JPH05251759A - Oxide superconductive current limiting conductor - Google Patents

Abstract

PURPOSE:To get an oxide superconductive-current limiting conductor the current limiting effect of which is large and in which the voltage between limit terminals is 100 V and over. CONSTITUTION:A Y (YB2Cu3O7-x) oxide superconductive film is made on a base material by electron beam deposition method by introducing oxygen gas. A silver layer is made hereon in vacuum by deposition. Executing these processes three times each, an oxide superconductive current limiting conductor, wherein superconductive layers and silver layers are stacked three layers each alternately, is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance current limiting device for use in a conductor that conducts a current using an oxide superconductor and a current limiting device capable of limiting an excessive current such as a short-circuit current. It is about conductors.

[0002]

2. Description of the Related Art In a superconductor, when any one of the critical temperature, the critical current, and the critical magnetic field exceeds the value, the superconducting state is destroyed, and the superconducting state is established and the electric resistance is increased. In recent years, research and development on superconducting current limiting conductors (elements) that utilize this phenomenon to limit an excessive current have become active. The technology of this entire field is described in, for example, a publication {Journal of the Institute of Electrical Engineers of Japan, Volume 110, No. 9, p. 705 (1990)}. Among these, superconducting current limiting conductors utilizing oxide superconductors have recently received attention. The structure of the element used for this is a simple structure in which a pair of electrodes are formed by depositing a metal such as silver, gold or indium on a part of the superconductor by using vapor deposition or paste on the rod-shaped or plate-shaped superconductor. It is something. As a typical example, a publication {Advances in Superco
nductivity, page 691 (1988)}. This uses a sintered body of Y-Ba-Cu-based oxide superconducting powder to form a zigzag-like (meaner structure) sheet by the doctor blade method, in a normal conducting state when a current exceeding a critical current flows. The current is limited by utilizing the high resistance. However, such a sintered body (one having a linear shape, a rod shape, or a plate shape) generally has a drawback that the critical current cannot be increased, and thus the short-circuit current can be limited only in a small proportion.

Therefore, a current limiting conductor to which a film-shaped superconductor formed on a substrate is applied has been considered. Due to the progress of film forming technology, it has recently become possible to obtain an oxide superconducting thin film capable of passing a very large critical current. Further, the film-shaped one has advantages as a current limiting conductor such that it has a better cooling characteristic than the above-mentioned one such as a linear one, and can easily have a high resistance. However, the oxide superconducting thin film has a large critical current over a large area because the composition shift tends to occur when the film thickness is increased and the composition becomes inhomogeneous when formed in a large area. It was unavoidable to give rise to the major drawback of difficulty in obtaining things. In particular, the occurrence of inhomogeneity in film quality such as composition when a film is formed on a relatively large area is an unavoidable problem in the current superconducting thin film manufacturing technology, and therefore a weak portion is melted during energization, It was not possible to increase the limit terminal voltage of the current limiting conductor (equivalent to the input power or circuit voltage until the fuse is cut).

[0004]

In order to solve the above-mentioned drawbacks, a kind of thermal and electrical stabilization may be performed by coating a metal thin film on the superconducting film of the element portion by a method such as vapor deposition. Conceivable. Such a technique can be easily conceived from the conventional technique described in, for example, a publication {edited by the Physical Society of Japan, Superconductivity, p. 276, 1979 (Maruzen Co., Ltd.)}. The inventors of the present invention have made the limit terminal voltage several tens of V by the stabilization by applying such a conventional technique.
I found that it is possible to raise up to. However, it is insufficient as a practical level, and at least 100V
It is necessary to withstand the above voltage, and it is desired to further improve the stabilizing performance of the current limiting conductor.

The present invention has been made to solve the above problems, and an object thereof is to obtain an oxide superconducting current limiting conductor having a large current limiting effect and a limit terminal voltage of 100 V or more. is there.

[0006]

The oxide superconducting current limiting conductor of the present invention is provided on a base material and this base material, and the oxide superconducting layer is on the base material side, and the oxide superconducting layer and the silver layer are provided. And a laminated body in which two or more layers are alternately laminated.

[0007]

In the present invention, an oxide superconducting layer is formed,
A silver layer is formed thereon to form a laminated structure. At this time,
When two or more superconducting layers and two or more silver layers are alternately laminated, when the superconducting current limiting conductor is energized, the current is shunted to the silver layers and the heat dissipation during heat generation is improved.
It is considered that the stabilization characteristics are improved.

[0008]

EXAMPLES Example 1. A rectangular MgO substrate having a width of 5 mm and a length of 20 mm is used as a base material, and then each component metal is used as a starting material, and a Y-based (YBa ₂
Cu ₃ O _7-X) was formed of the oxide superconductor film. At this time, oxygen gas was introduced to adjust the gas pressure to 1.5 × 10 ⁻⁴ Tor.
The temperature was adjusted to r, and after film formation, the film was gradually cooled to room temperature in this atmosphere. Thereafter, a silver layer was formed thereon by vapor deposition in a vacuum of 1.8 × 10 ⁻⁶ Torr. Each of the above steps was carried out three times, and a laminated body in which superconducting layers and silver layers were alternately laminated in three layers was provided on the substrate, and a current limiting conductor of one example of the present invention was manufactured. Then, the central portion of the superconducting film was covered with an insulating tape, and both ends were plated with gold without electric field to form terminal portions, and lead wires were attached thereto. The critical temperature of the superconducting layer was 86K, and the thickness of each of the superconducting layer and the silver layer was about 2000Å and 100Å.

Comparative Example 1. Using the same electron beam evaporation method and the same type of substrate as in Example 1, film formation was performed in the same composition as in Example 1 and in an oxygen gas stream with the same gas pressure to form a Y-based superconducting film of about 6000 Å to obtain the conventional composition. It was a superconducting current limiting conductor. The critical temperature of this superconducting layer was 86K.

Comparative Example 2. A 300 Å silver film was formed on the superconducting current limiting conductor obtained in Comparative Example 1 by vapor deposition to obtain a conventional stabilized superconducting current limiting conductor. The critical temperature of this superconducting layer was 86K.

Each of the current limiting devices of Example 1, Comparative Example 1 and Comparative Example 2 was placed in liquid nitrogen and cooled, and an AC circuit (frequency of 50 Hz) was used to change the terminal voltage applied to the devices. , The limit voltage between terminals until the element was blown was investigated. As a result, in Example 1, 15
The voltage was 5 V, the voltage of Comparative Example 2 was 60 V in the conventional case in which the stabilizing silver coating was applied simply by vapor deposition, and 6 V in Comparative Example 1 in the conventional method without any coating. That is, it is considered that the conventional ones cannot apply a high terminal voltage because the superconducting film is inhomogeneous and the weak portion is melted by heat during energization. On the other hand, according to the embodiment of the present invention, even if the superconducting film is inhomogeneous, the stability performance of the device is improved by the lamination with the silver layer.
It has been revealed that the element is a current limiting conductor that does not melt even when a high voltage exceeding V is applied. Further, in the current limiting conductor of one embodiment of the present invention, in the case of the above limit terminal voltage of 155V, the estimated short circuit current 370A of the used circuit could be greatly limited to 30A which is about 1/12 or less. ..

Example 2. A rectangular SrTiO ₃ substrate having the same size as in Example 1 was used as a base material. A YBa ₂ Cu ₃ O _7-X- based oxide superconducting layer was formed by the sputtering method. At this time, oxygen gas was introduced to adjust the gas pressure to 1.1 × 1.
It was adjusted to 0 ⁻⁴ Torr, and after film formation, it was gradually cooled to room temperature in this atmosphere. 1.8 × 10 ^-6 Torr on superconducting layer
A silver layer was sputtered in vacuum. The above process was performed twice, and a laminated body in which two superconducting layers and two silver layers were alternately laminated was provided on the substrate, and a current limiting conductor of another example of the present invention was produced. Next, both ends were electrolessly plated with gold to form terminals, and lead wires were attached to the terminals to obtain oxide superconducting current limiting devices. The critical temperature of the superconducting film was 88K, and the thickness of each of the superconducting layer and the silver layer was about 3000Å and 200Å.

Comparative Example 3. Using the same sputtering method and the same type of base material as in Example 2, film formation was performed in an oxygen stream of the same composition and gas pressure as in Example 2 to form a Y-based superconducting film of about 6000 Å to obtain a conventional superconducting limit. It was used as a flow conductor. The critical temperature of this superconducting layer was 88K.

Comparative Example 4. On the superconducting current limiting conductor obtained in Comparative Example 3, a 400 Å silver film was formed by vapor deposition to obtain a stabilized conventional superconducting current limiting conductor. The critical temperature of this superconducting layer was 88K.

Each of the current limiting elements of Example 2, Comparative Example 3 and Comparative Example 4 was placed in liquid nitrogen and cooled, and an AC circuit (frequency 50 Hz) was used to change the terminal voltage applied to the elements. , The limit voltage between terminals until the element was blown was investigated. As a result, in Example 2, 14
The voltage was 7 V, the voltage of Comparative Example 4 was 64 V in the conventional case where the stabilizing silver coating was applied only by vapor deposition, and the voltage of Comparative Example 3 was 8 V in the conventional case where no coating was applied. That is, it is considered that the conventional ones cannot apply a high terminal voltage because the superconducting film is inhomogeneous and the weak portion is melted by heat during energization. On the other hand, in the other embodiment of the present invention, even if the superconducting film is inhomogeneous, the electric and thermal stabilization performance of the device is improved, and therefore even if a high voltage exceeding 100 V is applied. It was revealed that the element was a current-limiting conductor that never melted. Further, in the current limiting conductor of another embodiment of the present invention, the above-mentioned limit terminal voltage 14
In the case of 7V, the estimated short circuit current 360A of the used circuit could be greatly limited to 28A which is about 1/13 of the estimated short circuit current.

The base material according to the present invention is Al
₂ O ₃ , SiO ₂ , MgO, SrTiO ₃ , ZrO ₂ , Y ₂ O
Ceramics such as ₃ and single crystals, gold, silver, stainless steel,
Metals such as copper and nickel and alloys thereof can be used. In the present invention, after forming the superconducting layer, it is necessary to form a silver layer having an arbitrary thickness on the superconducting layer. As the above method, there are so-called physical vapor deposition method, chemical vapor deposition method, and electrophoretic deposition method utilizing electrophoresis. However, as shown in the examples, it is optimal to use the same method for forming the superconducting layer and the silver layer. However, the present invention is not limited to this, and the silver layer may be formed by a film forming method different from the method of forming the superconducting layer. The thicknesses of the superconducting layer and the silver layer are not limited and can be arbitrarily selected. According to experiments, the superconducting layer has a thickness of about 100.
~ 3000Å is suitable, and the thickness of the silver layer is 50 ~.
500Å is suitable. Further, it was confirmed that the effect of the present invention can be obtained by alternately laminating two or more layers of these two layers. Therefore, in the present invention, it is suitable to stack two to three layers as shown in the embodiment.

In forming the oxide superconducting film on the substrate in the embodiment of the present invention, oxygen gas is generally introduced to form the film. An arbitrary value may be used as the oxygen gas pressure because it greatly differs depending on the method used. For example, in the CVD method, it is generally necessary to have a high gas pressure, and in the sputtering method and the vapor deposition method, the gas pressure is usually low (the degree of vacuum is high).

As a method of forming a metal coating to be an electrode terminal after forming the oxide superconductor current-limiting conductor of the embodiment of the present invention, a vapor phase film forming method, an electroless plating method, an electrolytic plating method, or pressure bonding. Either method may be used. Silver and gold are preferable for the electrode terminals.

By the way, in the embodiment, the Y-based material is used as an example of the oxide-based superconducting material, but the effect of the present invention is Y.
It was confirmed by the same examination as in the example that it is not limited to the system but is expressed in any oxide superconducting material such as Bi type, Tl type, Nd type and the like. Further, in the above embodiment, the case where the current limiting conductor is used for the current limiting element has been described, but the present invention is not limited to this. It goes without saying that there is no power loss and the current can be limited when an excessive current flows.

[0020]

As described above, the present invention provides a substrate,
And a current limiting effect by using a laminate provided on this substrate and having the oxide superconducting layer on the substrate side and alternately laminating two or more oxide superconducting layers and silver layers, respectively. It is possible to obtain an oxide superconducting current limiting conductor having a large value and a limit terminal voltage of 100 V or more.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sadajiro Mori 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Central Research Institute (72) Inventor Tatsuya Hayashi 8-1-1 Tsukaguchihonmachi, Amagasaki Mitsubishi Electric Central Research Institute Co., Ltd.

Claims (1)

[Claims] 1. An oxidation comprising a base material and a laminate provided on the base material, wherein the oxide superconducting layer is on the base material side and two or more oxide superconducting layers and two or more silver layers are alternately laminated. Superconducting fault current limiter.