JP5653846B2 - Drift current suppression method and superconducting cable - Google Patents

Description

  The present invention relates to a drift current suppressing method and a superconducting cable. More specifically, the present invention relates to a drift suppression method that suppresses drift that may occur in a superconducting conductor, and a superconducting cable that is configured by applying this drift suppression method.

  A superconducting cable is constructed by winding a plurality of superconducting conductors around the outer periphery of a core material and then applying insulation or electromagnetic shielding into a heat insulating tube to which liquid nitrogen is supplied. Here, as the superconducting conductor, for example, a plurality of superconducting thin wires formed into a tape shape with a base material such as silver is used.

  However, in a cable using such a superconducting conductor as a current-carrying conductor, when an alternating current is actually passed, magnetic coupling between superconducting wires, and hence magnetic coupling between tapes, will also be imbalanced, resulting in superconducting conductors. There is a known problem that the current density in the vicinity of the outermost peripheral surface is increased in a cross-sectional view without causing the current to flow uniformly, and the AC loss is greatly increased. Note that such a problem of current drift also exists not only in a superconducting cable but also in a so-called superconducting coil using a superconducting conductor as a coil.

  In recent years, in order to solve such problems, a technique has been proposed in which a plurality of superconducting thin wires are twisted to form a twisted wire structure (see, for example, Patent Document 1). In addition, in the same way as the superconducting thin wires constituting the tape have a twisted wire structure, a technique has been proposed in which the tape itself is made into a single set, and the tape is made into a multi-layer structure and each layer is rearranged. Yes. Thus, by twisting or recombining superconducting thin wires or tape, the current distribution in the superconducting conductor can be made uniform, and the AC loss can be reduced.

  In addition, for example, Patent Literature 2 proposes a technique in which a plurality of rectangular conductors are arranged radially and currents having different phases are caused to flow through the respective radial conductors. According to this technique, since the generated magnetic fields cancel each other, AC loss and leakage magnetic field can be reduced.

Japanese Patent Laid-Open No. 11-144535 JP 2006-331984 A

As described above, many techniques for suppressing the drift in the superconducting conductor have been proposed.
However, a technique for twisting or recombining superconducting thin wires or a tape as an assembly thereof, for example, the one shown in Patent Document 1 is complicated and the manufacturing method is complicated, and thus costs are increased. In addition, in order to twist or recombine the superconducting thin wires or tape, the burden on the superconducting thin wires becomes large, so that the mechanical strength of the entire cable is lowered. Moreover, the material which can be used as a superconducting thin wire is also limited, resulting in high costs.
Moreover, in the technique shown in Patent Document 2, insulation is required between the radial conductors, and the overall shape thereof becomes longer in the radial direction.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a drift suppression method that suppresses drift of a superconducting conductor with a simple configuration, and a superconducting cable that uses this drift suppression method.

  In order to achieve the above object, the present invention provides a superconducting conductor (for example, described below) formed by bundling a plurality of superconducting thin wires (for example, filament 32 described later) together with a base material (for example, matrix 33 described later). For the superconducting tape 31), there is provided a current drift suppressing method for suppressing the current flowing along the extending direction of the superconducting conductor from being partially biased. In this drift current suppressing method, a main current is passed through the superconducting conductor, and a magnetic flux substantially parallel to the extending direction of the superconducting conductor is generated around the superconducting conductor and in its base material.

  In the drift current suppressing method of the present invention, a superconducting conductor formed by bundling a plurality of superconducting thin wires with a base material is wound along a direction substantially perpendicular to the extending direction of the superconducting conductor, that is, the direction in which the main current flows. A current is passed through the coil conductor. Thus, around the superconducting conductor and in the base material excluding the inside of the superconducting thin wire among the superconducting conductors, that is, around each superconducting thin wire, the direction of the main current flowing in the superconducting thin wire is substantially parallel, that is, by the main current. Since a magnetic flux that is substantially perpendicular to the magnetic flux that is formed is formed, expansion of the magnetic flux formed by the main current is suppressed, so that the main current drift in the superconducting conductor can be suppressed.

  In this case, the magnetic flux substantially parallel to the extending direction of the superconducting conductor is a coil conductor (for example, a coil to be described later) wound outside the superconducting conductor along a direction substantially perpendicular to the extending direction of the superconducting conductor. It is preferably generated by passing a current through the conductor 5).

  In the present invention, in order to suppress the spread of the magnetic flux due to the main current, the magnetic flux is generated by passing a current through the coil conductor that is wound outside the superconducting conductor. Therefore, the magnetic flux density in the periphery of the superconducting conductor and in the base material inside the superconducting conductor can be changed only by changing the magnitude of the current flowing through the coil conductor.

  In order to achieve the above object, the present invention binds a core material (for example, a later-described former 2) and a plurality of superconducting thin wires (for example, a later-described filament 32) together by a base material (for example, a later-described base material 33). A superconducting cable (e.g., a superconducting cable described later) provided with a plurality of unit superconducting conductors substantially parallel to each other on the outer peripheral surface of the core material. Provide cable 1). In this superconducting cable, a coil conductor (for example, a coil conductor 5 to be described later) wound around a direction substantially perpendicular to the extending direction of the unit superconducting conductor is provided on the outer periphery of the plurality of unit superconducting conductors. It is characterized by.

  In the present invention, a plurality of unit superconducting conductors are provided substantially parallel to each other on the outer peripheral surface of the core material, and further on the outer periphery of the plurality of unit superconducting conductors along a direction substantially perpendicular to the extending direction of the unit superconducting conductors. A wound coil conductor was provided. Here, when a current is passed through the coil conductor, it flows in the superconducting wire around each unit superconducting conductor and in the base material excluding the inside of the superconducting wire among these unit superconducting conductors, that is, around each superconducting wire. Since a magnetic flux that is substantially parallel to the direction of the main current, that is, substantially perpendicular to the magnetic flux formed by the main current is formed, expansion of the magnetic flux formed by the main current is suppressed, so that the main current in the superconducting conductor The drift can be suppressed.

  According to the drift suppression method of the present invention, a superconducting thin wire or a unit superconducting conductor configured by bundling a plurality of superconducting thin wires is not twisted or reassembled, and is simply applied to a coil conductor provided around the unit. The main current drift can be suppressed only by flowing a large current. Therefore, the manufacturing cost can be significantly reduced by applying this method of suppressing drift to superconducting cables and superconducting coils.

It is a perspective view which shows the structure of the superconducting cable 1 to which the drift suppression method of this invention was applied. It is sectional drawing which shows the structure of a superconducting tape. It is a fragmentary sectional view along the extension direction of a superconducting cable. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 of the superconducting conductor layer in a state where a main current is passed. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3 of the superconducting conductor layer in a state where a main current is passed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a configuration of a superconducting cable 1 to which a drift suppression method according to the present embodiment is applied.

  A superconducting cable 1 includes a cylindrical former 2, a superconducting conductor layer 3 provided along the outer peripheral surface of the former 2, and an insulator layer 4 provided along the outer peripheral surface of the superconducting conductor layer 3. And the electromagnetic shield layer 6 provided along the outer peripheral surface of the insulator layer 4. This superconducting cable 1 is used by being inserted into a heat insulating pipe (not shown) to which liquid nitrogen is supplied in order to maintain the superconducting state of the superconducting conductor layer 3.

  As shown in FIG. 1, the superconducting conductor layer 3 is formed by winding a plurality of tape-shaped superconducting conductors (hereinafter referred to as “superconducting tape”) 31 along the outer peripheral surface of the former 2 in parallel with each other. .

  FIG. 2 is a cross-sectional view showing the configuration of the tape-shaped superconducting conductor 31. The superconducting tape 31 is formed in a tape shape by bundling a plurality of superconducting wires (hereinafter referred to as “filaments”) 32 together with a base material 33. As a superconducting material used for the filament 32, an oxide composed of Bi, that is, Bi, Sr, Ca, Cu, O, or the like is used. However, the present invention is not limited to this. Further, as the material of the base material 33, pure silver, a silver alloy, or the like is used, but the present invention is not limited to this.

  In addition, as for such a superconducting tape 31, a twisted wire structure in which the filaments 32 are twisted together is conventionally proposed in order to suppress the drift, but the superconducting cable to which the drift suppression method of the present invention is applied is proposed. According to this, the superconducting tape 31 does not need to have a stranded structure.

  Returning to FIG. 1, the insulator layer 4 is composed of two layers of an inner insulating layer 41 and an outer insulating layer 42, and the coil conductor 5 is interposed between the inner insulating layer 41 and the outer insulating layer 42. It is disguised. The coil conductor 5 extends outside the former 2, the superconducting conductor layer 3, and the inner insulating layer 41 along the direction in which the main current flows in the superconducting conductor layer 3, that is, the direction substantially perpendicular to the extending direction of the superconducting tape 31. It is rolled up.

Next, a description will be given of a drift suppression method for suppressing the bias of the main current flowing along the extending direction of the superconducting conductor layer 3 having the coil conductor 5 wound outside as described above.
FIG. 3 is a partial cross-sectional view along the extending direction of the superconducting cable 1. For the sake of clarity, the configuration of the insulator layer and electromagnetic shield layer in FIG. 3 is omitted.

  As shown in FIG. 3, the coil conductor 5 extends substantially perpendicular to the extending direction of the superconducting tape 31 constituting the superconducting conductor layer 3. When a direct current is passed through such a coil conductor 5, a magnetic flux substantially parallel to the extending direction of the superconducting tape 31 is generated inside and outside the coil conductor 5 as indicated by broken line arrows in FIG. 3.

  4 and 5 are cross-sectional views along line IV-IV of the superconducting conductor layer 3 in a state where a main current flows. More specifically, FIG. 4 is a diagram schematically showing a state in which no current is passed through the coil conductor 5, and FIG. 5 is a diagram schematically showing a state in which a current is passed through the coil conductor 5. For clarity of illustration, the configurations of the insulator layer and the electromagnetic shield layer in FIGS. 4 and 5 are omitted.

  First, if a main current is passed through the superconducting conductor layer 3, a magnetic flux is generated around it as shown by a broken line arrow in FIG. The main current drift phenomenon in the superconducting conductor layer 3 is that the magnetic flux generated by such a main current spreads to the neighboring filament 32 or the neighboring superconducting tape 31, thereby erasing the superconducting state of the other filament 32. It is thought to be a factor.

  On the other hand, as shown in FIG. 5, a magnetic flux substantially parallel to the extending direction of the superconducting tape 31 is generated inside the coil conductor 5 by flowing an appropriate current through the coil conductor 5. It becomes. Thus, the magnetic flux generated by the current flowing through the coil conductor 5 penetrates the base material 33 except for the filament 32 in the superconducting state in the superconducting tape 31 in addition to the periphery of the superconducting tape 31. Therefore, it is possible to suppress the magnetic flux generated by the main current flowing through the filament 32 from spreading to the neighboring filament 32 and the adjacent superconducting tape 31 by the magnetic flux generated by passing a current through the coil conductor 5. As a result, drift can be suppressed.

  In the above description, the current flowing through the coil conductor 5 is a direct current, but the present invention is not limited to this. The coil conductor 5 may be supplied with an alternating current or a variable current having no polarity change in addition to a direct current.

  Further, the optimum value of the current flowing through the coil conductor 5 is determined by performing an experiment. That is, when the current is increased, the magnetic flux density inside the coil conductor 5 is increased and the effect of suppressing the drift is considered to be improved, but conversely, the number of filaments in which the superconducting state disappears is also considered to increase. Therefore, the magnitude of the current is determined so as to optimize both the suppression of the drift and the maintenance of the superconducting state.

  By the way, in the superconducting cable 1 as described above, it is considered that most of the main current flows in each filament 32 in the superconducting state, but there are actually a few that flow between adjacent filaments 32 due to the tunnel effect. And it is thought that the electric current between these filaments 32 also contributes to increase AC loss. On the other hand, the effect of suppressing the current between the filaments 32 can be expected by generating a magnetic flux in the base material 33 that fills the gaps between the filaments 32 as in the method for suppressing the drift of the present invention.

Although one embodiment of the present invention has been described above, the present invention is not limited to this.
In the said embodiment, although the example which applied the drift suppression method of this invention to the superconducting cable was demonstrated, this invention is not restricted to this. For example, the superconducting conductor that constitutes the superconducting coil also has a problem in which a drift occurs. Therefore, it is considered that the drift can be suppressed in the same manner by flowing the current as described above after the coil conductor is wound in a toroidal shape on the superconducting conductor of such a superconducting coil.

1 ... Superconducting cable 2 ... Former (core material)
3 ... Superconducting conductor layer 31 ... Superconducting tape (unit superconducting conductor)
32 ... Filament (superconducting thin wire)
33 ... Base material

Claims (2)

A plurality of unit superconducting conductors formed in a tape shape by bundling a plurality of superconducting wires together with a base material are provided on the outer peripheral surface of the core material substantially parallel to each other, and are insulated along the outer peripheral surface of the plurality of unit superconducting conductors. An insulating layer composed of two layers, an outer insulating layer and an outer insulating layer, is interposed between the inner insulating layer and the outer insulating layer, and is substantially perpendicular to the extending direction of the unit superconducting conductor. A coil conductor wound around the base material along the direction is provided, and in a superconducting cable configured to include the insulating layer, the current flowing along the extending direction of the unit superconducting conductor is partially biased A method for suppressing drift in which
The superconducting cable is used by being inserted into a heat insulating pipe to which a coolant for maintaining a superconducting state is supplied,
With flowing a main current in the superconducting thin line, by supplying a current to the coil conductors substantially wound to the base material along a direction perpendicular to the extending direction of the superconducting thin line on the outside of the base material , around and their parent materials in of the unit superconductor, nonuniform flow suppression method characterized by generating an extending direction substantially parallel flux of the unit superconducting conductor. With heartwood,
A unit superconducting conductor formed into a tape shape by bundling a plurality of superconducting thin wires together with a base material,
A plurality of the unit superconducting conductors are provided substantially parallel to each other on the outer peripheral surface of the core material, and is a superconducting cable used by being inserted into a heat insulating pipe supplied with a coolant for maintaining a superconducting state,
A superconducting cable including an insulating layer composed of two layers of an inner insulating layer and an outer insulating layer along an outer peripheral surface of the plurality of unit superconducting conductors , wherein the inner insulating layer and the outer insulating layer And a coil conductor wound around the base material along a direction substantially perpendicular to the extending direction of the unit superconducting conductor. .

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