Abstract
A rotor for an electric machine having a central rotor axis is disclosed herein. The rotor includes a rotor carrier and at least one permanent-magnetic, superconducting magnet device mechanically supported by the rotor carrier and having one or more superconducting magnet elements. The respective superconducting magnet element is embedded in an appropriate, assigned radially outer recess of the rotor carrier. The respective superconducting magnet element is formed by at least one strip conductor stack made up of multiple superconducting strip conductors. The respective strip conductor stack is secured in the associated recess by a radially further outer pole cap such that the pole cap holds together the individual strip conductors in the strip conductor stack. An electric machine including a rotor of this type and a method for producing a rotor of this type is also disclosed.
Claims
1. A rotor for an electrical machine with a central rotor axis, the rotor comprising: a rotor support; and a superconducting permanent magnet device mechanically supported by the rotor support, the superconducting permanent magnet device having one or more superconducting magnet elements, wherein a superconducting magnet element of the one or more superconducting magnet elements is embedded in a matching, assigned radially external cutout of the rotor support, wherein the superconducting magnetic element is formed by at least one strip conductor stack composed of a plurality of superconducting strip conductors, and wherein the respective strip conductor stack is fixed in an associated cutout by a pole cap arranged radially further to the outside such that the pole cap holds individual superconducting strip conductors of the plurality of superconducting strip conductors together in the strip conductor stack.
2. The rotor of claim 1, wherein the individual superconducting strip conductors of the at least one strip conductor stack lie loosely above one another.
3. The rotor of claim 1, wherein the individual superconducting strip conductors of the at least one strip conductor stack are connected to one another within the associated cutout by adhesive bonding and/or encapsulation.
4. The rotor of claim 1, wherein the pole cap comprises a non-magnetic material.
5. The rotor of claim 1, wherein the pole cap comprises a ferromagnetic material.
6. The rotor of claim 5, wherein the pole cap thinner in azimuthal edge regions of the pole cap, and wherein the pole cap extends radially outwardly to a lesser extent than in an azimuthal center of the pole cap.
7. The rotor of claim 1, wherein the superconducting permanent magnet device is configured to generate a magnetic field with a magnetic flux density of at least 1.0 T.
8. The rotor of claim 1, wherein the at least one strip conductor stack comprises a plurality of strip conductor stacks arranged next to one another.
9. The rotor of claim 1, wherein an intermediate space comprising a filler is positioned between the strip conductor stack and walls of the associated cutout.
10. The rotor of claim 9, wherein the filler is a heat-conducting grease, an epoxy resin, a paraffin, a solder material with a low melting point, or a combination thereof.
11. The rotor of claim 10, wherein the filler has a specific thermal conductivity of at least 0.05 W/m.Math.K at an operating temperature of the rotor.
12. The rotor of claim 11, wherein the filler has a maximum layer thickness of at most 0.5 mm in the intermediate space between the strip conductor stack and the walls of the associated cutout.
13. The rotor of claim 1, wherein the individual strip conductors of the at least one strip conductor stack each have a normally conducting substrate and a high-temperature superconducting layer.
14. An electrical machine comprising: a stator that is arranged in a fixed manner; and a rotor, wherein the rotor comprises: a rotor support; and a superconducting permanent magnet device mechanically supported by the rotor support, the superconducting permanent magnet device having one or more superconducting magnet elements, wherein a superconducting magnet element of the one or more superconducting magnet elements is embedded in a matching, assigned radially external cutout of the rotor support, wherein the superconducting magnetic element is formed by at least one strip conductor stack composed of a plurality of superconducting strip conductors, and wherein the respective strip conductor stack is fixed in an associated cutout by a pole cap arranged radially further to the outside such that the pole cap holds individual superconducting strip conductors of the plurality of superconducting strip conductors together in the strip conductor stack.
15. A method for producing a rotor, the method comprising: providing a rotor support; and forming a superconducting permanent magnet device having a superconducting magnet element, wherein the superconducting magnetic element is formed by a strip conductor stack by sequentially introducing a plurality of superconducting strip conductors into a matching, radially external cutout of the rotor support, and subsequently mechanically fixing the strip conductor stack formed by a pole cap arranged radially further to the outside.
16. The rotor of claim 9, wherein the filler has a specific thermal conductivity of at least 0.05 W/m.Math.K at an operating temperature of the rotor.
17. The rotor of claim 9, wherein the filler has a maximum layer thickness of at most 0.5 mm in the intermediate space between the strip conductor stack and the walls of the associated cutout.
18. The rotor of claim 9, wherein the filler has a maximum layer thickness of at most 0.2 mm in the intermediate space between the strip conductor stack and the walls of the associated cutout.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] The disclosure will be described below using a number of exemplary embodiments with reference to the appended drawings, in which:
[0050] FIG. 1 depicts a schematic cross section through a first embodiment of an electrical machine.
[0051] FIGS. 2 to 5 depict details of similar exemplary machines in the field of superconducting magnet elements.
[0052] FIG. 6 depicts a schematic cross section through a further embodiment of an electrical machine.
[0053] In the figures, elements that are the same or have the same function are provided with the same reference signs.
DETAILED DESCRIPTION
[0054] FIG. 1 depicts a schematic cross section of an electrical machine 1, that is to say shows the electrical machine perpendicularly to the central axis A. The machine includes an external stationary stator 3 and an internal rotor 5 which is rotatably mounted about the central axis A. The electromagnetic interaction between the rotor 5 and the stator 3 takes place across the air gap 6 situated between them. What is involved is a permanently excited machine which has a plurality of superconducting permanent magnet elements 9 for the purpose of forming an excitation field in the region of the rotor. In the cross section of FIG. 1, here by way of example four permanent magnets of this type are distributed over the circumference of the rotor. The permanent magnets are arranged in corresponding radially external cutouts 12 of a rotor support 7, the rotor support 7 mechanically supporting the magnet elements 9. However, further magnet elements than the four shown here may also be present in the axial direction, not shown here, wherein however the number of magnetic poles of the electrical machine is not increased by such an axial subdivision.
[0055] The rotor support 7, together with the magnet elements 9 held thereon, is cooled to a cryogenic operating temperature, which is below the transition temperature of the superconductor material used in the magnet elements, by a cooling apparatus, not shown in any more detail here. In order to maintain this cryogenic temperature, the rotor support 7 and magnet elements 9 are arranged together in the interior of a cryostat 11. There is an annular vacuum space V for thermal insulation between the cryostat and the rotor support 7.
[0056] In the exemplary embodiment in FIG. 1, the individual magnet elements 9 are each in the form of a strip conductor stack 8 composed of individual superconducting strip conductors 10. In this case, a respective plurality of such superconducting strip conductors 10 are stacked one on top of the other in a radial direction. The individual strip conductors 10 of the respective strip conductor stacks are not connected to one another to form a prefabricated component here, but rather they have been inserted one after the other into the corresponding cutout 12 of the rotor support 7. The strip conductor stacks 8 were thus formed here in situ within the respective cutouts 12 of the rotor support 7. The strip conductor stacks 8 formed in this way were then each mechanically fixed by the arrangement of a pole cap 13 which is radially further to the outside. These pole caps 13 thus hold the individual strip conductors 10 of the strip conductor stacks formed in the cutouts together. For this purpose, the pole caps 13 are pressed with a radial contact pressure p from radially outside against the strip conductor stacks 8. After the strip conductor stacks have been formed, the individual strip conductors 10 are initially not fixedly connected to one another. It is possible that they lie only loosely one above the other in the finished rotor 5 and are held together only by the contact pressure p of the pole caps 13. As an alternative, however, after the stack has been formed, they may be additionally fixed to one another within the respective cutout 12, for example by an adhesive and/or a filler. These different variants will become clear in connection with the details described below.
[0057] Thus, FIG. 2 depicts a schematic cross section through a detail of the rotor of an electrical machine. The figure shows the region of a superconducting magnet element 9 which is embedded in a radially external cutout of the rotor support 7. The remaining part of the electrical machine may be configured, for example, similarly to the example of FIG. 1. The magnet element 9 is also formed here by a strip conductor stack 8 composed of a multiplicity of individual superconducting strip conductors 10. These individual strip conductors 10 are stacked one on top of the other in the radial direction r. They are fixed from radially outside by a pole cap 13, which is pressed with a contact pressure against the strip conductor stack 8. The means for forming this contact pressure are not shown here for the sake of clarity. In the example of FIG. 2, the individual strip conductors 10 of the strip conductor stack 8 are only loosely placed one on top of the other and are held together exclusively by the pressing on of the external pole cap 13. Otherwise, in principle, they may be displaced with respect to one another in the lateral direction. In particular, they are thus not adhesively bonded to one another or encapsulated together. Because the strip conductor stack has been formed here within the cutout by sequentially inserting the individual strip conductors 10, the strip conductors 10 may have a slight lateral offset in relation to one another. This lateral offset is shown in an exaggerated manner in FIG. 2 for the sake of clarity. A small intermediate space 15 is formed between the lateral edges of the individual strip conductors and the walls 18 of the associated cutout in the rotor support. This intermediate space 15 is also shown in an exaggerated manner here. The intermediate space may also be only a minimum gap that remains toward the walls of the cutout after the strip conductor has been inserted, some strip conductors also being able to touch the wall directly. The average width of this intermediate space or gap is denoted by b in FIG. 2. In comparison with a conventional prefabricated strip conductor stack, this average spacing b to the walls of the cutout may be selected to be particularly small. This is due to the fact that the strip conductor stack formed in situ does not require any outer enclosure to mechanically fix the individual strip conductors to one another and that, in comparison with the prefabricated component, a precise matching to the size of the cutout may achieve a particularly small lateral offset of the individual strip conductors.
[0058] The radially external pole caps 13 are shaped such that they reproduce or continue the circular outer cross-sectional shape of the rotor support in the azimuthal direction. Here, the individual pole caps 13 are each formed from a ferromagnetic material. This may advantageously bring about improved magnetic flux guidance and, in particular, homogenization of the magnetic flux penetrating radially outward.
[0059] FIG. 3 depicts a detail for a similar region of a rotor according to a further example. Also shown here is the region of a superconducting magnet element 8, which as a whole is formed in a manner similar to the example in FIG. 2. In contrast to the example in FIG. 2, the intermediate space between the lateral edges of the strip conductors and the walls 18 of the cutout is filled with a filler 17. This filler 17 may advantageously substantially completely or at least predominantly fill the lateral intermediate space. In principle, it may be either a filler which is liquid (if appropriate, highly viscously liquid) at room temperature or else a filler which is solid at room temperature. A solid filler may be obtained, for example, by pouring an originally liquid filler into the intermediate space and then chemically hardening it or solidifying it by cooling. Here, the filler may be introduced into the lateral intermediate space either subsequently after the arrangement of the entire strip conductor stack and/or during the stacking of the individual strip conductors. For example, the filler may be a heat-conducting grease, an adhesive, a potting agent, a solder with a low melting point, or a combination thereof.
[0060] A significant advantage of filling the intermediate space with such a filler 17 is that the thermal coupling of the strip conductor stack 8 to the rotor support 7 may be significantly improved in comparison with an unfilled intermediate space. This is the case in particular if the thermal conductivity of the filler 17 is comparatively high and/or if the average layer thickness d of the laterally enclosing filler 17 is selected to be comparatively small. For example, this average layer thickness may be below 0.5 mm. This average layer thickness may advantageously be chosen as considerably thinner than would be possible when using a prefabricated, already adhesively bonded or potted strip conductor stack.
[0061] It is also the case in the example of FIG. 3 that the individual strip conductors 10 of the strip conductor stack 8 have a mutual slight lateral offset, which is also shown in an exaggerated manner here. As a result of this lateral offset, the layer thickness d of the laterally adjacent filler 17 is not constant, but may vary considerably from position to position. If individual strip conductors touch the lateral wall 18, the lateral thickness may also be 0 or almost 0 at individual points. The maximum lateral layer thickness of the filler 17 is denoted by d.sub.max in FIG. 3. It may also advantageously be considerably less than in the case of a comparable prefabricated and already adhesively bonded or potted magnet element.
[0062] FIG. 4 depicts a similar detail of a rotor according to a further example. In contrast to the preceding examples, the magnet element 9 is not formed here by an individual strip conductor stack, but rather by a plurality of strip conductor stacks 8 arranged next to one another. Three strip conductor stacks 8 lying next to one another are shown here by way of example, it also being possible for this number to be chosen as lower or higher. In the example in FIG. 4, the individual strip conductor stacks are arranged next to one another in the azimuthal direction of the rotor. They are embedded together in a common cutout in the rotor support 7. Moreover, they are fixed together by a common pole cap 13 which projects beyond all three strip conductor stacks 8 of the magnet element 9 in the azimuthal direction. It is also the case here that the pole cap is selected from a ferromagnetic flux-guiding material. With the segmentation of the magnet element 9 that is present here, this selection is particularly expedient to achieve a homogenization of the magnetic flux which advances radially outward. In particular, this outwardly smooths the maxima of the magnetic flux that are formed over the individual strip conductor stacks 18.
[0063] In the example in FIG. 4, it is also fundamentally conceivable that the intermediate spaces 15 between the strip conductor stacks 8 and the walls of the cutout either remain free or are filled with a filler similar to the example of FIG. 3. The intermediate spaces 15a, which are formed between the individual strip conductor stacks 8, may also similarly either remain free or be filled with a filler. The use of a filler may be advantageous in order to improve the thermal coupling and thus the cooling of the individual strip conductor stacks.
[0064] FIG. 5 depicts a further detail of a rotor according to a further exemplary embodiment. The figure shows a plan view from radially outside onto a radially external surface of the rotor in the region of three external cutouts. These three cutouts are arranged next to one another in the axial direction of the rotor here. Three associated strip conductor stacks 8 are embedded in these three cutouts, e.g., one strip conductor stack in each case per cutout. These axially adjacent strip conductor stacks in particular together form a common magnetic pole of the rotor.
[0065] In the example of FIG. 5, only one respective strip conductor stack 8 is embedded in each of the cutouts. However, it is alternatively also possible for a magnet element 9 to be embedded in each of these cutouts, which magnet element, similar to the example in FIG. 4, is formed from a plurality of azimuthally adjacent strip conductor stacks. According to a further embodiment, it is also possible that, as an alternative or in addition, a plurality of axially adjacent strip conductor stacks are also arranged together in a common cutout in the rotor support.
[0066] It is also the case in the example in FIG. 5, similar to the example in FIG. 3, that the intermediate spaces between the strip conductor stacks and the lateral walls of the cutouts are filled with a filler 17 having a correspondingly low average layer thickness d. In principle, however, it is also possible for these intermediate spaces to have a relatively small width and to be formed without such a filling, similar to the example in FIG. 2.
[0067] FIG. 6 depicts a schematic cross-sectional illustration for a further embodiment of an electrical machine. Overall, this electrical machine is configured similarly to the electrical machine in FIG. 1. In contrast to this, however, here the pole caps 13 on their radially external side are not reproduced on the circular circumference of the rotor support 7, but rather they have a greater curvature. Similar to the example in FIG. 1, it is thus also the case here that the azimuthal edge regions 13a of the pole caps are each formed as thinner than the azimuthal center 13b. In the example of FIG. 6, however, the azimuthal centers 13b extend in the radial direction outwardly to a still greater extent than these azimuthal edge regions 13a. As a result of this greater curvature, the situation may advantageously be achieved in which the magnetic flux density that is formed has a substantially sinusoidal profile viewed over the circumference of the rotor. This advantageously leads to a low-harmonic electrical machine 1.
[0068] 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.
[0069] While the present disclosure has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. 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.
LIST OF REFERENCE SIGNS
[0070] 1 Electrical machine [0071] 3 Stator [0072] 5 Rotor [0073] 6 Air gap [0074] 7 Rotor support [0075] 8 Strip conductor stack [0076] 9 Superconducting magnet element [0077] 10 Strip conductor [0078] 11 Cryostat wall [0079] 12 Radially external cutout [0080] 13 Pole cap [0081] 13a Azimuthal edge region of the pole cap [0082] 13b Azimuthal center of the pole cap [0083] 15 Intermediate space [0084] 15a Intermediate space between strip conductor stacks [0085] 17 Filler [0086] 18 Wall of the cutout [0087] A Central rotor axis [0088] b Average width of the gap [0089] d Average layer thickness [0090] d.sub.max Maximum lateral layer thickness [0091] p Contact pressure [0092] r Radial direction [0093] V Vacuum space
