Abstract:
Arrangement for connecting a fiber-reinforced plastic pipe ( 18 ) to a stainless steel flange ( 12, 16 ), in which the end of the fiber-reinforced plastic pipe ( 18 ) is accommodated in a ring-shaped groove ( 12   a,    16   a ) in the flange ( 12, 16 ), the groove conforming to the dimensions of the fiber-reinforced plastic pipe ( 18 ), where the gap remaining between the end of the fiber-reinforced plastic pipe ( 18 ) and the ring-shaped groove ( 12   a,    16   a ) is filled with a sealant ( 19 ).

Description:
FIELD OF THE INVENTION  
       [0001]     The invention pertains to an arrangement for connecting a fiber-reinforced plastic pipe to a stainless steel flange.  
       BACKGROUND OF THE INVENTION  
       [0002]     In electrical equipment with conductors cooled to low temperature, it is often necessary to supply the electric current to the cooled conductors from a power supply at ambient temperature. This applies in particular to superconducting cables, the superconductors of which must be cooled down to a temperature below the transition temperature of the superconducting material.  
         [0003]     A superconducting cable is known from EP 1 363 062 A1, which passes through a so-called cryostat. The cryostat consists of two concentric, corrugated metal pipes. Between the corrugated metal pipes is a blanket of so-called superinsulation consisting of alternating layers of metal foil and cold-resistant plastic film, e.g., film based on polyester. The film obtainable commercially under the trade name “Mylar” is preferred. Mylar is a registered trademark of Du Pont de Nemours. The annular gap between the metal pipes is also evacuated.  
         [0004]     With respect to the current supply, care must be taken to ensure that the high voltage-carrying conductor of the power supply is isolated from the cryostat, which is at standard potential. It is also necessary for the vacuum present in the annular gap to be sealed off against the interior of the cryostat.  
       OBJECTS OF THE INVENTION  
       [0005]     The present invention is therefore based on the task of providing an arrangement which is able to isolate the cryostat from the current-carrying conductor or power supply and simultaneously to seal off the annular gap between the metal pipes of the cryostat in a vacuum-tight manner against the environment.  
         [0006]     The arrangement according to the principle of the invention is able to withstand repeated temperature cycles between 300 and 77 K without damage. The inventive arrangement is not subject to the shrinkage which normally occurs as a result of temperature changes.  
         [0007]     Another significant advantage is to found in that the arrangement can be produced without the need to subject the cable to a great deal of work after it has been laid. The arrangement is also characterized by high mechanical strength. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The invention is explained in greater detail below on the basis of the exemplary embodiments, which are illustrated schematically in  FIGS. 1-4 .  
         [0009]      FIG. 1  shows the power connection of a superconducting cable.  
         [0010]      FIG. 2  shows in greater detail how the pipe section  7  and the end of the superconducting cable  1  are connected to each other.  
         [0011]      FIGS. 3 and 4  show the enlarged areas of the grooves and the ends of the pipe from  FIG. 2 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     The superconducting cable is designated by the number  1 . It is located in a cryostat, which consists of a corrugated inner metal pipe  2 , preferably of stainless steel, and an outer metal pipe  3 .  
         [0013]     A corrugated metal pipe (not shown), which also consists advantageously of stainless steel, is welded to the end of the outer metal pipe  3 . A liquid coolant flows through the interior of the metal pipe  2 . If the superconducting material of the superconducting cable is a high-temperature superconducting material such as one of the materials based on mixtures of copper oxide, barium oxide, and yttrium oxide, or other oxide mixtures, liquid nitrogen is used as the liquid coolant. The space between the metal pipes  2  and  3  is filled by a series of alternating layers of metal foil and plastic film. The space is also evacuated. This type of insulation is referred to in superconducting technology as “superinsulation”.  
         [0014]     The evacuated annular space located between the metal pipes  2  and  3  is connected vacuum-tight to the interior space of a vessel  4 , which consists of two half-shells. The vessel  4  is connected by the connector  5  to a vacuum pump (not shown). A manometer  5   a  monitors the vacuum in the tank  4 .  
         [0015]     The metal pipe  3  is connected by a flange to the vessel  4  in a vacuum-tight manner.  
         [0016]     In the interior of the vessel  4 , a tank  6  for liquid nitrogen is provided, which is connected by a pipeline  6   a  to a reservoir for the coolant (not shown). The tank  6  is connected by a pipeline  6   b  to the interior of a section of pipe  7  and thus to the interior of the metal pipe  2 .  
         [0017]     The pipe section  7  consists of a metal of good electrical conductivity, preferably of copper, and is connected electrically to the conductor (not shown) of the superconducting cable.  
         [0018]     A component  8  consisting of a plurality of plates is electrically connected to the end of the pipe section  7  facing away from the connection to the conductor of the superconducting cable  1 . These plates are also made of copper. The opposite end  8   a  of the component  8  is connected to a power source (not shown).  
         [0019]     The components  8  and  8   a  are surrounded by an insulating body  9 , which is recessed vacuum-tight into the wall of the vessel  4 . The insulating body  9  has the job of electrically insulating the power supply passing through the components  8  and  8   a,  which are at high-voltage potential, from the vessel  4 . In the insulating body  9  there is also a sealing disk  10  of aluminum oxide, which seals off the interior of the vessel  4 , which is under vacuum, from the outside.  
         [0020]      FIG. 2  shows in greater detail how the pipe section  7  and the end of the superconducting cable  1  are connected to each other.  
         [0021]     The end of the metal pipe  2  is welded vacuum-tight to a first flange  10 , which is clamped by clamp bolts  11  to a second flange  12 .  
         [0022]     The end of the pipe section  7  is recessed into a third flange  13 . A metal body  14  of copper is soldered into the interior of the pipe section  7 . The copper body  14  has a bore  14   a,  which expands conically. The end of the conductor of the superconducting cable  1  is introduced into the conical expansion of the bore  14   a.  A nut  15  is screwed on to the end of the cable. Permanent electrically conductive contact is established for the end of the conductor of the superconducting cable  1  by the use of another flange  16 , which is clamped to the flange  13  by the clamp bolts  17 . As a result, the end of the conductor is firmly seated in the conical expansion of the bore  14   a.  Between the flanges  12  and  16  there is a pipe  18  of high-strength plastic. A pipe of fiber-reinforced epoxy resin is preferably used.  
         [0023]     The ends of the pipe  18  are recessed vacuum-tight into ring-shaped grooves  12   a  and  16   a  in the flanges  12  and  16 . The metal pipe  2  of the cryostat is galvanically separated from the flange  16  and thus from the power supply by the electrically insulating pipe  18 . In addition, the pipe  18  is recessed vacuum-tight into the grooves  12   a  and  16   a.    
         [0024]     The area of the grooves  12   a,    16   a  and the ends of the pipe  18  are shown on an enlarged scale in  FIGS. 3 and 4 . The width Y of the groove  12   a  is slightly larger than the wall thickness X of the pipe  18 , so that a gap is formed, which is filled with sealant  19 . It is especially advantageous for the width of the gap to be in the range of 0.1-0.5 mm. This also applies to the gap between the end surface of the pipe  18  and the base of the groove  12   a.    
         [0025]     The opposite end of the pipe  18  is recessed into the groove  16   a  of the flange  16  in the same way.  
         [0026]     To produce the connection, the ends of the pipe  18  are coated with a curable sealant and introduced into the grooves  12   a  and  16   a,  and/or the flanges  12  and  16  are pushed onto the sealant-coated ends of the pipe  18 .  
         [0027]     It is advantageous to use Stycast and Eccobond sold by Emerson &amp; Cuming as the sealant.  
         [0028]     In the exemplary embodiment according to  FIG. 4 , a bore  12   b  is introduced into the flange  12 , through which a screw bolt  20  is inserted. This bolt is screwed into a thread  18   a  in the pipe  18 . Thus a mechanically strong connection is established between the flanges  12 ,  16  and the pipe  18 , which will therefore remain vacuum-tight even over a prolonged period of time.