JP2009076401A - Superconductive cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multicore package type superconductive cable capable of using superconductive wire materials with different mechanical strength characteristics for suitable uses. <P>SOLUTION: In the multicore package type superconductive cable wherein a plurality of cable cores 9 for forming a superconductive shield layer 4 are twisted on an outer side of a superconductive conductor layer 2 via an insulated layer 3, the superconductive shield layer 4 is formed by winding the superconductive wire material 21 with superior bending rigidity identified by an EI value in a spiral shape, and the superconductive wire material 21 used for the superconductive shield layer 4 is formed by covering a bismuth oxide superconductor with a metal stabilizer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a superconducting cable that can suppress the occurrence of buckling of a superconducting layer.

  Bi-based superconducting tape wires represented by Bi-Sr-Ca-Cu-O tape wires are being put into practical use as superconducting wires. The Bi-based superconducting tape wire is a tape wire having a structure in which, for example, a plurality of superconducting filaments made of Bi2223 phase are embedded in a stabilizing material such as silver. Since this Bi-based superconducting tape wire is excellent in bending rigidity, it has excellent resistance to compressive stress and is difficult to buckle, but its strength against tensile force is slightly weaker than an RE (rare earth) -based superconducting thin film described later. A three-core superconducting cable using such a Bi-based superconducting tape wire is configured, for example, as shown in FIG. That is, in the figure, in order from the center, a former 1, a superconducting conductor layer 2 made of a Bi-based superconducting tape wire, an insulating layer 3, and a superconducting shield layer 4 made of a Bi-based superconducting tape wire are formed. Is configured. The three cable cores 9 are twisted together and covered with a double heat insulating pipe formed by the inner pipe 6 and the outer pipe 7, and the refrigerant flow passage 5 is formed in the inner pipe 6. Further, the outer tube 7 is covered with the anticorrosion layer 8, and the space between the inner tube 6 and the outer tube 7 is evacuated to form a vacuum layer.

  The configuration of the superconducting cable will be described in more detail. First, as shown in FIG. 4, for example, the cross section of the Bi-based superconducting tape wire 21 is composed of a number of superconducting filaments 21b made of Bi-based oxide superconductor made of silver or the like. It is covered with a metal sheath (metal stabilizing material) 21a and formed in a tape shape. For example, a cable core 9 as shown in FIG. 5 is formed by the Bi-based superconducting tape wire 21. That is, the cable core 9 includes, in order from the center, a former 1 composed of a stranded wire or a hollow pipe formed by twisting strands made of a normal conducting material such as Cu, and a superconducting conductor layer composed of a Bi-based superconducting tape wire 21. 2, an insulating layer 3 made of kraft paper or a composite paper laminated with kraft paper and a polyolefin film, a superconducting shield layer 4 made of a Bi-based superconducting tape wire 21, a normal conducting metal layer 25, and a protective layer 26. It is formed. For example, as shown in FIG. 6, three such cable cores 9 are forcibly twisted together in a state where a tensile force is applied, and are formed by an inner tube 6 and an outer tube 7 on the outer periphery thereof. A heavy heat insulating tube is fitted to form a three-core batch type superconducting cable as shown in FIG.

On the other hand, as a next-generation superconducting wire, development of a RE-based superconducting thin film wire is underway (for example, Patent Document 1). For example, as shown in FIG. 7, the RE-based superconducting thin film wire 11 is a tape wire formed by sequentially laminating an intermediate layer 13, a superconducting thin film 14, and a protective layer 15 on a tape-like metal substrate 12. As a specific example, for example, Hastelloy (registered trademark) is used as the metal substrate 12, YSZ is used as the intermediate layer 13, a Y-based 123 structure (YBa ₂ Cu ₃ Oy) thin film is used as the superconducting thin film 14, and silver is used as the protective layer 15. Usually, the intermediate layer 13 and the superconducting thin film 14 are formed only on one side of the metal substrate 12 by laser vapor deposition or the like. Such an RE-based superconducting thin film wire 11 can be formed thin and has a relatively excellent strength against tensile force due to the presence of the metal substrate 12, but the metal substrate 12 and the protection If the layer 15 is made thin, the bending rigidity is low, so that there is a problem that it is easy to buckle. When such a RE superconducting thin film wire 11 is used to form a three-core superconducting cable, the configuration is the same as that of the Bi superconducting tape wire 21.
JP 2001-31418

  By the way, in the manufacturing stage of the above-described three-core collective superconducting cable, an operation of forcibly twisting the three cable cores 9 while applying a tensile force is performed. At that time, particularly at the contact point between the cores, in the outer superconducting shield layer 4, the cores are locally forced to bend each other, so that there is a problem that damage such as buckling is likely to occur. . That is, when a tension force is applied to the three cable cores 9 to twist them together, the outer sides of the cable cores 9 are pulled, whereas the inner sides are locally bent and loosened. When the cores in which such slack occurs are compressed, the core is compressed, and the wire is bent when it cannot withstand it. This is called buckling.

  Such buckling also occurs in the handling stage after cable manufacture. For example, when a superconducting cable is bent when the cable is wound around a drum or when the cable is laid on site, a forced bending force acts on the superconducting layer in the cable. Due to the bending force, the larger the diameter of the superconducting layer, the greater the tensile force acts on the outer part and the greater the compressive force acts on the inner part. When such a large tensile force and compressive force act on the superconducting layer, the strain becomes large and buckling tends to occur. Such strain ε can be expressed as ε∝D / R, where R is the bending radius of the superconducting cable and D is the diameter of the superconducting layer. That is, when the superconducting cable is bent to the same extent, the larger the diameter D of the superconducting layer, the larger the strain ε and the more likely buckling occurs. Such a problem of buckling caused by bending of the cable is not limited to a multi-core batch type superconducting cable such as the above-described three-core batch type, but also occurs in a single-core type superconducting cable. In a single-core superconducting cable having a plurality of superconducting layers, buckling tends to occur in the outer superconducting layer.

  However, at the stage of studying the structure of the superconducting cable, the characteristics of the RE-based superconducting thin film wire that has excellent allowable elongation and the thickness of the wire can be reduced, and the Bi-based superconducting tape wire that has excellent bending rigidity and AC loss Development of superconducting wire has been promoted so that Bi-based superconducting tape wire and the like whose wire dimensions are thinned and thinned can be selected for the purpose of reducing the above. However, when taking them into the superconducting layer of the superconducting cable, the appropriate material for the superconducting wire has not been selected so that the characteristics of each wire can be fully utilized. For this reason, the buckling as described above often occurs, and countermeasures have been demanded.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a superconducting cable that can suppress the occurrence of buckling of a superconducting layer.

The superconducting cable of the present invention is a superconducting cable comprising a plurality of superconducting layers formed of a superconducting wire,
When the Young's modulus of the superconducting wire is E and the secondary moment of inertia is I, the outer superconducting layer formed on the outside is a superconducting wire having a larger EI value than the superconducting wire constituting the inner superconducting layer formed on the inside. It is characterized by having.

  When a plurality of superconducting layers are formed, the outer superconducting layer is more strained by bending the cable than the inner superconducting layer, so the EI value of the superconducting wire forming the outer superconducting layer is set to the inner superconducting layer. By setting it to be larger than the superconducting wire that forms the cable, it becomes possible to design the cable generated at the stage of superconducting cable production or handling so as to ensure the buckling strength necessary for bending.

  The EI value of the superconducting wire constituting the superconducting layer may be selected approximately in proportion to the diameter of the superconducting layer. If the cable is bent when the superconducting cable is wound around a drum or laid on site, the larger the diameter of the superconducting layer, the greater the tensile force acts on the outer part of the bend and the larger the inner part. Since compressive force acts, distortion becomes large and buckling tends to occur. Such strain ε can be expressed as ε∝D / R, where R is the bending radius of the superconducting cable and D is the diameter of the superconducting layer. That is, when the superconducting cable is bent to the same extent, the larger the diameter D of the superconducting layer, the larger the strain ε. Therefore, it is preferable to set the EI value to a large value in a superconducting layer having a large diameter so as to withstand such strain. Such a measure makes it difficult for the superconducting layer to buckle against bending of the cable when handling the superconducting cable.

  The superconducting cable may be a 3-core batch type. For example, in an AC three-core superconducting cable, a superconducting shield layer is formed on the outer side of the inner superconducting conductor layer. In this case, if the superconducting cable is bent, the distortion of the superconducting shield layer is greater than that of the superconducting conductor layer. Also grows. Therefore, by setting the EI value of the superconducting wire forming the superconducting shield layer having a large diameter to an appropriate value larger than that of the superconducting wire forming the superconducting conductor layer according to the diameter, sufficient buckling against bending is achieved. Yield strength can be secured. In addition, in the process of forcing the three cable cores to be twisted together while applying the tensile force to the three cable cores, the cores of the outer superconducting shield layer are locally forced to bend each other. Although damage such as bending is likely to occur, since the superconducting shield layer having a large diameter is filled with a superconducting wire having a large EI value, such buckling is unlikely to occur.

The superconducting wire used for the outer superconducting layer may be formed by covering a bismuth-based oxide superconductor with a metal stabilizing material. Bi-based superconducting tape wire formed by covering a bismuth-based oxide superconductor with a metal stabilizer has a relatively high bending rigidity and a relatively high EI value. Even when the cores are twisted together, the occurrence of damage such as buckling can be avoided. Also, buckling is less likely to occur when the superconducting cable is bent.

  The superconducting wire used for the outer superconducting layer may be one in which a RE superconducting thin film is formed on at least one side of a metal substrate. In the case of the RE-based superconducting thin film, the bending rigidity can be improved by increasing the thickness of the metal substrate. Therefore, when the required EI value can be secured, the RE-based superconducting thin film is preferably used for the outer superconducting layer. be able to. Examples of such RE-based superconducting thin films include those mainly composed of a Ho-based superconductor or a Y-based superconductor.

  In the superconducting cable of the present invention, the outer superconducting layer includes a superconducting thin film wire having an EI value larger than that of the superconducting wire forming the inner superconducting layer, so that the cable generated at the time of manufacturing or handling the superconducting cable is bent. However, the superconducting layer is less likely to buckle.

  The superconducting cable according to the embodiment of the present invention will be described below. FIG. 1 shows a cross-sectional configuration of a three-core batch type superconducting cable, and FIG. 2 shows a configuration of a cable core. First, as shown in FIG. 1, this superconducting cable is housed in a double heat insulating tube formed by an inner tube 6 and an outer tube 7 in which three cable cores 9 are twisted together. Then, a refrigerant flow passage 5 through which a cooling medium such as liquid nitrogen flows is formed in the inner tube 6, the outer tube 7 is covered with a protective layer 8, and the space between the inner tube 6 and the outer tube 7 is evacuated. A vacuum layer is formed. With such a configuration, the superconducting cable is maintained in an operable superconducting state.

  The cable core 9 is configured as shown in FIG. 2, for example. That is, the cable core 9 includes, in order from the center, the former 1, the interlayer insulation 24, the superconducting conductor layer (inner superconducting layer of the present invention) 2, the insulating layer 3, and the superconducting shield layer (outer superconducting layer of the present invention). 4, a normal conducting metal layer 25, and a protective layer 26. The former 1 is formed of a stranded wire formed by twisting strands made of a normal conducting material such as Cu or a hollow pipe, and the superconducting conductor layer 2 is formed of a superconducting thin film wire 11 (see FIG. 7). Is formed of kraft paper or composite paper laminated with kraft paper and polyolefin film, and the superconducting shield layer 4 is formed of a Bi-based superconducting tape wire 21 (see FIG. 4).

  As the superconducting thin film wire 11 for forming the superconducting conductor layer 2, for example, as shown in FIG. 7, an RE-based superconducting film in which an RE-based superconducting thin film 14 mainly composed of a Ho-based superconductor or a Y-based superconductor is formed on a metal substrate 12. A thin film wire can be used. Such a RE-based superconducting thin film wire 11 has the disadvantages that the bending rigidity is relatively low and the strength against compressive stress, that is, the buckling strength is somewhat low, but the thickness can be reduced. Due to its presence, it has excellent strength against tensile force and has a relatively large allowable elongation. On the other hand, the Bi-based superconducting tape wire 21 forming the superconducting shield layer 4 is slightly low in strength against tensile force, but has excellent bending rigidity and excellent strength against compressive stress, that is, buckling strength. That is, the EI value representing the bending rigidity when the Young's modulus of the superconducting wire is E and the secondary moment is I is relatively high. In this superconducting cable, the RE superconducting thin film wire 11 and the Bi superconducting tape wire 21 having different strength characteristics are properly used for the superconducting conductor layer 2 and the superconducting shield layer 4 as described above. Yes.

  First, regarding the superconducting shield layer 4, as described with reference to FIG. 6, in the step of twisting each other while applying the tensile force to the three cable cores 9, particularly the contact points between the cable cores 9 and 9 Then, since the cores are locally forcedly bent, the superconducting shield layer 4 disposed outside the cable core 9 is likely to buckle. In view of this point, in the present invention, since the Bi-based superconducting tape wire 21 having excellent bending rigidity is used for the superconducting shield layer 4, damage such as buckling is unlikely to occur. Further, in the handling stage after the cable is manufactured, when the cable is bent when the superconducting cable is wound around a drum or laid on the site, the superconducting shield layer 4 having a large diameter has a large outer portion of the bending. Since the tensile force acts and a large compressive force acts on the inner portion, the strain increases. However, since the superconducting shield layer 4 is composed of the Bi-based superconducting tape wire 21 having a large EI value, buckling is caused. Less likely to occur.

  Next, in the superconducting conductor layer 2, a superconducting wire is wound around the outer periphery of the former 1 via a relatively thin interlayer insulation 24. For this reason, when the cable core 9 is cooled by the circulation of the refrigerant in the use stage, the superconducting wire contracts, but since the interlayer insulation 24 is thin, there is not much shrinkage and troubles such as breakage are likely to occur. In view of this point, in the present embodiment, since the RE-based superconducting thin film wire 11 having excellent allowable elongation and tensile strength is used for the superconducting conductor layer 2, sufficient proof stress can be exerted, such as fracture. Trouble is less likely to occur.

  As described above, in the present invention, the superconducting thin film wire (RE-based superconducting thin film wire) 11 and the Bi-based superconducting tape wire 21 having different mechanical strength characteristics are appropriately applied to the superconducting conductor layer 2 and the superconducting shield layer 4. Since they are used properly, for example, considerations such as providing a looseness when twisting the cable core 9 required in the past and adjusting the tension when winding the superconducting wire are greatly eased. As a result, in the manufacturing stage, it is easy to form the superconducting conductor layer 2 that does not collapse by applying an appropriate tension to the RE-based superconducting thin film wire 11. Further, even if the three cable cores 9 are twisted together without loosening, the trouble that buckling occurs in the superconducting shield layer 4 is reduced, and the work efficiency at the time of cable production can be remarkably improved. Furthermore, buckling of the superconducting shield layer 4 is less likely to occur even when the cable is bent when the superconducting cable is wound around a drum or laid on site.

[Examination of strength characteristics of superconducting wire]
The mechanical strength characteristics required for the superconducting wire used in the superconducting layer of the superconducting cable are as follows: (1) Yield strength against tensile force, (2) Elongation tolerance: Elongation δ (allowable elongation), (3) Compressive stress Yield strength (flexural rigidity EI: E; longitudinal elastic modulus (Young's modulus), I: secondary moment of section) and the like. Table 1 shows the results of numerical studies conducted on the Bi-based superconducting tape wire and the superconducting thin film wire (Y-based superconductor) with respect to these mechanical strength characteristics.

Incidentally, 1 thickness) wire corresponds to the term h bh ^3/12 to give the second moment of the rectangular cross-section. 2) Young's modulus E (GPa) indicates a value at an absolute temperature of 77 K to normal temperature. 3) Elongation δ (%) is represented by δ = {(l′−l) / l} × 100, and indicates the ratio of the difference in distance between the gauge points before and after fracture, and the value at room temperature in the table. . 4) The cross-sectional secondary moment I is converted to a value when the wire width b = 1 mm. 5) It is confirmed that EI ≧ 150 × 10 ⁻⁴ GPa · mm ⁴ is preferably satisfied with respect to the EI value (in use) converted to the wire width b = 1 mm. Therefore, there is a boundary to be allowed between B and C in the superconducting thin film wire.

  From Table 1, it can be seen that the Bi-based superconducting tape wire is excellent in bending rigidity EI but has low elongation δ. On the other hand, it can be seen that the superconducting thin film wire (Y-based superconductor) has a large elongation δ but a low bending rigidity EI. For this reason, the superconducting thin film wire (Y-based superconductor) 11 is applied to the portion where a large elongation δ is required, that is, the superconducting conductor layer 2, and the portion where a large bending rigidity is required, that is, the superconducting shield layer 4 It is preferable to use a Bi-based superconducting tape wire.

Also, as the superconducting wire of the outer superconducting layer 4, when the EI value (when the cable is in use) is converted to the superconducting wire width b = 1 mm, RE satisfying the condition of EI ≧ 150 × 10 ⁻⁴ GPa · mm ⁴ A superconducting thin film 11 (see Table 1) can also be selected. If it has such a bending rigidity, the occurrence of buckling can be avoided even when the cable cores 9 are twisted together or wound around a drum. Therefore, in this case, both the inner superconducting layer 2 and the outer superconducting layer 4 can be formed of the RE superconducting thin film 11.

  When the Young's modulus of the superconducting wire is E and the cross-sectional secondary moment is I, the EI value of the superconducting wire forming the superconducting layer may be selected approximately in proportion to the diameter of the superconducting layer. That is, for the outer superconducting layer 4 having a large diameter, the necessary bending rigidity can be ensured by selecting a superconducting wire having a large EI value proportional to the diameter. The superconducting layer is less likely to buckle against bending. Such correspondence can be applied regardless of the material of the superconducting wire. Further, even in the same superconducting layer, the EI value of the superconducting wire forming the superconducting layer may be selected in proportion to the diameter of the wound superconducting wire. Furthermore, for the superconducting wire wound around the outermost layer, an appropriate EI value may be selected as needed without being restricted by the proportional relationship as described above.

  Alternatively, as a superconducting wire constituting the inner superconducting layer 4, for example, a superconducting wire having an elongation δ (at room temperature) of 0.2% or more, preferably 0.3% or more, such as a superconducting thin film wire (or Bi-based superconducting tape wire) (see Table 1). ), The cable core 9 can follow the contraction when it is cooled by the circulation of the refrigerant during use, thereby avoiding troubles such as breakage or breakage due to insufficient contraction allowance. can do.

  It should be noted that the present invention is not limited to the embodiment, and can be freely improved, changed, etc. as necessary without departing from the gist of the invention. The superconducting cable of the present invention is not limited to the three-core package type, and the number of core wires may be selected as appropriate. Further, the configuration of the present invention can be applied not only to alternating current but also to direct current superconducting cables and other alternating current superconducting cables. That is, the present invention can be applied to a single-core AC superconducting cable having a superconducting conductor layer and a superconducting shield layer, and a single-core DC superconducting cable in which the inner superconducting layer and the outer superconducting layer constitute the forward path and the return path. Alternatively, the present invention can also be applied to a three-phase AC type superconducting cable in which each phase of the superconducting conductor layer is arranged coaxially through an insulating layer, and further a superconducting shield layer is arranged through an insulating layer. Also in these cases, by selecting the EI value of the superconducting wire that forms the superconducting layer approximately in proportion to the diameter of the superconducting layer, the occurrence of buckling due to cable bending or the like is effectively prevented. Can be suppressed.

  The superconducting cable of the present invention is suitably applied to a power transmission cable or the like that requires high reliability because the superconducting layer is less likely to buckle even if the cable generated during the manufacturing stage or handling of the superconducting cable is bent. can do.

It is sectional drawing which shows the structure of the 3 core collective type superconducting cable which concerns on embodiment of this invention. It is a partially broken perspective view of the cable core. It is sectional drawing of the conventional 3 core lump type superconducting cable. It is sectional drawing of the same Bi type superconducting tape wire. It is a partially broken perspective view of the cable core. It is explanatory drawing which shows the twisted state of the cable core. It is a partially broken perspective view of the same superconducting thin film wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Former 2 Superconducting conductor layer (inner superconducting conductor layer) 3 Insulating layer 4 Superconducting shield layer (outer superconducting conductor layer) 6 Inner tube 7 Outer tube 8 Anticorrosion layer 9 Cable core 11 Superconducting thin film wire (RE-based superconducting thin film wire)
21 Bi-based superconducting tape wire 21a Metal sheath 21b Superconducting filament 24 Interlayer insulation 25 Normal conducting metal layer 26 Protective layer

Claims (6)

A superconducting cable comprising a plurality of superconducting layers formed of a superconducting wire,
When the Young's modulus of the superconducting wire is E and the secondary moment of inertia is I, the outer superconducting layer formed on the outside is a superconducting wire having a larger EI value than the superconducting wire constituting the inner superconducting layer formed on the inside. A superconducting cable characterized by comprising.   2. The superconducting cable according to claim 1, wherein the EI value of the superconducting wire constituting the superconducting layer is selected approximately in proportion to the diameter of the superconducting layer.   The superconducting cable according to claim 1 or 2, wherein the superconducting cable is a three-core package type.   The superconducting cable according to claim 2 or 3, wherein the superconducting wire used for the outer superconducting layer is formed by covering a Bi-based oxide superconductor with a metal stabilizing material.   The superconducting cable according to claim 2 or 3, wherein the superconducting wire used for the outer superconducting layer has an RE-based superconducting thin film formed on at least one side of a metal substrate.   The superconducting cable according to claim 5, wherein the RE-based superconducting thin film is mainly composed of a Ho-based superconductor or a Y-based superconductor.

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