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Title:
TRANSFORMER CORE JOINTS
Document Type and Number:
WIPO Patent Application WO/2019/133953
Kind Code:
A1
Abstract:
A transformer core has at least one limb extending between a pair of yokes. The at least one limb and yokes meet at core joints. The core joints are rounded to provide a curved magnetic flux path that does not have hard directional changes. The core joints are formed of laminations of flexible grain-oriented electrical steel fibers embedded in a non-magnetic material to provide the oriented magnetic flux direction from the at least one limb to the yokes of the core.

Inventors:
UPADHYAY PARAG (US)
PERICO ELIO (US)
Application Number:
US2018/068108
Publication Date:
July 04, 2019
Filing Date:
December 31, 2018
Export Citation:
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Assignee:
ABB SCHWEIZ AG (CH)
UPADHYAY PARAG (US)
International Classes:
H01F27/28; H01F41/06
Foreign References:
US2411374A1946-11-19
US20160300662A12016-10-13
US20140320253A12014-10-30
US2498747A1950-02-28
Attorney, Agent or Firm:
COLLIER, Douglas A. et al. (Taft Stettinius & Hollister LLP, One Indiana Square Ste. 350, Indianapolis IN, 46204, US)
Download PDF:
Claims:
I/We Claim:

1. A transformer core, comprising:

a pair yokes and at least one limb extending between the yokes, the yokes and at least one limb connected together at first and second joints on opposing sides of the core and wherein the first and second joints each include a rounded shape for directing the magnetic flux along the first and second joints in a curved path between the at least one limb and the pair of yokes of the core.

2. The transformer core according to claim 1, wherein the first and second joints are formed of grain-oriented electrical steel fibers bonded together and embedded in a non magnetic bonding material.

3. The transformer core according to claim 2, wherein the grain-oriented electrical steel fibers are bonded together to form a rectangular cross-section.

4. The transformer core according to claim 2, wherein the fibers have a length to width ratio between 1:1 and 1000:1.

5. The transformer core according to claim 2, wherein the fibers have a length to width ratio of at least 100:1.

6. The transformer core according to claim 1, wherein the at least one limb includes at least two limbs connected to the pair of yokes, and the rounded shape of the joints connecting the at least two limbs to the pair of yoks provides a rounded rectangular shape to the core.

7. The transformer core according to claim 1, wherein the at least one limb includes a pair of outer limbs connected to opposite ends of the pair of yokes with rounded joints, and the at least one limb includes a center limb between the outer limbs that is connected to the pair of yokes with curved joints.

8. The transformer core according to claim 7, wherein the curved joints are formed of first, second, and third curved sections, wherein curved portions of the first and second sections face one another and the third curved section is curved inwardly at a gap between first and second curved sections.

9. A transformer core, comprising:

a core having yokes and at least one limb extending vertically between the yokes, the yokes and the at least one limb connected together at joints and wherein the joints are each formed by first, second, and third curved sections, wherein curved portions of the first and second curved sections face one another and the third curved section is curved inwardly at a gap between first and second curved sections.

10. The transformer core according to claim 9, wherein the at least one limb includes a pair of outer limbs extending between the yokes at opposite ends of the yokes and a center limb between the pair of outer limbs, and the joints join the center limb to the yokes.

11. The transformer according to claim 10, wherein the outer limbs are connected to the yokes with rounded joints at outer corners of the transformer core.

12. The transformer according to claim 11, wherein each of the joints is comprised of grain-oriented electrical steel fibers bonded together and embedded in a non-magnetic material matrix.

13. A transformer, comprising: a core having a pair of yokes and at least one limb extending between the pair of yokes, the pair of yokes and the at least one limb connecting to one another at first and second joints, and wherein the first and second joints each include a rounded shape for directing the magnetic flux from the yokes to the at least one limb along a curved path through the first and second joints; and

a coil assembly mounted to the at least one limb of the core.

14. The transformer according to claim IB, wherein the at least one limb includes an outer limb connected to the pair of yokes with the first and second joints and an inner limb, wherein the inner limb is connected to the pair of yokes with first and second inner joints that each include first and second rounded sections facing one another to create a gap therebetween and a third inwardly curved section proximate to the gap.

15. The transformer according to claim 13, wherein each of the first and second joints are comprised of grain-oriented electrical steel fibers bonded together and embedded in non-magnetic material matrix.

16. The transformer according to claim 15, wherein the grain-oriented electrical steel fibers are bonded together to form a rectangular cross-section.

17. The transformer according to claim 15, wherein the fibers have a length to width ratio between 1:1 and 1000:1.

18. The transformer according to claim 15, wherein the fibers have a length to width ratio of at least 100:1.

19. The transformer according to claim 13, wherein the at least one limb includes a pair of outer limbs that are each connected to the pair of yokes with respective first and second joints having a rounded shape so that the core forms a rectangular shape with rounded corners.

20. The transformer according to claim IB, wherein the at least one limb includes an outer limb connected to the pair of yokes with the first and second joints and an inner limb, wherein the magnetic flux travels from the yokes to the inner limb of the core through curved sections of inner joints that connect the inner limb to the yokes.

21. The transformer according to claim 21, wherein the inner joints are lotus core joints and have core frames extending outwardly therefrom.

22. The transformer according to claim 13, wherein the core is stepped to increase a fill factor of the core in relation to the coil assembly.

Description:
TRANSFORMER CORE JOINTS

Field of the Invention

[0001] The present application is directed to a transformer that reduces noise, vibration, and magnetic losses.

BACKGROUND

[0002] Transformers play a fundamental role in power distribution for making available the increase or decrease of voltage along transmission lines. In a transformer core having one or more limbs extending between the yokes, the magnetic flux path crosses the joints between the limb(s) and yokes at hard angles. Additionally, the clearance between the limb(s) and yokes supports magnetic forces that can lead to vibrations and noise in the transformer during operation.

[0003] Referring to Figs. 1A and IB, transformer cores 10, 10' are shown with yokes 13 and at least one limb 15 extending vertically between the yokes 13. The cores 10, 10' can include coil assemblies (not shown in Figs. 1A, IB) mounted to the at least one limb 15. The coil assemblies are formed of concentrically arranged primary and secondary coil windings as is known in the art.

[0004] With continued reference to Figs. 1A and IB, joints 2, 2', 3, 3' of transformer cores 10, 10' are formed in the regions where laminations arranged vertically along the limbs overlap laminations that are arranged horizontally along the yokes. The joints 2, 2', 3, 3'' are represented by the circled portions of the core 10, 10". The joints 2, 2' of transformer core 10 and joints 3, 3' of transformer core 10' represent a source of noise, vibration, and magnetic losses since they are formed with hard angles between the laminations of the limbs and yokes, and the magnetic flux B crosses the joints in directions that do not correspond to those where magnetic properties are optimized. [0005] Conventional installations force the magnetic flux 16 to travel through hard directions such as at right angles, forty-five degree angles and other angles such as shown in the joints 2, 2', 3, 3'. For example, joint 2 is at an outer corner location of transformer core 10 where linear core limbs 15 and yokes 13 meet at a 90 degree angle, whereas joint 3 is located at a corner joint of the transformer core 10' where limbs 15 and yokes 13 meet at about a 45 degree angle. Center joint 2' and center joint 3' are at a location where the center core limb 15 meets the yokes 13 at 90 degrees (Fig. 1A) and at an angle (Fig. IB.)

[0006] Referring now to Figs. 2A and 2B, an interleaved center core limb joint 3' and an interleaved corner core limb joint 3 are shown. The center core limb joint 3' and corner core limb joint 3 are part of previously known core 10' configurations. Instead of having joint angles at 45 degrees, 55 degree angles and other angles, the laminations 4 used to form the center core limb joints 3' and/or corner core limb joint 3 are mitered and interleaved at approximately a 45 degree angle. However, this arrangement still forces the magnetic flux path to travel along hard angles and provides clearances between the yokes 13 and at least one core limb 15 that can lead to noise and vibration.

[0007] In certain known installations of distribution transformers, the hard angular joints 2, 2', 3, 3' are eliminated by using wound core technology and amorphous metals. However, such material is non grain-oriented, more expensive, more brittle, has a lower saturation magnetization, and can work only for small power ranges. Therefore, further improvements in this area of technology are needed.

SUMMARY

[0008] Embodiments of the present application include methods, systems and apparatuses relating to transformer cores. Embodiments of the present application also include methods, systems and apparatuses for relating to a transformer core for improved transmission of magnetic flux between parts of the transformer core. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for fabricating transformer cores. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the accompanying drawings, structural embodiments are illustrated that, together with the detailed description provided below, describe exemplary embodiments of a transformer having core joints formed to support a curved magnetic flux path along the joints. One of ordinary skill in the art will appreciate that a component may be designed as multiple components or that multiple components may be designed as a single component.

[0010] Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and written description with the same reference numerals, respectively. The figures are not drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration.

[0011] Figures 1A and IB show prior art transformer cores having angled joints between the yokes and limbs; and

[0012] Figure 2A shows a top view of a prior art transformer center limb core joint formed of interleaved lamination layers;

[0013] Figure 2B shows a side view of a prior art transformer outer limb core joint formed of interleaved lamination layers;

[0014] Figure 3A shows the flux path of core joints located on opposing sides of the core of Fig. 3D;

[0015] Figure 3B shows the flux path of core joints at the center limb of the core of Fig. 3D;

[0016] Figure 3C shows a known transformer core having center limb and conventional method of corner and center limb joints of the core with hard angles;

[0017] Figure 3D is an illustration of a transformer core having a curved center limb core joint along with rounded core joints on opposing corners of the core to support a curved magnetic flux path; [0018] Figure 4A shows a transformer core having a curved center limb joints and rounded corner limb joints;

[0019] Figure 4B is a front view of the rounded corner limb joint based at the corner shown in Fig. 4A;

[0020] Figure 4C is an isometric view of Fig. 4B;

[0021] Figure 5A shows the transformer core having a curved center limb joint and rounded corner limb joints;

[0022] Figure 5B shows the curved center limb joint of Fig. 5A in a magnified view;

[0023] Figure 5C is an isometric view of Fig. 5B;

[0024] Figure 6 is a top view of transformer cores having a different number of stepped laminations that provide various fill levels with respect to surrounding coil assemblies;

[0025] Figure 7A is a top view of an alternate embodiment of a curved center limb joint;

[0026] Figure 7B is a front view of the curved center limb joint of Fig. 7A; and

[0027] Figure 7C is a bottom view of the curved center limb joint of Fig. 7A.

DETAILED DESCRIPTION

[0028] The present disclosure focuses on areas where the magnetic flux 16 crosses the joints 2, 2', S, S' of the prior art cores 10, 10' at a 90 degree angle or other hard angle which includes all of joints 2, 2', 3, 3' as well as the clearance between the respective limbs 15 and yokes 13 which causes vibrations and noise. The present disclosure contemplates a soft magnetic material (SMM) to support magnetic flux levels for the transformer core during operation of the transformer. In one embodiment, the SMM suitable for forming the transformer core is a Fe-Si alloy such as grain oriented electric steel (GOES) having a thickness of from about 0.1 mm up to several millimeters. A particular characteristic of GOES is the orientation of crystalline planes parallel to or along the rolling direction of the material so that coercivity, permeability and other magnetic properties are optimized along the direction of the grain orientation of the GOES material.

[0029] In contrast to the prior art, the present disclosure mitigates the deleterious effects of magnetic flux travelling through the hard directional changes as shown in Figs. 1A, IB and 3C by using GOES fibers in the production of new transformer joints 12, 14 of Figs. 3A, 3B, and 3D for transformer core 100. The present disclosure provides a streamlined path for magnetic flux to travel along the core 100 through at least one limb 15, joints 12, 14 and yokes 13. In one embodiment, the core 100 includes joints formed of GOES fibers having a length to width ratio in the range from 1:1 to 1000:1. In another embodiment, the GOES fibers have a length to width ratio of at least 100:1.

[0030] The GOES fibers and laminations 18 (Figs. 4C, 5C) formed therefrom can be prepared as a joint 12, 14 using metallurgical bonding, polymeric binders or other methods such as 3-dimensional (3-D) printing to provide the predetermined electromagnetic and mechanical requirements. The core joints 12, 14 are formed of grain-oriented electrical steel fibers bonded together and embedded in a non-magnetic bonding material or non-magnetic material matrix. In one embodiment, pastes and/or glues are used to bind the GOES fibers together to form laminations 18, which are assembled to form the core joints 12, 14. In another embodiment, an epoxy resin is used to bond the grain-oriented electrical steel fibers together. In forming the core joints 12, 14 through a process such as additive manufacturing, the GOES fibers and non-magnetic materials are applied layer by layer to form the core joints 12, 14 of a single or multiple laminations 18.

[0031] The GOES fibers are mechanically bendable due to a reduced width which allows curved structures of any dimension to be formed. Laminations 18 formed of GOES fibers can be cut by different processes (laser beam and wire are few examples) under controlled dimensions such as length or width. The cutting procedure, in general, can provide fibers or laminations 18 of rectangular cross section, which will support the packing factor of the joint 12, 14 as shown in Figs. 4C and 5C.

[0032] With reference now to Fig. 3A, the smaller arrows 17 show the grain orientation of the core 100 material and the larger arrow 16 shows the intended magnetic field direction along the outer joint 12 of the core 100. With reference now to Fig. 3B, the flux path 16 along the inner joint 14 of the center limb of the core 100 is shown. The magnetic flux paths 16 of Figs. 3A and 3B are possible based on the shape of the core 100 joints 12, 14 of the present disclosure as shown in Fig. 3D.

[0033] With reference now to Figs. 4A and 5A, the transformer core 100 has rounded corner limb joints 12 and curved limb joints 14 that are made out of strands or fibers of GOES material. The rounded corner joints 12 provide a rounded overall rectangular shape to the core 10 where the corners are rounded and the limbs and yokes are generally linear between the rounded corners. The corresponding transformer yoke and limb sections 13, 15 can also be formed of GOES material. The strands of GOES material are made by cutting sheets of the fiber-embedded material widthwise and then cutting along the length to a predetermined size. The sheets or strands 18 are brought together in a grid or array to form the cross-section as is shown in Figs. 4C and 5C which are three-dimensional and isometric views of the core joints 12, 14. Thermoplastic or composite fibers can be molded to keep the GOES strands together. The number of strands along the depth of the joints as shown in conjunction with Figs. 4C and 5C can be variable and form a single lamination sheet up to multiple lamination sheets along the curved or radiused direction of the joints 12, 14.

[0034] The curved center limb joints 14 are formed of first, second, and third curved sections 21, 22, 23 such as is shown in Fig. 5B, where each curved section 21, 22, 23 can include multiple laminations 18. The convex part of the curved portions of the first and second curved sections 21, 22 face one another, and the convex part of the third curved section 23 is curved inwardly at the gap 24 between first and second sections 21, 22. First and second curved sections 21, 22 can connect the center limb to the adjacent yokes, and the third curved section 23 can extend across the joint to connect adjacent yoke sections to one another.

[0035] A thin former or mold may be made from SMM and run the length of the core joint 12, 14. A finished joint 12, 14 can have the appearance of a solid joint from the outside surfaces, although the joint assembly can be provided with generally alternating teeth that extend to fit the corresponding limb 15 and yoke 13 with laminations 18. It should be understood that the yoke 13 and at least one limb sections 15 connected to the joints 12, 14 are formed of conventional grain-oriented silicon steel laminations.

[0036] The curved corner and center limb joints 12, 14 provide flexibility to the core 100 regardless of the overall cross sectional shape of the core 100. For example, in Fig. 6 the joints 12, 14 can be formed in a circular or stepped fashion to match with the circular and stepped limbs and yokes in the stepped core portions 100a, 100b, 100c, lOOd, lOOe. The stepped fashion for forming the core 100a, 100b, 100c, lOOd, lOOe involves laminations of varying lengths and widths stacked upon one another. Coil assemblies 20 can be mounted to the limbs and yokes of the stepped cores to form a transformer 1. The stepped cores better fill the circular space within the coil assemblies 20.

[0037] The continuous change of magnetic flux path between laminations 18 of the present disclosure supports the reduction of noise, vibration and magnetic losses because the magnetic flux does not cross any hard magnetic directions. The present disclosure makes use of GOES fibers at the corner and center joints 12, 14 which can be used in many transformer applications. Scrap can also be reduced using the GOES fibers instead of the utilization of a punching process. Additionally, discarded laminations 18 can be reprocessed in order to produce new GOES fibers for use in forming new laminations 18. Depending on the size of the core window of the transformer, similar joints 12, 14 can be used for different power ratings.

[0038] It should be understood that the core 10 may be provided with only the outermost joints 12 having a rounded shape like joint 12, both outermost and center joints 12, 14 having rounded and curved shapes like joints 12 and 14, or only center joints having a curved shape like joint 14.

[0039] Referring now to Fig. 6, a top view of the transformer 1 is shown having various fill levels for stepped cores 100a, 100b, 100c, lOOd, lOOe with respect to the coil assemblies 20 mounted thereto around respective ones of the limbs 15a, 15b, 15c, 15d, 15e. Core fill levels for stepped cores 100a, 100b, 100c, lOOd, lOOe refer to the amount of space taken up inside of a coil assembly 20 by the corresponding limb. The core fill factor levels for stepped cores 100a, 100b, 100c, lOOd, lOOe will vary based upon the arrangement, number of steps of laminations having different dimensions and interleaving of the laminations.

[0040] With reference now to Figs. 7A and 7B, a lotus core joint 14' is shown. Core joint 14' can include any of the features or characteristics of center joint 14 discussed above unless specified otherwise. The lotus core joint 14' allows three core yokes (not shown) to extend outwardly therefrom and be joined by a single one of the at least one core limb 15 via joint 14'. Coil assemblies 20 may be mounted to the outward-most limbs of the core frames wherein the core frames are spaced apart from one another by about 120 degrees. Fig. 7C shows the lotus core joint 14' as it appears from the bottom of the core. Further, the lotus core joint 14' can utilize any number of core frames extending outwardly from the at least one core limb 15, such as in a multiple flux splitter of a transformer assembly. [0041] Various aspects of the present disclosure are contemplated According to one aspect, a transformer core includes a pair yokes and at least one limb extending between the yokes. The yokes and the at least one limb are connected together at first and second joints on opposing sides of the core. The first and second joints each include a rounded shape for directing the magnetic flux along the first and second joints in a curved path between the at least one limb and the pair of yokes of the core.

[0042] In one embodiment, the first and second joints are formed of grain- oriented electrical steel fibers bonded together and embedded in a non-magnetic bonding material. In a refinement of this embodiment, the grain-oriented electrical steel fibers are bonded together to form a rectangular cross-section. In another refinement, the fibers have a length to width ratio between 1:1 and 1000:1. In yet another refinement, the fibers have a length to width ratio of at least 100:1.

[0043] In another embodiment, the at least one limb includes at least two limbs connected to the pair of yokes, and the rounded shape of the joints connecting the at least two limbs to the pair of yoks provides a rounded rectangular shape to the core. In yet another embodiment, the at least one limb includes a pair of outer limbs connected to opposite ends of the pair of yokes with rounded joints, and the at least one limb includes a center limb between the outer limbs that is connected to the pair of yokes with curved joints. In a refinement of this embodiment, the curved joints are formed of first, second, and third curved sections, and curved portions of the first and second sections face one another and the third curved section is curved inwardly at a gap between first and second curved sections.

[0044] In another aspect, a transformer core includes a core having yokes and at least one limb extending vertically between the yokes. The yokes and the at least one limb are connected together at joints and the joints are each formed by first, second, and third curved section. Curved portions of the first and second curved sections face one another, and the third curved section is curved inwardly at a gap between first and second curved sections. [0045] In one embodiment, the at least one limb includes a pair of outer limbs extending between the yokes at opposite ends of the yokes and a center limb between the pair of outer limbs, and the joints join the center limb to the yokes. In a refinement of this embodiment, the outer limbs are connected to the yokes with rounded joints at outer corners of the transformer core. In a further refinement, each of the joints is comprised of grain-oriented electrical steel fibers bonded together and embedded in a non-magnetic material matrix.

[0046] According to another aspect of the present disclosure, a transformer includes a core having a pair of yokes and at least one limb extending between the pair of yokes. The pair of yokes and the at least one limb connect to one another at first and second joints. The first and second joints each include a rounded shape for directing the magnetic flux from the yokes to the at least one limb along a curved path through the first and second joints. The transformer also includes a coil assembly mounted to the at least one limb of the core.

[0047] In one embodiment, the at least one limb includes an outer limb connected to the pair of yokes with the first and second joints and an inner limb. The inner limb is connected to the pair of yokes with first and second inner joints that each include first and second rounded sections facing one another to create a gap therebetween and a third inwardly curved section proximate to the gap. In another embodiment of the transformer, the core is stepped to increase a fill factor of the core in relation to the coil assembly.

[0048] In another embodiment, each of the first and second joints are comprised of grain-oriented electrical steel fibers bonded together and embedded in non-magnetic material matrix. In a refinement of this embodiment, the grain-oriented electrical steel fibers are bonded together to form a rectangular cross-section. In another refinement, the fibers have a length to width ratio between 1:1 and 1000:1. In yet another refinement, the fibers have a length to width ratio of at least 100:1. [0049] In another embodiment of the transformer, the at least one limb includes a pair of outer limbs that are each connected to the pair of yokes with respective first and second joints having a rounded shape so that the core forms a rectangular shape with rounded corners.

[0050] In yet another embodiment of the transformer, the at least one limb includes an outer limb connected to the pair of yokes with the first and second joints and an inner limb, wherein the magnetic flux travels from the yokes to the inner limb of the core through curved sections of inner joints that connect the inner limb to the yokes. In a refinement of this embodiment, the inner joints are lotus core joints and have core frames extending outwardly therefrom.

[0051] To the extent that the term "includes" or "including" is used in the specification or the claims, it is intended to be inclusive in a manner similar to the term "comprising" as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term "or" is employed (e.g., A or B) it is intended to mean "A or B or both." When the applicants intend to indicate "only A or B but not both" then the term "only A or B but not both" will be employed. Thus, use of the term "or" herein is the inclusive, and not the exclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995). Also, to the extent that the terms "in" or "into" are used in the specification or the claims, it is intended to additionally mean "on" or "onto." Furthermore, to the extent the term "connect" is used in the specification or claims, it is intended to mean not only "directly connected to," but also "indirectly connected to" such as connected through another component or components.

[0052] While the present application illustrates various embodiments, and while these embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative embodiments, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.

IB