Abstract
The invention relates to a rotor (5) for an electric machine (1) having a central rotor axis (A). The rotor comprises a rotor carrier (7), at least one superconducting permanent magnet (9) carried mechanically separately by the rotor carrier (7), and a damper shield having at least one shielding element (13a, 13i), which surrounds the at least one superconducting permanent magnet (9) and which is formed from an electrically conductive material having an electric conductivity of less than 30.Math.10.sup.6 S/m. The invention further relates to an electrical machine (1) having a rotor (5) of this kind.
Claims
1. A rotor for an electrical machine with a central rotor axis, the rotor comprising: a rotor support; at least one superconducting permanent magnet that is mechanically supported by the rotor support; and a damping shield with at least one shielding element that surrounds the at least one superconducting permanent magnet and is formed from an electrically conductive material with an electrical conductivity σ of at least 30.Math.10.sup.6 S/m.
2. The rotor of claim 1, wherein the at least one shielding element has a thickness of at least 0.1 mm.
3. The rotor of claim 1, in which the electrically conductive material of the at least one shielding element comprises copper, aluminum, or copper and aluminum.
4. The rotor of claim 1, wherein the damping shield has an external shielding element that radially surrounds the at least one superconducting permanent magnet and the rotor support together.
5. The rotor of claim 4, wherein the external shielding element is provided with a plurality of cooling fins on an outer surface of the external shielding element.
6. The rotor of claim 1, wherein the damping shield has at least one internal shielding element that is associated with the at least one superconducting permanent magnet and surrounds the at least one superconducting permanent magnet locally such that the at least one internal shielding element, together with the at least one associated superconducting permanent magnet, is mechanically supported by the rotor support.
7. The rotor of claim 6, wherein the at least one internal shielding element is thermally more strongly coupled to the rotor support (7) than to the at least one associated superconducting permanent magnet.
8. The rotor of claim 7, further comprising a thermal insulation layer that is arranged between the at least one internal shielding element and the at least one associated superconducting permanent magnet.
9. The rotor of claim 6, wherein the at least one internal shielding element, together with the at least one associated superconducting permanent magnet, forms a prefabricated component.
10. The rotor of claim 6, wherein the at least one internal shielding element is composed of a shielding vessel and a shielding cover.
11. The rotor of claim 6, wherein the at least one superconducting permanent magnet comprises a plurality of superconducting permanent magnets that are surrounded either individually or combined in groups by respectively associated internal shielding elements, wherein the internal shielding elements are each arranged at least partly between the associated superconducting permanent magnet and the rotor support.
12. The rotor of claim 1, wherein the at least one superconducting permanent magnet comprises a high-temperature superconducting material.
13. The rotor of claim 1, wherein the at least one superconducting permanent magnet is formed by a stack of a plurality of superconducting strip conductors.
14. The rotor of claim 1, wherein the at least one superconducting permanent magnet is formed by a superconducting bulk element.
15. An electrical machine comprising: a rotor for an electrical machine with a central rotor axis, the rotor comprising: a rotor support; at least one superconducting permanent magnet that is mechanically supported by the rotor support; and a damping shield with at least one shielding element that surrounds the at least one superconducting permanent magnet and is formed from an electrically conductive material with an electrical conductivity a of at least 30.Math.10.sup.6 S/m; and a stator that is arranged in a fixed manner.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 shows a schematic cross section through a first embodiment of an electrical machine;
[0047] FIG. 2 shows a schematic cross section through a second embodiment of the electrical machine; and
[0048] FIGS. 3 to 6 show details of similar machines in the field of superconducting permanent magnets.
DETAILED DESCRIPTION
[0049] In the figures, elements that are the same or have the same function are provided with the same reference signs.
[0050] FIG. 1 shows a schematic cross section of one embodiment of an electrical machine 1. In other words, FIG. 1 shows the electrical machine 1 perpendicularly to a central axis A. The electrical machine 1 includes an external stationary stator 3 and an internal rotor 5 that is rotatably mounted about the central axis A. The electromagnetic interaction between the rotor 5 and the stator 3 takes place across an air gap 15 situated between the rotor 5 and the stator 3. The electrical machine 1 is a permanently excited machine that has a plurality of superconducting permanent magnets 9 in order to form an excitation field in a region of the rotor 5. In the cross section of FIG. 1, four (4) permanent magnets 9 of this kind are distributed over a circumference of the rotor 5 by way of example. The permanent magnets 9 are arranged in corresponding radially outer recesses of a rotor support 7, where the rotor support 7 mechanically supports the permanent magnets 9. However, yet further permanent magnets 9 than the four shown in FIG. 1 may also be present in the axial direction (not shown in in Figure), where the number of magnetic poles of the electrical machine is not increased by such an axial subdivision, however.
[0051] The rotor support 7, together with the permanent magnets 9 held thereon, is cooled to a cryogenic operating temperature that is below the critical temperature of the superconductor material used in the permanent magnets 9, by a cooling apparatus (not shown in any detail). In order to maintain this cryogenic temperature, the rotor support 7 and the permanent magnets 9 are arranged in the interior of a cryostat 11 together. There is an annular vacuum space V for thermal insulation between the cryostat and the rotor support 7. In the exemplary embodiment of FIG. 1, a damping shield of the rotor 5 is implemented by an external shielding element 13a. The external shielding element 13a is configured as a metallic hollow cylinder that radially encloses the outer wall of the cryostat 11. In this way, the elements 7 and 9 situated further on the inside are also radially surrounded by the external shielding element 13a. As a result, alternating electromagnetic fields from regions that are situated radially even further on the outside may be effectively shielded by the external shielding element 13a, so that interaction of such fields with the superconducting permanent magnets is greatly reduced. The heat released in the external shielding element 13a by the eddy currents that occur, for example, may be dissipated in the direction of the air gap 15. In order to increase the heat dissipation in the direction of the air gap, the external shielding element 13a may be provided, on an outer surface of the external shielding element 13a, with a plurality of cooling fins 14, only one of which is shown in FIG. 1 by way of example. The cooling fins may (as indicated here) either extending axially, or the cooling fins may be annular cooling fins in the circumferential direction or else cooling fins oriented in some other way (e.g., also in a spiral shape). The heat generated in the region of the external shielding element may, in addition to the air cooling described, also be dissipated by a cooling system provided in the region of the stator for cooling the stator winding (not shown in detail in FIG. 1).
[0052] FIG. 2 shows a schematic cross section through an alternative embodiment of an electrical machine 1. The electrical machine 1 is configured similarly to the machine of FIG. 1 in principle. In contrast to this, however, the electrical machine 1 also has an internal shielding element 13i around each superconducting permanent magnet 9. In the example shown in FIG. 2, these internal shielding elements 13i are provided in addition to the external shielding element 13a already described. Therefore, the internal shielding elements 13i form the superordinate damping shield together with the external shielding element 13a. However, as an alternative, the alternating electromagnetic fields may also be shielded predominantly or even exclusively by the inner shielding elements 13i. The external shielding element 13a is therefore to be regarded as optional for this exemplary embodiment.
[0053] The internal shielding elements 13i therefore provide local shielding of the alternating fields (e.g., remaining alternating fields) in the region of the superconducting permanent magnets 9. The internal shielding elements 13i are arranged locally around the superconducting permanent magnets 9, so that the internal shielding elements 13i also fill an intermediate space between the permanent magnets 9 and the rotor support 7. Each of the superconducting permanent magnets 9 is therefore completely enveloped at least in a radial direction by a respectively associated internal shielding element 13i. It is possible for precisely one such internal shielding element 13i to be associated with each permanent magnet 9. However, as an alternative, a plurality of permanent magnets 9 may also be surrounded in groups by a common inner shielding element 13i. For this purpose, a plurality of permanent magnets 9 may be arranged one behind the other, for example, within a common inner shielding element 13i in the axial direction (not shown in FIG. 2). The inner shielding elements 13i are also formed from an electrically highly conductive material and may therefore effectively shield the alternating electromagnetic fields present from the inside by forming eddy currents and therefore avoid direct interaction of these fields with the superconducting permanent magnet 9. The heat released as a result in the region of the inner shielding elements 13i may be dissipated via the rotor support 7, which is thermally coupled to the cooling system. For this purpose, the thermal resistance between the elements 13i and 7 may be smaller than the thermal resistance between the elements 13i and 9.
[0054] FIG. 3 shows a schematic cross section through a detail of the rotor of one embodiment of an electrical machine. FIG. 3 shows the region of a superconducting permanent magnet 9 that is embedded in a radially outer cavity of a rotor support 7. The remaining portion of the electrical machine may be configured, for example, similarly to the machine of FIG. 2. The permanent magnet 9 of FIG. 3 is also locally surrounded by an internal shielding element 13i, so that the permanent magnet 9, together with the internal shielding element 13i, forms a shielded magnetic element 16. This shielded magnetic element 16 may be produced as a prefabricated component and accordingly becomes embedded as a whole in the matching cavity of the rotor support 7. Yet further similar permanent magnets 9 may optionally be arranged as a group within a common shielding element 13i in the axial direction too (not shown). In the example of FIG. 3, the superconducting permanent magnet 9 is configured as a superconducting bulk element. For example, the superconducting permanent magnet may be a one-piece cuboid composed of YBCO or magnesium diboride. The material of the internal shielding element 13i may, in turn, include, for example, aluminum or copper as the main constituent. The thickness of the internal shielding element 13i is indicated by d13, for example. This thickness may be, for example, in the region of 2 mm. Good electromagnetic shielding of the alternating fields may be provided given a wall thickness of this kind. Due to the radially circumferential arrangement of the inner shielding element 13i, the permanent magnet 9 and the rotor support 7 are spaced apart at least by this thickness d17.
[0055] FIG. 4 shows a detail of a rotor according to a further exemplary embodiment. The region around a superconducting permanent magnet 9 that, together with an internal shielding element 13i, forms a shielded magnetic element 16 is shown in FIG. 4 too. However, in contrast to the example of FIG. 3, the superconducting permanent magnet 9 is not formed as a one-piece superconductor here, but rather, as a stack of individual superconducting strip conductors 10. These individual strip conductors may be connected to one another by a suitable adhesive or some other connector to form a solid stacked package.
[0056] The individual superconducting strip conductors are each formed by a layer system including a superconducting layer and optionally a plurality of further electrically conductive and or insulating layers on a strip-like support substrate. The superconductor layer is comparatively thin in comparison to this support substrate, so that the superconductor layer only forms a small constituent part of the total material of the strip conductor stack. Nevertheless, even with such a superconducting strip conductor stack, comparatively high magnetic flux densities may be achieved for forming an excitation field.
[0057] FIG. 5 shows a detail of a rotor according to a further exemplary embodiment. In addition to the elements shown in FIG. 4, a thermal insulation layer 17 that is arranged circumferentially around the superconducting permanent magnet 9 between the superconducting permanent magnet 9 and the internal shielding element 13i is also shown. The thickness d17 of this thermal insulation layer 17 may be, for example, between 0.2 mm and 1 mm. The material of this insulation layer may be given, for example, by an epoxy resin with a comparatively low thermal conductivity. Such a thermal insulation layer may provide that the heat released due to the electrical shielding in the element 13i is dissipated substantially through the rotor support 7 to the cooling system of the rotor and makes only a minor contribution to heating of the superconducting permanent magnet 9. The permanent magnet 9 and the associated inner shielding element 13i are spaced apart at least by the thickness d17 owing to the additional thermal insulation layer. The permanent magnet 9 and the associated inner shielding element 13i may be spaced apart substantially precisely by this thickness. In the example of FIG. 5, the permanent magnet 9 is once again shown as a stack of individual superconducting strip conductors. However, as an alternative, the permanent magnet may also again be a bulk element, similarly to the example of FIG. 3.
[0058] FIG. 6 shows a detail of a rotor according to a further exemplary embodiment. Instead of the unitary and, for example, one-piece inner shielding element 13i shown in FIG. 4, the superconducting permanent magnet 9 is surrounded by a two-part inner shielding element 13i. The inner shielding element 13i is formed by a shielding vessel 21 and a shielding cover 23. Both elements are formed continuously from a highly electrically conductive material and with a thickness suitable for shielding, as explained further above. For example, the slight lateral overlap between the shielding cover and the shielding vessel provides adequate shielding of the surrounding alternating electromagnetic fields with this two-part design, so that electrical interaction with the internal superconducting permanent magnet 9 is effectively avoided. In the example of FIG. 6, the permanent magnet 9 is once again shown as a stack of individual superconducting strip conductors. However, as an alternative, the permanent magnet may also again be a bulk element, similarly to the example of FIG. 3.
[0059] 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 invention. 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. Such new combinations are to be understood as forming a part of the present specification.
[0060] While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can 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.
