Transformer core and its manufacturing method

Abstract

The present invention relates to a transformer core having low no-load loss and no-load noise, and a manufacturing method thereof. The transformer core includes a pair of yokes formed by stacking a plurality of electrical steel sheets parallel to each other, and legs formed by stacking a plurality of electrical steel sheets and connecting the pair of yokes, wherein at a joint where the yoke and the leg are connected, an end of an electrical steel sheet constituting the yoke and an end of an electrical steel sheet constituting the leg have corresponding inclined surfaces, and shapes of the inclined surfaces are matched, and one electrical steel sheet constituting the yoke may be stacked on another electrical steel sheet constituting the yoke in a step-lap manner, and one electrical steel sheet constituting the leg may be stacked on the other electrical steel sheet constituting the leg in a step-lap manner.

Description

[Technical field]

[0001] The present invention relates to a transformer core having low no-load loss and low no-load noise, and a method for manufacturing the same. [Background technology]

[0002] A transformer is a device that changes AC voltage and current values ​​using electromagnetic induction, and is an essential component of electronic products. A transformer is manufactured by winding a coil, which is an electrical conductor, around a magnetic core. Electrical steel sheets with low magnetic loss are used as the core, and such cores are divided into stacked cores and wound cores.

[0003] The main characteristics of a transformer are loss and noise. In particular, no-load loss and no-load noise, which are power losses that occur every moment regardless of whether the transformer is in use, are regulated by a system. As a result, various methods for reducing no-load loss and no-load noise have been proposed. For example, Patent Document 1 discloses an example of a step lap core. This technology increases the structural rigidity of the core by laminating electrical steel sheets one by one to form a joint of the core, by laminating them so that a W-shaped separation is generated along the thickness direction of the core.

[0004] However, at the joints of the iron core, the cut surfaces of each electrical steel sheet extend perpendicular to the lamination surfaces of the electrical steel sheets to form separation parts that form steps perpendicular to adjacent electrical steel sheets, and holes that pass through the iron core are required to fix the assembled state of the iron core.

[0005] Since the air medium exists in the gaps and holes, and the magnetic resistance is very large, a bottleneck phenomenon occurs in which the magnetic field is concentrated in the iron core area where there are no gaps or holes. This causes a high magnetic flux density locally, and the iron loss increases rapidly due to the characteristics of the electrical steel sheet. In addition, although the holes have a sufficient tolerance for easy assembly, it causes spacing and uneven alignment at the joint.

[0006] To solve this problem, the applicant has proposed a technique of applying an insulating adhesive to the top and bottom surfaces (lamination surfaces) of each electrical steel sheet that constitutes a step-lap core and laminating them in Patent Document 2. Although this technique can reduce no-load loss, it causes a phenomenon in which no-load noise rapidly deteriorates. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent No. 10-1302830 [Patent Document 2] Korean Patent No. 10-2109279 Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a transformer core with reduced no-load loss and no-load noise, and a manufacturing method thereof. [Means for solving the problem]

[0009] The transformer core according to the present invention includes a pair of yokes formed by stacking a plurality of electrical steel plates parallel to each other, and legs formed by stacking a plurality of electrical steel plates and connecting the pair of yokes, wherein at a joint where the yoke and the leg are connected, ends of the electrical steel plates constituting the yoke and ends of the electrical steel plates constituting the leg have corresponding inclined surfaces, and shapes of the inclined surfaces may be matched, and one electrical steel plate constituting the yoke may be stacked on another electrical steel plate constituting the yoke in a step-lap manner, and one electrical steel plate constituting the leg may be stacked on the other electrical steel plate constituting the leg in a step-lap manner.

[0010] A method for manufacturing a transformer core according to the present invention includes the steps of preparing a plurality of electrical steel sheets, processing the electrical steel sheets into a shape of a yoke and a leg, partially applying an insulating adhesive to the electrical steel sheets and laminating them to form an iron core lamination, and heat treating the iron core lamination while applying pressure, wherein the processing step includes a step of obliquely cutting or machining ends of the electrical steel sheets to form an inclined surface, and the forming step may include laminating one electrical steel sheet constituting the yoke to another electrical steel sheet constituting the yoke in a step-lap manner, and laminating one electrical steel sheet constituting the leg to the other electrical steel sheet constituting the leg in a step-lap manner. Effect of the Invention

[0011] According to the present invention, the no-load loss of the transformer is reduced, the no-load noise is reduced, and the performance of the transformer is improved. [Brief description of the drawings]

[0012] [Figure 1] 1 is a perspective view showing a transformer core according to an embodiment of the present invention; [Diagram 2] 2A and 2B are views of a joint of a step-wrap core as viewed from the direction A in FIG. 1, where (a) shows a conventional core, and (b) and (c) show the lamination state of electrical steel sheets in the core of the present invention. [Diagram 3] FIG. 4 is a diagram showing adhesive application areas in a transformer core according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The primary coil of the transformer is connected to an input circuit whose voltage is to be changed, and the secondary coil is connected to an output circuit whose changed voltage is used, where magnetic energy is used to connect the electrical energies of the primary and secondary coils together.

[0014] Depending on whether or not a power load connected to the secondary coil is used, it can be divided into no-load characteristics and load characteristics. The no-load characteristics are when there is no load, and occur constantly regardless of whether the transformer is operating or not. The power loss consumed in the iron core is called no-load loss, and the noise generated at this time is called no-load noise.

[0015] In contrast, the load characteristic occurs when power is consumed by a load connected to the secondary coil. The load loss is determined by the Joule loss consumed in the coil, and the load noise occurs due to the electromagnetic force between the coil and the iron core.

[0016] In order to reduce the no-load loss, an electrical steel sheet with low iron loss can be used as the iron core. Since the thicker the electrical steel sheet, the greater the iron loss, it is preferable to select an electrical steel sheet with as small a thickness as possible.

[0017] No-load noise occurs when a magnetic field flows through an electrical steel plate, causing a series of vibrations (called magnetic deformation (magnetostriction)) in which the plate contracts and expands repeatedly. These vibrations cause vibrations and noise in the transformer.

[0018] More specifically, when a magnetic field is applied from the outside of an electrical steel sheet, a series of contractions and expansions occur in the magnetic domains of minute regions within the base iron of the electrical steel sheet, but the cycle is not constant, causing each electrical steel sheet in the laminated iron core to vibrate uniquely.

[0019] In reality, each sheet has a different vibration pattern, so the vibration becomes very complex. This causes the period of the vibration to become shorter rapidly, which means that the vibration frequency increases rapidly. In addition, harmonic vibrations occur in a chain reaction, which appears as micro-vibrations.

[0020] Ultimately, as the vibration frequency increases and more harmonics are generated, the noise becomes amplified and sounds very loud.

[0021] As mentioned above, when the technique proposed by the applicant in which an insulating adhesive is applied to the entire lamination surface of each electrical steel sheet that constitutes a step-lap core and then laminated and joined, is applied, the no-load loss can be reduced, but the no-load noise rapidly deteriorates.

[0022] If adhesive is applied to the entire laminated surface, the flatness of the core cannot be maintained consistently, resulting in warping and bending, and the laminated cores will not be aligned correctly, resulting in frequent floating.

[0023] The reason why warping occurs when applying adhesive to the entire lamination surface is due to the variation in thickness of the electrical steel sheet. Although the rolling technology for precisely controlling the thickness of electrical steel sheets is being improved, the variation in thin thickness cannot be completely eliminated. As a result, when the thickness of electrical steel sheets varies within about 3 to 6%, and adhesive is applied to the entire lamination surface and laminated and bonded, warping will inevitably occur.

[0024] This makes it difficult to assemble the joints of the step-lap core smoothly, which is a major obstacle in the manufacture of transformers and significantly reduces the manufacturing speed, i.e., productivity. Furthermore, the fastening state of the joints is not uniform, which causes micro-vibrations to become intense and noise to rapidly increase.

[0025] Therefore, the applicant has investigated and improved the cause of the sudden increase in noise in the transformer core, thereby studying a method for reducing no-load noise as well as reducing no-load loss, and has proposed the present invention.

[0026] The present invention will now be described in detail with reference to exemplary drawings. When referring to the components in each drawing, it should be noted that the same components are designated by the same reference numerals as far as possible even if they are shown in different drawings.

[0027] FIG. 1 is a perspective view showing a transformer core according to an embodiment of the present invention.

[0028] A transformer core according to one embodiment of the present invention may include an upper yoke 11, a lower yoke 12, and a plurality of legs 2 disposed between the upper yoke and the lower yoke and connecting the upper yoke and the lower yoke.

[0029] In this specification, the upper yoke 11 and the lower yoke 12 are selectively referred to as a yoke 1 .

[0030] As a non-limiting example, the upper yoke 11 and / or the lower yoke 12 may be integrally formed with one of the legs 2 .

[0031] The yoke 1 and the leg 2 are each formed by laminating a plurality of electrical steel sheets 3. For this purpose, first, two or more electrical steel sheets are prepared, and each electrical steel sheet is processed into the cross-sectional shape of the yoke or leg of the iron core.

[0032] For example, the electrical steel sheet 3 may be slit to the width of the transformer core, and then the electrical steel sheet slit to the appropriate width may be cut and punched to fit the shape of the joint 4 of the core, to form the yoke 1 and the leg 2.

[0033] This allows the electrical steel sheet to be formed to have the same cross-sectional shape as the upper yoke 11, the lower yoke 12, and the multiple legs 2.

[0034] The electrical steel sheet 3 used in the transformer core of the present invention is not particularly limited, and a grain-oriented electrical steel sheet or a non-oriented electrical steel sheet having a thickness of about 0.05 to 1.0 mm may be adopted.

[0035] If the thickness of the electrical steel sheet 3 is less than 0.15 mm, the iron loss decreases but the shape stability decreases. On the other hand, if the thickness of the electrical steel sheet 3 is more than 1.0 mm, the iron loss increases. Considering these points, the thickness of the electrical steel sheet may be limited to within about 0.05 to 1.0 mm.

[0036] FIG. 2 is a view of the joint of the step-wrap core as viewed from the direction A in FIG. 1, where (a) shows a conventional core, and (b) and (c) show the lamination state of the electrical steel sheets in the core of the present invention.

[0037] FIG. 2(a) shows a conventional core joint, in which the ends of each electrical steel sheet 3 are cut so that cut surface 32 extends perpendicular to lamination surface 31 of the electrical steel sheets.

[0038] A magnetic field has the property of flowing to the location where magnetic resistance is the least. Magnetic resistance is inversely proportional to magnetic permeability, which is an index showing how smoothly a magnetic field flows. If the magnetic permeability of air is assumed to be 1, the magnetic permeability of electrical steel sheets is several hundred to tens of thousands times that of air. Therefore, if something comes off the electrical steel sheets, the magnetic resistance will become extremely high.

[0039] The gap between the stacked electrical steel sheets in the thickness direction of the electrical steel sheets 3, i.e., the air gap (G) where the electrical steel sheets face each other laterally is much wider than the air layer (L). Therefore, the magnetic resistance is larger in the air gap than in the air layer.

[0040] As a result, when the magnetic field flowing within a single electrical steel sheet 3 reaches the gap G, the magnetic field is dispersed and moves to the electrical steel sheets stacked above or below the electrical steel sheet through the air layer L, which has less magnetic resistance than the gap.

[0041] Therefore, the magnetic field is concentrated in the contact area Lct shown in Fig. 2(a), and the magnetic flux density increases rapidly. In addition, due to the bottleneck phenomenon of the magnetic field, a complex magnetic field is generated in which various harmonics are contained in a sine wave. The iron loss of the electrical steel sheet 3 increases as the magnetic flux density increases, and when harmonics are contained, the increase in iron loss increases rapidly.

[0042] Here, the contact area Lct can be defined as the area where the end of the electrical steel sheet of the yoke and the end of the electrical steel sheet of the leg contact and overlap in the path through which the magnetic field flows.

[0043] To solve this problem, the length of the contact region Lct can be extended in FIG. 2(a). However, in this case, the exposed portion from the joint 4 of the core to the outer casing of the core increases by the length of the non-overlapping region Lov.

[0044] Here, the non-overlapping region Lov may be defined as a region where the position of one end of either the yoke electrical steel sheet or the leg electrical steel sheet changes based on the gap G. The non-overlapping region may include a gap.

[0045] The increase in exposed area generates a leakage magnetic field where the magnetic field flows outside the core, which is another factor that increases iron loss, and also results in increased noise due to the vibration of the exposed electrical steel sheets. For this reason, the method of increasing the length of the non-overlapping area Lov has limitations in its applicability, but for example, in stacked cores for transformers, the length of the non-overlapping area Lov is usually controlled to within 2 to 6 mm.

[0046] Therefore, in a transformer core according to one embodiment of the present invention, when the electrical steel sheets 3 are cut as shown in (b) and (c) of Figure 2, the ends of each electrical steel sheet corresponding to the joints 4 of the core are cut or cut at a predetermined angle to the lamination surfaces 31 of the electrical steel sheets, unlike the conventional method, so that the cross section has an inclined surface 33.

[0047] The inclined surface 33 may be formed, for example, by grinding ends of the upper yoke 11, the lower yoke 12, and the legs 2 that correspond to the joint portion 4 of the iron core. The inclined surfaces formed on the upper yoke and the legs, or the lower yoke and the legs, may be formed symmetrically to each other and arranged to correspond to each other, so that their shapes may match.

[0048] In this way, by forming the ends of the electrical steel sheets 3 at an incline, the gap G is minimized, and even if the same non-overlapping region Lov as in the past is applied, the magnetic field distribution inside the iron core flows more smoothly, reducing iron loss and noise.

[0049] Next, an insulating adhesive 5 is applied to the inclined surface 33 or the periphery of the inclined surface of the cut electrical steel sheet 3. When applying the adhesive, it is preferable to measure out a fixed amount and apply it evenly so that the adhesive is sufficiently applied to the inclined surface or the periphery thereof.

[0050] Any adhesive capable of bonding electrical steel sheets together can be used as the adhesive 5. Preferably, an adhesive capable of being used at high temperatures and having excellent insulating properties, such as an epoxy adhesive or a ceramic adhesive, can be used.

[0051] In a transformer core according to one embodiment of the present invention, there are no restrictions on the application method, but by limiting the application area of ​​the bonding agent 5 to the periphery of the joint 4 of the core, i.e., the inclined surface 33 of each electrical steel sheet 3 or its periphery, it is possible to avoid the occurrence of the above-mentioned warping.

[0052] For example, the bonding agent 5 can be applied not only to the inclined surface 33 but also to an area on the electrical steel sheet 3 that forms a right triangle with the diagonal of the joint 4 as its hypotenuse. Such an example is shown in Fig. 3(a), and Fig. 3(b) shows an example in which the bonding agent is applied only to the inclined surface.

[0053] In this way, in the transformer core according to one embodiment of the present invention, when applying the adhesive 5, instead of applying it to the entire lamination surfaces of the electrical steel sheets as in the conventional case, the adhesive is applied partially around the joints 4 of the core, as shown in Figures 3(a) and (b), so that the core can be fixed in place so that the electrical steel sheets 3 do not warp.

[0054] This allows smooth assembly at the joint 4 of the step-wrap core, and has the advantages of significantly improving the manufacturing speed, i.e., productivity, and reducing noise.

[0055] The adhesive 5 is about 0.2 to 5.0 g / mm 2 The amount applied is within 0.2g / mm 2 If the amount of adhesive is less than 5.0g / mm, the adhesive strength will be weak and the core will not be properly fixed. 2If it is too large, the space factor of the iron core will decrease, which will cause increased iron loss and noise.

[0056] Here, the space factor means the ratio of the effective area to a certain spatial area, and in the present invention, it means the effective area where a magnetic field is generated to the total area of ​​the electrical steel sheet constituting the iron core. When applying an insulating material, the space factor is reduced by the space occupied by the insulating material.

[0057] Next, the electrical steel sheets 3 may be laminated in a step-lap manner. Referring again to Fig. 2, one electrical steel sheet 3 constituting the yoke 1 may be laminated to another electrical steel sheet constituting the yoke in a step-lap manner, and one electrical steel sheet 3 constituting the leg 2 may be laminated to another electrical steel sheet constituting the leg in a step-lap manner.

[0058] The ends of the electrical steel sheets 3 that are laminated to form the yoke 1 may have, for example, an offset shape that repeats in a stepped manner, or a shape in which the inclined surfaces 33 of the ends are arranged in a shifted manner.

[0059] Similarly, the ends of the electrical steel sheets 3 that are stacked to form the leg 2 may have an offset shape that repeats in a stepped manner, or the inclined surfaces 33 of the ends may be arranged in a shifted manner.

[0060] A step-lap core in which multiple electrical steel sheets are laminated in six steps is shown in Figure 2. This type of step-lap method is more efficient and has less loss than other lamination methods applied to transformer cores (e.g., miter lamination).

[0061] The optimum number of steps in a step-wrap core may vary depending on the size and shape of the core, but the number of steps suitable for a transformer stack core may be 3 to 10 steps, or in some cases 4 to 7 steps.

[0062] 2(b) and 2(c), when the electrical steel sheets 3 are cut obliquely with inclined surfaces 33 provided in the thickness direction and laminated by the step lap method, it is preferable to laminate in a direction in which the contact area Lct expands as shown in Fig. 2(b). To achieve this, the electrical steel sheets should be laminated so that the length of the contact area Lct is at least longer than the length of the inclined surfaces 33 projected onto the lamination surface 31.

[0063] When the electrical steel sheets are laminated in a direction in which the contact area Lct shrinks, as in (c) of Figure 2, that is, when the electrical steel sheets are laminated so that the length of the contact area Lct is shorter than the length of the inclined surface 33 projected onto the lamination surface 31, iron loss and noise increase more than in the lamination in (b).

[0064] In this case, in the stacks of (b) and (c) of FIG. 2, the inclination angles of the inclined surfaces are the same, and the lengths of the non-overlapping regions Lov are also the same.

[0065] During lamination, the electrical steel sheets 3 cut into yokes 1 and the electrical steel sheets 3 cut into legs 2 are arranged according to the final shape of the iron core, and then joined and laminated to obtain an iron core laminate.

[0066] However, this is not necessarily limited to this. For example, the electrical steel sheets 3 cut to form the yoke 1 may be stacked to obtain a yoke laminate, the electrical steel sheets 3 cut to form the legs 2 may be stacked to obtain a leg laminate, and the yoke laminate and the leg laminate may then be assembled and joined to obtain an iron core laminate.

[0067] The transformer core according to an embodiment of the present invention can omit holes that penetrate the core to fix the assembled state of the core and a hole punching process for forming such holes. Since the electrical steel sheet 3 is bonded with the insulating adhesive 5 without forming holes in it, the transformer core according to an embodiment of the present invention can prevent the magnetic properties of the electrical steel sheet from being damaged by holes.

[0068] However, forming holes has the advantage that lamination of electrical steel sheets can be made easier, and therefore the formation of holes is not excluded from the scope of the present invention.

[0069] Then, in order to impart adhesive strength to the iron core laminate, both sides of the iron core laminate in the thickness direction are clamped with clamps and then a pressure of 0.01 to 0.8 MPa is applied. If the pressure is less than 0.01 MPa, the bonding strength of the iron core is weak and it may separate when the transformer is operated for a long time. On the other hand, if the pressure exceeds 0.8 MPa, noise increases due to the compressive stress of the electrical steel sheet.

[0070] Furthermore, the temperature of the iron core laminate is kept within the range of 70 to 180° C. for at least 20 minutes to harden the bonding agent 5. Such heat treatment can be performed using any heater such as an induction heater or an oven.

[0071] For example, when a thermosetting resin adhesive is used as a bonding agent, the adhesive contains epoxy and urethane components, so it will not harden below 70°C, but its adhesive strength will weaken above 180°C.

[0072] The present invention will now be described in more detail with reference to examples.

[0073] Transformer cores having the same weight were manufactured by the conventional manufacturing method and the manufacturing method of the present invention, and then the no-load loss and no-load noise were compared.

[0074] For example, Table 1 compares the characteristics of transformer cores manufactured using different cutting and lamination methods to configure the core joints, as shown in Figure 2. However, all cores had through holes drilled through them, and bolts were fastened into the holes to secure the cores in place.

[0075] In Comparative Example 1, the cut surface of each electrical steel sheet was formed so as to extend perpendicularly to the lamination surface of the electrical steel sheets, and the electrical steel sheets were laminated by the step lap method as in the conventional method.

[0076] In Example 1 and Comparative Example 2, the ends of the electrical steel sheets were inclined in accordance with the present invention to form inclined surfaces, and the sheets were laminated using the step lap method similar to that of Comparative Example 1, and bolts were fastened into the holes to fix the iron core.

[0077] Example 1 of the invention was configured as shown in (b) of Fig. 2, and Comparative Example 2 was configured as shown in (c) of Fig. 2. That is, Example 1 of the invention was laminated in a direction in which the contact area Lct expanded, and Comparative Example 2 was laminated in a direction in which the contact area Lct contracted.

[0078] The no-load noise value was expressed in decibels (dBA), which is a log-converted value reflecting the audible response, based on the no-load loss of Example 1, ie, Example 1 being 100%.

[0079] [Table 1]

[0080] The reason why the characteristics of Example 1 are superior is that the inclined surface alleviates the bottleneck phenomenon of the magnetic field, thereby reducing the generation of harmonics.

[0081] Next, Table 2 compares the characteristics of transformer cores manufactured by cutting, stacking, and fixing with adhesive in the same manner as in Example 1, but varying the area where the adhesive was applied and the clamp pressure.

[0082] In Comparative Example 3, the adhesive was applied to the entire laminated surface of the electrical steel sheets, and heat treatment was performed with a clamp pressurized to 5 MPa to minimize deformation of the iron core. When the pressure was reduced, springback occurred, the fastening state deteriorated, and it was difficult to fix with a low pressure. For heat treatment to harden the adhesive, the iron core was kept at a temperature of 160°C for 4 hours.

[0083] In Example 2 of the invention, as shown in (a) of Figure 3, an adhesive was applied to the inclined surface and the surrounding area forming a right-angled triangle, and the adhesive was hardened by maintaining the temperature of the iron core at 160°C for one hour while keeping the clamp pressurized at 0.5 MPa.

[0084] In Example 3 and Comparative Example 4, as shown in Fig. 3(b), the adhesive was applied to the inclined surface, and the adhesive was hardened by maintaining the temperature of the iron core at 160°C for one hour while applying pressure with a clamp. However, the pressure applied in Example 3 was 0.8 MPa, while in Comparative Example 4 it was increased to 0.9 MPa.

[0085] [Table 2]

[0086] Comparing the characteristics of the transformer cores produced by the conventional manufacturing method and the manufacturing method of the present invention, in Comparative Example 3, by eliminating the holes penetrating the core and applying an adhesive to the entire lamination surface to bond them, the no-load loss was reduced by 3.7% compared to Invention Example 1, but the no-load noise was significantly worse than Invention Example 1.

[0087] As in Examples 2 and 3, the noise was clearly reduced as the bonding area, i.e., the area where the bonding agent was applied, was reduced.

[0088] However, it was confirmed that when the applied pressure was increased beyond 0.8 MPa as in Comparative Example 4, the noise increased due to the compressive stress of the electrical steel sheet.

[0089] As described above, according to the present invention, holes penetrating the iron core can be eliminated, the gap between the electrical steel sheets can be minimized, and the magnetic field can flow smoothly at the joints of the iron core.

[0090] Therefore, the no-load loss of the transformer is lowered, the no-load noise is reduced, and the performance of the transformer is improved.

[0091] The above description is merely an illustrative example of the technical concept of the present invention, and various modifications and variations can be made by a person having ordinary knowledge in the technical field to which the present invention pertains without departing from the essential characteristics of the present invention.

[0092] Therefore, the embodiments disclosed in the specification and drawings are for illustrative purposes only and are not intended to limit the technical idea of ​​the present invention, and the scope of the technical idea of ​​the present invention is not limited by such embodiments. The scope of protection of the present invention should be interpreted according to the following claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the present invention. [Explanation of symbols]

[0093] 1: York 2: Reg 3: Electrical steel sheet 4:Joining part 5: Bonding agent 11: Upper yoke 12: Lower yoke 31: Laminated surface 32: Cut surface 33: Inclined surface

Claims

1. A pair of yokes formed by laminating a plurality of electrical steel plates and parallel to each other; A leg is formed by laminating a plurality of electrical steel plates and connects the pair of yokes. Including, at a joint portion where the yoke and the leg are connected, an end portion of the electrical steel sheet constituting the yoke and an end portion of the electrical steel sheet constituting the leg have inclined surfaces having corresponding shapes and inclined with respect to a lamination direction of the electrical steel sheets, a transformer core, wherein one electrical steel sheet constituting the yoke is laminated to another electrical steel sheet constituting the yoke in a step lap manner, and one electrical steel sheet constituting the leg is laminated to another electrical steel sheet constituting the leg in a step lap manner.

2. The transformer core according to claim 1 , wherein an insulating adhesive is applied to the inclined surfaces or peripheries of the inclined surfaces of the electrical steel sheets at the joints.

3. The transformer core according to claim 2 , wherein a periphery of the inclined surface includes an area on the electrical steel sheet that forms a right triangle with a diagonal line of the joint portion as a hypotenuse.

4. 2. The transformer core according to claim 1, wherein the electrical steel sheets are laminated such that a length of a contact area where the electrical steel sheets of the yoke and the electrical steel sheets of the legs come into contact and overlap on a surface where the electrical steel sheets are laminated is longer than at least a length of the inclined surface projected from a lamination direction of the electrical steel sheets onto the surface where the electrical steel sheets are laminated.

5. preparing a plurality of electrical steel sheets and processing the electrical steel sheets into a shape of a yoke and a leg; forming an iron core laminate by partially applying an insulating adhesive to the electrical steel sheets and laminating the applied insulating adhesive; heat treating the iron core laminations under pressure; Including, The processing step includes a step of obliquely cutting or cutting an end of the electrical steel sheet to form an inclined surface inclined with respect to a lamination direction of the electrical steel sheet, In the step of forming the core laminations, one electrical steel sheet constituting the yoke is laminated to another electrical steel sheet constituting the yoke in a step-lap manner, and one electrical steel sheet constituting the leg is laminated to another electrical steel sheet constituting the leg in a step-lap manner.

6. The method for manufacturing a transformer core according to claim 5 , wherein the insulating adhesive is applied to an inclined surface or a periphery of the inclined surface of the electrical steel sheet.

7. The insulating adhesive has a density of 0.2 to 5.0 g / mm ２ The method for manufacturing a transformer core according to claim 6, wherein the coating is applied in an amount ranging from 100 to 1500 μg / g.

8. 6. The method for manufacturing a transformer core according to claim 5, wherein the electrical steel sheets are laminated such that a length of a contact area where the electrical steel sheets of the yoke and the electrical steel sheets of the legs come into contact and overlap on a surface where the electrical steel sheets are laminated is longer than at least a length of the inclined surface projected from a lamination direction of the electrical steel sheets onto the surface where the electrical steel sheets are laminated.

9. 6. The method of claim 5, wherein the forming of the core laminations comprises arranging, joining, and laminating the electrical steel sheets processed into the yoke shape and the electrical steel sheets processed into the leg shape according to a shape of the core.

10. The step of forming the core laminations comprises: laminating the electrical steel sheets processed into the shape of the yoke to obtain a yoke laminate; laminating the electrical steel sheets processed into the shape of the leg to obtain a leg stack; assembling and bonding the yoke laminate and the leg laminate; The method of claim 5 , further comprising:

11. The method for manufacturing a transformer core according to claim 5, wherein the pressure is in the range of 0.01 to 0.8 MPa.

12. The method for manufacturing a transformer core according to claim 5, wherein the heat treatment is performed so that the temperature of the core laminate is kept within a range of 70 to 180° C. for a minimum of 20 minutes or more.

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