Abstract:
The invention relates to a coil for producing a magnetic field having at least one winding ( 12 ), which is manufactured from a superconductor, is cast into a plastic and whose winding end ( 19 ) which is arranged at the circumference ( 13 ) of the winding ( 12 ) is used for making contact with an electrical conductor ( 15 ). In order to provide coils with windings ( 12 ) consisting of superconductors which make robust contact-making possible given simple production, an electrically conductive connection piece ( 30 ) with a base region ( 31 ), which is connected to the winding end ( 19 ), and a top region ( 32 ) for connecting the conductor ( 15 ) is provided for contact-making purposes, the base region ( 31 ) of said connection piece ( 30 ) being covered partially in the radial direction by a reinforcing insert ( 14 ), which is cast into the plastic ( 20 ) and at least partially surrounds the winding ( 12 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of the filing date of International Application No. PCT/EP2006/010038, filed Oct. 18, 2006, which application claims priority to and the benefit of the filing date of German Application No. 10 2005 052 602.0, filed Nov. 2, 2005. 
         [0002]    The invention relates to a coil for producing a magnetic field, having at least one winding, which is manufactured from a superconductor and is encapsulated in a plastic, with a winding end which is arranged on the circumference of the winding being used as a contact for an electrical conductor. 
       BACKGROUND OF THE INVENTION 
       [0003]    Coils having a winding manufactured from a superconductor are used for construction of motors, generators and magnets when the aim is to exploit the benefits of the low resistance of cooled superconductors. High-temperature superconductors are frequently used, which are composed of a brittle composite of ceramic and metal but cannot withstand major tensile or shear forces even at room temperature, and in particular at lower temperatures. Furthermore, superconductors lose even more of their elasticity, which is low even at room temperature, when cooled down. When coils are installed, contact is generally made with the winding end by soldering on a metallic or superconducting conductor. Tensile and shear forces transmitted to the soldered-on conductor can damage the winding, as a result of which the winding may in the worst case be destroyed if the contact is not handled carefully. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is to provide coils with windings composed of superconductors which can be easily produced with a robust contact and in which the risk of damage to the winding is reduced. 
         [0005]    According to an aspect of the invention, the contact has an electrically conductive connecting piece with a foot area, which is connected over an area to the winding end, and with a head area for connection of the conductor, with the foot area being partially covered in the radial direction by a reinforcing insert which is encapsulated in the plastic and at least partially surrounds the winding. This has the advantage that the connecting piece is stabilized with respect to the winding by means of the reinforcing insert encapsulated in the plastic. Any forces which may act on the connecting piece are transmitted over a large area through the reinforcing insert to the plastic surrounding the coil, thus relieving the load from these forces, in particular on the winding end. 
         [0006]    The reinforcing insert, complemented by the connecting piece, can completely surround the winding, thus preventing local compression and tension loads on the winding. The reinforcing insert and the connecting piece can form an intrinsically closed strain relief means. In one advantageous embodiment, the reinforcing insert comprises a ring surrounding the winding, in particular such as a prefabricated sufficiently robust strip or split annular bodies. 
         [0007]    According to another aspect, the foot area may have limbs on both opposite side faces, as a result of which the foot area can rest over a large area on the winding end, and the reinforcing insert can also cover the limbs at the winding end over a large area. These limbs may project beyond the side faces of the connecting piece in the head area in the circumferential direction. In one particularly advantageous refinement, the reinforcing insert then covers both limbs and extends from one limb to the other along the circumference of an outer turn of the winding, thus providing a surrounding cover for the winding, along the circumference. This surrounding cover protects the coil against mechanical shocks on the circumference of the winding. In one alternative refinement, two reinforcing inserts may be arranged transversely with respect to the winding, in each case covering one of the limbs at the side and then surrounding the winding at the side, on the front face and rear face. The reinforcing inserts can then preferably pass through a winding former, on which the winding is wound, in order to completely surround the winding. Alternatively, the reinforcing insert can be attached to the winding former so that the connecting piece is supported on the winding former via the reinforcing insert. 
         [0008]    Irrespective of the arrangement of the reinforcing insert on the winding, it is advantageous for the reinforcing insert to engage in at least one recess between the head area and the foot area, in particular in an interlocking manner, thus likewise stabilizing the connecting piece. The connecting piece may have a recess in the form of a groove on each of its two side faces, in which the reinforcing insert, if it extends along the circumference, engages with both end faces, or through which it passes. If two reinforcing inserts are arranged on the front face and rear face transversely with respect to the winding, they can engage in the recesses at the side. The reinforcing insert can also be firmly clamped in the recesses. 
         [0009]    In one embodiment, the plastic is an electrical impregnation compound or an encapsulation compound. The encapsulation or impregnation of the coil in plastic is can be carried out by vacuum impregnation or using the vacuum impregnation process, with the plastic advantageously being composed of a resin, in particular an epoxy resin. The coil is can be in the form of a double-disk coil which is formed by two windings which are arranged alongside one another, are wound in opposite senses and merge into one another on the winding inner face, so that the two winding ends are arranged on the circumference and are each provided with a connecting piece. These double-disk coils are also referred to as “double-pancake coils”, and have the advantage that contact is made on the easily accessible circumference. The two connecting pieces are expediently arranged parallel to one another, and isolated from one another by a gap. An isolating layer can furthermore expediently be arranged in the gap. 
         [0010]    The winding is preferably manufactured from a high-temperature superconductor, which has the advantage that the coil can be cooled by nitrogen, although without being restricted to this. The winding is expediently wound from a ribbon conductor or layers formed from ribbon conductors, which can be manufactured using the “powder in tube” technique, or in the form of a thin-film conductor. A solder with a high melting temperature is preferably used for soldering the foot area to the winding end. A conductor can then be soldered to the head area using a solder with a lower melting temperature, without any possibility of melting of the solder at the foot area. By way of example, commercially available electrical solder can be used for the solder at the head area. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    Further advantages and refinements of the invention will become evident from the following description of exemplary embodiments for coils according to the invention as illustrated in the drawing, in which: 
           [0012]      FIG. 1  shows a schematic view of the front face of a coil according to the invention with a connecting piece according to a first exemplary embodiment; 
           [0013]      FIG. 2  shows a detailed section view of the coil from  FIG. 1 ; 
           [0014]      FIG. 3  shows a vertical section through the upper coil half of a double-disk coil with connecting pieces arranged on it; 
           [0015]      FIG. 4  shows a detailed view similar to  FIG. 2 , with a connecting piece according to a second exemplary embodiment; 
           [0016]      FIG. 5  shows a vertical section through the upper coil half of a double-disk coil with a third exemplary embodiment of a connecting piece; and 
           [0017]      FIG. 6  shows a detailed view of a coil with a connecting piece according to a fourth exemplary embodiment, and with a reinforcing insert running transversely with respect to the winding. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    Referring now in greater detail to the drawings wherein the showings are for the purposes of illustrating preferred embodiments of the invention only, and not for purposes of limiting the invention,  FIG. 1  shows, schematically, a coil  10  for producing a magnetic field and having a winding  12  which is wound on a tubular winding former  11 . The winding  12  comprises a ribbon conductor which is wound with superposed turns one on top of the other and is manufactured using the “powder in tube” technique from a ceramic high-temperature superconductor. A thin-film conductor or a stack of thin-film conductors can also be used for this purpose. A connecting piece  30  is used to make contact with the winding  12 . The connecting piece  30  is in the form of a block in this case, is composed of copper and has a recess  36  in the form of a slot in each case between a foot area  31  and a head area  32  on both side faces  30   a ,  30   b  pointing in the circumferential direction or winding direction, thus forming a short limb  33  on the side face  30   a  and a short limb  34  on the side face  30   b  at the foot area  31 . The foot area  31  is soldered to the longitudinal faces of the connecting piece  30  on the circumference  13  of the winding  12 . As can be seen from  FIG. 2 , the foot area  31  in this case rests flat over an area on a winding end  19  of the winding  12 , and is attached by soldering, which is not illustrated. An electrically conductive supply line  15  is soldered to the head area  32  of the connecting piece  30  and in one embodiment comprises a normal conductor or a further superconductor. 
         [0019]    A reinforcing insert  14  rests on the circumference  13  of the winding  12  and extends from the side face  33   a  of the connecting piece  30  along the circumference  13  to the other side face  33   b.  As can be seen from  FIG. 2 , each of the ends of the reinforcing insert  14  in this case engages in the recesses  36 , thus covering the two limbs  33 ,  34 . Together with the tubular winding former  11 , the reinforcing insert  14  and the connecting piece  30 , the winding  12  is encapsulated in epoxy resin  20 . The reinforcing insert  14  may comprise a reinforcing strip or a ring of adequate intrinsic stiffness, and/or fiber reinforcement. The reinforcing insert may, however, also be composed of loose or bonded reinforcing fibers, such as glass fibers, which are encapsulated in the plastic as well. The reinforcing insert  14  and the connecting piece  30  which is partially covered by it in the foot area thus form an intrinsically closed strain relief means for the contact. The effect of the reinforcing insert  14  is particularly good since they partially cover the foot area  31  of the connecting piece  30  in the radial direction, specifically in the area of the two short limbs  33 ,  34 . 
         [0020]      FIG. 3  shows another embodiment with two windings  112   a  and  112   b  which are connected to one another, are wound in opposite senses and in this case form a so-called “double-pancake” or double-disk coil  110 . The windings  112   a,    112   b  are wound from a ribbon superconductor. The windings  112   a  and  112   b  merge into one another over a common inner turn  112   c  on the outer circumference  116  of the winding former  111 . A connecting piece  150  is soldered to the outer circumference  113   a  of the winding  112   a,  and a second connecting piece  130  is soldered to the outer circumference  113   b  of the winding  112   b,  which connecting pieces  150 ,  130  are physically identical to the connecting piece  30  as illustrated in  FIG. 1 . In order to avoid repetition, reference is made here to the description of the connecting piece  30  illustrated in  FIGS. 1 and 2 . 
         [0021]    The two connecting pieces  130 ,  150  are arranged parallel to one another and alongside one another, and are separated from one another by an isolating gap  118 . The winding parts  112   a  and  112   b  are isolated from one another by an isolating layer  117 , which extends further into the gap  118  between the two connecting pieces  130 ,  150 . Once the connecting pieces  130 ,  150  have been soldered to the winding ends and the reinforcing inserts  113   a,    113   b  have been placed around the windings  112   a,    112   b,  the entire coil  110  is encapsulated in epoxy resin  120 , which also fills the gap  118  as additional insulation and covers the side surfaces of the connecting pieces  130 ,  150 . Only the head faces  135  and  155  of the connecting pieces are free of the epoxy resin  120 , in order to allow normal conductors to be soldered to the connecting pieces  130 ,  150  of the coil  110 , in order to make electrical contact with the windings  112   a  and  112   b.    
         [0022]      FIG. 4  shows a coil  210  with a connecting piece  230  manufactured from copper, according to a further exemplary embodiment, which is soldered over a large area to a winding  212  with limbs  233 ,  234  which project beyond a head area  232  in the winding direction or circumferential direction. The connecting piece  230  is connected to the winding  212  in a very highly conductive manner by means of the long limbs  233 ,  234 . The connecting piece  230  is provided with two slotted recesses  236  between the head area  232  and a foot area  231 , in which the ends of a reinforcing insert  214  engage. The winding  212 , the reinforcing insert  214  and the connecting piece  230  are encapsulated in epoxy resin  220 . Two S-shaped holding layers  237  and  238  lie on the side faces  230   a  and  230   b  (which have the recesses  236 ) of the head area  232  and are composed of a glass-fiber non-woven, which is likewise encapsulated in the epoxy resin  220 , which holding layers  237  and  238  partially clasp the head face  235  of the head area  232 , so that the head area  232  is also stabilized by the holding layers  237 ,  238 . A supply line  215  is soldered to the head face  235 . 
         [0023]      FIG. 5  shows a double-disk coil  310  with a first winding  312   a  and a second winding  312   b  composed of a ribbon superconductor, as described in  FIG. 3 , which are soldered to two connecting pieces  330  and  350 . The connecting piece  350  is provided with a slotted recess  316   a  along its outer longitudinal face  350   a,  and the connecting piece  330  is provided with a slotted recess  316   b,  extending in the winding direction, on its outer longitudinal face  330   b.  An annular reinforcing insert  314   a  is inserted into the recess  316   a,  and an annular reinforcing insert  314   b  is inserted into the recess  316   b.  The solid, possibly closed, rings  314   a,    314   b  surround the windings  312   a,    312   b  along their circumference, and in this case are encapsulated with the windings  312   a,    312   b  in an epoxy resin  320 . Instead of annular reinforcing inserts  314   a,    314   b,  fibers or fiber mats or the like could also be inserted into the side recesses  316   a,    316   b.    
         [0024]      FIG. 6  shows a winding  412  on a coil  410  with a connecting piece  430  which, in a similar manner to the connecting piece shown in  FIG. 4 , is provided on its side faces with limbs  433 ,  434  which lengthen the foot area  431  in the circumferential direction and project beyond the side faces of the head area  432 . Above the limbs  433 ,  434 , the connecting piece  430  is provided with two slotted recesses  436 . One limb  434  is covered by a first reinforcing insert  414   a,  which runs transversely with respect to the winding  412 , and the other limb  433  is covered by a second reinforcing insert  414   b,  which likewise runs transversely with respect to the winding  412 . The two reinforcing inserts  414   a,    414   b  comprise, for example, a plurality of glass-fiber strips, which together surround the winding  412  and are encapsulated with the connecting piece  430  and the winding  412  in a plastic  420 . The two reinforcing inserts may in this case engage in an inner opening in a winding former, or may pass through it, so that the connecting piece  430  is fixed to two limbs  433 ,  434  in the radial direction relative to the winding former. 
         [0025]    In the exemplary embodiments which are illustrated in the figures, in particular in  FIGS. 2 and 4 , the head area  32 ,  232  of the connecting piece  30 ,  230  projects somewhat radially beyond the reinforcing insert  14 ,  214  and the plastic  20 ,  220  in which it is embedded. The projecting subarea in these exemplary embodiments could also be removed subsequently, for example by being ground off or removed, so that it can endflush with the plastic in which the reinforcing insert is encapsulated, or else a connecting piece (not shown) is used during an assembly process which has only a head area which is short in the radial direction and projects beyond the limbs and the foot area which, after being encapsulated or embedded in plastic, once again, it can endflush with the plastic. In this refinement, it would then also be possible not to form any recesses between the foot area and the head area for the ends of the reinforcing inserts to engage in. 
         [0026]    For a person skilled in the art, numerous modifications will be evident, and equivalence thereto from the description and these are intended to be covered by the scope of protection of the attached claims.