GB2132002A

GB2132002A - Electrical superconductor

Info

Publication number: GB2132002A
Application number: GB08330640A
Authority: GB
Inventors: Gerhard Mier
Original assignee: Alusuisse Holdings AG; Schweizerische Aluminium AG
Current assignee: Rio Tinto Switzerland AG
Priority date: 1982-12-11
Filing date: 1983-11-17
Publication date: 1984-06-27
Also published as: DE3245903C2; IT1233250B; DE3245903A1; GB8330640D0; GB2132002B; FR2537770B1; IT8324063A0; FR2537770A1; CH662203A5

Abstract

An electrical superconductor 1 comprising at least one superconductive filament consisting of for example niobium/titanium, or Nb3Sn and arranged in a strand 3 of high purity copper or high purity aluminium as primary stabiliser, which is in turn enclosed in an extruded aluminium profile 2 as secondary stabiliser and joined to it by a metallic bond. The profile may have coolant ducts 4. Apparatus for producing one or more superconductors by extruding aluminium around the strand 3 are disclosed (Figures 2 and 3). <IMAGE>

Description

SPECIFICATION Electrical superconductor and process for its production The invention relates to an electrical superconductor comprising at least one filament consisting of niobium/titanium, Nb3Sn or other superconductor material and arranged in a strand of high purity copper or high purity aluminium as primary stabiliser, which is connected to a metallic secondary stabiliser. In addition, the invention includes a process for the production of such a superconductor.

Niobium alloys, high purity copper and high purity aluminium lose their electrical resistance almost completely at temperatures close to absolute zero (-273 C), that it to say, the electrical resistance becomes too small to measure. This effect is described as electrical superconduction. Superconductive magnet coils are used for magnetic cable railways, superconductive cables for no-loss or low-loss generation, transmission and storage of electrical energy and superconduction is utilized also in nuclear technology for generating intense magnetic fields for particle acceleration. For this purpose, the superconductor is immersed in liquid or boiling helium and cooled to a temperature close to absolute zero (-273 C).

Thus electric currents having a current intensity of many thousand amperes can be conducted through a thin filament consising of niobium/titanium or Nb3Sn, which is embedded in high purity copper or aluminium for mechanical protection. A strand of this kind, having a thickness of, for example, 0.5 to 0.8 mm, is described as the primary stabiliser.

However, the latter has not only the function of giving mechanical protection to superconductive threads, e.g. filaments having a diameter of 30 to 50 Fm, but it also carries part of the electric current at particularly high current impulses.

It is known to join the superconductive strand, in turn, to steel or aluminium in order to enable the operation to be maintained to a certain extent, even in the case of temporary breakdown of the associated refrigerating plant. This second jacketing is described as the secondary stabiliser. The custom aryjoining method forthe superconductive strand and the secondary stabiliser is cumbersome, timeconsuming and expensive and is effective, in most cases, by soldering the strand onto the secondary stabiliser.Neither the mechanical protection of the superconductor nor the electrical operation of the secondary stabiliser are at optimum level, since there is no metallic, that is to say atomic, bond between the two and the electrical transition resistance between the superconductive wire and the secondary stabiliser remains relatively large and the latter is not given adequate mechanical protection.

Before the superconductive wire can be soldered on, the aluminium profile, which serves as the secondary stabiliser, has to be given an electrolytic copper coat. In that case, however, care has to be taken that the electrolytically deposited copper layer does not become unduly thick. In general, not more than 10 Fm is permissible, so that the inevitable inpurities do not impair excessively the superconductive effect of the secondary stabiliser. Again, the dimensional tolerances of the superconductive wire and of the aluminium profile make production of the end product more difficult and reduce its quality.

In view of these facts, the inventor has aimed at improving a superconductor and a process of the type mentioned at the beginning in such a way that, on the one hand, the mechanical protection is improved and the transition resistance referred to is reduced and, on the other hand, the production is simplified and becomes more economical.

The solution of this problem lies, in accordance with the invention, in that the filament of superconductor material, particularly a niobium material, such as niobium/titanium or Nb3Sn together with its strand of high purity copper or high purity aluminium, as primary stabiliser, is enclosed by an extruded aluminium profile and is joined to the latter by a metallic, that is to say atomic, bond. The aluminium profile preferably has a purity of at least 99.995%.

Thus the primary stabiliser may be embedded in the aluminium profile in a single operation by means of a compound extrusion press and is then joined to the profile by a metallic bond, without the need of applying electrolytically deposited intermediate layers, which impair the superconductivity. In contrast to known designs, in which the primary stabiliser is open on one side, moreover, it is fully enclosed by the aluminium profile of the secondary stabiliser and is therefore given optimum mechanical protection.

A compound-extruded superconductor can be produced in many geometric shapes, so that it can be adapted to the particular intended use, which is in no way possible with the known superconductors.

Flat rectangular cross-sections for winding superconductive coils are equally possible, such as profile cross-sections having a high moment of resistance at high mechanical stress.

The aluminium profile may possess at least one chamber or other duct for coolant, such as liquid or boiling helium; in order to maintain, e.g., coils made of the superconductor, at about -269 C.

The coolant duct or ducts, can readily extend in the extruded profile longitudinally of the superconductor, e.g. adjacent and parallel to the primary stabiliser strand. The ducts can be adapted in shape and size to the technical requirements regarding throughput of coolant, flow velocity and pressure drop. The ducts are desirably capable of resisting coolant pressure upto 15 bar, or even 20 bar.

The compound-extruded superconductor according to this invention fulfils the above-mentioned requirements and, nevertheless, is essentially produced in one piece and in a single industrial operation, without additional manual labour, apart from economic advantages, also leads to an extremely uniform quality, which can be monitored automatically. This is not the case with the known superconductors either.

The composition of the metallic compound ingredients, moreover may be seected in such a way, that the superconductor can be readily wound.

The invention als includes a process for the production of an electrical superconductor comprising at least one filament consisting of superconductive material and arranged in a strand of high purity copper or high purity aluminium as primary stabilis or, which is joined to a metal profile as secondary stabiliser, characterised in that the primary stabiliser strand is extruded with an aluminium matrix at a temperature below 350 C, preferably 280-300 C, to form a compound profile, with the formation of an intermetallic phase between the two compound ingredients.

The extrusion press may be operated at a lower moulding pressure than is usual for direct extrusion.

Preferably, the superconductor is produced as a compound profile by means of extrusion over a mandrel through a moulding cross-section of a die and, at this juncture, the filament, embedded in high purity copper or aluminium, is passed through a duct of the extrusion press in such a way that it comes into contact with the matrix of the secondary stabiliser at the moulding cross-section. With this refinement the forces exerted by the matrix on the primary stabiliser strand remain small enough so that the latter does not crack.

In the case of a mechanically particularly sensitive superconductive strand, the tearing forces can be reduced further still by simultaneous pressing of several superconductors from a multiple die. In that case, the primary stabiliser strands may be passed as a bundle through ducts of the extrusion press towards mandrels in such a way that they come simultaneously into contact with the matrix of the second stabiliser at the moulding cross-sections of the die.

The invention will now be described by way of example by reference to the accompanying drawings in which: Figure 1 is a perspective sectional view of a superconductor according to the invention, in much enlarged reproduction, compared to real size; Figure 2 is a diagrammatic longitudinal section through a device for the production of a superconductor; and, Figure 3 is a section corresponding to Figure 2, of a different device.

A superconductor 1, in which electrical resistance ceases to appear at temperatures close to absolute zero and which can be employed for example for low-loss energy transmission, consists, as shown in Figure 1, of a profiled body 2 of rectanglar crosssection and a conductive strand 3, provided in the latter and comprising filaments, not illustrated in the drawing, of niobium/titanium or Nb3Sn, which are embedded in high purity aluminium or optionally, high purity copper. This conductive strand 3, together with its high purity aluminium, which serves as the primary stabiliser, is joined by a metallic bond to the profiled body 2, which acts as the secondary stabiliser and consists of super-purity aluminium or another aluminium material.With the aid of this metallic bond, the profiled body takes over part of the current in the best possible manner in case of electrical impulse or in case of breakdown of the refrigerating plant, (secondary stabilisation).

As can be seen, the profiled body 2, on both sies of the conductive strand 3, which lies along the transverse axis Q of the profile, contains cooling ducts 4, through which liquid or boiling helium at about 15 bar may be passed during the operation of the conductor.

Production of this superconductor 1 is effected by means of extrusion through a moulding crosssection 9 of a stationary die 10 and similarly stationary, hollow press part 11, which follows on in the pressing direction x. The die 10 is surrounded by a relatively movable container 12, a bore 13 of which has an aluminium billet 14, perforated along its longitudinal axis, inserted into it and is covered, at its end, by a closure plate 15. A mandrel 17, extending from a stationary base plate 18, projects through a central recess 16 in the closure plate 15 towards the moulding cross-section 9. The base plate as well as its mandrel 17 possess a duct 20, curved at 19, as a guide for the conductive strand 3, consisting of high purity aluminium wire or copper wire, with niobium/titanium filaments or Nb3Sn filaments embedded. The mandrel parts for the creation of the cooling ducts 4 have been omitted from the drawing for reasons of clarity.

Several superconductors 1 can be moulded simultaneiously by means of the device 30 according to Figure 3, that is to say through several moulding cross-sections 9 of a multiple die 10.

Claims

1. An electrical superconductor comprising at least one filament consisting of superconductor material and arranged in a strand of high purity copper or high purity aluminium as primary stabiliser, which is joined to a metal profile as secondary stabiliser, characterised in that the filament with its strand is enclosed by an extruded aluminium profile and is joined to the latter by a metallic bond.

2. A superconductor according to claim 1, characterised in that the aluminium profile has a purity of at least 99.995%.

3. A superconductor according to claim 1 or claim 2, characterised in that the aluminium profile possesses at least one coolant duct.

4. A superconductor according to claim 3, characterised in that at least one of the coolant ducts is adjacent and parallel to the primary stabiliser strand.

5. A superconductor according to claim 3 or claim 4, characterised in that the coolant duct is capable of resisting a pressure of up to 15 bar.

6. A superconductor according to claim 5, characterised in that the coolant duct is capable of resisting a pressure of up to 20 bar.

7. A superconductor according to any one of the preceding claims, characterised in that the secondary stabiliser and the primary stabiliser are so shaped thatthey can be wound into a coil.

8. A superconductor according to any one of the preceding claims, characterised in that the superconductor material is niobium/titanium or Nb3Sn.

9. A superconductor substantially as described with reference to Figure 1 of the accompanying drawings.

10. A process for the production of an electrical superconductor comprising at least one filament consisting of superconductor material and arranged in a strand of high purity copper or high purity aluminium as primary stabiliser, which is joined to a metal profile as secondary stabiliser, characterised in that the primary stabiliser strand is extruded with an aluminium matrix at a temperature below 3500C to form a compound profile, with the formation of an intermetallic phase between the two compound ingredients.

11. A process according to claim 11, characterised in that the extrusion temperature is between 280 and 300 C.

12. A process according to claim 10 or claim 11, characterised in that the superconductor is produced as a compound profile by means of extrusion over a mandrel through a moulding cross-section of a die and that, at this juncture, the filament, embedded in high purity copper or aluminium, is passed through a duct of the extrusion press in such a way that it comes into contact with the matrix of the secondary stabiliser at the moulding cross-section.

13. A process according to any one of claims 10 to 12, characterised in that two or more profiles are pressed simultaneously through a multiple die and that several strands are passed as a bundle through ducts of the extrusion press towards mandrels in such a way that they come simultaneously into contact with the matrix of the secondary stabiliser at the moulding cross-sections of the die.

14. A process for the production of electrical superconductor(s) substantially as described with reference to Figures 2 or 3 of the accompanying drawings.