EP2406871A1

EP2406871A1 - Rotating transformer for supplying the field winding in a dynamoelectric machine

Info

Publication number: EP2406871A1
Application number: EP10709470A
Authority: EP
Inventors: Hossein Safari Zadeh
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2009-03-11
Filing date: 2010-03-09
Publication date: 2012-01-18
Also published as: WO2010102987A1; CN102349221A; CH700533A1; US8228010B2; US20120038308A1

Abstract

The invention relates to a rotating transformer that is suitable in particular for supplying current to the excitation winding of a synchronous machine. A stationary primary winding arrangement (3) is fed by an alternating voltage source (4). A secondary winding arrangement (2) is attached to a rotor (1), which secondary winding arrangement is inductively coupled with the primary winding arrangement. In order to enable a simple installation, the primary winding arrangement comprises at least two primary windings (32), which each extend over a predetermined sector relative to the direction of rotation of the rotor. It thus becomes possible to install the primary windings separately and to arrange the device in a space-saving manner in areas of a dynamoelectric machine otherwise remaining unused.

Description

TITLE

Rotating transformer for supplying the field winding in a dynamoelectric machine

TECHNICAL AREA

The present invention relates to a device for transmitting electrical energy from a stator to a rotor. Such a device is also referred to as a rotating transformer. The invention also relates to a dynamoelectric machine equipped with such a rotary transformer.

STATE OF THE ART

Electric generators constructed as synchronous machines have one or more field windings (field windings) on the rotor (rotor). An excitation winding is a conductor arrangement which, in operation, generates a DC magnetic field which rotates with the rotor in order to induce an AC voltage in the windings of the stator (stator). To energize the rotating field winding, brushes and slip rings may be present. However, these are susceptible to wear. Therefore, a so-called brushless exciter is often provided in which an auxiliary generator designed as an external pole generator is provided, which supplies the excitation winding of the actual generator with electricity. In this auxiliary generator, a rotor winding mounted on the rotor rotates in a static magnetic field generated in the stator. The voltage generated in the rotor winding of the auxiliary generator is after appropriate rectification to supply the field winding of the actual generator available. However, such an auxiliary generator requires a relatively large amount of space.

In WO 95/26069 it has therefore been proposed to use a rotating transformer for transmitting electrical energy from the stator to the rotor instead of an auxiliary generator.

The proposed there rotary transformer comprises two concentric around the

Rotary axis wound coils, which face axially along the axis of rotation.

Due to this construction, the rotating transformer in practice only on

End of the rotor shaft are arranged, which significantly limits the design freedom, so that this solution especially for large-scale used

Generators is not very suitable.

Also in US 6,483,218 a dynamoelectric machine has been proposed with such a rotating transformer. Here, the transformer also includes two wound around the rotor axis, concentric windings, wherein the primary winding is disposed radially outside the secondary winding and this partially surrounds. However, this arrangement also greatly restricts the possible designs of the dynamoelectric machine. In addition, a very specific sequence must be observed during assembly.

In US 3,758,845 a rotary transformer for an electrical machine has been proposed in which on an outer surface of the rotor, a flat, rectangular secondary winding is mounted, which faces a corresponding primary winding radially. Although this transformer allows for easy installation and allows flexible designs for a dynamo-electric machine equipped therewith, but is by design only suitable for the transmission of small signals. In addition, the transferable power is heavily dependent on the current rotor position.

PRESENTATION OF THE INVENTION

It is therefore an object of the present invention to provide a device for transmitting electrical energy from a stator to a rotatable rotor, the can be designed to save space, which is easy to assemble, and allows a transfer of greater benefits with less rotation angle dependence.

This object is achieved by a device having the features of claim 1. Preferred embodiments are given in the dependent claims.

Thus, there is provided a device for transmitting electrical energy from a stator to a rotor, comprising: an AC voltage source for generating an AC voltage; a stator having a primary winding arrangement which is electrically connected to the

AC power source is powered; and a rotor having a secondary winding assembly having one or more secondary windings inductively coupled to the primary winding assembly, the rotor being rotatable about an axis of rotation and defining a direction of rotation.

This device is characterized in that the primary winding arrangement comprises at least two, preferably three or more, primary windings which are not penetrated by the axis of rotation of the rotor, wherein each of the primary windings extends over a predetermined sector (angular range) with respect to the direction of rotation of the rotor, and wherein the primary windings are arranged offset with respect to the direction of rotation.

The term at least two primary windings is also intended to include one embodiment of a two-half coil, which are connected together during assembly and then form a winding. Preferably, each primary winding extends over a sector of at most 180 °, and the primary windings are not overlapping and in particular with respect to the direction of rotation arranged one behind the other.

By at least two separate primary windings are formed, which are not penetrated by the rotor axis, it is on the one hand possible to mount the primary windings separately from each other and thus to provide the transformer in places where mounting of a transformer with coaxial windings would not be possible. In particular, the transformer does not need to be located at one end of the rotor be, as is the case with solutions from the prior art. Compared to an auxiliary generator, the space requirement is also significantly lower, so that the rotor does not need to be extended unnecessarily. In particular, this contributes to the fact that a transformer with relatively high frequencies is operable, which allows a high power density. On the other hand, a uniform transmission and higher performance is ensured by the fact that not only a single primary winding is present, but that several such primary windings are distributed over the circumference.

A winding in the present context is to be understood as meaning any loop-type conductor arrangement which is suitable for being flowed through by a current and thereby generating a magnetic field or being suitable for being permeated by a magnetic flux and owing to changes in this flux to deliver an induced voltage. A winding can be traditionally configured as a wire coil with one or more windings. But it can also be e.g. consist of a single conductor loop and / or be constructed of metal rods, bands or hollow conductors, which can be flowed through for the purpose of cooling water or gas.

Preferably, each of the primary windings is disposed on a separate magnetic core. In this way, leakage losses are minimized and improved efficiency is achieved. By having a separate core associated with each primary winding, each primary winding is easily assembled separately with its core. The core can have different shapes depending on the specific requirements. In particular, the core in cross section may have an E-shaped profile, a U-shaped profile or in the simplest case an I-shaped profile.

To facilitate fabrication, the magnetic core may comprise a plurality of separately manufactured core segments, each of these core segments extending over only a portion of the sector (a partial angle range) of the associated primary winding. This is possible because in the design of the transformer proposed here, no appreciable magnetic flux in the circumferential direction (direction of rotation) takes place and therefore the unavoidable gaps between the core segments have no significant effect on the magnetic properties of the core. Preferably, all primary windings have the same dimensions and are preferably constructed identically. In order to ensure a uniform energy transfer, preferably at least three primary windings are present, and the primary windings are distributed uniformly with respect to the direction of rotation.

The primary and secondary winding arrangement preferably face each other radially, that is to say that the surfaces defined or enclosed by the windings have a surface normal which extends substantially in the radial direction. In other words, the primary and secondary windings are preferably each substantially on a circular cylindrical surface. In other words, the magnetic field passing through the windings preferably overcomes the gap between the primary and secondary circuits essentially in the radial direction, that is, the inductive coupling between the primary and secondary windings takes place substantially radially. But it is also conceivable that the primary and the secondary winding arrangement axially, spaced from the axis of rotation, facing each other.

Each primary winding preferably has two substantially parallel sections, which extend substantially in the circumferential direction (direction of rotation) and are in opposite directions flowed through by electricity, the length of these sections is considerably greater than their distance, that is, the winding has a along the rotational direction or circumferential direction elongated, curved shape. As a result, a particularly narrow construction of the transformer is achieved. However, other forms of winding are possible.

To save space, the primary winding assembly is preferably disposed in a region radially surrounding the secondary winding assembly, and the primary and secondary winding assemblies are preferably disposed on the circumference of the rotor.

The efficiency of the proposed transformer can be significantly improved by operating in resonance. For this purpose, preferably forms each of the primary windings part of a resonant resonant circuit, and the AC voltage source is designed such that it is in operation an AC voltage with an operating frequency in the Area generates a resonance of the resonant circuit. An example of a resonant-powered transformer is given, for example, in the following document: R. Mecke and C.Rathge, High frequency resonant inverter for contactless energy transmission over large air gaps, IEEE 35th Annual Power Electronics Specialists Conference (PESC), 2004, Volume 3 , pp. From 1737 to 1743. Here, each primary winding may be part of a separate resonant circuit, or several or all primary windings may be interconnected to form a single resonant circuit.

The operating frequency of the transformer is preferably in the medium to high frequency range, in particular in the range above about 400 Hz. The AC voltage source is accordingly designed to be an AC voltage with such

To generate operating frequency and may e.g. be formed by a correspondingly operated inverter or frequency converter. Suitable AC sources are from the

Known in the art. Preferably, the operating frequency is about 1 kHz to 20 kHz, but it can also exceed this range and reach 50 kHz or more, for example. The choice of the working frequency occurs among other things depending on the

Loss properties of the magnetic cores used.

In a preferred embodiment, not only a plurality of primary windings are present, but also the secondary array has at least two

Secondary windings, each secondary winding over a predetermined

Sector with respect to the direction of rotation of the rotor extends, and wherein the

Secondary windings are arranged offset from one another with respect to the direction of rotation.

This makes it possible in particular to construct the rotor compensated for possible imbalances. In particular, a plurality of secondary windings of the same dimensions and preferably also of the same construction can be distributed uniformly in the circumferential direction or in the direction of rotation.

A particularly elegant and simple construction results when the secondary windings are arranged on a common magnetic core, which surrounds the rotor on its radial outer side (on its circumference). This may comprise at least one circumferentially wound around the rotor plate. The invention further relates to a dynamoelectric machine, in particular an electric generator in the form of a synchronous machine, whose field winding is fed by a device for energy transmission, as indicated above. The dynamoelectric machine comprises for this purpose at least one exciter winding connected to the rotor for generating a magnetic field rotating with the rotor and at least one rectifier device connected to the rotor. The secondary winding assembly is electrically connected to the rectifier means to rectify the secondary voltage induced in the secondary winding assembly, and the rectifier means is electrically connected to the field winding for feeding the rectified winding with the rectified secondary voltage.

The dynamo electric machine may also have a fan connected to the rotor. In order to save space, then the secondary winding assembly may be disposed in a region of the rotor, which lies with respect to the axial direction between the field winding and the fan.

The proposed exciter power supply allows a great flexibility in the supply of the exciter. In particular, it is possible for the dynamoelectric machine to have two or more excitation windings which are fed separately from different secondary windings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described below with reference to the drawings, which are given by way of illustration only and are not to be interpreted as limiting. In the drawings show:

1 shows a schematic longitudinal section through a rotating transformer according to a first embodiment of the invention.

FIG. 2 is a schematic perspective view of the primary winding assembly of the rotary transformer of FIG. 1; FIG. Fig. 3 is a schematic perspective view of a single segment of

Primary winding arrangement; Fig. 4 is an illustration of the connection between two consecutive

segments; Fig. 5 is an electrical circuit diagram for a rotary transformer with two

Primary windings and four secondary windings; Fig. 6 is a schematic illustration of the arrangement of a rotating

Transformer between rotor cap and fan;

7 shows a schematic longitudinal section through a rotating transformer according to a second embodiment of the present invention;

Fig. 8 is an illustration of a rotor wound on a core for the

Secondary winding arrangement of a rotary transformer according to a third embodiment;

9 shows a schematic representation of the rotor with core and secondary windings arranged thereon; such as

Fig. 10 is a schematic representation of the complete secondary winding assembly with core, secondary windings and end rings.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a first embodiment of the present invention. A rotor 1, which is indicated only very schematically in FIG. 1, is rotatably mounted about a rotation axis 11. Along its circumference is a rotatable transformer having a primary side 3 and a secondary side 2. The secondary side 2 is fixed to the circumference of the rotor 1 and rotates with this, while the primary side 3 is stationary. The primary side 3 is fed by an AC voltage source 4 in the form of an inverter or inverter with a primary voltage in the medium-frequency range (about 2 kHz to 50 kHz).

The secondary side 2 comprises a magnetic core 21 which is constructed in a manner known per se from iron sheets in order to minimize eddy current losses. The magnetic core 21 has an E-shaped profile in cross-section, which two in Defined circumferential direction (direction of rotation) extending to the radial outside open, parallel grooves. In these grooves secondary windings 22 are inserted. Several identical secondary windings 22 are arranged distributed over the circumference of the rotor one behind the other, wherein each of these secondary windings 22 extends only over a certain sector (angular range) of the circumference. For this purpose, the core 21 is repeatedly interrupted at least so far with respect to the direction of rotation that the secondary windings 22 can be closed in the region of these interruptions. Instead of a multiply interrupted core 21, it is also possible for a plurality of separate cores 21 to be present, each secondary winding 22 being assigned its own core 21. The secondary windings 22 each include a curved surface whose surface normal points radially outward. In order to achieve a good balance of the rotor 1, preferably at least three secondary windings 22 are uniformly distributed over the circumference.

The secondary windings 22 are connected via only schematically indicated lines 23 with a likewise only schematically indicated rectifier device 24, as is known per se from the prior art, to rectify the secondary winding induced in the secondary windings 22. The output of the rectifier device 24 is connected to an exciter winding arrangement, not shown in FIG. 1, which is also arranged on the rotor 1, and feeds the exciter windings with the rectified secondary voltage.

A possible embodiment for the primary side is illustrated in more detail in FIGS. The primary side is made up of three identical segments uniformly distributed around the circumference of the rotor and located radially outside the secondary windings in an area surrounding the secondary windings. Each of these segments comprises a magnetic core 31 which has a profile with an E-shaped cross-section and thereby defines two parallel grooves extending along the circumferential direction and radially inwardly open. In the two grooves of each segment, a primary winding 32 is inserted.

Each primary winding 32 consists in the present example of four turns (see Fig. 1), but can of course also more or fewer turns, in the extreme case only include a single turn. It has an elongate, substantially rectangular-curved basic shape with the long sides of the rectangle running along the circumferential direction and being inserted in the grooves of the core 31, while the short sides connect these two long sides in the axial direction and outside the core 31 run. Overall, this results in a respect to the axial direction very narrow design of each segment. The curved surface enclosed by the primary winding 32 has a surface normal which points everywhere in the radial direction, ie the primary windings are radially opposite the secondary windings, the pole faces of the cores of the primary and secondary sides point in the radial direction, and the magnetic flux between Primary and secondary side overcomes the gap between these pole faces substantially in the radial direction.

The magnetic core 31, in turn, itself consists of a plurality of core segments 311, 312. Each of these core segments 311, 312 has a U-shaped cross-section and is usually formed from sheets to minimize eddy current losses. In each case two core segments 311, 312 are arranged side by side in the axial direction, so that such a pair of segments forms an overall E-shaped cross-section. A plurality of these E-shaped pairs are arranged one behind the other in the circumferential direction so as to form the entire magnetic core of the primary side.

If in this case recourse is made to commercially available standard parts, then, as can be seen in particular in FIG. 4, gaps may occur between adjacent core segment pairs 311, 312 in the circumferential direction due to the curvature. However, these are not critical to the operation of the transformer, since the magnetic field lines follow substantially the U-shape of each individual core segment and thus no significant magnetic field acts in the circumferential direction. As a result, the magnetic flux need not overcome the gaps between successive core segments in practice, so that these gaps remain without appreciable influence on the operation. However, a gapless arrangement of the core segments 311, 312 is preferred, which is achieved by a shaping of the core segments 311, 312 adapted to the curvature of the stator.

The core 31 with the primary winding 32 inserted therein is by a housing acting bracket 33 fixed. The holder 33 comprises two part-shell-shaped halves, which are arranged axially next to one another. By screws 34, which are shown for the sake of clarity only in FIG. 1, the two halves are held together axially and exert a clamping force on the core 31 in the axial direction. At their ends, the holder in each case has connecting flanges 37 whose surface normal points in the circumferential direction, the connecting flanges 37 of adjacent holders facing one another along the circumferential direction and being connected to one another by means of screws 38 shown only in FIG.

A schematic electrical circuit diagram for a transformer according to the invention is shown in FIG. 5. In the example of FIG. 5, the primary side 3 has only two primary windings 32. The secondary side 2 has in this example, four secondary windings 22, which are each provided with three terminals. The secondary windings 22 are inductively coupled to the primary windings 32 via a common magnetic core 21 of the secondary side and cores 31 of the primary side. The middle terminals of the secondary windings 22 are connected together and form a first pole of a DC intermediate circuit 25. The other two terminals of the secondary windings 22 are connected via diodes, which together form a rectifier arrangement 24, with the second pole of the intermediate circuit 25. For this intermediate circuit 25, the field winding, not shown here is fed.

In order to achieve higher efficiency and to minimize losses, the system is preferably operated in resonance. For this purpose, each of the two primary windings 32 is supplemented by a capacitor 36 to a resonant circuit whose resonant frequency is given in a known manner by the inductance of the primary winding 32 and the capacitor 36. The AC voltage source, not shown in FIG. 5, with which the thus completed primary circuit is supplied, is tuned with its operating frequency to this resonance frequency, ie it operates the primary circuit at or near the resonance frequency. While a series resonant circuit is shown in FIG. 5, the resonant circuit can also be designed as a parallel resonant circuit or, particularly preferably, in a combination of series-connected and parallel-connected capacitances. FIG. 6 illustrates how a transformer of the type proposed here can be arranged in a space-saving manner between a so-called rotor cap 13 and the fan 6 of an electrical generator. The here only partially and schematically illustrated rotor 1 carries a in Fig. 6 only indicated exciter winding 12 to produce a rotating with the rotor 1 magnetic field. This generates in induction coils, not shown, which are connected to a stator 5, an induced voltage. The area of the rotor 1 in which the field winding ends is covered with the rotor cap 13. At a certain axial distance from the rotor cap 13, a fan 6 adjoins the rotor shaft. In this area, there is enough space available to accommodate a rotating transformer of the type described above with secondary side 2 and primary side 3, both of which are only very schematically indicated here.

An alternative embodiment of a rotary transformer is schematically illustrated in FIG. The primary side here comprises a U-shaped magnetic core 31 ', while the magnetic core 21' of the secondary side here has an I-shaped cross-section. The primary winding 32 'consists in the present case of a single conductor loop, which is formed from a flat, hollow conductor. This is also provided with hollow, only schematically indicated connection lines 35 '. This allows a cooling liquid, e.g. Cooling water to pump through the conductor. A

AC voltage source 4 in the form of a known inverter or inverter supplies the primary side with a primary voltage. The secondary windings 22 'are each formed by a single conductor loop from a flat, hollow conductor, which is traversed by a gas for cooling. The secondary windings 22 'are in turn connected to a rotor-fixed rectifier 24, which is indicated here only schematically.

FIGS. 8 to 10 illustrate a production-technically advantageous variant for the construction of the secondary side. A magnetic core 21 "of a metal strip is wound onto a rotor 1, which is only schematically indicated here, for which purpose known strips can be used, in particular nanocrystalline core strips or Fe-Si strips, which are well suited for rather low operating frequencies formed common core are a plurality of secondary windings 22 "applied, which are indicated here only very schematically. The connections 23 of these windings 22 "are led out in the axial direction and are bent over radially inwards toward the surface of the rotor Finally, the arrangement is provided at its axial ends with two circumferential end rings 26a, 26b which serve to fix the secondary winding arrangement and to further minimize the stray fields.

It will be understood that the foregoing description illustrates only preferred embodiments of the invention and is not intended to limit the invention. In particular, a variety of variations and modifications of the above embodiments are possible. Thus, e.g. one or more of the secondary windings feed individual field windings separately; For this purpose, a plurality of independent rectifier arrangements can be provided. The secondary windings can, unlike in the preceding embodiments, also be arranged overlapping and in particular be formed by axially parallel conductor bars, which are connected to collecting rings, as is known per se from EP 1 708 342. The present invention also makes it possible, in particular, to easily realize a high-current supply for the excitation windings, which allows high currents in the range of 20 kA or more, in particular up to 100 kA.

LIST OF REFERENCE NUMBERS

1 rotor 31, 31 'core

11 rotor axis 311, 312 core segment

12 field winding 32, 32 'primary winding

13 rotor cap 33 holder

2 secondary side 34 screw

21, 21 ', 21 "core 35, 35' supply line

22, 22 ', 22' 'secondary winding 36 capacity

23 Cable 37 Mounting flange

24 Rectifier device 38 Screw

25 DC link 5 stator

26a, 26b Fixing ring 6 Fan

3 primary side

Claims

A device for transmitting electrical energy from a stator to a rotor (1), the device comprising: an AC voltage source (4) for generating an AC voltage; a stator (5) having a primary winding assembly (3) electrically powered by the AC power source (4); and a rotor (1) having a secondary winding assembly (2) inductively coupled to the primary winding assembly (3), the rotor (1) being rotatable about an axis of rotation (11) and defining a direction of rotation, characterized in that the primary winding assembly (3) has at least two primary windings (32; 32 ') that are not penetrated by the axis of rotation (11) of the rotor (1), each of the primary windings (32; 32') extending over a predetermined sector with respect to the direction of rotation of the rotor (1), and wherein the primary windings (32; 32 ') are offset from one another with respect to the direction of rotation.

2. Device according to claim 1, wherein each of the primary windings (32; 32 ') is arranged on its own magnetic core (31; 31').

The apparatus of claim 2, wherein the magnetic core (31, 31 ') comprises a plurality of core segments (311, 312), each of said core segments (311, 312) extending over a portion of the sector of the associated primary winding (32, 32) ') extends.

4. Device according to one of the preceding claims, wherein the primary windings (32, 32 ') have the same dimensions and are distributed uniformly with respect to the direction of rotation.

5. Device according to one of the preceding claims, wherein each of the Primary windings (32; 32 ') includes an area whose surface normal points in a substantially radial direction.

6. Device according to one of the preceding claims, wherein the primary winding assembly (3) is arranged in a region which surrounds the secondary winding assembly (2) radially.

7. Device according to one of the preceding claims, wherein each of the primary windings (32; 32 ') forms part of a resonant resonant circuit, and wherein the AC voltage source (4) is adapted to generate an AC voltage having an operating frequency in the range of a resonance of the resonant circuit ,

8. Device according to one of the preceding claims, wherein the AC voltage source (4) is adapted to generate an AC voltage with an operating frequency of 400 Hz or more.

9. Device according to one of the preceding claims, wherein the secondary winding assembly (2) at least two secondary windings (22; 22 '; 22 "), each secondary winding (22; 22'; 22") over a predetermined sector with respect to the direction of rotation of Rotor (1) extends, and wherein the secondary windings (22; 22 '; 22 ") are arranged offset with respect to the rotational direction to each other.

10. The device according to claim 9, wherein the secondary windings (22, 22 ', 22 ") have the same dimensions and are distributed uniformly in the direction of rotation.

11. Device according to one of the preceding claims, wherein the secondary windings (22; 22 ', 22 ") on a common core (21; 21'; 21") are arranged, which surrounds the rotor (1) on its outer side.

12. The device according to claim 11, wherein the core (21; 21 ', 21 ") at least one in Circumferentially around the rotor (1) wound sheet comprises.

13. Device according to one of the preceding claims, wherein the secondary winding assembly (2) is connected to a rectifier means (4) to rectify a secondary voltage induced in the secondary winding assembly.

14. A dynamoelectric machine having a device according to one of the preceding claims, wherein the dynamoelectric machine at least one of the rotor (1) connected to the exciter winding (12) for generating a with the rotor (1) rotating magnetic field and connected to the rotor rectifier means ( 24), the secondary winding assembly (2) being electrically connected to the rectifier means (24) for rectifying a secondary voltage induced in the secondary winding assembly (2), and wherein the rectifier means (24) is electrically connected to the field winding (12) to feed the excitation winding with the rectified secondary voltage.

15. A dynamoelectric machine according to claim 14, having a fan (6) connected to the rotor (1), wherein the secondary winding arrangement (2) is arranged in a region of the rotor (1) which is movable relative to the axial direction between the exciter winding (12 ) and the fan (6).