JPH09172206A - Superconducting current limiting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evade quality deterioration of current limiting operation, by constituting a cylindrical superconducting magnetic shielding body of a cylindrical laminate of a cylindrical superconductor layer and a cylindrical conductive substratum layer having a current blocking part which prevents generation of an internal current in the circumferential direction. SOLUTION: A superconducting cylinder 1 constituting a cylindrical superconductor layer is laminated on the outer surface of a silver cylinder 2. In the silver cylinder 2, a slit 3 reaching both ends in the axial direction is formed. An eddy current which is to flow in the circumferential direction of the silver cylinder 2 is blocked by the slit 3. When short-circuiting occurs, and an overcurrent flows through a coil 42 of a current limiting device, magnetic flux generated from the coil 42 rapidly increases, and magnetic shielding effect by a superconducting magnetic shielding body 41 is lost. The magnetic flux permeates the hollow part of the cylinder, and the inductance of the coil 42 increases rapidly, so that current limiting action to the overcurrent is generated. In this case, an eddy current is generated in the silver cylinder 2 by the change of magnetic flux in the hollow part of the shielding body 41, but an internal current in the circumferential direction is not generated in the silver cylinder 2 by the effect of the light 3, so that magnetic flux change effective in current limiting action is not hindered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting fault current limiter that limits an overcurrent by using a superconductor.

[0002]

2. Description of the Related Art When a short-circuit accident occurs in a power system, an overcurrent flows, which may damage equipment in the system. For this reason, a current limiting device that limits an overcurrent at the time of a short circuit is generally connected to the power system. This fault current limiter is required to have the capability of instantaneously interrupting an overcurrent, low impedance, and low power consumption during normal times when no short circuit occurs.Therefore, various superconducting fault current limiters using superconductors are required. Proposed. To one of such superconducting fault current limiters, connect a coil for current limiting to the power system,
There is a type called a magnetic shield type superconducting fault current limiter in which a tubular superconductor is electromagnetically coupled to this coil.

The current limiting action of the overcurrent by this superconducting fault current limiter is performed as follows. Cool the fault current limiter sufficiently with a cooling container to put the superconductor in the superconducting state. When an alternating current flows through the coil in this state, the magnetic flux generated from the coil is shielded by the Meissner effect of the superconductor in the current limiter in normal times. Therefore, the inductance of the coil has a very small value, and therefore the power loss due to the superconducting fault current limiter is extremely small in normal times.

However, when a short circuit accident occurs in the power system and the magnetic flux rapidly increases due to an overcurrent flowing in the coil, the critical state is broken, and the magnetic flux from the coil is coupled to the coil without being shielded. For this reason, the inductance of the coil sharply increases, and the overcurrent flowing through the coil is limited accordingly.

[0005]

In such a superconducting fault current limiter, when a high-temperature superconductor is used as the superconductor, the high-temperature superconductor has a very brittle ceramic material, so that a structural base material for reinforcement is used. Is preferably provided, and the superconductor layer is formed thereon. A good conductor such as silver is used as the substrate for forming the high temperature superconductor layer, but in this case, there are the following problems.

That is, when a short circuit accident occurs in the power system and an overcurrent flows through the coil, the magnetic flux generated from the coil rapidly increases and breaks the critical state of the superconductor, whereby the superconductor enters the normal conducting state. Therefore, the effect of shielding the magnetic flux generated from the coil is lost and the current limiting action occurs. In this state, however, an eddy current (shielding current) is generated in the conductive substrate due to the change in the magnetic flux. Occurs. Since this eddy current flows so as to suppress the change in magnetic flux, the increase in the inductance of the coil necessary for current limiting operation is limited, and therefore the overcurrent flowing in the coil cannot be sufficiently limited. It will reduce the performance of the fault current limiter.

Accordingly, the present invention has an object to provide a high-performance superconducting fault current limiter in which a superconducting conductor is laminated on a conductive substrate so as to avoid deterioration in performance of current limiting operation. Is.

[0008]

In order to achieve the above-mentioned object, the invention according to claim 1 has a superconducting limit having a cylindrical superconducting magnetic shield and a coil provided around the cylindrical superconducting magnetic shield. In the current transformer, the cylindrical superconducting magnetic shield comprises a concentric lamination of a cylindrical superconducting layer and a cylindrical conductive substrate layer having a current blocking portion that prevents the generation of an internal current in the circumferential direction. It is a feature.

That is, during the current limiting operation, the tubular superconductor layer is in the normal conducting state, and at this time, the superconductor layer itself has a high resistance, but the tubular conductive substrate layer, which is the structural substrate, is changed by the magnetic flux change. Eddy current is generated. When this eddy current causes a circumferential internal current to be generated in the base layer, the change in magnetic flux is suppressed, and this is prevented by the current blocking portion.

"To prevent the generation of an internal current in the circumferential direction" means to completely cut off the eddy current which tends to flow in the circumferential direction inside the cylindrical conductive substrate layer, or to determine the magnitude of this eddy current. To make it smaller. The current blocking portion can also be formed by interposing an insulator or a high resistance material in the base layer. For example, an impurity injection region may be formed in a part of the cylindrical conductive base layer and used as a current blocking portion, or a part of the cylindrical conductive base layer may be thinned and used as a current blocking portion. .

The invention according to claim 2 is the invention according to claim 1, wherein the current blocking portion is formed by a gap.

According to a third aspect of the present invention, in a superconducting fault current limiter having a cylindrical superconducting magnetic shield and a coil provided around the cylindrical superconducting magnetic shield, the cylindrical superconducting magnetic shield has an annular shape. The present invention is characterized in that the superconductor layer and a ring-shaped conductive base layer having a current blocking portion that prevents the generation of an internal current in the circumferential direction are laminated at their end faces.

That is, during the current limiting operation, the annular superconductor layer is in a normal conducting state, and at this time, the superconductor layer itself has a high resistance, but the annular conductive substrate layer, which is the structural substrate, has an eddy current due to a change in magnetic flux. Occurs. When this eddy current causes a circumferential internal current to be generated in the base layer, the change in magnetic flux is suppressed, and this is prevented by the current blocking portion.

Also in this case, "to prevent the generation of the internal current in the circumferential direction" means to completely cut off the eddy current that tends to flow in the circumferential direction inside the annular conductive substrate layer, or to prevent this eddy current. It means reducing the size. The current blocking portion can also be formed by interposing an insulator or a high resistance material in the base layer. For example, an impurity injection region may be formed in a part of the ring-shaped conductive base layer and used as a current blocking part, or a part of the ring-shaped conductive base layer may be thinned and used as a current blocking part.

Further, in order to further enhance the current limiting action of the superconducting fault current limiter, all of the annular conductive substrate layers of each of the laminated layers constituting the cylindrical superconducting magnetic shield are provided with current blocking portions. Is desirable.

The invention according to claim 4 is the invention according to claim 3, characterized in that the current blocking portion is formed by a gap.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. The first embodiment of the present invention is a magnetic shield type superconducting fault current limiter using a cylindrical integral type superconducting magnetic shield made of a conductive cylinder and a superconducting cylinder.

FIG. 1 shows the structure of a cylindrical integral superconducting magnetic shield used in the superconducting fault current limiter according to the first embodiment. Silver cylinder 2 forming a cylindrical conductive substrate layer
A superconducting cylinder 1 forming a cylindrical superconductor layer is laminated on the outer surface of the, and a silver cylinder 2 is provided with a slit 3 extending axially between both ends. Therefore, the eddy current that tends to flow in the silver cylinder 2 in the circumferential direction is blocked by the slit 3, and the circumferential internal current is not generated.

This superconducting magnetic shield is manufactured as follows. A slurry obtained by mixing a powder of Bi ₂ Sr ₂ CaCu ₂ Ox, an alcohol and a binder is spray-coated on the surface of the silver cylinder 2 to form a layer, which is then fired.
After that, the silver cylinder 2 is axially cut from the inner surface of the cylinder to form the slit 3. The slit 3 may be filled with an insulating material.

In the superconducting fault current limiter, as shown in FIG. 4, a coil 42 is wound around the superconducting magnetic shield 41 produced as described above, and a magnetic material core is provided in the hollow portion of the cylinder of the superconducting magnetic shield 41. It is constituted by disposing 43 through and forming a closed magnetic circuit.

When using this superconducting fault current limiter, the coil of the fault current limiter is inserted in series in the circuit of the power system. The superconducting fault current limiter is used by cooling the superconducting shield to a superconducting state by cooling it below a critical temperature in a cooling container filled with liquid nitrogen or the like. For example, FIG. 5 shows a superconducting fault current limiter connected to a fault current limiter performance test circuit capable of simulating a short circuit accident in a power system. In this circuit, a coil 51 of a current limiting device is connected in series to a load 54 connected to an AC power source 52, and a switch 5 for pseudo short circuit is connected in parallel with the load 54.
3 is provided. In this circuit, the superconducting fault current limiter is sufficiently cooled in a cooling container (not shown).

The superconducting fault current limiter thus constructed operates as follows. During normal times when a short-circuit accident does not occur in the electric power system, the magnetic flux generated from the coil 42 of the current limiter cannot enter the hollow portion of the cylinder of the superconducting magnetic shield 41 due to the Meissner effect of the superconductor, and the inside of the core 43. No magnetic flux flows through. However, when a short circuit occurs and an overcurrent flows through the coil 42 of the current limiter, the magnetic flux generated from the coil 42 increases rapidly, and the magnetic shielding effect of the superconducting magnetic shield 41 is lost. For this reason, magnetic flux enters the hollow portion of the cylinder and a large amount of magnetic flux flows in the closed magnetic circuit of the core 43, so that the inductance of the coil 42 suddenly increases and a current limiting action against overcurrent occurs. At this time, an eddy current is generated in the silver cylinder due to a change in the magnetic flux in the hollow cylindrical portion of the superconducting magnetic shield 41, but since the silver cylinder has the slit 3, the circumferential internal current is not generated. . Therefore, the magnetic flux change effective for the current limiting action is not hindered, and accordingly, the increase in the inductance of the coil is not hindered, and as a result, the current limiting action is not suppressed. in this way,
Even when a good conductor silver cylinder is used as the structural substrate of the high temperature superconductor layer, it is possible to prevent the performance of the current limiting action from being deteriorated.

In the first embodiment, a slit formed by cutting a part of a silver cylinder is used as the current blocking portion for preventing the generation of the circumferential internal current, and the circumferential internal current is completely cut off. Therefore, a current blocking unit that suppresses the generation of a circumferential internal current may be used. For example, in addition to this, it is also effective to inject impurities into a part of the silver cylinder to form a high resistance region, or to thin a part of the silver cylinder.

In the first embodiment, a silver cylinder is used as a cylindrical structural substrate for forming a cylindrical superconducting magnetic shield, but the present invention is not limited to this, and the superconductor layer is not limited thereto. A conductive material other than silver may be used as long as the material is suitable for the structure.

In the first embodiment, the cylindrical superconducting magnetic shield is used. However, the superconducting magnetic shield of the current limiter according to the present invention is not limited to the cylindrical shape, and a coil may be wound around it. It may be of a tubular shape having an arbitrary shape such as a rectangular cross section that allows the magnetic flux (core) to pass through the hollow portion.

In the first embodiment, the magnetic material core is provided in the hollow portion of the cylinder of the superconducting magnetic shield to form the current limiter, but it is not always necessary to provide the core. However, in order to increase the difference in coil inductance between the normal state and the short-circuit accident, it is desirable to provide a core with high magnetic permeability.

The second embodiment according to the present invention uses a superconducting magnetic shield having a superconducting fault current limiter in which a plurality of annular superconductors are laminated in the axial direction.

FIG. 2 shows the structure of the laminated superconducting magnetic shield according to the second embodiment. This superconducting magnetic shield is formed into a cylindrical shape by stacking a plurality of annular superconductors in a tubular shape in the axial direction. The annular superconductor comprises an annular silver substrate 22 and a superconducting layer 21 formed thereon,
A gap 23 in the radial direction is provided in the silver base 22 so that a circumferential internal current does not flow.

The annular superconductor is manufactured as follows. A paste layer in which a powder of Bi ₂ Sr ₂ CaCu ₂ Ox, an alcohol, and a binder are mixed is formed on a silver sheet by screen printing in an annular shape, and is baked. After that, the silver sheet in the hollow portion of the circular ring of the superconductor is punched out and removed to produce a circular superconductor having a superconductor layer on the silver base. Furthermore, a part of the silver base 22 is shown in FIG.
As shown in, the cutting is performed from the silver side so as to block the path of the annular current. A cylindrical superconducting magnetic shield is produced by axially stacking the plurality of annular superconductors produced in this way at their end faces. The gap 23 may be filled with an insulator.

A superconducting fault current limiter using such a superconducting magnetic shield is also shown in FIG.
1. A coil 42 is wound around 1 to provide a superconducting magnetic shield 41.
The magnetic material core 43 is penetrated through the hollow part of the cylinder to form a closed magnetic circuit.

When this superconducting fault current limiter is used, as in the case of the first embodiment, the coil 42 is connected in the circuit of the power system and the fault current limiter is cooled in the cooling container before use. To do.

The superconducting fault current limiter configured as described above operates as follows. During normal times when a short-circuit accident does not occur in the electric power system, as in the case of the first embodiment, the magnetic flux generated from the coil 42 of the current limiting device cannot enter the hollow portion of the cylinder of the superconducting magnetic shield 41. No magnetic flux flows in the core 43. However, a short circuit occurs and the current limiter coil 42
When an overcurrent flows in the magnetic field, the magnetic flux generated from the coil 42 suddenly increases, and the magnetic shielding effect of the superconducting magnetic shield 41 is lost. Therefore, the magnetic flux enters the hollow portion of the cylinder and the core 43
When a large amount of magnetic flux flows through the closed magnetic circuit, the inductance of the coil 42 suddenly increases and a current limiting action against overcurrent occurs. At this time, an eddy current is generated in the silver base due to a change in magnetic flux in the hollow cylindrical portion of the superconducting magnetic shield 41, but since the silver base has the gap 23, a circumferential internal current is generated. do not do. Therefore, the magnetic flux change effective for the current limiting action is not hindered, and therefore the increase of the inductance of the coil is not hindered, and as a result, the current limiting action is not suppressed. As described above, it is possible to prevent the performance of the current limiting action from being deteriorated even if the good conductive silver base is used as the structural base of the high temperature superconductor layer.

In the second embodiment, the gap in which a part of the silver substrate is cut is used as the current blocking portion for preventing the generation of the circumferential internal current, and the circumferential internal current is completely cut off, but the high resistance portion is used. Therefore, a current blocking unit that suppresses the generation of a circumferential internal current may be used. For example, it is effective to inject impurities into a part of the silver substrate to form a high resistance region, or to thin a part of the silver substrate.

In the second embodiment, the gaps are formed in all the silver bases of the stacked layers forming the cylindrical superconducting magnetic shield, but the gaps need not necessarily be formed in all the silver bases. However, in order to further enhance the current limiting action of the superconducting fault current limiter, it is desirable that gaps be formed in all the silver substrates.

In the second embodiment, a cylindrical laminated superconducting magnetic shield in which a plurality of annular superconductors are laminated in the axial direction is used, but the superconducting magnetic shield of the current limiting device according to the present invention is used. The body is not limited to a cylindrical shape, but any body may be used as long as a coil can be wound around it and a magnetic flux (core) can pass through the hollow portion. For example, a plurality of rectangular annular superconductors can be laminated. The magnetic shield may be used.

In the second embodiment, the silver substrate is used as the structural substrate for forming the cylindrical superconducting magnetic shield, but the present invention is not limited to this, and the structure of the superconducting layer is used. A conductive material other than silver may be used as long as it is a suitable material.

In the second embodiment, the magnetic material core is provided in the hollow portion of the cylinder of the superconducting magnetic shield to form the current limiting device, but the core is not necessarily provided. However, in order to increase the difference in coil inductance between the normal state and the short-circuit accident, it is desirable to provide a core with high magnetic permeability.

[0038]

EXAMPLES Example 1 Integrated Superconducting Shield A superconducting cylinder having a thickness of 200 μm was laminated by spray coating on the surface of a silver cylinder having a diameter of 50 mm, a length of 70 mm and a thickness of 1 mm. When the critical current density of this superconducting cylinder was measured, it was 1800 A / cm.
^{Was 2} . Then, the silver cylinder was axially cut to form slits.

A superconducting fault current limiter was prepared by winding 100 layers of enamel-coated copper wire having a diameter of 1 mm around the superconducting cylinder in two layers for 100 turns. Further, this superconducting fault current limiter was connected to the fault current limiter performance test circuit shown in FIG. 5, and the fault current limiter was immersed in liquid nitrogen in a cooling container (not shown).

In this circuit, after a current having a peak current value of 5 A was applied at a frequency of 50 Hz with the switch open, the switch was closed to cause a short circuit accident, and the current value was measured. As a result, the current value became 25 A for a moment, but thereafter, it was limited to 5 A.

Comparative Example 1: Integrated Superconducting Shield Diameter 5
A superconducting cylinder having a thickness of 200 μm is laminated on the surface of a silver cylinder having a thickness of 0 mm, a length of 70 mm and a thickness of 1 mm by spray coating,
The silver cylinder was left without slits. When the critical current density of this superconducting cylinder was measured, it was 1800 A / cm.
^{Was 2} . A current limiting device was produced under the same conditions as in Example 1, the current limiting device was connected to the circuit of FIG. 5, and the current limiting device was immersed in liquid nitrogen in the cooling container. In this circuit, the first embodiment
A short circuit accident was simulated under the same conditions as above, and the current value was measured. As a result, the current value was 25 A for a moment, and then the current was limited, but it was 6.5 A.

Comparing the results of Example 1 and Comparative Example 1,
The fault current limiter of Example 1 was able to limit overcurrent due to a short circuit accident more than the fault current limiter of Comparative Example 1.

(Example 2: Laminated type superconducting shield) Diameter 6
An annular superconductor having an outer diameter of 50 mm, an inner diameter of 40 mm and a thickness of 200 μm was laminated by screen printing on a silver substrate having a thickness of 0 mm and a thickness of 50 μm. When the critical current density of this superconductor was measured, it was 1600 A / cm ² . Then, the silver in the hollow portion of the superconductor was punched out to produce an annular superconductor. Further, this annular superconductor was scraped from the silver side to provide a radial gap in the silver substrate.

A superconducting magnetic shield is manufactured by stacking 50 annular superconductors, and two layers of enamel-coated copper wire having a diameter of 1 mm are wound around the superconducting magnetic shield for 100 turns. Was produced. Further, as in Example 1, the superconducting fault current limiter was connected to the circuit of FIG. 5, and the fault current limiter was immersed in liquid nitrogen in a cooling container (not shown).

In this circuit, a current with a peak current value of 5 A was applied at a frequency of 50 Hz with the switch open, and then the switch was closed to cause a short circuit accident, and the current value was measured. As a result, the current value became 50 A for a moment, but after that, it was limited to 15 A.

(Comparative Example 2: Laminated type superconducting shield) Diameter 6
0 mm, 50 μm thick on a silver sheet, 50 mm outer diameter,
An annular superconductor having an inner diameter of 40 mm and a thickness of 200 μm was laminated by screen printing. When the critical current density of this superconductor was measured, it was 1600 A / cm ² . Then, the hollow silver sheet of the superconductor was punched out to form an annular superconductor, and the silver sheet was left without any gaps. Under the same conditions as in Example 2, a superconductor and a current limiting device were produced, the current limiting device was connected to the circuit of FIG. 5, and the current limiting device was immersed in liquid nitrogen in the cooling container.

In this circuit, a short circuit accident was simulated under the same conditions as in Example 2 and the current value was measured. As a result, the current value became 50 A for a moment, and then the current was limited,
It was 20A.

Comparing the results of Example 2 and Comparative Example 2,
The fault current limiter of Example 2 was able to limit overcurrent due to a short circuit accident more than the fault current limiter of Comparative Example 2.

[0049]

As described above, the invention according to each of the claims of the present invention can be applied to a superconducting fault current limiter having a superconducting magnetic shield composed of a superconductor layer even when a conductive substrate layer is used. In addition, it has an effect of producing a sufficient current limiting action and preventing performance degradation of the current limiting device.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a configuration of an integrated superconducting magnetic shield used in a superconducting fault current limiter according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a configuration of a laminated superconducting magnetic shield used in a superconducting fault current limiter according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a state of a gap provided in an annular conductive substrate.

FIG. 4 is a schematic diagram showing a schematic configuration of a superconducting fault current limiter.

FIG. 5 is a circuit diagram of a current limiter performance test circuit.

[Explanation of symbols]

 1: Superconducting cylinder 2: Silver cylinder 3: Slit 21: Superconducting layer 22: Silver base 23: Gap 31: Silver base 32: Gap 41: Superconductor 42: Coil 43: Magnetic material core 51: Superconducting fault current limiter 52: AC Power supply 53: Switch 54: Load

Claims (4)

[Claims] 1. A superconducting fault current limiter having a cylindrical superconducting magnetic shield and a coil provided around the cylindrical superconducting magnetic shield, wherein the cylindrical superconducting magnetic shield is a cylindrical superconducting layer. A superconducting fault current limiter comprising a concentric stack with a tubular conductive substrate layer having a current blocking portion that prevents the generation of an internal current in the circumferential direction. 2. The superconducting fault current limiter according to claim 1, wherein the current blocking portion is formed by a gap. 3. A superconducting fault current limiter having a cylindrical superconducting magnetic shield and a coil provided around the cylindrical superconducting magnetic shield, wherein the cylindrical superconducting magnetic shield comprises an annular superconducting layer and a peripheral superconducting layer. A superconducting fault current limiter, comprising a laminated body in which an annular conductive substrate layer having a current blocking portion that prevents the generation of an internal current in the direction is laminated at the end faces of each other. 4. The superconducting fault current limiter according to claim 3, wherein the current blocking portion is formed by a gap.