DE8804371U1 - Superconducting cable with oxide ceramic high-temperature superconductor material - Google Patents

Description

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Siemens AG

(Superconducting cable with oxide ceramic high temperature superconducting material >

The innovation relates to a superconducting cable with at least one rigid inner tube in which at least one superconducting conductor core with an oxide ceramic high-temperature

xw lotuisupiaiCiici-natcuiai aiiycuiuiici aouj uao &tgr;&ugr;&igr;&igr; aiiism oni.-speaking cooling medium, and which is enclosed by a rigid outer tube, with an evacuated space being formed between the inner and the outer tube. A superconducting cable with such a tube system is indicated, for example, in the publication by A.P.Malozeioff et al: "Applications of High Temperature Superconductivity", IBM T.J.Watson Research Center and Massachusetts Institute of Technology, August 1987.

For three-phase current transmission, particularly at the usual voltage level of 110 kV, cables are required that are designed for very high powers of, for example, 1 GVA at high currents of, for example, 5 kA and that enable low transmission costs with a small space requirement. Such high powers have so far only been transmitted using artificially cooled oil cables or SF _g cables.

Superconducting high-performance cables with liquid helium cooling and high vacuum insulation have also been developed, but not yet used for economic reasons (cf. e.g. contribution by G. Bögfier in ^B Nätö Advanced Study institutes Series", Series B: Physics, Vol. 21: "Superconductor Applications··, Plenum Press, New York 1977, Chapter 20, Section V: "Superconducting Cables", pages 672-717). Such cables have

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each have an inner tube in which at least one superconducting conductor wire is arranged. This conductor wire must be cooled by liquid helium (LHe) which is guided inside this inner tube. The inner tube is therefore often referred to as a helium (He) tube. This He tube is enclosed by a vacuum-tight outer tube, whereby the space between the inner and outer tubes is evacuated for thermal insulation. Steel is generally used as the material for the outer tube. In addition,

A cooled thermal radiation shield is arranged on the He-cold inner tube.

At least the He tube of such a superconducting cable must be made of metal, because the extremely small helium atoms could easily penetrate other materials and then impair the high vacuum insulation. However, eddy currents are induced in metallic coolant tubes, which produce considerable heat. The associated additional losses must be dissipated by the coolant at a correspondingly great expense. To avoid this difficulty, coaxial, shielded conductor wires were always used in known superconducting three-phase cables. However, such a coaxial structure requires at least twice as much superconducting material as would be required for a simple conductor structure. In addition, an appropriately adapted, unusual wiring technology is required for such cables.

Since the beginning of 1987, superconducting materials have been known whose jump temperature T is so high that they can no longer be cooled with liquid helium (LHe) at about 4 K, but for which cooling with liquid nitrogen (LN ₂ ) is sufficient. These materials are special metal oxides, such as those based on the material system Y-Ba-Cu-O (see e.g. "Euro-35

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Physics Letters», Vol. 4, No. 2, 15.7.87, pages 247 to 252 and Vol. 4, No. 5, 1.9.87, page 637 or "Physical Butter", Vol. 43, No. 9, 1987, pages 357 to 363). Films or thin layers of these metal oxide compounds are often produced using special vapor deposition or sputtering processes. Here, a polycrystalline or amorphous precursor with the components of the selected material system is first deposited on a suitable substrate, whereby the oxygen content is generally not precisely adjusted. This process

au prOuürvu Wx?u SnaCiiixcMCMU m^bbciS SxmST &pgr;&agr;&Ggr;&iacgr;&idiagr;&idiagr;&egr;&mdash; UMU jäücISuCi &igr;&mdash; treatment into the material with the desired superconducting phase. In addition to the material system Y-Ba-Cu-O mentioned, other material systems also have such high transition temperatures that they can be kept at their superconducting operating temperature with LN ₂ . For example, materials based on the material system Bl-Sr-Ca-Cu-O ("Superconducting News Supplement", Vol. 1, No. 3, February 1988) or on the material system Tl-Sr-Ca-Cu-O ("International Conference on High T_ Superconductors and Materials and Mechanisms of Superconductivity", 29.2. - 4.3.1988, Interlaken, CH) or on the material system La-Sr-Nb-O ("Journal of Low Temperature Physics", Vol. 69 _t Nos.5/6, 1987, pages 451 to 457 or "The Japan Times" from 21.1.1988) have become known.

All of these superconducting materials are classified as oxide ceramics, so that the corresponding high-T superconductors are often also referred to as oxide-ceramic superconductors.

In the article by A.P.Malozemoff et al mentioned at the beginning, it was proposed that such oxide-ceramic superconductors could also be used for superconducting cables ("Superconducting Power Transmission Lines-SPTL"). This is based on known concepts of superconducting cables with superconductors to be cooled by LHe. However, these known concepts have the following disadvantages:

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1 mentioned problems regarding eddy currents, superconducting material requirements, and welding technology.

The innovation is now based on the task of specifying a superconducting cable based on this cable concept, whose at least one superconducting conductor core is to be made of a known oxide-ceramic high-temperature superconductor material. This cable should have the simplest possible structure of its pipe system and a high-temperature superconductor (HTSC)-

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the additional thermal losses caused by eddy currents in metallic pipe parts in known cables can be at least largely avoided.

According to the innovation, this task is solved by

at least the inner tube is made of a vacuum and coolant-tight plastic material.

By using an inner tube made of an electrically non-conductive material, problems caused by eddy currents generated in metallic parts are eliminated from the outset. Suitable plastic materials that are coolant-tight with regard to LN ₂ are generally known.
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Advantageous embodiments of the superconducting cable emerge from the subclaims.

To further explain the innovation, reference is made to the following schematic drawing, in which Figure 1 shows a cross-section through a cable pipe system. Figures 2 and 3 each show a longitudinal section of a connecting section of parts of this pipe system. In the figures, corresponding parts are marked with the corresponding 35

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The superconducting cable according to the innovation can be designed in particular as a three-phase cable. According to the cross-section shown schematically in Figure 1, the corresponding cable, generally designated 2, contains an inner tube 3 which consists of a vacuum and coolant-tight plastic material. The inner tube 3 is concentrically enclosed by an outer tube 4 so that a gap 5 is formed between the tubes. The material of the inner tube can be selected as the material for the outer tube, for example. The two tubes 3 and 4 can in particular be made of fiber-reinforced plastic. Epoxy resins or thermoplastics reinforced with glass, Kevlar or carbon fibers are suitable for this. The two tubes 3 and 4 are held in their concentric position by means of thermally poorly conductive support structures. Half of a corresponding support ring 6 is indicated in the figure. This support ring is designed in such a way that relatively long paths are formed between the support points 7 and 8 on the inner tube 3 and the outer tube 4. In the intermediate space 5 evacuated for thermal reasons, a known multi-layer super insulation 9 can also be located to limit the heat introduction to the inner tube 3. In addition, a sorbent 10, e.g. activated carbon or zeolite, can be attached to the vacuum side of the inner tube 3, which binds the remaining molecules in the vacuum space when the cable is cold.

Inside the inner tube 3 there are three superconducting conductor wheels 11 to 13, which are constructed in a known manner with superconductors made of a known HTSL material. This material should have such a high transition temperature _ΔT that it can be cooled with LN _2. The cooling medium is fed through the interior 14 of the tube 3. This interior is 33

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also referred to as a coolant chamber. Each conductor wire contains, for example, a central support body 15, around which a winding 16 made of a strip-shaped conductor with the HTSL material is wound.

This conductor winding 16 is surrounded by an insulation 17. This insulation can, for example, be designed such that it is impregnated with the LN ₂ .

The cooling medium is, for example, in a supercooled, liquid state, ie boiling of the cooling medium is impossible in normal operation. For example, LN ₂ is introduced into the inner tube 3 at a temperature of approx. 70 K and an absolute pressure of approx. 5 bar. As it flows through the tube, the cooling medium is heated and the pressure decreases. At the end, the cooling medium still exits in a supercooled state, eg with a

Temperature of approx. 80 K and an absolute pressure of approx. 3 bar.

Finally, as can be seen from Figure 1, the outer tube 4 of the superconducting cable 2 can be covered by a protective layer 18, consisting for example of bitumen. This way, mechanical damage and the ingress of water can be avoided.

The pipe system ensuring the thermal insulation of the superconducting conductor wires 11 to 13 and the surrounding LN ₂

of the superconducting cable is generally designated 20 in Figure 1. This pipe system is advantageously assembled from prefabricated sections with an outer and inner pipe. A connecting area between two such sections is shown in Figure 2. In the figure, only the upper halves of these sections 21 and 22 with respect to the cable axis A are shown as a longitudinal section. As can be seen from the figure, each section 21 and 22 is designed in such a way that the vacuumed space 5 between the outer pipe 4 and the inner pipe 3 is sealed vacuum-tight at the end faces 23 and 24.

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During production, each part is then evacuated at an evacuation nozzle 25, which is then sealed vacuum-tight. In order to further improve the vacuum tightness of the individual plastic parts, thin metallized films 26 can be incorporated as diffusion barriers in the outer and inner tubes 4 and 3, respectively, as well as in the connecting parts on the end faces 23 and 24.

The facing end faces 23 and 24 of the sections

21 and 22 of the pipe system 20 are designed in such a way that one end of each section projects concentrically into the other end of the other section. In this way, heat that wants to flow from the warm outer pipe 4 to the cold inner pipe 3 flows through the concentrically interlocking pipe parts and has to overcome a correspondingly long path. The heat introduction into the LN ₂ area inside the inner pipe 3 is correspondingly low. A narrow gap 27 remains between the interlocking parts of the sections 21 and 22 on the end faces 23 and 24. In an axially running part of this gap there is a sealing element 28 that separates the cold interior 14 with the LN ₂ from the environment. In addition, the gap 27 can be covered on the outside by means of a tubular sleeve 29 so that convection with heat transport in the gap 27 between the two parts 21 and 22 is prevented. The sleeve 29 allows a mutual axial displacement of the two parts 21 and 22, ie it is rigidly connected to at most one of these parts. Each of the parts 21 and 22 also has a device 30 for expansion compensation, with which the change in length of the inner tube 3 is compensated during cooling. In the embodiment of the part 21 shown in Figure 2, this device 30 is integrated into the outer tube 4 near its front side 23. Finally, as is indicated in Figure 2, the connection can be

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The area between the two sections 21 and 22 must be bridged with a cylindrical part 31 for mechanical protection.

In Figure 3, a further possible design of a connection between two prefabricated sections 33 and 34 of a pipe system according to the innovation in Figure 2 is indicated. This embodiment differs from the embodiment according to Figure 2 essentially only in that a special sealing element is dispensed with in the gap formed between the two front ends of these sections and only a sealing connecting element 29 is provided on the outside. In addition, in the embodiment shown, the device 30 for compensating for expansion between the outer pipe 4 and the inner pipe 3 is integrated into the inner pipe.

12 Protection claims

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Claims (12)

G 88 04 371.1 9 " VPA 88 G *3127# DE Protection claims 1. Superconducting cable with at least one rigid inner tube, - in which at least one superconducting conductor wire is connected to a oxide ceramic high temperature superconductor material which is cooled by an appropriate cooling medium, and - which is concentrically enclosed by a rigid outer tube, an evacuated intermediate space being formed between the inner and outer tubes, characterized in that at least the inner tube (3) consists of a vacuum and coolant-tight plastic material. 2. Cable according to claim 1, characterized in characterized in that the outer tube (4) consists of a vacuum-tight plastic material. 3. Cable according to claim 1 or 2, characterized in that the plastic material is a epoxy resin or a thermoplastic. 4. Cable according to claim 3, characterized in that the plastic material is mechanically reinforced with fibers. 5. Cable according to one of claims 1 to 4, characterized in that films (26) are embedded in its plastic parts to increase the vacuum tightness. 6. Cable according to one of claims 1 to 5, characterized in that a super insulation (9) is arranged in the evacuated intermediate space (5). 02 01 II«· Ml 35 lit* · G 88 04 371.1 10 VPA 8*8 G 3127* DE 7. Cable according to one of claims 1 to 6, characterized in that sorbents (10) are applied to the outside of the inner tube (3) delimiting the evacuated intermediate space (5). 5 8. Cable according to one of claims 1 to 7, characterized in that it can be assembled from several prefabricated sections (21, 22} 33, 34). 9. Cable according to claim 8, characterized in that the sections (21, 22; 33, ><&diams;) have self-contained, evacuable spaces (5) between the respective inner and outer tubes (3 and 4). 10. Cable according to claim 8 or 9, characterized in that adjacent sections (21, 22; 33, 34) are designed to engage with one another on their mutually facing end faces (23, 24), a gap (27) being formed between them, which is closed with at least one sealing device (28, 29). 11. Cable according to claim 10, characterized in that the gap (27) is sealed after the parts (21, 22; 33, 34) have been assembled by means of a tubular element (29) connecting the two parts at their outer tubes (4). 12. Cable according to one of claims 1 to 11, characterized in that the inner tube (3) and/or the outer tube (4) contains a device (30) for expansion compensation. 02 02