Transformer core, transformer, and a method of producing a transformer core

Abstract

A transformer core (1) comprising a plurality of legs (2) is specified, wherein - the legs (2) comprise a plurality of core sheets (21), - a flitch plate (3) is attached to the core sheets (21) of one of the legs (2), the flitch plate (3) being configured to mechanically stabilize the leg (2), - the flitch plate (3) comprises a plurality of sheets (31), and - adjacent sheets (31) of the flitch plate (3) are bonded to one another via an adhesive layer (32). Further, a transformer (10) and a method of producing a transformer core (1) are specified.

Description

[0001] The present disclosure relates to a transformer core, to a transformer and to a method of producing a transformer core.

[0002] Embodiments of the disclosure relate to ways to provide a transformer core with superior properties.

[0003] According to an embodiment, a transformer core comprises a plurality of legs wherein the legs comprise a plurality of core sheets. A flitch plate is attached to the core sheets of one of the legs, the flitch plate being configured to mechanically stabilize the leg. The flitch plate comprises a plurality of sheets, wherein adjacent sheets of the flitch plate are bonded to one another via an adhesive layer.

[0004] Thus, the flitch plate (also referred to as "tie-plate") is not formed from a single piece of metal, but rather from several sheets bonded together.

[0005] It has been found that such a stack of bonded sheets may have mechanical properties that are comparable or even superior to the mechanical properties of a single metal element having the same dimension.

[0006] Further, the adhesive layer may electrically insulate the adjacent sheets from one another so that losses caused by eddy currents within the flitch plate can be avoided or at least greatly reduced.

[0007] For example, the core sheets of the leg are arranged between two flitch plates. Thus, two flitch plates are arranged on opposite sides of the leg in a cross-sectional view of the leg. Further, at least two legs or all legs of the transformer core may comprise such flitch plates formed from bonded sheets.

[0008] During operation of the transformer core as intended, the legs are oriented vertically in space. The legs may be interconnected to one another by yokes of the transformer core that extend horizontally in space.

[0009] Further, the flitch plate can be arranged within a coil winding mounted to the leg when seen in a horizontal cross-sectional view. In other words, the flitch plate that mechanically stabilizes the leg is surrounded by the coil winding.

[0010] The flitch plate may be used to mount the leg to other components of the transformer core such as a yoke or to components of a transformer comprising the transformer core. For example, the flitch plate is configured to be mounted to one or more mounting parts of the transformer arranged below the transformer core and / or above the transformer core.

[0011] For example, the flitch plate extends beyond the core sheet directly adjoining the flitch plate in a direction extending parallel to an axis of the leg. This protruding portion of the flitch plate may be used to form a connection to one of the yokes and / or to components such as mounting parts.

[0012] The flitch plate may also be used to apply a pressure between a top mounting part and a bottom mounting part. Additional tie rods connecting the upper and lower mounting parts can be dispensed with. Such tie rods located outside the coil windings in a top view onto the transformer core may limit the maximum voltage of the transformer. Further, such tie rods may cause extra losses.

[0013] According to a further embodiment of the transformer core, the flitch plate is arranged within a circle circumscribing the core sheets in a cross-sectional view of the leg. In particular, the circle has the diameter of the leg. Thus, the flitch plate can be arranged within the coil winding without having to increase the inner diameter of the coil winding.

[0014] According to a further embodiment of the transformer core, the sheets of the flitch plate comprise magnetic steel, in particular silicon steel. As silicon steel has a high permeability, the flitch plate may be used to collect the magnetic flux inside the transformer core in the same manner as the core sheets.

[0015] According to a further embodiment of the transformer core, the sheets of the flitch plate comprise grain oriented steel. The flux density can be further increased by means of grain oriented steel.

[0016] The grain orientation directions of adjacent sheets may be oriented in parallel. A parallel orientation may maximize the flux density. Alternatively, the flitch plate may comprise sheets with different grain orientation directions, for example grain orientation directions that extend perpendicular or at least substantially perpendicular with respect to one another.

[0017] According to a further embodiment of the transformer core, the sheets of the flitch plate have a thickness of at least 0.1 mm or at least 0.15 mm or at least 0.18 mm and / or of at most 0.5 mm or at most 0.4 mm or at most 0.35 mm. For example, the thickness is in a range from 0.1 mm to 0.5 mm.

[0018] According to a further embodiment of the transformer core, the flitch plate has a thickness in a range from 5 mm to 20 mm. For example, the flitch plate comprises at least 10 or at least 20 sheets and / or at most 200 or at most 100 sheets.

[0019] A width of the flitch plate may be in a range from 50 mm to 300 mmm, for example. A length of the flitch plate may be in a range from 1 m to 4 m, for example.

[0020] Depending on the specific requirements, the mechanical properties of the flitch plate can be chosen appropriately by adapting the above parameters.

[0021] Further, the material of the adhesive layer may have a significant impact on the mechanical properties such as the rigidity of the flitch plate.

[0022] For example, the adhesive layer may comprise an epoxy resin or a cyanoacrylate as adhesive material. However, other adhesive materials may also be used. Further, the adhesive material may comprise further substances such as hardeners.

[0023] According to a further embodiment of the transformer core, the flitch plate has a stepped side face. Thus, the flitch plate comprises portions with different widths. In other words, the side face laterally delimiting the flitch plate in a cross-sectional view comprises a plurality of steps. For example, the width of the flitch plate may decrease or increase with increasing distance from the axis of the leg in one or more steps.

[0024] A stepped side face may help to minimize core losses at an interface between the leg and a yoke.

[0025] According to a further embodiment of the transformer core, the yoke comprises an outer portion that overlaps with the flitch plate in a side view of the transformer core. In particular, a part of the outer portion that overlaps with the flitch plate may be configured to match the stepped side face of the flitch plate. If, for example, the cross-section of the flitch plate has regions with different widths, the outer portion of the yoke may have corresponding regions having different lengths along a direction that extends in parallel to an axis of the yoke. This may help to minimize gaps between the yoke and the flitch plate.

[0026] However, the joint between the flitch plate and the yoke may be varied in wide limits as long as the joint does not cause significant core losses. For example, a step-lap or a step-in connection may be formed between the yoke and the flitch plate.

[0027] Further, a transformer is specified wherein the transformer comprises a transformer core as described above. Further, the transformer comprises a coil winding mounted to one of the legs.

[0028] For example, the transformer is a three-phase transformer with three coil windings mounted to three legs of the transformer core. However, the number of legs may also be smaller than or larger than three.

[0029] The transformer may be configured to be mounted in a tank so that the transformer core is immersed in a fluid having insulating and / or cooling properties during operation. Alternatively, the transformer may be configured as a dry transformer.

[0030] Further, a method of producing a transformer core is specified.

[0031] According to an embodiment of the method, a transformer core is produced wherein a flitch plate is attached to core sheets of the transformer core wherein producing the flitch plate comprises the steps of providing a plurality of sheets, arranging an adhesive material between adjacent sheets and curing the adhesive material to form adhesive layers.

[0032] In particular, all of the sheets to be used for the flitch plate can be stacked with intervening adhesive material before the adhesive material is cured. Thus, a single curing step is sufficient to form the flitch plate.

[0033] According to a further embodiment of the method, the sheets are heated during the step of curing the adhesive material. Heating the sheets may accelerate the cross-linking process of the adhesive material.

[0034] For example, the adhesive material may comprise an epoxy resin or a thermo hardener or a cyanoacrylate.

[0035] According to a further embodiment of the method, the sheets are heated by means of electromagnetic radiation during the curing process. In particular, radio frequency waves may be used to efficiently cure the adhesive material.

[0036] It has been found that this method helps to significantly reduce the curing times to a few hours or even to a few minutes without forming any bubbles inside the adhesive material when solidified.

[0037] The method is particularly suited to produce a transformer core as described above. Thus features described in connection with the transformer core may also apply for the method and vice versa.

[0038] The flitch plates formed from bonded sheets help to provide transformers having a compact setup and small core losses.

[0039] Compared to conventional solutions using flitch plates formed in a single piece, core losses may be significantly reduced since eddy currents within the flitch plates can be avoided.

[0040] The whole cross-section of the legs formed by the core sheets and the flitch plates can be used to collect the flux inside the transformer core.

[0041] Thus, the described flitch plates can provide the required mechanical stability of the legs without reducing the cross-section of the leg that is available to transport the magnetic flux.

[0042] In this way, an increase in material costs due to an increased diameter of the leg may be avoided.

[0043] Further, the flitch plates may provide the possibility of allowing a compression of the active part of the transformer.

[0044] Thus, tie rods used for this purpose and located outside the coil windings may be omitted. Such tie rods may cause additional losses and reduce the space available for the coil windings.

[0045] Features described above in connection with one embodiment of the transformer core or the method can be combined with other features described in connection with other embodiments of the transformer core or the method as long as they are not contradictory.

[0046] The accompanying figures are included to provide a further understanding. In the figures, elements of the same structure and / or functionality may be referenced by the same reference signs. It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0047] In the Figures: Figure 1A illustrates a cross-sectional view of a leg of a transformer core according to an embodiment; Figures 1B and 1C show details of Figure 1A; Figure 2 shows a schematic perspective representation of a transformer core according to an embodiment; Figure 3 shows a schematic perspective representation of a transformer core according to an embodiment; Figure 4 shows an embodiment of a transformer with a transformer core in a cross-sectional view through a leg of the transformer; and Figure 5 shows an exemplary embodiment of a method of producing a transformer core.

[0048] While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the figures and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure defined by the appended claims.

[0049] Figure 1A illustrates a cross-sectional view of a leg 2 of a transformer core 1 comprising a plurality of legs 2. An axis 20 of the leg extends perpendicular to the drawing plane.

[0050] The leg 2 comprises a plurality of core sheets 21. A detail 99 of the leg 2 is illustrated in Figure 1C, showing the core sheets 21 with an insulating material 22 arranged at an interface between adjacent core sheets 21. The insulating material 22 may be provided on one or on two opposite sides of the magnetic material of the core sheets 21. Thus, the prefabricated core sheets 21 may directly adjoin each other. In particular, there is no bonding material between adjacent core sheets 21. For example, the insulating material 22 may comprise a glass applied to the magnetic steel of thecore sheets 21.

[0051] A flitch plate 23 is attached to the core sheets 21 of leg 2.

[0052] In the exemplary embodiment shown, the core sheets 21 are arranged between two flitch plates 3. Thus, two flitch plates are arranged on opposite ends of the leg 2 in a cross-sectional view. The flitch plates 3 comprise a plurality of sheets 31 wherein adjacent sheets 31 of the flitch plates 3 are bonded to one another via an adhesive layer 32.

[0053] The adhesive layers 32 provide an electrical insulation between adjacent sheets and ensure a high mechanical stability.

[0054] For example, an adhesive material 320 of adhesive layer 32 comprises an epoxy resin or another type of electrically insulating glue such as a cyanoacrylate or a thermo hardener.

[0055] The flitch plates 3 are made from a ferromagnetic material such as magnetic steel like silicon steel. In particular, the sheets 31 may comprise or consist of grain oriented steel.

[0056] This material is particularly suitable due to its high permeability. In particular the sheets 31 of the flitch plate 3 can be made from the same material as the core sheets 21.

[0057] The core 2 comprises a plurality of core steps 25, wherein each of the core steps 25 comprises a plurality of core sheets 21. Along a direction perpendicular to an axis 20 of the leg 2, the widths of the core steps 25 decrease with increasing distance from the axis 20 so that the core sheets 21 are located within a circle 29 having the diameter of the leg 2.

[0058] Further, the flitch plates 3 are arranged within the circle 29 circumscribing the core sheets 21. Thus, the provision of the flitch plates 3 does not require additional space. In contrast to conventional flitch plates, the flitch plates 3, made from stacked sheets 31, do not negatively affect the magnetic properties of the leg 2 of the core 1.

[0059] Further, it has been found that the flitch plates 3 formed from stacked sheets 31 may have substantially the same mechanical properties as conventional flitch plates having the same dimensions.

[0060] For example, the flitch plate 3 comprises at least 10 or at least 20 sheets 31 and / or at most 200 sheets or at most 100 sheets.

[0061] A thickness of the sheets 31 of the flitch plate 3 may be in a range from 0.1 mm to 0.5 mm.

[0062] The entire flitch plate 3 may have a thickness in a range from 5 mm to 20 mm.

[0063] A width of the flitch plate 3 may be in a range from 50 mm to 300 mm, for instance. A length of the flitch plate 3 in a direction parallel to the axis 20 of the leg 2 may be in a range from 1 m to 4 m.

[0064] Figure 2 illustrates a detail of a transformer core 1 showing an interconnection between a leg 2 and a yoke 41.

[0065] A step-lap connection is formed between the leg 2 and the yoke 41. Step-lap connections allow core losses to be reduced by minimizing magnetic flux leakage.

[0066] The flitch plate 3 has a side face 35 with a plurality of steps. In the exemplary embodiment shown, the width of the flitch plate decreases in several steps in a direction away from an axis of the leg 2.

[0067] An outer portion 411 of the yoke 41 is formed such that it overlaps with the flitch plate 3. In the embodiment shown, the length of the outer portion 411 increases stepwise with increasing distance from an axis of the yoke 41.

[0068] The outer portion 411 may be produced from the same material as the core sheets 21 and / or the flitch plate 3.

[0069] The stepped side face 35 of flitch plate 3 together with the corresponding shape of the outer portion 411 of the yoke 41 allows to minimize energy losses within the transformer core 1.

[0070] Different joint geometries between the outer portion 411 and the flitch plate 3 may be used, including joints in graded, step-lap, or step-in configuration.

[0071] A connection between the leg 2 and a lower yoke of the transformer core 1 may be configured in a similar manner as the connection between the leg 2 and the upper yoke.

[0072] As illustrated in Figure 2, the flitch plate 3 may extend beyond the adjoining core sheets 21 of the leg 2 in a direction parallel to axis 20 of the leg 2.

[0073] This protruding portion of the flitch plate 3 may be used to mount the flitch plate 3 to other parts such as mounting parts arranged below or above the transformer core 1.

[0074] Figure 3 illustrates a further schematic perspective representation of a transformer core.

[0075] The transformer core 1 comprises three legs 2 extending in parallel to one another.

[0076] During operation of the transformer comprising the transformer core 1, the legs 2 are oriented vertically in space.

[0077] The legs 2 are interconnected by means of two yokes 41. Figure 3 illustrates the upper yoke. The lower yoke may have substantially the same configuration as the upper yoke.

[0078] In the exemplary embodiment of Figure 3, the transformer core 1 is configured for a three-phase transformer and comprises three legs 2. However, the number of legs may be different for other applications.

[0079] Figure 4 schematically illustrates a cross-sectional view of a transformer 10 comprising a transformer core 1 configured as described in connection with the previous figures.

[0080] The transformer 10 further comprises a coil winding 5 extending about the leg 2. The flitch plates 3 are located within the coil winding 5 in the horizontal cross-sectional view.

[0081] During operation of the transformer 10, the flitch plates 3 and the remaining layers of the transformer core 1 may be grounded.

[0082] The flitch plates 3 further allow for a compression of the active part of the transformer 10. Thus, tie rods located outside the coil windings 5 may be dispensed with.

[0083] This facilitates the production of compact transformers for high voltage applications.

[0084] Further, the space available for the coil windings 5 is increased as the risk of an electrical discharge between the coil winding 5 and the external tie rods is avoided.

[0085] Figure 5 illustrates a method of producing a transformer core according to an exemplary embodiment. For the sake of better understanding, structural features mentioned in connection with the method steps are provided with the same reference signs as in the previous figures, even though these reference signs are not explicitly depicted in Figure 1.

[0086] In a step S1, a plurality of sheets 31 is provided. For example grain oriented steel or grain steel may be used.

[0087] If grain oriented steel is used, the grain orientation directions of the sheets may be arranged such that the directions extend in parallel.

[0088] Alternatively, different orientation directions may be used. For example, the grain orientation directions of two sheets 31 extend in particular to one another.

[0089] In a step S2, an adhesive material 320 is arranged between adjacent sheets.

[0090] In a step S3, the adhesive material 320 is cured to form the adhesive layers 32. In particular, the adhesive material may be cured at a stage where all sheets 31 of one flitch plate 3 to be produced are stacked on above the other so that only one curing step is required to produce the flitch plate 3.

[0091] The curing step may be accelerated by heating the sheets 31 during the curing process. In particular, it has been found that the sheets can be efficiently heated by means of electromagnetic radiation, in particular by electromagnetic radiation in the radio frequency range.

[0092] It has been found that this method allows flitch plates 3 to be produced that can be used to mechanically stabilize the transformer core 1.

[0093] The flitch plates 3 may have a substantially planar configuration, as described in connection with Figures 1A to 3. However, other shapes may also be obtained. For example, a curved flitch plate 3 may be formed by bending the sheets 31 prior to the curing of the adhesive layers 32.

[0094] The embodiments shown in the Figures 1A to 5 as stated represent exemplary embodiments of the improved transformer core and transformer and for the method for producing the transformer core; therefore, they do not constitute a complete list of all embodiments according to the improved transformer core and transformer and for the method for producing the transformer core. Actual arrangements and methods may vary from the embodiments shown in terms of arrangements, dimensions, or components, for example.Reference Signs

[0095] 1transformer core 10transformer 2leg 20axis 21core sheet 22insulating material 25core step 29circle 3flitch plate 31sheet 32adhesive layer 320adhesive material 35side face 41yoke 411outer portion 5coil winding 99detail S1step S2step S3step

Claims

1. A transformer core (1) comprising a plurality of legs (2), wherein - the legs (2) comprise a plurality of core sheets (21), - a flitch plate (3) is attached to the core sheets (21) of one of the legs (2), the flitch plate (3) being configured to mechanically stabilize the leg (2), - the flitch plate (3) comprises a plurality of sheets (31), and - adjacent sheets (31) of the flitch plate (3) are bonded to one another via an adhesive layer (32).

2. The transformer core according to claim 1, wherein the flitch plate (3) is arranged within a circle (29) circumscribing the core sheets (21) in a cross-sectional view of the leg.

3. The transformer core according to claim 1 or 2, wherein the sheets (31) of the flitch plate (3) comprise magnetic steel.

4. The transformer core according to any one of the preceding claims, wherein the sheets (31) of the flitch plate (3) comprise grain oriented steel.

5. The transformer core according to any one of the preceding claims, wherein the sheets (31) of the flitch plate (3) have a thickness in a range from 0.1 mm to 0.5 mm.

6. The transformer core according to any one of the preceding claims, wherein the flitch plate (3) has a thickness in a range from 5 mm to 20 mm.

7. The transformer core according to any one of the preceding claims, wherein the flitch plate (3) has a stepped side face (35).

8. The transformer core according to any one of the preceding claims, wherein the transformer core (1) comprises a yoke (41) interconnecting the plurality of legs (2).

9. The transformer core according to claim 8, wherein the yoke (41) comprises an outer portion (411) that overlaps with the flitch plate (2) in a side view of the transformer core (1).

10. A transformer (10) comprising a transformer core (1) according to any one of the preceding claims and a coil winding (5) mounted to one of the legs (2).

11. A method of producing a transformer core (1), wherein a flitch plate (2) is attached to core sheets (21) of the transformer core (1), wherein producing the flitch plate (3) comprises the steps of: a) providing a plurality of sheets (31); b) arranging an adhesive material (320) between adjacent sheets (31); and c) curing the adhesive material (320) to form adhesive layers (32) .

12. The method according to claim 11, wherein the sheets (31) are heated during step c).

13. The method according to claim 11 or 12, wherein the sheets (31) are heated by means of electromagnetic radiation during step c).

14. The method according to any one of claims 11 to 13, wherein a transformer core (1) according to any one of claims 1 to 9 is produced.

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