GB2420913A

GB2420913A - Transformer assembly including a cooling arrangement

Info

Publication number: GB2420913A
Application number: GB0426567A
Authority: GB
Inventors: Wilhelm Kramer; Harry Reinold
Original assignee: Bombardier Transportation GmbH
Current assignee: Alstom Transportation Germany GmbH
Priority date: 2004-12-03
Filing date: 2004-12-03
Publication date: 2006-06-07
Also published as: GB0426567D0

Abstract

A transformer 1, or its method of manufacture, comprises a cooling device 8e arranged between and in mechanical contact with a respective surface of first and second core sections 4e, 4f. Core sections 4a-h and cooling devices 8a-f may be arranged around primary and secondary windings and are clamped together by pressure plates with a convex surface pressing on the top and bottom surfaces when tension means is applied to the ends of the said pressure plates. The cooling device 8 may include contact surfaces made from respective layers of electrically insulating material. The cooling device 8 may comprise a body formed of aluminium containing a serpentine steel tube 12. The tube 12 may carry cooling fluids such as esters and/or adiabatically expanded gas which may be of the same type used for cooling one or more of the windings of the transformer. The transformer assembly is intended to provide a compact high power and medium frequency transformer such as a railroad traction system transformer operating at 200KVA or more and 2- 25 kHz.

Description

1 2420913 Transformer The present invention relates to a transformer and a

method of manufacturing a transformer. More particularly, the present invention relates to high-power medium frequency transformers.

DE 100 58 080 Al describes a medium frequency transformer which insulates pri- mary DC (direct current) intermediate circuits from secondary DC intermediate circuits in a DC/DC converter. The medium frequency transformer has a two-part core, in addition to a primary winding and a divided secondary winding, a first and a second part of the divided secondary winding being configured on a respective side of the primary winding. Each winding may consist of a bundle of moulded hollow-cored conductors that are insulated in common and are traversed by a liq- uid coolant. In order to remove heat produced in the core, the core comprises a cooling body. Cooling tubes are provided outside of the cooling body.

In particular for high-power applications in which energy is provided to decentral- ized driving units of railroad vehicles in the range of 200 kVA and higher (in par- ticular 750 kVA and/or higher), medium frequency (in particular in the range of 2 to kHz, preferably in the range of 6 to 20 kHz) transformers can be used. How- ever, due to the combination of high power and medium frequency, significant high heat densities appear in the core and the windings.

It is an object of the present invention to provide a transformer capable of transforming electric voltages for high power applications, which is compact in size and which can be manufactured in different sizes and, thus, for different applications.

It is a further object of the invention to provide a method of manufacturing such a transformer.

It is proposed to provide a magnetic and/or magnetizable core having two or more core sections and to arrange a cooling device in between at least two of the core sections. Preferably, the cooling device is actively cooled, for example by forced circulation of a cooling fluid. In particular, the cooling device may be shaped so as to conduct the cooling fluid during operation of the transformer.

Due to the cooling device, the size of the core can be adapted to the needs and specifications. E.g. it can be adapted to different numbers of windings and/or to different values of the maximum electric power, so that the whole core can be kept at moderate temperatures in all cases. The core sections and the at least one cooling device are preferably arranged so that the magnetic flux lines are not ex- tending through the cooling device. For example, contact surfaces of a contact area of the cooling device and the core sections may be arranged so as to extend in a plane, wherein the plane is oriented parallel to the planes of the magnetic flux lines in the core.

The transformer may be part of a DC/DC transformer (e.g. for transforming a 3 kV DC main line voltage to a 1.5 kV intermediate circuit voltage) and more particularly adapted and/or used to provide energy to at least one decentralized driving unit of a railroad vehicle in the operational ranges mentioned above.

In particular, the following is proposed: A transformer, in particular a high-power medium frequency transformer, having a primary winding, a secondary winding and a magnetic and/or magnetizable core, wherein - the core comprises a first core section and a second core section, - a cooling device for cooling the core is arranged between the first core sec- tion and the second core section, - the cooling device mechanically contacts the first core section at a first sur- face of the cooling device and mechanically contacts the second core sec- tion at a second surface of the cooling device.

In particular, the first core section may extend around a first winding section of the primary winding and/or of the secondary winding and the second core section may extend around a second winding section of the primary winding and/or of the secondary winding. The first winding section and the second winding section are consecutive winding sections along a path of an electric current carried by the pri- mary winding and/or the secondary winding. In this embodiment, the core sec- tions may consist of two U-shaped halves. However, the principle of arranging a cooling device in between two core sections is not limited to the use of U-shaped cores. "Extending around" does not mean that the core needs to form a complete closed loop around a winding section and/or needs to perform a single closed or open loop around the windings. Rather, the core may comprise an E-shaped or I- shaped cross section, for example. More generally speaking, the first core section may extend along a plane perpendicular to the current path of the first winding section and the second core section may extend along a plane perpendicular to the current path of the second winding section (if the core sections are I-shaped,

for example).

The magnetic and/or magnetizable material of the core may be an amorphous material or a nano-crystalline material or a ferrite. In particular, the core may comprise a plurality of layers of a magnetic and/or magnetizable material, wherein the layers extend in parallel to each other around the primary winding and/or the secondary winding. In this embodiment, it is preferred that the first surface and the second surface of the cooling device mechanically contact faces of each of the plurality of layers which are arranged in parallel to each other. The first surface may contact all layers of the first core section and the second surface may contact all layers of the second core section.

It is an advantage of the present invention that cores of arbitrary height (measured in the direction which is circumferenced by the core) can be used in the trans- former. If the height becomes too large, the core can be divided into more sections and a cooling device may be provided between each pair of neighbouring core sections. Due to the more effective cooling (i.e the lower temperatures during op- eration of the transformer), a core with a smaller cross section can be used. As a consequence, the lengths of the windings can be reduced and the total dimen- sions of the transformer and the ohmic losses become smaller.

The first surface of the cooling device and the second surface of the cooling de- vice may be located at opposite sides of the cooling device. In particular, the cool- ing device may comprise a single cooling body made of a heat conducting material (for example metal, in particular aluminium). The cooling body forms the outlines of the cooling device, but does not necessarily form the first and second surface (see below). In addition, the cooling body may contain and/or may be combined with devices for conducting a cooling fluid (see below). For example, a liquid such as pure (de-ionized) water can be used as the cooling fluid. Alternatively, cooling oil, cooling ester (e.g. polyol ester), a refrigerating medium and/or adiabatically expanded gas (e.g. air) can be used as the cooling medium, for example.

In a method of operating the transformer in one of the embodiments described in this description, the cooling device may comprise a cooling body which contains and/or which is combined with a conducting device for conducting a cooling fluid.

In this case, the same type of cooling fluid may be used for cooling the cooling device and for cooling the primary and/or secondary winding of the transformer.

For example, the cooling fluid comprises one of the cooling fluids mentioned be- fore, in particular an ester and/or adiabatically expanded gas. Since the same type of cooling fluid is used, the same equipment can be used for cooling both the winding or windings and the cooling device (i.e. the core).

According to a preferred embodiment, the gas is compressed (in a closedcircuit cooling circuit) using a rotary vane compressor and is adiabatically expanded dur- ing the cooling process using corresponding expanding element (e.g. an expand- ing nozzle). This type of compressors is particularly energy-effective during opera- tion and can be manufactured at low costs. This arrangement can be used for cooling the transformer winding or windings and/or for cooling the cooling device.

Weight and required space for the arrangement can be reduced compared to a conventional cooling arrangement with de-ionized water.

In particular, the cooling device may comprise a tube for conducting a cooling fluid, wherein the tube is embedded in a block of thermally conducting material (e.g. the cooling body described above). More particularly, the tube may be adapted to conduct the cooling fluid in serpentines. In particular, the tube may comprise a single flow path for the cooling fluid, wherein the flow path comprises a serpentine- like section. However, other embodiments adapted to conduct the cooling fluid inside the cooling device are also possible. For example, the cooling device may comprise two parts of a cooling block, wherein the parts comprise corresponding cut-outs to form a canal for the cooling fluid when the parts are attached to each other.

Additional cooling devices may be arranged at at least one outer side of the core.

These cooling devices may be constructed in the same manner as the at least one cooling device between the first and the second core section.

The first surface and/or the second surface of the cooling device may be formed by an insulating layer of an electrically insulating material. Thus, the cooling de- vice can be electrically insulated from the core.

The first surface and the second surface of the cooling device may be essentially planar surfaces abutting on (i.e. mechanically contacting) the first core section or on the second core section.

Preferably, the first core section and the second core section each form a flat sur- face. The flat (in particular planar) services are arranged so as to face each other, i.e. the flat surfaces are viewing the flat surface of the other (neighbouring) core section. However, at least one cooling device is arranged between the first core section and the second core section so that the whole area of the flat surfaces is mechanically contacted by the first surface of the cooling device or by the second surface of the cooling device. As a result, hot spots or areas in the core sections can be avoided, in particular if the core is constituted by layers as described above.

According to a preferred embodiment, the first core section, the cooling device and the second core section form a stack and are pressed together so as to mechani- cally contact each other under pressure. Thus, the heat transfer from the core sections to the cooling device can be improved.

In particular, a pressure device for generating the pressure may comprise an abut- ting part which abuts on an outer surface of the stack, wherein the abutting part comprises a convex surface which is pressed against the outer surface by ten- sions applied at opposite sides of the abutting part. More particularly, the abutting part is made of an elastic material (preferably an electrically insulating material) and/or the outer surface of the stack is (essentially) a flat, planar surface. Thus, the pressurising force applied via the abutting part onto the stack produces a ho- mogeneous pressure.

Furthermore, a method of manufacturing a transformer, in particular a high-power medium frequency transformer, may comprise the steps: providing a primary winding; - providing a secondary winding; - providing a magnetic and/or magnetizable core having a first core section and a second core section; and - arranging a cooling device for cooling the core between the first core sec- tion and the second core section so that the cooling device mechanically contacts the first core section at a first surface of the cooling device and mechanically contacts the second core section at a second surface of the cooling device.

In the following, optional details of the present invention will be described with ref- erence to the drawing which shows the most preferred embodiment of the inven- tion. However, the invention is not restricted to this embodiment. Any detail and feature of the embodiment can be combined with other embodiments. The figures of the drawing show: Fig. I a side view of a transformer; Fig. 2 a sectional view along the line A - A in Fig. 1; Fig. 3 a sectional view along the line B - B in Fig. 1; Fig. 4 a sectional view along the line C - C in Fig. 1; Fig. 5 a perspective view of a stack of core sections and cooling devices form- ing an E-shaped half of the core arrangement of the transformer of Fig. 1; Fig. 6 a perspective view of a stack of core sections with additional fastening means for pressu rising the stack; Fig. 7 a face view of a stack corresponding to the stack of Fig. 5; Fig. 8 a cooling device to be arranged between core sections of the trans- former of Fig. 1; Fig. 9 a partial view of a tube for conducting cooling fluid through a cooling device; Fig. 10 a part for pressurising the stack of Fig. 5.

The transformer I shown in Fig. I comprises a core unit 3 and a winding unit 5.

The left half 3a of the core unit 3 is shown in Fig. 5. It comprises four U-shaped core sections 4a, 4b, 4c, 4d. Each two of the core sections 4a, 4b and 4c, 4d are stacked upon each other to form a space 6a, 6b for receiving a section of the winding unit 5.

Fig. 2 shows a corresponding sectional view showing the other (right) half 3b of the core unit 3 which is constructed in the same manner as the left half 3a. Sec- tions of the winding unit 5 are located in the two spaces 6c, 6d formed by the four U-shaped core sections 4e, 4f, 4g, 4h. Other sections of the winding unit 5 are lo- cated above and below the core unit 3. As can be recognised from Fig. I and Fig. 4, the core sections 4a, 4e and 4b, 4f and 4c, 4g and 4d, 4h contact each other at the open end of the U to form a double 0-shaped (see Fig. 4) core, i.e. spaces 6a, 6c and 6b, 6d each form one space with 0-shaped boundaries.

The core sections 4 comprise a plurality of layers 7a, 7b, 7c, 7d made from mag- netic or magnetizable material (see for example Fig. 7 which shows the second half 3b of the core unit 3). The layers 7 extend in parallel to each other half way around the spaces 6. Fig. 7 is a schematic drawing and the layers 7 are indicated for two of the faces of the core sections 4 only, namely for the faces on the right hand sides of core section 4g and of core section 4h. However, all faces of the core sections 4 show the same structure of the layers 7. Furthermore, in reality there are more layers arranged in parallel to each other than shown in the schematic view of Fig. 7.

Since the heat resistance for heat transfer from any of the layers 7 to its neighbouring layer(s) is high, heat can be removed from the layers via their faces in a much more effective way. Therefore, cooling devices 8 are located at the top of the core unit 3, between the upper core sections 4a, 4c, 4e, 4g and the lower core sections 4b, 4d, 4f, 4h and at the bottom of the core unit 3. Correspondingly, each of the cooling devices 8 mechanically contacts faces (showing U-shaped lines) of the layers 7 in order to remove heat from the core unit 3.

In the embodiment shown in the figures, six separate cooling devices 8a, 8b, 8c (for example shown in Fig. 5) and 8d, 8e, 8f (for example shown in Fig. 2) are pro- vided. Each of the cooling devices 8a, 8d (at the top of the core unit 3) and 8c, 8f (at the bottom of the core unit 3) is in contact with two core sections 4. The cool- ing devices 8b, 8e are in contact with four core sections 4, namely with two core sections above and with two core sections below each cooling device (see Fig. 1).

Thus, the cooling devices 8b, 8e comprise a first contact surface 9a for mechani- cally contacting the core sections 4 above them and a second contact surface 9b for mechanically contacting the core sections 4 below them (Fig. 7). The first con- tact surface 9a and the second contact surface 9b are located at opposite sides of the respective cooling device 8b, 8e.

Fig. 8 shows one of the cooling devices (8b) having two contact surfaces. Fig. 3 shows a cross-section of the transformer I through both cooling devices 8b, 8e with two contact surfaces. Each of the contact surfaces (and the same applies to the contact surfaces of the other cooling devices 8a, 8c, 8d, 8f) comprises two U- shaped recesses II for receiving an electrically insulating, U-shaped foil 10. Only one of the two foils 10 for the cooling device 8b is shown in Fig. 8. The foil 10 is placed in the recess 11, so that it separates (and electrically insulates) the corresponding core section 4 and the cooling device 8 from each other. The foil is forming the outer surface of the cooling device 8b. A good thermal contact is pro- vided from the core section 4 via the foil 10 to the cooling device 8.

As can be recognised from the Fig. 3, a serpentine-shaped tube 12a, 12b is embedded in the cooling device 8b, 8e. The same applies to the other cooling devices 8a, 8c, 8d, 8f. Each of the cooling devices 8 comprises an E-shaped cross-section having two outer legs 14a, 14b and a middle leg 14c. The first outer leg 14a and the middle leg I 4c define opposite boundaries of the space 6b for receiving the winding unit 5. The second outer leg 14b and the middle leg 14c are defining opposite boundaries of the space 6a for receiving another section of the winding unit 5. The tube I 2a extends (in consecutive order of the flow direction) from a fluid inlet 13a via the first outer leg 14a, via the middle leg 14c and via the second outer leg 14b to a fluid outlet 13b. Thus, the whole surface area which is in contact with the core sections 4 can be cooled in the same effective manner.

All cooling devices basically have the same configuration concerning the shape and arrangement of the tube. However, the inlets and outlets of the cooling de- vices 8a, 8c, 8d, 8f at the top and at the bottom of the core unit 3 are both located on the same side of the respective cooling device, whereas the inlets and the out- lets of the cooling devices 8b, 8e are located at opposite sides of the respective cooling device. Therefore, the cooling devices 8a, 8b, 8c and 8d, 8e, 8f can easily be connected in order to form two series connections for the cooling fluid. During operation of the transformer 1, the same cooling fluid flows through the cooling device 8a, 8d at the top, then through the cooling device 8b, 8e in the middle and finally through the cooling device 8c, 8f at the bottom. Corresponding connection ducts 15a to 15d are shown in Fig. 1.

The tube 12a, 12b is embedded in the cooling device 8. According to a preferred way of manufacturing the cooling device 8, a tube (e.g. made of steel) may be provided which comprises a circular cross-section 16 (Fig. 9). First, the tube may be bent and/or assembled from separate pieces to form the serpentine-like flow path shown in Fig. 3. Then, the tube is compressed in a direction perpendicular to the plane of the serpentine so that tube comprises an oval cross-section 17. It is preferred that the material (e.g. aluminium) which will form the outer shape of the cooling device is molten, the tube 12 is positioned in the molten material and the arrangement is cooled down so that the molten material is solidified. Preferably, the tube 12 is covered by a thin section of the solidified material so that the heat resistance for heat transfer from the core section 4 via the foil 10 and via the solidi- fied material to the tube 12 is small. For example, the thin covering section may be less than 2 mm in thickness, preferably less than 1mm thick, in its thinnest ar- eas (i.e. where the tube's outer surface is nearest to the surface of the cooling de- vice).

As shown in Fig. 6 and in Fig. 1, the cooling devices 8 and the core sections 4 are stacked and the stack is pressed together in the vertical direction shown in Fig. 1.

In each case three spring-like parts 18a, 18b, 18c and 18d, 18e, 18f are arranged at the top of the stack and at the bottom of the stack (or, more generally speaking, at opposite sides of the stack). Tensioning rods I 9a, 19b, I 9c for applying the pressure onto the stack are provided. Each of the rods 19a, 19b, 19c connects one of the spring-like parts I 8a, 18b, I 8c with a spring-like part I 8d, I 8e, I 8f on the opposite side of the stack. The T-shaped fastening parts 20a, 20b, 20c, 20d shown in Fig. 6 are used to fasten the core unit 3 to the winding unit 5 (Fig. 1). The whole arrangement may be fixed to a plate 22 (Fig. 1).

Fig. 10 shows the spring-like part 18b. The construction is identical to the construction of the other spring-like parts 18, except for the fastening holes at the opposite ends of the parts 18. The parts 18 may be made of a synthetic resin and/or may be reinforced with fibre material. Preferably, the material is resin reinforced with glass fibre. The lower surface of the part 18b shown in Fig. 10 is convex when the part I 8b is not pressed against the outer surface of the cooling device 8. In this case, the upper surface of the part I 8b is planar. Thus, the thickness of the part 1 8b is smaller in the end sections 20a, 20b (thickness value x) compared to the thickness in the middle region 21 (thickness value y).

In the process of tensioning the tensioning rods 19, the lower surface is pressed against the cooling devices 8 in the middle region 21 first. By increasing the ten- sion, the part 18b is bent so that an increasingly larger section of the part 18b is pressed against the cooling devices 8. At the end of the tensioning process, the

II

pressure applied by the part 18 to cooling devices 8 is constant (e.g. does not de- pend on the section of the lower surface area).

In the course of assembling the transformer 1, the two halves 3a, 3b of the core unit 3 are assembled (Fig. 5) by stacking the cooling devices 8 and the core sec- tions 4. Then, the two halves 3a, 3b are combined with the winding unit 5, for ex- ample by moving the halves 3a, 3b from opposite sides of the winding unit 5 so as to form the double 0-shaped spaces 6 filled with the sections of the winding unit 5.

The winding unit 5 comprises an outer insulation 25, a primary winding 27 and a secondary winding 26, which is divided into an outer secondary winding 26a and an inner secondary winding 26b (Fig. 2, Fig. 4). The outer secondary winding 26a and the primary winding 27 are separated from each other by an insulating layer 28a. The inner secondary winding 26b and the primary winding 27 are separated from each other by an insulating layer 28b. The outer secondary winding 26a and the inner secondary winding 26b are electrically connected in series to each other.

The primary winding 27 and the secondary winding 26a, 26b preferably comprise hollow-cored electrical conductors, wherein cooling fluid is flowing through the conductors during operation of the transformer 1. Thus, cooling of the transformer 1 can be performed in a highly effective manner, without hot spots or hot areas.

Claims

Claims A transformer (1), in particular a high-power medium frequency

transformer, having a primary winding (27), a secondary winding (26) and a magnetic and/or magnetizable core (3), wherein - the core (3) comprises a first core section (4a) and a second core sec- tion (4b), - a cooling device (8b) for cooling the core (3) is arranged between the first core section (4a) and the second core section (4b), - the cooling device (8b) mechanically contacts the first core section (4a) at a first surface (9a) of the cooling device (8b) and mechanically contacts the second core section (4b) at a second surface (9b) of the cooling device (8b).
2. The transformer of claim 1, wherein the first core section (4a) extends around a first winding section of the primary winding and/or of the secondary winding, wherein the second core section (4b) extends around a second winding section of the primary winding and/or of the secondary winding and wherein the first winding section and the second winding section are consecutive winding sections along a path of an electric current carried by the primary winding and/or the secondary winding.
3. The transformer of one of the preceding claims, wherein the first surface (9a) of the cooling device (8b) and the second surface (9b) of the cooling device (8b) are located at opposite sides of the cooling device (8b).
4. The transformer of one of the preceding claims, wherein the core (3) com- prises a plurality of layers (7) of a magnetic and/or magnetizable material, wherein the layers (7) extend in parallel to each other around the primary winding (27) and/or the secondary winding (26), and wherein the first sur- face (9a) and the second surface (9b) of the cooling device (8b) mechani- cally contact faces of each of the plurality of layers (7).
5. The transformer of one of the preceding claims, wherein the first surface (9a) and/or the second surface of the cooling device is formed by an insu- lating layer (10) of an electrically insulating material.
6. The transformer of one of the preceding claims, wherein the cooling device (8b) comprises a tube (12) for conducting a cooling fluid and wherein the tube (12) is embedded in a block of thermally conducting material.
7. The transformer of one of the preceding claims, wherein the cooling device comprises a cooling body which contains and/or which is combined with a conducting device (12) for conducting a cooling fluid and wherein the cool- ing fluid comprises an ester and/or adiabatically expanded gas.
8. The transformer of one of the preceding claims, wherein the first surface (9a) and the second surface (9b) of the cooling device (8b) are essentially planar surfaces abutting on the first core section (4a) or on the second core section (4b).
9. The transformer of one of the preceding claims, wherein an additional cool- ing device (8a, 8c) is arranged at an outer side of the core (3).
10. The transformer of one of the preceding claims, wherein the first core sec- tion (4a), the cooling device (8b) and the second core section (4b) are form- ing a stack and are pressed together so as to mechanically contact each other under pressure.
11. The transformer of the preceding claim, wherein a pressure device for generating the pressure comprises an abutting part (18), which abuts on an outer surface of the stack and wherein the abutting part (18) comprises a convex surface which is pressed against the outer surface by tensions applied at opposite sides of the abutting part (18).
12. A method of operating the transformer of one of the preceding claims, wherein the cooling device comprises a cooling body which contains and/or which is combined with a conducting device (12) for conducting a cooling fluid and wherein the same type of cooling fluid is used for cooling the cool- ing device and for cooling the primary and/or secondary winding of the transformer.
13. A method of manufacturing a transformer, in particular a high-power me- dium frequency transformer, wherein the method comprises the steps: providing a primary winding (27); - providing a secondary winding (26); providing a magnetic and/or magnetizable core (3) having a first core section (4a) and a second core section (4b); and - arranging a cooling device (8b) for cooling the core (3) between the first core section (4a) and the second core section (4b) so that the cooling device (8b) mechanically contacts the first core section (4a) at a first surface (9a) of the cooling device (8b) and mechanically con- tacts the second core section (4b) at a second surface (9b) of the cool- ing device (3).