JPWO2015033768A1 - Superconducting cable - Google Patents

Abstract

Provided is a superconducting cable that can flow a large current using the longitudinal magnetic field effect and that can realize a function for limiting the current with the cable itself when an excessive current occurs. A superconducting cable 1 having an inner conductor 3 for energizing a direct current using a longitudinal magnetic field effect and a shield layer 5 for energizing a direct current in the opposite direction to the inner conductor so that the longitudinal magnetic field in the inner conductor 3 increases. Thus, when the current capacity of the shield layer 5 is smaller than the current capacity of the inner conductor 3, the current is shunted when the current flowing through the shield layer 5 exceeds the current capacity of the shield layer 5. And the inner conductor 3 has an inner conductive layer 6a for shunting current when the current flowing through the inner conductor 3 exceeds the current capacity of the inner conductor 3. When a current is passed through the layer 6b and the inner conductive layer 6a, the outer conductive layer 6b and the inner conductive layer 6a are formed so that the longitudinal magnetic field is reduced by the current.

Description

  The present invention relates to a superconducting cable having a current limiting function utilizing a longitudinal magnetic field effect.

  As a superconducting cable that realizes a force-free state or a state close to a force-free state using the longitudinal magnetic field effect, a technique shown in Patent Document 1 developed by the inventors is known. In the technique shown in Patent Document 1, in a superconducting cable that transmits power using a superconductor, the longitudinal direction of the superconducting cable is set as a reference direction, and at a positive or negative angle relative to the reference direction. A conductive portion made of a superconductive material arranged in a spiral shape, the conductive portion is composed of a plurality of layers, and the spiral angle is sequentially different from the reference direction from the innermost layer toward the outermost layer, A magnetic field is generated in the same direction as the current flow by the current flowing through the conductive portion, and the layer formed by the conductive portion is an inner layer, and is formed by the conductive portion made of the superconductive material. With respect to the reference direction, an outer layer disposed in a spiral direction opposite to a spiral direction of the conductive portion disposed in the inner layer, and an insulation disposed between the inner layer and the outer layer. A direct current superconducting reciprocating transmission cable comprising a layer.

  The force-free superconducting power cable shown in Patent Document 1 applies a longitudinal magnetic field effect in which a critical current density is greatly increased under a longitudinal magnetic field to a DC superconducting power cable. FIG. 4A shows the difference in critical current density between a metallic superconductor under a transverse magnetic field (white circle) and a longitudinal magnetic field (black circle). In a force-free superconducting power cable, the characteristics under this longitudinal magnetic field are shown. Use. Therefore, the structure shown in FIG. 4B is used, and the current flowing through the outer shield superconductor on the return path is twisted in one direction so as to give a longitudinal magnetic field to the inner superconductor. On the other hand, in such a longitudinal magnetic field, a special force-free state (a state in which the Lorentz force does not work) is achieved in which the local current direction (direction of the superconductor to be wound) and the magnetic field are parallel to each other in the inner conductor. Apply a proper method of winding the superconducting wire. By adopting such a structure, the current capacity can be greatly increased as compared with a normal superconducting cable. FIG. 4C is a calculation example, and shows that the current capacity increases dramatically as the number of conductor layers in the cable increases.

  By the way, one of the obstacles to the spread of power generation using solar energy and wind power using renewable energy is the processing of surplus power, and for that purpose, without installing an expensive energy storage device, It is effective to achieve regional stabilization by expanding the power grid over a wide area and smoothing excesses and deficiencies. Although it is desired to develop a power network for such a stable power supply, at present, an excessive current due to a short circuit accident or a lightning strike becomes a problem, and a sufficient power network is not formed. In order to build such a wide-area power network, it is important to install a current limiter that can prevent excessive current in the event of an accident. In particular, in Europe and the United States, current limiters are being developed at a rapid pace.

  As a current limiter using superconductivity, (1) resistance transition type and (2) inductance type are well known. (1) The resistance transition type uses a high electrical resistance generated by the transition of the superconductor to the normal state, and (2) the inductance type is a current transformer with a large number of windings. The current is limited by utilizing the fact that the impedance viewed from the primary side becomes extremely large when the secondary side transitions to the normal conduction state, and is dedicated to alternating current. In addition to this, there is, for example, a superconducting transformer that has a current limiting function using (2).

  As a technique related to the above, for example, a technique shown in Patent Document 2 is disclosed. The technique shown in Patent Document 2 is a cryogenic container connected to the end of the superconducting cable so as to be able to flow through the cooling medium flow path of the superconducting cable, and cooling for circulating and supplying liquid nitrogen to the cryogenic container. And a superconducting current limiting element disposed in a cryogenic container and immersed in liquid nitrogen and electrically connected to a normal device through a current lead.

International Publication No. 2011/043376 JP 2009-27843 A

  However, the technique shown in Patent Document 2 has a problem that it is necessary to separately provide a current limiting function in the superconducting cable, and the structure becomes complicated, and it takes time and effort to manufacture and maintain.

  The present invention provides a superconducting cable that can flow a large current using the longitudinal magnetic field effect and can realize a function for limiting the current with the cable itself when an excessive current occurs.

  The superconducting cable according to the present invention increases the longitudinal magnetic field in the inner layer outside the insulating layer, the inner layer that conducts a direct current using the longitudinal magnetic field effect, the insulating layer that covers the inner layer, and the insulating layer. Thus, a superconducting cable having an outer layer that conducts a direct current in the opposite direction to the inner layer, the current capacity of the outer layer being smaller than the current capacity of the inner layer, and the outermost layer of the outer layer. The outer layer has a conductive layer for shunting current when the current flowing through the outer layer exceeds the current capacity of the outer layer, and when the current is passed through the conductive layer, The conductive layer is formed so that the magnetic field is reduced.

  Thus, in the superconducting cable according to the present invention, the inner layer that conducts a direct current using the longitudinal magnetic field effect, the insulating layer that covers the inner layer, and the inner layer outside the insulating layer A superconducting cable having an outer layer that conducts a direct current in the opposite direction to the inner layer so that a longitudinal magnetic field increases, and the current capacity of the outer layer is smaller than the current capacity of the inner layer, When the outermost layer has a conductive layer for shunting the current when the current flowing through the outer layer exceeds the current capacity of the outer layer, and the current is passed through the conductive layer Since the conductive layer is formed so that the longitudinal magnetic field is reduced by the current, when an excessive current flows, the current is shunted to the conductive layer included in the outer layer, and the longitudinal magnetic field is generated by the shunted current. The resistance is reduced by decreasing Transitions to an effect that it is possible to realize a current limiting function.

  In the superconducting cable according to the present invention, the longitudinal direction of the superconducting cable is a reference direction, and the inner layer is spirally arranged at an angle of either positive or negative with respect to the reference direction. A plurality of superconducting layers made of a superconducting member, wherein an angle of the spiral is gradually increased with respect to the reference direction from the innermost layer to the outermost layer of the plurality of superconducting layers, and the outer layer Has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer included in the inner layer with respect to the reference direction, and the conductive layer is formed on the outer side. The conductive layer is disposed in a spiral direction opposite to the spiral direction of the superconducting layer of the layer.

  As described above, in the superconducting cable according to the present invention, the longitudinal direction of the superconducting cable is a reference direction, and the inner layer is spiral at an angle of either positive or negative with respect to the reference direction. A plurality of superconducting layers made of superconducting members, and the angle of the spiral is gradually increased with respect to the reference direction from the innermost layer to the outermost layer of the plurality of superconducting layers. The outer layer has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer included in the inner layer with respect to the reference direction, and the conductive layer Since the layer is made of a conductive member arranged in a spiral direction opposite to the spiral direction of the superconducting layer of the outer layer, the longitudinal magnetic field can be reduced by the current flowing in the conductive layer, and the current limiting function The effect that can be realized

  In the superconducting cable according to the present invention, the direction of the current flowing through the conductive layer is the same as the direction of the current flowing through the outer layer.

  Thus, in the superconducting cable according to the present invention, the direction of the current flowing in the conductive layer is the same as the direction of the current flowing in the outer layer, so that the longitudinal magnetic field can be reduced by the current flowing in the conductive layer. The current limiting function can be realized.

  The superconducting cable according to the present invention increases the longitudinal magnetic field in the inner layer outside the insulating layer, the inner layer that conducts a direct current using the longitudinal magnetic field effect, the insulating layer that covers the inner layer, and the insulating layer. Thus, a superconducting cable having an outer layer that conducts a direct current in the opposite direction to the inner layer, the current capacity of the outer layer being smaller than the current capacity of the inner layer, A conductive layer for shunting the current when the current flowing through the inner layer exceeds the current capacity of the inner layer, the outer layer being inside the insulating layer; In this case, the conductive layer is formed so that the longitudinal magnetic field is reduced by the current.

  Thus, in the superconducting cable according to the present invention, the inner layer that conducts a direct current using the longitudinal magnetic field effect, the insulating layer that covers the inner layer, and the inner layer outside the insulating layer A superconducting cable having an outer layer that conducts a direct current in the opposite direction to the inner layer so that a longitudinal magnetic field increases, and the current capacity of the outer layer is smaller than the current capacity of the inner layer, A conductive layer for shunting the current when the current flowing through the inner layer exceeds the current capacity of the inner layer, the outermost layer of the inner layer and inside the insulating layer; When the current is applied to the current layer, the conductive layer is formed so that the longitudinal magnetic field is reduced by the current, so when an excessive current flows, the current is shunted to the conductive layer of the inner layer, A longitudinal magnetic field is generated by the shunt current. By decreasing transitions to resistance state, an effect that it is possible to realize a current limiting function.

  In the superconducting cable according to the present invention, the longitudinal direction of the superconducting cable is a reference direction, and the inner layer is spirally arranged at an angle of either positive or negative with respect to the reference direction. A plurality of superconducting layers made of a superconducting member, wherein an angle of the spiral is gradually increased with respect to the reference direction from the innermost layer to the outermost layer of the plurality of superconducting layers, and the outer layer Has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer included in the inner layer with respect to the reference direction, and the conductive layer is formed on the inner side. The conductive layer is disposed in a spiral direction opposite to the spiral direction of the superconducting layer of the layer.

  As described above, in the superconducting cable according to the present invention, the longitudinal direction of the superconducting cable is a reference direction, and the inner layer is spiral at an angle of either positive or negative with respect to the reference direction. A plurality of superconducting layers made of superconducting members, and the angle of the spiral is gradually increased with respect to the reference direction from the innermost layer to the outermost layer of the plurality of superconducting layers. The outer layer has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer included in the inner layer with respect to the reference direction, and the conductive layer Since the layer is made of a conductive member disposed in a spiral direction opposite to the spiral direction of the superconducting layer of the inner layer, the longitudinal magnetic field can be reduced by the current flowing in the conductive layer, and the current limiting function The effect that can be realized

  In the superconducting cable according to the present invention, the direction of the current flowing through the conductive layer is the same as the direction of the current flowing through the inner layer.

  Thus, in the superconducting cable according to the present invention, the direction of the current flowing through the conductive layer is the same as the direction of the current flowing through the inner layer, so that the longitudinal magnetic field can be reduced by the current flowing through the conductive layer. The current limiting function can be realized.

  The superconducting cable according to the present invention increases the longitudinal magnetic field in the inner layer outside the insulating layer, the inner layer that conducts a direct current using the longitudinal magnetic field effect, the insulating layer that covers the inner layer, and the insulating layer. Thus, a superconducting cable having an outer layer that conducts a direct current in the opposite direction to the inner layer, the current capacity of the outer layer being smaller than the current capacity of the inner layer, and the outermost layer of the outer layer. The outer layer has an outer conductive layer for shunting the current when the current flowing through the outer layer exceeds the current capacity of the outer layer, and is the outermost layer of the inner layer and inside the insulating layer. When the current flowing in the inner layer exceeds the current capacity of the inner layer, the inner conductive layer for shunting the current is provided, and the current is passed through the outer conductive layer and the inner conductive layer. , So that the longitudinal magnetic field is reduced by the current In which Kisotogawa conductive layer and the inner conductive layer is formed.

  Thus, in the superconducting cable according to the present invention, the inner layer that conducts a direct current using the longitudinal magnetic field effect, the insulating layer that covers the inner layer, and the inner layer outside the insulating layer A superconducting cable having an outer layer that conducts a direct current in the opposite direction to the inner layer so that a longitudinal magnetic field increases, and the current capacity of the outer layer is smaller than the current capacity of the inner layer, The outermost layer of the outer layer has an outer conductive layer for shunting current when the current flowing through the outer layer exceeds the current capacity of the outer layer, and is the outermost layer of the inner layer, Inside the insulating layer, there is an inner conductive layer for shunting the current when the current flowing through the inner layer exceeds the current capacity of the inner layer, and current is passed through the outer conductive layer and the inner conductive layer. When energized, the current Since the outer conductive layer and the inner conductive layer are formed so as to reduce the field, when an excessive current flows, the current is divided into the conductive layers of the inner layer and the outer layer, and the divided current is divided. By reducing the longitudinal magnetic field due to the current, it is possible to transition to the resistance state and realize the current limiting function.

  In the superconducting cable according to the present invention, the longitudinal direction of the superconducting cable is a reference direction, and the inner layer is spirally arranged at an angle of either positive or negative with respect to the reference direction. A plurality of superconducting layers made of a superconducting member, wherein the angle of the spiral is gradually increased with respect to the reference direction from the innermost layer to the outermost layer of the superconducting layers, The outer layer has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer included in the inner layer with respect to the reference direction, and the outer conductive layer includes The conductive layer is disposed in a spiral direction opposite to the spiral direction of the superconducting layer of the outer layer, and the inner conductive layer is opposite to the spiral direction of the superconducting layer of the inner layer. The conductive member is arranged in the spiral direction.

  As described above, in the superconducting cable according to the present invention, the longitudinal direction of the superconducting cable is a reference direction, and the inner layer is spiral at an angle of either positive or negative with respect to the reference direction. A plurality of superconducting layers made of superconducting members, and the spiral angle gradually increases with respect to the reference direction from the innermost layer to the outermost layer of the plurality of superconducting layers. The superconducting layer is composed of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer included in the inner layer with respect to the reference direction. The outer conductive layer is made of a conductive member disposed in a spiral direction opposite to the spiral direction of the superconductive layer included in the outer layer, and the inner conductive layer is formed of the superconductive layer included in the inner layer. Is it a conductive member arranged in a spiral direction opposite to the spiral direction? Becomes therefore, the current flowing in the conductive layer can be reduced vertical magnetic field, an effect that it is possible to realize a current limiting function.

  In the superconducting cable according to the present invention, the direction of the current flowing in the outer conductive layer is the same as the direction of the current flowing in the outer layer, and the direction of the current flowing in the inner conductive layer is the direction of the current flowing in the inner layer. And the same direction.

  Thus, in the superconducting cable according to the present invention, the direction of the current flowing through the outer conductive layer is the same as the direction of the current flowing through the outer layer, and the direction of the current flowing through the inner conductive layer is the inner layer. Therefore, the longitudinal magnetic field can be reduced by the current flowing through the conductive layer, and the current limiting function can be realized.

  In the superconducting cable according to the present invention, the spiral angles of the outer conductive layer and the inner conductive layer with respect to the reference direction are 20 ° or more and 60 ° or less, respectively.

  Thus, in the superconducting cable according to the present invention, a sufficient current-limiting effect can be obtained by setting the spiral angles of the outer conductive layer and the inner conductive layer with respect to the reference direction to 20 ° or more and 60 ° or less, respectively. While achieving the above, there is an effect that the amount of the conductive wire in the conductive layer can be suppressed and winding can be facilitated to increase manufacturing efficiency.

It is a figure which shows the 1st structure of the superconducting cable which concerns on 1st Embodiment. It is a figure which shows the 2nd structure of the superconducting cable which concerns on 1st Embodiment. It is a figure which shows the 3rd structure of the superconducting cable which concerns on 1st Embodiment. It is a figure which shows the characteristic of a force free superconducting power cable.

  Embodiments of the present invention will be described below. The present invention can be implemented in many different forms. Also, the same reference numerals are given to the same elements throughout the present embodiment.

(First embodiment of the present invention)
A superconducting cable according to the present embodiment will be described with reference to FIGS. The superconducting cable according to the present embodiment is obtained by adding a current limiting function to a force-free superconducting power cable that can realize a force-free state or a state close to a force-free state and allow a large current to flow. That is, the present invention relates to a current limiting function of a superconducting cable that increases the current capacity by utilizing the longitudinal magnetic field effect.

  As shown in FIG. 4 (B), the force-free superconducting power cable is formed in a cylindrical shape and has a structure in which inner conductors having different cross-sectional diameters are laminated in multiple layers (three layers in the figure). The laminated inner conductor is covered with an insulating layer. On the outside of the insulating layer, a shield layer is formed in a multilayer structure (three layers in the figure) that energizes current in the opposite direction to the inner conductor and shields the magnetic field generated by the inner conductor. . Each layer is hollow and is filled with a refrigerant such as liquid nitrogen.

  The inner conductor is formed by juxtaposing a plurality of superconducting tapes, and the superconducting tape in each layer has a longitudinal direction of the force-free superconducting power cable as a reference direction and is positive or negative with respect to the reference direction. They are arranged in a spiral at any one angle. In addition, the outer shield layer is formed by arranging a plurality of superconducting tapes in the same manner as the inner conductor, and the superconducting tape in each layer has a spiral in a direction opposite to the spiral direction in the inner conductor with respect to the reference direction. If the inner conductor is a positive angle, the shield layer is disposed at a negative angle, and if the inner conductor is a negative angle, the shield layer is disposed at a positive angle.

  Further, in each of the inner conductor layer and the outer shield layer, the angle of the spiral in which the superconducting tape is disposed is changed from the innermost layer which is the innermost layer to the radial direction to the outermost layer with respect to the radial direction. The spiral angle with respect to the reference direction gradually increases toward the outermost layer. The direction of the arrow in each layer in FIG. 4B is the direction in which the superconducting tape is disposed, and indicates the direction in which current flows. That is, the current flows in a spiral shape toward the reference direction and is transmitted.

  Here, if the current flowing through the inner conductor is I, the current I can be divided into a vertical component parallel to the reference direction and a horizontal component perpendicular to the reference direction. When the current I flows through the inner conductor and the angle of the spiral from the reference direction is θ, the longitudinal component current I cos θ generates a transverse magnetic field for the force-free superconducting power cable, and the transverse component current Isin θ is A longitudinal magnetic field is generated for the force-free superconducting power cable. As described above, since the critical current density of the superconductor increases under a longitudinal magnetic field, a large amount of power can be transmitted.

  Further, in the outer shield layer, the spiral direction is opposite to the inner conductor, and the current direction is also opposite. Therefore, the transverse magnetic field generated in the inner conductor can be canceled for the longitudinal current (ie, , And a longitudinal magnetic field generated by the inner conductor can be increased with respect to the current of the transverse component. That is, as shown in FIG. 4C, the critical current density can be significantly increased by applying a larger longitudinal magnetic field.

  The superconducting tape in the force-free superconducting power cable ideally spirals so that the current flows in an angle in which the direction of the flowing current and the direction of the longitudinal magnetic field are parallel, that is, J × B = 0. The angle is set and disposed (refer to Patent Document 1 for details). In addition, in the force-free superconducting power cable, in addition to the force-free state ideally satisfying J × B = 0, J × B = 0 is not completely satisfied, but the state is close to the force-free state. Things are also included.

  A current limiting function is added to such a force-free superconducting power cable. In other words, as described above, the characteristic of the resistance transition type fault current limiter is that when an excessive current flows, it quickly transitions to a resistance state and quickly attenuates the excessive current by generating a high resistance. The superconducting cable according to the embodiment uses the characteristic structure of the force-free superconducting power cable.

  FIG. 1 is a diagram showing a first structure of a superconducting cable according to the present embodiment. In FIG. 1, a superconducting cable 1 includes a former 2 disposed in a central portion and a plurality of layers (three layers in the figure) of inner conductors formed by arranging a plurality of superconducting tapes outside the former 2. 3, an insulating layer 4 outside the inner conductor 3, a plurality of layers (three layers in the figure) of the shielding layer 5 formed by arranging a plurality of superconducting tapes outside the insulating layer 4, and a shielding layer 5 A conductive layer 6 for diverting an excessive current is formed on the outside.

  In the inner conductor 3, the current flows in the reference direction, and as described above, each layer of the inner conductor 3 moves from the innermost layer toward the outermost layer in order to realize a force-free state or a force-free state. The spiral angle with respect to the reference direction is gradually increased. On the other hand, in the shield layer 5, current flows in a direction opposite to the reference direction, and each layer is formed in a spiral direction opposite to each layer of the inner conductor 3.

  The conductive layer 6 is not a superconductor but is made of a normal conductor (for example, copper or aluminum), and the current that was flowing in the shield layer 5 when an excessive current is generated is divided and flows in the shield layer 5. Current flows along the conductor in the same direction as the reference direction, that is, in the direction opposite to the reference direction. The conductive layer 6 is formed by being wound in a direction opposite to the spiral direction of the shield layer 5. That is, the transverse magnetic field of the inner conductor 3 is canceled by the longitudinal component current, and the longitudinal magnetic field of the inner conductor 3 is canceled by the transverse component current. As the longitudinal magnetic field of the inner conductor 3 decreases, the critical current decreases and the transition to the resistance state is performed at high speed.

  The current limiting process when an excessive current flows due to a ground fault or lightning strike will be described below. The superconducting cable 1 is formed such that the current capacity of the shield layer 5 is smaller than the current capacity of the inner conductor 3. Since the outer shield layer 5 is not realized force-free, there is no significant increase in current density. That is, the current capacity is reduced by reducing the superconducting material used for the shield layer 5.

  When an excessive current occurs, the shield current exceeding the current capacity of the shield layer 5 starts to shunt to the conductive layer 6, but the conductive layer 6 is wound in a direction opposite to the spiral direction of the shield layer 5, The longitudinal magnetic field is reduced. As a result, the current capacity of the inner conductor 3 decreases, resistance transition easily occurs, and a current limiting function is realized.

  FIG. 2 is a diagram showing a second structure of the superconducting cable according to the present embodiment. 2 is different from the case of FIG. 1 in that the conductive layer 6 is formed between the inner conductor 3 and the insulating layer 4. That is, when a resistance transition occurs in the inner conductor 3, a current flows along the conductor in the same direction as the current flowing in the inner conductor 3 in the conductive layer 6, that is, in the reference direction. Since the conductive layer 6 is wound in a direction opposite to the spiral direction of the inner conductor 3, the longitudinal magnetic field of the inner conductor 3 is reduced. Thereby, the current capacity of the inner conductor 3 is reduced, resistance transition is easily caused, and the current limiting function is realized.

  FIG. 3 is a diagram showing a third structure of the superconducting cable according to the present embodiment. The superconducting cable 1 in FIG. 3 has a structure in which the superconducting cable 1 in FIGS. 1 and 2 is combined, and an inner conductive layer 6 a is formed between the inner conductor 3 and the insulating layer 4, and the shield layer 5. An outer conductive layer 6b is formed on the outer side of the first electrode. The inner conductive layer 6 a and the outer conductive layer 6 b are made of a normal conductor such as copper or aluminum, and when an excessive current is generated in the inner conductor 3 or the shield layer 5, the current flowing through each layer is divided. That is, a current flows in the outer conductive layer 6b along the conductor in the same direction as the current flowing in the shield layer 5, that is, in a direction opposite to the reference direction, and the current flowing in the inner conductor 3 in the inner conductive layer 6a. A current flows along the conductor in the same direction, that is, in the reference direction. The inner conductive layer 6a is wound in a spiral direction opposite to the spiral direction of the inner conductor 3, and the outer conductive layer 6b is wound in a spiral direction opposite to the spiral direction of the shield layer 5. The reduction of the longitudinal magnetic field of the inner conductor 3 is promoted by the currents in the outer conductive layer 6b and the inner conductive layer 6a. Thereby, the current capacity of the inner conductor 3 is reduced, resistance transition is easily caused, and the current limiting function is realized.

  The current limiting process when an excessive current flows will be described below. Here again, the superconducting cable 1 is formed such that the current capacity of the shield layer 5 is smaller than the current capacity of the inner conductor 3. Since the outer shield layer 5 is not realized in a force-free state or a state close to a force-free state, there is no significant increase in current density. That is, the current capacity is reduced by reducing the superconducting material used for the shield layer 5.

  When an excessive current occurs, the shield current exceeding the current capacity of the shield layer 5 starts to shunt to the outer conductive layer 6b. However, the outer conductive layer 6b is wound in a direction opposite to the spiral direction of the shield layer 5. Therefore, the longitudinal magnetic field is reduced. As a result, the current capacity of the inner conductor 3 is reduced, and resistance transition easily occurs.

  When the inner conductor 3 starts a resistance transition, a part of the current flows to the inner conductive layer 6a. In particular, the inner conductive layer 6a formed just outside the inner conductor 3 has a direction opposite to the spiral direction of the inner conductor 3. When the current flows in the spiral direction, the longitudinal magnetic field is greatly reduced, the critical current is greatly reduced, the resistance transition is accelerated at once, and a strong current limit occurs. By such a process, when the transition to the high-speed resistance state starts, the speed of the temperature rise due to the generated heat increases, and the transition to the normal conduction state occurs at once, and the current is limited safely and reliably.

  In this way, in the force-free superconducting power cable, by making a structure that reduces the longitudinal magnetic field when an excessive current flows, the critical current decreases, and the transition to the normal state is performed at high speed. Safe and reliable current limiting function can be realized.

  In the above embodiment, each layer of the inner conductor 3 has a configuration in which the spiral angle with respect to the reference direction is sequentially increased from the innermost layer to the outermost layer in order to realize a force-free state or a force-free state. However, the spiral angle may be 0 °, that is, a state parallel to the reference direction. That is, the inner conductor 3 may have a configuration in which the current is supplied by increasing the current capacity in the reference direction of the inner conductor 3 by the longitudinal magnetic field effect by the shield layer 5 without generating a longitudinal magnetic field.

  In the following, the current limiting characteristics will be analyzed using one superconducting cable as an example. Here, the analysis is performed based on the structure of the superconducting cable 1 shown in FIG.

  Consider a case where the number n of superconducting layers of the inner conductor is eight. The radius of this superconducting layer is R = 2.0 × 10 ^-2m, and in this case, the longitudinal magnetic field due to the return flow through the shield layer 5 is μ₀H_e= 0.517 T, the average shielding current density of the shielding layer 5 is <J_c⊥> = 4.0 × 10¹⁰A / m²The critical current density of the inner conductor 3 in the force-free state is J_c‖= 8.0 × 10¹⁰A / m²The current capacity of the cable at this time is I_t= 89.6 kA. Details of these operations are based on a reference (T. Matsushita, M. Kiuchi, ESOtabe "Innovative superconducting force-free cable concept", Superconductors Science and Technology, Vol. 25 (2012) 125009, 8pp). Is.

Here, the current capacity of the shield layer 5 and (1-ε) _{I t,} here, the epsilon = 0.05. Next, the radius of the outer conductive layer 6b (copper) is R _s = 2.5 × 10 ⁻² m, and the winding angle θ _s is 40 °. The proportion of the stabilized copper disposed inside the insulating layer 4 that is disposed outside the inner conductor 3, that is, the proportion of the inner conductive layer 6a (copper) is represented by β (1-β is the central former ( Copper)), β = 1, and the winding angle θ _i is also 40 °.

  The outline will be briefly described below before entering into specific calculations. First, assuming that a current exceeding the current capacity flows in the superconducting layer, the magnetic flux flow state is reached. The resistance of the superconductor corresponding to this state is obtained. For example, it contributes to generation, and the cross-sectional area of the superconductor of the shield layer 5 is such that the thickness of the superconductive layer of the superconductive coated wire is d = 1.0 μm,

It becomes. Therefore, when the flow resistivity is ρ _f = 1.0 μΩcm, the resistance of the superconductor per 1 m of length is R _f ′ = 1.0 × 10 ⁻⁸ /1.25×10 ⁻⁶ = 80 [mΩ / m]. However, since the resistance of the stabilized copper is much less than 1 mΩ / m, all excess current may flow through the stabilized copper.

As an index of the current limiting characteristic, the current I _Cu flowing in the copper layer of the center conductor portion (former of the cable center portion) is used. The transport current I, when a decrease of the current capacity and [Delta] I _t,

Can be written. This decrease in current capacity is due to the decrease in the longitudinal magnetic field. Of these, if the decrease in the longitudinal magnetic field due to the current in the shield layer 5 is ΔB _s , and the decrease in the longitudinal magnetic field due to the current in the inner conductor 3 is ΔB _i ,

become that way. Here, α is a proportionality constant. Since the shield layer 5 is almost out of the force-free state, there is no need to consider the change in the critical current density due to the change in the longitudinal magnetic field, and ΔB _s is simply the transport current I being the current capacity (1-ε) of the shield layer 5. determined by the amount that exceeds the I _t.

On the other hand, ΔB _i is not easily obtained. Because it is simply not given at twice the vertical magnetic field produced in the opposite direction by the current I-I _t exceeding the current capacity, it obtains the current capacity decreases further by, its effect must be considered is there. In the following, we will check these while performing specific calculations.

(1) First when I = _{I t,} a current equal to the current capacity _{I t} flows into the cable. Yet, when the temperature of the superconductor does not change, 4.48KA is 5% of the current in the shield layer 5 contributes to the resistance generated corresponding to the magnetic flux flow state, which represents the I _f. Since the outer conductive layer 6b is tilted by 40 ° in the opposite direction, this current creates a longitudinal magnetic field in the opposite direction to the direction that has been created so far.

It becomes. Next, the reduction in the current capacity of the inner conductor due to the reduction in the longitudinal magnetic field is calculated. Correctly, since the magnetic field is slightly deviated from the direction of the current, the influence of this is also added, but since the influence of the deviation is relatively small, the decrease in the current capacity is simply calculated as a change due to the decrease in the longitudinal magnetic field. . Since the critical current density decrease due to the decrease in the longitudinal magnetic field by ΔB _s approximates the dependence on the longitudinal magnetic field B as J _c‖ = 5.0 × 10 ¹⁰ + 6.0 × 10 ¹⁰ B,

It becomes. From the ratio of the decrease ΔJ ′ _{c に 対 す る with} respect to the original J _c‖ = 8.0 × 10 ¹⁰ A / m ² , the decrease in current capacity is

It becomes. The current of 2.60 kA flows through the stabilized copper, which is the outer conductive layer 6b facing in the opposite direction, and reduces the longitudinal magnetic field. The decrease in longitudinal magnetic field due to this is

It becomes. This decrease in the longitudinal magnetic field further reduces the current capacity of the central conductor. If the rate of reduction is δ, it is given by the ratio of the resulting ΔB _i ^{(1) to} the original cause ΔB _s ,

ΔB _i ⁽¹⁾ yields the next decrease ΔB _i ⁽²⁾ at the same rate, which also results in a decrease. Since the decrease in current capacity also occurs at the same rate, the final decrease in current capacity is

It becomes. In this case, since the first term of the equation (2) is 0, I _Cu = 9.49 × 10 ³ A, and 10.6% of the current capacity flows to the copper layer.

(2) When I = 1.02I _t The current flowing through the copper of the outer conductive layer 6b is I _f = 0.07I _t = 6.27 kA, and the longitudinal magnetic field decrease ΔB can be calculated by the same calculation as in equation (5). _s = 5.40 × 10 ⁻² [T] is obtained. As described above, this lowers the current capacity of the inner conductor 3, thereby causing a current to flow through the inner conductive layer 6a and further reducing the longitudinal magnetic field. The total amount is

It becomes. In addition, the decrease in the longitudinal magnetic field directly caused by the excess current ΔI = I−I _t = 1.79 × 10 ³ [A] of the inner conductor 3 is similar to the equation (8),

It becomes. Therefore, the final decrease in the longitudinal magnetic field due to this is

It becomes. From this, the decrease in the overall longitudinal magnetic field is

It becomes. The decrease in critical current density due to this is

And the current capacity is

Only decrease. Therefore, the current flowing through copper is

Next, it reaches 22.1 percent of _{I t.}

(3) When I = 1.04I _{t Since} the decrease in the longitudinal magnetic field due to the current flowing through the copper of the outer conductive layer 6b is proportional to _If according to the equation (11),

It becomes. On the other hand, excessive current and 0.04I _t of the inner conductor 3, since twice the time of I = 1.02I _t, is the decrease in vertical magnetic field by this,

It becomes. From this, the total decrease in the longitudinal magnetic field is

It becomes. The decrease in critical current density due to this is

And the current capacity is

Only decrease. Therefore, the current flowing through copper is

Next, reaching 34.4% of the _{I t.}

The analysis results are examined below. Since the analysis method has been described above, the influence of parameters will be considered here. Specifically, the influence of the twist angles θ _s and θ _i of the copper layer will be considered.

(4) First when _{θ s = θ i = 30 °} , when _I = I _t, (5) formula becomes ^{_{ΔB s = 2.01 × 10 -2 T}} . ΔI _t ⁽¹ ) in the equation (7) also changes by the same ratio and becomes ΔI _t ⁽¹⁾ = 1.39 × 103A. Thus, B _i ⁽¹ ) in the equation (8) becomes B _i ⁽¹⁾ = 0.803 × 10 ⁻² T, and δ = 0.389. As a result, the decrease in current capacity is

Thus, 2.5% of the current capacity flows in the copper layer.

Then, when I = 1.02I _t, obtain ^{_{ΔB s = 2.81 × 10 -2 T}} , ΔB s + ΔB i1 = 4.60 × 10 -2 T. Further, from B _i2 ⁽¹⁾ = 1.03 × 10 ⁻² T, ΔB _i2 = 1.69 × 10 ⁻² T, ΔB = 6.29 × 10 ⁻² T, and ΔJ _{c ＝=} 3.77 × 10 ⁹ [Am ⁻² ], ΔI _t = 4.23 × 10 ³ A, I _Cu = 6.02 × 10 ³ A are obtained. This is 6.7% of the _{I t.} By similar analysis, when the I = 1.04I _t in ^{_{I Cu = 9.83 × 10 3 A}} , which is 11.0% of the _{I t.}

  (5) θ_s= Θ_i= 35 °
  Although details are omitted, current I flowing in copper_CuIs I = I_tWhen I_Cu= 4.09 × 10 ³A (4.6%), I = 1.02I_tWhen I_Cu= 9.78 × 10³A (10.9%), I = 1.04I_tWhen I_Cu= 1.54 × 10⁴A (17.1%).

(6) When θ _s = θ _i = 25 °, only the result is shown. I _Cu is, I = When ^{_{I t I Cu = 1.29 × 10}} 3 A (1.4%), when _{I = 1.02I t I Cu = 3.59} × 10 3 A (4.0% ), the time of _{I = 1.04I t I Cu = 5.90} × 10 3 a (6.6%).

  The above results are shown in Table 1 below.

  The current limiting characteristics vary greatly depending on the winding angle of the conductive layer 6, and the effect appears approximately 25 ° to 30 ° or more. In addition, the larger the angle, the greater the current limiting effect. However, in reality, winding at an angle of 60 ° or more requires a large amount of copper in addition to a technical problem. It is considered to be the upper limit.

  As described above, from the results of the above analysis, it was clarified that in the superconducting cable according to the present invention, a current is rapidly shunted to copper. Therefore, in actuality, heat is generated when a current flows through copper, and a normal conduction transition occurs and current is limited. From the above, it is clear that the superconducting cable of the present invention not only can increase the current capacity by using force-free, but also has an excellent current limiting function for preventing excessive current.

  As a second analysis, when the configuration includes only the inner conductive layer 6a, the configuration includes only the outer conductive layer 6b, and the longitudinal magnetic field decreases when the configuration includes the inner conductive layer 6a and the outer conductive layer 6b. Analysis was performed to compare minutes. The results are shown in Table 2 below.

  As can be seen from the table, when the inner conductive layer 6a alone is used, and when the outer conductive layer 6b is used alone, a current limiting effect can be seen in each case, but both the inner conductive layer 6a and the outer conductive layer 6b are provided. In the case of, the effect is greatly increased. Since this is considered to be due to each synergistic effect, the inner conductive layer 6a alone and the outer conductive layer 6b may be configured alone, but preferably both the inner conductive layer 6a and the outer conductive layer 6b are combined. It is good to have a configuration provided.

DESCRIPTION OF SYMBOLS 1 Superconducting cable 2 Former 3 Inner conductor 4 Insulating layer 5 Shield layer 6 Conductive layer 6a Inner conductive layer 6b Outer conductive layer

Claims (10)

An inner layer that conducts a direct current using the longitudinal magnetic field effect, an insulating layer that covers the inner layer, and a direction opposite to the inner layer so that a longitudinal magnetic field in the inner layer increases outside the insulating layer. A superconducting cable having an outer layer carrying a direct current,
The current capacity of the outer layer is smaller than the current capacity of the inner layer;
In the outermost layer of the outer layer, when the current flowing in the outer layer exceeds the current capacity of the outer layer, a conductive layer for shunting the current,
A superconducting cable, wherein the conductive layer is formed so that a longitudinal magnetic field is reduced by the current when a current is passed through the conductive layer. The superconducting cable according to claim 1,
The longitudinal direction of the superconducting cable is the reference direction,
The inner layer has a plurality of superconducting layers made of a superconducting member spirally arranged at any one of positive and negative angles with respect to the reference direction, and the plurality of superconducting layers From the innermost layer toward the outermost layer, the angle of the spiral is gradually increased with respect to the reference direction,
The outer layer has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer in the inner layer with respect to the reference direction;
The superconducting cable, wherein the conductive layer is made of a conductive member disposed in a spiral direction opposite to the spiral direction of the superconductive layer of the outer layer. The superconducting cable according to claim 2,
The direction of the electric current which flows into the said conductive layer is the same direction as the direction of the electric current which flows into the said outer layer, The superconducting cable characterized by the above-mentioned. An inner layer that conducts a direct current using the longitudinal magnetic field effect, an insulating layer that covers the inner layer, and a direction opposite to the inner layer so that a longitudinal magnetic field in the inner layer increases outside the insulating layer. A superconducting cable having an outer layer carrying a direct current,
The current capacity of the outer layer is smaller than the current capacity of the inner layer;
A conductive layer for shunting current when the current flowing through the inner layer exceeds the current capacity of the inner layer, the outermost layer of the inner layer and inside the insulating layer;
A superconducting cable, wherein the conductive layer is formed so that a longitudinal magnetic field is reduced by the current when a current is passed through the conductive layer. The superconducting cable according to claim 4, wherein
The longitudinal direction of the superconducting cable is the reference direction,
The inner layer has a plurality of superconducting layers made of a superconducting member spirally arranged at any one of positive and negative angles with respect to the reference direction, and the plurality of superconducting layers From the innermost layer toward the outermost layer, the angle of the spiral is gradually increased with respect to the reference direction,
The outer layer has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer in the inner layer with respect to the reference direction;
The superconducting cable, wherein the conductive layer is made of a conductive member disposed in a spiral direction opposite to the spiral direction of the superconductive layer of the inner layer. The superconducting cable according to claim 5,
A superconducting cable characterized in that the direction of current flowing through the conductive layer is the same as the direction of current flowing through the inner layer. An inner layer that conducts a direct current using the longitudinal magnetic field effect, an insulating layer that covers the inner layer, and a direction opposite to the inner layer so that a longitudinal magnetic field in the inner layer increases outside the insulating layer. A superconducting cable having an outer layer carrying a direct current,
The current capacity of the outer layer is smaller than the current capacity of the inner layer;
The outermost layer of the outer layer has an outer conductive layer for shunting the current when the current flowing through the outer layer exceeds the current capacity of the outer layer,
An inner conductive layer for shunting the current when the current flowing through the inner layer exceeds the current capacity of the inner layer, the outermost layer of the inner layer and inside the insulating layer;
The superconducting cable, wherein the outer conductive layer and the inner conductive layer are formed so that the longitudinal magnetic field is reduced by the current when the outer conductive layer and the inner conductive layer are energized. . The superconducting cable according to claim 7,
The longitudinal direction of the superconducting cable is the reference direction,
The inner layer has a plurality of superconducting layers made of a superconducting member spirally arranged at any one of positive and negative angles with respect to the reference direction, and the plurality of superconducting layers From the innermost layer toward the outermost layer, the angle of the spiral is gradually increased with respect to the reference direction,
The outer layer has a superconducting layer made of a superconducting member disposed in a spiral direction opposite to the spiral direction of the superconducting layer in the inner layer with respect to the reference direction;
The outer conductive layer is made of a conductive member disposed in a spiral direction opposite to the spiral direction of the superconductive layer included in the outer layer, and the inner conductive layer is formed of the superconductive layer included in the inner layer. A superconducting cable comprising a conductive member disposed in a spiral direction opposite to the spiral direction. The superconducting cable according to claim 8,
The direction of the current flowing through the outer conductive layer is the same as the direction of the current flowing through the outer layer, and the direction of the current flowing through the inner conductive layer is the same as the direction of the current flowing through the inner layer. Superconducting cable. The superconducting cable according to claim 8 or 9,
The superconducting cable, wherein the outer conductive layer and the inner conductive layer have spiral angles with respect to the reference direction of 25 ° or more and 60 ° or less, respectively.

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