JPH10126960A - Variable set-value current limiter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the degree of freedom of cooling temperature setting by a method wherein a mechanism by which the cooling temperature of an oxide current limiting element can be varied is provided. SOLUTION: An oxide superconducting current limiter system has a mechanism which controls a temperature by using a plurality of cooling media or cooling device to vary the current limiting characteristics. Liquefied argon is used as coolant and the temperature of the coolant is controlled by adjusting the temperature of the cooling unit of a refrigerator within a range of 86K-78K. As for the current limiting characteristics, Ic is about 450A at 86K and Ic is 1500A at 78K. Then, if the cooling temperature is 81K, Ic can be 1000A. By this system, a current limiter by which Ic can be set arbitrarily within a range of 450A-1500A can be manufactured. With this constitution, a current value at which a current limiting operation is started can be set arbitrarily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting-normal conduction type current limiter using an oxide superconductor.

[0002]

2. Description of the Related Art When a short circuit occurs in a power circuit, an extremely large short circuit current flows. The short-circuit current is interrupted by the circuit breaker, but the short-circuit current generates a strong electromagnetic force and a large amount of Joule heat, and the power equipment and the electric circuit are greatly damaged mechanically and thermally. Accident fault current limiters (current limiters) that reduce the short circuit current in the event of such an accident and reduce the duty of the circuit breaker
The development of is desired. Further, such a current limiter has an extremely large effect attributable to stabilization of various power transmission and distribution systems, and early realization of the current limiter is expected.

[0003] Many types of current limiters have been proposed, but at present there are few which have high practicality. Current limiting reactors, permanent fuses, current limiting wires, and arc current limiters are relatively widely used, but current limiting performance is high due to high electrical resistance when load current is applied and high heat generation or slow response. Is low.

[0004] Items required for the current limiter include low electric resistance and low heat generation when a normal load is applied, and quick response and high electric resistance when a short circuit occurs. In this regard, a current limiter using a superconductor is considered to be ideal. As a superconducting current limiter, a superconducting-normal conduction transition type, a reactor type, a rectifying type, a coil type, and the like have been proposed. Among them, the superconducting / normal conduction transition type current limiter most directly utilizes the superconducting / normal conduction transition of the superconductor. When a load current is applied, only a current equal to or less than the critical current flows through the superconductor, so that the resistance of the superconductor is extremely small. However, when a short circuit accident occurs, a current equal to or greater than the critical current flows through the superconductor, and the superconductor transitions from the superconducting state to the normal conducting state, generating electric resistance. This resistance limits the short-circuit current. This superconducting / normal-conducting transition type current limiter has a feature that its structure is simpler and smaller than those of other types of superconducting current limiters.

[0005] Some of the superconducting current limiters use a metal-based superconductor and an oxide-based superconductor. Metal-based superconductors have low electrical resistance in the normal conduction state, which increases the size of the entire apparatus, requires use near the temperature of liquid helium, and increases operating costs. However, there is a problem that the size of the device increases. Therefore, development of a current limiter using an oxide superconductor that has a high electric resistance in a normal conduction state and can maintain a superconducting state at a relatively high temperature is expected.

[0006]

In a current limiter, it is necessary to set a current value or the like at which a current limiting operation is started based on a rated voltage and a rated current value of an installed power system. At this time, a mechanism for changing the current limiting characteristic is required so that the current limiting characteristic suitable for the installed power system is obtained.

Further, in a superconducting current limiter using an oxide superconducting material, a current value at which a current limiting operation is started and a current limiting operation speed change depending on a cooling temperature, and also affects an AC conduction loss. Therefore, it is necessary to set the cooling temperature of the oxide superconducting current limiter to an optimum temperature that meets the specifications. However, in the conventional method of cooling to the boiling point of one kind of refrigerant or in the cooling method using only heat transfer by a refrigerator, the degree of freedom of the cooling temperature is limited, and the uniformity of the cooling temperature and the ideal temperature distribution are not obtained. Design was difficult.

[0008]

Accordingly, an object of the present invention is to provide an oxide superconducting current limiting system having a mechanism for controlling the temperature by using a plurality of cooling media or cooling devices and varying the current limiting characteristics. Liquid argon, liquid nitrogen and liquid oxygen include refrigerants having boiling points in a relatively high temperature range where a 90K-class Y and rare-earth or Bi superconductor can maintain a superconducting state. It is easy to obtain a uniform cooling temperature by arbitrarily setting the temperature of these to below their boiling points using a refrigerator.

A desired temperature distribution can be obtained by selecting a plurality of refrigerants from among refrigerants such as liquid argon, liquid nitrogen, and liquid oxygen.

Further, the superconducting conductors and the connection between the superconductor and the normal conductor have a contact resistance and thus easily generate heat, and the connection between the superconductors and the connection between the superconductor and the normal conductor are controlled by the cooling temperature of the superconductor. Is also set to be low.

In order to perform the current limiting operation in a shorter time, it is preferable that the refrigerant is not in direct contact with the superconducting conductor, and it is sometimes desirable that the portion other than the electrode portion is housed in an insulating container. .

[0012]

The oxide superconducting material has a limit value (Jc: critical current density) of a current that can flow in a substantially zero-resistance state (it does not become a completely zero-resistance state by alternating current) depending on the temperature. . This Jc changes greatly depending on the cooling temperature. Therefore, it is necessary to set the critical current (Ic) of the superconductor to a value higher than the current value during normal energization. (Ic is estimated by the product of Jc and the cross-sectional area.) Therefore, it is necessary to set the cooling temperature to an optimum temperature according to the specification. Therefore, by cooling with a plurality of refrigerants or refrigerators, the degree of freedom in setting the cooling temperature can be increased.

The superconducting conductors and the connection between the superconductor and the normal conductor have a contact resistance and thus easily generate heat, and the connection between the superconductors and the connection between the superconductor and the normal conductor is somewhat lower than the cooling temperature of the superconductor. By setting it to be low, the occurrence of quench from the electrode is suppressed, and the entire device is put into a resistance state by the propagation of quench from the superconducting conductor part, that is, by increasing the uniformity of the quench characteristics of the entire device, a quick limit Flow operation can be realized.

[0014]

【Example】

Example 1 QMG (Physica C 235-240) shaped as shown in FIG.
(1994) 209-212), a current limiting system having a cooling system as shown in FIG. 1 and performing a current limiting operation at a current value of 1000 A or more was manufactured. Liquid argon was used as the refrigerant, and the temperature of the refrigerant was controlled by adjusting the temperature of the cooling unit of the refrigerator from 86K to 78K. First, regarding the current limiting characteristics at 86K,
Ic was about 450A, and at 78K Ic was 1500A. Then, when the cooling temperature was set to 81K, Ic could be set to 1000A. 450A to 1500A with this system
The current limiter which can set Ic arbitrarily in the range of was able to be manufactured.

Embodiment 2 As shown in FIG. 3, by controlling the liquid level of the liquid nitrogen tank, the temperature of the liquid argon in the liquid argon tank was controlled to 1000 A.
A current limiting system that performs a current limiting operation with the above current values was manufactured. The characteristics of the current limiting element were controlled by adjusting the temperature of the liquid argon from 86K to 78K. First, regarding the current limiting characteristics at 86K, Ic is about 450A, and at 78K, Ic is
c was 1500A. Then, when the liquid surface of liquid nitrogen was adjusted and the cooling temperature was set to 81K, Ic was able to be set to 1000A. With this system, a current limiter capable of arbitrarily setting Ic in the range of 450A to 1500A could be manufactured.

Embodiment 3 As shown in FIG. 4, a temperature-limiting system for controlling the liquid level of a liquid nitrogen tank to control the temperature of liquid argon in a liquid argon tank and performing a current limiting operation at a current value of 1000 A or more. did.
The electrode portion of the current limiting element is in contact with a copper block that transmits cold heat from the liquid nitrogen tank via aluminum nitride for insulation. The characteristics of the current limiting element were controlled by adjusting the temperature of the liquid argon from 86K to 78K. First, with respect to the current limiting characteristics at 86K, Ic was about 500A, and at 78K, Ic was 1700A. These results are somewhat higher than when the electrode section was not particularly cooled. This suggests that the critical current Ic of the superconducting conductor has decreased somewhat due to heat generation at the electrode portion. Then, when the liquid temperature of liquid nitrogen was adjusted and the cooling temperature was set to 81.5K, Ic became
It was able to be 1000A. With this system, it was possible to fabricate a current limiter capable of setting Ic arbitrarily in the range of 500A to 1700A.

Embodiment 4 As shown in FIG. 5, a current limiting system was prepared in which the temperature of liquid argon in a liquid argon tank was controlled by a refrigerator to perform a current limiting operation at a current value of 1000 A or more. 86K liquid argon
To 78K to control the characteristics of the current limiting element. First, regarding the current limiting characteristics at 86K, Ic was about 400A, and at 78K, Ic was 1300A. These results are somewhat lower than when the superconductor was cooled by the refrigerant. This suggests that the critical current Ic of the superconducting conductor is somewhat reduced due to a decrease in the cooling efficiency of the superconductor. Therefore, the refrigerator temperature was reduced to 79.8K
As a result, Ic was able to be set to 1000A. With this system, it was possible to fabricate a current limiter capable of setting Ic arbitrarily in the range of 400A to 1300A.

[0018]

As described above, the present invention provides a current limiter system characterized in that the current value for starting the current limiting operation can be arbitrarily set, and its industrial effect is enormous. is there.

[Brief description of the drawings]

FIG. 1 is a current limiter having a cooling system for controlling a critical current value by cooling liquid argon using a refrigerator.

FIG. 2 Shape of superconducting current limiting element

FIG. 3 is a current limiter system having a cooling system combining liquid nitrogen and liquid argon.

FIG. 4 shows a current limiter system in which an electrode part is cooled to a lower temperature.

FIG. 5 is a current limiter system having a structure in which a superconducting current limiting element does not directly touch liquid argon.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuru Sawamura 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Steel Corporation Advanced Technology Research Laboratory (72) Inventor Kei Kei Tanemoto 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Address Nippon Steel Corporation Advanced Technology Laboratory

Claims (7)

[Claims] 1. A current limiter having a mechanism for varying a cooling temperature of an oxide current limiting element. 2. The current limiting device according to claim 1, wherein the mechanism for varying the cooling temperature of the element is a mechanism using a plurality of cooling media or cooling devices. 3. The method according to claim 1, further comprising a mechanism for arbitrarily setting the temperature of any one of liquid argon, liquid nitrogen, and liquid oxygen to a temperature lower than its boiling point by using a refrigerator. Oxide superconducting current limiter. 4. The current limiter according to claim 1, wherein two or more of liquid argon, liquid nitrogen, and liquid oxygen are used in combination. 5. The method according to claim 1, 2, 3, or 4,
A current limiter having a mechanism for setting the connection between superconductors and the connection between the superconductor and the normal conductor to be lower than the cooling temperature of the central portion of the superconductor during normal operation. . 6. The connecting part according to claim 5, wherein the connecting part is in contact with a low-temperature end of the refrigerator or an electric heating copper block from a refrigerant other than the refrigerant in which the superconductor is immersed, via an insulator. Current limiter. 7. The current limiter according to claim 5, wherein the portion other than the electrode portion is housed in an insulating container so that the superconductor performing the current limiting operation does not directly contact the liquid refrigerant.