core

Abstract

The present invention provides a magnetic core for electromagnetic devices that minimizes the distribution of magnetic flux density, thereby reducing core losses and the required core mass. [Solution] The magnetic core 200 comprises three arc-shaped rims 202. Each rim has a first end and a second end and is arranged around a central axis. The first ends of the rims are connected to each other at a first position along the central axis, and the second ends of the rims are connected to each other at a second position along the central axis. Each rim comprises a plurality of bent electromagnetic steel strips.

Description

Technical Field

[0001]

[0001] The following disclosure relates to cores for electromagnetic devices.

Background Art

[0002]

[0002] Cores are utilized across various electromagnetic devices such as transformers, motors, generators, and inductors. Transformers have two types of structures: core type and shell type. The important difference between these types lies in the arrangement of the core and windings. In the case of a core-type transformer, the windings surround the core, while in a shell-type transformer, the core surrounds the windings.

[0003]

[0003] In a core-type single-phase transformer, the core is typically in the form of a closed square or rectangular ring made of electromagnetic steel laminations, and the primary and secondary windings surround the core at the rims on both sides of the ring. However, transformers with primary and secondary coils on separate rims generally exhibit large magnetic flux leakage, resulting in unsatisfactory voltage regulation and overall unsatisfactory performance.

[0004]

[0004] A toroidal transformer is a core-type single-phase transformer composed of a doughnut-shaped core. The primary and secondary windings of a toroidal transformer are typically wound across the entire surface of the core separated by an insulating material. Some of the advantages of toroidal transformers include higher efficiency, inherent shielding from electromagnetic interference, minimal signal distortion, a more compact structure, low mechanical humming, low heat, and small off-load losses.

Summary of the Invention

Problems to be Solved by the Invention

[0005]

[0005] Three-phase power is often used in power distribution systems. Three-phase power conversion requires either three single-phase or three-phase transformers in a three-phase bank. An exemplary magnetic core 100 for a three-phase transformer is described with reference to Figure 1. The magnetic core 100 includes three substantially rectangular rings 102, each rectangular ring 102 having a first rim 104 and a second rim 106. Primary windings and secondary windings (not shown) are wound around each of the first rims 104. The three rectangular rings 102 are interconnected along the second rims 106 and are spaced 120 degrees apart. Each of the rectangular rings 102 comprises an electromagnetic steel ring 108 stacked on top of each other. Generally, each electromagnetic steel ring 108 is cut from a sheet of electromagnetic steel, yielding waste material, i.e., the central portion of each electromagnetic steel ring 108.

[0006]

[0006] Furthermore, in terms of performance, transformers incorporating cores such as the magnetic core 100 suffer power losses due to harmonic distortion and noise in the power grid, particularly low-voltage distribution networks, due to the increasing introduction of nonlinear loads, for example. [Means for solving the problem]

[0007]

[0007] A core suitable for electromagnetic devices is provided. The core may be suitable for electromagnetic devices such as transformers, electric motors, generators, and inductors. The core comprises three arc-shaped rims. Each rim has a first end and a second end and is arranged around a central axis. The first ends of the rims are connected to each other at a first position along the central axis, and the second ends of the rims are connected to each other at a second position along the central axis. Each rim comprises a plurality of bent electromagnetic steel strips. [Effects of the Invention]

[0008]

[0008] The core shape improves the material-radiation interaction and physical form of the magnetic circuit compared to cores having a rectangular ring, such as the magnetic core 100, minimizing the distribution of magnetic flux density and thus minimizing both dead spots and saturation at low magnetic flux density. This reduces core losses and the required core mass.

[0009]

[0009] For example, instead of planar arc-shaped steel strips cut from a sheet of electrical steel being stacked on top of each other, the stacked electrical steel strips are bent into an arc shape. This reduces the amount of waste material when forming the rim.

[0010]

[0010] The arc-shaped rim may be semicircular, that is, it may have a size of 180 degrees. In other examples, the arc-shaped rim may be subarctic, that is, it may have a size of less than 180 degrees. Alternatively, the arc-shaped rim may be superarctic, that is, it may have a size greater than 180 degrees.

[0011]

[0011] The core may be suitable for a three-phase transformer. The core may include three or more arcuate rims to accommodate further phases.

[0012]

[0012] The electrical steel strip may be grain-oriented electrical steel. For example, compared to a planar arc-shaped steel strip cut from a sheet of grain-oriented electrical steel, a bent arc-shaped grain-oriented electrical steel strip ensures that the particle orientation is maintained along the rim. This maintains the symmetrical behavior of the rim, as the optimal magnetic properties are observed in the particle direction.

[0013]

[0013] Each rim may be arranged at equal intervals around the central axis. For example, in a core consisting of three rims, the rims may be arranged at 120-degree intervals.

[0014]

[0014] Each of the multiple bent electrical steel strips may comprise a first group of steel strips, a second group of steel strips, and a third group of steel strips, the first group of steel strips being positioned between the second group of steel strips and the third group of steel strips. The first group of steel strips may have a first thickness, the second group of steel strips may have a second thickness, and the third group of steel strips may have a third thickness, the first thickness may be greater than both the second and third thicknesses. The second thickness may be equal to the third thickness.

[0015]

[0015] The first group of steel strips may consist of a first predetermined number of steel strips, the second group of steel strips may consist of a second predetermined number of steel strips, the third group of steel strips may consist of a third predetermined number of steel strips, and the first predetermined number of steel strips may be greater than both the second predetermined number of steel strips and the third predetermined number of steel strips. The second predetermined number of steel strips may be equal to the third predetermined number of steel strips.

[0016]

[0016] The first group of steel strips may have a first width, the second group of steel strips may have a second width, and the third group of steel strips may have a third width, and the first width may be greater than both the second width and the third width. The second width may be equal to the third width.

[0017]

[0017] Each rim may be positioned to receive its respective primary winding and its respective secondary winding.

[0018]

[0018] An electromagnetic device is provided comprising the above-described core, a primary winding arranged around each rim, and a secondary winding arranged around each rim. The electromagnetic device may be, for example, a transformer, an electric motor, a generator, or an inductor.

[0019]

[0019] A method for manufacturing a core suitable for electromagnetic devices is provided. The core may be suitable for electromagnetic devices such as transformers, electric motors, generators, and inductors. The method includes, for example, forming a set of three strips from one or more sheets of electromagnetic steel by cutting, stamping, or punching. Each set of strips comprises multiple strips, and one or more sheets of electromagnetic steel comprises an insulating surface layer. The method includes arranging each of the three sets of strips as its respective stack and bending each stack to form an arc-shaped rim. Each rim has a first end and a second end. The method includes arranging each rim around a central axis, connecting the first ends of the rims together at a first position along the central axis and connecting the second ends of the rims together at a second position along the central axis.

[0020]

[0020] As explained above, for example, by bending the electrical steel strip instead of cutting the steel strip in a planar arc shape, the amount of waste material when forming the rim is reduced.

[0021]

[0021] The method may include, with respect to each rim, adding a primary winding around the rim and a secondary winding around the rim between bending each stack into an arc-shaped rim and connecting the second ends of the rims at a second position along the central axis. Adding a winding around the rim may include winding a wire around the rim to form a winding. Alternatively, adding a winding around the rim may include winding the wire onto a bobbin and inserting the rim into the bobbin. Winding the wire around the rim before joining the rims together simplifies the winding process because the rims have open ends.

[0022]

[0022] Each rim may comprise a first group of steel strips, a second group of steel strips, and a third group of steel strips, with the first group of steel strips being positioned between the second group of steel strips and the third group of steel strips. The first group of steel strips may have a first thickness, the second group of steel strips may have a second thickness, and the third group of steel strips may have a third thickness, with the first thickness being greater than both the second and third thicknesses. The second thickness may be equal to the third thickness.

[0023]

[0023] The first group of steel strips may consist of a first predetermined number of steel strips, the second group of steel strips may consist of a second predetermined number of steel strips, the third group of steel strips may consist of a third predetermined number of steel strips, and the first predetermined number of steel strips may be greater than both the second predetermined number of steel strips and the third predetermined number of steel strips. The second predetermined number of steel strips may be equal to the third predetermined number of steel strips.

[0024]

[0024] The first group of steel strips may have a first width, the second group of steel strips may have a second width, and the third group of steel strips may have a third width, and the first width may be greater than both the second width and the third width. The second width may be equal to the third width.

[0025]

[0025] For each rim, this method may include machining the first end to form a first edge having a 120-degree included angle for alignment with the central axis at a first position, machining the second end to form a second edge having a 120-degree included angle for alignment with the central axis at a second position, between bending each stack to form an arcuate rim and connecting the first ends of the rims to each other at a first position along the central axis. The machining may include grinding, milling, sanding, and / or cutting. The cutting may be by water jet or laser. The included angle is the angle between the outer surfaces of the ends. Machining the ends of the rim enables accurate alignment of the rims and minimizes potential gaps at the connections at the first and second positions.

[0026]

[0026] Placing each rim around the central axis may include placing each rim equidistantly around the central axis.

[0027]

[0027] The insulating surface layer may comprise a curable varnish, and this method may include curing the varnish of each rim before placing each rim around the central axis.

[0028]

[0028] Connecting the first ends of the rims to each other and connecting the second ends of the rims to each other may include using an adhesive. The adhesive may be an intermetallic structural adhesive. Examples of suitable intermetallic adhesives include epoxy adhesives such as 3M's EC-2216 B / A or Henkel's MasterBond 11HT, paste adhesives such as 3M's EC-9323 B / A, or structural adhesive films such as 3M's AF31 or LOCTITE's EA 9673 AERO. Connecting the first ends of the rims to each other and connecting the second ends of the rims to each other may include fixing the rims to each other without an adhesive.

[0029]

[0029] The method may include annealing each rim before placing each rim around the central axis, for example, to improve the magnetic properties of the rim and to relieve internal mechanical stress on the rim. [Brief explanation of the drawing]

[0030]

[0030] Further details, aspects, and embodiments of the present invention will be described by reference to the drawings, merely as examples. The elements in the drawings are shown for simplicity and clarity and are not necessarily drawn to scale. For ease of understanding, each drawing is given the same reference number. [Figure 1] This is a schematic diagram of a conventional three-phase magnetic core. [Figure 2A] This is a schematic diagram of a magnetic core. [Figure 2B] Figure 2A is a schematic exploded view of the magnetic core. [Figure 2C] Figure 2A is a schematic top view of the magnetic core. [Figure 2D] Figure 2A is a schematic front view of the magnetic core. [Figure 2E] This table shows the number of layers in the rim of the magnetic core in Figure 2A. [Figure 3] This is a schematic diagram of a magnetic core. [Figure 4] This is a flowchart of the process for manufacturing the core of a magnetic core. [Figure 5] This is a schematic top view of the net for the steel strip to be cut. [Modes for carrying out the invention]

[0031]

[0031] Referring to Figures 2A to 2D, the magnetic core 200 comprises three arc-shaped rims 202 arranged at equal intervals around a central axis 204. Each rim 202 is substantially identical. The arc-shaped rims 202 are 180-degree arcs. Each rim has a first end 206 and a second end 208. Each first end 206 has a first edge 210 located along the central axis 204. Each second end 206 has a second edge 212 located along the central axis 204. The first ends 206 are joined to each other, and the second ends 208 are joined to each other. One or more of the following may be wound around each rim 202: a primary winding, a secondary winding, and a regulating winding (not shown).

[0032]

[0032] Each rim 202 comprises multiple electrical steel strips that are stacked and bent together. The use of stacked thin steel reduces power loss caused by eddy currents induced when a sinusoidal voltage is applied to the windings. The cross-section of each rim approximates a circle by varying the width of the steel strips of the rim. The electrical steel strips of each rim 202 are grouped into 15 sets of steel strips, including a central set of steel strips 220 and sets of steel strips 222, 224, 226, 228, 230, 232, 234, 236, 238, 240, 242, and 244.

[0033]

[0033] The sets of steel strips on either side of the central steel strip are paired, and each of the paired sets of steel strips has approximately the same width and thickness. Set 222 of steel strips is paired with set 224 of steel strips, and these are located on either side of the central set 220 of steel strips. Set 226 of steel strips is paired with set 228 of steel strips, and set 226 is located adjacent to set 222 of steel strips, and set 228 is located adjacent to set 224 of steel strips. Set 230 of steel strips is paired with set 232 of steel strips, and set 230 is located adjacent to set 226 of steel strips, and set 232 is located adjacent to set 228 of steel strips. Set 234 of steel strips is paired with set 236 of steel strips, and set 234 is located adjacent to set 230 of steel strips, and set 236 is located adjacent to set 232 of steel strips. Set 238 of steel strips is paired with set 240 of steel strips, and set 238 is located adjacent to set 234 of steel strips, and set 240 is located adjacent to set 236 of steel strips. Set 242 of steel strips is paired with set 244 of steel strips, and set 242 is located adjacent to set 244 of steel strips, and set 238 of steel strips is located adjacent to set 240 of steel strips.

[0034]

[0034] The widths of steel strip sets 222 and 224 are smaller than the width of the central steel strip set 220. The widths of steel strip sets 226 and 228 are smaller than the widths of steel strip sets 222 and 224. The widths of steel strip sets 230 and 232 are smaller than the widths of steel strip sets 226 and 228. The widths of steel strip sets 234 and 236 are smaller than the widths of steel strip sets 230 and 232. The widths of steel strip sets 238 and 240 are smaller than the widths of steel strip sets 234 and 236. The widths of steel strip sets 242 and 244 are smaller than the widths of steel strip sets 238 and 240.

[0035]

[0035] Referring to Figure 2E, the thickness of each set of steel strips is influenced by the number of steel strips in each set of steel strips, i.e., the number of layers of electrical steel. Each layer may have a thickness of 0.2 to 0.5 millimeters. In the magnetic core 200, the number of steel strips in sets 222 and 224 is less than the number of steel strips in set 220 of the central steel strip. The number of steel strips in sets 226 and 228 is less than the number of steel strips in sets 222 and 224 of the steel strips. The number of steel strips in sets 230 and 232 is less than the number of steel strips in sets 226 and 228 of the steel strips. The number of steel strips in sets 234 and 236 is less than the number of steel strips in sets 230 and 232 of the steel strips. The number of steel strips in sets 238 and 240 is less than the number of steel strips in sets 234 and 236 of the steel strips. The number of steel strips in sets 242 and 244 is the same as the number of steel strips in sets 238 and 240. In other examples, the number of steel strips in sets 242 and 244 may be less than the number of steel strips in sets 238 and 240.

[0036]

[0036] The grouping of the steel strips used in the magnetic core 200 is one example of approximating a circular cross-section, and it should be understood that many variations are possible. For example, each steel strip or laminate on either side of the central steel strip may have a progressively smaller width than the central steel strip. Alternatively, there may be a different number of sets of steel strips. The number of sets of steel strips may be odd to allow for symmetry in the thickness and width of the sets of steel strips around the central set of steel strips.

[0037]

[0037] Figure 3 shows a core 250 which is substantially the same in structure as the magnetic core 200, for example, having three arc-shaped rims 252 arranged at equal intervals around a central axis. The core 250 differs from the magnetic core 200 in that all of the electromagnetic steel strips of the rims 252 have the same width. Therefore, the cross-section of each rim is rectangular rather than approximates a circle.

[0038]

[0038] In the alternative configuration, the magnetic core has substantially the same overall shape as the magnetic core 200, but the arc-shaped rim is formed from multiple planar arc-shaped steel strips, rather than from a bent steel strip which may be cut from, for example, a sheet of electromagnetic steel. In other words, the orientation of the steel strips is perpendicular to the orientation of the steel strips of the magnetic core 200.

[0039]

[0039] Figure 4 shows a process 300 for manufacturing a core such as a magnetic core 200. In step 302, a set of electrical steel strips is formed, with one set of strips being for the rim of the core. The strips may be formed, for example, by punching, stamping, or laser cutting each strip to the width and length from a sheet of electrical steel. The electrical steel may be, for example, Thyseen-Krupp powercore® C or powercore® H.

[0040]

[0040] Figure 5 shows an exemplary set of templates 500 for cutting multiple steel strips 502 from sheets 504a, 504b, and 504n of electrical steel.

[0041]

[0041] Alternatively, the length of the steel strip can be cut from a roll of electrical steel having the same width as the steel strip. As described in relation to the magnetic core 200, the steel strips in each set of electrical steel strips may have the same width, or the width of the steel strips may vary, for example, to approximate the circular cross-section of the rim.

[0042]

[0042] In step 306, each set of steel strips is arranged as a stack. In step 310, each stack is bent into an arc-shaped rim, for example, using a jig. The stack is bent by applying an external load perpendicular to the plane formed by the length and width of the steel strips.

[0043]

[0043] The electrical steel strip may include a surface coating of an electrical insulating material. The surface coating may be curable, such as a varnish or paint. The curable surface coating of the steel strip stack may be cured in step 314. For example, the curable surface coating may be cured by heating the stack in an autoclave. The electrical insulating surface coating may be formed during the annealing of the electrical steel strip. For example, the electrical steel strip may be annealed in an air atmosphere in a roller furnace at a maximum temperature of 860°C for a soaking time of 1 to 2 minutes. Due to the air atmosphere, the cut edges of the electrical steel strip oxidize and an insulating coating is formed. A coating thickness of 2 to 5 micrometers provides good electrical resistance and a high stacking coefficient.

[0044]

[0044] Each rim has a first end and a second end. In step 318, the ends of the rims may be machined to create angled ends that allow the rims to fit together tightly. For example, if the core to be manufactured has three rims, the ends are machined at a 120-degree angle. Machining may include one or more of sanding, grinding, milling, and cutting such as waterjet cutting or laser cutting. Instead of or in addition to step 318, the steel strip may be formed in step 302 to have angled ends. In some examples, the ends of the rims may be machined to create lap joints that allow the rims to fit together tightly.

[0045]

[0045] In step 322, the rim may be annealed. If the curable surface coating is heat-cured in step 314, the annealing in step 322 may be included in step 314. In some examples, the core may be annealed after the rim is joined in step 334. The annealing may be magnetic annealing to improve the magnetic properties of the rim. In addition or instead, the annealing may be stress-relieving annealing to relieve internal mechanical stress on the rim, for example, due to bending in step 310. For example, the annealing may include soaking at 820°C to 850°C for 2 hours in a box furnace preferably with a protective atmosphere of 100% nitrogen, followed by cooling to about 200°C to 300°C in the furnace.

[0046]

[0046] In step 326, one or more of the primary winding, secondary winding, and adjustment winding may be added to each rim. The addition of windings to the rims may be performed at any point before the ends of each rim are joined together in step 338, in other words, when there is at least one open end. Adding windings around the rims may involve winding a wire around the rims to form the windings. Alternatively, adding windings around the rims may involve winding a wire onto a bobbin and inserting the rims onto the bobbin. The winding process is simplified by winding the wire around the rims before joining the rims together. The windings may be distributed to the rims with or without spacers.

[0047]

[0047] In step 330, the rim is positioned around the central axis. For example, the rim may be held in place using clamps and / or fixtures. In step 334, the first ends of the rim are joined together. In step 338, the second ends of the rim are joined together. Joining the ends of the rim together in steps 334 and 338 may include using an adhesive such as an intermetallic adhesive. Instead of, or in addition to, joining the ends of the rim together in steps 334 and 338 may include fixing the rims together. Steps 334 and 338 may be performed simultaneously.

[0048]

[0048] Although the present invention has been described in relation to some embodiments, it is not intended to be limited to the specific forms described herein. Rather, the scope of the present invention is limited only by the appended utility model claims. In addition, although features may appear to be described in relation to specific embodiments, those skilled in the art will recognize that various features of the described embodiments can be combined in accordance with the present invention. In the utility model claims, the terms “equip” or “include” do not preclude the presence of other elements. [Items of the invention] [Item 1] A core suitable for an electromagnetic device, wherein the core comprises three arc-shaped rims, each of which is arranged around a central axis, each of which has a first end and a second end, the first ends of which are interconnected at a first position along the central axis, and the second ends of which are interconnected at a second position along the central axis, and each of which has a plurality of bent electromagnetic steel strips. [Item 2] The core according to item 1, wherein each of the rims is arranged at equal intervals around the central axis. [Item 3] The core according to item 1 or 2, wherein each of the plurality of bent electrical steel strips comprises a first group of steel strips, a second group of steel strips, and a third group of steel strips, and the first group of steel strips is positioned between the second group of steel strips and the third group of steel strips. [Item 4] The core according to item 3, wherein the first group of steel strips has a first thickness, the second group of steel strips has a second thickness, and the third group of steel strips has a third thickness, and the first thickness is greater than both the second and third thicknesses. [Item 5] The core described in item 4, wherein the second thickness is equal to the third thickness. [Item 6] The core according to any one of items 3 to 5, wherein the first group of steel strips has a first width, the second group of steel strips has a second width, and the third group of steel strips has a third width, and the first width is greater than both the second width and the third width. [Item 7] The core described in item 6, wherein the second width is equal to the third width. [Item 8] A core as described in any one of items 1 through 7, each being a rim arranged to receive its respective primary winding and its respective secondary winding. [Item 9] The core described in any one of items 1-8, Each primary winding is arranged around each of the rims, Each of the secondary windings arranged around each of the rims and An electromagnetic device equipped with the following features. [Item 10] A method for manufacturing a core suitable for an electromagnetic device, wherein the method is A step of forming a set of three steel strips from one or more sheets of electrical steel, wherein each set of steel strips comprises a plurality of steel strips, and the one or more sheets of electrical steel comprises an insulating surface layer. The steps include: arranging each of the three sets of steel strips as its respective stack; A step of bending each of the stacks to form an arc-shaped rim, wherein each of the rims has a first end and a second end, The steps of placing each of the rims around the central axis, A step of connecting the first ends of the rims to each other at a first position along the central axis, A step of connecting the second ends of the rim to each other at a second position along the central axis; Methods that include... [Item 11] Between the step of bending each of the stacks to form the arc-shaped rim and the step of connecting the second ends of the rims to each other at the second position along the central axis, The steps include adding a primary winding around the rim, The steps include adding a secondary winding around the rim and The method described in item 10, including the method described in item 10. [Item 12] The method according to item 10 or 11, wherein each of the rims comprises a first group of steel strips, a second group of steel strips, and a third group of steel strips, and the first group of steel strips is positioned between the second group of steel strips and the third group of steel strips. [Item 13] The method according to item 12, wherein the first group of steel strips has a first thickness, the second group of steel strips has a second thickness, and the third group of steel strips has a third thickness, and the first thickness is greater than both the second and third thicknesses. [Item 14] The method according to item 13, wherein the second thickness is equal to the third thickness. [Item 15] The method according to any one of items 12 to 14, wherein the first group of steel strips has a first width, the second group of steel strips has a second width, and the third group of steel strips has a third width, and the first width is greater than both the second width and the third width. [Item 16] The method according to item 15, wherein the second width is equal to the third width. [Item 17] Between the step of bending each of the stacks to form the arc-shaped rim and the step of connecting the first ends of the rims to each other at a first position along the central axis, with respect to each of the rims, A step of machining the first end to form a first edge for alignment with the central axis at the first position, wherein the first edge has an interior angle of 120 degrees, A step of machining the second end to form a second edge for alignment with the central axis at the second position, wherein the second edge has an interior angle of 120 degrees. The method described in any one of items 10 to 16, including the method described in item 10 to 16. [Item 18] The method according to any one of items 10 to 17, wherein the step of placing each of the rims around the central axis includes the step of placing each of the rims at equal intervals around the central axis. [Item 19] The method according to any one of items 10 to 18, wherein the insulating surface layer comprises a curable varnish, and the method includes the step of curing the varnish on each of the rims before the step of placing each of the rims around the central axis. [Item 20] The method according to any one of items 10 to 19, wherein the step of connecting the first ends of the rims together and the step of connecting the second ends of the rims together include the step of using an adhesive. [Item 21] The method according to any one of items 10 to 20, comprising the step of annealing each of the rims before the step of arranging each of the rims around the central axis. [Explanation of symbols]

[0049] 200 magnetic core 202 Arc-shaped rim 204 Center axis 206 First end 208 Second end 210 First edge 212 Second edge 220 Central steel strip set Set of steel strips: 222, 224, 226, 228, 230, 232, 234, 236, 238, 240, 242, 244 250 cores 252 Arc-shaped rim 300 processes 302, 306, 310, 314, 318, 322, 326, 330, 334, 338 steps Set of 500 templates 502 Steel Strip Sheets of 504a, 504b, and 504n electrical steel

Claims

1. A magnetic core (200) suitable for an electromagnetic device, wherein the magnetic core comprises three arc-shaped rims (202), the rims are arranged around a central axis (204), each of the rims has a first end (206) and a second end (208), the first ends of the rims are interconnected at a first position along the central axis, the second ends of the rims are interconnected at a second position along the central axis, and each of the rims comprises a plurality of bent electromagnetic steel strips (222, 224, 226, 228, 230, 232, 234, 236, 238, 240, 242, 244), Each of the plurality of bent electrical steel strips comprises a first group of steel strips, a second group of steel strips, and a third group of steel strips, wherein the first group of steel strips is positioned between the second group of steel strips and the third group of steel strips. The first group of steel strips has a first thickness, the second group of steel strips has a second thickness, and the third group of steel strips has a third thickness, wherein the first thickness is greater than both the second and third thicknesses. A magnetic core in which the first group of steel strips has a first width, the second group of steel strips has a second width, and the third group of steel strips has a third width, and the first width is greater than both the second width and the third width.

2. The magnetic core according to claim 1, wherein the rims are arranged at equal intervals around the central axis.

3. The magnetic core according to claim 1 or 2, wherein the second thickness is equal to the third thickness.

4. The magnetic core according to claim 1 or 2, wherein the second width is equal to the third width.

5. The magnetic core according to claim 1 or 2, wherein each is a rim arranged to receive its respective primary winding and its respective secondary winding.

6. A magnetic core according to claim 1 or 2, Each primary winding is arranged around each of the rims, Each of the secondary windings arranged around each of the rims and An electromagnetic device equipped with the following features.

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