JP4662203B2 - Superconducting cable - Google Patents

Description

  The present invention relates to a superconducting cable. In particular, the present invention relates to a superconducting cable having excellent bending characteristics.

  As a superconducting cable, the superconducting cable shown in FIG. 1 has been proposed. This superconducting cable 100 has a configuration in which a three-core cable core 10 is housed in a heat insulating tube 20 (for example, Patent Document 1).

  The cable core 10 includes a former 11, a superconducting conductor layer 12, an insulating layer 13, a superconducting shield layer 14, and a protective layer 15 in order from the center. Usually, the former 11 is composed of a stranded wire or a pipe material. The conductor layer 12 is configured by spirally winding a superconducting wire on the former 11 in multiple layers. Typically, a tape-like material in which a plurality of filaments made of an oxide superconducting material are arranged in a stabilizing metal such as a silver sheath is used as the superconducting wire. The insulating layer 13 is configured by winding insulating paper. The shield layer 14 is formed by spirally winding a superconducting wire similar to the conductor layer 12 on the insulating layer 13. Insulating paper or the like is used for the protective layer 15.

  The heat insulating tube 20 has a structure in which a heat insulating material (not shown) is disposed between the double tubes composed of the inner tube 21 and the outer tube 22, and the inside of the double tube is evacuated. An anticorrosion layer 23 is formed outside the heat insulating tube 20. Then, a refrigerant such as liquid nitrogen is filled and circulated in the former 11 (in the case of a hollow) or a space formed between the inner tube 21 and the core 10 and the insulating layer 13 is impregnated with the refrigerant. Is done.

Japanese Patent Laid-Open No. 2001-202837 (FIG. 1)

  However, the above-mentioned superconducting cable has a problem that its bending characteristics mainly depend on the strength of the superconducting wire constituting the superconducting shield layer, and sufficient bending characteristics are not necessarily obtained.

  Since the diameter of the superconducting shield layer is larger than the diameter of the superconducting conductor layer, when the cable core is bent, the strain applied to the superconducting shield layer is larger than that of the superconducting conductor layer. Therefore, the allowable bending diameter of the cable core mainly depends on the strength of the superconducting wire constituting the shield layer.

  The present invention has been made in view of the above circumstances, and a main object thereof is to provide a superconducting cable capable of improving bending characteristics.

  The present invention achieves the above object by changing the strength of the superconducting wire constituting the inner peripheral superconducting layer and the strength of the superconducting wire constituting the outer superconducting layer.

  The superconducting cable of the present invention includes a first superconducting layer composed of a first superconducting wire, an insulating layer formed outside the first superconducting layer, and a second superconducting wire composed outside the insulating layer. A superconducting cable having a superconducting layer, wherein the tensile strength of the second superconducting wire is higher than the tensile strength of the first superconducting wire.

  By increasing the tensile strength of the second superconducting wire arranged on the outer peripheral side rather than the first superconducting wire arranged on the inner peripheral side, the tensile strength against the second superconducting wire acting with greater strain at the time of cable bending is increased. The bending property of the superconducting cable can be improved.

  Specific means for making the tensile strength of the second superconducting wire higher than the tensile strength of the first superconducting wire include several means as follows.

<Formation of coating layer on bare superconducting wire>
As the first superconducting wire, a bare superconducting wire in which a superconducting filament is coated with a stabilizing metal is used. As the second superconducting wire, a wire composed of a bare superconducting wire and a covering layer covering the bare superconducting wire is used. By using a bare superconducting wire having a coating layer as the second superconducting wire, the strength of the superconducting wire can be increased as compared with a bare superconducting wire having no coating layer. Therefore, if the 2nd superconducting layer located in the outer peripheral side is formed with the 2nd superconducting wire which has a coating layer, the bending characteristic of a cable can be improved.

  As the bare superconducting wire, a known superconducting wire that has been conventionally used can be used. The superconducting filament is composed of a superconducting material, and an oxide superconducting material, more specifically, composed of a Bi2223 phase can be suitably used. As the stabilizing metal, silver or a silver alloy can be suitably used. Examples of the silver alloy include an Ag—Mn alloy and an Ag—Mg alloy.

  As the coating layer, various materials that can improve the tensile strength of the bare superconducting wire can be used. Typical examples include metal plating and resin coating. As specific examples of metal plating, copper plating, tin plating, solder plating, and the like can be suitably used. Specific examples of the resin coating include enamel coating and fluororesin coating. The thicknesses of these coating layers may be selected appropriately depending on the material of the coating layer so that a predetermined tensile strength as the second superconducting wire can be obtained.

<Tape layer bonding to bare superconducting wire>
As the first superconducting wire, a bare superconducting wire in which a superconducting filament is coated with a stabilizing metal is used. As the second superconducting wire, a wire composed of a bare superconducting wire and a tape layer joined to the bare superconducting wire is used. By bonding the tape layer to the bare superconducting wire, the tensile strength of the bare superconducting wire can be reinforced. Therefore, if the 2nd superconducting layer located in the outer peripheral side is formed with the 2nd superconducting wire which has a tape layer, the bending characteristic of a cable can be improved. As this tape layer, a metal tape, more specifically, a copper tape, an aluminum tape, a stainless steel tape or the like can be suitably used.

<Use of pressure sintering method>
A superconducting wire obtained by a method other than the pressure sintering method is used as the first superconducting wire. And the 2nd superconducting wire uses the superconducting wire obtained by the pressure sintering method. The superconducting wire obtained by the pressure sintering method has higher tensile strength than the superconducting wire obtained by methods other than the pressure sintering method, so it can be used for the second superconducting wire located on the outer peripheral side. The bending characteristics of the cable can be improved.

  The pressure firing method is a method in which external pressure is applied isotropically to a wire by applying pressure with a gas when sintering the original wire of the superconducting wire in the Powder in tube method for producing a superconducting wire. This pressurization suppresses a decrease in the filament density of the wire, and a superconducting wire having a high tensile strength can be obtained.

  As the gas at the time of pressurization by the pressure firing method, a mixed gas of an inert gas and oxygen is suitable. The pressure applied at that time is preferably 15 to 50 MPa. In the case of a mixed gas of an inert gas and oxygen, the oxygen partial pressure is preferably 7 kPa or more and 21 kPa or less. By this pressure adjustment, an external pressure due to the atmospheric gas is applied isotropically to the wire, and the relative density of the superconductor can be improved. Inert gases include nitrogen, argon, helium, and neon. The atmosphere of this heat treatment may be air. When the primary heat treatment / secondary heat treatment is performed on the base wire of the superconducting wire, the pressure-adjusted heat treatment may be performed on both heat treatments or only the secondary heat treatment. This pressure firing method is described in, for example, “Development of bismuth-based superconducting wire” Kohei Yamazaki, “SEI Technical Review”, No.164, pages 36-41, March 2004.

  The superconducting cable of the present invention is typically composed of a cable core and a heat insulating tube that houses the cable core. Among these, the cable core has a basic configuration including a first superconducting layer, an insulating layer, and a second superconducting layer. Usually, a former is provided inside the first superconducting layer. In addition, it is preferable to provide a protective layer outside the second superconducting layer.

  The former is disposed inside the first superconducting layer in order to keep the first superconducting layer in a predetermined shape. As the former, a pipe-shaped member, a strip-shaped member formed into a spiral, or a stranded wire structure can be used. The material is preferably a nonmagnetic metal material such as copper or aluminum. In addition, various plastic materials can be used. When the former is pipe-shaped, it is preferable to use a corrugated tube in consideration of flexibility. If it is a pipe-shaped former, the inside of a former can be made into the flow path of a refrigerant | coolant.

  The first superconducting layer is composed of a first superconducting wire, and is typically configured as a superconducting conductor layer. For example, the superconducting conductor layer is formed by winding the first superconducting wire in a spiral manner on the outside of the former. As a specific example of the first superconducting wire, a tape-shaped one in which a plurality of filaments made of a Bi2223 oxide superconducting material are arranged in a stabilizing material such as a silver sheath can be cited.

  The winding of the first superconducting wire may be a single layer or multiple layers. Usually, in order to suppress the drift of the first superconducting layer wound in multiple layers and reduce the AC loss, the winding direction or the winding pitch of the first superconducting wire is changed for each layer or for each of a plurality of layers. In addition, in the case of using multiple layers, when used in AC applications, it is necessary to provide an interlayer insulating layer for insulating each layer in order to reduce AC loss. The interlayer insulating layer may be provided by winding an insulating paper such as kraft paper or a composite tape such as PPLP (manufactured by Sumitomo Electric Industries, Ltd., registered trademark).

  The insulating layer is made of an insulating material having a dielectric strength corresponding to the voltage of the first superconducting layer. For example, at least one of kraft paper, plastic tape, and composite tape of kraft paper and plastic tape (for example, PPLP: registered trademark) can be suitably used.

  In each of the above materials, the structure in which the insulating layer is formed only from kraft paper is the lowest cost. If the composite tape and kraft paper are used in combination, the amount of expensive composite tape used can be reduced and the cable cost can be reduced as compared with the case where the insulating layer is formed of only the composite tape. On the other hand, it is preferable in terms of electrical characteristics to use a composite tape for the insulating layer. As the composite tape, a laminate of kraft paper and polypropylene film is suitable.

  A second superconducting layer is formed outside the insulating layer. As described above, the second superconducting layer is composed of the second superconducting wire having a higher tensile strength than the first superconducting wire. The second superconducting layer is typically configured as a superconducting shield layer in the case of an AC cable, and is configured as an external superconducting conductor layer in the case of a DC cable. The superconducting shield layer cancels out the magnetic field generated from the superconducting conductor layer by inducing a current in the opposite direction with the same magnitude as that of the superconducting conductor layer, and prevents leakage of the magnetic field to the outside. The external superconducting conductor layer can be used, for example, as a return circuit when the superconducting conductor layer is an outbound circuit.

  This second superconducting layer may also be formed by spirally winding the second superconducting wire. The winding of the second superconducting wire may be a single layer or multiple layers. Usually, in order to suppress the drift of the second superconducting layer wound in multiple layers and reduce the AC loss, the winding direction or the winding pitch of the second superconducting wire is changed for each layer or for each of a plurality of layers. Moreover, when using it by alternating current as a multilayer, it is necessary to provide an interlayer insulation layer.

  Moreover, it is preferable to provide a protective layer outside the second superconducting layer. This protective layer has a function of insulating the heat insulating tube together with mechanical protection of the second superconducting layer. As the material of the protective layer, insulating paper such as kraft paper or cloth tape can be used.

  Further, a semiconductive layer may be formed at least one of the inner and outer circumferences of the insulating layer, that is, between the first superconducting layer and the insulating layer, or between the insulating layer and the second superconducting layer. Forming the former inner semiconductive layer and the latter outer semiconductive layer is effective in stabilizing electrical performance.

  In addition, a cushion layer may be formed on at least one of the first superconducting layer and the second superconducting layer, and a presser wound layer may be further formed thereon. The cushion layer can be made of kraft paper, and the presser wound layer can be made of copper tape. This cushion layer avoids metal-to-metal contact by each superconducting layer and the presser wound layer, and the presser wound layer clamps the first (second) superconducting layer to the inner peripheral side via the cushion layer to cool the first ( 2) Make the diameter of the superconducting layer behave smoothly.

  On the other hand, the heat insulating tube may have any structure as long as the heat insulation of the refrigerant can be maintained. For example, the structure which arrange | positions a heat insulating material between the double tubes of the double structure which consists of an outer tube and an inner tube, and evacuates between an inner tube and an outer tube is mentioned. Usually, a super insulation layered with a metal foil and a plastic mesh is disposed between the inner tube and the outer tube. The inner tube contains the first superconducting layer and the second superconducting layer, and is filled with a refrigerant such as liquid nitrogen that cools the superconducting layer.

  This refrigerant shall maintain a superconducting wire in a superconducting state. Currently, the use of liquid nitrogen is considered the most practical refrigerant, but other uses such as liquid helium and liquid hydrogen are also conceivable.

  The superconducting cable as described above may be a single-core cable or a multi-core cable. A specific example of the multi-core cable is a three-core superconducting cable formed by twisting three cable cores each having a first superconducting layer, an insulating layer, and a second superconducting layer.

  According to the superconducting cable of the present invention, the following effects can be obtained.

  (1) The second superconducting wire that is more susceptible to stress during cable bending by configuring the tensile strength of the second superconducting wire disposed on the outer peripheral side higher than that of the first superconducting wire disposed on the inner peripheral side The tensile strength of can be increased. Thereby, the bending characteristic of the cable can be improved.

  (2) By using the first superconducting wire as a bare superconducting wire and the second superconducting wire as a wire provided with a coating layer on the bare superconducting wire, the tensile strength of the second superconducting wire can be easily increased.

  (3) By using the first superconducting wire as a bare superconducting wire and the second superconducting wire as a wire obtained by joining a tape layer to the bare superconducting wire, the tensile strength of the second superconducting wire can be easily increased.

  (4) The first superconducting wire is a superconducting wire obtained by a method other than the pressure sintering method, and the second superconducting wire is a superconducting wire obtained by the pressure sintering method. The tensile strength can be higher than the tensile strength of the first superconducting wire.

  Embodiments of the present invention will be described below.

[Overall structure]
As shown in FIG. 1, the superconducting cable 100 of the present invention includes a three-core cable core 10 and a heat insulating tube 20 that houses the core 10.

[Cable core]
Each core 10 includes a former 11, a superconducting conductor layer 12 (first superconducting layer), an insulating layer 13, a superconducting shield layer 14 (second superconducting layer), and a protective layer 15 in this order from the center.

<Former>
For the former 11, a stainless corrugated tube was used. When the hollow former 11 is used, the inside thereof can be a flow path for a refrigerant (here, liquid nitrogen).

<Superconducting conductor layer>
For the superconducting conductor layer 12, a Bi2223-based Ag sheathed tape wire having a thickness of 0.24 mm and a width of 3.8 mm was used. This tape wire is a bare superconducting wire in which a plurality of Bi2223 phase superconducting filaments are arranged in Ag as a stabilizing material.

  This bare superconducting wire is manufactured by a method other than the pressure sintering method. Here, the production of bare superconducting wire is performed by the process of “preparation of raw material powder → preparation of clad wire → production of multi-core wire → production of primary rolled wire → primary heat treatment → production of secondary rolled wire → secondary heat treatment” . More specifically, a raw material powder mainly composed of the Bi2212 phase is inserted into a silver pipe, and this is drawn to obtain a single-core clad wire. Next, a plurality of clad wires are inserted into another silver pipe, and the silver pipe is drawn to produce a multi-core wire. The obtained multifilamentary wire is rolled at a reduction rate of 80% (primary rolling) and processed into a tape-shaped primary rolled wire. The obtained primary rolled wire is subjected to a primary heat treatment in an inert gas and oxygen atmosphere at a total pressure of 0.1 MPa, an oxygen partial pressure of 8 kPa, and 830 ° C. for 30 hours to obtain a primary heat treated wire in which a Bi2223 phase is generated. This primary heat-treated wire is re-rolled at a rolling reduction of 10% (secondary rolling) to obtain a secondary rolled wire having a width of 3.8 mm and a thickness of 0.24 mm. Then, the secondary rolled wire is subjected to a secondary heat treatment in an inert gas and oxygen atmosphere at a total pressure of 0.1 MPa, an oxygen partial pressure of 8 kPa, and 820 ° C. for 50 hours to obtain a bare superconducting wire.

  The bare superconducting wire is wound in multiple layers on the former to form the superconducting conductor layer 13. Here, a superconducting wire is wound around the four layers. The winding direction of each layer was S-S-Z-Z in order from the inner layer side.

<Insulating layer>
An insulating layer 13 is formed outside the superconducting conductor layer 12. Here, the insulating layer 13 is made of PPLP (registered trademark) obtained by laminating kraft paper and polypropylene tape. The ratio of the thickness of the polypropylene tape to the total thickness of this PPLP is 60%.

  Although not shown, an internal semiconductive layer is formed between the insulating layer 13 and the superconducting conductor layer 12, and an external semiconductive layer is formed between the insulating layer 13 and the superconducting shield layer 14 described below. ing. All the semiconductive layers were formed by winding carbon paper.

<Superconducting shield layer>
A superconducting shield layer 14 is provided outside the insulating layer 13. This superconducting shield layer 14 cancels out the magnetic field generated from the superconducting conductor layer 12 by inducing reverse current in the same magnitude as the superconducting conductor layer 12 during cable operation (AC), and Prevent leakage.

  Here, (1) a plated wire obtained by copper plating the bare superconducting wire used for the superconducting conductor layer 12, (2) a joined wire obtained by joining stainless steel tape to the bare superconducting wire, (3) produced by pressure sintering Three types of pressure-sintered wire rods were prepared, and a superconducting shield layer 14 was formed on each of them to constitute three types of superconducting cables.

  The thickness of the copper plating layer in the plating wire is 20 μm. The stainless steel tape used for the bonding wire is made of SUS316 having a thickness of 25 μm. The bare superconducting wire and stainless steel tape were joined by soldering. The pressure sintered wire was obtained by performing the secondary heat treatment in the above-described bare superconducting wire in an atmosphere of inert gas and oxygen at a total pressure of 30 MPa and an oxygen partial pressure of 8 kPa. Secondary heat treatment conditions other than this pressure are the same as those for producing the bare superconducting wire. When the tensile strength of the bare superconducting wire is 1.0, the tensile strength of the plated wire is 1.3, the tensile strength of the bonding wire is 1.6, and the tensile strength of the pressure sintered wire is 1.7. Superconducting shield layer 14 composed of these second superconducting wires is laminated in two layers, and the winding direction of each layer is SS.

<Protective layer>
A protective layer 15 made of an insulating material is provided outside the superconducting shield layer 14. Here, the protective layer 15 is formed by winding kraft paper. With this protective layer 15, the superconducting shield layer 14 can be mechanically protected and insulated from the heat insulating pipe (inner pipe 21).

[Insulated pipe]
The heat insulating tube 20 is a double tube including an inner tube 21 and an outer tube 22, and a vacuum heat insulating layer is formed between the inner and outer tubes 21 and 22. A so-called super-insulation in which a plastic mesh and a metal foil are laminated is disposed in the vacuum heat insulating layer. A space formed between the inner side of the inner tube 21 and the core 10 serves as a refrigerant flow path. Further, if necessary, the anticorrosion layer 23 may be formed on the outer periphery of the heat insulating tube 20 with polyvinyl chloride or the like.

[Test example]
Of the above superconducting cables, the superconducting conductor is a superconducting conductor with a superconducting shield layer made of a plated wire as sample 1, a cable core made of a bonding wire as sample 2, and a cable core made of a pressure sintered wire as sample 3. The cable core comprised of a bare superconducting wire for both the layer and the superconducting shield layer was used as sample 4, and the allowable bending diameter was determined for each sample core. The allowable bending diameter was a bending diameter at which the critical current Ic was 95% for each sample without bending. The results are shown in Table 1. As is clear from this table, it was confirmed that Sample 1 to Sample 3 had a smaller allowable bending radius than Sample 4.

  The superconducting cable of the present invention can be used as a power transportation means. In particular, it can be suitably used as a superconducting cable laid on a bent line having a relatively small bending diameter.

It is a cross-sectional view of a superconducting cable.

Explanation of symbols

100 superconducting cable
10 core
11 Former 12 Superconducting conductor layer 13 Insulating layer 14 Superconducting shield layer
15 Protective layer
20 Insulated pipe
21 Inner pipe 22 Outer pipe 23 Anticorrosion layer

Claims (3)

Superconducting having a first superconducting layer composed of a first superconducting wire, an insulating layer formed outside the first superconducting layer, and a second superconducting layer composed of a second superconducting wire outside the insulating layer A cable,
The first superconducting wire consists of a bare superconducting wire in which a superconducting filament is coated with a stabilizing metal,
The second superconducting wire is composed of a bare superconducting wire and a resin coating covering the bare superconducting wire,
A superconducting cable, wherein the tensile strength of the second superconducting wire is higher than the tensile strength of the first superconducting wire. Superconducting having a first superconducting layer composed of a first superconducting wire, an insulating layer formed outside the first superconducting layer, and a second superconducting layer composed of a second superconducting wire outside the insulating layer A cable,
The first superconducting wire is composed of a bare superconducting wire in which a superconducting filament is coated with a stabilizing metal made of silver or a silver alloy,
The second superconducting wire comprises a bare superconducting wire and a metal plating covering the bare superconducting wire, and the metal plating is selected from copper plating, tin plating, and solder plating,
A superconducting cable, wherein the tensile strength of the second superconducting wire is higher than the tensile strength of the first superconducting wire. Superconducting having a first superconducting layer composed of a first superconducting wire, an insulating layer formed outside the first superconducting layer, and a second superconducting layer composed of a second superconducting wire outside the insulating layer A cable,
The superconducting cable is a three-core superconducting cable formed by twisting three cable cores having a first superconducting layer, an insulating layer, and a second superconducting layer,
A superconducting cable, wherein the tensile strength of the second superconducting wire is higher than the tensile strength of the first superconducting wire.

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