A superconductive cable has at least one electrical conductor made of a special material, which enters the superconductive state at a sufficiently low temperatures. The electrical resistance of a correspondingly constructed conductor thereby tends towards zero. Suitable materials are for example YBCO (yttrium-barium-copper oxide) or BiSCCO (bismuth-strontium-calcium-copper oxide). Sufficiently low temperatures for such material to achieve the superconductive state lie, for example, between 4 K and 110 K. Suitable refrigerants are for example nitrogen, helium, neon and hydrogen or mixtures of these substances, respectively in the gaseous or liquid state. Cold-dielectric and warm-dielectric superconductive cables are known.
In a cold-dielectric superconductive cable, the conductor is enclosed by a dielectric consisting of layers of insulating material, in which a liquid refrigerant is present as an impregnating medium in the dielectric. Such a cable is distinguished in that very high powers can be transmitted in the high-voltage range. It consists for example of the conductor as an inner conductor and a screen or return conductor arranged concentrically therewith, which are separated and kept apart by a dielectric (insulation). The individual superconductive elements of such a cable consist, for example, of strips comprising superconductive material such as YBCO or BiSCCO, which are wound close together with a long pitch around a support in mutually insulated concentric layers (EP 0 830 694 B1). A corresponding cable is enclosed by a cryostat, which carries the refrigerant and consists of two concentric metal tubes insulated from one another by vacuum insulation.
Warm-dielectric superconductive cables have a conductor which is arranged directly in such a cryostat carrying the refrigerant. The dielectric and the screen or return conductor are fitted over the cryostat. In such a cable as well, the conductor consists of mutually insulated concentric layers of strips comprising superconductive material lying close together.
This structure of the conductor also applies to the known superconductive AC cable according to DE 197 19 738 B4, which was mentioned in the introduction. The conductor of this cable consists of circular wires made of oxidic superconductive materials. The wires are arranged in a plurality of concentric layers around a tube. The layers are mutually insulated. The insulating interlayers between the individual layers of the wires are intended to improve the current distribution in the conductor. However, they entail additional outlay on material and for production of the conductor. Furthermore, the conductor therefore has a relatively large diameter which also leads overall to larger dimensions of the cable.