JPH0618090B2 - AC superconducting conductor - Google Patents

Description

The present invention relates to a superconducting conductor suitable for a superconducting AC device.

[Conventional technology]

Superconducting conductors used in conventional AC devices have been developed by a method in which a superconducting conductor is made into a filament shape in a normal conducting metal body such as copper or aluminum and concentrated on the outer peripheral portion thereof. FIG. 3 Hereinafter, the structure and efficacy will be described in detail with reference to FIG.

As shown in the figure, the conventional AC superconducting conductor 1 is Nb-T.
A superconducting element wire 2 in which a first normal conducting metal 5 and a second normal conducting metal 6 are doubly coated is placed on a superconducting filament 4 such as i, Nb ₃ Sn or the like, and a third normal conducting metal is provided. 7, the normal conducting wire 3 coated with the fourth normal conducting metal 8 is arranged in the central portion, and the outermost layer thereof is covered with the fifth normal conducting metal 9. Usually, the first to fifth normal-conducting metals are used in a combination of two or three kinds of conductive, aluminum and Kyupro-Nickel, and especially, the first and third normal-conducting metals 5 and 7 are low resistance metals. A high resistance metal is often used for the second, fourth and fifth normal conducting metals 6, 8 and 9. In order to reduce the magnetization loss, the superconducting wire 2 is thinned to 1
The normal conducting wire 3 has a diameter of about μm and is thinned to almost the same size as that of the normal conducting wire 3 in order to reduce eddy loss. The high resistance metal is used to block the coupling current between the superconducting wires 2 and the eddy current between the normal conducting wires 3, and finally contributes largely to reduce the AC loss of the AC superconducting conductor 1. . Also, the AC superconducting conductor 1 is twisted around the central axis.
It is devised so that the blocking of the coupling current becomes more effective.

In order to increase the current capacity of the conductor, a plurality of alternating-current superconducting conductors 1 shown here are bundled and formed into a concentric or rectangular shape by stranded wire. In addition, the outer periphery of the AC superconducting conductor 1 may be covered with an insulating layer depending on the application.

When a current flows through this AC superconducting conductor 1, it is biased to the outer peripheral portion of the conductor by the skin action and flows concentratedly in the superconducting filament 4 which has zero resistance, and not only the normal conductive wire group in the central portion but also the outer peripheral portion. The current does not flow into the normal conductor that is interposed between the superconducting element wires in the above section, so that it is possible to sufficiently suppress the heat generation of the jule and it is expected that the AC loss will be greatly reduced. Furthermore, if a current flows in the superconducting wire group in the outer peripheral part, the self-magnetic field generated by this current will be zero in the central part, and there will be no eddy loss in the normal conducting wire group, and there will be no AC loss. The reduction effect is further enhanced. The following are the effects for this seed conductor.

However, the above effects are limited to the case where the seed conductor is a single wire. Since the superconducting filament is made into ultra-fine wire to reduce AC loss, the straight line of the manufacturing process rise line is also extremely thin (<1 mm), and its current capacity is also small (<number + A).
It is extremely inconvenient for practical use. Therefore, in order to increase the current as described above, it is usual that a plurality of these single wires are bundled and twisted. However, when the stranded wire is used, the magnetic field from another adjacent single wire is vertically applied to the focused single wire (proximity effect), and the above effect cannot be always expected. Regarding superconducting wires for alternating current, see
It is disclosed in JP-A-60-158510 and JP-A-62-67156.

[Problems to be solved by the invention]

The prior art described above does not consider practically large current, and has a problem of increasing loss due to the proximity effect associated with twisted wires.

The present invention has been made in view of the above points, and an object thereof is to provide an AC superconducting conductor as a single wire that can reduce AC loss as compared with the related art so as to be able to cope with a large current. To provide.

[Means for solving problems]

The above-mentioned object is for an ultrafine multi-core alternating current consisting of a large number of superconducting element wires which are successively coated with a low-resistance layer of a normal-conductive metal and a high-resistance layer of a normal-conductive metal having a higher resistance than the low-resistance layer around a superconductor. In a superconducting conductor, it is achieved by arranging the superconducting element wire in a central portion and an outer peripheral portion of the superconducting conductor, and providing a high resistance layer of the normal conducting metal in the middle of the central portion and the outer peripheral portion and outside the outer peripheral portion. .

[Action]

Breaking down the AC loss of the AC superconducting conductor by the loss mechanism, the magnetization loss in the superconducting filament accounts for about 80%, the eddy loss in the normal conductor is about 5%, and the remaining about 1%.
It is said that 5% is the coupling loss between superconducting filaments via the normal conducting metal. Moreover, it is said that the loss due to the magnetic field is about two orders of magnitude (about 100 times) larger than the loss due to the current. Based on these two facts, considering the case where an AC current flows through an AC superconducting conductor and a vertical AC magnetic field is acting (a large-current stranded conductor), a superconducting filament is a conductor that is one structural unit. There is a possibility that AC loss can be reduced by devising the arrangement method of.

In conventional AC superconducting conductors, superconducting filaments,
That is, when the number of superconducting wires 2 is divided into two, a part of the superconducting wires 2 is placed in the outer peripheral portion, the rest is placed in the central portion, and a normal conducting metal is placed in the middle portion, the outer peripheral portion is exposed to an externally applied magnetic field. The superconducting wire group in the central part is exposed to the external magnetic field, but the loss (magnetization loss) is reduced by the number of filaments reduced, and the loss in the superconducting wire group in the central part becomes almost zero due to the shielding effect by the outer peripheral part. . Therefore, the overall AC loss is reliably reduced. If the number of superconducting element wires arranged in the outer peripheral portion is reduced as much as possible and the external magnetic field is efficiently shielded, the total AC loss can be further reduced. As a means for that, take a sufficient distance between the outer peripheral part and the central part,
There are two possible methods: a method of arranging a normal-conducting (low-resistance) metal in this intermediate portion, and a method of lengthening the twist pitch of the superconducting element wire in the outer peripheral portion to make the coupling stronger.

〔Example〕

One embodiment of the present invention is shown in FIG. 1, and its configuration, action and effect will be described. AC superconducting conductor 1 according to the present invention
The configuration is as follows. On the outside of the superconducting (Nb-Ti) filament 4, there are 857 superconducting element wires 2 in which the first normal conducting metal (copper) and the second normal conducting metal (Kyupro Nickel) 6 are double-coated in the central portion. 643 are densely arranged on the outer periphery and the sixth normal conducting metal (Kyupro.
Nickel) 10 was provided, and a fifth normal conducting metal (Kyupro Nickel 40 μm thick) 9 was arranged on the outermost periphery.

This specific manufacturing method will be described later. For comparison, a conventional conductor having the same specifications as this embodiment was separately prepared. In the present embodiment, a set of seven superconducting filaments 4 each having a diameter of 1 μm is embedded in the first normal conducting metal 5, but a method of forming a three-layer structure for each one is more general. This configuration will not be a particular problem here.

Next, the operation of each component will be described. Superconducting wires 2 are arranged at the outer peripheral portion and the central portion, and serve to carry an alternating current. The layer of the normal-conductivity metal 10 in the middle portion has a function of not electrically coupling the superconducting element wires in the central portion and the outer peripheral portion, and also having a function of slightly increasing the distance to weaken the magnetic coupling and reduce the AC loss. . In addition to the role of firmly maintaining the shape of the AC superconducting conductor 1, the outermost normal-conducting metal 9 is a high-resistance metal, which makes it difficult for eddy currents and coupling currents to flow and is a low-resistance metal. , It has the function of reducing eddy currents and coupling currents in the superconducting element wires inside it, and reducing AC loss as a whole. The second normal conducting metal 6 forming the superconducting element wire 2 also has the same function as the normal conducting metal 9. Further, the superconducting wire groups at the central portion and the outer peripheral portion were twisted with the same 4 mm pitch as the conductor of the conventional example used in the comparative experiment. As described above, the twist has a function of cutting off the electrical coupling between the superconducting element wires 2 and reducing the AC loss.

Further, the effect of the AC superconducting conductor 1 of the present invention will be described. FIG. 4 shows the result of the AC loss measurement of the AC superconducting conductor according to the conventional example and the present invention. The solid line is the present invention,
The dotted line shows the AC loss of the conventional conductor. That is, when compared with an AC magnetic field of 1.0 T, the AC loss was reduced to 1 / 2.3 as compared with the conductor 1 of the conventional example. This result suggests that the present invention is effective in reducing AC loss.

In this embodiment, the AC loss can be further reduced by selecting different values for the twist pitches of the superconducting element wire group in the central part and the superconducting element wire group in the outer peripheral part. As described above, in order to efficiently shield the externally applied magnetic field and reduce the magnetic fields of the superconducting element wire group in the central part and the normal conducting metal layer 10 in the middle part, the twist pitch of the superconducting element wire group in the outer peripheral part is used. The length may be increased so that the coupling current can easily flow. An increase in the coupling current leads to an increase in the coupling loss, but it does not make the twist pitch infinite, and the coupling loss is one of the total losses.
Considering that it is / 5 or less, it will not affect many people. Also, if the superconducting wire group in the central part and the outer peripheral part are twisted with the same pitch, the outer peripheral part has a larger inductance than the central part, and it is difficult for the alternating current to flow, and it is possible that the alternating current does not flow evenly in the superconducting wire. There is a nature.
Therefore, it is necessary to lengthen the twist pitch at the outer peripheral portion and lower the impedance to make it equal to that at the central portion. The selection of the twist pitch should be made in the direction of reducing the AC loss in consideration of the difference in the number of the superconducting wires 2 included in the central portion and the outer peripheral portion. Therefore, the twist pitch of the outer peripheral portion is not always longer than that of the central portion, and it is not necessary to make the twist directions the same.

Another embodiment of the present invention will be described with reference to FIG. The structure is different from that shown in FIG. 1 in the normal conducting metal layer 10 in the middle part. That is, in FIG. 1, a single normal-conducting metal pipe is used, but in FIG. 2, the normal-conducting metal pipe is made into a multi-layer, and different kinds of normal-conducting metals and normal-conducting element wires 3 are combined. The details are shown in Fig. 2 (c).
The four configurations are shown in FIG. a cross section is 6th inside and outside
The normal-conducting metal 11 is arranged, and the seventh normal-conducting metal 12 is arranged in the middle of the normal-conducting metal 11, and the section b is the reverse arrangement. The c-section has the eighth normal-conducting metal 13 arranged on the inner side, the normal-conducting element wires 3 densely arranged on the outer side thereof, and the d-section has the opposite arrangement.

This is a countermeasure when it is necessary to increase the amount of low-resistance metal in order to improve the stability of the AC superconducting conductor 1. Since placing a low-resistance metal in a pipe shape increases eddy loss and coupling loss. It is intended for subdivision or multi-layering. Naturally, various methods other than the above can be considered for the method of subdividing and multilayering.

The effects expected from this embodiment are reduction of loss and further improvement of stability, as in the above-mentioned embodiments.

A very basic example of a manufacturing method for embodying the present invention will be described below.

FIG. 5 shows the first manufacturing method of the present invention.
(A) shows the starting point of manufacture, and the superconducting wire 14 at the center is a round wire and has already been twisted. The superconducting wires 15 and 15 ′ that are the outer peripheral portions are rectangular wire shapes, but the required number is determined by their dimensions and twist pitches. As shown in (b) of these superconducting wires, the superconducting wire 14 serving as the central portion and the superconducting wires 15, 1 serving as the outer peripheral portion are formed.
Wrap 5 '. Then, for example, they are passed through a die and brought into close contact with each other to form one AC superconducting conductor 1 as shown in (c).

FIG. 6 shows a second manufacturing method of the present invention.
(A) shows the starting point of manufacturing, in which the superconducting wire 14 at the center is a round wire and has already been twisted, and the superconducting wire 16 at the outer peripheral part is a pipe, and A twist has been added. As shown in (b) of these superconducting wires, the central superconducting wire 14 is inserted into the outer peripheral superconducting wire 16. Then, they were passed through a die and brought into close contact with each other to form one AC superconducting conductor 1 as shown in (c). In the above-mentioned two manufacturing methods, the twist is not particularly added after the contact processing, but it is needless to say that a twist may be further added after the contact processing to obtain a desired twist pitch. Further, the twist directions of the central portion and the outer peripheral portion do not have to be the same, and may be opposite to each other. Needless to say, it is extremely easy to provide the normal-conducting metal layers 9 and 10 in the middle of the central portion and the outer peripheral portion and in the outermost peripheral portion in both the above manufacturing methods.

The embodiment described with reference to FIG. 1 is based on the manufacturing method described with reference to FIG. 5, and the superconducting wire 16 at the outer peripheral portion is pre-wound with the superconducting element wire 2 on the outside of the intermediate normal-conducting metal layer 10 and the outside thereof. The outermost normal conducting metal layer is coated on the superconducting wire 14, and the superconducting wire 14 in the central portion is obtained by the usual method for manufacturing an ultrafine multifilamentary wire. The number of superconducting filaments (the number of superconducting wires 2) and twist pitch are as described above.

〔The invention's effect〕

According to the present invention described above, it is possible to provide an AC superconducting conductor that can further reduce the AC loss as compared with the conventional conductor having the smallest AC loss, and it is possible to reduce the loss even if the current is increased. The industrial effects in the field of AC application are enormous.

[Brief description of drawings]

FIG. 1 (a) is a sectional view showing an AC superconducting conductor of an embodiment of the present invention, FIG. 1 (b) is a detailed sectional view of the superconducting element wire, and FIG. 2 (a) is another embodiment of the present invention. FIG. 2 (b) is a detailed cross-sectional view of the superconducting element wire, FIG. 2 (c) is a cross-sectional view of conductors showing various combinations of normal-conducting metal layers, and FIG. 2 (d) is a detailed sectional view of the normal conducting wire, FIG. 3 (a) is a sectional view showing a conventional AC superconducting conductor, and FIG. 3 (b) is a detailed sectional view of the superconducting wire. FIG. 3 (c) is a cross-sectional view of the normal conducting wire, FIG. 4 is a characteristic diagram showing actually measured AC loss characteristics of the AC superconducting conductor of the present invention having the same specifications, and FIG. 5 (a). ),
6 (b) and 6 (c) and FIGS. 6 (a), 6 (b) and 6 (c) are process order diagrams showing examples of the manufacturing method for embodying the AC superconducting conductor of the present invention. 1 ... AC superconducting conductor, 2 ... Superconducting element wire, 3 ... Normal conducting element wire, 4 ... Superconducting filament, 5 ... First normal conducting metal, 6 ... Second normal conducting metal, 7 ...... Third normal conducting metal, 8 ...... Fourth normal conducting metal, 9 ...... Fifth normal conducting metal, 10 ...... Normal conducting metal layer, 11 ...... Sixth normal conducting metal, 12 ...... Seventh normal conducting metal, 13 ... Eighth normal conducting metal, 14 ... Central superconducting wire, 15, 15 '...
… Superconducting wire that becomes the outer peripheral portion, 16… Pipe-shaped superconducting wire that becomes the outer peripheral portion.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-50-39492 (JP, A) JP-A-60-158510 (JP, A) JP-A-62-67156 (JP, A) JP-B 43- 5063 (JP, B1) JP-B-51-13867 (JP, B1)

Claims (2)

[Claims] 1. An ultrafine multi-core alternating current composed of a large number of superconducting element wires in which a low-resistance layer of a normal-conductive metal and a high-resistance layer of a normal-conductive metal having a higher resistance than the low-resistance layer are sequentially coated around a superconductor. In the superconducting conductor for use, the superconducting element wire is arranged in a central portion and an outer peripheral portion of the superconducting conductor, and the high resistance layer of the normal conducting metal is provided between the central portion and the outer peripheral portion and outside the outer peripheral portion. Superconducting conductor for alternating current. 2. A superconducting conductor for alternating current according to claim 1, wherein the superconducting element wire groups in the central portion and the outer peripheral portion are twisted at different pitches.