JPH08161983A - Current limiter and its manufacture - Google Patents

Abstract

PURPOSE: To make a current limiter more practical that uses an oxide superconductor by forming a protective film that protects the superconductor from an external environment and can impart a desired current limiting effect to the superconductor. CONSTITUTION: This current limiter 10 which performs current limiting function by means of resistance generated during transition from a superconducting state to a normal conducting state has a current limiting portion 3 made of an oxide superconductor and a protective film 4 covering the current limiting portion 3. The protective film 4 comprises a first layer 4a provided over the current limiting portion 3 and made of an amorphous material having almost the same composition as the oxide superconductor and a second layer 4b covering the first layer 4a and made of a corrosion resistant metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fault current limiter for preventing an overcurrent from flowing in a power equipment in a power system, for example, when a short-circuit accident due to a lightning strike occurs. The present invention relates to a current limiting device used in a flow action part and a method for manufacturing the same.

[0002]

2. Description of the Related Art A current limiting device used in a power system is required to have a characteristic that a voltage drop during load operation is small and an abnormally large current can be quickly suppressed. A practical current limiting device that fully exhibits such characteristics is currently desired.

While a superconductor can maintain a non-resistance state, it has a property of rapidly generating resistance when a current exceeding its critical current value (superconducting-normal conducting transition) is used, so that it is used as a material for a fault current limiter. It is one of the promising candidates.

Currently, superconductors are roughly classified into metal type and oxide type. Since the metal superconductor using liquid helium as a coolant covers the surroundings with copper for stabilization against quenching, the resistance value per unit length in the normal conducting state does not become so large. In addition, the metal-based superconductor requires a special heat insulation mechanism for cooling,
It is disadvantageous for economy and compactness. For these reasons, the range of application of metal-based superconductors to current limiting devices is limited.

On the other hand, an oxide superconductor which is in a superconducting state in liquid nitrogen can utilize a simple cooling facility and does not require any countermeasure against quenching. Therefore, the resistance generated by the transition from superconducting to normal conducting can be effectively used. Therefore, it can be applied to a wide range of fault current limiters.

The oxide superconductor can be formed from any of solid phase, liquid phase and gas phase. For example Y ₁
In the case of Ba ₂ Ca ₃ O _7-X (0 ≦ X ≦ 1), by epitaxially growing from a vapor phase on a single crystal substrate,
A superconducting thin film having good crystallinity and a high critical current density can be obtained. If such a thin film can be used as a current limiting action part and a high critical current (Ic) can be passed, I
It is considered that when a current larger than c flows, a high resistance is generated to effectively limit the current. In particular,
In an oxide superconductor film deposited on a single crystal substrate, the crystal axis can be oriented in a direction parallel to the plane of the substrate,
Since there are few weak bonds at grain boundaries, a high resistance value can be generated at the time of transition. For example, Industrial Materials, 1993 Vol. 41, No. 3, p38-43 report that a superconducting thin film was formed on a single crystal substrate and etched into a zigzag shape for application to a current limiting device.

[0007]

For example, in order to stably operate a current limiting element formed by forming an oxide superconducting film on a substrate for a long period of time, an oxide superconducting film that performs a current limiting action should be protected from the external environment. A protective layer is needed to protect it.

An object of the present invention is to protect a superconductor from the external environment in a fault current limiter using an oxide superconductor, and
An object of the present invention is to provide a protective film that can bring a desired current limiting effect to a superconductor, and to provide a more practical current limiting device.

[0009]

A current limiting device according to the present invention comprises:
A current limiting device that performs a current limiting operation by resistance generated at the time of transition from a superconducting state to a normal conducting state, comprising a current limiting action part made of an oxide superconductor, and a protective film covering the current limiting action part, The protective film is provided on the current limiting portion and is composed of a first layer made of an amorphous material having substantially the same composition as the oxide superconducting material, and a second layer made of a corrosion-resistant metal and covering the first layer.
And a layer of.

In the current limiting device of the present invention, the current limiting action part is constructed.
The oxide superconductors formed are yttrium-based oxide superconductors.
Conductors, bismuth oxide superconductors, etc. can be used
It For yttrium-based oxide superconductors, Y₁Ba₂C
u₃O_7-X(0 ≦ X ≦ 1) can be preferably used
It In addition to this material, Y_1-XPb_XBa₂Cu₃O
₇(X = 0.05 to 0.5), Y_1-XBr_XBa₂Cu
₃O₇(X = 0.01 to 0.1), Y₁Ba₂Cu_3-X
Fe_XO₇(X = 0.01 to 0.1), Y₁Ba₂Cu
_3-XCr_XO₇(X = 0.01-0.2), etc.
Use a material with higher resistance in the superconducting state
Can also be. Bi is a Bi-based oxide superconductor.
₂Sr₂Ca₁Cu₂O_10-Y(0 ≦ Y ≦ 1), (Bi,
Pb)₂Sr₂Ca₁Cu₂O_10-YSuch as (0 ≦ Y ≦ 1)
Bi-based 2212 phase oxide superconductor, Bi₂Sr₂C
a₂Cu₃O_10-Y(0 ≦ Y ≦ 1), (Bi, Pb)₂S
r ₂Ca₂Cu₃O_10-YBismuth system such as (0 ≦ Y ≦ 1)
It is possible to preferably use a 2223 phase oxide superconductor or the like.
Wear.

The current limiting action part made of an oxide superconductor is covered with a protective film. The protective film is provided on the current limiting action portion, and includes a first layer made of an amorphous material (amorphous material) having substantially the same chemical composition as the oxide superconducting material,
A second layer provided thereon and made of a corrosion resistant metal. The yttrium-based oxide superconductor, the bismuth-based oxide superconductor, or the like described above can be used as the oxide superconducting material. It is preferred that it has approximately the same composition as the material selected from the group consisting of More specifically, the first layer is formed of Y ₁ Ba.
₂ Cu ₃ O _7-X (0 ≦ X ≦ 1), Bi ₂ Sr ₂ Ca ₁ C
u ₂ O _10-Y (0 ≦ Y ≦ 1) and Bi ₂ Sr ₂ Ca ₂ C
It is preferably formed from a material having a composition selected from the group consisting of u ₃ O _{10 -Y} (0 ≦ Y ≦ 1).

The second layer of the protective film comprises a corrosion resistant metal. As the corrosion resistant metal, for example, a material selected from the group consisting of noble metals, noble metal alloys, nickel alloys and iron alloys can be used. For precious metals, Ag, A
u, Pd, Pt, Rh, Ir, Ru, and Sr are included.
Corrosion resistant nickel alloys include Ni-Cu based and Ni-Mo
System, Ni-Cr system, Ni-Mo-Cr system, Ni-Cr-
There are alloy materials (hastelloyt) such as Mo-Fe type and Ni-Si type. Examples of the corrosion-resistant iron alloy may include stainless steel.

Further, according to the present invention, there is provided a method for manufacturing a current limiting device which performs a current limiting operation by the resistance generated at the transition from the superconducting state to the normal conducting state. A step of depositing a layer made of an oxide superconductor as a current limiting action part, a step of depositing an amorphous film having a composition substantially the same as that of the oxide superconducting material on the layer by a laser ablation method; Depositing a layer of corrosion resistant metal on the film.

In the present invention, various materials can be used for the base material, but a long material can be preferably used because the electric path for generating resistance is longer. Therefore, the wire rod can be preferably used as the base material. When a long metal having flexibility is used as the base material, in order to prevent the reaction between the metal and the oxide superconductor, yttria-stabilized zirconia (YS) is used.
It is desirable to form a reaction preventive layer composed of Z) or the like on the surface of the base material and deposit the oxide superconductor thereon. As the metal for the base material, for example, Hastelloyt, stainless steel or the like can be used.

Conventionally, oxide superconducting thin films for current limiting devices have been produced on a single crystal substrate, and the size of the thin film has been limited to the size of available single crystals. Since the resistance value of the thin film is proportional to the electric path length, the thin film was often etched in a zigzag pattern. For example, in the above-mentioned prior art, a zigzag thin film having a 40 mm long electric path is formed, but in an experimental example using this element, the applied voltage is 200 Vr. m. s. For a 500 kV system used as the backbone of a power transmission system or a 6.6 kV system used in a distribution substation, the voltage value applied per unit length becomes too large with one element. From the viewpoint of this withstand voltage, it is necessary to combine several elements in series. Further, in order to satisfy the current capacity, it is necessary to combine them in parallel. When using the oxide superconducting thin film thus produced on a single crystal substrate as a current limiting element for high voltage, connect a plurality of current limiting elements in series for withstanding voltage and in parallel for current capacity. There was a need. Such connection has a problem that it requires a high technology and a great deal of time, which is industrially disadvantageous. From the viewpoints described above, forming an oxide superconducting film on a long tape-shaped substrate has a very important meaning.

The oxide superconductor layer as the current limiting action portion is
It can be formed by various vapor phase methods, but particularly preferably by a laser ablation method. In the laser ablation method, a pulsed laser beam is irradiated onto a target made of an oxide superconducting material to cause ablation, and the generated chemical species (plasma) is deposited on the substrate. The thickness of the formed oxide superconducting layer is arbitrary and can be set according to the desired current limiting characteristics.

Next, a film in an amorphous state having substantially the same composition as the oxide superconducting material is deposited on the oxide superconducting layer. This film preferably has the same composition as the underlying oxide superconductor, and such a film can be formed by partially modifying the conditions under which the superconductor layer is deposited.

The amorphous film can be formed by various vapor phase methods, but can be preferably formed by, for example, the laser ablation method described above. In the case of laser ablation, a target made of an oxide superconducting material is irradiated with pulsed laser light to cause ablation, and the generated chemical species are deposited on the superconductor layer. At this time, when forming the superconducting layer, the substrate is appropriately heated to a temperature of 650 to 850 ° C. By reducing or not heating this, an amorphous material can be deposited. . Thus, amorphous films can be deposited at room temperature, for example. Laser ablation is suitable for forming a relatively thick film at high speed. The thickness of the amorphous film is also arbitrary and can be appropriately set according to the desired performance of the current limiting device, but is, for example, 0.1 μm to 100 μm, preferably 0.5 μm.
It can be set to ˜50 μm.

On the amorphous film, a layer made of a corrosion resistant metal is deposited for protection against the environment. The corrosion resistant metal used is as described above. This layer can be deposited by various vapor phase methods such as sputtering. The thickness of this layer can also be appropriately set according to the thickness of the superconductor. This layer is preferably thinner than the superconductor, but may be thicker than the superconductor. The thickness of this layer can be, for example, 1 to 100 μm.

[0020]

In order to operate a structure having an oxide superconducting film as a current limiting action part, for example, an oxide superconducting wire as a current limiting device, it is placed in liquid nitrogen or in a vacuum atmosphere controlled to a predetermined temperature. Will be installed. It is necessary to avoid deterioration of the characteristics of the superconducting film from the time when this structure is manufactured to the time when it is incorporated into a current limiting device as a current limiting device. Further, even if the current limiter is operated and then exposed to the atmosphere for some reason, or if dew condensation occurs, it is necessary to take measures so as not to deteriorate the characteristics thereof. In order to solve these problems and operate the current limiting element stably for a long period of time, a protective film for the superconducting film is required.

As the protective film, a corrosion-resistant metal that is capable of blocking external gases and liquids and is stable is effective. However, the corrosion resistant metal has high conductivity at the same time. If this corrosion-resistant metal is directly formed on the oxide superconductor, a parallel structure (1 / R = 1 / R ₁ (superconductor) + 1 / R ₂ (corrosion-resistant metal)) is formed, and the oxide superconductor becomes normal conductor. Even if the transition occurs and a high resistance is generated, a higher resistance, that is, a higher current limiting effect cannot be obtained as the entire fault current limiter because of the low resistance of the corrosion resistant metal. Therefore, instead of directly forming the layer of the corrosion resistant metal on the oxide superconductor, it is provided via the layer of the amorphous material. Since the amorphous material layer (first layer) according to the present invention has the composition of the oxide superconducting material but is amorphous, it does not exhibit superconducting properties and acts as an insulating material. The first layer cuts off electrical coupling between the second layer made of a corrosion resistant metal and the oxide superconductor layer.
Because of the first layer, the current limiting effect as designed is obtained without the current being shunted to the corrosion resistant metal during the current limiting action.

According to the present invention, the protective film has such a laminated structure to obtain environmental stability and at the same time,
It does not impair the current limiting characteristics. For example, until the structure according to the present invention is incorporated as a current limiting device, the superconducting property does not deteriorate in the atmosphere even if the storage location is not specified. Further, even after the current limiting device is operated, even if it is exposed to the atmosphere for some reason or condensation occurs, its characteristics are maintained.

Further, in the present invention, a noble metal, a noble metal alloy, a Ni alloy or an Fe alloy is preferable as a corrosion resistant metal and further enhances the resistance of the fault current limiter to the environment and prolongs the life of the fault current limiter.

In the method according to the present invention, in particular, the amorphous layer is deposited by the laser ablation method without heating the substrate, so that the first layer in the protective film can be formed more easily and at high speed. it can.

[0025]

【Example】

Example 1 On a Hastelloy tape (for example, Hastelloy C-276 tape) (size: width 1.0 cm × length 15 cm × thickness 0.5 mm) which is flexible and long and available, as a reaction-preventing layer Yttria-stabilized zirconia (YSZ)
The film deposited by the laser ablation method was used as the substrate. Then, three types of superconducting films were deposited on the YSZ film by the laser ablation method according to the usual method. The superconducting film is (1) Y ₁ Ba ₂ C
u ₃ O _7-X (0 ≦ X ≦ 1), (2) Bi ₂ Sr ₂ Ca ₁
Cu ₂ O _10-Y (0 ≦ Y ≦ 1) or (3) Bi ₂ Sr
It is composed of ₂ Ca ₂ Cu ₃ O _10-Z (0 ≦ Z ≦ 1) and has the same shape with a width of 1.0 cm and a length of 1
The thickness was 5 cm and the thickness was 1.0 μm.

Next, a protective film was formed on the superconducting film.
(A) Y ₁ Ba ₂ Cu ₃ O _7-X (0 ≦ X ≦ 1), (b)
Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _10-Y (0 ≦ Y ≦ 1), or (c) Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10-Z (0 ≦ Z ≦
A material obtained by sintering the material having the composition of 1) on a disk was used as a target, and a pulsed excimer laser was incident on the target at an angle of 45 ° to coat the evaporated particles on the superconducting film. Table 1 shows the film forming conditions.
(A) on the film of (1), (b) on the film of (2),
Each of (c) was deposited on the film of (3).

Next, as a second layer of the protective film, Ag, A
u, Ir, Pd, Pt, Rh, Ru, Os, Fe alloy (SUS303), and Ni alloy (Inconel) were deposited in a sputtering apparatus to a thickness of about 5 μm.

FIG. 1 shows the structure of a current limiting device sample having a two-layer structure protective film obtained as described above. In the current limiting element sample 10, the YSZ film 2 is formed on the Hastelloy tape 1, and the oxide superconducting film 3 is deposited thereon. The film 3 is covered with a protective film 4, which is an amorphous layer 4 a directly deposited on the film 3.
And a corrosion-resistant metal layer 4b covering it.

The Ic of each of the 36 samples thus obtained was measured, and the resistivity (R value) was determined by conducting an IV measurement while energizing up to 100A. In the IV measurement, the measurement voltage distance was 10 cm. The obtained results are shown in Table 2. Further, in order to investigate the durability of the measured sample to the environment, the sample was stored for 2000 hours in a constant temperature and humidity layer kept at 40 ° C.-85 RH%. After 2000 hours,
When Ic was measured and the R value was obtained by applying an electric current up to 100 V and measuring IV, almost the same result as before the durability test was obtained. The obtained results are shown together in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that the first layer of the protective layer was not formed, and Ic and IV were used.
Was measured. Also, as in Example 1, 40 ° C.-85
After the sample was stored for 2000 hours in the constant humidity and constant temperature layer kept at RH%, Ic and IV measurements were performed. Table 3 shows the obtained results.

[0033]

[Table 3]

As is clear from Table 3, it was found that the R value was greatly reduced without the first layer.

Comparative Example 2 A sample was prepared in the same manner as in Example 1 except that the second layer of the protective film was not formed, and Ic and IV were used.
Was measured. Further, as in Example 1, 40 ° C.-8
After the sample was stored for 2000 hours in a constant temperature and constant temperature layer kept at 5 RH%, Ic and IV measurements were performed. The results obtained are shown in Table 4.

[0036]

[Table 4]

As is clear from Table 4, after the durability test,
Ic was 0 in all samples.

[0038]

As described above, the current limiting device of the present invention has the first layer, which functions as an insulating layer, on the current limiting action part made of the oxide superconductor and the gas and liquid from the outside. It has a protective film comprised of a second layer of corrosion resistant metal that prevents permeation and permeation. The current limiting device having such a structure can sufficiently exert the characteristics of the current limiting action part,
As a current limiter used in a power system, it is possible to minimize the resistance during normal operation (DC resistance does not generate resistance, but AC current causes AC loss).
Further, in the event of an accident, it is possible to generate a large resistance by the current limiting action section and prevent an overcurrent from flowing in the power system.

The characteristics of the current limiting device of the present invention are retained by the protective film even when the current limiting device is installed in the apparatus and stored in the atmosphere.
Further, for performance investigation, even if Ic is measured or the cryogen disappears for some reason, the protective film prevents the characteristics from being deteriorated. As a matter of course, in liquid nitrogen or in a vacuum environment of a predetermined temperature obtained by a refrigerator or the like, deterioration of the characteristics does not occur.

The current limiting device of the present invention can be manufactured by various methods. For example, the first layer of the protective film is
It is desirable that the superconducting film is formed by a dry process so that the characteristics of the superconducting film are not deteriorated. The method of vapor deposition using a pulsed laser is another dry process, CVD.
The film formation speed is orders of magnitude higher than that of the sputtering method, sputtering method, vapor deposition method, and the like. In particular, when manufacturing a long film, the process using a pulse laser is advantageous in terms of cost and the like.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an example of a current limiting element according to the present invention.

[Explanation of symbols]

 1 Hastelloy Tape 2 YSZ Film 3 Oxide Superconducting Film 4 Protective Film 4a Amorphous Layer 4b Corrosion Resistant Metal Layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Noriyuki Ashida 1-3-1, Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Gozo Fujino 1-1-1, Shimaya, Konohana-ku, Osaka City No. 3 Sumitomo Electric Industries Co., Ltd. Osaka Works (72) Inventor Tsukushi Hara 4-1, Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Electric Power Technology Research Institute, Tokyo Electric Power Co., Inc. (72) Hideo Ishii Yokohama-shi, Kanagawa 4-1, Egasaki-cho, Tsurumi-ku TEPCO Electric Power Technology Laboratory

Claims (4)

[Claims] 1. A current limiting device that performs a current limiting operation by a resistance generated at the time of transition from a superconducting state to a normal conducting state, and covers a current limiting acting portion made of an oxide superconductor and the current limiting acting portion. A protective film, the protective film being provided on the current limiting portion, the first layer being made of an amorphous material having substantially the same composition as the oxide superconducting material; and the first layer. And a second layer formed of a corrosion-resistant metal. 2. The composition according to claim 1, wherein the first layer has substantially the same composition as a material selected from the group consisting of yttrium-based oxide superconducting materials and bismuth-based oxide superconducting materials. Current limiter. 3. The fault current limiter according to claim 1, wherein the corrosion resistant metal is at least one material selected from the group consisting of noble metals, noble metal alloys, Ni alloys and Fe alloys. . 4. A method for producing a current limiting device that performs a current limiting operation by the resistance generated at the time of transition from a superconducting state to a normal conducting state, comprising: oxide superconducting as a current limiting acting portion on a base material. A step of depositing a layer made of a body, a step of depositing a film in an amorphous state having substantially the same composition as the oxide superconducting material on the layer by a laser ablation method, and made of a corrosion resistant metal on the film. A method of manufacturing a fault current limiter, comprising: depositing a layer.