JP4604775B2 - Superconducting cable - Google Patents

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 reduce the outer diameter of the cable.

  Conventionally, as a superconducting cable for alternating current, a three-core package type cable in which three cable cores are integrated is known. FIG. 4 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, bipolar power transmission is performed using each cable core as a positive electrode core, a negative electrode core, and a neutral wire core.

JP 2003-249130 A

  The superconducting cable disclosed in Patent Document 1 can perform bipolar power transmission with a single cable. However, since this cable has three cable cores in one cable, the outer diameter of the cable increases, so it may not be applicable depending on the installation space. Therefore, it is desired to develop a superconducting cable capable of reducing the outer diameter of the cable when performing DC power transmission. Also, the AC superconducting cable shown in FIG. 4 has a three-core core in a single cable, so that the outer diameter of the cable is large like the cable of Patent Document 1.

  Accordingly, a main object of the present invention is to provide a superconducting cable having a smaller cable outer diameter. 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 number of cores provided in one cable.

  That is, the superconducting cable of the present invention is formed by twisting two cable cores having the following configuration. Each cable core includes 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 DC power transmission method of the present invention is a power transmission method using the superconducting cable, and performs power transmission using a superconducting conductor layer and an external superconducting layer included in the cable core as follows.
(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 let the external superconducting layer of each core be a neutral wire layer.

  In the AC superconducting cable shown in FIG. 4 and the DC superconducting cable disclosed in Patent Document 1, the cores are twisted in three strands so that the cable core contracts during cooling. Yes. However, a configuration in which a single cable has a three-core core increases the cable diameter.

  For example, three cores of cable cores, including a former, superconducting conductor layer, insulating layer, copper shield layer, and protective layer, are prepared in order from the center, and each core is a positive core, negative core, and neutral wire core. Consider the size of the cable. When the outer diameter of the superconducting conductor layer including the former is 20 mm, the thickness of the insulating layer is 5 mm, the thickness of the shield layer is 1 mm, and the thickness of the protective layer is 2 mm, the diameter of the envelope circle of the three cores is (36 /√3+18)×2≒77.6mm. Further, when a spacer having a thickness of 5 mm is disposed between the cores to give slack, the diameter of the envelope circle at this time is (41 / √3 + 18) × 2≈83.3 mm.

  On the other hand, when a DC superconducting cable is used as an external superconducting layer with a shield layer formed of a superconducting material and used as a return line or neutral wire layer, the core can be made of two cores. The cable diameter can be made smaller than the superconducting cable provided. For example, in the same way as above, in order from the center, prepare two cable cores including a former, superconducting conductor layer, insulating layer, external superconducting layer, and protective layer, and each core superconducting conductor layer for positive and negative power transmission, respectively. We consider a superconducting cable that uses the outer superconducting layer of both cores as a neutral wire layer. When the outer diameter of the superconducting conductor layer including the former is 20 mm, the thickness of the insulating layer is 5 mm, the outer superconducting layer is 1 mm, and the thickness of the protective layer is 2 mm, the diameter of the envelope circle of the two cores is (20 + 5 × 2 + 1 × 2 + 2 × 2) × 2 = 72mm. In addition, when a spacer having a thickness of 5 mm is disposed between the cores so as to have a slack, the diameter of the envelope circle is 72 + 5 = 77 mm. When two cores are used in this way, the cable diameter can be reduced as compared with the superconducting cable having a structure in which three cable cores are twisted together.

  Even in superconducting cables for AC, three-phase AC power transmission can be performed by using superconducting cables with two cores in multiple strips, and the outer diameter of one strip can be reduced. .

  Therefore, the present invention stipulates that the core has two cores. Hereinafter, the present invention will be described in more detail.

  The superconducting cable of the present invention is formed by twisting two cable cores comprising 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. To do. In particular, in the present invention, an external superconducting layer is used as a return line in unipolar transmission, and an external superconducting layer is formed of a superconducting material in order to flow positive and negative imbalance currents and abnormal currents in bipolar transmission. To do.

  The superconducting conductor layer may be formed, for example, by spirally winding a tape-like wire material in which a plurality of filaments made of Bi2223 series superconducting material are arranged in a matrix such as a silver sheath, and may be a single layer or a multilayer . 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.). Such a superconducting conductor layer is formed by winding a wire made of the 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. The former functions as a shape maintaining member for the superconducting conductor layer. A cushion layer may be interposed between the former and the superconducting conductor 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 insulating layer may be formed by winding semi-synthetic insulating paper such as PPLP (registered trademark) or insulating paper such as kraft paper. This insulating layer has an insulation strength necessary for insulation between the superconducting conductor layer and the ground.

  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. Therefore, it is preferable that the outer diameter of the cable can be made smaller. 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, if the insulating layer has a high ε layer having a dielectric constant higher than that of other portions in the vicinity of the superconducting conductor 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 can be suitably used for direct current power transmission. On the other hand, most of current transmission lines are composed of alternating current. In the future, when considering shifting the power transmission method from AC to DC, a case is assumed in which AC is transiently transmitted using the cable of the present invention before shifting to 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?

  An external superconducting layer is provided on the insulating layer. This external superconducting layer is formed of a superconducting material in the same manner as the superconducting conductor layer. The superconducting material used for the external superconducting layer may be the same as that used for forming the superconducting conductor layer. Further, the external superconducting layer is set to the ground potential. When performing bipolar power transmission using the superconducting cable of the present invention, the positive current and the negative current are generally almost the same size and cancel each other, so the external superconducting layer functioning as a neutral wire layer has a voltage 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. In order to flow through the external superconducting layer (function as a return line for monopolar power transmission), the external superconducting layer is formed of a superconducting material. 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.

  By preparing two cable cores having the above configuration and twisting the two cores, the superconducting cable of the present invention can have a shrinkage allowance when the cable is cooled. An example of a configuration that has a shrinkage allowance, that is, a configuration that absorbs heat shrinkage, is to provide a slack in twisting of each core. 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 superconducting cable of the present invention is configured by twisting the two cores and storing them 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 surface of the cable 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 cable core, and this space serves as a refrigerant flow path. 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.

  It is preferable that the refrigerant flow path in the inner pipe of the heat insulating pipe be a refrigerant forward path and be provided with a refrigerant return path separately because intrusion heat can be reduced. An example of the refrigerant return path is to use a refrigerant pipe. It is preferable that the refrigerant pipe be twisted together with the two cores because it is easy to arrange in the heat insulating pipe. In order to prevent the outer diameter of the cable from increasing by providing the refrigerant pipe, the diameter of the refrigerant pipe is less than the diameter of the core, and the diameter of the envelope circle between the two cores and the refrigerant pipe is the envelope circle of the two cores. The size is the same as the diameter of. There may be one or more such refrigerant tubes.

  It is preferable that the refrigerant pipe has a stretchability capable of contracting when the cable is cooled. Examples of the stretchable refrigerant pipe include a corrugated pipe made of a metal material such as stainless steel having excellent strength even at the refrigerant temperature. In the case of using a stretchable refrigerant tube, it may be twisted with the two cores without having a slack for contraction when the cable is cooled as in the case of twisting the two cores. This is because the contraction can be absorbed by the stretchability of the refrigerant pipe itself without securing the slack for contraction like twisting of the two cores. Further, a kraft paper or the like may be wound around the outer periphery of the refrigerant pipe to provide a protective layer. By providing the protective layer, it is possible to suppress problems such as the refrigerant pipe coming into contact with the core and the heat insulating pipe and damaging them.

  The superconducting cable of the present invention having the above configuration can perform unipolar power transmission by using the superconducting conductor layer provided in both cores for the forward line and using 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 one of the positive electrode and 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 provided in each core is a neutral wire Bipolar power transmission can be performed by using it as a layer. 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 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. When direct current power transmission is performed after single-phase alternating current power transmission using this superconducting cable, either unipolar power transmission or bipolar power transmission may be performed. When performing three-phase AC power transmission, prepare two or three superconducting cables of the present invention 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 reserved, the remaining three cores are used for power transmission in each phase, and the external superconducting layer is used. It is good to use as a shield layer. When using three cables, the superconducting conductor layer of each cable should be used for power transmission in each phase, and the external superconducting layer should be used as a shield layer. In other words, it is better to perform one-phase power transmission with two cores. When direct current power transmission is performed after three-phase alternating current power transmission using these superconducting cables, each cable may perform either unipolar power transmission or bipolar power transmission.

  The superconducting cable of the present invention having the above configuration can perform bipolar power transmission with a single cable while reducing the outer diameter of the cable. In addition, when an abnormality occurs in one of the poles, power transmission can be performed by switching from bipolar transmission to unipolar transmission. Furthermore, the superconducting cable of the present invention can reduce intrusion heat by providing the refrigerant pipe without increasing the cable outer diameter.

  In addition, in the core provided in the superconducting cable of the present invention, by making the insulating layer subjected to ρ grading, the DC electric field distribution is smoothed over the entire thickness direction of the insulating layer, and the DC withstand voltage characteristics are improved. The thickness of the insulating layer can be reduced. Therefore, the outer diameter of the cable can be further reduced. Further, by providing the insulating layer so that the vicinity of the superconducting conductor layer has a high ε in addition to the ρ grading, the Imp. Withstand voltage characteristic can be improved in addition to the improvement in the DC withstand voltage characteristic described above. 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.

  FIG. 1 (A) is a schematic configuration diagram showing a state in which a DC transmission line for single-pole power transmission is constructed using the superconducting cable of the present invention, and (B) is a diagram in which spacers are interposed between the cable cores of the cable. It is a schematic sectional drawing which shows a state. In the drawings, the same reference numerals denote the same items. The superconducting cable 1 has a configuration in which two cable cores 2 having a superconducting conductor layer 4 and an external superconducting layer 6 made of a superconducting material are twisted together and accommodated in a heat insulating tube 8. Each cable core 2 includes a former 3, a superconducting conductor layer 4, an insulating layer 5, an external superconducting layer 6, and a protective layer 7 in order from the center.

  In this example, the superconducting conductor layer 4 and the external superconducting layer 6 were formed of Bi2223 superconducting tape wires (Ag-Mn sheath wires). The superconducting conductor layer 4 was formed on the outer periphery of the former 3 and the outer superconducting layer 6 was formed on the outer periphery of the insulating layer 5 by spirally winding the superconducting tape wire. The former 3 was formed by twisting a plurality of copper wires, and a cushion layer (not shown) was formed between the former 3 and the superconducting conductor layer 4 with insulating paper. The insulating layer 5 was formed by winding semi-synthetic insulating paper (PPLP: registered trademark of Sumitomo Electric Industries, Ltd.) around the outer periphery of the superconducting conductor layer 4. This insulating layer 5 was provided so as to have an insulation strength necessary for insulation between the superconducting conductor layer 4 and the ground. The protective layer 7 was provided by winding kraft paper around the outer periphery of the external superconducting layer 6.

  In this example, two cable cores 2 comprising these former 3, superconducting conductor layer 4, insulating layer 5, external superconducting layer 6 and protective layer 7 are prepared, and have slack so as to have a shrinkage margin necessary for heat shrinkage. They are twisted together and stored in the heat insulating tube 8. In this example, the heat insulating pipe 8 uses a SUS corrugated pipe, and in the same manner as the conventional superconducting cable shown in FIG. 4, a heat insulating material (not shown) is provided between the double pipe consisting of the outer pipe 8a and the inner pipe 8b. Were arranged in multiple layers, and a vacuum multi-layer heat insulation configuration was formed in which the inside of the double tube was evacuated. A space 9 surrounded by the inner tube 8b and the two cable cores 2 serves as a flow path for a refrigerant such as liquid nitrogen. Further, an anticorrosion layer (not shown) was formed on the outer periphery of the heat insulating tube 8 with polyvinyl chloride. Further, in order to twist the cable core 2 with a slack, twist it with the spacer 90 interposed between the cable cores 2 as shown in FIG. The spacer 90 was removed when forming 8). In this example, the spacer 90 is a 5 mm thick felt having a rectangular cross section.

  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 10 connected to an AC system (not shown) is connected to one end side of a superconducting conductor layer 4 provided in the right core 2 in FIG. A cross flow converter 11 connected to an AC system (not shown) is connected to the other end side of the superconducting conductor layer 4 via a lead 22. In FIG. 1 (A), a cross flow converter 10 is similarly connected to one end side of the superconducting conductor layer 4 provided in the left core 2 via a lead 23 and a lead 21, and the other end of the superconducting conductor layer 4 is connected. On the side, the cross flow converter 11 is connected via a lead 22. The external superconducting layers 6 of both cores 2 are connected to the crossflow converter 10 via leads 24, leads 25 and leads 26, and are connected to the crossflow converter 11 via leads 27. In this example, the lead 26 is grounded. By this grounding, the external superconducting layer 6 becomes a ground potential. In this example, one-end grounding is used, but the lead 27 may also be grounded and both-end grounding. The leads 20 to 27 electrically connect the superconducting conductor layer 4 and the external superconducting layer 6 to the crossflow transducers 10 and 11.

  In a DC transmission line having the above configuration, a unipolar current is passed through the superconducting conductor layer 4 provided in both cores 2 to be used as an outgoing line, and a return current is supplied to the external superconducting layer 6 provided in both cores 2 to return. Unipolar power transmission can be performed by using it as a track. In addition, since this superconducting cable has a slack and twists the two cable cores, the slack can absorb heat shrinkage during cooling. Furthermore, since the superconducting cable 1 has a smaller number of cores than the conventional cable, the cable diameter can be reduced.

  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 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 of one core and an external superconducting layer. It is a schematic block diagram which shows the state which constructed | assembled the DC power transmission line which performs monopolar power transmission. 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, a cross flow converter connected to an AC system (not shown) on one end side of the superconducting conductor layer 4 provided in one core 2 (the right core 2 in FIG. 2A). 12 is connected via a lead 30, and a cross flow converter 13 connected to an AC system (not shown) is connected to the other end side of the superconducting conductor layer 4 via a lead 31. Further, a cross flow converter 12 is connected to one end side of the external superconducting layer 6 included in the core 2 via leads 32 and 33, and a cross flow converter 13 is connected to the other end side of the external superconducting layer 6. Connected via lead 34. On one end side of the superconducting conductor layer 4 included in the other core 2 (the left core 2 in FIG. 2A), a cross flow converter 14 connected to an AC system (not shown) is connected via a lead 35. A cross flow converter 15 connected to an AC system (not shown) is connected to the other end of the superconducting conductor layer 4 via a lead 36. Further, a cross flow converter 14 is connected to one end side of the external superconducting layer 6 included in the core 2 via leads 37 and 33, and a cross flow converter 15 is connected to the other end side of the external superconducting layer 6. Connected via lead 34. The lead 33 is grounded. By this grounding, the external superconducting layer 6 becomes a ground potential. In this example, only the lead 33 is grounded and one end is grounded, but the lead 34 may be grounded and both ends grounded. The leads 30 to 37 are for electrically connecting the superconducting conductor layer 4 and the external superconducting layer 6 to the crossflow transducers 12, 13, 14, and 15.

  With the above configuration, the cross flow converter 13, the lead 31, the superconducting conductor layer 4, the lead 30, the cross flow transducer 12, the lead 33, the lead 32, the external superconducting layer 6, the lead on the right core 2 in FIG. A positive route of 34 is established. Also, the cross flow converter 15, the lead 36, the superconducting conductor layer 4, the lead 35, the cross flow converter 14, the lead 33, the lead 37, the external superconducting layer 6, and the lead 34 on the left core 2 in FIG. A negative path is established. Bipolar power transmission can be performed by these positive and negative paths. At this time, the external superconducting layer 6 of both cores 2 is used not only as a neutral wire layer 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, a single pole using the superconducting conductor layer of the pole that does not cause an abnormality Electric power can be transmitted. For example, when an abnormality occurs in the left core 2 or the crossflow converters 14 and 15 in FIG. 2 (A), that is, when an abnormality occurs in the negative electrode, the left core 2 is used in FIG. 2 (A). Stop power transmission. At this time, as shown in FIG. 2 (B), a transmission line for unipolar power transmission using one core 2 (the right core 2 in FIG. 2) is constructed, and the superconducting conductor layer 4 of this core 2 is connected to the outgoing line. Then, unipolar power transmission can be performed using the external superconducting layer 6 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 with the superconducting conductor layer 4 of the other core 2 (the left core 2 in FIG. 2) as the forward line and the external superconducting layer 6 as the return line.

  As described above, the superconducting cable of the present invention is a single cable, and can perform both bipolar power transmission and monopolar power transmission. In particular, since the number of cable cores provided in one cable is two, the outer diameter of the cable can be reduced as compared with a configuration including three cores.

When direct current power transmission is performed as described above, if ρ grading is performed so that the resistivity on the inner peripheral side of the insulating layer 5 is low and the resistivity on the outer peripheral side is high, the DC electric field distribution in the thickness direction of the insulating layer is smoothed. As a result, the thickness of the insulating layer can be further reduced. 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. In addition, when a high ε layer is provided in the vicinity of the superconducting conductor layer 4 in the insulating layer 5, the Imp. Withstand voltage characteristic can be improved in addition to the improvement in 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. Further, in addition to the ρ grading, if the insulating layer 5 is 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 performing three-phase AC power transmission using the superconducting cable 1, it is preferable to prepare the superconducting cable 1 with two or three. When using two-wire cable 1, out of the four cores 2 included in the two-wire cable 1, one core 2 is used as a spare core, and the remaining three cores 2 are each of the superconducting conductor layer 4 It is preferable to use the outer superconducting layer 6 of the core 2 as a shield layer for power transmission. When using the three cable 1s, each cable 1 is used for phase transmission. That is, one-phase power transmission is performed by the two cores 2 included in each cable 1. At this time, the superconducting conductor layer 4 of the two cores 2 provided in each cable 1 is used for phase power transmission, and the external superconducting layer 6 provided on the outer periphery of these superconducting conductor layers 4 is used as a shield layer. When single-phase AC power transmission is performed using superconducting cable 1, one superconducting cable 1 is prepared, superconducting conductor layer 4 of each core 2 is used for power transmission in the same phase, and the outer periphery of superconducting conductor layer 4 is provided. The external superconducting layer 6 may be used as a shield layer.

  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.

  Next, a configuration including both the refrigerant forward path and the refrigerant return path will be described. FIG. 3 is a schematic cross-sectional view of a superconducting cable of the present invention formed by twisting two cores and a refrigerant pipe. In the first and second embodiments, the configuration in which the inner pipe of the heat insulating pipe is used as the refrigerant flow path has been described. However, as shown in FIG. 3, the refrigerant pipe 40 is separately provided, the space 9 in the inner pipe is used as the refrigerant forward path, and the refrigerant The inside of the pipe 40 may be a refrigerant return path. Thus, by providing a reciprocating path of the refrigerant, intrusion heat can be reduced.

  In this example, two refrigerant pipes 40 are prepared and twisted together with two cable cores 2. Particularly in this example, a stainless corrugated pipe was used as the refrigerant pipe 40. When a flexible tube such as a corrugated tube is used, the contraction during cooling of the cable can be absorbed by the stretchability of the refrigerant tube 40 itself. Therefore, when twisting with the two cable cores 2, the refrigerant tube 40 was twisted without giving the slack for shrinkage.

  The refrigerant tube 40 has a diameter smaller than the diameter of the cable core 2, and as shown in FIG. 3, an envelope circle between the two refrigerant tubes 40 and the two cores 2 (broken line in FIG. 3). The diameter of the circle) was made equal to the diameter of the envelope circle of the core 2 with 2 cores. Therefore, even if the refrigerant tube 40 is provided in addition to the two-core cable core 2, this superconducting cable is compared with the superconducting cable 1 shown in Examples 1 and 2 that does not include the refrigerant tube 40. Will not grow. In this example, the number of the refrigerant tubes 40 is two, but may be one, or may be three or more. However, the size of the refrigerant tube is selected so that the diameter of the envelope circle between the refrigerant tube and the two-core cable core is equal to the diameter of the envelope circle of the two-core core.

  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.

(A) is a schematic configuration diagram showing a state in which a DC transmission line is constructed using the superconducting cable of the present invention, (B) is a schematic cross-sectional view showing a state in which a spacer is interposed between cable cores in the cable. It is. (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, (B) is a single pole using a superconducting conductor layer of one core and an external superconducting layer. It is a schematic block diagram which shows the state which constructed | assembled the DC power transmission line for power transmission. It is a cross-sectional schematic diagram of the superconducting cable of the present invention formed by twisting a two-core cable core and a refrigerant pipe. It is sectional drawing of the superconducting cable for three-phase collective type three-phase alternating current.

Explanation of symbols

1 Superconducting cable 2 Cable core 3 Former 4 Superconducting conductor layer
5 Insulating layer 6 Outer superconducting layer 7 Protective layer 8 Heat insulation tube 8a Outer tube 8b Inner tube
9 space 10-15 cross flow transducer
20 to 27, 30 to 37 Lead 40 Refrigerant tube 90 Spacer
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 (10)

A superconducting cable formed by twisting a plurality of cable cores,
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;
A superconducting cable formed by twisting two cable cores.   2. The superconducting cable according to claim 1, wherein the twisted structure of the two-core core has a shrinkage allowance when the cable is cooled. Furthermore, the two cores and at least one refrigerant pipe are twisted together,
The refrigerant pipe has a diameter less than that of the core;
3. The superconducting cable according to claim 1, wherein the diameter of the envelope circle between the two cores and the refrigerant tube is the same as the diameter of the envelope circle of the two cores.   4. The refrigerant tube according to claim 3, wherein the refrigerant tube has a stretchable property that can be contracted when the cable is cooled, and is twisted together with a core of two cores without giving a slack for contracting when the cable is cooled. Superconducting cable.   5. The superconducting cable according to claim 4, wherein the refrigerant pipe is a metal corrugated 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 1 to 5, wherein   7. The superconducting cable according to claim 6, 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.   7. The superconducting cable according to claim 6, 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 8,
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 1 to 8,
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 power transmission is performed using the external superconducting layers of both cores as a neutral wire layer.

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