JPH0223029A - Current limiter - Google Patents

Abstract

PURPOSE:To reduce the quantity of refrigerant and the number of parts by connecting electrical lines respectively to a plurality of superconductors connected to one end of a single superconductor having the other end connected with an electrical line, and containing all superconductors in a common container. CONSTITUTION:A main current terminal 1 is fixed liquid-tightly through an insulating bushing 3 to a container 8 filled with cryogenic liquid 9 and connected with one end of a superconductor 5. A plurality of superconductors 6 are connected in parallel through the other terminal 7 of the superconductor 5, and the terminal 2 is fixed liquid-tightly through a plurality of insulating bushings 4 to the container 8. Critical current level of the superconductor 5 is set higher than that of the superconductor 6. When abnormal overcurrent flows through a load connected with any one of the superconductors 5, 6, the superconductor is quenched to increase the resistance quickly thus limiting the current. When a plurality of circuits are abnormal simultaneously and the current exceeds over the critical current level of the superconductor 5, the superconductor 5 is also quenched thus limiting the current. By such arrangement, the size of the current limiter is reduced and thereby necessary quantity of refrigerant is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a current limiting device that utilizes the transition of a superconductor from a superconducting state (hereinafter referred to as S state) to a normal conducting state (hereinafter referred to as N state). It is also.

[Prior Art] FIG. 2 is a sectional view of a conventional current limiting and interrupting device disclosed in, for example, Japanese Patent Application Laid-Open No. 47-24291. In the figure, a superconductor (5) is immersed in a cryogenic fluid (9) filled in a cryogenic container (8). Terminals (1) and (2) of the superconductor (5) are connected to the respective insulators (3) and (4).
The container (8) is drawn out to the outside while keeping the container (8) in a sealed state.

In this current limiting and interrupting device, the energizing path is terminal (1) - superconductor (5) and one terminal (2), and during normal energization, the superconductor (5) is in an S state cooled by cryogenic liquid (9). It is in. When a large current begins to flow through the superconductor (5), the superconductor (5) rapidly transitions from the S state to the N state (hereinafter, this transition is referred to as quench). As a result, a superconductor (5
) The resistance determined by the length and cross-sectional area of the terminal (1
) and terminal (2), and the current is limited by the resistance. Due to this current limiting effect, the superconductor (5) generates a large amount of heat, so that the cryogenic liquid (9) in contact with its surface is vaporized. This vaporization causes the cryogenic container (8
) increases, but this increase in gas pressure is due to the increase in the gas pressure inside the pipe (11) 1. :Thus, the current is transmitted to the connected interrupting section (12), and the current is interrupted by operating a circuit breaker (not shown) provided in the interrupting section (12).

[Problems to be Solved by the Invention] In the conventional current limiting device as described above, only one superconductor is provided in one cryogenic container (8).
In order to protect multiple electrical circuits, multiple current limiting devices are required, and as the volume occupied by the current limiting devices increases,
Cooling costs are high because a large amount of cryogenic liquid is required.

The present invention aims to reduce the volume occupied by the current limiting device and the cooling cost.

[Means for Solving the Problems] The current limiting device of the present invention has a plurality of first
A second superconductor is connected to a connecting portion where one terminal of the superconductor is connected, the other terminal of the first superconductor is commonly connected, and the first and second superconductors are placed in a cooling container. It is housed inside.

[Operation] A plurality of superconductors are housed in one cooling container, and only the superconductor in which the accident occurred is quenched.

[Example] FIG. 1 shows a side sectional view of an embodiment of the invention.

In the figure, a superconductor (5
) and one terminal (7) of the superconductor (5), for example, five branched superconductors (6) connected in a branched manner are housed. The other terminal (1) of the superconductor (5) is an insulator (3)
It is drawn out to the outside while maintaining a tight seal with the container (8) via the container (8). The other terminal (2) of each branched superconductor (6) is connected to the container (8) via each insulator (4).
It is pulled out to the outside while maintaining a tight seal. Superconductor (
The critical current value (current value for transition from S state to N state) of 5) is larger than that of superconductor (6). The container is filled with a cryogenic liquid (9), and a pressure regulating valve (1G) is provided above the container to adjust the gas pressure within the container. The other terminal (2) of each branch superconductor (6)
are connected to respective electrical circuits, and each electrical circuit is provided with a circuit breaker (not shown) that interrupts the electrical circuit when an excessive current flows.

Next, the operation of this embodiment will be explained. Under normal energizing conditions, current from the main circuit flows through the terminals (1 superconductor (5), 1 terminal (7) - each branch superconductor (6) - each branch superconductor (
6) is flowing through the path of terminal (2).

At this time, each branch superconductor (6) and superconductor (5) are kept in the S state because they are in the cryogenic liquid (9).

When an accident occurs in any of the electrical circuits connected to each branch superconductor (6) and a large current begins to flow, the current in the branch superconductor (6) connected to the electrical circuit where the accident occurred reaches its critical level. When the current becomes larger than the current, the superconductor (6
) quenches. As a result, the resistance value of the branched superconductor increases rapidly and the current is limited. This rapid increase in resistance offsets the decrease in impedance due to the fault in the electrical circuit where the fault occurred. Therefore, the current does not increase much and a voltage drop at the terminal (7) can be prevented, and the influence of the accident can be prevented from reaching other electrical circuits where the accident has not occurred. It is particularly effective as a means of protecting against malfunctions and damage to electronic equipment that is susceptible to fluctuations in power supply voltage.

Fault current is detected and interrupted by a circuit breaker connected to the electrical circuit where the fault occurred.

In addition, when an accident occurs in multiple electrical circuits, when the current of the superconductor (6) connected to each electrical circuit where the accident occurred becomes thicker than the critical current, each superconductor (6)
quenches, limits the fault current in each circuit, and protects each circuit. At this time, when the sum of the currents in each circuit becomes larger than the critical current of the superconductor (5), the superconductor (5)
) is quenched to limit the current in the main circuit and protect the main circuit electrical path.

As mentioned above, when an accident occurs in multiple electrical circuits, the current flowing through the main circuit is limited by quenching the superconductor (6) connected to each electrical circuit where the accident occurred and the superconductor (5) in the main circuit. As the current flows, the circuit breaker for each circuit interrupts that circuit. Therefore, it is possible to interrupt the fault current without operating the switchgear connected to the main circuit. Furthermore, even if an accident occurs in a plurality of electrical circuits, unless the main circuit breaker is activated, the power supply to the branch circuits where no accident has occurred will not be cut off. Furthermore, if the conditions of the load connected to the current limiting device change and the estimated short circuit current at the time of an accident changes, the protection coordination of the circuit can be maintained by replacing the superconductor in the current limiting device.

[Effect of the invention] According to this invention, superconductor (6) and superconductor (5)
Since the superconductor is housed in a single cryogenic container (8), the ratio of surface area to volume is smaller than when using multiple containers containing one superconductor. Become. Therefore, the amount of cryogenic liquid (9) that is vaporized and lost due to heat from outside the container can be reduced, reducing cooling costs.Furthermore, a single cryogenic container (8) is used. This makes it possible to reduce the number of parts and the amount of materials required for the current limiting device, and because the protection coordination of the electric circuit can be easily performed by replacing the superconductor, it is possible to reduce the cost of the current limiting device, and to reduce the cost of the current limiting device. It becomes possible to reduce the volume occupied by the

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a current limiting device according to an embodiment of the invention,
FIG. 2 is a sectional view of a conventional current limiting device. (1), (2) are terminals, (S), (6) are superconductors,
(8) is a container, and (9) is a cryogenic liquid. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A plurality of first superconductors each having one terminal connected to a plurality of electrical circuits, one terminal being connected to a connection portion where the other terminal of each of the first superconductors is commonly connected, and the other terminal A current limiting device comprising: a second superconductor connected to an electric circuit; and a cooling container housing the first superconductor and the second superconductor. (2) The current limiting device according to claim 1, wherein the critical current of the second superconductor is larger than the critical current of the first superconductor.