JP4096406B2 - Oxide superconducting stranded wire and oxide superconducting cable conductor, and oxide superconducting stranded wire and oxide superconducting cable manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductor for an oxide superconducting stranded wire and an oxide superconducting cable using an oxide superconductor or a precursor and a wire covering the metal, and a technique for producing them, in particular, a high critical current. The present invention relates to a technique for providing an oxide superconducting stranded wire having a density and a conductor for an oxide superconducting cable.
[0002]
[Prior art]
Since the oxide superconducting wire exhibits a superconducting state at a liquid nitrogen temperature, it is expected to be applied to a superconducting magnet, a superconducting cable, and the like, and its development is being promoted. In particular, research and development have been conducted on metal-coated bismuth-based oxide superconducting wires in order to obtain a high critical current density.
[0003]
As for the oxide superconducting cable conductor, a structure in which a tape-like silver-coated bismuth-based superconducting wire is spirally wound in multiple layers on a core material is known. However, this structure has a problem in that the AC loss during energization is large because of the occurrence of drift due to the difference in impedance between the inner and outer layers of the conductor. Also, a large AC loss becomes a factor that reduces the critical current.
As a conductor for an oxide superconducting cable having a small AC loss, an oxide superconducting cable conductor composed of a sub cable having a stranded wire structure has been proposed. Although the AC loss can be reduced by increasing the number of strands in the sub-cable and using a multi-stranded structure, the size of the sub-cable increases. In this case, if the strain is applied, the critical current characteristics of the oxide superconducting wire are likely to deteriorate, and the critical current characteristics of the superconducting cable conductor produced by assembling the sub-cables are reduced. The critical current density characteristic of becomes low.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a technique for producing an oxide superconducting stranded wire and an oxide superconducting cable conductor having excellent critical current characteristics using an oxide superconducting wire.
[0005]
[Means for Solving the Problems]
The present invention provides a method for producing an oxide superconducting stranded wire and a conductor for an oxide superconducting cable using an oxide superconducting material or precursor and a strand made of silver or a silver alloy covering the material. In this method, an oxide superconducting material or precursor and a wire made of silver or a silver alloy covering the material, a step of providing an electric insulating layer on the wire, and twisting the wires And a step of heating the stranded wire to a temperature necessary for generating the oxide superconducting material and heat-treating it.
[0006]
As the electrical insulating layer of the wire in the production method of the present invention, a paint mainly composed of a silicon-based organometallic polymer, a paint mainly composed of aluminum phosphate, or the like can be used as the electrical insulating layer. Moreover, in the manufacturing method by this invention, after stranding a strand, the obtained twisted wire can be shape | molded, for example so that the cross section may become a flat or a fan shape. Next, the formed stranded wire is heated to a temperature necessary for the production of the oxide superconducting material and subjected to heat treatment. Thus, after forming a stranded wire, the influence at the time of stranded wire formation is reduced by performing heat treatment, and a superconducting stranded wire exhibiting high critical current and critical current density is obtained. The formed superconducting stranded wire is useful for forming a compact cable conductor.
[0007]
This invention provides the manufacturing method of the conductor for oxide superconducting cables provided with the process of winding the some strand wire obtained by the manufacturing method mentioned above around a cylindrical core material.
[0008]
According to the present invention, a plurality of the above-described stranded wires are wound around a cylindrical core material, and then heated to a temperature necessary for the production of the oxide superconducting material, and the oxide superconducting stranded wire obtained by heat treatment is subjected to heat treatment. By assembling the stranded wire before the heat treatment on the flexible core material having the same outer diameter as the core material used in the above, with the same pitch wound around the cylindrical core material, a plurality of A conductor for an oxide superconducting cable obtained by winding an oxide superconducting stranded wire around a cylindrical core material can be provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the production of an oxide superconductor, for example, a bismuth-based 2223 phase oxide superconductor coated with a metal such as silver or silver alloy, in order to produce an oxide superconductor material, for example, about 850 ° C. Heat treatment is performed at a high temperature. The oxide superconducting material produced by the heat treatment is relatively weak to bending, and is liable to cause deterioration of the critical current at a bending strain exceeding 0.3%, for example. Therefore, when a plurality of oxide superconducting wires obtained through the heat treatment step are twisted together, the oxide superconducting material is destroyed by bending strain, and characteristics such as critical current deteriorate in the oxide superconducting wire. The inventor of the present application prepares a strand, and after the twisting step of twisting the strands, an oxide superconducting strand and oxide exhibiting excellent superconducting properties by performing a heat treatment for generating an oxide superconductor It has been found that a conductor for a superconducting cable can be obtained.
[0010]
A predetermined amount of raw material of the oxide superconducting material is weighed and calcined, and the oxide superconducting material precursor powder 1 prepared by calcination is filled in a metal tube 2 made of silver or a silver alloy, as shown in FIG. A composite material is obtained.
[0011]
A tape-like composite material as shown in FIG. 2 is obtained by rolling the composite material of the oxide superconductor precursor powder and the metal.
[0012]
The tape-like composite material of FIG. 2 is arranged around the core wire 3 made of silver or silver alloy, inserted into a metal tube 5 made of silver or silver alloy, and subjected to diameter reduction processing such as wire drawing. As shown in FIG. 3, a composite material 6 provided with a multilayer portion 4 made of a powder of an oxide superconductor precursor is obtained. The amount of the oxide superconductor precursor can be adjusted by adjusting the amount of the tape-shaped composite material to be wound.
[0013]
As shown in FIG. 4, a plurality of composites 6 of FIG. 3 are inserted into a silver or silver alloy metal tube 7 and then subjected to diameter reduction processing such as wire drawing, as shown in FIG. Further, a strand 9 in which a plurality of composite materials 6 of FIG. 3 are embedded in a silver or silver alloy base material 8 in multiple cores is obtained. The amount of the oxide superconductor precursor can be adjusted by the number of the composite materials 6 shown in FIG. Further, by adjusting the thickness of the metal tube 5 made of silver or silver alloy, the distance between the oxide superconductors generated by the heat treatment can be adjusted by adjusting the distance between the cores, and the high critical current. An oxide superconducting wire having a low value and low AC loss can be obtained.
[0014]
As shown in FIG. 5, an electrical insulating layer 10 is formed on the outer periphery of the wire 9. As this electrical insulating layer, it has been found that organometallic polymers such as silicon-based organometallic polymers, compounds such as aluminum phosphate, or boron nitride are excellent from the viewpoint of heat resistance, adhesion to strands and strength. . When these materials are used, it is possible to form a coating layer that is difficult to peel off at the time of stranded wire and has excellent strength. By applying an electrical insulating layer to the surface of the strands, the coupling current between the strands can be reduced and the AC loss can be reduced.
[0015]
As described above, the plurality of strands 9 on which the electrical insulating layer 10 is formed are twisted together to form a stranded wire. When twisting together, dislocation is applied to the strand 9 to reduce the drift between the oxide superconductors in the strand.
[0016]
By repeating the stranded wire process, a secondary or higher order stranded wire can be obtained. FIG. 6 shows an example of a secondary stranded wire in which six strands 9 are primary twisted on a silver or silver alloy core wire 11 and four primary twisted wires are further twisted. A stranded wire having a large current capacity can be obtained depending on the number of stranded wires and the twist order. In addition, as the number of twists increases, the effect of dislocation increases, the impedance of the outer and inner layers of the stranded wire can be made uniform, drift between the stranded wires can be reduced, and AC loss can be reduced. it can.
[0017]
In addition, by forming the obtained stranded wire into a shape such as a flat or fan shape, the packing factor can be increased, a more compact stranded wire can be obtained, and the current density can be improved. FIG. 7 is an example in which FIG. 6 is flat-shaped, and a compact formed stranded wire with a small space between the strands and between the stranded wires can be obtained.
[0018]
As shown in FIG. 8, the stranded wire thus produced is wound as a sub-cable 13 around a cylindrical sintering core material 12 at a predetermined pitch. As shown in FIGS. Sub conductors 13 can be assembled to produce a superconducting cable conductor. The sintering core 12 uses a metal tube that can withstand the temperature required for heat treatment of the oxide superconducting material.
[0019]
The heat treatment for producing the oxide superconductor is performed, for example, at a temperature of 800 to 900 ° C., preferably 840 to 850 ° C. In this way, the cylindrical core material for sintering is wound at a predetermined pitch, and after twisted wires are assembled, heat treatment is performed to reduce the influence of distortion during twisting, and high critical current and critical current density characteristics are achieved. The stranded wire shown is obtained.
[0020]
A plurality of stranded wires are wound around a cylindrical sintering core 12 at a predetermined pitch, heat-treated, and then the winding diameter is increased by loosening the twisting of the sub-cable, etc. Remove material 12. Thereafter, a flexible core material having the same outer diameter as that of the sintering core material 12 is replaced and assembled at the same pitch wound around the cylindrical core material before the heat treatment. A conductor can be obtained. As a flexible core material of a conductor for a superconducting cable, for example, it can be formed from copper, aluminum, FRP (fiber reinforced plastic) or the like, and it is preferable to use a copper core material from the viewpoint of strength and flexibility.
[0021]
In addition, the sub-cable composed of a plurality of stranded wires is wound around the cylindrical sintering core member 12 at a predetermined pitch, heat-treated, and then the conductor is disassembled. In this case, after the conductor is disassembled, the sub-cable is disassembled so as to maintain the wound shape, and the sub-cable after the conductor is disassembled is reassembled into a flexible core copper tube having the same diameter as the sintering core material. By gathering on this core material, an oxide superconducting cable conductor can be obtained.
Also in this case, it is possible to select a core material suitable for the sintering core material and the flexible core material from the viewpoints of heat resistance and flexibility.
[0022]
By assembling the sub cables made of stranded wires in this way, it is possible to reduce the influence of distortion when producing a conductor for an oxide superconducting cable. Higher critical current characteristics can be obtained than oxide superconducting cable conductors produced by assembling while winding stranded wires or oxide superconducting cable conductors produced by assembling while winding stranded wires that have been heat-treated. .
Hereinafter, the present invention will be described in more detail by way of examples.
[0023]
【Example】
Example 1
Using powders of Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO, powders having a composition ratio of Bi: Pb: Sr: Ca: Cu = 1.8: 0.4: 2: 2: 3 are mixed. did. This powder was calcined at 700 ° C. for 12 hours and 8 hours at 800 ° C. for 8 hours, and further calcined at 850 ° C. for 8 hours.
The calcined powder was pulverized with a ball mill. This powder was deaerated by heating at 800 ° C. for 15 minutes, and then filled into a silver pipe as shown in FIG. The silver pipe was drawn to 1.15 mmφ and then rolled to a thickness of 0.2 mm as shown in FIG. As shown in FIG. 3, seven oxide superconducting material precursors and silver composite materials in which a plurality of rolled tape wires are arranged concentrically with a silver bar as an axis are used and fitted to a silver pipe as shown in FIG. Thereafter, the wire was drawn to 0.9 mmφ to produce a round wire as shown in FIG. The element wire was subjected to heat treatment at 850 ° C. for 50 hours, and after the electrical insulating layer 10 was provided using a SiO ₂ -based inorganic insulating material, stranded wire processing was performed. In the primary stranded wire processing, six strands were twisted at a twist pitch of 40 mm with a silver wire 5 of 0.9 mmφ as the center line. In the secondary stranded wire processing, the four primary stranded wires are twisted together at a twist pitch of 80 mm as shown in FIG. 6 and formed into a width of 8 mm and a thickness of 3 mm. A secondary stranded wire sub-cable as shown in FIG. Produced.
[0024]
As shown in FIG. 8, the sub-cable was wound around a stainless steel tube core having an outer diameter of 19 mmφ and an inner diameter of 17 mmφ with a winding pitch P of 200 mm, bound with glass tape, and then subjected to heat treatment at 850 ° C. for 100 hours. When Ic was measured in liquid nitrogen while being wound after the heat treatment, Ic was 40A.
[0025]
Comparative Example 1
The straight secondary stranded wire before heat treatment obtained in Example 1 was subjected to heat treatment at 850 ° C. for 100 hours. A part of the sub-cable was cut out after the heat treatment, and the critical current Ic was measured in liquid nitrogen. As a result, Ic was 40A.
On the other hand, as shown in FIG. 8, the sub-cable after the heat treatment in a straight shape is wound with a winding pipe P of 200 mm using a stainless steel core material 12 having an outer diameter of 19 mmφ and an inner diameter of 17 mmφ, and is still wound. When Ic was measured in liquid nitrogen, Ic was reduced to 12A.
[0026]
From this, in the oxide superconducting stranded wire of the present invention of Example 1, Ic similar to the oxide superconducting stranded wire heat-treated in a straight state can be obtained, and the oxidized wire obtained by winding the heat-treated stranded wire around the core material It was confirmed that high critical current characteristics can be obtained compared to a superconducting stranded wire.
[0027]
Comparative Example 2
As shown in FIGS. 9 and 10, a copper straight pipe is used as a core, the sub cable 13 obtained in Example 1 is heat-treated, and the seven sub cables are used to form a one-layer conductor having a length of 5 m. Produced. The winding pitch of the sub cable around the core material was 200 mm, and Mylar tape was wound around the conductor surface. After producing this conductor, the conductor was wound around a drum having a body diameter of 1.6 mφ.
When the conductor was unwound from the drum, the conductor was disassembled and the appearance was examined, no buckling or tearing was observed in the core material and the sub-cable. By this test, it was confirmed that the copper straight pipe was satisfactory as a conductor core material in terms of flexibility.
On the other hand, when a part of the sub-cable after the conductor disassembly was cut out and Ic measurement was performed, Ic was reduced to 10A. This is because, in addition to the mechanical strain at the time of assembly of the sub-cable after heat treatment, mechanical strain due to bending when being wound around the drum is newly added to the sub-cable.
[0028]
Comparative Example 3
Moreover, a stainless steel straight pipe was used as a core material, and seven sub-cables before heat treatment produced in Example 1 were used to produce a single-layer conductor having a length of 5 m. The winding pitch of the sub cable around the core material was 200 mm. After subjecting this conductor to a secondary heat treatment at 850 ° C. for 100 hours, the conductor was wound around a drum having a body diameter of 1.6 mφ.
Thereafter, the conductor was unwound from the drum and the conductor was disassembled. When a part of the sub-cable after the conductor disassembly was cut out and Ic measurement was performed, it was found that Ic was 3 times higher than that of Comparative Example 2 at 30A.
However, after disassembling, an external inspection was conducted and it was found that the stainless steel straight tube was buckled and torn, and the stainless steel straight tube used was not sufficient in terms of flexibility as a conductor core material. I found out.
[0029]
Example 2
A stainless steel straight pipe was used as a core material, and 7 sub-cables before heat treatment produced in Example 1 were used to produce a single-layer wound conductor having a length of 5 m. The winding pitch of the sub cable around the core material was 200 mm. After subjecting this conductor to heat treatment at 850 ° C. for 100 hours, the stainless steel straight pipe was pulled out and a copper pipe was inserted at the same time to form a one-layer conductor having a copper pipe as the core material. Mylar tape was wrapped around the conductor surface for the purpose of protection and fixation.
Further, after winding the conductor around a drum having a drum diameter of 1.6 mφ, the conductor was rewound, and a part of the sub-cable after disassembly was cut out and Ic measurement was performed. Ic was found to be 3 times higher.
When the conductor was disassembled and the appearance was examined, it was found that the appearance of the core material and the sub-cable was not buckled or broken, and that this conductor had no problem in terms of flexibility.
As described above, it was found that the conductor produced by this method has flexibility and high critical current characteristics.
[0030]
Example 3
As another example, a stainless steel straight pipe was used as a core material, and seven sub-cables before heat treatment produced in Example 1 were used to produce a 1-m long single-layer wound conductor. The winding pitch of the sub cable around the core material was 200 mm. The conductor was heat-treated at 850 ° C. for 100 hours, and then the conductor was disassembled. The sub-cable maintained the twisted shape after the conductor was disassembled.
The seven sub-cables after the conductors were disassembled were reassembled with a copper tube having the same diameter (19 mmφ) as the stainless steel tube as a core material to form a one-layer winding conductor with a winding pitch of 200 mm. Mylar tape was wrapped around the conductor surface for the purpose of protection and fixation.
This conductor was wound around a drum having a drum diameter of 1.6 mφ, and then rewound from the drum. When a part of the sub-cable after disassembly was cut out and Ic measurement was performed, it was found that Ic was 28 A, which is about 3 times higher than that in Comparative Example 2.
Moreover, when the conductor was disassembled and the appearance was examined, it was found that the core material and the sub-cable were not buckled or broken, and that this conductor had no problem in terms of flexibility.
As described above, it is possible to dismantle the sub-cable after the heat treatment and replace the core material used for the heat treatment with a flexible core material while maintaining the shape of the sub-cable. The fabricated conductor was found to have flexibility and high critical current characteristics.
[0031]
Comparative Example 4
Further, a conductor for an oxide superconducting cable was produced using a tape-shaped silver sheath oxide superconducting wire (width 3.5 mm, thickness 0.2 mm).
Using 14 tape-shaped oxide superconducting wires, winding was performed on a stainless steel straight pipe at a winding pitch of 200 mm, and two conductors having a length of 1 m were produced. The conductor was subjected to a secondary heat treatment at 850 ° C. for 100 hours, and then one conductor was disassembled. The tape-shaped oxide superconducting wire is easily deformed, and it is difficult to maintain the shape of the wire rod after being disassembled from the conductor.
Further, when the remaining one conductor was used and the stainless steel tube was pulled out and the copper tube was inserted at the same time, the oxide superconducting wire was disturbed during operation. As described above, the method of replacing the core material cannot be applied to a conductor using a tape-shaped oxide superconducting wire, and may be effective in the case of producing a conductor for a superconducting oxide cable using a sub cable as in the present invention. all right.
[0032]
【The invention's effect】
As described above, in the present invention, using an oxide superconducting material or a precursor and a strand made of silver or a silver alloy covering it, the strand is subjected to dislocation by twisting, and a plurality of the strands are After the oxide superconducting stranded wire is assembled on a cylindrical core material and heat-treated to produce an oxide superconducting stranded wire, the oxide superconducting stranded wire holding the shape wound at a predetermined pitch on the cylindrical core material is By using the sub-cable constituting the conductor for the oxide superconducting cable, the oxide superconducting stranded wire and the oxide superconducting cable conductor having excellent critical current characteristics can be manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional structure of a composite material composed of a precursor powder of an oxide superconductor used in the present invention and a metal.
FIG. 2 is a schematic diagram showing a cross-sectional structure of a tape-shaped composite material made of a precursor powder of an oxide superconductor and metal used in the present invention.
FIG. 3 is a schematic diagram showing a cross-sectional structure of a composite material provided with a multilayer portion made of a precursor of an oxide superconductor used in the present invention.
4 is a schematic view showing a cross section of a composite material in which a plurality of composite materials of FIG. 3 used in the present invention are inserted into a metal tube.
5 is a schematic diagram of a cross-sectional structure of a strand in which a plurality of composite materials of FIG. 3 are embedded in a base material of silver or a silver alloy.
FIG. 6 is a schematic diagram showing a cross-sectional structure of a secondary stranded wire used in the present invention.
FIG. 7 is a schematic diagram showing a cross-sectional structure of a molded secondary stranded wire used in the present invention.
FIG. 8 is a perspective view showing a state of a sub cable wound around a sintering core material at a winding pitch P;
FIG. 9 is a perspective view showing a state in which a sub cable is wound around a core material in manufacturing an oxide superconducting cable.
FIG. 10 is a schematic view showing a cross-sectional structure of a conductor for an oxide superconducting cable used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Oxide superconductor precursor powder 2 Silver or silver alloy metal tube 3 Silver or silver alloy core wire 4 Multilayer part 5 made of oxide superconductor precursor powder Silver or silver alloy metal tube 6 Composite 7 Silver or silver alloy metal tube 8 Base material 9 made of silver or silver alloy Wire 10 Electrical insulation layer 11 Core material 12 Core material 13 Sub cable

Claims (2)

  An oxide superconducting material or a precursor and a strand made of silver or a silver alloy covering the strand are twisted to dispose the strand, and a plurality of the strands are assembled on a cylindrical core material, followed by heat treatment After forming the oxide superconducting stranded wire, the oxide superconducting stranded wire holding the shape wound around the cylindrical core material at a predetermined pitch is used as the subconductor constituting the oxide superconducting cable conductor. A conductor for an oxide superconducting cable, characterized by being a cable.   Displacement is performed on the strand by twisting a strand made of an oxide superconducting material or precursor and silver or a silver alloy covering the oxide superconducting material or precursor, and a plurality of the strands are placed on a cylindrical core material at a predetermined pitch. The oxide superconducting stranded wire obtained by winding and then heat-treating the stranded wire on a flexible core material having the same outer diameter as that of the core material used for the heat treatment, before the heat treatment. A method for producing a conductor for an oxide superconducting cable, wherein the conductors are gathered at the same pitch wound on a core material.

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