FR2772180A1 - HIGH CRITICAL TEMPERATURE SUPERCONDUCTING COIL, AND METHOD FOR MANUFACTURING SUCH A COIL - Google Patents

Abstract

the invention relates to a coil with an HTc superconductive multifilament strand comprising at least one winding made up of a plurality of turns made from a HTc superconductive multifilament strand, said strand comprising a plurality of HTc superconductive filaments embedded in a silver matrix, andan oxidized metallic material, at least on the surface, interposed between the turns, electrically insulating the turns from one another, according to the invention, the oxidized metallic material is an aerated material.

Description

HIGH CRITICAL TEMPERATURE SUPERCONDUCTING COIL, AND

  PROCESS FOR THE MANUFACTURE OF SUCH A COIL

  The invention relates to a critical high temperature superconductive coil, and to a method for manufacturing such a coil. A critical high temperature (HTc) superconductive coil comprises at least one winding of a superconductive HTc multifilament strand. The HTc superconducting multifilament strand includes

  a plurality of HTc superconductive ceramic filaments embedded in a silver matrix.

  The HTc superconducting multifilament strand is produced using Powder In Tube (PIT) technology. This consists of filling a billet of powdery reagents which, after heat treatment, can transform into a superconductive material of the ceramic type.

  HTc. This billet is then closed under vacuum and stretched, bundled in a new billet itself closed under vacuum and stretched in turn. The resulting multifilament strand 20 can undergo the same steps, and so on until the number of filaments per unit area desired.

  The strand thus produced is then put into final shape then heat treated for the transformation of powdery reagents into HTc superconductive ceramic. In a first embodiment of HTc superconductive coil, called "react and wind", the strand HTc superconducting multifilament is first heat treated then the coil and produced from the superconducting multifilament strand in phase

superconductive.

  This manufacturing method overcomes the problems of insulation of the turns constituting the winding. In fact, the insulation can be added cold when the coil is made up. 35 On the other hand, this manufacturing method induces mechanical stresses in the superconducting multifilament strand HTc in the superconductive phase, harmful to

  electrical performance of the coil thus produced.

  In a second embodiment of an HTc superconductive coil, called "wind and react", the coil is produced with a superconductive HTc multifilament strand in non-superconductive phase, then the coil thus produced is heat treated in order to synthesize the powdery reagents in

HTc superconductive ceramic.

  This second embodiment makes it possible to overcome a large part of the problems of mechanical stresses in the coil and therefore to improve performance.

  intrinsic electrical components of the coil.

  However, this second embodiment presents difficulties in isolating the turns from each other. Indeed it is necessary that the turns of the silver matrix coil do not touch during treatment

  otherwise it would automatically create short-

circuits between the turns.

  The use of insulating ceramic paper is known which is co-wound with the multifilament strand in the non-conductive phase. However, this type of paper has several disadvantages, namely: the improvement in the Ampere.tours / volume ratio is, in part, a function of the thickness of the insulation. The finer the thickness of the insulation, the more favorable the above ratio. The ceramic papers sold are of the order of 0.3 mm, which is far too large. he

  the thickness of the insulation should not exceed 0.1 mm.

  However, ceramic paper of this thickness is very fragile and does not allow large-scale industrial use.

  series at affordable production costs.

  Another drawback is due to the fact that the ceramic paper, in order to be able to be handled, is impregnated with an organic product releasing CO 2 during the heat treatment. This C02 is a polluting agent which can cause

  peril the synthesis of superconductive ceramics.

  Finally, once the heat treatment has been carried out, the ceramic paper is no longer self-supporting and therefore the coil is very difficult to handle, in particular during the consolidation and reinforcement stages, for example by

resin injection.

  It is necessary to find a material having a high electrical resistivity, easily shaped, not constituting a danger of pollution of silver and / or powdery precursors during the critical synthesis phase,

  and self-supporting both before and after the heat treatment.

  EP-A-0772208 describes a coil and a "react and wind" manufacturing method for an HTc superconductive coil. The HTc multifilament strand is co-wound with a solid sheet of metallic material whose surface has been

previously oxidized.

  EP-A-0772208 makes it possible to improve the mechanical strength of the coil while reducing the thicknesses required for

the insulation (of the order of 0.03 mm).

  However, the use of the solid sheet of metallic material induces other drawbacks, namely the synthesis of the precursors in the superconductive phase requires oxygen. This oxygen is transported to the precursors through the silver matrix of the strand

  multifilament. However, in the process proposed by EP-A-

  0772208, only the thickness of the multifilament strand is in contact with the oxygenated atmosphere surrounding the coil. The rest of the strand is sandwiched between two metal sheets

  full, hardly accessible to oxygen.

  In addition, knowing that during the synthetic heat treatment, the precursors are partially in a liquid phase, in the event of a snag in the silver sheath, the fraction of the precursors in the liquid phase flows by capillarity between the oxidized metal sheet and the silver matrix, thereby inducing pollution of the precursors by metal oxide, and a variation in the stoichiometric composition of the precursors which may affect

  substantially synthesis in the superconducting phase.

  The object of the present invention is to propose a method for manufacturing a multifilament strand coil

  HTc overcoming the drawbacks resulting from the above process

  above, and a coil thus produced.

  To this end, the invention relates to a coil with a HTc superconducting multifilament strand comprising at least one winding consisting of a plurality of turns made from a HTc superconducting multifilament strand, said strand comprising a plurality of HTc superconductive filaments embedded in a silver matrix, and an oxidized metallic material, at least on the surface, interposed between the turns, electrically insulating the

whorl each other.

  According to the invention, the oxidized metallic material is a

ventilated material.

  In one embodiment the aerated oxidized metallic material consists of a plurality of metallic wires

oxidized woven fabrics.

  In another embodiment, the material

  aerated oxidized metal is an expanded oxidized metal.

  the oxidized metallic material is chosen from Fe, Ni, Al, Cu, or a mixture of these.

  The invention also relates to a method for manufacturing a coil with an HTc multifilament superconductive strand as described above, in which: the non-synthesized HTc multifilament strand is co-wound with the aerated metallic material, thereby making a non-HTc superconductive coil synthesized, and the coil thus produced is thermally treated in an oxygenated atmosphere in order to synthesize the HTc superconductive strand in the superconductive phase and for

  oxidize, at least on the surface, the aerated metallic material.

  In an alternative embodiment, the aerated metallic material can undergo a preliminary pre-oxidation heat treatment. A series of advantages of the present invention results from the aerated nature of the metallic material: This makes it possible to substantially increase the surface of the silver sheath in contact with the oxygenated atmosphere. Synthesis in the superconducting phase is more complete and lasts

shorter time.

  Oxidation of aerated metallic material can be done

  together with synthetic heat treatment.

  The surface of the oxidized metallic material in contact with the silver sheath being substantially reduced compared to a solid sheet, the capillary leakage of the

  liquid phase precursors are also reduced.

  For the same reasons, metal pollution

  oxidized precursors is limited.

  Other advantages, such as the attenuation of the influence of snags in the silver sheath on the performance of the coil, the reduction of the manufacturing time of a coil, allow the application of the method according to the invention to the great series, while maintaining the

  performance of the coils manufactured.

  Other advantages and features of this

  invention will result from the description which follows

  reference to the accompanying drawings in which: Figure 1 is a schematic sectional view

  transverse of a coil according to the present invention.

  Figure 2 is a schematic view in longitudinal section of a detail of an insulation between two turns of a coil according to the invention in a first embodiment. Figure 3 is a schematic view in longitudinal section of a detail of an insulation between two turns of a coil according to the invention in a second embodiment. The invention relates to a coil with a multifilament superconductive strand HTc 3 comprising at least one winding 1 consisting of a plurality of turns 2, 2a, 2b produced from a multifilament superconductive strand HTc 3, said strand 3 comprising a plurality of filaments HTc 4 superconductors embedded in a silver matrix 5, and an oxidized metallic material 6, 7, 8, at least on the surface, interposed between the turns 2, 2a, 2b, electrically insulating the turns 2, 2a, 2b one of the other. The

  oxidized metallic material 6, 7, 8 is an aerated material.

  By aerated oxidized metallic material is meant a metallic material at least surface non-oxidized, having through holes. The multifilament strand is made according to any

  known method, in particular the PIT (Powder In Tube) methods.

  In the representation of FIG. 2, the aerated oxidized metallic material 6 consists of a plurality of oxidized metallic wires 7 woven together. The fabric thus produced allows oxygen circulation between the 25 turns of the coil during the synthetic heat treatment

and oxidation.

  In the representation of FIG. 3, the aerated oxidized metallic material 6 is an expanded made of oxidized metal 8. The mesh of the expanded metallic allows a circulation of oxygen between the turns of the coil during the treatment

  thermal synthesis and oxidation.

  The metallic material intended to be oxidized is chosen from the most oxidizable metals, in particular from Fe, Ni,

Al, Cu, or a mixture thereof.

  The invention also relates to a method for manufacturing a coil with an HTc superconducting multifilament strand as described above. The process steps are as follows: a non-synthesized HTc 3 multifilament strand is wound together with the aerated metallic material 6, 7, 8 thus producing a non-synthesized HTc 3 multifilament superconducting strand coil, and the coil is heat treated thus produced to synthesize the superconductive strand HTc 3 in the superconductive phase and to oxidize, at least at the surface, the aerated metallic material 6. In an alternative embodiment, the aerated metallic material 6 undergoes a prior heat treatment of

pre-oxidation.

Claims (6)

  1. Coil with HTc superconducting multifilament strand comprising at least one winding (1) consisting of a plurality of turns (2, 2a, 2b) produced from a HTc superconductive multifilament strand (3), said strand (3) comprising a plurality of HTc superconductive filaments (4) embedded in a silver matrix (5), and an oxidized metallic material (6), at least on the surface, interposed between the turns (2,2a, 2b), electrically insulating the turns (2,2a, 2b) each other,   characterized in that the oxidized metallic material (6) is an aerated material.   2. HTc superconducting multifilament strand coil according to claim 1 characterized in that the aerated oxvdé metallic material (6) consists of a plurality of   oxidized metallic threads (7) woven.   3. HTc superconducting multifilament strand coil   according to claim 1 characterized in that the aerated oxidized metallic material (6) is an expanded oxidized metal (8).   4. HTc superconducting multifilament strand coil   according to any one of claims 1 to 3 characterized   in that the metallic material which has been oxidized is chosen   from Fe, Ni, Al, Cu, or a mixture thereof.   5. Method of manufacturing a coil with a multifilament strand superconductive HTc (3) according to one   any one of claims 1 to 3 characterized in that a HTc multifilament strand is wound together   (3) not synthesized with the aerated metallic material (6,7,8) thus realizing a coil with HTc superconducting multifilament strand (3) not synthesized, and a heat treatment of the coil thus produced is carried out to synthesize the HTc superconducting strand ( 3) in the superconductive phase and to oxidize, at least at the surface,   the aerated metallic material (6,7,8).   6. Method according to claim 5 characterized in that the aerated metallic material (6) undergoes a treatment   thermal pre-oxidation.