique for reducing iron loss by irradiating the surface of a steel sheet with a laser, plasma jet, electron beam, etc., to generate magnetic domains called closure domains on the surface of the steel sheet. The closure domains are generated along the easy magnetization direction of the electrical steel sheet. Usually <001> The orientation is concentrated in the rolling direction, but is equivalent to that orientation and perpendicular to it. <100> , <010> The orientation is also the easy direction of magnetization. These two orientations are a composite component of the direction perpendicular to the rolling direction and the thickness direction. Since the closure domains occur along these orientations, they are magnetic domains with components perpendicular to the rolling direction and the thickness direction.

[0003] Transformers are broadly classified into wound core transformers and stacked core transformers based on their core structure. Wound core transformers have a core formed by winding and stacking steel sheets. On the other hand, stacked core transformers have a core formed by stacking steel sheets cut to a specific shape. There are various characteristics required for a transformer core, but the most important are low iron loss and low noise.

[0004] In order to reduce the iron loss of a transformer, it is generally believed that it is necessary to reduce the iron loss (material iron loss) of the grain-oriented electromagnetic steel sheet, which is the core material. The use of magnetic steel sheets with magnetic domain refinement as the core material also reduces the iron loss of the transformer. However, it is known that the iron loss in a transformer core, especially a wound-core transformer with three or five legs of electromagnetic steel sheets and three-phase excitation, is larger than the material iron loss. The value obtained by dividing the iron loss value (transformer iron loss) when an electromagnetic steel sheet is used as the iron core of a transformer by the iron loss value of the material obtained by the Epstein test or the Single Sheet Magnetic Measurement Test (SST test) is generally called the Building Factor (BF). In other words, in a wound-core transformer with three or five legs and three-phase excitation, the BF is generally more than 1.

[0005] It is generally known that the concentration of magnetic flux in the inner core, which occurs mainly due to the difference in magnetic path length, is the reason why the transformer iron loss in a wound core transformer increases compared to the material iron loss. Figure 1 shows a schematic diagram of the magnetic flux flow when a three-legged wound core transformer is excited in three phases and only the left leg and the center leg are excited. When the inner core 1 and the outer core 2 are both excited, the magnetic path of the inner core 1 is shorter than that of the outer core 2, so the magnetic flux is concentrated in the inner core 1. When the excitation magnetic flux density becomes relatively large, the inner core 1 alone cannot support the excitation, and more magnetic flux also passes through the outer core 2, so the magnetic flux concentration is alleviated. However, as shown in Figure 1, the magnetic flux passing through the outer core 2 flows toward the non-excited right leg, and when it tries to return to the excited center leg, the magnetic flux passes through the inner core 1, and an interlayer magnetic flux crossover 3 occurs between the inner core 1 and the outer core 2. Magnetization occurring in the perpendicular direction causes in-plane eddy current loss, increasing the transformer iron loss.

[0006] The noise of a transformer is generally caused by magnetostriction, which is the distortion that occurs when magnetic steel sheets are magnetized, the inherent vibration of the iron core, and electromagnetic vibration caused by magnetized steel sheets. Of these, electromagnetic vibration caused by magnetized steel sheets is a minute vibration that occurs when magnetization changes over time in the case of AC excitation, and the attractive force between laminated steel sheets also changes over time. In-plane magnetization, such as the interlayer magnetic flux transfer 3 between the inner iron core 1 and the outer iron core 2, also changes the attractive force between the steel sheets, causing electromagnetic vibration, which is one of the causes of transformer noise.

[0007] Based on a qualitative understanding of the factors that increase transformer iron loss and transformer noise, the following, for example, have been proposed as measures to reduce transformer iron loss and transformer noise.

[0008] Patent Document 1 discloses that transformer iron loss can be effectively reduced by arranging an electromagnetic steel sheet with inferior magnetic properties to the outer periphery side, where the magnetic path length is short and the magnetic resistance is small, and an electromagnetic steel sheet with superior magnetic properties to the inner periphery side, where the magnetic path length is long and the magnetic resistance is large. Patent Document 2 discloses that transformer noise can be effectively reduced by arranging a wound core wound with a grain-oriented silicon steel sheet on the inner part and winding a magnetic material with lower magnetostriction than the grain-oriented silicon steel sheet on the outside of this wound core to form a combined core. Patent Document 3 discloses a technology that can reduce iron loss by performing a magnetic domain refining process only on the lap part of a transformer core that is laminated and wound with a lap part. Patent Document 4 discloses a technology related to a wound core called Unicore, in which the distortion of the iron core is reduced by individually bending and assembling the iron core material, and the distortion relief annealing performed after the formation of the iron core is unnecessary, and thus a magnetic domain refining material with low iron loss due to thermal distortion can be used as the iron core material. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2010-87536 A [Patent Document 2] Japanese Patent Application Publication No. 3-268311 [Patent Document 3] International Publication No. 2020 / 121691 [Patent Document 4] JP 2021-163943 A [Patent Document 5] JP 2011-75297 A Summary of the Invention [Problem to be solved by the invention]

[0010] As disclosed in Patent Documents 1 and 2, by utilizing the concentration of magnetic flux on the inner core and applying different materials to the inner core and outer core, it is possible to efficiently improve the transformer characteristics. However, as disclosed in Patent Document 3, when the excitation magnetic flux density increases, magnetic flux also flows to the outside of the core with large loss, and the effect of improving the transformer characteristics is reduced. In addition, at this time, the magnetic flux passing through the outer core passes to the inner core, and this interlayer magnetic flux transfer not only increases eddy current loss at the interlayer magnetic flux transfer portion, but also increases noise due to electromagnetic vibration between the steel sheets, which are the material, and the transformer characteristics are significantly deteriorated. Even if a low-loss magnetic domain-refined material is used as the core material as in Patent Document 4, the iron loss of the iron core increases due to the above-mentioned interlayer magnetic flux transfer in a three-phase three-leg wound core.

[0011] Therefore, an object of the present invention is to provide a three-phase, three-legged wound core that uses, as the core material, a grain-oriented electrical steel sheet that has been subjected to a magnetic domain refinement process by introducing thermal strain, and that has excellent iron loss reduction and noise reduction effects. [Means for solving the problem]

[0012] In three-phase three-limbed wound core transformers, the transformer iron loss can be reduced by using a low-loss material that has been treated with magnetic domain refinement as the core material, but the complex magnetization state inside the core, typified by the occurrence of magnetic flux transfer, deteriorates the transformer iron loss, and the improvement in transformer iron loss is smaller than the improvement in iron loss of the core material due to magnetic domain refinement.By suppressing magnetic flux transfer from the outer core to the inner core and suppressing the occurrence of eddy current loss, it is possible to reduce this difference in improvement, further reduce transformer iron loss, and further suppress transformer noise, and we have investigated a method to achieve this.

[0013] Since magnetic flux transfer is the transfer of magnetic flux in the thickness direction from the outer core to the inner core of a three-phase, three-legged wound core transformer, it was thought that magnetic flux transfer could be suppressed by reducing the amount of magnetic flux in the thickness direction flowing in the part where magnetic flux transfer occurs. Therefore, the inventors attempted to reduce the magnetic flux that passes from the outer core to the inner core of the transformer core.

[0014] In the grain-oriented electrical steel sheet that has been subjected to the domain refinement treatment by thermal strain, as described above, closure domains having components in the direction perpendicular to the rolling direction and the sheet thickness direction are formed in the thermal strain-introduced portion. Although the closure domains reduce the iron loss of the steel sheet as a whole, when the steel sheet is considered as an iron core material for a transformer, the closure domains promote the magnetic flux transfer, which is the magnetization in the sheet thickness direction, and there is a problem that the transformer iron loss is locally increased. Therefore, in order to investigate the effect of the closure domains on the magnetic flux transfer, a three-phase three-legged wound core was manufactured using a material that has not been subjected to the magnetic domain refinement treatment by thermal strain only in the interlayer magnetic flux transfer portion where the magnetic flux transfer occurs in the transformer core, and an experiment was conducted to investigate the magnetic flux transfer portion's iron loss, the transformer's iron loss, and the transformer noise. The details of the experiment are explained below.

[0015] A three-phase three-legged wound core was manufactured in the wound core shape shown in FIG. 2 by using a grain-oriented electromagnetic steel sheet having a magnetic flux density B8 of 1.92 T at 800 A / m, which was subjected to magnetic domain refining treatment by thermal strain introduction by irradiating a laser on the surface of the steel sheet with a steel strip width of 150 mm. This three-phase three-legged wound core is composed of two adjacent inner cores 10 made using the above-mentioned core material and one outer core 12 surrounding the two inner cores 10. It is also a unicore having a bent portion (bent portion) at each corner. The magnetic domain refining treatment by thermal strain introduction was applied to the entire sheet width (full width) of the steel sheet. In addition, in the region (interlayer magnetic flux crossing portion) 4 where the magnetic flux crossing occurs between the outer core and the inner core between the legs when assembled into a wound core, the magnetic domain refining treatment by thermal strain introduction was not applied to the region forming the non-processed portion 5 described later. As shown in FIG. 2, in the present invention, the interlayer magnetic flux crossing portion 4 is a region between adjacent legs 6 (between adjacent legs 6) when the wound core is viewed from the side. More specifically, the length f of the interlayer magnetic flux crossing portion 4 is defined as the length between adjacent legs 6. The thickness g of the interlayer magnetic flux crossing portion 4 is defined as the same as the sum of the thickness e of the outer core from the adjacent portion 8, which is the point where the inner core 10 and the outer core 12 contact at the center position 7 between the adjacent legs 6 (center position between the legs), and the thickness e' of the inner core from the adjacent portion 8 to the inside. In this specification, the side view refers to the view of the wound core in a direction perpendicular to the winding direction of the grain-oriented electromagnetic steel sheet, i.e., in the width direction of the long grain-oriented electromagnetic steel sheet that constitutes the wound core.

[0016] Then, in the interlayer magnetic flux crossing portion 4, a region (also referred to as "non-treated portion" in this specification) 5 formed of a grain-oriented electrical steel sheet that has not been subjected to a magnetic domain refinement treatment by thermal strain introduction was formed. Specifically, the non-treated portion 5 is a region having a thickness of L in the outward direction from the adjacent portion 8 of the outer core and the inner core, and a region having a thickness of M in the inward direction from the adjacent portion 8 (a region shown by hatching in FIG. 2). The thicknesses L and M of the non-treated portion 5 were adjusted by changing the number of stacks in the thickness direction of the wound core of the core material having a region that has not been subjected to a magnetic domain refinement treatment by thermal strain introduction. Then, three-phase three-legged wound core transformers with different thicknesses L and M of the non-treated portion 5 were manufactured, and three-phase excitation of 50 Hz and 1.7 T was performed, and iron loss and noise measurements were performed on each three-legged wound core transformer. At the same time as measuring the iron loss, as disclosed in Patent Document 5, an infrared camera was used to measure the average temperature rise of the interlayer magnetic flux crossing section 4 on the end face of the iron core during excitation, and it was confirmed that the iron loss had actually increased locally in the interlayer magnetic flux crossing section 4. Then, the local iron loss of the interlayer magnetic flux crossing section 4 was measured.

[0017] The transformer noise was measured during excitation for each of the wound core transformers at a position half the core height d, at a distance of 30 cm from the surface of the wound core transformer, and at eight points surrounding the wound core transformer, and the average value was taken as the transformer noise.

[0018] The transformer iron loss was calculated by winding 50 turns on both the primary and secondary sides of each leg of the three-phase, three-legged wound core, performing three-phase excitation under conditions of a maximum excitation magnetic flux density of 1.7 T and a frequency of 50 Hz, measuring the primary current and secondary voltage with a wattmeter, calculating the no-load loss, and dividing it by the weight of the core. Table 1 shows the values ​​of transformer iron loss, transformer noise, and iron loss in interlayer magnetic flux crossover section 4 (average iron loss in interlayer magnetic flux crossover section 4) for each wound core transformer manufactured by changing the thickness of L and M of non-processing section 5.

[0019] [Table 1]

[0020] It was found that by providing the interlayer magnetic flux crossing portion 4 with the region (non-processed portion) 5 formed of grain-oriented magnetic steel sheet not subjected to magnetic domain refinement treatment by thermal strain introduction, the transformer iron loss, transformer noise, and interlayer magnetic flux crossing portion iron loss were significantly reduced compared to a wound core transformer (No. 1 in Table 1) whose entire core was made of grain-oriented magnetic steel sheet subjected to magnetic domain refinement treatment by thermal strain introduction. In particular, when the thickness of the non-processed portion 5 was 20% or more of the thickness of both the outer core and the inner core, the effect of suppressing the interlayer magnetic flux crossing was further enhanced, and the effect of reducing both the transformer iron loss and the transformer noise was further enhanced. It is presumed that the reduction in the iron loss of the interlayer magnetic flux crossing portion 4 is a result of reflecting the reduction in the amount of magnetic flux crossing at the interlayer magnetic flux crossing portion 4.

[0021] In a three-phase three-legged core, magnetic flux transfer occurs from the inside of the outer core, which has a long magnetic path, to the outside of the inner core, which has a short magnetic path. Grain-oriented electrical steel sheets are materials that increase the magnetic permeability in the rolling direction and are specialized for magnetization only in the rolling direction, so magnetic flux transfer, which is magnetization in the thickness direction, increases iron loss because it is magnetization in the direction of low magnetic permeability in grain-oriented electrical steel sheets. In addition, eddy currents flowing on the rolled surface of grain-oriented electrical steel sheets also lead to an increase in eddy current loss. The closure domains formed by magnetic domain refinement have a component in the thickness direction of grain-oriented electrical steel sheets, so they work to increase the magnetic permeability in the thickness direction and promote interlayer magnetic flux transfer. The amount of magnetic flux flowing from the outer core to the inner core increases if the magnetic permeability in the thickness direction of the magnetic flux transfer part of the outer core is high, and if the magnetic permeability in the thickness direction of the inner core is high, the amount of magnetic flux transfer that the inner core can accept increases. Therefore, by applying a material that has not been subjected to a magnetic domain refinement treatment by introducing thermal strain to the area where magnetic flux transfer occurs in the outer core, the increase in magnetic permeability is suppressed and the magnetic flux that tries to flow into the inner core is suppressed, and by applying a material that has not been subjected to a magnetic domain refinement treatment by introducing thermal strain to the area where magnetic flux transfer occurs in the inner core, the amount of magnetic flux that the inner core can accept is similarly reduced, and it is believed that both of these effects have made it possible to suppress interlayer magnetic flux transfer. Therefore, it is inferred that the reduction in transformer iron loss is due to the reduction in iron loss in the interlayer magnetic flux transfer area by suppressing interlayer magnetic flux transfer, which in turn reduces the transformer iron loss. In addition, when the thickness of the non-treated area is 20% or more of the thickness of each of the inner and outer cores, the transformer iron loss is further improved. This is presumably because the increased thickness of the non-treated areas enhances the effect of suppressing magnetic flux transfer, and the reduction in iron loss due to the suppression of magnetic flux transfer far exceeds the increase in iron loss due to not applying magnetic domain refining treatment by introducing thermal distortion to the iron core material.

[0022] A reduction in transformer noise was observed in all wound core transformers with non-treated sections. In particular, a significant improvement in transformer noise was observed when the thickness of the non-treated section L was 20% or more of the thickness of the outer core, and the thickness of the non-treated section M was 20% or more of the thickness of the inner core. It is generally known that when a wound core transformer is manufactured using a magnetic domain refined material, the transformer noise is larger than that of a wound core transformer manufactured using a core material that has not been subjected to magnetic domain refinement. Therefore, the transformer noise decreases as the non-treated area in the wound core transformer increases. However, the significant reduction in transformer noise when the area is 20% or more of the thickness of each of the outer core and the inner core is presumably due to the suppression of electromagnetic vibration caused by in-plane magnetization due to the reduction in interlayer magnetic flux transfer, in addition to the reasons mentioned above.

[0023] Based on the above experimental facts and assumptions, it was found that in order to reduce the transformer iron loss and transformer noise in a three-phase three-legged wound core transformer, it is essential to reduce the magnetic flux transfer at the interlayer magnetic flux transfer section. Furthermore, it was also found that in order to reduce the magnetic flux transfer at the interlayer magnetic flux transfer section, it is effective to provide a region (non-treated region) formed of grain-oriented electrical steel sheet that has not been subjected to magnetic domain refinement treatment by introducing thermal strain in the region where the interlayer magnetic flux transfer occurs, and to form the other region of grain-oriented electrical steel sheet that has been subjected to magnetic domain refinement treatment by introducing thermal strain. Furthermore, it was found that when the non-treated region is 20% or more of the thickness of each of the inner core and the outer core, the effect of suppressing the interlayer magnetic flux transfer is large, and both the transformer iron loss and the transformer noise are greatly improved, so it is particularly preferable that the non-treated region is 20% or more (20 to 100%) of the thickness of each of the inner core and the outer core.

[0024] Based on the above findings, the present invention has been completed. That is, the present invention has the following features. [1] A three-phase three-legged core consisting of two adjacent inner cores made of grain-oriented electromagnetic steel sheets and one outer core surrounding the two inner cores, The three-phase three-legged wound core is The magnetic material has a region formed of a grain-oriented electrical steel sheet that has been subjected to a magnetic domain refinement treatment by introducing thermal strain, and a region formed of a grain-oriented electrical steel sheet that has not been subjected to a magnetic domain refinement treatment by introducing thermal strain, A three-phase, three-legged wound core, in which, when viewed from the side perpendicular to the winding direction, a region between the legs where magnetic flux transfer occurs between the outer core and the inner core has a region formed of directional electromagnetic steel sheet that has not been subjected to the magnetic domain refining treatment by introducing thermal distortion. [2] The three-phase, three-legged wound core described in [1], in which, when viewed from the side in a direction perpendicular to the winding direction, the region formed by the grain-oriented electrical steel sheet that has not been subjected to the magnetic domain refinement treatment by introducing thermal strain is a region between the legs, and a region that is 20 to 100% of the thickness of the outer core from the adjacent portion of the outer core and the inner core in an outward direction, and a region that is 20 to 100% of the thickness of the inner core in an inward direction from the adjacent portion. [3] A three-phase, three-legged wound core according to [1] or [2], wherein the magnetic domain refining treatment by introducing thermal strain is applied to all or part of the sheet width of the steel sheet. [4] A three-phase three-legged wound core transformer using the three-phase three-legged wound core described in [1] or [2] above. [5] A three-phase three-legged wound core transformer using the three-phase three-legged wound core described in [3] above. Effect of the Invention

[0025] According to the present invention, it is possible to provide a three-phase, three-limbed wound core that uses, as the core material, a grain-oriented electrical steel sheet that has been subjected to a magnetic domain refining process by introducing thermal strain, and that has excellent iron loss reduction and noise reduction effects.

[0026] According to the present invention, it is possible to provide a three-phase three-limbed wound core and a three-phase three-limbed wound core transformer in which transformer iron loss and transformer noise are reduced by forming an area where non-heat-resistant magnetic domain refinement treatment is not applied in the magnetic flux transfer section where the inner core and outer core meet in a three-phase three-limbed wound core that uses oriented electrical steel sheet (non-heat-resistant magnetic domain refinement material) that has been subjected to magnetic domain refinement treatment by introducing thermal distortion. According to the present invention, particularly in a unicore using a non-heat-resistant magnetic domain refinement material, interlayer magnetic flux crossover can be suppressed even when the excitation magnetic flux density is relatively high, thereby achieving excellent iron loss reduction effects and noise reduction effects. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram (side view) that shows a schematic diagram of interlayer magnetic flux transfer occurring from an outer core to an inner core in a three-phase, three-legged wound core. [Diagram 2] FIG. 2 is a side view showing the configuration of a three-phase, three-legged wound core produced in the experiment. [Diagram 3] FIG. 3 is a side view showing the configuration of a three-phase, three-legged wound core produced in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention will be specifically described below.

[0029] A method of manufacturing a three-phase, three-legged wound core according to one embodiment of the present invention will be described with reference to FIG.

[0030] By irradiating the surface of the grain-oriented electromagnetic steel sheet as the material with a laser, plasma jet, electron beam, or the like, thermal distortion is introduced into the steel sheet, which is subjected to a magnetic domain refinement process, thereby reducing the iron loss of the steel sheet. This magnetic domain refinement process by irradiation with a laser or the like is not performed over the entire length of the grain-oriented electromagnetic steel sheet as the core material, but rather, the irradiation is not performed on the area of ​​the steel sheet that will become the joint of the core between the legs (area where magnetic flux transfer occurs) when assembled into a wound core. A wound core is assembled using the core material produced by the above method, and a suitable wound core to which the present invention can be applied is the Unicore, which is an iron core that undergoes little distortion when assembled.

[0031] Unicore is produced by cutting out grain-oriented electromagnetic steel sheets, which are the core material, to the length of each layer of the core, and then folding and winding them. In the core material produced by the above method, no thermal strain is introduced into the parts between the legs when the core is assembled, so a three-phase three-legged wound core having a non-processed part 5 as shown in FIG. 2 can be produced. It is most preferable to introduce this thermal strain into the entire sheet width (steel strip width) of the grain-oriented electromagnetic steel sheets, which are the material, from the viewpoint of reducing iron loss, but even if the core material has thermal strain introduced into only a part of the sheet width (steel strip width), the effect of the present invention can be exhibited and an iron core with reduced iron loss can be provided. In addition, the present invention is preferably applied to Unicore, but is not limited to Unicore and can be suitably applied to other iron cores. For example, it can be suitably applied to an iron core called a trunco, which is wound with a steel strip.

[0032] Next, the reasons for limiting each component in the present invention will be described.

[0033] It was revealed that in the iron loss of a three-phase, three-limbed wound core transformer, a flow of magnetic flux occurs that tries to return to the excited leg from the non-excited leg, resulting in magnetic flux transfer from the outer core to the inner core, and that magnetic flux transfer is one of the factors that increases the transformer iron loss.

[0034] Therefore, since magnetic flux transfer is a phenomenon that occurs through the contact portion between the outer core and the inner core, and magnetization occurs in the thickness direction, a region (non-treated portion) formed of directional electromagnetic steel sheet that has not been subjected to magnetic domain refinement treatment by thermal strain introduction is provided in the region where magnetic flux transfer occurs, in order to suppress magnetic flux transfer, and a lower iron loss is achieved compared to a transformer core made of directional electromagnetic steel sheet that has been subjected to magnetic domain refinement treatment by thermal strain introduction. Note that if strain relief annealing is performed on the core after formation, the magnetic domain refinement effect due to thermal strain introduction is removed from the entire core, so the present invention is applicable to transformers and cores that do not undergo strain relief annealing after formation. Based on the above-mentioned experimental results, the thickness of the non-treated portion at this time is preferably 20% or more of the thickness of the outer core and the inner core, respectively, in order to obtain a particularly excellent iron loss reduction effect. By performing magnetic domain refinement treatment by thermal strain introduction, magnetic domains called closure domains that are oriented in the thickness direction of the steel sheet are formed directly under the irradiation portion of the laser or the like. Since the closure domains are oriented in the sheet thickness direction, the presence of these domains in the flux crossing portion promotes flux crossing, leading to an increase in transformer iron loss. In the present invention, the non-processed portion is provided in the core to locally remove the closure domains, thereby suppressing flux crossing, so the method of domain refinement introduced in places other than the flux crossing portion is not particularly limited as long as it is a method that introduces closure domains by thermal distortion.

[0035] Furthermore, although the present specification describes the characteristics of a three-phase, three-legged wound core of a specific shape, the present invention is suitable for all other three-phase wound cores in which magnetic flux transfer occurs in three-phase wound core transformers, and the shape and dimensions are not limited.

[0036] The core material used in the present invention is not particularly limited, and may be, for example, a heat-resistant material with thermal domain refinement treatment. In addition, any grain-oriented electrical steel sheet may be used as the core material, regardless of the degree of orientation of the Goss grains in the base material.

[0037] By using the three-phase three-legged wound core of the present invention to form a three-phase three-legged wound core transformer, the transformer's iron loss and transformer noise can be reduced. The shape and characteristics of this transformer are not limited, and the present invention can be applied to any wound core transformer. EXAMPLES

[0038] [Example 1] Grain-oriented electrical steel sheets with different magnetic flux densities B8 at 800 A / m shown in Table 2 were used as materials, and were subjected to laser irradiation (magnetic domain refinement treatment by introducing thermal distortion) to obtain iron core materials. Then, using the iron core materials, unicores with the iron core shape shown in FIG. 3 were produced, and 50-turn winding coils were attached to both the primary and secondary sides to produce three-phase three-leg wound core transformers. Excitation was performed under conditions of an excitation magnetic flux density of 1.7 T and a frequency of 50 Hz, and the transformer iron loss and transformer noise were measured by the above-mentioned method. The laser irradiation was performed over the entire width of the steel sheet. In addition, the iron core materials were not irradiated with laser in areas corresponding to areas (interlayer magnetic flux crossing areas) where magnetic flux crossing occurs between the legs and the inner core when assembled into a wound core, and non-treated areas were provided in the areas where the magnetic flux crossing occurs. Furthermore, wound cores were produced in which the thickness of the untreated areas, L and M, were changed by changing the number of layers of core material having areas that were not irradiated with laser in the thickness direction of the wound core. However, for some wound cores, the entire wound core did not use core material having areas that had not been subjected to magnetic domain refinement treatment by introducing thermal strain, that is, the wound core was composed only of core material that had been subjected to magnetic domain refinement treatment by introducing thermal strain, and no untreated areas were provided in the wound core (wound cores in Table 2 where the thickness of L and the thickness of M are both 0%).

[0039] The measurement results of the transformer iron loss and transformer noise are shown in Table 2. In the compatible example (invention example) of the present invention, by providing a non-processed portion in the interlayer magnetic flux crossover portion, it was found that both the transformer iron loss and the transformer noise were better than in a transformer wound core that did not have a non-processed portion, and that the transformer exhibited excellent transformer characteristics.

[0040] [Table 2] [Explanation of symbols]

[0041] 1, 10 Inner core 2, 12 Outer core 3 Flux transfer between layers 4 Interlayer magnetic flux transfer section 5 Non-processing section 6 legs 7 Center position between legs 8 Adjacent parts

Claims

1. A three-phase three-legged core including two adjacent inner cores and one outer core surrounding the two inner cores, the inner cores being made of grain-oriented electromagnetic steel sheets, The three-phase three-legged wound core is The magnetic material has a region formed of a grain-oriented electrical steel sheet that has been subjected to a magnetic domain refinement treatment by introducing thermal strain, and a region formed of a grain-oriented electrical steel sheet that has not been subjected to a magnetic domain refinement treatment by introducing thermal strain, a region between legs where magnetic flux transfer occurs between the outer core and the inner core when viewed from the side perpendicular to the winding direction, the region being formed of a grain-oriented electrical steel sheet that has not been subjected to the magnetic domain refining treatment by introducing thermal strain, A three-phase, three-legged wound core, wherein areas other than an area formed from grain-oriented electromagnetic steel sheet that has not been subjected to the magnetic domain refinement treatment by introducing thermal strain are formed from grain-oriented electromagnetic steel sheet that has been subjected to the magnetic domain refinement treatment by introducing thermal strain.

2. 2. The three-phase, three-legged wound core according to claim 1, wherein, when viewed from the side in a direction perpendicular to the winding direction, a region formed by directional electrical steel sheet that has not been subjected to the magnetic domain refinement treatment by introducing thermal strain is a region between the legs, and a region that is 20 to 100% of the thickness of the outer core from an adjacent portion between the outer core and the inner core in an outward direction, and a region that is 20 to 100% of the thickness of the inner core in an inward direction from the adjacent portion.

3. 3. A three-phase, three-legged wound core according to claim 1, wherein the magnetic domain refining treatment by introducing thermal strain is applied to the whole or a part of the sheet width of the steel sheet.

4. A three-phase, three-legged wound core transformer using the three-phase, three-legged wound core according to claim 1 or 2.

5. A three-phase, three-legged wound core transformer using the three-phase, three-legged wound core according to claim 3.

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