ROTOR WITH SUPERCONDUCTING WINDING FOR CONTINUOUS CURRENT MODE OPERATION

Abstract

A rotor for an electrical machine is disclosed herein. The rotor includes a rotor housing, a winding carrier arranged therein, at least one first axial connecting element mechanically interconnecting the winding carrier and the rotor housing, and a superconducting rotor winding configured to produce a magnetic field. The rotor winding is mechanically retained by the winding carrier and is part of a self-contained circuit inside the rotor in which circuit a continuous current may flow. The self-contained circuit has a continuous current switch with a switchable conductor section that may be switched between a superconducting state and a normally conducting state. The switchable conductor section is arranged on the first axial connecting element. A machine including the rotor and a method for operating the rotor is also disclosed herein.

Claims

1. A rotor for an electrical machine, the rotor comprising: a rotor outer housing; a winding carrier arranged, within the rotor outer housing, a first axial connecting element, which mechanically connects the winding carrier and the rotor outer housing to one another; and a superconducting rotor winding configured to form a magnetic field, wherein the superconducting rotor winding is mechanically held by the winding carrier, wherein the superconducting rotor winding is part of a self-contained circuit within the rotor, in which a continuous current is configured to flow, wherein the self-contained circuit comprises a continuous current switch having a switchable conductor section configured to be switched between a superconducting state and a normally conducting state, and wherein the switchable conductor section is arranged on the first axial connecting element.

2. The rotor of claim 1, further comprising: two current feeds for connecting the superconducting rotor winding to an external circuit, wherein the two current feeds are arranged at least partially on the first axial connecting element.

3. The rotor of claim 1, wherein the switchable conductor section has at least one switchable coil element.

4. The rotor of claim 3, in wherein the switchable coil element is a bifilar wound coil element.

5. The rotor of claim 1, wherein the first axial connecting element has a tubular design.

6. The rotor of claim 1, wherein the first axial connecting element is arranged on a drive side of the rotor in relation to the winding carrier.

7. The rotor of claim 1, wherein the first axial connecting element is arranged on an operating side of the rotor in relation to the winding carrier.

8. The rotor of claim 1, wherein the switchable conductor section has a resistance of at least 100 MOhm in the normally conducting state.

9. The rotor of claim 1, wherein at least one of the rotor winding or the switchable conductor section comprises a high-temperature superconducting conductor material.

10. The rotor of claim 1, wherein the rotor winding and the switchable conductor section are formed from different superconducting conductors.

11. The rotor of claim 10, wherein the switchable conductor section comprises a superconducting material with a lower transition temperature than a superconducting material of the rotor winding.

12. The rotor of claim 1, wherein the switchable conductor section has a superconducting conductor which has a smaller material cross-section of normally conducting conductor material than the superconducting conductor of the rotor winding.

13. An electrical machine comprising: a stator; and a rotor comprising: a rotor outer housing; a winding carrier arranged within the rotor outer housing; an axial connecting element mechanically connecting the winding carrier and the rotor outer housing to one another; and a superconducting rotor winding configured to form a magnetic field, wherein the superconducting rotor winding is mechanically held by the winding carrier, wherein the superconducting rotor winding is part of a self-contained circuit within the rotor, in which a continuous current is configured to flow, wherein the self-contained circuit comprises a continuous current switch having a switchable conductor section configured to be switched between a superconducting state and a normally conducting state, and wherein the switchable conductor section is arranged on the axial connecting element.

14. A method for operating a rotor, the method comprising: providing the rotor having a rotor outer housing, a winding carrier arranged within the rotor outer housing, an axial connecting element mechanically connecting the winding carrier and the rotor outer housing, and a superconducting rotor winding mechanically held by the winding carrier, wherein the superconducting rotor winding is part of a self-contained circuit within the rotor, wherein the self-contained circuit comprises a continuous current switch having a switchable conductor section, and wherein the switchable conductor section is arranged on the axial connecting element; connecting the superconducting rotor winding to an external current source via two connecting nodes arranged within the self-contained circuit, in each case adjacent to the switchable conductor section; subsequently supplying a current to the superconducting rotor winding by the external current source; and subsequently disconnecting the superconducting rotor winding from the external current source.

15. The method of claim 14, further comprising: generating, following the disconnecting of the rotor winding, a rotating electromagnetic field in an electrical machine by a continuous current flowing in the superconducting rotor winding.

16. The rotor of claim 2, wherein the switchable conductor section has at least one switchable coil element.

17. The rotor of claim 16, wherein the switchable coil element is a bifilar wound coil element.

18. The rotor of claim 2, wherein the first axial connecting element has a tubular design.

19. The rotor of claim 2, wherein the first axial connecting element is arranged on a drive side of the rotor in relation to the winding carrier.

20. The rotor of claim 2, wherein the first axial connecting element is arranged on an operating side of the rotor in relation to the winding carrier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The disclosure is described below with the aid of several exemplary embodiments and with reference to the attached drawings, in which:

[0059] FIG. 1 depicts a possible embodiment of an electrical machine in a schematic longitudinal section.

[0060] FIG. 2 depicts a detailed illustration of the rotor of the machine of FIG. 1.

[0061] FIG. 3 depicts an alternative embodiment of a rotor in a schematic longitudinal section.

[0062] FIG. 4 depicts an example of a schematic equivalent circuit diagram of a rotor winding with a normally conducting switchable conductor section.

[0063] FIG. 5 depicts an example of a corresponding equivalent circuit diagram, in which the switchable conductor section is superconducting.

[0064] FIG. 6 depicts an example of a schematic cross-sectional illustration of a bifilar wound switchable coil element 13.

[0065] In the figures, identical or functionally identical elements are denoted by the same reference signs.

DETAILED DESCRIPTION

[0066] FIG. 1 depicts an electrical machine 2 according to a first exemplary embodiment in a schematic longitudinal section, e.g., along the central machine axis A. The machine 2 includes a stationary machine outer housing 3, which is at room temperature and has a stator winding 4 therein. Within this (for example, evacuable) outer housing and surrounded by the stator winding 4, a rotor 5 is mounted in bearings 6 such that it is rotatable about an axis of rotation A, which rotor includes, on its drive side AS, a solid axial rotor shaft part 5a mounted in the corresponding bearing. The rotor has a rotor outer housing 7 which is configured as a vacuum vessel and in which a winding carrier 9 with a superconducting rotor winding 10 is mounted. Serving this purpose, on the drive side AS, there is a (first) rigid, tubular connecting element 8a between the winding carrier 9 and a disk-shaped side part 7a, fixedly connected to the rotor shaft part 5a, of the rotor outer housing 7. The substantial proportion of the torque transmission also takes place via the rigid connecting element 8a. In an advantageous manner, this connecting device includes a hollow cylinder which has a poor heat conductivity and is made, in particular, of a plastic material reinforced with glass fibers. This material provides a sufficiently high mechanical rigidity and high shear modulus (G modulus) for the torque transmission along with a low heat conductivity. On the operating side, which is opposite the drive side AS and is denoted below by BS, a second connecting element 8b is arranged between the winding carrier 9 and a disk-shaped side part 7b of the rotor outer housing 7.

[0067] The superconducting rotor winding 10 may be connected to an external circuit and, in particular, a current source 19 via two parallel-routed current feeds. However, this current source 19 is not a component part of the electrical machine 2, but may instead be disconnected from the machine following the supply of an operating current. The arrangement of the current feeds in FIG. 1 is only represented extremely schematically, in particular, in the region of the rotor shaft part 5a. The only significant aspect is that the current feeds are both arranged in the region of the drive side here and are routed on the first connecting element 8a within the rotor 7. Alternatively to the illustrated variants, the current feeds may also terminate with a plug connection in the region of the element 7a, for example. Cables may then be connected externally here, merely for the current supply act. The current feeds each have a superconducting conductor section 15 and a normally conducting conductor section 17. The superconducting conductor sections 15 are arranged accordingly on the colder axial end of the first connecting element 8a, which faces the cryogenic winding carrier 9. This winding carrier 9 and the superconducting rotor winding 10 arranged thereon are cooled to a cryogenic operating temperature by a cooling system (not illustrated in more detail here). To represent the cooling system, a coolant tube 21, through which a fluid cryogenic coolant 23 may arrive in the region of the rotor 5 which is to be cooled, is shown on the operating side BS of the machine. This fluid coolant therefore circulates in an inner cavity 25 of the rotor. The superconducting rotor winding 10 is thus kept at a cryogenic temperature below the transition temperature of the superconductor material used. The superconducting sections 15 of the current feeds are arranged axially adjacent to this cryogenic region of the rotor. However, as a result of the thermally insulating properties of the first connecting element 8a supporting the current feeds, the operating temperature in this region of the rotor is likewise still below the transition temperature of the superconductor material used for the current feeds 15.

[0068] The two superconducting current feeds 15 are electrically connected to a switchable conductor section 13, which is likewise mechanically supported by the first connecting element 8a. This switchable conductor section 13 act as a continuous current switch and enables the supply of a (e.g., pseudo) continuous current to the closed circuit of the superconducting rotor winding 10. The switchable conductor section 13 is at an intermediate temperature, which is above the operating temperature of the superconducting rotor winding but below the warm external ambient temperature. This intermediate temperature may be a temperature in the range of 50 K and 80 K, for example. The temperature of the continuous current switch may be selected such that a sufficiently high critical current density for the continuous current is achieved in the superconducting state of the continuous current switch, but easy thermal switching is still possible in the normally conducting state. In particular, comparatively rapid switching with a low heat input is thus enabled. Axially adjacent to the switchable conductor region 13, this latter is connected to the normally conducting sections 17 of the current feeds. These normally conducting conductor sections 17 are at a somewhat higher temperature level compared to the switchable conductor region 13. Unlike the superconducting conductor sections 15, these normally conducting conductor sections 17 are no longer part of the closed circuit in which the continuous current flows after the power supply process. However, they are required in the open state of the continuous current switch for supplying a current by the external current source 19. In order to be able to transport a sufficiently high supply current, a sufficiently large normally conducting conductor cross-section is necessary here.

[0069] An illustration of a detail of the rotor 5 of the electrical machine of FIG. 1 is shown in FIG. 2. The region shown is essentially that within the rotor outer housing 7 (which may include the two side parts 7a and 7b). In addition to the elements already illustrated in FIG. 1, a radiation shield 27 is further shown here, which is arranged between the switchable conductor section 13 and the rotor winding 10 within the vacuum space V such that heat transfer between these two elements as a result of heat radiation is effectively reduced. Like the other supporting elements of the rotor, this radiation shield 27 is configured to be substantially rotationally symmetrical about the axis of rotation A. The radiation shield 27 is merely interrupted locally by a recess in the region of the of the superconducting current feeds 15. One or more additional radiation shields (not illustrated here) may possibly also be provided, (for example, between the switchable conductor section 13 and the element 7a), which are likewise operated at significantly different temperatures.

[0070] The position of the current feeds 15 and 17 is also only illustrated extremely schematically in this figure. In this case, the two current feed paths extending next to one another may be arranged in a common circumferential position on the rotor, as indicated here. However, the current feed paths may also be arranged in an offset circumferential position. In particular, they may also be routed directly on the connecting element and they may also surround this spirally, for example. In any case, the rotational symmetry of the rotor is, at the most, slightly disrupted by the current feed paths. Their mass is comparatively low so that only a slight unbalance of the rotor is generated, which may be easily compensated. However, at least the switchable conductor region is advantageously configured to be rotationally symmetrical so as to thus prevent any further unbalance. In the example shown, the switchable conductor region 13 may be a switchable coil element with a circular cylindrical basic form.

[0071] The switchable coil element may be arranged directly on the connecting element 8a, for example, so that this connecting element assumes the function of a winding carrier. This variant is particularly advantageous in the case of a comparatively large external diameter of the connecting element 8a. Alternatively, however, an additional (e.g., advantageously likewise circular cylindrical) winding carrier may be present between the connecting element and the switchable coil element 13.

[0072] The elements of the rotor which are radially enclosed by the rotor outer housing 7 are located within a vacuum space V so that they are thermally insulated from the outer wall. In this case, the elements at the coldest temperature level are in the axially inner region, which is represented as the cryogenic region 31 in FIG. 2. The operating temperature in the cryogenic region 31 may be below 50 K, for example, and in particular in the range of 20K and 25K. Adjoining the cryogenic region 31 axially on the right and left are two regions with a moderate temperature, in which the elements enclosed radially by the vacuum space V are at a moderate temperature level. In turn, adjoining these regions axially are two comparatively warm regions 35, in which the two side parts 7a and 7b of the rotor outer housing are arranged. These are at a comparatively warm ambient temperature. The warm regions 35 may be approximately at room temperature, for example.

[0073] An alternative embodiment of a rotor is shown in a corresponding longitudinal section in FIG. 3. Overall, the rotor 5 is configured similarly to the rotor of FIG. 2 and, in particular, may also be integrated in an electrical machine 2 in a manner similar to the example of FIG. 1. In contrast to the previous example, the switchable conductor section 13 is not arranged on the A side AS here, but on the B side BS of the rotor. This conductor section 13 is also configured as a switchable coil element here, which is mechanically supported accordingly by the B-side second connecting element 8b here. The statements made in connection with the previous example with regard to the moderate temperature level of the switchable conductor region, the rotational symmetry, the heat input, and the radiation shielding apply accordingly in this case.

[0074] In the example of FIG. 3, the switchable coil element 13 is located on the side of the rotor on which the fluid coolant 23 is also supplied. This coolant 23 is conducted through a coolant tube 21 in the interior of the second connecting element 8b here. The cooling of this conductor section 13 here, and of the current feeds 15 and 17 likewise arranged on the B side, is additionally facilitated as a result of the spatial proximity of the switchable conductor section 13 to the coolant supply.

[0075] Alternatively to the two examples shown here, it is also possible for the coolant supply, together with the current feed and the continuous current switch, to be arranged on the A side. In any case, it is advantageous if the switchable conductor section is arranged on the same axial side as the current feeds, so that it may be easily spatially integrated therewith.

[0076] A schematic equivalent circuit diagram of a rotor winding 10 is shown in FIG. 4, which rotor winding is connected to a current source 19 for the current supply. In principle, this may be one of the rotor windings from the two previous exemplary embodiments. The rotor winding 10 is connected to a switchable conductor region 13 via a first connecting node 44 and a second connecting node 45, which conductor region acts as a continuous current switch. The rotor winding 10 here is assembled to form a coil winding (only illustrated very schematically), although, in an actual rotor, it may be structured as a plurality of individual pole coils which are then electrically connected to form a continuous winding. The rotor winding 10 is connected to the switchable conductor region via two superconducting current feeds 15 to form a closed circuit 43 in which a current may flow annularly, at least when the continuous current switch is closed. The conductor elements of this closed circuit 43 are superconducting at operating temperature. They may be surrounded by a common cryostat 41, for example, as indicated here by the dotted line. In this case, however, it should not be ruled out that additional normally conducting contact elements are present between the two individual superconducting conductor elements. As a result of these additional ohmic resistances, a pseudo continuous current mode is possibly achieved rather than a purely continuous current mode.

[0077] Adjoining the two connecting nodes 44 and 45 on the right, this circuit may be connected to an external current source 19 via two normally conducting current feeds 17. A direct current may be supplied to the rotor winding 10 as a charging current I.sub.1 via this current source. However, this current source 19 is not a fixed component part of the rotor, but may instead be removed from this during operation and does not contribute to the mass of the rotor.

[0078] The switchable conductor section 13 is illustrated schematically in an open configuration in FIG. 4. However, this open configuration is not intended to mean that an electrical connection is not present at all here, but simply that the switchable conductor section is in the normally conducting and not in the superconducting state. Analogously, the closed state of the switch is intended to refer to a superconducting state of the switchable conductor region. The switchable conductor section is therefore a resistor which may be switched between two significantly different values. I.sub.2 here denotes the low leakage current which may flow through the normally conducting switchable conductor region 13 during charging.

[0079] FIG. 5 depicts a similar schematic equivalent circuit diagram for the rotor winding 10 and the switchable conductor section 13, which is now in the superconducting state. The external current source 19 has been removed, wherein the disconnection of this connection (as indicated by the remaining conductor sections) may take place outside the cryostat 41 and at the outer end of the two normally conducting current feeds 17. After the disconnection of the current source 19 has taken place, a merely slowly decaying continuous current I.sub.3 now flows through the annularly closed circuit 43. This continuous current flowing over the rotor winding 10 may be used during the operation of an electrical machine including the rotor to generate an exciting field without the current source 19 being part of the electrical machine.

[0080] FIG. 6 depicts a schematic cross-sectional illustration (perpendicularly to the axis of rotation A) of a switchable conductor region 13, which is configured as a bifilar wound switchable coil element. This switchable coil element 13 is arranged radially externally on a circular cylindrical connecting element 8, wherein, in principle, this may be an A-side connecting element 8a or a B-side connecting element 8b as in the previous examples. Analogously to the equivalent circuit diagrams of FIGS. 4 and 5, the switchable coil element 13 here is connected to the superconducting current feeds 15 and the normally conducting current feeds 17 in an electrically conductive manner in each case via two connecting nodes 44 and 45.

[0081] The switchable coil element 13 itself is wound from a superconducting strip conductor as a bifilar flat coil. This bifilar coil includes two conductor branches 51 and 52, which are routed next to one another in adjacent windings such that their currents flow in mutually opposite directions. Substantial compensation of the inductances of the two conductor branches is realized as a result of this contrary direction of rotation of the current flow within the flat coil winding. On the radially inner side, the two conductor branches are electrically connected via a normally conducting contact element 53. However, in principle, a continuously superconducting conductor may also be present here, which is simply turned around in the interior of the coil.

[0082] On the radially outer side of the coil winding, the two conductor branches may either be connected to the current feeds in different circumferential positions (as shown here) or, in principle, in the same circumferential position. The latter embodiment has the advantage that the conductor lengths of the two conductor branches may then be selected to be substantially the same.

[0083] Although the disclosure has been described and illustrated more specifically in detail by the exemplary embodiments, the disclosure is not restricted by the disclosed examples and other variations may be derived therefrom by a person skilled in the art without departing from the scope of protection of the disclosure. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.

[0084] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.