Superconducting coil device having a coil winding

Abstract

A plurality of windings in a coil winding of a superconducting coil device includes at least one superconducting strip conductor that has a strip-shaped substrate strip and a superconducting layer arranged on the substrate strip. The coil device is subdivided into a plurality of segments in which adjacent windings are cast or adhered together within each segment, adjacent windings being, at most, weakly connected or adhered together in at least one sub-region, in the intermediate region between two adjacent segments.

Claims

1. A superconducting coil device comprising: a coil winding with a plurality of turns comprising a racetrack coil or a rectangular coil; at least one superconducting tape conductor with a strip-shaped substrate tape and a superconducting layer arranged on the substrate tape; the coil winding subdivided into a plurality of segments, neighboring turns within each segment being at least one of encapsulated together and adhesively bonded to one another, and, in an intermediate region between two neighboring segments, the neighboring turns being at most weakly connected or adhesively bonded to one another in at least in one subregion; and a plurality of subregions having at most a weak connection of the neighboring turns of neighboring segments lie within curved regions of the coil winding.

2. The coil device as claimed in claim 1, wherein, in the intermediate region between two neighboring segments, the neighboring turns are at most connected by an adhesive forming a connection breakable at a stress below 10 MPa in the at least one subregion.

3. The coil device as claimed in claim 1, wherein, in the intermediate region between two neighboring segments, the at least one subregion in the intermediate region between the neighboring turns is free of adhesive bonding or encapsulation compound.

4. The coil device as claimed in claim 1, further comprising an encapsulation compound enclosing the neighboring turns within the segment.

5. The coil device as claimed in claim 1, further comprising a coating of a separating medium or an inlaid tape of a separating medium in the at least one subregion in the intermediate region between two neighboring segments.

6. The coil device as claimed in claim 5, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a material having a thermal expansion coefficient lower than an effective thermal expansion coefficient of the tape conductor.

7. The coil device as claimed in claim 6, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a flexible material having a tensile strength of less than 10 MPa.

8. The coil device as claimed in claim 1, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a material having a thermal expansion coefficient lower than an effective thermal expansion coefficient of the tape conductor.

9. The coil device as claimed in claim 1, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a flexible material having a tensile strength of less than 10 MPa.

10. The coil device as claimed in claim 1, wherein the superconducting layer includes a second-generation high-temperature superconductor.

11. The coil device as claimed in claim 10, wherein the superconducting layer includes ReBa.sub.2Cu.sub.3O.sub.x.

12. A superconducting coil device, comprising: a coil winding with a plurality of turns, the coil winding comprising a racetrack coil or a rectangular coil; at least one superconducting tape conductor with a strip-shaped substrate tape and a superconducting layer arranged on the substrate tape; the coil winding being subdivided into a plurality of segments, neighboring turns within each segment being at least one of encapsulated together and adhesively bonded to one another, and, in an intermediate region between two neighboring segments, the neighboring turns being at most weakly connected or adhesively bonded to one another in at least in one subregion; a plurality of subregions having at most a weak connection of the neighboring turns of neighboring segments lie within curved regions of the coil winding and transition regions respectively adjacent on both sides; wherein, in the intermediate region between two neighboring segments, the neighboring turns are at most connected by an adhesive forming a connection breakable at a stress below 10 MPa in the at least one subregion.

13. The coil device as claimed in claim 12, wherein, in the intermediate region between two neighboring segments, the at least one subregion in the intermediate region between the neighboring turns is free of adhesive bonding or encapsulation compound.

14. The coil device as claimed in claim 12, further comprising an encapsulation compound enclosing the neighboring turns within the segment.

15. The coil device as claimed in claim 12, further comprising a coating of a separating medium or an inlaid tape of a separating medium in the at least one subregion in the intermediate region between two neighboring segments.

16. The coil device as claimed in claim 15, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a material having a thermal expansion coefficient lower than an effective thermal expansion coefficient of the tape conductor.

17. The coil device as claimed in claim 12, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a material having a thermal expansion coefficient lower than an effective thermal expansion coefficient of the tape conductor.

18. The coil device as claimed in claim 12, wherein, in the intermediate region between two neighboring segments, the tape conductor is provided in the at least one subregion with an additional layer formed from a flexible material having a tensile strength of less than 10 MPa.

19. The coil device as claimed in claim 12, wherein the superconducting layer includes a second-generation high-temperature superconductor.

20. The coil device as claimed in claim 19, wherein the superconducting layer includes ReBa.sub.2Cu.sub.3O.sub.x.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects and advantages will become more apparent and more readily appreciated with the aid of two exemplary embodiments described below with reference to the accompanying drawings of which:

(2) FIG. 1 is a schematic cross section of a superconducting tape conductor,

(3) FIG. 2 is a cross section of a detail of a coil winding according to a first exemplary embodiment, and

(4) FIG. 3 is a coil winding according to a second exemplary embodiment in schematic plan view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

(6) FIG. 1 shows a cross section of a superconducting tape conductor 1, in which the layer structure is represented schematically. In this example, the tape conductor has a substrate tape 2, which in this case is a 100 μm thick substrate such as a nickel-tungsten alloy. As an alternative, steel tapes or tapes of an alloy, for example Hastelloy, may also be used. Arranged over the substrate tape 2, there is a 0.5 μm thick buffer layer 4, which here contains the oxide materials CeO.sub.2 and Y.sub.2O.sub.3. This is followed by the actual superconducting layer 6, here a 1 μm thick layer of YBa.sub.2Cu.sub.3O.sub.x, which is in turn covered with a 50 μm thick cover layer 8 of copper. As an alternative to the material YBa.sub.2Cu.sub.3O.sub.x, it is also possible to use corresponding compounds REBa.sub.2Cu.sub.3O.sub.x of other rare earths RE. Arranged on the opposite side of the substrate tape 2, there is in this case a further 50 μm thick cover layer 8 of copper, followed by an insulator 10, which in this example is configured as a 25 μm thick Kapton tape. The insulator 10 may, however, also be made of other insulating materials, for example other plastics. In the example shown here, the width of the insulator 10 is somewhat greater than the width of the other layers of the tape conductor 1, so that turns W.sub.i, W.sub.i+1 that come to lie on one another when the coil device is being wound are reliably insulated from one another. As an alternative to the example shown, the tape conductor 1 may also have insulator layers on both outer surfaces, or the lateral regions of the superconducting tape conductor 1 may additionally be protected by insulating layers. It is furthermore possible to wind an insulator tape into the coil device as a separate tape during the actual production of the coil winding. This is particularly advantageous when a plurality of tape conductors, which do not need to be insulated from one another, are wound in parallel. Then, for example, an assembly of from 2 to 6 tape conductors lying above one another without their own insulating layer may be wound together with an additionally inlaid insulator tape in common turns.

(7) Typically, the substrate tape 2, the buffer layer 4, the superconducting layer 6 and the cover layer 8 in their entirety experience a thermal contraction of about 0.3% when they are cooled from about 300 K to about 30 K. For known materials of the insulator 10 and of the epoxides used as an encapsulation compound or adhesive compound, the thermal contraction is however substantially higher, about 1.2%. In the case of planar stacks of tape conductors and on the straight sections of a coil winding, these differences can be compensated for by different shrinkages in the plane and perpendicularly to the plane of the tape conductor. In the curved regions, however, they lead to the formation of radial tensile stresses. In the following two exemplary embodiments, the way in which the radial tensile stresses can be reduced by the subdivision into segments is shown. It is particularly advantageous for the layers having a high thermal contraction in this case to be made as thin as possible, above all in the curved regions. Both exemplary embodiments below will be based on the tape conductor represented in FIG. 1 as the winding material. Here, at 25 μm, the insulator 10 is advantageously made relatively thin in comparison with the remaining overall thickness of the tape conductor 1.

(8) FIG. 2 shows a detail of a first coil winding 12 according to a first exemplary embodiment. In this example, the coil winding 12 is configured as a rectangular coil. The detail in FIG. 2 shows a region around the four curved corners of the rectangular coil. FIG. 2 in this case represents only a part of the coil winding 12, namely a section of the winding with six turns of tape conductors 1 lying above one another, each of which is constructed according to the example in FIG. 1. Three of the turns are part of an inner segment S.sub.i, and three of the turns represented are part of an outer segment S.sub.i+1. As indicated, each segment has more than the three turns represented by way of example. For example, each segment may have between 10 and 200 turns, particularly advantageously between 50 and 100 turns. The overall coil winding may for example have between 2 and 50 such segments, particularly advantageously between 5 and 10 segments. Inside each segment S.sub.i, S.sub.i+1, in this exemplary embodiment all the turns W.sub.i are encapsulated with an epoxide encapsulation compound 14. The encapsulation compound 14 in this exemplary embodiment was introduced by vacuum encapsulation after winding of the coil (so-called dry winding). As an alternative, an impregnating resin or an adhesive may also be introduced already during the winding of the coil winding (so-called wet winding), in which case the tape conductor is typically wetted on both sides with the impregnating resin or adhesive before the winding. In this exemplary embodiment, the neighboring turns W.sub.i−1, W.sub.i are also encapsulated together in a plurality of subsections in the intermediate regions 20 between the segments S.sub.i, S.sub.i+1. Of the four straight subsections 28 of the rectangular coil, two are represented schematically in FIG. 2. Within these subsections 28, all the turns W.sub.i of the entire coil are firmly connected to one another by the encapsulation compound 14, including in the intermediate region 20 between two neighboring segments S.sub.i, S.sub.i+1. In the curved regions 24, of which the overall rectangular coil includes four, however, the neighboring turns W.sub.−1, W.sub.i of different segments S.sub.i, S.sub.1+1 are not connected to one another by encapsulation compound 14. The same applies for the transition regions 26, adjacent to each curved region 24 on both sides, in which likewise no encapsulation compound 14 is arranged between the neighboring turns W.sub.i−1, W.sub.i of different segments S.sub.i, S.sub.1+1. Instead, a PTFE tape 16 is inlaid in this entire subregion 22 between the segments S.sub.i, S.sub.i+1, which prevents this subregion 22 from being filled with encapsulation compound 14 during the encapsulation of the wound coil. In this example, the PTFE tape 16 has a layer thickness similar to the average thickness of the encapsulation compound introduced during the encapsulation, in this case a thickness of 25 μm. The inlaid PTFE tape 16 thus advantageously prevents adhesive bonding of the tape conductors 1 of neighboring turns W.sub.i−1, W.sub.i to the encapsulation compound 14 in the subregion 22, so that the PTFE tape 16 laid inbetween is not wetted by the encapsulation compound 14. In this way, furthermore, the formation of a strong connection of the neighboring tape conductors 1 in this subregion 22 is avoided. In this exemplary embodiment, no chemical adhesive bond at all is formed in this subregion 22. As an alternative to this example, the tape conductor may also be coated with a separating medium, for example PTFE, in the subregion 22. Depending on the properties of the coating, either no adhesive bond at all or only a weak adhesive bond may then be formed between the neighboring tape conductors 1. As an alternative or in addition to the separating medium 16 represented here, a further layer may also be introduced in the intermediate region 20. Either the material of this further layer may have a low or even negative thermal expansion coefficient, and/or the layer may include a flexible material having a tensile strength of less than 10 MPa. In both configurations, the further layer contributes to reducing radial tensile stresses in the intermediate regions 20, and to increasing the mechanical strength of the coil in the curved regions 24 and the adjacent transition regions 26.

(9) A feature common to all the variants described above is that the tensile stress on the turns W.sub.i of the entire coil is reduced by the at most weak connection of the neighboring tape conductors 1 in the subregions 22. Owing to the at most weak connection in these subregions 22, the maximum tensile strength on the tape conductor 1 due to thermal contraction of the various materials behaves approximately as in the case of a coil winding which only has the number of turns of an individual segment S.sub.1. The rectangular coil of the exemplary embodiment shown has four relatively long straight regions 32 and four relatively short curved regions 24, respectively with transition regions 26 adjacent on both sides. Above all, mechanical decoupling and tensile relief of the segments in the curved regions 24 is effective for reduction of the tensile stress on the tape conductor. The rectangular coil may therefore be encapsulated entirely as in known methods in the straight regions 32, and therefore have a large part of the mechanical stability achieved by these methods. Advantageously, the at most weak connection of the neighboring tape conductors 1 between two neighboring segments S.sub.i, S.sub.i+1 is also present in transition regions 26 adjacent on both sides, in addition to the curved regions 24, so that excessively high tensile, compressive or shear stresses are not formed at the transition from the straight regions 32 into the curved regions 24 and at the transition from the strongly connected to the weakly connected intermediate regions.

(10) FIG. 3 shows a second coil winding 30 according to a second exemplary embodiment in schematic plan view. This second coil winding 30 is configured as an approximately cylindrical winding, in this example the cylindrical shape being formed only approximately from straight regions 32 and curved regions 24. In the example shown here, the coil winding respectively includes eight straight regions 22 and eight curved regions 24, although the number of individual regions may also be substantially greater. In the second exemplary embodiment shown, the coil winding has only two segments S.sub.i and S.sub.i+1. The number of segments may however also be substantially greater, and it may for example be between 2 and 50 and particularly advantageously between 5 and 10. Throughout the encapsulated region 34 of the second exemplary embodiment shown, all neighboring turns are firmly connected to one another by encapsulation compound, even over the boundary 36 of the two segments. Only in the eight subregions 22 on the boundary 36 of the segments is the encapsulation compound between the neighboring tape conductors 1 interrupted. In this second exemplary embodiment, the tape conductors 1 adjacent to the subregions 22 are coated with the separating medium PTFE, which has a dewetting effect for the encapsulation compound and therefore leads to cavities without encapsulation compound being formed in the subregions 22. In the subregions 22, the neighboring tape conductors are therefore not connected to one another in this example, and the formation of the cavities particularly effectively leads to tensile relief of the radial tensile stresses occurring to an increased amount in the curved regions 24. Owing to the expansion or compression of the cavities when the temperature changes, both tensile and compressive stresses on the tape conductors 1 of the coil winding 30 can be reduced.

(11) A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).