JP2006012775A - Superconductive cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconductive cable facilitating formation of a twisted structure even in the case of using a plurality of cable cores, and a direct current feeding method using the superconductive cable. <P>SOLUTION: The superconductive cable 1 is formed by twisting two cable cores (a first core 2 and a second core 3) differed in structure and housing them in a heat insulating tube 7. The first core 2 includes a first superconductive layer 2a used as an outgoing line or a polar feed line in DC feeding, and has no superconductive layer other than the first superconductive layer 2a. The second core 3 includes a second superconductive layer 3a used as a returning line or a neutral conductor in DC feeding, and has no superconductive layer other than the second superconductive layer 3a. The second superconductive layer 3a has an inside diameter larger than the outer diameter of the first superconductive layer 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a superconducting cable formed by twisting a plurality of cable cores, and a DC power transmission method using the superconducting cable. In particular, the present invention relates to a superconducting cable that can easily form a twisted structure.

  Conventionally, as a superconducting cable for alternating current, a three-core type cable having three cable cores twisted together is known. FIG. 7 is a cross-sectional view of a three-core collective three-phase AC superconducting cable. The superconducting cable 100 has a configuration in which three cable cores 102 are twisted and housed in a heat insulating tube 101. The heat insulating tube 101 has a structure in which a heat insulating material (not shown) is disposed between the double tubes composed of the outer tube 101a and the inner tube 101b, and the outer tube 101a and the inner tube 101b are evacuated. is there. An anticorrosion layer 104 is provided on the outer periphery of the heat insulating tube 101. Each cable core 102 includes, in order from the center, a former 200, a superconducting conductor layer 201, an insulating layer 202, a superconducting shield layer 203, and a protective layer 204. A space 103 surrounded by the inner tube 101b and each cable core 102 is liquid nitrogen or the like. It becomes the flow path of the refrigerant.

  When AC power transmission is performed using the superconducting cable, an AC loss due to inductance occurs, or a current at the time of a short circuit is large, and the temperature may excessively increase due to the loss at this time. On the other hand, in the case of DC power transmission using a superconducting cable instead of AC power transmission, there is no AC loss and the short-circuit current can be reduced. As a DC superconducting cable, Patent Document 1 proposes a superconducting cable in which three cable cores each having a superconducting conductor and an insulating layer are twisted together. In this superconducting cable, each core includes a superconducting conductor, an insulating layer provided on the outer periphery thereof, and a return conductor made of a superconducting wire provided on the outer periphery of the insulating layer. Unipolar power transmission is performed by using a conductor for the return line.

JP 2003-249130 A

  The superconducting cable disclosed in Patent Document 1 can perform DC power transmission such as monopolar power transmission and bipolar power transmission with a single cable. Moreover, since it is set as the twisted structure of several cable cores, the shrinkage allowance at the time of cable cooling can be given. However, since this cable uses a cable core having a superconducting conductor and a return conductor made of a superconducting material, the amount of superconducting material used in each core increases, and the bending rigidity of the core tends to increase. Therefore, it is difficult to twist the three cable cores, and improvements are desired. Also, in the case of the AC superconducting cable shown in FIG. 7, since the cable core having the superconducting conductor and superconducting shield layer made of a superconducting material is used, it is difficult to twist the cores.

  Therefore, a main object of the present invention is to provide a superconducting cable in which a twisted structure is easily formed while using a plurality of cable cores. Another object of the present invention is to provide a superconducting cable suitable for direct current power transmission. Furthermore, the other object of this invention is to provide the direct current power transmission method using the said superconducting cable.

  The present invention achieves the above object by reducing the amount of superconducting material used in the entire cable.

(Two types of cable cores twisted together: Type 1)
As a means to reduce the amount of superconducting material used in the entire cable, we propose to reduce the amount of superconducting material used per cable core.
That is, the present invention is a superconducting cable formed by twisting a plurality of cable cores each having a superconducting layer and an insulating layer, and includes a core having the following configuration.
First core: having a first superconducting layer.
Second core: has a second superconducting layer. The second superconducting layer has an inner diameter that is larger than the outer diameter of the first superconducting layer.

The direct current power transmission method of the present invention proposes the following as a power transmission method using a type 1 superconducting cable having the first core and the second core.
(Single pole transmission)
The first superconducting layer provided in the first core is used for the forward line, and the second superconducting layer provided in the second core is used for the return line.
(Bipolar transmission)
A plurality of first cores are provided, and the first superconducting layer provided in at least one of the first cores is used for power transmission of one of the positive electrode and the negative electrode, and the first superconducting layer provided in the remaining first cores is provided. Used for transmission of other poles. The second superconducting layer provided in the second core is used as a neutral wire.

  As a form different from the type having the two different types of cable cores, a configuration in which a core having a superconducting layer made of a superconducting material and a member not having a superconducting layer are twisted together is proposed.

(Type with refrigerant pipe: Type 2)
That is, the present invention is a superconducting cable formed by twisting a plurality of cable cores, and this cable twists a refrigerant tube having the same diameter as the cable core and two cable cores having the following configuration. It is characterized by being formed together.
Cable core: a superconducting conductor layer, an insulating layer provided on the outer periphery of the superconducting conductor layer, and an external superconducting layer provided on the outer periphery of the insulating layer.

The direct current power transmission method of the present invention proposes the following as a power transmission method using a type 2 superconducting cable formed by twisting the above-mentioned two cores and a refrigerant pipe.
(Single pole transmission)
The superconducting conductor layer provided in both cores is used for the outgoing line, and the external superconducting layer provided in both cores is used for the return line.
(Bipolar transmission)
The superconducting conductor layer provided in one core is used for power transmission of one of the positive electrode and the negative electrode, and the superconducting conductor layer provided in the other core is used for power transmission of the other electrode. And the external superconducting layer provided in each core is used as a neutral wire.

  The AC superconducting cable shown in FIG. 7 and the DC superconducting cable disclosed in Patent Document 1 have a three-core core twisted structure in order to ensure a contraction allowance when the cable is cooled. Patent Document 1 proposes to use a core in which a superconducting conductor and a return conductor are formed of a superconducting material when performing unipolar power transmission. However, if a large amount of superconducting material is used in the cable core of the superconducting cable, the bending rigidity of each core becomes high and it becomes difficult to twist the three wires. Therefore, the present invention proposes to reduce the amount of superconducting material used per cable core (one strip) and to facilitate twisting. Specifically, it does not have an external superconducting layer (a layer used as a return conductor in DC power transmission, a layer used as a shield in AC power transmission), but a superconducting conductor layer (a layer used as a forward conductor in DC power transmission) A core (corresponding to the first core) having only a conductor used in AC power transmission, and a core having only the outer conductor layer without the superconducting conductor layer (the first core). Equivalent to two cores). Alternatively, in the present invention, it is proposed that one of the three cores is a member that does not use any superconducting material to facilitate twisting. Specifically, a refrigerant pipe is used instead of a single cable core. Hereinafter, the present invention will be described in more detail.

(Type 1)
The superconducting cable of the present invention is formed by twisting a first core and a second core having a superconducting layer and an insulating layer. The first core includes a first superconducting layer composed of a superconducting material, and does not include a superconducting layer composed of a superconducting material in addition to the first superconducting layer. The second core includes a second superconducting layer made of a superconducting material, and does not include a superconducting layer made of a superconducting material in addition to the second superconducting layer. That is, the first core has a superconducting layer on the center side of the core, does not have a superconducting layer on the outer peripheral side of the core, and the second core has a superconducting layer on the outer peripheral side of the core. It does not have a superconducting layer on the inner circumference side. Then, the second superconducting layer of the second core is formed to have an inner diameter larger than the outer diameter of the first superconducting layer.

  The superconducting layers of the first core and the second core may be formed, for example, by spirally winding a tape-like wire rod in which a plurality of filaments made of a Bi2223 series superconducting material are arranged in a matrix such as a silver sheath. Single layer or multiple layers may be used. In the case of a multilayer structure, an interlayer insulating layer may be provided. The interlayer insulating layer may be provided by winding insulating paper such as kraft paper or semi-synthetic insulating paper such as PPLP (registered trademark of Sumitomo Electric Industries, Ltd.).

  The first superconducting layer is formed by winding a wire made of the above superconducting material around the outer periphery of the former. The former may be a solid body or a hollow body formed of a metal material such as copper or aluminum, and examples thereof include a configuration in which a plurality of copper wires are twisted together. The copper wire may be insulated. This former functions as a shape maintaining member for the first superconducting layer. A cushion layer may be interposed between the former and the first superconducting layer. The cushion layer avoids direct contact between metals between the former and the superconducting wire, and prevents damage to the superconducting wire. In particular, when the former has a stranded wire structure, the cushion layer also has a function of making the former surface smoother. As a specific material of the cushion layer, insulating paper or carbon paper can be suitably used.

  The second superconducting layer is formed by winding a wire made of the above superconducting material around the outer periphery of the core material. The core material may be formed of a material that does not increase rigidity, may be formed of an insulating material, or may be formed of a conductive material (except for a superconducting material). For example, it may be formed of the same insulating material as the insulating layer forming material described later, plastic may be used, a metal wire such as a copper wire may be twisted together, plastic, It is good also as a structure which wound the insulating material around the outer periphery of the metal strand wire.

  A refrigerant pipe may be used as the core material. At this time, it is preferable to use a refrigerant flow path surrounded by the first core and the second core and a heat insulating pipe, which will be described later, as a refrigerant forward path and a refrigerant pipe as a core material as a refrigerant return path (return). By having the refrigerant pipe on the inner peripheral side of the second core, the space surrounded by the first core, the second core, and the heat insulation pipe is not reduced by the presence of the refrigerant pipe, and the forward and backward paths of the refrigerant in the heat insulation pipe Can have. Therefore, the configuration including the refrigerant pipe in the second core is surrounded by the first core, the second core, and the heat insulating pipe as compared with the configuration including the refrigerant pipe for the return path separately from the core in the heat insulating pipe. Sufficient space can be secured. That is, a sufficient refrigerant forward path is ensured, and the refrigerant can be sufficiently circulated in the refrigerant forward path. Here, the refrigerant circulation path formed by the forward path and the return path includes a refrigerator for cooling the refrigerant and a pump for pumping the refrigerant, and the refrigerant is circulated at an appropriate temperature by these devices. Thus, the size of the circulation path (cooling section) is determined. In the case where the refrigerant is sufficiently circulated in the refrigerant forward path as described above, since the refrigerant flow rate is large, the temperature rise of the refrigerant due to intrusion heat is smaller, and the refrigerant in an appropriate temperature state can be transported over a long distance. 1 cooling section can be long. Further, since a sufficient space for circulating the refrigerant can be ensured as described above, the circulation pressure of the refrigerant can be reduced, and the pressure loss can be reduced, for example, the driving power of the pump can be reduced.

  The refrigerant pipe is preferably made of a metal material having excellent strength even at the refrigerant temperature. For example, a metal tube, a spiral steel strip, and a hollow shape in which a metal wire (such as a copper wire) is wound on the spiral steel strip can be mentioned. A metal corrugated tube is preferable because it is excellent in flexibility and easily contracts when the cable is cooled. When a refrigerant tube made of a metal material is used, an insulating layer is formed of an insulating material on the outer periphery of the refrigerant tube, and a second superconducting layer is provided on the insulating layer. In particular, when a corrugated tube is used, this insulating layer is preferably provided on the corrugated tube so that the surface on which the second superconducting layer is formed is smooth.

  An insulating layer is provided on the outer periphery of the first superconducting layer in the first core. In addition, an insulating layer is provided on the outer periphery of the second superconducting layer in the second core. These insulating layers may be formed by winding semi-synthetic insulating paper such as PPLP (registered trademark) or insulating paper such as kraft paper. The insulating layer provided on the first core is provided on the first superconducting layer so as to have an insulation strength necessary for the first superconducting layer to be insulated against the ground voltage. The insulating layer provided on the second core is provided on the second superconducting layer so as to have an insulation strength necessary for the second superconducting layer to be insulated against the ground voltage.

  When using the superconducting cable of the present invention for DC power transmission, the insulating layer has a low resistivity on the inner peripheral side of the insulating layer so that the DC electric field distribution in the radial direction (thickness direction) is smoothed, Ρ grading may be applied so that the resistivity on the side becomes higher. By applying ρ grading in this way and gradually changing the resistivity in the thickness direction of the insulating layer, the DC electric field distribution in the entire thickness direction of the insulating layer can be smoothed, and the thickness of the insulating layer is reduced. be able to. The number of layers for varying the resistivity is not particularly limited, but is practically about 2 or 3 layers. In particular, when the thickness of each of these layers is made uniform, the DC electric field distribution can be smoothed more effectively.

  In order to perform ρ grading, it is better to use insulating materials with different resistivity (ρ) .For example, when using insulating paper such as kraft paper, the density of kraft paper is changed, dicyandiamide is added to kraft paper, etc. Thus, the resistivity can be changed. In the case of composite paper consisting of insulating paper and plastic film, such as PPLP (registered trademark), the ratio of the thickness tp of the plastic film to the total thickness T of the composite paper, k = (tp / T) x 100, or the density of the insulating paper The resistivity can be changed by changing materials, additives and the like. The value of the ratio k is preferably in the range of about 40% to 90%, for example. Usually, the resistivity ρ increases as the ratio k increases.

  Furthermore, when the insulating layer has a high ε layer having a higher dielectric constant than other portions in the vicinity of the superconducting layer, the Imp. Withstand voltage characteristic can be improved in addition to the improvement of the direct current withstand voltage characteristic. The dielectric constant ε (20 ° C) is about 3.2 to 4.5 for general kraft paper, about 2.8 for composite paper with a ratio k of 40%, about 2.6 for composite paper of 60%, and about 80% for composite paper. About 2.4. In particular, if the insulating layer is composed of composite paper using kraft paper having a high ratio k and high air density, both DC withstand voltage and Imp.

  In addition to the ρ grading, the insulating layer may be configured such that the dielectric constant ε is higher on the inner peripheral side and the dielectric constant ε is lower on the outer peripheral side. This ε grading is also formed over the entire radial direction of the insulating layer. Further, by applying ρ grading as described above, the superconducting cable of the present invention becomes a cable having excellent direct current characteristics and is suitable for direct current power transmission. On the other hand, most of current transmission lines are composed of alternating current. In the future, when considering changing the power transmission method from AC to DC, there may be a case where AC is transiently transmitted using the cable of the present invention before the DC power transmission. For example, a part of the cable of the transmission line is replaced with the superconducting cable of the present invention, but the remaining part remains the AC power transmission cable, or the AC power transmission cable of the power transmission line is replaced with the superconducting cable of the present invention. This is the case when the power transmission equipment is still used for AC. In this case, AC power transmission is transiently performed with the cable of the present invention, and then, finally, transition to DC power transmission is performed. Therefore, the cable of the present invention is preferably designed not only with excellent direct current characteristics but also with consideration for alternating current characteristics. In consideration of AC characteristics, a cable having excellent impulse characteristics such as surge can be constructed by using an insulating layer having a higher dielectric constant ε on the inner peripheral side and lower dielectric constant ε on the outer peripheral side. And when the said transition period passes and direct current power transmission will be performed, this invention cable used in the transition period can be utilized as a direct current cable as it is. That is, the cable of the present invention that has been subjected to ε grading in addition to ρ grading can be suitably used as a cable for both AC and DC.

  Normally, the above-mentioned PPLP (registered trademark) has a high ρ low ε when the ratio k is increased. For this reason, if the insulating layer is configured using PPLP (registered trademark) having a higher ratio k toward the outer peripheral side of the insulating layer, the outer peripheral side becomes higher ρ, and at the same time, the outer peripheral side becomes lower ε.

  On the other hand, kraft paper generally has high ρ and high ε when the air density is increased. For this reason, it is difficult to construct an insulating layer having a higher ρ on the outer peripheral side and a lower ε on the outer peripheral side with kraft paper alone. Therefore, when kraft paper is used, it is preferable to configure the insulating layer in combination with composite paper. For example, by forming a kraft paper layer on the inner peripheral side of the insulating layer and forming a PPLP layer on the outer side, the resistivity ρ becomes kraft paper layer <PPLP layer, and the dielectric constant ε becomes kraft paper layer> PPLP layer. What should I do?

  In addition, a semiconductive layer may be formed between the first superconducting layer and the insulating layer, or between the insulating layer and the second superconducting layer. By forming such a semiconductive layer, the adhesion between the superconducting layer and the insulating layer is improved, and deterioration due to the occurrence of partial discharge is suppressed.

  The superconducting cable of the present invention is a multi-core cable in which a first core and a second core having the above-described configuration are twisted in total, two or more in total. The number of first cores and the number of second cores may be the same or different from each other, but the amount of superconducting material used for the first superconducting layer of the first core and the number of second cores The number of cores is adjusted so that the amount of superconducting material used for the two superconducting layers is equal. For example, if the first core is provided more than the second core, the amount of superconducting material per second core (1 article) should be greater than the amount used per 1 core (1 article). Good. As described above, the cable of the present invention is provided with the first superconducting layer and the second superconducting layer so that the inner diameter of the second superconducting layer is larger than the outer diameter of the first superconducting layer. Therefore, even if the number of first cores is made larger than the number of second cores and the same amount of superconducting material is used, the thickness of the second superconducting layer of the second core is not excessively increased. Therefore, the bending rigidity of the second core is not excessively increased. For unipolar power transmission, use a superconducting cable that prepares and twists at least one of each of the first and second cores, and has at least one first core and at least one second core. . When conducting not only unipolar transmission but also bipolar transmission, at least two first cores and one second core are twisted together, and a multi-core superconducting cable with two cores and one core is provided. Use the first core for pole power transmission and the second core for neutral wires. In addition, it is preferable that the outer diameter of the first core and the outer diameter of the second core are the same, since they are easily twisted together.

  The type 1 superconducting cable including the first core and the second core may be configured by housing a twisted first core and second core in a heat insulating tube. As the heat insulating tube, for example, a structure in which a heat insulating material is disposed between a double-structured tube composed of an outer tube and an inner tube, and a vacuum is drawn between the inner tube and the outer tube. A space surrounded by the outer peripheral surfaces of the first core and the second core in the inner tube and the inner peripheral surface of the inner tube is filled with a refrigerant such as liquid nitrogen that cools the first core and the second core. An anticorrosion layer or the like may be provided on the outer periphery of the heat insulating tube with a resin such as polyvinyl chloride. The same applies to the type 2 superconducting cable described later.

  Since the superconducting cable of type 1 has a twisted structure of a plurality of cores, it can have a shrinkage allowance when the cable is cooled, like a conventional superconducting cable having a three-core twisted structure. In order to provide the shrinkage allowance, for example, the cores are twisted together with a slack. As a method of giving slack, there is a method in which a spacer is disposed between cores, the cores are twisted together, and the twisted cores are accommodated in a heat insulating tube (when a heat insulating tube is formed), and the spacers are removed. Examples of the spacer include felt having a thickness of about 5 mm. The thickness of the spacer may be appropriately changed according to the cable core diameter. The matters relating to the shrinkage allowance are the same in the type 2 superconducting cable described later.

  The type 1 superconducting cable having the above configuration can perform unipolar power transmission by using the first superconducting layer of the first core for the outgoing line and the second superconducting layer of the second core for the return line. .

  In addition, the type 1 superconducting cable having the above-described configuration is provided with a plurality of first cores, and the first superconducting layer provided in at least one first core is used for power transmission of any one of the positive electrode and the negative electrode, Bipolar power transmission can be performed by using the first superconducting layer included in the remaining first core for power transmission of the other pole and using the second superconducting layer included in the second core as a neutral wire. Furthermore, when an abnormality occurs in one pole during bipolar transmission, for example, an abnormality occurs in the first superconducting layer of the pole or the cross-flow converter connected to the cable, When stopping power transmission, unipolar power transmission can be performed using the first core and the second core of the pole where no abnormality has occurred. At this time, the first superconducting layer of the first core may be the outgoing line, and the second superconducting layer of the second core may be the return line.

  It should be noted that the second superconducting layer is set to the ground potential in both the unipolar transmission and the bipolar transmission. In the case of performing bipolar power transmission, the positive current and the negative current are usually almost the same size and cancel each other, so that almost no voltage is applied to the second superconducting layer functioning as a neutral line. However, in the present invention, when an unbalance current flows when an imbalance occurs between the positive electrode and the negative electrode, or when an abnormality occurs in one of the poles and a change is made from bipolar transmission to unipolar transmission, a current equivalent to the transmission current is used. The second superconducting layer is kept at ground potential in order to flow (function as a return line for unipolar power transmission).

  The superconducting cable of the present invention including the first core and the second core can be suitably used not only for direct current power transmission but also for alternating current power transmission by providing the insulating layer subjected to ε grading as described above. When performing AC power transmission, the first core and the second core do not have a conductor portion that functions as a shield. Therefore, when high-voltage power transmission is performed using this superconducting cable, the leakage electric field may increase. Therefore, when performing AC power transmission with this superconducting cable, it is preferable to use low voltage power transmission. When performing single-phase AC power transmission, it is recommended to use a superconducting cable in which the first and second cores are twisted one by one, and each core has one core, and the superconducting layers of both cores are used for phase power transmission. The superconducting layer of one of the cores may be used for phase power transmission, and the remaining one core may be used as a spare. When direct current power transmission is performed after single phase alternating current power transmission with this superconducting cable, it can be used for single pole power transmission. On the other hand, when performing three-phase AC transmission, superconducting cables with a total of three or more cores of the first and second cores are used. The extra core should be reserved. When direct current power transmission is performed after three-phase alternating current power transmission using this superconducting cable, either unipolar power transmission or bipolar power transmission can be performed. Alternatively, when performing three-phase AC power transmission, twist the first core and the second core one by one, prepare two or three superconducting cables each having one core, and the total number of cores is three You may make it become the above. When using two cables, the total number of cores is four, so it is recommended that one be a spare. When using 3 cables, each cable should be used for power transmission in each phase. In other words, it is better to perform one-phase power transmission with two cores.

(Type 2)
The type 2 superconducting cable of the present invention has a three-core twisted structure formed by twisting two cable cores and one refrigerant tube. Each cable core includes, in order from the center, a superconducting conductor layer composed of a superconducting material, an insulating layer composed of an insulating material, and an external superconducting layer composed of a superconducting material.

  The superconducting conductor layer may be formed by spirally winding a wire made of a Bi2223-based superconducting material, like the first superconducting layer of the first core and the second superconducting layer of the second core. In addition, the superconducting conductor layer may be a single layer or multiple layers, like the first superconducting layer of the first core and the second superconducting layer of the second core. This superconducting conductor layer is formed on the outer periphery of the former in the same manner as the first superconducting layer of the first core.

  The insulating layer may be formed by winding semi-synthetic insulating paper, kraft paper or the like on the superconducting conductor layer in the same manner as the insulating layer of the first core. This insulating layer has an insulation strength necessary for insulation between the superconducting conductor layer and the ground. In addition, this insulating layer is subjected to ρ grading so that the resistivity on the inner peripheral side is low and the resistivity on the outer peripheral side is high, like the insulating layers of the first core and the second core. The DC electric field distribution in the entire thickness direction may be smoothed. Furthermore, this insulating layer may include a high ε layer having a higher dielectric constant than other portions in the vicinity of the superconducting conductor layer, like the insulating layers of the first core and the second core. By providing such a ρ grading and a high ε layer, a superconducting cable suitable for direct current power transmission can be obtained. In addition, this insulating layer is configured so that the dielectric constant ε is higher on the inner peripheral side and the dielectric constant ε is lower on the outer peripheral side together with the ρ grading, like the first core and second core insulating layers. Thus, a superconducting cable suitable for both direct current transmission and alternating current transmission can be obtained.

  The external superconducting layer is formed on the outer periphery of the insulating layer with a superconducting material in the same manner as the superconducting conductor layer. You may form with the material similar to what was utilized for formation of a superconducting conductor layer. This external superconducting layer is kept at ground potential. When performing bipolar transmission using a type 2 superconducting cable, the positive and negative currents are usually of the same magnitude and cancel each other, so there is no voltage on the external superconducting layer that functions as a neutral wire. It hardly takes. However, in the present invention, when an unbalance current flows when an imbalance occurs between the positive electrode and the negative electrode, or when an abnormality occurs in one of the poles and a change is made from bipolar transmission to unipolar transmission, a current equivalent to the transmission current is used. The outer superconducting layer is formed of a superconducting material in order to flow through the outer conductor layer (to function as a return line for monopolar power transmission). It is preferable to provide a protective layer also serving as an insulation on the outer periphery of the external superconducting layer.

  In addition, a semiconductive layer may be formed at least one of the inner and outer circumferences of the insulating layer, that is, between the superconducting conductor layer and the insulating layer, or between the insulating layer and the external superconducting layer. By forming the former inner semiconductive layer and the latter outer semiconductive layer, the adhesion between the superconducting conductor layer and the insulating layer or between the insulating layer and the outer superconducting layer is improved, resulting in the occurrence of partial discharge, etc. Suppress deterioration.

  The refrigerant pipe to be twisted with the two cable cores described above is used as a refrigerant return path (return), whereas the refrigerant flow path surrounded by both cores and the refrigerant pipe and the heat insulation pipe is the forward path of the refrigerant. Such a refrigerant tube is preferably made of a metal material that is excellent in strength at the refrigerant temperature as well as the refrigerant tube provided in the second core. In particular, it is preferable to use a refrigerant tube having a shape excellent in flexibility, specifically, a metal corrugated tube. Since the corrugated tube can be stretched and contracted, it is possible to absorb heat shrinkage due to the stretchability of the tube itself without providing a slack for the shrinkage when cooling the cable when twisting together with both cores. That is, when a corrugated pipe is used as the refrigerant pipe, even when twisted with the core without providing the slack, it is possible to sufficiently cope with the shrinkage at the time of cooling the cable. Further, in the present invention, the outer diameter of the refrigerant pipe is set to the outside of the core so as to ensure a sufficient size as a refrigerant return path and to stably form a twisted structure with the two cable cores. Same diameter (same diameter). And this type 2 superconducting cable is constructed by accommodating the above-mentioned two cable cores and a refrigerant tube in a twisted manner in the heat insulating tube.

  When a metal pipe is used as the refrigerant pipe, the refrigerant pipe comes into contact with the heat insulation pipe when the integrated product of both cores and the refrigerant pipe is stored in the heat insulation pipe (inner pipe). There is a possibility that the refrigerant pipe is damaged or metal powder is generated, and this metal powder is caused to flow to the end of the cable due to the circulation of the refrigerant, causing an electrical failure at the end. Therefore, a protective layer for preventing contact with the heat insulating pipe may be provided on the outer periphery of the refrigerant pipe in order to prevent problems caused by contact with the heat insulating pipe. For example, the protective layer may be formed by winding kraft paper.

  The type 2 superconducting cable having the above configuration can perform unipolar power transmission by using the superconducting conductor layer provided in both cores for the outgoing line and the external superconducting layer provided for both cores for the return line. . Also, the superconducting conductor layer of one core is used for power transmission of either the positive electrode or the negative electrode, the superconducting conductor layer of the other core is used for power transmission of the other electrode, and the external superconducting layer of each core is used for the neutral wire Thus, bipolar transmission can be performed. Furthermore, when an abnormality occurs in one pole during bipolar transmission, for example, an abnormality occurs in the superconducting conductor layer of that pole or the cross-flow converter connected to the cable, and the transmission of one pole occurs. When the operation is stopped, unipolar power transmission can be performed using the core of the pole where no abnormality has occurred. At this time, it is preferable to use the superconducting conductor layer of the core having no abnormality as the outgoing line and the external superconducting layer as the return line. In both cases of unipolar transmission and bipolar transmission, the external superconducting layers of both cores are kept at ground potential.

  The type 2 superconducting cable of the present invention can be suitably used not only for direct current power transmission but also for alternating current power transmission by providing an insulating layer subjected to ε grading as described above. When performing single-phase AC power transmission, one superconducting cable may be used, the superconducting conductor layer of each core may be used for phase power transmission, the external superconducting layer of each core may be used as a shield layer, The superconducting conductor layer may be used for phase power transmission, the outer superconducting layer of the core may be used as a shield layer, and the remaining core may be used as a spare core. On the other hand, when performing three-phase AC power transmission, prepare two or three superconducting cables so that the total number of cores is three or more. When using two cables, the total number of cores is four, so one core is used as a spare core, and the remaining three cores are used for power transmission in each phase. An external superconducting layer provided on the outer periphery of the layer may be used as a shield layer. When using three cables, the superconducting conductor layer of each cable may be used for power transmission in each phase, and the external superconducting layer provided on the outer periphery of these superconducting layers may be used as a shield layer. In other words, it is better to perform one-phase power transmission with two cores.

  The superconducting cable of the present invention having the above-described configuration is easy to twist using a core (refrigerant tube) that uses less superconducting material to reduce the bending rigidity by using less superconducting material per core of the cable core. By doing so, there is a specific effect that it is easy to form a twisted structure.

  In particular, in the type 1 superconducting cable in which two different types of cores are twisted together, when the second core containing the refrigerant pipe is used, the return path of the refrigerant is ensured while ensuring a sufficient space surrounded by the core and the heat insulating pipe. Can have. On the other hand, in a type 2 superconducting cable in which two cores and a refrigerant pipe are twisted together, a refrigerant pipe is provided instead of a single core, so that a flow path having the maximum volume can be secured as a refrigerant return path. it can. Further, by providing a protective layer on the outer periphery of the refrigerant pipe, the refrigerant pipe can be prevented from coming into contact with the heat insulating pipe, and damage to the refrigerant pipe and the heat insulating pipe due to this contact, generation of metal powder, and the like can be suppressed. it can.

  Furthermore, in the core provided in the superconducting cable of the present invention, the insulation layer with ρ grading smoothes the DC electric field distribution throughout the thickness direction of the insulation layer, improves the DC withstand voltage characteristics, and provides insulation. The thickness of the layer can be reduced. In addition to the above-described improvement in DC withstand voltage characteristics, Imp. withstand voltage characteristics can also be improved by providing an insulating layer so that the vicinity of the superconducting layer used as a conductor becomes high ε in addition to ρ grading. In particular, the superconducting cable of the present invention can be a cable having excellent AC electrical characteristics by setting the ε higher toward the inner peripheral side of the insulating layer and lower ε toward the outer peripheral side. Therefore, the superconducting cable of the present invention can be suitably used not only for DC power transmission and AC power transmission, but also in a transition period in which the power transmission method is changed between AC and DC.

  Embodiments of the present invention will be described below. First, a type 1 superconducting cable of the present invention in which two types of cores having different configurations are twisted together will be described.

  FIG. 1 is a schematic configuration diagram showing a state in which a DC transmission line for monopolar power transmission is constructed using the superconducting cable of the present invention. Hereinafter, the same reference numerals in the drawings denote the same items. The superconducting cable 1 is a cable in which two types of cable cores (first core 2 and second core 3) having different configurations are twisted and accommodated in a heat insulating tube 7. Specifically, the first core 2 includes the first superconducting layer 2a made of a superconducting material on the inner peripheral side of the insulating layer 4, and does not include the layer made of the superconducting material on the outer peripheral side of the insulating layer 4. The second core 3 includes a core material 5b on the center side, a second superconducting layer 3a made of a superconducting material on the outer peripheral side of the core material 5b, and a layer made of a superconducting material on the inner peripheral side of the core material 5b. I don't have it. The inner diameter of the second superconducting layer 3a is larger than the outer diameter of the first superconducting layer 2a.

(First core 2)
In this example, the first superconducting layer 2a is formed by using a Bi2223 superconducting tape wire (Ag-Mn sheath wire) and winding the tape wire around the former 5a in a spiral manner in multiple layers. The former 5a was made by twisting a plurality of copper wires, and a cushion layer (not shown) was formed of insulating paper between the former 5a and the first superconducting layer 2a. An insulating layer 4 is provided on the outer periphery of the first superconducting layer 2a. The insulating layer 4 was configured by winding semi-synthetic insulating paper (PPLP: registered trademark of Sumitomo Electric Industries, Ltd.) so as to have insulation strength necessary for insulation between the first superconducting layer 2a and the ground. In this example, two such first cores 2 were prepared. All the first cores 2 have the same diameter.

(Second core 3)
In this example, the second core 3 is formed as one (one core), and the outer diameter thereof is formed to be the same as the outer diameter of the first core 2. First, the core material 5b was formed. In this example, a semi-synthetic insulating paper (PPLP: registered trademark of Sumitomo Electric Industries, Ltd.) was wound around the outer periphery of a core material (not shown) formed by twisting copper wires to form a core material 5b. A second superconducting layer 3a is provided on the outer periphery of the core material 5b. The second superconducting layer 3a is made of the same superconducting material as the first superconducting layer 2a of the first core 2 (Bi2223 series superconducting tape wire (Ag-Mn sheath wire)), and is similarly spirally wound in multiple layers. Configured. The amount of the tape wire used for forming the second superconducting layer 3a was the same as the amount of the tape wire used for constituting the first superconducting layer 2a of the first core 2 of the above-mentioned two articles. Then, the size of the core material 5b is adjusted in the second core 3, and the second superconducting layer 3a of the second core 3 is larger than the outer diameter of the first superconducting layer 2a of the first core 2 (the inner diameter of the insulating layer 4). The inner diameter (the outer diameter of the core material 5b) was made larger. Therefore, the second superconducting layer 3a can be formed without excessively increasing the number of windings (number of layers) of the second superconducting layer 3a, and the bending rigidity of the second core 3 is not excessively increased. Then, an insulating layer 6 was provided on the outer periphery of the second superconducting layer 3a. The insulating layer 6 was formed by winding kraft paper so as to have insulation strength necessary for insulation between the second superconducting layer 3a and the ground.

(Superconducting cable 1)
The superconducting cable 1 is formed by twisting a first core 2 having only a first superconducting layer 2a as a layer made of a superconducting material and a second core 3 having only a second superconducting layer 3a as a layer made of a superconducting material, thereby insulating heat. It is housed in a tube 7 and configured. In this example, when these three cores 2 and 3 were cooled by the refrigerant and caused thermal contraction, they were twisted together so as to have a contraction allowance. Specifically, when the first core 2 and the first core 2 and the second core 3 are respectively twisted by interposing a spacer (not shown) and housed in the heat insulating tube 7 (forming the heat insulating tube 7). In this case, the spacer is removed so that it is stored in the heat insulating tube 7 with a slack. In this example, a 5 mm thick felt having a rectangular cross section was used as the spacer. Further, in this example, the heat insulating pipe 7 uses a SUS corrugated pipe, and in the same manner as the conventional superconducting cable shown in FIG. 7, a heat insulating material (not shown) is provided between the double pipes composed of the outer pipe 7a and the inner pipe 7b. ) Are arranged in multiple layers, and a vacuum multi-layer insulation structure is formed in which the inside of the double pipe is evacuated. A space 8 surrounded by the inner tube 7b and the cores 2 and 3 of the three cores serves as a flow path for a refrigerant such as liquid nitrogen. An anticorrosion layer (not shown) was formed of polyvinyl chloride on the outer periphery of the heat insulating tube 7.

  The superconducting cable 1 of the present invention having the above-described configuration can be used for DC power transmission, specifically, bipolar power transmission or unipolar power transmission. First, the case of performing unipolar power transmission will be described. In order to perform unipolar power transmission, it is preferable to construct a power transmission line as shown in FIG. Specifically, a cross flow converter 10a connected to an AC system (not shown) is connected to one end side of the first superconducting layer 2a included in one first core 2 via leads 20 and 21. Then, a cross flow converter 10b connected to an AC system (not shown) is connected to the other end of the first superconducting layer 2a via a lead 22. Further, the cross flow converter 10a is connected to one end side of the first superconducting layer 2a included in the other first core 2 via the lead 23 and the lead 21, and the other end side of the first superconducting layer 2a is The cross flow converter 10b is connected via the lead 22. A cross flow converter 10a is connected to one end side of the second superconducting layer 3a included in the second core 3 via a lead 24, and a cross flow converter 10b is connected to the other end side of the second superconducting layer 3a. Connected via lead 25. The lead 24 is grounded. By this grounding, the second superconducting layer 3a becomes the ground potential. In this example, one-end grounding is used, but the lead 25 may be grounded and both-end grounding may be performed. The leads 20 to 25 electrically connect the superconducting layers 2a and 3a and the cross flow converters 10a and 10b.

  In the DC power transmission line having the above-described configuration, the second superconducting layer 3a provided in the second core 3 is used as a forward line by flowing a unipolar current through the first superconducting layer 2a provided in the first core 2 of the two cores. Unipolar power transmission can be performed by supplying a return current to the line and using it as a return line. In addition, since the superconducting cable 1 is slackened and the three cores are twisted together, the slack can absorb heat shrinkage during cooling. Furthermore, this superconducting cable 1 is compared with a conventional superconducting cable in which three layers of a cable core comprising two layers of a superconducting material (superconducting conductor and external superconducting layer) are twisted together. Usage is low. Therefore, the bending rigidity of the core is small, and a twisted structure is easily formed.

  Next, the case where bipolar transmission is performed will be described. FIG. 2 (A) is a schematic configuration diagram showing a state where a DC power transmission line for bipolar power transmission is constructed using the superconducting cable of the present invention, and (B) is one of the first cores of two cores and It is a schematic block diagram which shows the state which constructed | assembled the DC power transmission line which performs monopolar power transmission using a 2nd core. Superconducting cable 1 used in Example 1 can also be used for bipolar power transmission. In order to perform bipolar power transmission, a power transmission line as shown in FIG. Specifically, an AC system is connected to one end side of the first superconducting layer 2a included in one of the two cores of the first core 2 (the upper first core 2 in FIG. 2A). A cross flow converter 11a connected to (not shown) is connected via a lead 30, and a cross flow converter connected to an AC system (not shown) on the other end side of the first superconducting layer 2a. 11b is connected via the lead 31. On one end side of the first superconducting layer 2a provided in the other first core 2 (the first core 2 on the left side in FIG. 2 (A)), there is a cross flow converter 12a connected to an AC system (not shown). A cross flow converter 12b connected to the AC system (not shown) is connected to the other end side of the first superconducting layer 2a via a lead 33. The cross flow converters 11a and 12a are connected to one end side of the second superconducting layer 3a included in the second core 3 via a lead 34, and directly connected to the other end side of the second superconducting layer 3a via a lead 35. The AC converters 11b and 12b are connected. The lead 34 is grounded. By this grounding, the second superconducting layer 3a becomes the ground potential. In this example, only the lead 34 is grounded and one end is grounded, but the lead 35 may be grounded and both ends grounded. The leads 30 to 35 electrically connect the superconducting layers 2a and 3a and the cross flow transducers 11a, 11b, 12a, and 12b.

  With the above configuration, the cross flow converter 11b, the lead 31, the first superconducting layer 2a of the upper first core 2 in FIG. 2 (A), the lead 30, the cross flow converter 11a, the lead 34, and the second core 3 A positive electrode path including the two superconducting layers 3a and the leads 35 is constructed. Also, the cross flow converter 12b, the lead 33, the first superconducting layer 2a of the left first core 2 in FIG. 2A, the lead 32, the cross flow converter 12a, the lead 34, and the second superconducting of the second core 3. A negative electrode path of layer 3a and lead 35 is constructed. Bipolar power transmission can be performed by these positive and negative paths. At this time, the second superconducting layer 3a of the second core 3 is used not only as a neutral wire but also for flowing an unbalanced current or an abnormal current between positive and negative electrodes. In this example, in FIG. 2 (A), the upper first core 2 is used as the positive electrode and the left first core 2 is used as the negative electrode.

  On the other hand, when an abnormality occurs in the first superconducting layer or cross-flow converter of either pole and power transmission of that pole is stopped, unipolar power transmission is performed using the first superconducting layer of the pole that does not cause an abnormality. It can be carried out. For example, if an abnormality occurs in the left first core 2 or the cross flow converters 12a and 12b in FIG. 2 (A), that is, if an abnormality occurs in the negative electrode, the left first core in FIG. Stop power transmission using Core 2. At this time, as shown in FIG. 2 (B), a transmission line for unipolar power transmission using one first core 2 (the upper first core 2 in FIG. 2) is constructed. Unipolar power transmission can be performed using the one superconducting layer 2a as the outgoing line and the second superconducting layer 3a of the second core 3 as the return line. In addition, although the case where abnormality occurred in the negative electrode was described in this example, the same applies to the case where abnormality occurs in the positive electrode. At this time, when unipolar power transmission is performed using the first superconducting layer 2a of the other first core 2 (the first core 2 on the left side in FIG. 2) as the outgoing line and the second superconducting layer 3a of the second core 3 as the return line. Good.

  As described above, the superconducting cable of the present invention can perform both bipolar power transmission and monopolar power transmission.

When performing DC power transmission as described above, ρ grading is performed so that the resistivity on the inner peripheral side is low and the resistivity on the outer peripheral side is high in the insulating layer 4 of the first core 1 and the insulating layer 6 of the second core 2. When applied, the DC electric field distribution in the thickness direction of the insulating layer can be smoothed. The resistivity can be changed by using PPLP (registered trademark) having a different ratio k, and the resistivity tends to increase as the ratio k increases. If a high ε layer is provided in the insulating layer 4 in the vicinity of the first superconducting layer 2a, the Imp. Withstand voltage characteristic can be improved in addition to the improvement of the DC withstand voltage characteristic. For example, the high ε layer may be formed using PPLP (registered trademark) having a small ratio k. At this time, the high ε layer also becomes a low ρ layer. Furthermore, in addition to the ρ grading, if the insulating layers 4 and 6 are formed so that the dielectric constant ε is higher on the inner peripheral side and lower on the outer peripheral side, the AC characteristics are also excellent. Therefore, the superconducting cable 1 can be suitably used for AC power transmission. For example, by using PPLP (registered trademark) having different ratios k as described below, an insulating layer may be provided so that the resistivity and the dielectric constant are different in three stages. The following three layers should be provided in order from the inner periphery (X and Y are constants)
Low ρ layer: Ratio k = 60%, resistivity ρ (20 ° C) = X Ω · cm, dielectric constant ε = Y
Middle ρ layer: Ratio k = 70%, resistivity ρ (20 ° C) = about 1.2X Ω · cm, dielectric constant ε = about 0.95Y
High ρ layer: Ratio k = 80%, resistivity ρ (20 ° C) = about 1.4X Ω · cm, dielectric constant ε = about 0.9Y

  When superconducting cable 1 is used for three-phase AC power transmission, superconducting layers 2a and 3a of cores 2 and 3 may be used for phase power transmission. When single-phase AC power transmission is performed using the superconducting cable 1, the superconducting layers 2a and 3a of the cores 2 and 3 are preferably used for power transmission in the same phase. Since each of the cores 2 and 3 does not have a superconducting layer that functions as a shield, when performing AC power transmission using the superconducting cable 1, it is preferable to use low-voltage power transmission.

  The superconducting cable 1 can also perform direct current power transmission such as the above-described unipolar power transmission or bipolar power transmission after performing the above alternating current power transmission. Thus, the superconducting cable of the present invention having the insulating layer subjected to ρ grading or ε grading can be suitably used as a DC / AC dual-purpose cable. The matters regarding these ρ grading and ε grading are the same as in Example 3 described later.

  In the first and second embodiments, the configuration using the copper stranded wire as the core material of the second core has been described. However, a refrigerant pipe may be used as the core material. FIG. 3 is a schematic cross-sectional view of the superconducting cable of the present invention having a refrigerant pipe inside the second superconducting layer of the second core. The basic structure of the second core 3 shown in this example is the same as that shown in the first and second embodiments, except that a refrigerant pipe 9a is provided as a core material of the core material 5b. Hereinafter, this point will be mainly described.

  In this example, the refrigerant pipe 9a uses a SUS corrugated pipe, and semi-synthetic insulating paper is wound around the outer circumference of the refrigerant pipe 9a to form the insulating layer 9b. In particular, in this example, semi-synthetic insulating paper is wound so as to make the corrugated tube uneven, so that the second superconducting layer 2a has a uniform insulating thickness, so that the outer peripheral surface of the insulating layer 9b becomes smooth. An insulating layer 9b was provided. A second superconducting layer 3a and then an insulating layer 6 are provided on the outer periphery of the insulating layer 9b in the same manner as in Example 1, so that the outer diameter of the second core 3 is the same as the outer diameter of the first core 2. did.

  By using the second core 3 including the refrigerant pipe 9a, the space 8 surrounded by the inner pipe 7b and the three cores 2 and 3 is used as a forward path for a refrigerant such as liquid nitrogen, and the refrigerant pipe 9a is used as a return path for the refrigerant. (Return) can be used. In particular, since the refrigerant pipe 9a is provided in the second core 3, compared with the case where the refrigerant pipe 9a is provided in the space 8 outside the second core 3, the refrigerant return path is reduced without reducing the volume of the space 8. Can have. Further, in this example, since the corrugated pipe having excellent flexibility is used as the refrigerant pipe 9a, the refrigerant pipe 9a itself can be easily contracted when the cable is cooled. Thus, the core material 5b provided inside the second superconducting layer 3a may be formed of different materials (in this example, the refrigerant pipe 9a and the insulating layer 9b).

  Next, a type 2 superconducting cable of the present invention in which two cable cores and a refrigerant pipe are twisted together will be described.

  FIG. 4 is a schematic configuration diagram showing a state in which a DC transmission line for monopolar power transmission is constructed using the superconducting cable of the present invention. In FIG. 4 and FIG. 5 described later, the refrigerant circulation path is omitted. The superconducting cable 40 is formed by twisting two cable cores 41 having a superconducting conductor layer 44 and an outer superconducting layer 46 made of a superconducting material coaxially and a single refrigerant pipe 42 and storing them in the heat insulating pipe 7. Cable. Each cable core 41 includes a former 43, a superconducting conductor layer 44, an insulating layer 45, an external superconducting layer 46, and a protective layer 47 in order from the center.

(Cable core 41)
In this example, the superconducting conductor layer 44 and the external superconducting layer 46 were formed of Bi2223 superconducting tape wires (Ag-Mn sheath wires). The superconducting conductor layer 44 was formed on the outer periphery of the former 43, and the outer superconducting layer 46 was formed on the outer periphery of the insulating layer 45 by winding the superconducting tape wire in a multilayered manner in a spiral manner. The former 43 is formed by twisting a plurality of copper wires, and a cushion layer (not shown) is formed of insulating paper between the former 43 and the first superconducting conductor layer 44. The insulating layer 45 is configured by winding semi-synthetic insulating paper (PPLP: registered trademark of Sumitomo Electric Industries, Ltd.) around the outer periphery of the superconducting conductor layer 44. This insulating layer 45 was provided so as to have an insulation strength necessary for insulation between the superconducting conductor layer 44 and the ground. The protective layer 47 was provided by winding kraft paper around the outer periphery of the external superconducting layer 46. Two such cable cores 41 were prepared. Further, the outer diameter of any core 41 is the same.

(Refrigerant tube 42)
In this example, a SUS corrugated pipe having an outer diameter that is the same as the outer diameter of the core 41 is used as the refrigerant pipe 42 twisted together with the two cable cores 41 described above.

(Superconducting cable 40)
The superconducting cable 40 is constituted by twisting two cable cores 41 including the superconducting conductor layer 44 and the external superconducting layer 46 and the refrigerant pipe 42 and storing them in the heat insulating pipe 7. When the two cores 41 were cooled by the refrigerant, they were twisted together with a slack so as to have a shrinkage margin necessary for heat shrinkage. The slack was formed by disposing a spacer (5 mm thick felt) between the cores 41 in the same manner as in Example 1 and twisting them, and removing the spacer when housed in the heat insulating tube 7. Since the refrigerant tube 42 uses a corrugated tube that can be expanded and contracted, a sufficient contraction allowance can be ensured even when twisted together with the core 41 without giving any slack. In this example, the heat insulating tube 7 uses a SUS corrugated tube, and in the same manner as the conventional superconducting cable shown in FIG. 7, a heat insulating material (not shown) is provided between the double tubes composed of the outer tube 7a and the inner tube 7b. It was set as the vacuum multilayer heat insulation structure which has arrange | positioned in the multilayer and evacuated the inside of a double tube. A space 8 surrounded by the inner pipe 7b, the two cable cores 41, and the refrigerant pipe 42 is a forward path for a refrigerant such as liquid nitrogen, and the refrigerant pipe 42 is a return path for the refrigerant. Further, an anticorrosion layer (not shown) was formed of polyvinyl chloride on the outer periphery of the heat insulating tube 7.

  The superconducting cable 40 of the present invention having the above-described configuration can be used for DC power transmission, specifically, bipolar power transmission or unipolar power transmission. First, the case of performing unipolar power transmission will be described. In order to perform unipolar power transmission, it is preferable to construct a power transmission line as shown in FIG. Specifically, the cross flow converter 13a connected to the AC system (not shown) is connected to one end side of the superconducting conductor layer 44 included in the right core 41 in FIG. 4 via the lead 50 and the lead 51. Then, a cross flow converter 13b connected to an AC system (not shown) is connected to the other end side of the superconducting conductor layer 44 via a lead 52. In FIG. 4, one end side of the superconducting conductor layer 44 provided in the left core 41 is similarly connected to the cross flow converter 13a via the lead 53 and the lead 51, and the other end side of the superconducting conductor layer 44 is The cross flow converter 13b is connected via the lead 52. The external superconducting layers 46 of both cores 41 are connected to the crossflow converter 13a through leads 54, leads 55, and leads 56, and are connected to the crossflow converter 13b through leads 57. In this example, the lead 56 is grounded. By this grounding, the external superconducting layer 46 becomes a ground potential. Although one-end grounding is used in this example, the lead 57 may be grounded and both-end grounding may be performed. The leads 50 to 57 are for electrically connecting the superconducting conductor layer 44 and the external superconducting layer 46 to the cross flow transducers 13a and 13b.

  In a DC transmission line having the above configuration, a unipolar current is passed through the superconducting conductor layer 44 provided in both cores 41 to be used as an outgoing line, and a return current is supplied to the external superconducting layer 46 provided in both cores 41 to return. Unipolar power transmission can be performed by using it as a track. In addition, the superconducting cable 40 has a slack in the two cable cores 41 and twists a refrigerant pipe 42 made of an expandable / collapsed corrugated pipe. Can absorb the minute. Furthermore, this superconducting cable 40 has a refrigerant tube 42 instead of a single core, as compared with a superconducting cable in which three cores comprising a superconducting conductor layer made of a superconducting material and an external superconducting layer are twisted. Because of the configuration, it is possible to have a refrigerant return path (return) without reducing the volume of the space 8. In particular, since the outer diameter of the refrigerant pipe 42 is the same as the outer diameter of the cable core 41, the cable 40 can have a refrigerant return path with the maximum volume. Further, since the cable 40 can have the same diameter as that of the cable having a three-core twisted structure, the cable diameter is not increased.

  Next, the case where bipolar transmission is performed will be described. FIG. 5 (A) is a schematic configuration diagram showing a state in which a DC transmission line for bipolar transmission is constructed using the superconducting cable of the present invention, and (B) is a diagram using a superconducting conductor layer and an external superconducting layer of one core. It is a schematic block diagram which shows the state which constructed | assembled the DC power transmission line which performs monopolar power transmission. The superconducting cable 40 used in Example 4 can also be used for bipolar power transmission. In order to perform bipolar power transmission, a power transmission line as shown in FIG. Specifically, a cross flow converter connected to an AC system (not shown) on one end side of the superconducting conductor layer 44 provided in one core 41 (the right core 41 in FIG. 5A). 14a is connected via a lead 60, and a cross flow converter 14b connected to an AC system (not shown) is connected to the other end side of the superconducting conductor layer 44 via a lead 61. In addition, a cross flow converter 14a is connected to one end side of the external superconducting layer 46 included in the core 41 via leads 62 and 63, and a cross flow converter 14b is connected to the other end side of the external superconducting layer 46. Connected via lead 64. On one end side of the superconducting conductor layer 44 included in the other core 41 (the left core 41 in FIG. 5A), a cross flow converter 15a connected to an AC system (not shown) is connected via a lead 65. A cross flow converter 15b connected to an AC system (not shown) is connected to the other end side of the superconducting conductor layer 44 via a lead 66. In addition, a cross flow converter 15a is connected to one end side of the external superconducting layer 46 included in the core 41 via a lead 67 and a lead 63, and a cross flow converter 15b is connected to the other end of the external superconducting layer 46. Connected through 64. The lead 63 is grounded. By this grounding, the external superconducting layers 46 of both cores 41 become the ground potential. In this example, only the lead 63 is grounded and one end is grounded, but the lead 64 may be grounded and both ends grounded. The leads 60 to 67 electrically connect the superconducting conductor layer 44 and the external superconducting layer 46 to the crossflow transducers 14a, 14b, 15a, and 15b.

  With the above configuration, the cross flow transducer 14b, the lead 61, the superconducting conductor layer 44 of the right core 41 in FIG. 5 (A), the lead 60, the cross flow transducer 14a, the lead 63, the lead 62, and the outside of the right core 41. A positive electrode path including the superconducting layer 46 and the lead 64 is constructed. Also, the cross flow transducer 15b, the lead 66, the superconducting conductor layer 44 of the left core 41 in FIG. 5A, the lead 65, the cross flow transducer 15a, the lead 63, the lead 67, and the external superconducting layer of the left core 41. 46, lead negative 64 is constructed. Bipolar power transmission can be performed by these positive and negative paths. At this time, the external superconducting layer 46 of both cores 41 is used not only as a neutral wire, but also for flowing positive and negative unbalance currents and abnormal currents. In this example, the right core is used as the positive electrode and the left core is used as the negative electrode in FIG.

  On the other hand, when an abnormality occurs in the superconducting conductor layer or cross flow converter of any pole, and power transmission by the superconducting conductor layer of that pole is stopped, the superconducting conductor layer and the external superconducting layer of the pole that does not cause an abnormality are used And unipolar power transmission. For example, when an abnormality occurs in the left core 41 or the cross flow converters 15a and 15b in FIG. 5 (A), that is, when an abnormality occurs in the negative electrode, the left core 41 in FIG. 5 (A) is used. Stop power transmission. At this time, as shown in FIG. 5 (B), a transmission line for unipolar power transmission using one core 41 (the right core 41 in FIG. 5) is constructed, and the superconducting conductor layer 44 of this core 41 is connected to the outgoing line. Then, unipolar power transmission can be performed using the external superconducting layer 46 as a return line. In addition, although the case where abnormality occurred in the negative electrode was described in this example, the same applies to the case where abnormality occurs in the positive electrode. At this time, unipolar power transmission may be performed using the superconducting conductor layer 44 of the other core 41 (the left core 41 in FIG. 5) as the forward line and the external superconducting layer 46 as the return line.

  As described above, the superconducting cable of the present invention can perform both bipolar power transmission and monopolar power transmission. In particular, the number of cable cores provided in a single cable is two, and one core is a refrigerant tube, so the amount of superconducting material used in the entire cable is reduced compared to a configuration with three cores. The twisted structure can be formed more easily.

When performing DC power transmission as described above, the insulating layer 45 of the core 41 may also be subjected to ρ grading as described above to smooth the DC electric field distribution in the thickness direction of the insulating layer. A high ε layer may be provided in the vicinity of the conductor layer 44 to improve DC withstand voltage characteristics and Imp. Withstand voltage characteristics. In addition to the ρ grading in the insulating layer 45, the ε grading is applied as described above so that the AC characteristic is excellent, so that the superconducting cable 40 is publicly used not only for the DC power transmission but also for the AC power transmission. You may be able to do it. For example, by using PPLP (registered trademark) having different ratios k as described below, an insulating layer may be provided so that the resistivity and the dielectric constant are different in three stages. The following three layers should be provided in order from the inner periphery (X and Y are constants).
Low ρ layer: Ratio k = 60%, resistivity ρ (20 ° C) = X Ω · cm, dielectric constant ε = Y
Middle ρ layer: Ratio k = 70%, resistivity ρ (20 ° C) = about 1.2X Ω · cm, dielectric constant ε = about 0.95Y
High ρ layer: Ratio k = 80%, resistivity ρ (20 ° C) = about 1.4X Ω · cm, dielectric constant ε = about 0.9Y

  When three-phase AC power transmission is performed using the superconducting cable 40, the superconducting cable 40 may be prepared in two or three sections. When using the two-line cable 40, of the four cores 41 included in the two-line cable 40, one core 41 is used as a spare core, and the superconducting conductor layer 44 of the remaining three cores 41 is phased. It is preferable to use the outer superconducting layer 46 of the core 41 as a shield layer. When the three-line cable 40 is used, each cable 40 is used for phase transmission. That is, one-phase power transmission is performed by the two cores 41 included in each cable 40. At this time, the superconducting conductor layer 44 of the two cores 41 provided in each cable 40 is used for phase power transmission, and the external superconducting layer 46 provided on the outer periphery of these superconducting conductor layers 44 is used as a shield layer. When performing single-phase AC power transmission using the superconducting cable 40, one superconducting cable 1 is prepared, and the superconducting conductor layer 44 of each core 41 is used for power transmission in the same phase and is provided on the outer periphery of the superconducting conductor layer 44. The external superconducting layer 46 may be used as a shield layer.

  The superconducting cable 40 can perform direct current power transmission such as unipolar power transmission and bipolar power transmission described above after performing the above alternating current power transmission. Thus, the superconducting cable of the present invention having the insulating layer subjected to ρ grading or ε grading can be suitably used as a DC / AC dual-purpose cable. The matters related to ρ grading and ε grading are the same as in Example 6 described later.

  Next, another configuration of the superconducting cable according to the present invention in which two cable cores and a refrigerant pipe are twisted together will be described. FIG. 6 is a schematic cross-sectional view showing an example in which a protective layer is provided on the outer periphery of the refrigerant pipe.

  In the structures shown in Examples 4 and 5, when the two cable cores 41 and the refrigerant pipe 42 are twisted and inserted into the heat insulation pipe (see FIGS. 4 and 5), the outer peripheral surface of the refrigerant pipe 42 and the heat insulation pipe (inner There is a risk that metal powder may be produced and the refrigerant pipe 42 and the heat insulating pipe may be damaged. Therefore, as shown in FIG. 6, a protective layer 42b for preventing contact between the refrigerant tube 42a and the heat insulating tube may be provided on the outer periphery of the refrigerant tube 42a. In this example, the protective layer 42b was formed by winding kraft paper. In this example, the diameter of the refrigerant pipe 42a is selected so as to be the same as the outer diameter of the cable core 41 in a state where the protective layer 42b is provided. With this configuration, the refrigerant pipe 42a and the heat insulating pipe do not come into contact with each other, and problems due to contact can be prevented.

  The superconducting cable of the present invention is preferably used for a power transmission line. In particular, the superconducting cable of the present invention can be suitably used for transmitting alternating current in a transition period in which the power transmission method is shifted from alternating current to direct current, in addition to the direct current power transportation means. The direct current power transmission method of the present invention can be suitably used when direct current power transmission is performed using the superconducting cable of the present invention.

It is a schematic block diagram which shows the state which constructed | assembled the DC power transmission line for monopolar power transmission using the superconducting cable of this invention formed by twisting a 1st core and a 2nd core. (A) is a schematic configuration diagram showing a state where a DC transmission line for bipolar transmission is constructed using the superconducting cable of the present invention formed by twisting the first core and the second core, and (B) is the superconducting cable. FIG. 2 is a schematic configuration diagram showing a state in which a DC transmission line for monopolar power transmission is constructed using the first superconducting layer of one first core and the second superconducting layer of the second core. It is a cross-sectional schematic diagram which shows the example which provides a refrigerant pipe inside the 2nd superconducting layer of a 2nd core in the superconducting cable of this invention formed by twisting a 1st core and a 2nd core. It is a schematic block diagram which shows the state which constructed | assembled the DC power transmission line for monopolar power transmission using the superconducting cable of this invention formed by twisting together 2 cores and a refrigerant pipe. (A) is a schematic configuration diagram showing a state in which a DC transmission line for bipolar transmission is constructed using the superconducting cable of the present invention formed by twisting two cores and a refrigerant pipe, and (B) is the superconducting cable. FIG. 1 is a schematic configuration diagram showing a state in which a DC transmission line for monopolar power transmission is constructed using a superconducting conductor layer and an external superconducting layer of one core. In the superconducting cable of this invention formed by twisting two cores and a refrigerant pipe, it is a cross-sectional schematic diagram which shows another structure, and is an example which provides a protective layer in the outer periphery of a refrigerant pipe. It is sectional drawing of the superconducting cable for three-phase collective type three-phase alternating current.

Explanation of symbols

1,40 Superconducting cable 2 First core 2a First superconducting layer
3 Second core 3a Second superconducting layer 4, 6, 9b Insulating layer 5a Former 5b Core material
7 Heat insulation pipe 7a Outer pipe 7b Inner pipe 8 Space 9a Refrigerant pipe
10a, 10b, 11a, 11b, 12a, 12b, 13a, 13b, 14a, 14b, 15a, 15b Cross flow converter
20 ~ 25,30 ~ 35,50 ~ 57,60 ~ 67 Lead
41 Cable core 42, 42a Refrigerant tube 42b Protective layer 43 Former
44 Superconducting conductor layer 45 Insulating layer 46 External superconducting layer 47 Protective layer
100 Three-phase AC superconducting cable 101 Insulated tube 101a Outer tube 101b Inner tube
102 Cable core 103 Space 104 Anticorrosion layer
200 Former 201 Superconducting conductor layer 202 Insulating layer 203 Superconducting shield layer
204 Protective layer

Claims (21)

A superconducting cable formed by twisting a plurality of cable cores having a superconducting layer and an insulating layer,
A first core having a first superconducting layer;
A superconducting cable comprising a second core having a second superconducting layer having an inner diameter larger than the outer diameter of the first superconducting layer.   2. The superconducting cable according to claim 1, wherein the second core has a refrigerant pipe inside the second superconducting layer.   3. The superconducting cable according to claim 2, wherein the refrigerant pipe is one of a metal pipe, a spiral steel strip, and a metal corrugated pipe.   The superconducting cable according to any one of claims 1 to 3, wherein two first cores and one second core are twisted together.   The superconducting cable according to any one of claims 1 to 4, wherein the outer diameter of the first core and the outer diameter of the second core are the same.   6. The superconducting cable according to claim 1, wherein the twisted structure of the core has a shrinkage allowance when the cable is cooled.   The insulating layer is ρ-graded so that the resistivity on the inner peripheral side of the insulating layer is low and the resistivity on the outer peripheral side is high so that the DC electric field distribution in the radial direction is smoothed. The superconducting cable according to any one of claims 1 to 6,   8. The superconducting cable according to claim 7, wherein the insulating layer has a high ε layer having a higher dielectric constant than other portions in the vicinity of the superconducting layer.   8. The superconducting cable according to claim 7, wherein the insulating layer has a higher dielectric constant ε toward the inner peripheral side and a lower dielectric constant ε toward the outer peripheral side. A DC power transmission method using the superconducting cable according to any one of claims 1 to 9,
The first superconducting layer provided in the first core is used for the outgoing line,
A DC power transmission method, wherein unipolar power transmission is performed using a second superconducting layer provided in a second core as a return line. A DC power transmission method using the superconducting cable according to any one of claims 1 to 9,
A superconducting cable has multiple first cores,
The first superconducting layer provided in at least one first core is used for power transmission of any one of the positive electrode and the negative electrode,
The first superconducting layer provided in the remaining first core is used for power transmission from the other pole.
A DC power transmission method, wherein bipolar power transmission is performed using a second superconducting layer provided in a second core as a neutral wire. A superconducting cable formed by twisting a plurality of cable cores,
This cable is formed by twisting two cable cores and a refrigerant pipe,
The cable core is
A superconducting conductor layer;
An insulating layer provided on the outer periphery of the superconducting conductor layer;
Comprising an external superconducting layer provided on the outer periphery of the insulating layer;
The superconducting cable is characterized in that the refrigerant pipe has the same diameter as the cable core.   13. The superconducting cable according to claim 12, wherein the twisted structure of the two-core core has a shrinkage allowance when the cable is cooled.   The refrigerant pipe according to claim 12 or 13, characterized in that the refrigerant pipe has a stretchability that can be shrunk when the cable is cooled, and is twisted together with the two cores without having a slack for shrinking when the cable is cooled. The superconducting cable described.   15. The superconducting cable according to claim 14, wherein the refrigerant pipe is a metal corrugated pipe.   16. The superconducting cable according to claim 12, further comprising a protective layer on an outer periphery of the refrigerant pipe.   The insulating layer is ρ-graded so that the resistivity on the inner peripheral side of the insulating layer is low and the resistivity on the outer peripheral side is high so that the DC electric field distribution in the radial direction is smoothed. The superconducting cable according to any one of claims 12 to 16,   18. The superconducting cable according to claim 17, wherein the insulating layer has a high ε layer having a higher dielectric constant than other portions in the vicinity of the superconducting conductor layer.   18. The superconducting cable according to claim 17, wherein the insulating layer is configured such that the dielectric constant ε is higher toward the inner peripheral side and the dielectric constant ε is lower toward the outer peripheral side. A DC power transmission method using the superconducting cable according to any one of claims 12 to 19,
The superconducting conductor layer provided in both cores is used for the outgoing line,
A direct current power transmission method characterized by performing unipolar power transmission using external superconducting layers provided in both cores as return lines. A DC power transmission method using the superconducting cable according to any one of claims 12 to 19,
The superconducting conductor layer provided in one core is used for power transmission of either the positive electrode or the negative electrode,
The superconducting conductor layer provided on the other core is used for power transmission on the other pole,
A direct current power transmission method, wherein bipolar transmission is performed using an external superconducting layer provided in each core as a neutral wire.

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