METHOD OF PRODUCING A SUPERCONDUCTING CABLE

Abstract: By a method of producing a superconducting cable, a thin layer of plastics (13) is optionally applied onto a preferably flexible pipe (1). A layer of superconducting tape (2) is applied according to a helical line onto the layer (13) prior to, during or after the application of a lubricant (11) admixed solid particles (12). Yet another layer of plastics and of superconducting tape (2) is applied onto the layer of superconducting tape (2) a number of times, the angle of inclination of the superconducting tape being variable. The last-mentioned layer of superconducting tape is applied yet another layer of plastics following by a steel pipe (4) and finally yet another pipe (5) so as to provide a vacuum between said pipes, spacers (6) being placed between said pipes (4, 5). As a result, a superconducting cable is obtained which is flexible at room temperature and which presents a considerable strength at the temperatures at which the superconducting properties can be utilized.

Description: Title: Method of producing a superconducting cable. Technical Field The invention relates to a method of producing a superconducting cable. Background Art The known superconducting cables are encumbered with the draw-back that they are not sufficiently flexible at room temperature. Brief Description of the Invention. The object of the invention is to provide a method of producing a superconducting cable which is flexible at room temperature and which discloses a considerable strength at the temperatures at which the superconducting properties are utilized. A method of the above type is according to the invention characterised in that a layer optionally made of plastics is applied onto a preferably flexible pipe, and that at least one layer of superconducting tape is applied according to a helical line onto said first layer at the same time as a lubricant is applied, whereafter a steel pipe is applied and finally an additional pipe so as to provide a vacuum between said steel pipe and said additional pipe. The lubricant provides the desired flexibility at room temperature at the same time as it turns solid at a comparatively lower temperature and thus provides the necessary mechanical resistance. Solid particles may optionally be admixed the lubricant. Moreover, an additional layer of plastics and superconducting tapes may according to the invention be applied onto the layer of superconducting tape a number of times, the angle of inclination of the superconducting tapes, however, being varied, where- after yet another layer of plastics is applied onto the final layer of superconducting tape. Furthermore, the lubricant may according to the invention be formed by silicone oil, peanut oil, petroleum gelly, engine oil or organic grease or melted lubricant which is viscous in a temperature interval, such as the temperature interval -20 °C to -60 °C, and which hardens at comparatively lower temperatures, such as temperatures lower than 110°K. The admixed particles may advantageously be formed by aluminium oxide, zirconium oxide, manganese oxide, B-nitride, wolfram carbide or ceramic particles or metal particles or plastic particles or a mixture of these types of particles, which through a mixing with the lubricant can easily result in a reduced static friction and optionally in a maintaining of the lubricant through capillary forces. Moreover, some of the admixed particles may according to the invention be of a size of 0.01 to 10 μm. Brief Description of the Invention. The invention is explained in greater detail below with reference to the accompanying drawings, in which Fig. 1 illustrates a cable according to the invention comprising a plurality of superconducting lamellas wound round a cooling pipe, Fig. 2 is a sectional view of the innermost portion of the cable, and Fig. 3 is a sectional view of each superconducting lamella. Best Mode for Carrying Out the Invention The cable according to the invention shown in Fig. 1 comprises an internal, circular cooling duct 1 for a flowing coolant in form of liquid nitrogen. The duct 1 may for instance be formed of a circular former of a diameter of about 3 cm. The former 1 may for instance be made of aluminium, steel, etc. A number of layers of superconducting tape 2, such as for instance eight layers, are wound round the former. The tapes 2 of each layer are twisted. The twists provides the cable with a predetermined flexibility. By twisting the tapes in different ways, the axial magnetic field is furthermore substantially eliminated. It is, however, not necessary to twist the tapes alter- nately in opposite directions. The three first layers may for instance be twisted in one direction, while the fourth layer is twisted in the opposite direction. The superconducting tapes 2 are wound so as to substantially abut each other. A space between the adjacent tapes may, however, be present. A layer of plastics 13 is inserted between the wound layers of superconducting tapes 2. These plastic layers are for instance of a thickness of approximately 50 μm. The outermost layers of superconducting tapes and the superposed plastic layer are surrounded by an inner 4 and an outer corrugated pipe 5. A vacuum is established between these pipes 4, 5 so as to provide a thermal insulation of the layers of superconducting tapes 2. This vacuum is maintained by means of pumps arranged along the cable and connected thereto. A number of twist- ed spacers 6 are provided between the pipes 4, 5 so as to maintain the distance between said pipes 4, 5. These spacers 6 are made of plastics. A number of layers of aluminium film 7 can optionally be provided below the spacers 6. The corrugations of the pipes 4, 5 serve to provide a predetermined flexibility of the completed cable. The outer pipe 5 is covered by a layer of dielectric 8 material. This dielectric layer has not been cooled, but has the ambient temperature. The dielectric layer 8 may for instance be made of polypropylene or polyethylene. The dielectric layer 8 is covered by a sheath of for instance copper or lead or aluminium and yet another sheath of polyethylene 9. According to the invention, a lubricant 11 admixed solid particles 12 are applied prior to, during or after the application of the superconducting tapes 2 in such a manner that a thin film is formed on the surface of said superconducting tapes 2. The lubricant 11 has the property of reducing the friction when the cable is being manipulated or bent within the temperature interval -20 °C to +60°C, said lubricant 11 being fluid and not particularly viscous within said temperature interval. However, the lubricant hardens at comparatively lower temperatures, such as 110°K to 4.2°K and presents therefore a large mechanical resistance at these temperatures. The admixed solid particles 12 have the property of reducing the static friction at the tape or wire surface. Some of the powder 12 presents a round or close to round particle shape with the result that a function is obtained which corresponds substantially to a roller bearing function. Some of the particles 12 can have the property of maintaining the lubricant 11 in place through capillary forces, also in a non-horizon- tal section of the cable without making the mixture too viscous. The lubricant 11 and the admixed particles 12 can furthermore serve to increase the thermal conductivity in such a manner that the thermal conductivity between the conductors and the passing coolant is increased. At low temperatures the tapes 2 are thus maintained in place in such a manner that they are not displaced although they are subjected to electromagnetic forces. Examples of lubricants are silicone oil, peanut oil or petroleum gelly or engine oil or organic grease or "lubricating gelly" or other lubricants of a suitable viscosity for a predetermined temperature interval and admixed particles 12 of Al-oxide, Zr-oxide, Mg-oxide, B-nitride, wolfram carbide or ceramic particles or metal particles or plastic particles or a mixture of several of these types of particles. The particles 12 present a suitable size distribution in such a manner that round particles are of a size of 1 to 50 μm, and small particles are of a size of 0.01 to 10 μm. The amount of particles and the size distribution are selected such that the mixture does not flow in the cable when said cable is vertically held at said high temperature interval, and such that the mixture is sufficiently fluid for allowing the tapes 2 to slide at a possible bending of said cable. When the lubricant is of the gelly type, the small particle fraction is not necessary. Fig. 3 shows the cross section of each tape. The total width is approximately 4 mm and the total thickness is approximately 0.2 mm. The thickness of each filament is 0.02 mm. The filament arrangement can be random or be oriented in rows and columns. There are typically 1 to 1000 filaments in the finished tape.

Claims: Claims 1. A method of producing a superconducting cable, characterised in that a layer (13) optionally made of plastics is applied onto a preferably flexible pipe (1), and that at least one layer of superconducting tape (2) is applied according to a helical line onto said first layer (13) at the same time as a lubricant (11) is applied, whereafter a steel pipe (4) is applied and finally an additional pipe (5) so as to provide a vacuum between said steel pipe (4) and said additional pipe (5). 2. A method according to claim 1, characterised by using a lubricant admixed solid particles. 3. A method as claimed in claim 1, characterised by applying an additional layer of plastics (13) and superconducting tapes (2) onto the layer of superconducting tape a number of times, the angle of inclination of the superconducting tapes (2) being varied, and by applying yet another layer of plastics onto the final layer of superconducting tape (2). 4. A method as claimed in claim 1 or 2, characterised in that the lubricant (11) is formed by silicone oil, peanut oil, petroleum gelly, engine oil or organic grease or melted lubricant which is viscous in a temperature interval, such as the temperature interval -20 °C to -60 °C, and which hardens at comparatively lower temperatures, such as temperatures lower than 110°K. 5. A method as claimed in one or more of the preceding claims, characterised in that the admixed particles (12) are formed by aluminium oxide, zirconium oxide, manganese oxide, B-nitride, wolfram carbide or ceramic particles or metal particles or plastic particles or a mixture of these types of particles, which through a mixing with the lubricant can easily result in a reduced static friction and optionally in a maintaining of the lubricant through capillary forces. 6. A method as claimed in one or more of the preceding claims, character- is e d in that some of the admixed particles (12) are of a size of 0.01 to 10 μm. 7. A method as claimed in one or more of the preceding claims, character- i s e d in that some of the admixed particles are of a size of 1 to 50 μm. 8. A method as claimed in one or more of the preceding claims, character- is e d in that the superconducting tapes (2) are applied with an angle of inclination of 10 to 30°. 9. A method as claimed in one or more of the preceding claims, character- i s e d in that the used plastic layer (13) presents a thickness of 2 to 500 μm.

Inventors: GLEJBOEL KRISTIAN, RASMUSSEN CLAUS NYGAARD, WILLEN DAG, GLEJBOEL, KRISTIAN, RASMUSSEN, CLAUS, NYGAARD, WILLEN, DAG
Applicants: GLEJBOEL KRISTIAN, NKT RES CT AS, RASMUSSEN CLAUS NYGAARD, WILLEN DAG, GLEJBOEL, KRISTIAN, NKT RESEARCH CENTER A/S, RASMUSSEN, CLAUS, NYGAARD, WILLEN, DAG
Application year: 2000
Main classification: H01B12
IPC codes: H01B12, H01B13