JPH06325957A - Superconducting current limiter - Google Patents

Abstract

PURPOSE:To realize a superconducting current limiter having a large cooling efficiency of its superconductor, by disposing its superconductor on the outer peripheral side of a coil which is connected in series with a power system to cover the coil. CONSTITUTION:A superconducting current limiter comprises a solid oval supporting body 2 made of iron wherein cores 1 are provided left and right and a pair of cylindrical parts 3 provided respectively near the upper and lower ends of the supporting body 2. A coil 4 is wound around the upper cylindrical part 3, and both the ends of the coil 4 are subjected to a series connection with a power transmission system. A superconducting cylindrical body 5 is disposed on the outer peripheral side of the coil 4. It is formed in the form of a cylinder out of a bismuth based high-temperature superconductor. The superconducting cylindrical body 5 is not supported especially by external supportors, but through the outer peripheral side of the coil 4 it is engaged with the cylindrical part 3 while a clearance is left between them. Thereby, the cooling efficiency of the superconductor can be improved in comparison with the case wherein the superconductor is provided on the inner peripheral side of the coil 4.

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 which utilizes the property that a superconductor is quenched (transitioned) from a superconducting state to a normal conducting state when it exceeds a critical current value.

[0002]

2. Description of the Related Art Conventionally, it has been proposed to arrange a fault current limiter for limiting a fault current in a power transmission system. The current limiter serves as a resistance when an overcurrent flows, and suppresses the overcurrent, and functions to suppress the load applied to the breaker and the transformer to a predetermined level or less. Although various techniques have been proposed as a method of a current limiting device, in recent years, as a current limiting device, for example, a current limiting device that uses a superconductor as disclosed in Japanese Patent Laid-Open No. 2-105402 has been proposed. Has been done.

The basic principle of this superconducting fault current limiter is as follows. First, a coil connected in series to a power transmission system is wound around the outer circumference of a superconductor, and iron cores are arranged concentrically in the superconductor to form a superconducting fault current limiter. When the coil is energized, self-inductance causes impedance. However, when the superconductor is in the superconducting state, the magnetic flux is cut off, so the magnetic field generated by the coil is completely shielded from the iron core (Meissner effect), and theoretically the self-inductance of the coil disappears. That is, since the impedance is extremely small, the loss of the transmission current in the steady state is small.

However, once an overcurrent flows through the coil due to a short circuit, a lightning strike, or the like, the critical magnetic field of the superconductor is exceeded, so that the superconductor is quenched from the superconducting state to the normal conducting state. Then, the magnetic flux is linked to the superconductor like a normal substance (flux switching effect), so that self-inductance is again generated in the coil and the overcurrent can be limited.

[0005]

By the way, in the current superconductor, it is necessary to maintain the cooling state in order to bring the superconductor into the superconducting state. Therefore, in a superconducting fault current limiter using a superconductor, the entire fault current limiter is immersed in a cooling liquid such as liquid nitrogen for cooling. However, in the past, the coil was wound around the outer periphery of the superconductor, so that the cooling efficiency was not sufficient. That is, in this conventional type, the superconductor comes into contact with the cooling liquid only on the inner peripheral surface side,
In particular, when formed to be thick, the cooling efficiency was not sufficient. Further, as disclosed in Japanese Patent Application Laid-Open No. 2-105402, in the case where the superconductor is sandwiched between the iron core as the core and the coil, the contact area between the cooling liquid and the superconductor is further reduced, and the cooling efficiency is also improved. Will be lower. In addition, there is a problem that the quenching current becomes small due to being sandwiched by the eddy current loss generated in the iron core and the Joule loss generated by the resistance component of the coil.

An object of the present invention is to provide a superconducting fault current limiter having a large cooling efficiency for a superconductor.

[0007]

In order to solve the above-mentioned problems, the inventor of the present invention proposes that, in the invention of claim 1, superconductivity is provided on the outer peripheral side of the coil connected in series to the power system. The body was placed in a cover. Further, in the invention of claim 2, a superconductor is arranged on the outer peripheral side of the coil connected in series to the power transmission system so as to cover the coil, and at least the superconductor is kept cold by a cooler. . In the invention of claim 3, the superconductor has a tubular shape and is arranged so as to cover the entire coil. Further, in the invention of claim 4, the superconductor is formed in a coil shape, and is arranged so as to cover the inner coil.

[0008]

According to the above-mentioned structure, in the invention of claim 1, the superconductor is arranged on the outer peripheral side of the coil in a covering shape, so that the cooling effect is higher than that in the case of being arranged on the inner peripheral side of the coil. As the size of the superconductor increases, only the Joule loss generated from the inside due to the resistance of the coil causes the outer circumference to be open, so that the quenching current can be increased. In the invention of claim 2, when at least the superconductor is kept cool by the cold insulation means, the superconductor is arranged on the outer peripheral side of the coil in a covering state, so that the cooling effect is compared to the case where it is arranged on the inner peripheral side of the coil. As the size of the superconductor increases, only the Joule loss generated by the resistance of the coil from the inside causes the outer periphery to be in contact with the cooling liquid at all times, so that the quenching current can be increased. Further, in the invention of claim 3, since the coil is completely surrounded by the cylindrical superconductor, the leakage current is reduced. Further, in the invention of claim 4, since the cooling liquid is introduced into the gap between the superconductors by adopting the coil shape, the cooling efficiency is further improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A superconducting fault current limiter 10 which is one prototype of the present invention will be described in detail below with reference to FIGS.

As shown in FIG. 1, a core 1 is an oval support 2 made of solid soft iron arranged on the left and right in the figure, and a pair of columnar parts 3 provided on the upper and lower sides of the support 2. It is composed of The cylindrical portion 3 is made of medium-density soft iron having a diameter of 38 mm and a length of 60 mm, and is fixed to the support body 2 with a screw (not shown). A coil 4 is wound around the upper cylindrical portion 3, and both ends of the coil 4 are originally connected to the power transmission system. The coil 4 is formed by winding one layer of an enameled wire having a diameter of 0.3 mm for 120 turns.

A superconducting cylinder 5 is arranged on the outer peripheral side of the coil 4. The superconducting cylinder 5 is a bismuth-based high-temperature superconductor formed in a cylindrical shape, and the superconducting cylinder 5 has an inner diameter of 40 mm.
The diameter is 50 mm, the outer diameter is 50 mm, and the length is 50 mm.
When calculated from this value, the inner peripheral area of the superconducting cylinder 5 is about 6
280 mm ² next outer circumferential area is about 7850mm ^2. The superconducting cylinder 5 is not particularly supported from the outside,
The coil 4 is loosely fitted in the columnar portion 3 from the outer peripheral side.

Bi-Sr-Ca-Cu-as a bismuth-based high-temperature superconductor which constitutes the superconducting cylinder 5 of this embodiment.
O system was used. Bi: Sr: Ca: Cu = 2: 2:
Each powder of Bi ₂ O ₃ , CuO and SrCO ₃ was prepared so as to be 1: 2. Critical current density (Jc) of the bismuth-based high-temperature superconductor in this embodiment (Jc) = 1000 A / c
m ² , critical magnetic field (Bc) = 50 gauss.

The superconducting fault current limiter 10 of the present invention is immersed in a cooling tank 6 which is a cooling means. In the embodiment, since a bismuth-based high temperature superconductor is used, liquid nitrogen is used as a cooling liquid as a cooling means.

The operation of the superconducting fault current limiter 10 will be described by adding a more detailed principle. The cylindrical superconducting cylinder 5 arranged to cover the coil 4 from the outer periphery has the same action as the coil 4 having a resistance value of 0Ω in the superconducting state. That is, induced electromotive force is generated in the superconducting cylinder 5 by the magnetic flux generated by the coil 4. Then, a current flows in the opposite direction to the coil 4 inside the superconducting cylinder 5,
The magnetic flux generated by the coil 4 is offset by the magnetic flux generated by the superconducting cylinder 5. Therefore, in the superconducting cylinder 5 in the superconducting state, the inductance of the coil 4 is extremely suppressed, and the superconducting fault current limiter 10 does not limit the transmission current while the steady current flows through the coil.

On the other hand, when an overcurrent flows through the coil 4 due to a short-circuit accident or the like, the amount of current accompanying the induced electromotive force flowing through the superconductor also increases at once and exceeds the critical current value of the superconductor. Then, the superconducting cylinder 5 is quenched from the superconducting state to the normal conducting state. Then, the self-inductance is generated again in the coil to limit the overcurrent.

With the above structure, the superconducting fault current limiter 10 of the present embodiment has the following effects. That is,
Even if the superconducting cylinder 5 is arranged on the outer peripheral side of the coil 4,
In the superconducting state of the superconducting cylinder 5, the inductance of the coil 4 disappears. On the other hand, in the event of an accident, the superconductor quenches to the normal conductor, causing inductance in the coil 4,
The current limiting function of the superconducting fault current limiter 10 of limiting the short-circuit current is maintained. Further, the superconducting cylinder 5 is provided on the outer circumference of the coil 4.
Since the superconducting cylinder 5 is arranged, the superconducting cylinder 5 comes into contact with liquid nitrogen on its outer peripheral surface. According to the above calculation, the contact area of the outer peripheral surface is larger than that of the inner peripheral surface by 1600 mm ² (about 25.5% increase from the inner peripheral surface). Further, as the heat source, the coil 4 is only inside the superconductor, and the outer periphery is always in contact with the cooling liquid. Therefore, the cooling efficiency can be increased and the quenching current can be increased.

Further, in the conventional type in which the coil is wound around the outer periphery of the superconductor, the coil is a hindrance when replacing the superconductor. If removed, the superconducting cylinder 5 can be easily replaced. Further, since the coil 4 is not directly wound around the superconductor 5, mechanical stress on the superconducting cylinder 5 is reduced.

Next, the data of the experiment conducted based on the above-mentioned embodiment will be explained based on the graph shown in FIG.
This graph shows current-coil characteristics (IL characteristics) when the superconducting fault current limiter 10 is viewed as one circuit. The vertical axis represents the inductance of the entire circuit, and the horizontal axis represents the current value. A to G are measured values.

As a result, it was confirmed that the critical current was reached at 6 to 7 amps. This value varies depending on the critical magnetic field and the critical temperature. In general, the quenching current value is inversely proportional to the number of coil turns, and the inductance is directly proportional to the square of the number of coil turns.

Although one embodiment of the present invention has been described in detail above, the present invention can be modified and implemented in the following modes. 1) To form a flange portion on the outer circumference of the superconducting cylinder 5.
For example, both ends of the tubular body 5 and the like.

2) As shown in FIG. 3, the superconducting cylinder 15 is ground into a coil shape, and the coil 4 is arranged so as to be covered from the outside. With this configuration, the nitrogen gas derived from the liquid nitrogen generated around the coil 4 can be smoothly discharged.

3) Use liquid helium as the cooling liquid. Since liquid helium has a lower temperature, a NbTi-based superconductor or the like can be used. It is also free to use other coolants. On the contrary, when it is applied to a high-temperature superconductor exceeding the current bismuth-based high-temperature superconductor, it does not necessarily have to be immersed in the cooling liquid.

4) It is free to change the thickness of the superconducting cylinder 5. As the thickness increases, the area difference between the inner peripheral surface and the outer peripheral surface occurs, and the effect of the invention is greater. Also, the coil 4 itself can be made of a superconductor.

5) A heat insulating material may be inserted between the coil 4 and the superconducting cylinder 5. Then, the Joule heat of the coil 4 due to the Joule loss becomes harder to be transmitted. 6) The coil 4 and the superconducting cylinder 5 may be closely fitted to each other or may have a gap as in this embodiment. Theoretically, the closer the coils are to each other, the more the magnetic flux leaks in the coil 4 and the less the current loss during steady power transmission.

7) The superconducting cylinder 5 is not integrally molded and may be formed by laminating ring-shaped thin plates. 8) Although the core is made of solid soft iron, it may be formed by laminating thin plates. In addition, soft iron is a concept including ferrite and amorphous alloy.

9) B as a high temperature bismuth superconductor
It may be carried out with a composition other than i: Sr: Ca: Cu = 2: 2: 1: 2. It is also possible to use, for example, a yttrium-based superconductor other than bismuth-based one.

Others The present invention can be freely modified and implemented without departing from the spirit of the invention.

[0028]

As described above, according to the present invention, since the superconductor is arranged on the outer peripheral side of the coil, the cooling efficiency of the superconductor is improved as compared with the case where the superconductor is arranged on the inner peripheral side of the coil.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating an outline of a superconducting fault current limiter according to the present invention.

FIG. 2 is a graph of the IL characteristic of the superconducting fault current limiter in the same example.

FIG. 3 is a perspective view illustrating a superconducting fault current limiter according to another embodiment.

[Explanation of symbols]

4 ... Coil, 5 ... Superconducting cylinder which is a superconductor, 10 ... Superconducting fault current limiter.

Claims (4)

[Claims] 1. A superconducting fault current limiter, characterized in that a superconductor is arranged on the outer peripheral side of a coil connected in series to an electric power system so as to cover the coil. 2. A superconductor is arranged on the outer periphery of a coil connected in series to an electric power system so as to cover the coil,
A superconducting fault current limiter characterized in that at least a superconductor is kept cold by a cold keeping means. 3. The superconducting fault current limiter according to claim 1, wherein the superconductor has a tubular shape and is arranged so as to cover the entire coil. 4. The superconducting fault current limiter according to claim 1, wherein the superconductor has a coil shape, and is arranged in a cover shape with respect to the inner coil.