JP2011065879A - Superconducting cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconducting cable suppressing temperature rise in an accident while having a small diameter. <P>SOLUTION: A superconducting cable 100 includes, sequentially from the center: a former 11; a superconductive conductor layer 12; an electric insulating layer 13; a superconductive shield layer 14; and a cable core 10 having a protective layer 15. The superconductive shield layer 14 includes a superconductive wire 1s for shield, and does not include a normal conductive shield layer consisting of copper and the like on both inner and outer peripheral sides. A proportion of a normal conductive phase in the superconductive wire 1s for shield is smaller than a proportion of a normal conducting phase in a superconductive wire 1c for a conductor constituting the superconductive conductor layer 12. Since the superconducting cable 100 does not include the normal conductive shield layer, a diameter of the superconducting cable is small. Since the superconductive shield layer 14 includes the superconductive wire 1s for shield including less normal conductive phase, an induced current hardly flows in accident, and temperature rise accompanying heat generation due to the induced current to the normal conductive phase can be suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a superconducting cable comprising a superconducting conductor layer and a superconducting shield layer functioning as a magnetic shielding layer. In particular, the present invention relates to a superconducting cable that has a small diameter and can suppress a temperature rise during an accident such as a short circuit or a ground fault.

  Superconducting cables are being developed as power cables constituting power supply paths. A superconducting cable is typically a cable core having a former, a superconducting conductor layer, an electric insulation layer, and a superconducting shield layer in order from the inner peripheral side, and a heat insulating tube that houses the cable core and is filled with a refrigerant such as liquid nitrogen. With. The superconducting conductor layer and the superconducting shield layer are generally configured by winding a plurality of superconducting wires having the same specifications. A typical superconducting wire includes a superconducting phase made of an oxide and a normal conducting phase made of a normal conducting material of a good conductor having a small specific resistance even at the operating temperature of a superconducting cable such as copper or aluminum.

  For example, when AC power transmission is performed by the superconducting cable, a current of almost the same magnitude is induced in the superconducting shield layer in the opposite direction to the current (conductor current) flowing in the superconducting conductor layer during normal operation. By canceling the magnetic field due to the conductor current with the magnetic field due to this induced current (shield current), the leakage magnetic field to the outside of the superconducting cable can be made almost zero.

  When the superconducting cable is introduced into the actual line, a large current (accident current) may flow through the superconducting conductor layer due to an accident such as a short circuit or a ground fault. At this time, a large current is also induced in the superconducting shield layer. Here, when a large current exceeding the critical current Ic flows through the superconducting wire, the superconducting phase transitions (quenches) to the normal conducting state. Then, not the superconducting phase of the superconducting wire, but a current flows mainly in the normal conducting phase, resulting in Joule heat, which may damage the superconducting wire as the temperature rises due to this heat generation. Therefore, in order to reduce the accident current flowing in the superconducting wire, the former is made of a normal conductor material such as copper, and the accident current is shunted to this former, or just above (outer) or directly below the superconducting shield layer. It has been proposed to provide a normal conducting shield layer made of copper or the like (inner circumference) and to divert the induced current based on the accident current to the normal conducting shield layer (see, for example, Patent Document 1).

JP 2006-331894 A

However, if the normal conducting shield layer is provided, there is a problem that the superconducting cable is enlarged.
In constructing a superconducting cable line, it is considered to install a superconducting cable as an alternative to the OF cable in an existing pipe line where the OF cable is installed. In consideration of the drawing into the conduit, it is desirable that the superconducting cable be as small as possible. Further, since the superconducting cable has a small diameter, it is excellent in manufacturability and can be easily transported and laid.

  For example, instead of providing the normal conducting shield layer, it is conceivable to increase the amount of superconducting wire used so as to have a current capacity that does not shift to the normal conducting state even when the accident current flows. However, this configuration is also uneconomical because it causes an increase in size of the superconducting cable and requires a large amount of expensive superconducting wire.

  Accordingly, an object of the present invention is to provide a superconducting cable that is capable of suppressing a temperature rise during an accident while having a small diameter.

  The present invention is not based on the idea that the normal conducting shield layer is provided in order to shunt the accident current (inductive current), and in particular, the conduction of the induced current that causes the temperature rise of the superconducting shield layer is suppressed. Propose to be a configuration. More specifically, the superconducting wire constituting the superconducting shield layer includes a wire having a specific structure in which an accident current is difficult to be induced.

  The present invention relates to a superconducting cable including a cable core having a former, a superconducting conductor layer, an electrical insulating layer, and a superconducting shield layer in order from the center. The superconducting conductor layer and the superconducting shield layer are composed of a plurality of superconducting wires including a superconducting phase and a normal conducting phase. Then, the proportion of the normal conducting phase in at least one of the superconducting wires constituting the superconducting shield layer (hereinafter referred to as a shielding superconducting wire) is the superconducting wire constituting the superconducting conductor layer (hereinafter referred to as the superconducting wire for conductor). Is smaller than the proportion occupied by the normal conducting phase.

  According to the above configuration, the superconducting wire for shielding that constitutes the superconducting shield layer has a low normal conducting phase, and thus has a high electrical resistance when it is transferred to the normal conducting state at the time of an accident. Therefore, even if an accident current flows through the superconducting conductor layer or the former in the event of an accident, the superconducting shield layer has little current induced from the accident current. In other words, the induced current can be sufficiently attenuated. In particular, depending on the proportion of the normal conducting phase in the superconducting wire for shielding, the induced current from the accident current can be substantially eliminated. That is, as one form of the superconducting cable of the present invention, the cable core is made of a normal conducting material on both the inner peripheral side and the outer peripheral side of the superconducting shield layer, and is used for shunting an accident current (inductive current). It can be set as the form which does not have a conductive shield layer. Such a superconducting cable of the present invention can suppress an increase in temperature due to an induced current flowing through the normal conducting phase of the superconducting wire for shielding, and therefore can suppress damage to the superconducting wire due to this temperature increase.

  In addition, since the superconducting cable of the present invention has a configuration in which an induced current flows through the superconducting shield layer as much as possible in the event of an accident as described above, the ratio of the normal conducting shield layer that has been indispensable for accident countermeasures conventionally is reduced Can do. Ultimately, the normal conducting shield layer for diverting the induced current induced in the superconducting shield layer can be omitted. Therefore, the superconducting cable of the present invention has a smaller diameter than the conventional superconducting cable.

  In addition, the former provided in the superconducting cable of the present invention is made of a normal conductor material of a good conductor, such as copper or aluminum, having a low specific resistance at the operating temperature of the superconducting cable, so that the fault current is mainly passed to the former. Can do. Therefore, the superconducting cable of the present invention can also suppress the temperature of the superconducting conductor layer from rising due to the energization of the accident current.

  As described above, the superconducting cable of the present invention has a smaller diameter than the conventional superconducting cable while avoiding damage to the superconducting wire due to the temperature rise at the time of an accident.

Hereinafter, the present invention will be described in more detail.
The superconducting phase contained in the superconducting wire can use liquid nitrogen as a refrigerant and has a high critical current high-temperature oxide superconducting phase, typically a Bi-based oxide superconducting phase called BSCCO or REBCO An oxide superconducting phase (RE: rare earth element, such as Y, Ho, Gd, etc.) is preferable. The wire material comprising the Bi-based oxide superconducting phase is prepared by packing the Bi-based oxide superconducting phase powder in a silver or silver alloy pipe, and subjecting the pipe to plastic working and heat treatment to form a tape (hereinafter referred to as a tape). Typical examples are Bi-based oxide superconducting wires. Wire rods with RE-based oxide superconducting phase are formed from a metal-based substrate such as stainless steel or nickel alloy with an RE-based oxide superconducting phase formed on a good conductor such as silver, copper, or its alloy. And a thin film wire (hereinafter referred to as RE-based oxide thin film wire) on which a stabilizing layer is formed.

As described above, the superconducting wire generally has a specific resistance of 1 × 10 ⁻⁸ Ω · m or less at a working temperature of a superconducting cable such as silver, a silver alloy, or copper (when liquid nitrogen is used as a refrigerant, about 65K to 80K), Furthermore, it comprises a normal conducting phase composed of a normal conducting material having a good conductor of 5 × 10 ⁻⁹ Ω · m or less. When the normal conducting phase of the superconducting wire for shielding is constituted by the normal conducting material having a small specific resistance, the induced current flowing through the wire tends to increase at the time of an accident. Therefore, in the present invention, at least one of the plurality of shielding superconducting wires has a ratio of the normal conducting phase smaller than that of the conductor superconducting wires, thereby suppressing a temperature rise during an accident. It is more preferable that all the shielding superconducting wires constituting the superconducting shield layer are wires having a small proportion of the normal conducting phase described above.

  The ratio of the normal conducting phase in the superconducting wire is, for example, the cross section of the superconducting wire (the plane cut in the direction perpendicular to the longitudinal direction of the superconducting wire), and the area ratio of the normal conducting phase in this cross section is image processed. This area ratio can be used by using an apparatus or the like. Alternatively, the rectangular thickness (short side) when the normal conducting phase is deformed into a rectangle having an area equal to the area of the normal conducting phase in the cross section and having a predetermined width (long side) is equivalent. The equivalent thickness can be used as the ratio of the normal conducting phase. As the width of the rectangle, for example, the width of the substrate of the shielding superconducting wire can be used.

  When evaluating the ratio of the normal conducting phase based on the equivalent thickness, when the equivalent thickness of the normal conducting phase in the shielding superconducting wire is taken, this equivalent thickness is equivalent to the normal conducting phase in the conductor superconducting wire. Thinner than thickness. In particular, when the equivalent thickness of the normal conducting phase relative to the width of the substrate is taken as described above in the superconducting wire for shielding, the normal conducting phase in the superconducting wire occupies that the equivalent thickness is 10 μm or less. The ratio is sufficiently small, and it is preferable that an accident current is not easily induced in the superconducting shield layer. The equivalent thickness is more preferably 5 μm or less, and it is preferably as thin as possible. Therefore, there is no particular lower limit.

  As an aspect of the present invention, the conductor superconducting wire and the shield superconducting wire are superconducting wires having different specifications, for example, the conductor superconducting wire is the Bi-based oxide superconducting wire, and the shield A form in which the superconducting wire is the RE-based oxide thin film wire can be mentioned. In general, the RE-based oxide thin film wire is thin in that the proportion of the normal conducting phase in the wire is smaller than the proportion of the normal conducting phase in the Bi-based oxide superconducting wire. Therefore, if the superconducting wire for shielding is an RE-based oxide thin film wire, it is possible to reduce the current induced in the superconducting shield layer at the time of an accident and contribute to further reducing the diameter of the superconducting cable.

As one form of this invention, the form in which the said superconducting wire for shielding is provided with the reinforcement layer which consists of material with a high specific resistance is mentioned. As described above, in the present invention, since the ratio of the normal conducting phase in the superconducting wire for shielding is reduced, the mechanical characteristics such as heat capacity and strength may be lowered. On the other hand, by providing a reinforcing layer made of a material having a high specific resistance, a decrease in heat capacity and mechanical characteristics can be reduced, or heat capacity and mechanical characteristics can be improved. The material constituting the reinforcing layer is preferably a material having a specific resistance at the operating temperature of the superconducting cable of more than 1 × 10 ⁻⁸ Ω · m.

  The superconducting cable of the present invention can suppress a temperature rise at the time of an accident while having a small diameter.

FIG. 1 is a perspective view showing a schematic configuration of the superconducting cable of the first embodiment. FIG. 2 (I) is a schematic cross-sectional view of the shielding superconducting wire used in the test example, and FIG. 2 (II) is a schematic cross-sectional view illustrating the equivalent thickness t of the normal conducting phase in this shielding superconducting wire. It is. FIG. 3 is a graph depicting the waveform of the conductor current and the waveform of the shield current in the simulation test at the time of the accident. FIG. 4 is a graph showing the relationship between the time during which an accident current flows and the temperature rise ΔT of the superconducting shield layer in a simulation test at the time of an accident. FIG. 5 is a graph showing the relationship between the equivalent thickness t of the normal conducting phase in the shielding superconducting wire and the temperature rise ΔT of the superconducting shield layer in the simulation test at the time of the accident.

(Embodiment 1)
Hereinafter, the superconducting cable 100 of Embodiment 1 will be described with reference to FIG.
[overall structure]
The superconducting cable 100 is a three-core type cable in which three-core cable cores 10 are twisted and housed in one heat insulating tube 20, and is typically used for AC power transmission. The cable core 10 includes a superconducting conductor layer 12 made of a conductor superconducting wire 1c and a superconducting shield layer 14 made of a shielding superconducting wire 1s. Further, the superconducting cable 100 does not have a normal conducting shield layer made of a normal conducting material such as copper on both the inner and outer peripheral sides of the superconducting shield layer. Hereinafter, each configuration will be described in more detail.

[Insulated pipe]
The heat insulating tube 20 is a double structure tube composed of an inner tube 21 and an outer tube 22, and is a vacuum heat insulating structure in which the space between the inner tube 21 and the outer tube 22 is evacuated. The inner tube 21 is filled with a refrigerant such as liquid nitrogen, and the superconducting conductor layer 12 and the superconducting shield layer 14 of the cable core 10 are cooled by this refrigerant and maintained in a superconducting state. Between the inner tube 21 and the outer tube 22, a heat insulating material 23 such as a super insulation, and a spacer (not shown) that keeps the distance between the two tubes 21, 22 are arranged. On the outer periphery of the outer tube 22, an anticorrosion layer 24 formed by extruding a material having excellent corrosion resistance such as polyvinyl chloride is provided.

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

<Former>
In addition to functioning as a support for the superconducting conductor layer 12, the former 11 is used in the superconducting cable 100 as a flow path for diverting a large accident current that occurs instantaneously at the time of an accident such as a short circuit or a ground fault. The former 11 is formed of a normal conductor material of a good conductor such as copper or aluminum having a specific resistance of 1 × 10 ⁻⁸ Ω · m or less at the operating temperature of the superconducting cable 100 (here, about 65K to 80K). Solid bodies and hollow bodies (tubular bodies) can be used. Here, the former 11 is a solid body formed by twisting a plurality of copper wires having an insulation coating such as polyvinyl chloride (PVC) or enamel. Due to the stranded wire structure, effects such as reduction of eddy current loss and excellent bending characteristics during AC power transmission can be obtained.

<Superconducting conductor layer>
The superconducting conductor layer 12 and the superconducting shield layer 14 are configured by winding a tape-like superconducting wire having an oxide superconducting phase in a single layer or in a spiral manner. Here, a Bi-based oxide superconducting wire having Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} (Bi2223) in the superconducting phase and Ag as a metal matrix is used as the conductor superconducting wire 1c. The metal matrix has a specific resistance of 1 × 10 ⁻⁸ Ω · m or less at the operating temperature of the superconducting cable 100 (here, about 65K to 80K), and constitutes a normal conducting phase of the conductor superconducting wire 1c. The superconducting conductor layer 12 has a multilayer structure in which the conductor superconducting wire 1c is wound in four layers. For the superconducting conductor layer 12, the superconducting wire specifications (metal matrix ratio, cross-sectional area, etc.) and the number thereof may be selected according to the desired current capacity.

  When the superconducting conductor layer 12 has a multilayer structure, an interlayer insulating layer in which insulating paper such as kraft paper is wound can be provided between the layers formed by the conductor superconducting wire 1c. Superconducting conductor layer 12 is allowed to include an interlayer insulating layer in addition to the portion made of conductor superconducting wire 1c. Furthermore, an inner semiconductive layer can be provided by winding carbon paper or the like directly on the superconducting conductor layer 12.

  An insulating tape made of insulating paper such as kraft paper or semi-synthetic insulating paper composed of kraft paper and plastic (for example, PPLP (registered trademark of Sumitomo Electric Industries, Ltd.)) is wound around the outer periphery of the former 11. When the cushion layer is formed, it is easy to form the superconducting conductor layer 12, and it is possible to prevent the superconducting conductor layer 12 from being damaged by the copper wire constituting the former 11.

<Electrical insulation layer>
The electrical insulating layer 13 is formed by winding an insulating tape such as the above-described kraft paper or semi-synthetic insulating paper on the superconducting conductor layer 12 (or inner semiconductive layer). Here, the electrical insulating layer 13 is made of PPLP (registered trademark of Sumitomo Electric Industries, Ltd.). Furthermore, an outer semiconductive layer can be provided by winding carbon paper or the like directly on the electrical insulating layer 13.

<Superconducting shield layer>
A superconducting shield layer 14 is formed on the electrical insulating layer 13 (or outer semiconductive layer). Here, as the superconducting wire 1s for shielding, REBa ₂ Cu ₃ O _x (RE123), for example, a RE-based oxide thin film wire in which a RE-based oxide superconducting phase such as YBCO, HoBCO, GdBCO is formed on a substrate is used. ing. More specifically, on a substrate made of an iron-based alloy such as stainless steel or a Ni alloy such as Hastelloy (registered trademark), an intermediate layer made of an oxide such as YSZ (yttria stabilized zirconia) or MgO is used. A superconducting phase is formed, and a stabilizing layer made of a normal conducting material such as silver or copper is provided so as to cover the superconducting phase. The stabilizing layer has a specific resistance of 1 × 10 ⁻⁸ Ω · m or less at the operating temperature of the superconducting cable 100 (here, about 65K to 80K), and the substrate has a specific resistance of 1 × 10 ^−8. It is over Ω · m. Here, a portion made of a material having a specific resistance of 1 × 10 ⁻⁸ Ω · m or less in the superconducting wire 1s for shielding is defined as a normal conducting phase. Accordingly, here, the normal conducting phase of the shielding superconducting wire 1s is constituted by the stabilizing layer. The superconducting shield layer 14 has a multilayer structure in which the shielding superconducting wire 1s is wound in two layers.

  Similar to the superconducting conductor layer 12 described above, an interlayer insulating layer can be provided between the layers formed by the shielding superconducting wire 1s. The superconducting shield layer 14 allows an interlayer insulating layer to be included in addition to the portion made of the shielding superconducting wire 1s.

  During the normal operation, the superconducting shield layer 14 is supplied with an induced current substantially equal to the current flowing through the superconducting conductor layer 12 (conductor current), and cancels out the magnetic field generated by the conductor current by the magnetic field generated by the induced current. Thus, the magnetic field due to the conductor current has a function of suppressing leakage to the outside. Therefore, the superconducting shield layer 14 may be selected in accordance with the specifications and number of superconducting wires so that at least a current having the same magnitude as the conductor current can flow.

  For example, when the superconducting cable 100 is used for three-phase AC power transmission, each cable core 10 is configured such that the superconducting shield layers 14 of the cable cores 10 are short-circuited at both ends of each cable core 10. The induced current can flow through the superconducting shield layer 14 of the core 10.

  The most characteristic feature of the superconducting cable 100 is that the ratio of the normal conducting phase (here, the stabilization layer) in the shielding superconducting wire 1s is the normal conducting phase (here, the metal matrix) in the conductor superconducting wire 1c. Is less than the proportion of

  More specifically, the cross sections of the conductor superconducting wire 1c and the shield superconducting wire 1s are taken. Each wire rod 1c, 1s has an area equal to the area occupied by the normal conducting phase of each wire rod 1c, 1s in the cross section of each wire rod 1c, 1s, and each wire rod 1c, 1s has a rectangular shape having a long side as the width of the substrate of the superconducting wire rod 1s The thickness (short side) when the normal conducting phase is deformed is defined as the equivalent thickness. At this time, the equivalent thickness of the shielding superconducting wire 1s is smaller (thinner) than the equivalent thickness of the conductor superconducting wire 1c. Here, the equivalent thickness of all the shielding superconducting wires 1s constituting the superconducting shield layer 14 is smaller than the equivalent thickness of the conductor superconducting wire 1c.

<Protective layer>
A protective layer 15 for mechanically protecting the superconducting shield layer 14 is provided on the outer periphery of the superconducting shield layer 14. The protective layer 15 can be formed by winding an insulating tape such as the above-described kraft paper or semi-synthetic insulating paper.

[effect]
In the superconducting cable 100 having the above configuration, even if a large accident current occurs instantaneously at the time of an accident such as a short circuit or a ground fault, the accident current flows mainly to the former 11 and forms the superconducting conductor layer 12. The amount flowing through the wire 1c can be reduced. Therefore, the temperature rise of superconducting conductor layer 12 can be suppressed. Therefore, the superconducting cable 100 can prevent the conductor superconducting wire 1c from being damaged by an accident current flowing through the normal conducting phase of the conductor superconducting wire 1c and the temperature rising.

  In addition, the superconducting wire 1s for shielding constituting the superconducting shield layer 14 has less normal conducting phase than the superconducting wire 1c for conductor, so that the induced current from the accident current flowing in the former 11 and the superconducting conductor layer 12 is difficult to flow. That is, the induced current flowing through the shielding superconducting wire 1s can be kept very small or can be substantially eliminated. Therefore, the temperature rise of superconducting shield layer 14 can also be suppressed. Therefore, the superconducting cable 100 can prevent the shield superconducting wire 1s from being damaged when the induced current of the accident current flows through the normal conducting phase of the shielding superconducting wire 1s and the temperature rises.

  In this way, the superconducting cable 100 has a configuration with sufficient countermeasures in case of an accident, but the superconducting shield layer 14 is substantially composed of only the superconducting wire 1s for shielding, and the inner and outer sides of the superconducting shield layer 14 Neither side has a normal conducting shield layer made of a normal conducting material such as copper. Therefore, since the cable core 10 has a smaller diameter than the cable core of the conventional superconducting cable having the normal conducting shield layer, the superconducting cable 100 has a smaller diameter than the conventional superconducting cable.

  In addition, the superconducting wire 1c for the conductor constituting the superconducting conductor layer 12 is a Bi-based oxide superconducting wire, and the superconducting wire 1s for shielding constituting the superconducting shield layer 14 is a RE-based oxide thin film wire. The superconducting cable 100 in which the proportion of the normal conducting phase in the superconducting wire 1s is smaller than that in the conductor superconducting wire 1c can be easily realized.

<Modification 1>
In the first embodiment, the three-core type configuration in which the three-core cable cores are accommodated in one heat insulation tube has been described. However, the single-core type configuration in which the one-core cable core is accommodated in one insulation tube may be used. However, a multi-core batch type in which two or four or more multi-core cable cores are housed in one heat insulating tube may be adopted.

<Modification 2>
In the first embodiment, a form that does not have a normal conductive shield layer made of a normal conductive material such as copper has been described, but a form in which a normal conductive shield layer is provided on at least one of the inner peripheral side and the outer peripheral side of the superconductive shield layer; can do. In this embodiment, since an induced current can be shunted to the normal conducting shield layer in the event of an accident, it is possible to more effectively reduce the temperature rise caused by energizing the shielding superconducting wire. However, considering the reduction of the diameter of the superconducting cable, it is preferable that the normal conducting shield layer is not provided as in the first embodiment.

(Embodiment 2)
In the first embodiment, the conductor superconducting wire is made of a Bi-based oxide superconducting wire and the shield superconducting wire is made of an RE-based oxide thin film wire. However, both the conductor superconducting wire and the shield superconducting wire are described. It is good also as a superconducting wire of the same specification.

  For example, both the superconducting wire for conductors and the superconducting wire for shielding can be Bi-based oxide superconductors. At this time, the superconducting wire for shielding is a wire having a small metal matrix ratio (typically silver ratio or silver alloy ratio). The metal matrix ratio refers to the ratio of the area of the metal matrix portion to the area of the superconducting phase portion in the cross section of the superconducting wire.

  Alternatively, both the superconducting wire for conductors and the superconducting wire for shielding can be RE-based oxide thin film wires. At this time, the superconducting wire for shielding is a wire having a small number of stabilizing layers, for example, a wire having a thin equivalent thickness as described above. When the superconducting portion included in the superconducting cable is configured by the thin film wire, the superconducting cable can be further reduced in diameter compared to the case where the superconducting portion is configured by the Bi-based oxide superconducting wire.

(Embodiment 3)
In the first embodiment, as the superconducting wire for shielding, a form including a substrate, a superconducting phase, and a stabilizing layer has been described. However, a superconducting wire including a reinforcing layer can be used.

The constituent material of the reinforcing layer is preferably a material having a specific resistance of more than 1 × 10 ⁻⁸ Ω · m at the operating temperature of the superconducting cable (about 65 K to 80 K when the refrigerant is liquid nitrogen). Examples of such a material include metals such as a copper alloy such as a CuNi alloy and an iron-based alloy such as stainless steel. These metals have higher strength than copper, silver, and silver alloys, and have low conductivity and high resistance. Alternatively, a high-strength, high-resistance or insulating material such as carbon fiber, glass fiber, or resin containing these fibers can be used. Such a reinforcing layer can be integrated with the superconducting wire by using an adhesive, brazing material, solder, or welding to the substrate or the stabilization layer. When the above-mentioned RE-based oxide thin film wire is used as the shielding superconducting wire, and the substrate made of the material having a high specific resistance such as stainless steel is used for the substrate, the thickness of the substrate may be slightly increased.

  By using a superconducting wire having such a reinforcing layer, mechanical properties such as strength can be improved even if the normal conducting phase is small, and the superconducting cable can be made without excessively increasing the diameter of the superconducting cable. The heat capacity can be increased. That is, the temperature rise rate can be moderated, in other words, the temperature rise rate can be slowed. Therefore, the superconducting cable using the superconducting wire having the reinforcing layer can more effectively suppress the temperature rise of the superconducting wire at the time of the accident. In addition, since the said reinforcement layer has high resistance or insulation, an accident current is very hard to be induced or it is not induced | guided | derived substantially.

[Test example]
For the superconducting cable of the three-core type described in the first embodiment, the magnitude of the current induced in the superconducting shield layer when an overcurrent assuming an accident current is passed through the superconducting conductor layer, and the temperature rise of the superconducting shield layer The degree was investigated by simulation.

  In this test, sample Nos. 1 to 4 including cable cores using superconducting wires having different equivalent thicknesses of normal conducting phases were prepared. Table 1 shows the specifications of the superconducting cable core used in this test. The outer diameters of sample Nos. 1 to 4 are different from each other because the equivalent thicknesses are different, but are within an error range.

  The superconducting wire for conductors used for the superconducting conductor layer is a BSCCO wire made by Sumitomo Electric Industries, Ltd., the first and second layers: TypeHT (lamination material: copper alloy), the third and fourth layers: TypeACT ( Lamination material: copper alloy).

As shown in FIG. 2 (I), the superconducting wire 1s for shielding used for the superconducting shield layer is formed on one surface of a substrate 110 made of stainless steel (SUS steel) having a width w: 4.5 mm × thickness t _b : 100 μm. The superconducting phase (here YBCO) 111 of width w: 4.5 mm × thickness t _s : 1 μm is coated, and the outer periphery of the laminate of the substrate 110 and the superconducting phase 111 is coated with the normal conducting phase 112. The normal conducting phase 112 is composed of a silver layer and a copper plating layer, and the specific resistance at the operating temperature of the superconducting cable (here, about 65K to 80K) satisfies 1 × 10 ⁻⁸ or less. The specific resistance of the substrate 110 is more than 1 × 10 ⁻⁸ (about 5 × 10 ⁻⁷ ).

  Without changing the area occupied by the normal conducting phase 112 in the cross section of this shielding superconducting wire 1s, when the substrate 110 is deformed into a rectangle with a width w of 4.5 mm as a long side as shown in FIG. Is the equivalent thickness t. In this test, samples having equivalent thicknesses t of 50 μm, 20 μm, 10 μm, and 5 μm were prepared (sample Nos. 1, 2, 3, and 4 in order). The proportion of the normal conducting phase in the shielding superconducting wire used for Sample Nos. 1 to 4 is smaller than the proportion of the normal conducting phase in the conductor superconducting wire (both TypeHT and TypeACT). In FIG. 2, the thickness of each component is exaggerated for easy understanding.

  The superconducting shield layers of the cable cores are short-circuited at both ends of the cable cores, and the induced current from the superconducting conductor layer can flow.

In this test, it is assumed that an overcurrent of 31.5 kA x 2 sec flows in the superconducting conductor layer, and using the analysis program, the magnitude of the current flowing in the superconducting shield layer of each sample and the temperature rise of the superconducting shield layer Degree ΔT (difference between temperature T _n measured every 0.001 sec (1 msec) after energization of overcurrent and temperature T ₀ before energization of overcurrent: T _n -T ₀ ), equivalent thickness t and temperature rise The relationship with the degree ΔT was examined. FIG. 3 shows the magnitude of the current, FIG. 4 shows the temperature rise degree ΔT, and FIG. 5 and Table 2 show the relationship between the equivalent thickness t and the temperature rise degree ΔT. The above analysis program can calculate the current distribution and temperature distribution using the electric circuit equation and the heat conduction equation, and uses commercially available electromagnetic field analysis software capable of magnetic field analysis and temperature analysis. can do.

  As shown in FIG. 5 and Table 2, it can be seen that the degree of temperature increase ΔT of the superconducting shield layer is smaller as the proportion of the normal conducting phase in the superconducting wire for shielding (here, equivalent thickness) is smaller (thinner). The reason for this is that, as shown in FIG. 3, as the ratio of the normal conducting phase decreases, the current induced by the superconducting shield layer (shield current) against the fault current (conductor current) flowing between the former and the superconducting conductor layer. This is probably because the temperature rise accompanying the energization of the shield current is suppressed because the current) is small. In addition, as shown in FIG. 4, the higher the proportion of the normal conducting phase, the faster the temperature of the superconducting shield layer rises, and the possibility of damage to the superconducting wire increases with the temperature rise. .

Furthermore, from this test result, even if the normal conducting phase is composed of a material having a specific resistance at the operating temperature of the superconducting cable of 1 × 10 ⁻⁸ Ω · m or less, the equivalent of the normal conducting phase It can be seen that when the thickness is 10 μm or less, the temperature rise of the superconducting shield layer can be sufficiently suppressed in the event of an accident. Actually, in the sample No. 3 where the equivalent thickness is 10 μm, the ratio of the shield current to the conductor current is about 5%, and in the sample No. 4, it is about 2%. The ratio of the shield current to the conductor current is obtained using the current value 2 seconds after the occurrence of overcurrent, which is about to be interrupted. Thus, it is considered that adjusting the equivalent thickness so that the ratio of the shield current to the conductor current is about 5% or less is effective in suppressing the temperature rise.

  In this test, the three-core superconducting cable described in the first embodiment was examined, but it is expected that the same results can be obtained for the second and third embodiments and the first and second modifications. In particular, when the reinforcing layer is provided, the heat capacity can be increased, so that it is expected that the temperature increase degree ΔT can be further reduced.

  The above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the superconducting cable of the present invention may be used not only for AC transmission but also for DC transmission.

  The superconducting cable of the present invention can be suitably used as a constituent member of a superconducting cable line.

1c Superconducting wire for conductor 1s Superconducting wire for shield
10 Cable core 11 Former 12 Superconducting conductor layer 13 Electrical insulation layer
14 Superconducting shield layer 15 Protective layer
20 Heat insulation pipe 21 Inner pipe 22 Outer pipe 23 Insulation material 24 Anticorrosion layer
100 superconducting cable
110 Substrate 111 Superconducting phase 112 Normal conducting phase

Claims (8)

A superconducting cable comprising a cable core having a former, a superconducting conductor layer, an electrical insulating layer, and a superconducting shield layer in order from the center,
The superconducting conductor layer and the superconducting shield layer are composed of a plurality of superconducting wires including a superconducting phase and a normal conducting phase,
A superconducting cable characterized in that the proportion of the normal conducting phase in at least one of the superconducting wires constituting the superconducting shield layer is smaller than the proportion of the normal conducting phase in the superconducting wire constituting the superconducting conductor layer. In the superconducting wire constituting the superconducting shield layer, the normal conducting phase is composed of a normal conducting material having a specific resistance at a working temperature of the superconducting cable of 1 × 10 ⁻⁸ Ω · m or less. Item 2. The superconducting cable according to item 1.   In the superconducting wire constituting the superconducting shield layer, when the equivalent thickness of the normal conducting phase is taken, the equivalent thickness is thinner than the equivalent thickness of the normal conducting portion in the superconducting wire constituting the superconducting conductor layer. The superconducting cable according to claim 1 or 2, wherein   4. The superconducting cable according to claim 1, wherein the superconducting wire constituting the superconducting shield layer is a thin film wire having a RE-based oxide superconducting phase on a substrate.   5. The superconducting cable according to claim 4, wherein the superconducting wire constituting the superconducting conductor layer is a wire having a Bi-based oxide superconducting phase.   In the superconducting wire constituting the superconducting shield layer, when the equivalent thickness of the normal conducting phase is taken with respect to the width of the substrate, the equivalent thickness of the normal conducting phase is 10 μm or less. Item 6. The superconducting cable according to item 4 or 5. The superconducting wire constituting the superconducting shield layer comprises a reinforcing layer made of a material having a specific resistance at the operating temperature of the superconducting cable of more than 1 × 10 ⁻⁸ Ω · m. The superconducting cable according to any one of the above.   8. The cable core according to any one of claims 1 to 7, wherein the cable core does not have a normal conductive shield layer made of a normal conductive material on both an inner peripheral side and an outer peripheral side of the superconductive shield layer. The superconducting cable described in the section.

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