JPH07272959A - Superconducting current limiter - Google Patents

Abstract

PURPOSE:To provide a superconducting current limiter in which a superconductor is not quenched in an ordinary power transmission operation, in which a superconducting state can be maintained and in which the superconductor can be returned to the super-conducting state in a short time after it has been quenched in an abnormality. CONSTITUTION:A superconducting current limiter S is provided with a superconductor 3 which is formed on the outer circumferential face of a cylindrical support 11 and with a coil 5 which is wound on the outer circumference of the superconductor 3 and which is connected to a power line. Uneven parts 4 are formed on the outer circumferential face of the superconductor 3. Then, the critical current value of the superconducting current limiter S can be increased by the uneven parts 4 on the superconductor 3, the cooling time of the superconductor 3 is shortened, and the return time to a superconducting state can be shortened. In addition, the density of the uneven parts 4 is made denser the closer they approach end parts of the superconductor 3, and the height of the uneven parts 4 is formed to be higher the closer they approach the end parts of the superconductor 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, one having a structure as shown in FIG. 7 is known. That is, the cylindrical body 11 made of a superconductor is arranged on the outer periphery of the cylindrical core 12 made of an iron-based material. The coil 14 is formed of a covered wire such as an enameled wire, is arranged in a wound state on the outer periphery of the cylindrical body 11 with a heat insulating material 13, and is connected to a power line such as a power transmission line.

During normal operation, the magnetic field generated by the coil 14 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 14 becomes small at the same time. Therefore, power transmission loss when power is transmitted through the coil 14 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, an inductance is generated in the coil 14 to increase the impedance and suppress a short circuit current. 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.

[0006]

By the way, the following matters are required for such a superconducting fault current limiter. First
The requirement is that the superconductor does not quench during normal power transmission.
It is to shield the magnetic field created by the coil. Second
The requirement is that when an abnormality occurs, the superconductor is quenched and its temperature rises, but the subsequent return to the superconducting state takes a predetermined short time.
For example, it is within 0.5 to 1 second for 500 kV.

In order to satisfy the first requirement, a method of improving the performance of the superconductor such as a critical current or a critical magnetic flux and a method of increasing the thickness of the superconductor can be considered. here,
The following relation (1) exists between the property of the superconductor and the critical current of the superconducting fault current limiter.

Jc × δ × L = Ic × N (1) where Jc is the critical current density of the superconductor, δ is the thickness of the superconductor, L is the length of the superconductor, and Ic is the superconducting fault current limiter. Critical current value, that is, the operation start current value, and N represents the total number of turns of the coil.

From the above equation, it is necessary to increase Jc or δ when L is constant, but at present, Jc cannot be increased because the performance of the superconductor is not sufficient.
That is, it is necessary to increase the thickness of the superconductor.

By the way, as shown in FIG. 8, between the time for the superconductor to return to the superconducting state again after it is quenched and the temperature difference between the superconductors, the thinner the thickness is from 1 mm to 10 μm, the shorter the recovery time is. There is a relationship of being done.
Therefore, in order to satisfy the second requirement, it is necessary to reduce the thickness of the superconductor. Thus the first and second
As a result, there is a problem in that contradictory conditions regarding the thickness of the superconductor are required, which causes difficulty in design.

The present invention has been made by paying attention to the problems existing in the prior art. Its purpose is to prevent the superconductor from being quenched during normal power transmission, to maintain the superconducting state, and to return to the superconducting state in a short time after the superconductor is quenched during an abnormal condition. It is to provide a sink.

[0012]

In order to achieve the above object, in the superconducting fault current limiter of the invention described in claim 1, a cylindrical superconductor and an inner circumference or an outer circumference of the superconductor. In a superconducting fault current limiter that has a coil connected to a power line and exhibits a superconducting state in a low temperature atmosphere, at least the outer surface of the superconductor is formed in an uneven shape.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the density of the unevenness is further increased toward the end of the superconductor. Further, the invention according to claim 3 is characterized in that, in the invention according to claim 1, the height of the unevenness is further increased toward the end of the superconductor.

[0014]

In the superconducting fault current limiter of the present invention, at least the outer surface of the cylindrical superconductor is formed in an uneven shape. For this reason, the surface area of the superconductor increases, the contact area with the cooling liquid such as liquid nitrogen increases, and the cooling effect increases,
The superconductor is cooled effectively. Since there is an inversely proportional relationship between the temperature of this superconductor and the critical current value,
The critical current value of the superconducting fault current limiter becomes large. Moreover, the length along the surface of the superconductor becomes long, and the critical current value of the superconducting fault current limiter becomes large. Therefore, during normal power transmission, the superconductor is less likely to be quenched, and the superconducting state can be maintained.

In addition, the improvement of the cooling effect with the increase of the surface area of the superconductor shortens the time for cooling to the superconducting state after the superconductor is quenched and the temperature rises at the time of an abnormality. As a result, the return to the superconducting state is performed in a short time.

[0016]

Embodiments Embodiments embodying the present invention will be described below with reference to the drawings. As shown in FIG. 1, a cylindrical support 1 has an outer peripheral surface formed in an uneven shape and is arranged on the outer periphery of a cylindrical core 2. The superconductor 3 is formed on the outer periphery of the support 1 so as to form a thin film having a thickness of about 100 μm. The support 1 is made of an insulating material such as magnesia, and the surface thereof is covered with a superconductor 3. The superconductor 3 is bismuth (Bi): strontium (Sr): calcium (Ca): copper (Cu) = 2: 2:
A 1: 2 composition or the like is used, but any material having superconductivity at a predetermined low temperature may be used.

The superconductor 3 is crushed and dispersed in an organic solvent such as alcohol to form a slurry of the superconductor 3. This slurry is applied to the support 1 by spraying, dried at room temperature for about one day, and then baked at 890 ° C. for 30 minutes to 2 hours. In this way, a thin film of the superconductor 3 is formed on the surface of the support 1. In the superconductor 3, the uneven portion 4 is formed along the uneven surface of the support 1, the contact area with a cooling liquid such as liquid nitrogen is increased, and the cooling efficiency is improved. Note that the thickness of the superconductor 3 and the uneven portion 4 thereof in FIG. 1 are greatly exaggerated in the drawing. Further, the core 2 is formed of an iron-based material such as soft iron or a silicon steel plate, and forms a closed circuit for magnetic flux.

The coil 5 is made of a covered electric wire such as an enameled wire, and is wound around the outer circumference of the superconductor 3. The coil 5 is wound a predetermined number of times with a constant wire diameter to form a single layer. The length of the superconductor 3 is formed longer than the length of the wound coil 5 along the superconductor 3, so that the magnetic flux generated in the coil 5 does not leak to the outside of the superconductor 3 and the superconducting current limit The power transmission efficiency of the container S is improved. 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 superconductor 3 has the uneven portion 4 on its outer peripheral surface. For this reason, the surface area of the outer peripheral surface of the superconductor 3 is increased, the contact area with the cooling liquid such as liquid nitrogen is increased, and the cooling effect is increased. Generally, the critical current value of the superconducting fault current limiter S is inversely proportional to the temperature and increases as the temperature decreases, so that the critical current value of the rapidly cooled superconducting fault current limiter S increases. Moreover, since the length along the surface of the superconductor 3 becomes long, the critical current value of the superconducting fault current limiter S becomes large. Therefore, during normal power transmission, the superconductor 3 is less likely to be quenched, and the superconducting state can be reliably maintained.

By the way, assuming that the above equation (1), that is, Jc × δ × L = Ic ₁ × N (1), is assumed that the depth of the superconductor 3 is a and the number of the uneven portions 4 is b. , The following equation (2) holds.

Jc × δ × (L + 2ab) = Ic ₂ × N (2) Therefore, from (2) / (1), Ic ₂ / Ic ₁ = (L + 2ab) / L (3) Therefore, when the length L of the superconductor 3 is 1 m, the depth a of the concave-convex portion 4 of the superconductor 3 is 5 mm, and the number b of the concave-convex portions 4 is 20, it becomes 1.2 from the formula (3), and 20%. Therefore, the critical current value of the superconducting fault current limiter S increases.

In addition, due to the improvement of the cooling effect with the increase of the surface area of the superconductor 3, the time for cooling the superconductor 3 to the superconducting state after the quenching of the superconductor 3 in an abnormal condition and the temperature rise is shortened. Therefore, the return from the quenched state at the time of abnormality to the superconducting state is performed in an extremely short time.

Further, since the outer peripheral surface of the superconductor 3 has the uneven portion 4 to improve the rigidity and the stress resistance performance,
Good resistance to shrinkage and expansion due to temperature change.
When the coil 5 is wound around the outer peripheral surface of the superconductor 3,
Due to the surface resistance of the uneven portion 4 formed on the outer peripheral surface of the superconductor 3, the coil 5 can be easily wound.
When the coil 5 is used after being wound, even if vibration is applied to the superconducting fault current limiter S, the coil 5 is locked to the uneven portion 4 on the surface of the superconductor 3, so that it is difficult to move, and the initial State is retained.

The present invention is not limited to the above-described embodiments, but may be embodied by arbitrarily changing the configuration as follows without departing from the spirit of the invention. (1) As shown in FIG. 2, the number of the concave-convex portions 4 on both end portions 3a of the superconductor 3 is set to be larger than that of the intermediate portion. With such a configuration, the critical current value of the superconductor 3 at both ends 3a can be increased, and the critical current value of the superconducting fault current limiter S can be increased. (2) As shown in FIG. 3, the height of the uneven portions 4 at both ends 3a of the superconductor 3 is increased, and the coil 5 is wound around the outer periphery of the intermediate portion of the superconductor 3. With this configuration, the magnetic flux between the coil 5 and the superconductor 3 is blocked, and the self-inductance of the coil 5 can be reduced. (3) To improve the performance of the superconducting fault current limiter S by configuring the coil 5 with the superconductor 3. (4) As the superconductor 3, yttrium-based (Y-based), tellurium-based (Tl-based), 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). (5) The support 1 is formed in an elliptic cylinder shape, a polygonal cylinder shape, or the like,
Form the superconductor 3 on the outer peripheral surface thereof. Further, as shown in FIG. 4, the support 1 should be formed in a wavy shape. (6) Forming the coil 5 in multiple layers. (7) A heat insulating material is interposed between the superconductor 3 and the coil 5. (8) Winding the coil 5 around the inner circumference of the superconductor 3. (9) Omitting the core 2 in the above embodiment. (10) As shown in FIG. 5, the superconductor 3 is formed by alternately stacking a ring-shaped superconductor piece 3b having a large diameter and a ring-shaped superconductor piece 3c having a small diameter to form an uneven portion 4 on the outer peripheral surface. To form. (11) As shown in FIG. 6, the superconductor 3 is formed in a cylindrical shape, and the uneven portion 4 is provided on the outer peripheral surface thereof.

[0025]

As described above in detail, according to the present invention, the superconductor is not quenched during normal power transmission, and the superconducting state can be surely maintained, and at the same time, the superconductor is quenched after an abnormal condition. It has an excellent effect that it is possible to return to the system in a short time.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a main part of a superconducting fault current limiter showing another example of the present invention.

FIG. 3 is a cross-sectional view of a main part of a superconducting fault current limiter showing still another example of the present invention.

FIG. 4 is a partial cross-sectional view of a superconducting fault current limiter showing another example of the present invention.

FIG. 5 is a sectional view of a superconducting fault current limiter showing still another example of the present invention.

FIG. 6 is a sectional view of a superconducting fault current limiter showing another example of the present invention.

FIG. 7 is a cross-sectional view of essential parts showing a conventional superconducting fault current limiter.

FIG. 8 is a graph showing the relationship between the temperature and the return time to the superconducting state regarding the thickness of the superconductor.

[Explanation of symbols]

3 ... Cylindrical superconductor, 3a ... End part, 3b, 3c ... Superconductor piece, 3d ... Superconductor with uneven surface, 4 ... Uneven part, 5
… Coil, S… Superconducting fault current limiter.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical indication location H02H 9/02 ZAA Z (72) Inventor Shuichiro Motoyama 2-5, Sudamachi, Mizuho-ku, Nagoya-shi Insulator of Japan Within the corporation

Claims (3)

[Claims] 1. A superconducting fault current limiter comprising a cylindrical superconductor and a coil wound around the inner or outer periphery of the superconductor and connected to a power line, wherein a superconducting state is exhibited in a low temperature atmosphere. A superconducting fault current limiter in which at least an outer surface of the superconductor is formed in an uneven shape. 2. The superconducting fault current limiter according to claim 1, wherein the density of the irregularities is further increased toward the end of the superconductor. 3. The superconducting fault current limiter according to claim 1, wherein the height of the unevenness is further increased toward the end of the superconductor.