JPH09289113A - Terminal for ac superconducting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable terminal for enabling an enough performance of an AC superconducting device such as superconducting transformer or current limiter which passes a specially large current. SOLUTION: In a terminal for an AC superconducting device, an oxide superconducting wire 3 with a covering which exhibits good electrical and thermal conduction is disposed and connected in parallel to an AC superconducting wire 1. With this construction the local Joule heating by skin effect associated with AC current passage is reduced and efficiently cooled. Also, by using an oxide superconducting material representing superconducting properties at relatively high temperature, the superconducting properties of the terminal 4 heated by the Joule heating is maintained for steadily operating the AC superconducting device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal of an AC superconducting device, and more particularly to a superconducting power device such as a superconducting transformer, a fault current limiter or an armature of an all superconducting generator.

[0002]

2. Description of the Related Art A terminal structure of a conventional AC superconducting device is described in detail in Japanese Patent Laid-Open No. 82882/1993, so an outline will be described with reference to FIG. When AC is energized, a skin effect occurs at the connection between the terminal plate 4 and the AC superconducting wire 1 and the AC superconducting wire 1
Since the local Joule heating of the above raises the temperature of the AC superconducting wire and causes quenching (transition from the superconducting state to the normal conducting state), the AC superconducting wire 1 is loosened with a small stranded wire or superconducting element wire 2 and each is used as a terminal board. Local Joule heat generation was dispersed by brazing (soldering) according to the current distribution of the terminal plate due to the skin effect. Conventionally, it operated soundly with a small current of about 100 A, but under a large current of several thousand to tens of thousands A, the Joule heat generated by energization is extremely large because it is proportional to the square of the current, and the temperature of the terminal rises. Then the quench happened easily.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a terminal for an AC superconducting device that overcomes the above-mentioned drawbacks of the prior art and operates stably with a large current.

[0004]

In order to solve the above-mentioned problems, the present invention connects an oxide superconducting wire having a coating having a low electric resistance and a good thermal conductivity at the terminals of an AC superconducting device in parallel with the AC superconducting wire. Is arranged so as to reduce local Joule's heat generation due to the skin effect during AC energization and to effectively diffuse and cool the generated Joule heat. Moreover, by using an oxide superconducting material exhibiting superconductivity at a relatively high temperature, the superconductivity of the terminal can be maintained and the AC superconducting device can be stably operated even when the temperature of the terminal portion rises due to Joule heat generation.

By using the terminals of the AC superconducting device described above, the localization of Joule heat generation due to the current concentration due to the skin effect during AC energization is suppressed, and a stable terminal of the AC superconducting device can be obtained.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present embodiment, details of terminals of an AC superconducting device that operates stably when an AC current is applied will be described. FIG.
FIG. 3 is a schematic diagram showing a configuration of terminals of an AC superconducting device according to an embodiment of the present invention. The terminals of the AC superconducting device of the present invention constitute an AC superconducting wire 1 and an AC superconducting wire 1, and are loosened small strands or superconducting element wires 2, oxide superconducting wires 3 and terminals coated with an electrically conductive material. Electrical connection between the plate 4, the terminal plate 4, the oxide superconducting wire 3 coated with the electrically conductive material, and the oxide superconducting wire 3 coated with the electrically conductive material and the small stranded wire or the superconducting element wire 2, respectively. Brazing (soldering)
It is composed of part 5. When connecting a small stranded wire or a superconducting element wire 2 to a terminal board 4, the oxide superconducting wire 3 coated with an electrically conductive material having a small electric resistance, good thermal conductivity and superconducting characteristics at a relatively high temperature is small. The arrangement of the stranded wire or superconducting element wire 2 and the terminal board 4 is a major feature of the present invention.
Therefore, even if a large current is applied to the AC superconducting coil, due to the low electrical resistance and high thermal conductivity of the oxide superconducting wire 3 coated with an electrically conductive material, the Joule heat during AC energization can be reduced quickly. Can be cooled. By using the oxide superconducting material exhibiting superconductivity at a relatively high temperature, even if the temperature of the terminal rises due to Joule heat generation, the superconductivity of the terminal can be maintained and the AC superconducting device can be operated stably.

In order to reduce the AC loss, the base material of the superconducting element wire of the AC superconducting wire generally used in AC superconducting equipment is Cu.
-High electrical resistance material such as Ni alloy is used, but Cu
-Electrical resistance and heat conduction characteristics of Ni alloy at cryogenic temperature (4.2K) are 1000 times higher than Cu according to "Superconductivity / Low Temperature Engineering Handbook" edited by Low Temperature Engineering Society.
The thermal conductivity is 1/5. Comparing Cu-Ni alloy and Ag, the electrical resistance value is 200 times and the thermal conductivity is 1/300. Especially, regarding the thermal conductivity, Ag and Cu-Ni alloy have a remarkable difference, and Cu-Ni alloy has It can be seen that the material has higher electrical resistance and lower thermal conductivity than general metals. On the other hand, let us consider the process in which the terminals of an AC superconducting device reach quench. The superconducting state is maintained if the heat generation and cooling of the superconducting wire are well balanced and the superconducting wire is kept at a temperature below the critical temperature. However, in the terminals of the AC superconducting equipment, an AC current is passed, so that local Joule heat is generated at the connection portion, and the balance between heat generation and cooling is likely to be lost. In particular, since the above Cu-Ni alloy is used as the base material of the superconducting wire,
Due to its high electrical resistance and low thermal conductivity, the balance is likely to be lost. "Superconducting Magnets" MARTIN
N. WILSON p. 131-p. According to 133, when the temperature of the superconducting wire rises for some reason, the critical current density decreases, and the magnetic flux penetrating the superconducting wire moves to generate heat. Next, it is explained that the heat generated by heat generation leads to quenching in a cycle in which the temperature of the superconducting wire is further raised. However, the cycle can follow the reverse course even if heat is generated, provided that the superconducting wire is cooled under good conditions. The current that tries to flow beyond the cooling performance flows in the oxide superconducting material, keeps the heat generation of the terminal to a minimum when a large current is passed, and cools the heat generation using a member with good cooling characteristics to maintain superconductivity. Show what you can do. In the present invention, the reverse process of the above cycle is achieved in the terminal portion of the AC superconducting device. The oxide superconducting wire 3 coated with an electrically conductive material corresponds to the above-mentioned member of the present invention, and is an important constituent element of the terminal of the AC superconducting device of the present invention which operates stably.
The present embodiment is characterized in that the oxide superconducting wire 3 coated with an electrically conductive material is provided between the terminal plate 4 and the small stranded wire or superconducting element wire 2. Au, Ag, Ag- with low electrical resistance and good thermal conductivity
Au alloy is used. The oxide superconductor is YBa ₂ Cu.
₃ O _x , Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x , Bi ₂ Sr ₂ Ca ₂ Cu
₃ O _x , Tl ₂ CaBa ₂ Cu ₂ O _x , Tl ₂ Ca ₂ Ba ₂ Cu ₃
A material having superconductivity at a relatively high temperature such as O _x is desirable. An oxide superconducting wire 3 coated with an electrically conductive material is placed between a terminal plate 4 and a small strand wire or a superconducting element wire 2 and each is brazed (soldered) so that a joule is formed at a connection portion when an alternating current is applied. It is possible to obtain a terminal of an AC superconducting device which generates little heat and has good heat diffusion. FIG. 2 is a schematic diagram showing the overall configuration of an AC superconducting device when a connection test of the terminals of the AC superconducting device of the present invention is performed on the AC superconducting coil. AC superconducting coil 8, AC superconducting wire 1, small stranded wire or superconducting element wire 2, oxide superconducting wire coated with electrically conductive material 3, terminal plate 4, terminal plate 4 and oxidation coated with electrically conductive material Brazing (soldering) part 5 for electrically connecting the superconducting wire 3 and the oxide superconducting wire 3 coated with an electrically conductive material to the small strand or the superconducting element wire 2 and the current supply lead 10.
Is cooled by a refrigerant (liquid helium) 6 stored in a cryostat 7. AC current is supplied to the AC superconducting coil 8 from the outside through the current supply lead 10.
An attempt was made to test the characteristics of the AC superconducting coil. FIG. 3 shows a cross-sectional structure of the AC superconducting wire 1 used for the AC superconducting coil 8. The AC superconducting wire 1 is a superconducting element wire 2a and a small stranded wire 2
b, a center line 11a, and a center line 11b. 7
The center twisted line 11b obtained by twisting the center lines 11a of the two books is located at the center of the AC superconducting wire 1 and has six small twisted wires 2b around it.
Are better matched. Small strand 2b is centered on centerline
1a is arranged and a superconducting wire 2a is twisted around it. Since the center line 11a plays a role of mechanically reinforcing the AC superconducting wire 1, a normal conducting alloy that does not exhibit superconducting property is generally used. In this embodiment, a Cu-Ni alloy is used for the center line 11a and the center line 11b.
You can use wood. Table 1 shows the main specifications of the AC superconducting wire used in the examples.

[0008]

[Table 1]

The superconducting element wire 2a is composed of two strands of superconducting element wire 2a, a small stranded wire 2b, and a small stranded wire 2b to an AC superconducting wire 1. Table 2 shows the main design specifications of the AC superconducting coil used in the examples.

[0010]

[Table 2]

The AC superconducting coil was manufactured by winding the AC superconducting wire 1 in a solenoid shape for 50 turns per layer for four layers. The design current of the AC superconducting coil is 590Arms,
The maximum empirical magnetic field is 1.0 Tpeak. In order to verify the effect of the present invention, the results of the quench test of the above AC superconducting coil are shown in FIG. In the figure, the test results using the conventional example are also shown for comparison. According to the present invention, the characteristics of the AC superconducting coil were up to 95% of the AC superconducting wire characteristics (marked with a circle in the figure), and good results were obtained. But,
In the conventional example, the characteristics of the AC superconducting coil were reduced to 55% of the characteristics of the AC superconducting wire (marked with ● in the figure). In the conventional example, the terminal portion was quenched earlier than the AC superconducting coil. Therefore, the characteristics of the AC superconducting coil were not the original performance of the AC superconducting device. On the other hand, in the present invention, quenching occurred at the AC superconducting coil and the terminal almost at the same time, and the original performance of the AC superconducting device could be obtained.

Although the terminal plate 4 is described as having a cylindrical shape, the terminal plate 4 is not limited to a cylindrical shape and may have any shape as long as it can disperse and connect flat strands, cylinders, conical strands or the superconducting element wires 2. FIG. 5 is a perspective view when a flat plate is used for the terminal plate of the terminal of the AC superconducting device of the present invention. The AC superconducting wire 1 is loosened by a small stranded wire or a superconducting element wire 2, and each is brazed (soldered) to an oxide superconducting wire 3 coated with an electrically conductive material. Oxide superconducting wire coated with electrically conductive material 3
The superconducting element wire or the oxide superconducting wire 3 side of the superconducting element wire 2 which is brazed (soldered) to the electrically conductive material is dispersedly arranged on the terminal board 4 and brazed (soldered).
The total AC current that is about to flow in the AC superconducting coil 8 is distributed and flows to each of the small strand wires or the superconducting element wires 2 connected via the oxide superconducting wire 3 coated with an electrically conductive material.

[0013]

According to the present invention, since the thermal conductivity is good and the heat generation is remarkably reduced, it is possible to obtain a highly stable terminal for an AC superconducting device, and a transformer, current limiter or SMES (Superconducting magnet)
It is possible to provide an AC superconducting device such as ic storage).

[Brief description of drawings]

FIG. 1 is an explanatory diagram of terminals of an AC superconducting device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an entire AC superconducting device according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of an AC superconducting wire used in the AC superconducting coil of the embodiment of the invention.

FIG. 4 is a characteristic diagram of an AC superconducting coil with respect to characteristics of a short AC superconducting wire.

FIG. 5 is a perspective view in which a flat plate shape is adopted for the terminal plate of the terminal of the AC superconducting device of the present invention.

FIG. 6 is a sectional view of a terminal of a conventional AC superconducting device.

[Explanation of symbols]

1 ... AC superconducting wire, 2 ... small stranded wire or superconducting element wire, 3
… Oxide superconducting wire coated with electrically conductive material, 4 ... Terminal plate, 5 ... Brazed (soldered) part.

Claims (4)

[Claims] 1. A small stranded wire or superconducting element wire in which the AC superconducting wire is loosened is evenly distributed to the terminal plate at a connecting portion between the AC superconducting wire and the terminal board, which are formed by superposing small stranded wires or strands. A terminal for an AC superconducting device, characterized in that an oxide superconducting wire coated with an electrically conductive material is arranged between the terminal plate and the small strand or superconducting element wire when arranged and connected. 2. The oxide superconducting wire coated with the terminal plate and the electrically conductive material, and the oxide superconducting wire coated with the electrically conductive material and the small stranded wire or the superconducting element wire according to claim 1, respectively. Terminals for AC superconducting devices that are connected together. 3. The electrically conductive material of the oxide superconducting wire coated with the electrically conductive material according to claim 1 or 2, wherein the electrically conductive material is a pure metal of gold or silver, a silver-gold alloy, or an alloy containing them as a main component. AC superconducting equipment terminal. 4. The superconducting material of the oxide superconducting wire coated with the electrically conductive material according to claim 1, 2, or 3.
A terminal of an AC superconducting device which is an oxide superconductor made of a system-based, Bi-based or Tl-based material and which exhibits superconducting properties at a relatively high temperature.