EP2801989B1

EP2801989B1 - Transformer with improved cooling

Info

Publication number: EP2801989B1
Application number: EP13166747.9A
Authority: EP
Inventors: Andreas Ecklebe; Daniel Kearney; Uwe Drofenik
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2013-05-07
Filing date: 2013-05-07
Publication date: 2015-11-04
Anticipated expiration: 2033-05-07
Also published as: EP2801989A1

Description

TECHNICAL FIELD

The present disclosure generally relates to electromagnetic devices, in particular transformers. In particular, it relates to medium frequency transformers with improved cooling.

BACKGROUND OF THE INVENTION

Cooling is a critical aspect in the design of transformers, as heat is inevitably generated by the current flowing through the windings. It is also a critical enabler for the advancement of electromagnetic components. The power density of a transformer is limited by the maximum operating temperatures, which are a result of ambient temperature, core and windings transformer losses and thermal resistances. For low frequency transformers, the losses are mainly located in the windings and are simply cooled by air or oil convection through the windings. However, increasing the frequency of the transformer will decrease the volume and hence increase the overall power density. Contemporary designers of such devices can direct the losses to both core and the windings. Therefore, an optimized cooling solution is required to address both. However, in most cases only one element - either the core or the windings - is cooled by a system which is complex and expensive. Some solutions employ a bobbin between a winding and the core on which it is wound, wherein the bobbin serves for maintaining an air gap between core and winding, enabling a coolant flow. From US 2 992 405 a transformer is known, in which improved cooling is obtained by means of copper tabs which are connected to bobbin members. However, for example due to a restricted space for the bobbin due to size limitations, such configurations are still improvable.
In view of the above, there is a need for electromagnetic devices which avoid the disadvantages of the known solutions.

SUMMARY OF THE INVENTION

The problems mentioned above are at least partly solved by an electromagnetic device according to claim 1.
In a first aspect, an electromagnetic device is provided. It comprises a core, at least one winding having a middle axis and defining two boundary parallel planes perpendicular to the axis, the winding being located in an intermediate region between the planes, a bobbin including a thermally conductive material, having elongated elements extending between the planes in thermal contact with the core and the at least one winding, and at least one heat sink portion in thermal contact with an end portion of at least one elongated element and at least partially protruding in a region outwards from the intermediate region, wherein the at least one heat sink portion comprises at least one cooling element chosen from the list consisting of: fins, pins, rods, and ripples, for enhancing a heat exchanging surface of the at least one heat sink portion.
Further aspects, advantages and features of the present invention are apparent from the dependent claims, the description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure, including the best mode thereof, to one of ordinary skill in the art is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein:

Fig. 1 schematically shows a perspective view of an electromagnetic device according to embodiments;
Fig. 2 schematically shows a front view of the electromagnetic device of Fig. 1;
Fig. 3 schematically shows a side view of the electromagnetic device of Fig. 1;
Fig. 4 schematically shows a perspective view of a bobbin of the electromagnetic device of Figs. 1 to 3.
Fig. 5 shows a heat sink portion of an electromagnetic device according to embodiments.
Fig. 6 shows a further heat sink portion of an electromagnetic device according to embodiments.
Fig. 7 shows a yet further heat sink portion of an electromagnetic device according to embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. It is intended that the present disclosure includes such modifications and variations.
Within the following description of the drawings, the same reference numbers refer to the same components. Generally, only the differences with respect to the individual embodiments are described. When several identical items or parts appear in a figure, not all of the parts have reference numerals in order to simplify the appearance.
The systems and methods described herein are not limited to the specific embodiments described, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. Rather, the exemplary embodiment can be implemented and used in connection with many other applications.
Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
Embodiments described herein generally relate to electromagnetic devices, such as transformers, inductors, or coils, having a core and a winding provided on the core. Thereby, the winding is wound on a bobbin of thermally conductive material, wherein the bobbin has at least one heat sink portion, which extends out of an intermediate region defined by two planes delimiting the winding, the planes being perpendicular to a longitudinal axis of the winding.
Fig. 1 shows an electromagnetic device 10 according to embodiments. It comprises a core 20 having at least one leg 22. At least one winding 30 is wound about the leg 22 of core 20. The winding has a middle axis L, which is typically also a middle axis of leg 22 of core 20. Winding 30 is, for illustrational purposes, only schematically shown represented by a few loops in Fig. 1, whereas in typical embodiments, it goes without saying that the number of loops in the winding is significantly higher. Between the winding 30 and the core 20, a bobbin 40 is provided. The bobbin typically includes a thermally conductive, dielectric material, typically a polymer. Examples are thermally conductive plastics, or carbon fibre where the thermally conductive fibers are aligned in a normal direction to the core.
The winding 30 extends between two substantially parallel boundary planes a, b, which are perpendicular to the middle axis L of the winding. The planes a and b are exemplarily shown with the dashed lines protruding in oblique angles in Fig. 1. The winding 30 is located in an intermediate region A between the planes a, b. Also between the planes a, b extend elongated elements 42, 44, 46, 48 of the bobbin 40, which are typically arranged about edge portions of the leg 22 of the core 20, and are in thermal contact with the core 20 with their inner sides directed towards the middle axis L. On their outer sides, which are directed away from the middle axis L, the elongated elements 42, 44, 46, 48 are in thermal contact with the winding 30. Winding 30, which is in contact with the elements, is in the following also called inner winding 30. A second or outer winding 32 (not shown in Fig. 1) may in embodiments be wound on the outer face of the inner winding 30. Second winding 32 is typically also limited by the planes a, b and typically has the same middle axis L as the inner winding 30.
In embodiments, the elongated elements 42, 44, 46, 48 abut heat sink portions 50, 51, 52, 53, 54, 55, 56, 57 of the bobbin 40 at their end portions. Typically, but not necessarily, in embodiments the heat sink portions are integrally formed during manufacturing with the elongated elements from the same material. Typically, each elongated element 42, 44, 46, 48 has two heat sink portions, which are located at its two end portions. The heat sink portions 50, 51, 52, 53, 54, 55, 56, 57 comprise cooling elements 75 which serve for enhancing the surface area of the bobbin 40 for exchanging thermal energy with a surrounding coolant medium. Typically, this is a gaseous dielectric medium such as air, and can also exclusively comprise gases such as nitrogen or argon. In embodiments, the cooling medium may be a fluid, such as oil, deionized water or a refrigerant.
In Fig. 2, the heat sink portions 50, 51, 52, 53, 54, 55, 56, 57 including the cooling elements 75 are shown with respect to the planes a, b, and the intermediate region A enclosed by the planes. Outwards from the planes a, b, the regions B are located. The heat sink portions protrude in regions B outwards from the intermediate region A located between the planes a, b. In Fig. 1 and Fig. 2, the cooling elements 75 have the shape of elongated rods 75. A variety of different shapes of the cooling elements for enhancing the surface of the heat sink portion(s) is possible according to embodiments, such as ripples, fins, pins, and the likes. Also, in embodiments there may be only one cooling element 75 per heat sink portion 50, 51, 52, 53, 54, 55, 56, 57, the element having an elevated surface due to modifications of the surface, such as ripples or fins or a wave structure, or combinations thereof. It goes without saying that the person skilled in the art may deduce a number of varying designs for the heat sink portion and the cooling elements 75, which are thus regarded to fall under the scope of the present disclosure.
Fan 11 serves for enforcing a coolant flow along axis L of device 10. The arrows symbolize a coolant stream, e.g. air, from the fan over the device 10. For illustrational purposes, only one half of the flow is shown, and only the portion in the left lower segment of Fig. 2. When the air hits cooling element 75, respectively heat sink portion 50 adjacent the fan, a turbulent flow is caused, further enhancing the heat exchange of the air with the heat sink portion 50. A part of the air enters the space between the winding 30 and the leg 22 of core 20 through passage 70 (not visible in Fig. 2, refer e.g. to Fig. 3) in side element 64. After streaming along the core 20 and winding 30, it leaves through passage 70 in element 68 and a part of the air stream flows turbulently around heat sink portion 54 with cooling elements 75. The advantageous turbulent behavior of the flow around the heat sink portions is promoted by the fact that the heat sink portions have at least one surface oriented perpendicular to the direction of air flow, i.e., also perpendicular to axis L. Differently expressed, the heat sink portion 50, 51, 52, 53, 54, 55, 56, 57 typically comprises at least one face perpendicular to the axis L, from which the at least one cooling element 75 protrudes.
Typically, the length of the at least one heat sink portion 50, 51, 52, 53, 54, 55, 56, 57, measured from one of the boundary planes a, b outwards in a direction parallel to the middle axis L, is at least 10 percent of the length of the bobbin 40 between the planes a, b. Thereby, the typical length of a heat sink portion in a region B, measured in the direction of axis L, is at least 5 percent, more typically at least 10 percent, e.g. 12, 15, 18, or 20 percent of the width of the winding 30 (region A) between planes a and b.
In embodiments, the elongated elements 42, 44, 46, 48 are typically substantially parallel to each other. They are connected at their end portions by elongated side elements 60, 61, 62, 63, 64, 65, 66, 67, 68. In embodiments according to Fig. 1 and Fig. 2, eight side elements are present. They are typically arranged in the form of two squares at the end of the parallel elongated elements 42, 44, 46, 48. Hence, the elongated elements and the eight side elements together form a cuboid, with the elongated elements 42, 44, 46, 48 and the side elements 60, 61, 62, 63, 64, 65, 66, 67, 68 forming the edges of the cuboid. In some embodiments, the number of elongated and side elements may differ, and they may together form a polyhedron. In an example, the leg 22 of core 20 may have a hexagonal cross section, such that the number of elongated elements is six, accordingly arranged at the edges of the hexagonal shaped leg 22.
In embodiments according to Figs. 1 to 3, at least some of the side elements 60, 61, 62, 63, 64, 65, 66, 67, 68 have at least one passage 70 arranged perpendicular to their longitudinal axes. The passages 70 enable the coolant to flow along the leg 22 of core 20 in a direction parallel to the longitudinal axis L. Thus, a coolant enters a space between the inner winding 30 and the leg 22 through a passage 70. It flows along the leg 22 of core 20 and takes up thermal energy from the inner side of the inner winding 30, from the core 20 and from the elongated elements 42, 44, 46, 48. Subsequently, after flowing along axis L, it flows through another passage 70 out of the electromagnetic device 10. Typically, two, or all four side elements arranged adjacent a plane a, b in a square, comprise one or more passages 70. By enforcing a flow of the coolant via a fan in a direction of axis L, for example, the device may be more efficiently cooled. Additionally, before and after entering a passage 70, a part of the coolant streams around the heat sink portions 50, 51, 52, 53, 54, 55, 56, 57 with the cooling elements 75. A bobbin 40 according to embodiments of a device 10 as shown in Figs. 1 to 3 is shown in Fig. 4.
In embodiments, at least one of the heat sink portions 50, 51, 52, 53, 54, 55, 56, 57, preferably all of the heat sink portions, each comprise at least 2, more typically at least 4, even more preferably at least 8 cooling elements 75. Typically, the at least one heat sink portion 50, 51, 52, 53, 54, 55, 56, 57 comprises multiple cooling rods as cooling elements 75. Typically, they extend in parallel to the middle axis L. Thus, there exists at least one cross section through the at least one heat sink portion 50, 51, 52, 53, 54, 55, 56, 57, which exhibits at least 2, 4 or 8 distinct areas representing the thermally conductive material of the heat sink portion. Such a heat sink portion is exemplarily shown in Fig. 5.
Fig. 6 shows an example of a heat sink portion 54, having 12 cooling elements 75, as of an electromagnetic device 10 according to embodiments. The elements 75 are arranged in a 4 x 3 matrix. Fig. 6 shows a further example of a heat sink portion 54 having three cooling elements 75 in the form of fins. It goes without saying that the number, shape, arrangement, and size of the cooling elements 75 of a heat sink portion may be varied in a wide range according to embodiments of device 10. The number of elements may range from 1 to well over a hundred, more typically the number is from 2 to 40, even more typically from 4 to 20. A characteristic parameter of a heat sink portion is the maximal number of distinct areas representing the thermally conductive material, when a cross sectional view through the heat sink portion is regarded. It is easily retrieved that the heat sink portion in Fig. 5 shows 12 distinct areas, whereas in Fig. 6, there are three distinct areas. This number is typically, but not necessarily identical to the number of cooling elements 75 in a heat sink portion 50, 51, 52, 53, 54,55,56,57.
In embodiments, the bobbin 40 comprises an orthotropic thermally conductive material. Examples for the material are thermally conductive plastics, or carbon fiber materials (such as DIALEAD K13C6U). The material has at least one orientation with a higher thermal conductivity than it has in other orientations. Typically, the orthotropic material is provided in an orientation which promotes the heat conduction in a direction from the elongated elements 42, 44, 46, 48 towards the heat sink portions 50, 51, 52, 53, 54, 55, 56, 57. In Fig. 4, a bobbin from a device 10 according to embodiments is shown. The orthotropic material has its direction of optimal heat conduction in a direction of the elongation of elongated elements 40, 42, 44,46.
In embodiments, the electromagnetic device 10 can be a transformer, or an inductor. More specifically, the device 10 may be a dry type transformer or a liquid-cooled transformer. Typically, it is a medium frequency transformer, for example for operating frequencies from 1 kHz to 500 kHz.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims.

Claims

An electromagnetic device (10), comprising:
a core (20),

at least one winding (30) having a middle axis (L) and defining two boundary parallel planes (a, b) perpendicular to the axis, the winding being located in an intermediate region (A) between the planes (a, b),

a bobbin (40) comprising a thermally conductive material, having elongated elements (42, 44, 46, 48) extending between the planes (a, b) in thermal contact with the core (20) and the at least one winding (30), and at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57) in thermal contact with an end portion of at least one elongated element (42, 44, 46, 48) and at least partially protruding in a region (B) outwards from the intermediate region (A),

wherein the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57) comprises at least one cooling element (75) chosen from the list consisting of: fins, pins, rods, and ripples, for enhancing a heat exchanging surface of the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57).
The device of claim 1, wherein the length of the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57) from the boundary plane (a, b) outwards in a direction parallel to the middle axis (L) is at least 10 percent of the length of the bobbin between the planes (a, b).
The device of claims 1 or 2, wherein the elongated elements (42, 44, 46, 48) are substantially parallel to each other, and are connected at their end portions by elongated side elements (60, 61, 62, 63, 64, 65, 66, 67, 68).
The device of claim 3, wherein at least one of the elongated side elements (60, 61, 62, 63, 64, 65, 66, 67, 68) has at least one passage (70) perpendicular to its longitudinal axis, which enables a dielectric coolant to flow along the core (20) in a direction parallel to the longitudinal axis (L) of the winding (30).
The device of any preceding claim, wherein the elongated elements (42, 44, 46, 48) are located parallel and adjacent to edges of a leg (22) of the core (20), around which the winding (30) is provided.
The device of any preceding claim, wherein the elongated elements (42, 44, 46, 48) and the side elements (60, 61, 62, 63, 64, 65, 66, 67, 68) of the bobbin are arranged on the edges of a polyhedron, preferably a cuboid.
The device of any preceding claim, wherein the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57) comprises at least 4, preferably at least 8 cooling elements (75).
The device of any preceding claim, wherein the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57, 58) comprises multiple rods as cooling elements (75), extending in parallel to the middle axis (L).
The device of any preceding claim, wherein the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57) has at least one cross section which exhibits at least four distinct areas representing the thermally conductive material of the heat sink portion (50, 51, 52, 53, 54, 55, 56, 57).
The device of any preceding claim, wherein the at least one heat sink portion (50, 51, 52, 53, 54, 55, 56, 57) comprises at least one face perpendicular to the axis (L), from which the at least one cooling element (75) protrudes.
The device of any preceding claim, wherein the bobbin (40) comprises an orthotropic thermally conductive material.
The device of claim 11; wherein the bobbin (40) comprises the conductive orthotropic material in an orientation which promotes the heat conduction in a direction from the elongated elements (42, 44, 46, 48) towards the heat sink portions (50, 51, 52, 53, 54, 55, 56, 57).
The device of any preceding claim, wherein the device is at least one of: a dry type transformer, and a medium frequency transformer.
The device of any preceding claim, wherein the device is a transformer having a nominal power rating from 10 kW to 500 kW.
The device of any preceding claim, wherein the core is one of: an E-shaped type, and a D-shaped type.