JPH0714493A - Superconductivity current limiter - Google Patents

Abstract

PURPOSE:To make an impedance of a coil small, and thereby enhance power transmission efficiency by preventing the magnetic line of force generated by the coil at the time of normal operations from leaking from a superconductor. CONSTITUTION:A cylindrical body 1 composed of a superconductor is disposed over the outer circumference of a core made of iron. A coil 3 is wound around the outer circumference of the cylindrical body 1 while being formed into one layer so as to be connected to a distribution electrical wire. The length of the cylindrical body 1 is made longer than that of the coil 3, so that magnetic fluxes generated by the coil 3 are prevented from leaking from the end section of the cylindrical body 1. Besides, when the coil 3 is wound around the outer circumference of the core 2 while the outer circumference is being enclosed by the cylindrical body 1, the length of the cylindrical body 1 is made longer than that of the coil 3.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a superconducting fault current limiter utilizing the magnetic shielding effect of a superconducting magnetic shield.

[0002]

2. Description of the Related Art In recent years, as the demand for electric power has increased, the transmission and distribution systems have become larger in capacity and larger in scale, and a very large short-circuit current tends to flow in the event of an accident such as a lightning strike. In order to protect power transmission and distribution equipment from this short-circuit current, it was necessary to increase the capacity of transformers and circuit breakers. Therefore, a method has been proposed in which a current limiting device is installed in order to suppress a short circuit current that occurs when an accident occurs in the power transmission and distribution system, and the short circuit current is suppressed to a predetermined level or less by the impedance of the current limiting device.

As such a superconducting fault current limiter, JP-A-2-
There is one disclosed in Japanese Patent No. 105402. That is, the basic structure of this magnetically shielded superconducting fault current limiter is one in which a coil is wound around the outer circumference of a cylinder made of a superconducting magnetic shield. During normal operation, the magnetic field generated by the coil is rejected by the magnetic shielding effect (Meissner effect) of the superconducting magnetic shield, so that the inductance becomes extremely small and the impedance of the coil becomes small. Therefore, the power transmission loss when transmitting power via the coil is reduced.

However, once an accident occurs and a short-circuit current flows, the superconducting magnetic shield is transferred to the normal conductor (quenching).
However, inductance is generated in the coil, the impedance increases, and the short-circuit current is suppressed. To bring this superconducting magnetic shield into a superconducting state, it is necessary to bring it to an extremely low temperature.
Therefore, at least the superconducting magnetic shield is immersed in a cooling liquid such as liquid nitrogen.

[0005]

In such a superconducting fault current limiter, it is necessary to reduce impedance as much as possible during normal operation to reduce power transmission loss and improve power transmission efficiency. However, the conventional superconducting fault current limiter has a problem that the magnetic flux generated by the coil leaks from the end portion of the superconductor and the impedance increases during normal operation.

The present invention has been made in view of such conventional problems, and an object thereof is to prevent leakage of magnetic flux generated by a coil during normal operation from a superconductor to reduce impedance. Another object of the present invention is to provide a superconducting fault current limiter that can improve power transmission efficiency.

[0007]

In order to achieve the above object, in a superconducting fault current limiter of the present invention, a tubular body made of a superconductor and a coil wound around the outer periphery of the tubular body and connected to a power line. And a superconducting fault current limiter that exhibits a superconducting state in a low temperature atmosphere, wherein the length of the cylindrical body is longer than the length between both ends of the coil in the wound state. Further, according to the invention described in claim 2, there is provided a tubular body made of a superconductor and a coil arranged in an inner circumference of the tubular body in a wound state and connected to the power line, and the superconducting state is maintained in a low temperature atmosphere. In the expressed superconducting fault current limiter,
It is characterized in that the length of the cylindrical body is longer than the length between both ends of the coil in the wound state.

[0008]

In the superconducting fault current limiter of the present invention, the length of the tubular body made of the superconductor is formed to be longer than the length between both ends of the coil arranged around the outer or inner circumference of the tubular body in a wound state. Has been done. Therefore, it is possible to minimize the leakage of the magnetic flux generated by the coil from the end portion of the cylindrical body. Therefore, the generation of the inductance of the coil is suppressed, the impedance is reduced, and the power transmission efficiency can be improved.

Moreover, when the coil is arranged on the outer periphery of the cylinder, the cylinder is exposed from the coil, and the exposed portion is in direct contact with the cooling atmosphere, so that the superconductor is effectively cooled. When the coil is arranged on the inner circumference of the tubular body, the outer circumferential surface of the outer tubular body is in direct contact with the cooling atmosphere, and the inner and outer circumferential surfaces of the tubular body longer than the coil are directly exposed to the cooling atmosphere. Since they come into contact with each other and the contact area with the cooling atmosphere is increased, the cooling efficiency of the superconductor is further improved.

[0010]

First Embodiment (First Embodiment) A first embodiment of the invention according to claim 1 will be described below with reference to the drawings.

As shown in FIG. 1, a cylindrical body 1 made of a superconductor is arranged on the outer periphery of a cylindrical core 2. The cylinder 1 is made of a composition such as bismuth (Bi): strontium (Sr): calcium (Ca): copper (Cu) = 2: 2: 1: 2, which has superconductivity at a predetermined low temperature. If The core 2 is formed of an iron-based material such as soft iron or silicon steel plate, and forms a closed circuit for magnetic flux.

The coil 3 is made of a covered electric wire such as an enameled wire, and is wound around the outer circumference of the cylindrical body 1. This coil 3
Is wound a predetermined number of times with a constant wire diameter to form a single layer. The length L of the cylindrical body 1 is formed longer than the length H of the wound coil 3 to prevent the magnetic flux generated in the coil 3 from leaking outward from the cylindrical body 1. And
The superconducting fault current limiter S is immersed in a cooling liquid such as liquid nitrogen or liquid helium, and is cooled and maintained at a predetermined cryogenic temperature.

In the superconducting fault current limiter S of this embodiment, the length L of the cylindrical body 1 made of a superconductor is longer than the length H of the coil 3 wound around its outer circumference. Therefore, leakage of the magnetic flux generated by the coil 3 from the cylindrical body 1 can be suppressed as much as possible. Therefore, coil 3
It is possible to suppress the generation of inductance in the capacitor and reduce its impedance. As a result, the power transmission efficiency of the superconducting fault current limiter S can be improved. In addition, the cylindrical body 1 made of a superconductor projects outward from the coil 3, and the inner and outer peripheral surfaces and end surfaces of the projecting portion directly contact the cooling liquid to increase the contact area, so that the cooling efficiency of the superconductor is improved. improves.

Next, the following test was conducted using such a superconducting fault current limiter S. In the test equipment,
The core 2 is made of soft iron and has an outer diameter of 38 mm and a length of 60 mm. The cylinder 1 has a composition of bismuth (Bi): strontium (Sr): calcium (Ca): copper (Cu) = 2: 2: 1: 2, and has an outer diameter of 50 mm and an inner diameter of 40 mm. Further, as shown in Table 1, the length was changed from 50 to 70 mm at 5 mm intervals and the test was conducted. Its critical current density is 1000 A / cm ² at a temperature of 77K. The coil 3 is made of an enameled wire, and is wound 200 times with a diameter of 1 mm to form one layer.

Then, the voltage of the AC power supply was adjusted so that a steady current of 3 A could flow through the superconducting fault current limiter S, and the inductance of the coil 3 was obtained from the voltage and current generated across the coil 3. The results are shown in Table 1.

[0016]

[Table 1]

As shown in Test Nos. 2 to 5 in Table 1, the length L of the cylindrical body 1 made of a superconductor is 1.1 to 1.4 times longer than the length H of the coil 3. The inductance of the superconducting fault current limiter S during normal operation can be rapidly reduced to 52 to 13% as compared with the test No.1.
This is because the magnetic flux is concentrated at the end of the coil 3, but the superconductor projects to this part to shield the magnetic flux and prevent leakage of the magnetic flux, so that the inductance sharply decreases even if the amount of protrusion is small. it is conceivable that. Therefore, the impedance of the coil 3 is reduced, the transmission loss during normal operation can be reduced, and effective power transmission can be performed. (Second Embodiment) A second embodiment embodying the invention described in claim 2 will be described below with reference to the drawings. In this embodiment, the arrangement of the cylinder 1 and the coil 3 is different from that of the first embodiment.

That is, as shown in FIG. 2, the coil 3 is wound around the core 2 a predetermined number of times to form a single layer. The cylindrical body 1 made of a superconductor is arranged on the outer circumference of the coil 3. The length L of the cylindrical body 1 is longer than the length H of the coil 3.

In the superconducting fault current limiter S of this embodiment, the length L of the cylindrical body 1 made of a superconductor is formed longer than the length H of the coil 3 which is wound around the inner periphery thereof. ing. Therefore, leakage of the magnetic flux generated by the coil 3 from the cylindrical body 1 can be suppressed as much as possible. Therefore,
The impedance of the coil 3 can be reduced and the power transmission efficiency can be improved. In addition, the cylindrical body 1 made of a superconductor is located at the outermost circumference and protrudes outside the coil 3. Therefore, the outer peripheral surface of the cylindrical body 1 and the inner and outer peripheral surfaces and the end surfaces of the projecting portion are in direct contact with the cooling liquid, and the contact area with the cooling liquid is increased, so that the cooling efficiency of the superconductor is improved.

Next, using such a superconducting fault current limiter S,
The same test as in the first embodiment was conducted. The results are shown in Table 2.
Shown in.

[0021]

[Table 2]

As shown in Test Nos. 7 to 10 of Table 2,
The length L of the cylindrical body 1 made of a superconductor is set to the length H of the coil 3.
By making the length 1.1 to 1.4 times longer, the inductance of the superconducting fault current limiter S is 56 to 60 times larger than that of the test No.1.
It can be significantly reduced to 14%.

The present invention is not limited to the above embodiments, but may be embodied by arbitrarily changing the configuration as follows without departing from the spirit of the invention. (A) To improve the performance of the superconducting fault current limiter S by configuring the coil 3 with a superconductor. (B) Yttrium-based (Y-based), tellurium-based (Tl-based) superconductors, bismuth (Bi) -strontium (Sr) -calcium (Ca) -copper (Cu) -oxygen (O) And a niobium alloy compound made of niobium (Nb) -titanium (Ti) or niobium (Nb) -tin (Sn). (D) A tubular body made of a superconductor is composed of a plurality of ring-shaped thin plates. Also, the tubular body should be formed into an elliptic tubular shape, a polygonal tubular shape, or the like. (C) Forming the coil 3 in multiple layers. (D) Disposing the superconductor on both the outer circumference and the inner circumference of the coil 3 so as to sandwich the coil 3.

[0024]

As described in detail above, according to the present invention, the magnetic flux generated by the coil during normal operation is prevented from leaking from the end of the superconductor, the impedance is reduced, and the power transmission efficiency is improved. It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing a superconducting fault current limiter of a first embodiment embodying the present invention.

FIG. 2 is a sectional view of an essential part showing a superconducting fault current limiter of a second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylindrical body, 3 ... Coil, L ... Length of a cylinder made of a superconductor, H ... Length of coil, S ... Superconducting fault current limiter.

Claims (2)

[Claims] 1. A superconducting fault current limiter, comprising: a cylindrical body made of a superconductor; and a coil wound around the outer circumference of the cylindrical body and connected to a power line, wherein a superconducting state is exhibited in a low temperature atmosphere. A superconducting fault current limiter, characterized in that the length of the tubular body is made longer than the length between both ends of the coil in a wound state. 2. A superconducting current limiter comprising a tubular body made of a superconductor, and a coil arranged in an inner circumference of the tubular body in a wound state and connected to a power line, wherein a superconducting state is exhibited in a low temperature atmosphere. A superconducting fault current limiter, characterized in that the length of the tubular body is longer than the length between both ends of the coil in the wound state.