JPH03145169A - Current limiting device - Google Patents

Abstract

PURPOSE:To shield a current limiting device from an external magnetic field and a self-generated magnetic field so as to enable it to display a highly reliable current limiting effect to the shortcircuit trouble of a power system by a method wherein the current limiting element formed of oxide superconductive material is provided, and a superconductive magnetic shielding member is provided enveloping the element concerned. CONSTITUTION:A current limiting element 10 is connected to a bus cable 11 of a power system. The current limiting element 10 is mounted inside a cryostat 12 with the bus cable 11. The cryostat 12 is composed of a coolant chamber 13 filled with liquid nitrogen which cools an oxide superconductive material down to a critical temperature or below and a heat insulating layer 14 provided at the outer peripheral face of the coolant chamber 13 to thermally insulate the inside of the chamber 13 through vacuum. An oxide superconductive material layer 15 is formed on the inner peripheral face of the coolant chamber 13. The oxide superconductive material concerned becomes perfectly diamagnetic at a critical temperature or below to shield the inside of the chamber 13 from an external magnetic flux through Meissner effect. Therefore, a superconductive magnetic shielding member provided with an oxide superconductive material layer is able to shield a current limiting element from an external magnetic field displaying a magnetic shielding effect enough.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 3] The present invention relates to a current limiting device that suppresses abnormal current caused by a short circuit in a power system.

[Prior Art] When a short circuit occurs in a current system, a large amount of abnormal current flows at the short circuit location. As a result, a loss in the amount of current occurs in the current system. Therefore, in the event of a short-circuit accident, it is necessary to flow more current to compensate for the current loss.

That is, the current system is required to have a current capacity corresponding to the peak current at the time of a short circuit accident. Such an increase in current capacity requires changes to the equipment of the current system, resulting in a large economic burden. Therefore, it is important to reduce the abnormal current caused by the short circuit (hereinafter referred to as short circuit current) as much as possible. Therefore, various current limiting devices have been devised to reduce the short circuit current.

Short circuit accidents occur extremely rarely. For this reason, it is preferable that the current limiting element be made of a material that has no electrical loss under normal conditions. These include oxide superconductor materials that can use inexpensive liquid nitrogen. Oxide superconductor materials also have large normal conductivity resistance. Therefore, focusing on this characteristic, a current limiting device using an oxide superconductor material as the material of the current limiting element has been devised (Japanese Patent Application Laid-Open No. 1-4085
issue).

[Problems to be Solved by the Invention] However, in such a current limiting device, the oxide superconductor material constituting the current limiting element is likely to cause a quench phenomenon. This is because the critical current (I,) of the oxide superconductor material is easily influenced by the magnetic field.

The reason why the critical current of an oxide superconductor material is easily affected by the magnetic field is due to the weak crystal cohesion at the grain boundaries of the oxide superconductor material and the weak pinning force within the crystal grains. . If the critical current or critical current density (Jc) of the oxide superconductor material used in the current limiting element is unstable, it will adversely affect reliable operation of the current limiting device. It also has an adverse effect on the design of the current limiting device.

Generally, the magnetic field acting on the current limiting device is
One is given by force equipment, the other is self-generated.2
There are FJ types.

Magnetic fields acting from external power supply equipment are
sIt is inversely proportional to the power of the distance between it and the power equipment. For this reason, for magnetic fields acting from external power supplies,
1 current limiting device! It is sufficient to install it separately from the i-source power equipment. However, it is impossible to predict the extent to which a large magnetic field generated in pulses due to a surge or the like will affect the current limiting device. Furthermore, it is not possible to set a distance in ms that will not be affected by this large magnetic field.

The self-generated magnetic field reduces the critical current density and critical current of the current limiting element. The effect of this self-generated magnetic field on the current limiting device is predictable and can be taken into account to some extent in power system design 05. However, the influence of self-generated magnetic fields cannot be sufficiently eliminated.

The present invention has been made in view of the above points, and an object of the present invention is to provide a current limiting device that can block external and self-generated magnetic fields and exhibit a highly reliable current limiting effect against short-circuit accidents in power systems. With the goal.

[Means for Solving the Problems] Based on the experience of developing current limiting devices using oxide superconductor materials, the present inventors have developed magnetic field dependence, which is an essential characteristic of oxide superconductor materials. As a result of intensive studies to overcome this problem, we have come up with the present invention.

The present invention is a current limiting device characterized by comprising a current limiting element made of an oxide superconducting material and a superconducting magnetic shield member disposed to enclose the current limiting cord.

Here, the oxide superconductor material used for the current limiting rope and the superconducting magnetic shield member exhibits superconducting properties such as a large critical current density at liquid nitrogen temperature, and becomes a normal conductor at the critical temperature. A material that can rapidly transition from a superconductor to a superconductor is preferable. An example of such a material is an oxide superconductor material having a homogeneous structure. The specific resistance value of an oxide superconductor material in a normal conducting state is more than 100 times larger than that of a metallic superconductor material. Therefore, a current limiting rope using an oxide superconductor material has a large current limiting effect of suppressing short circuit current. For example, LnBa2Cu10y (Ln: rare earth element) whose critical temperature (Tc) is about 90 or less
Bi25r2Ca with Tc between 80 and 110
Cu20s and (B i, Pb)2 S r2 Ca
'2 Bi type such as Cu30to, and T, Q, BaCaCu20. ,,
Or TJ? Ba2Ca.

Examples include Tjl-based materials such as Cu30a and s.

The shape of the current limiting element is preferably a non-inductive wiring type in order to avoid the influence of a self-generated magnetic field. FIG. 4 is a plan view of a non-inductive wiring type current limiting element.

40 in the figure is a current limiting rope. The current limiting element 40 is composed of an oxide superconductor material 41 and a terminal portion 42 . The self-generated magnetic field reduces the critical current and critical current density, and has an adverse effect on the magnetic shielding effect of the superconducting magnetic shielding member. However, such a non-inductive wiring type current limiting element,
The zigzag shape allows self-generated magnetic fields to cancel each other out. Furthermore, by using a non-inductive wiring type, the current limiting element can be made smaller.

Since the current capacity of each current-limiting cable is set to be less than the critical current, the current capacity may be adjusted by installing a plurality of current-limiting elements in parallel as necessary.

A method for manufacturing a current limiting element is, for example, by forming a molten oxide superconductor material on a substrate by a method such as screen printing, doctor blade, extrusion coating, etc., forming a sheet-like material, and punching it into a Y31 shape. Oxide m inside objects or metal pipes
Examples include those in which the metal tube is filled with a conductor material and heat-treated together with the metal tube.

Examples of superconducting magnetic shielding members include those in which an oxide superconducting material layer is formed on a metal or ceramic substrate by a method such as plasma spraying. Furthermore, the magnetic shield member may be directly molded using an oxide superconductor material. That is, the magnetic shield member includes a current limiting element, and at least the portion facing the current limiting cord is made of an oxide superconductor material. Any material may be used as long as it has a layer and blocks external magnetic fields and self-generated magnetic fields.

[Function] The current limiting device of the present invention is characterized by having a current limiting element made of an oxide superconductor material and a superconducting magnetic shield member disposed to enclose the current limiting element.

Oxide superconductor materials are completely diamagnetic at temperatures below their critical temperature, ie, they shield external magnetic flux due to the Meissner effect. This shielding effect can be calculated using the following general formula.

B, 閤μ.・D◆Jc Here, B'A is the shielding effect, μ. is vacuum permeability, D
represents the thickness of the oxide superconductor material, and Jc represents the critical 7rS flow density, respectively.

By varying the oxide superconductor material thickness D in the above equation, the shielding effect can be adjusted.

Therefore, the superconducting/magnetic shielding member having the oxide superconductor material layer can sufficiently exhibit the magnetic shielding effect and protect the current limiting element from the external magnetic field.

Furthermore, by making the current limiting rope a non-inductive wiring type, self-generated magnetic fields can be suppressed.

As a result, the current limiting element is not affected by the magnetic field and can stably exert a current limiting effect.

〔Example] Hereinafter, the current limiting device of the present invention will be explained with reference to the drawings.

1 to 3 are cross-sectional views of the current limiting device of the present invention. Note that additional circuits such as circuit breakers are omitted in the figure. 1st
10 in the figure is a current limiting element. The current limiting element 10 is connected to a bus cable 11 that constitutes a power system. The current limiting element 10 is connected to the cryostat 1 together with the bus cable 11.
It is placed in 2. The cryostat 12 consists of a refrigerant chamber 13 filled with liquid nitrogen for cooling the oxide superconductor material below a critical temperature, and a heat insulating layer 14 provided on the outer circumferential surface of the refrigerant chamber 13 to vacuum insulate the inside. It is configured. An oxide superconductor material layer 15 is formed on the inner peripheral surface of the refrigerant chamber 13 .

Note that the oxide superconductor material layer 15 may be formed on the entire west peripheral surface of the refrigerant chamber 13, or may be formed on a part of the inner peripheral surface of the refrigerant chamber 13 to the extent that it exhibits a magnetic shielding effect. .

Alternatively, the oxide superconductor material layer 15 may be formed directly on the current limiting element without forming the oxide superconductor material layer 15 on the cryostat.

The parts in FIGS. 2 and 3 that overlap with those in FIG. 1 are designated by the same reference numerals as in FIG. 1, and the explanation thereof will be omitted.

20 in the f12 diagram is a superconducting magnetic shield tube.

An oxide superconductor material layer 21 is formed on the outer peripheral surface of the superconducting magnetic shield tube 20 . Further, a current limiting element 10 connected to the bus cable 11 is placed inside the superconducting magnetic shield n20. This superconducting magnetic shield tube 20 is placed inside a cryostat 22.

In FIG. 3, 30 is a flat plate made of an oxide superconductor material. The current limiting element 10 is placed between two opposing flat plates 30, and is fixed by a total of four supports 31, two for each flat plate. Two current-limiting cables 1o fixed to a plate 30 are placed in a cryostat 32.

The current limiting device of the present invention is not limited to the example shown above.

Experimental examples are shown below to clarify the effects of the present invention.

Experimental Example First, YBa2 Cu, 07 calcined powder having a particle size of approximately 10 μm, a cellulose binder, and a cellosolve solvent were mixed and thoroughly mixed. Using this mixture, a green sheet with a thickness of about 1 vlIm was produced by a doctor blade method. This green sheet was punched out into the non-inductive wiring type shown in FIG. The line width at this time was 10 mm.

This was subjected to heat treatment at 400° C. for 12 hours in an 02 air flow, and cooled at a cooling rate of 3° C./min. A current limiting element was produced in this way. The oxide superconductor line length at this time is 7
It was 50 mm.

Ag was vapor-deposited on both ends of the obtained current limiting element to form terminal parts. Thereafter, a Cu wire was soldered to the terminal portion.

Next, an SU with an outer diameter of 100IIIlφ and a length of 300 am
Ag was deposited on the outer peripheral surface of a cylinder made of S by a metal spray method. Furthermore, HoBa2 Cus 07 powder with a particle size of about 25t1m was sprayed onto this Ag to a thickness of about 0.5i+m using a low-pressure plasma spray method to form a HoBa
2CusOy layers were formed. Thereafter, this cylinder was subjected to heat treatment at 700° C. for 6 hours in an 02 air stream. Furthermore, A
g The steps from deposition to heat treatment were repeated once again. In this way, a superconducting magnetic shield cylinder was produced.

The above current limiting element is placed inside a superconducting magnetic shield cylinder,
A current limiting device of the present invention was obtained.

The critical current and short circuit peak current of the obtained current limiting device were investigated. The results are shown in Table 1 below. Note that the critical current is 25.75 when the current limiting device is immersed in liquid nitrogen, where external magnetic fields other than the earth's magnetic field can be ignored, and when an electromagnet is used.
Measurements were made with a Gaussian magnetic field applied. Further, the short circuit peak current was measured as follows using the circuit shown in FIG. 5 while applying a magnetic field of 25 Gauss. In the figure, 50 is a DC constant voltage power supply. A current limiting element 51 is connected to the DC constant voltage power supply 5o. A switch 52 and a resistor 53 are connected in parallel between the DC constant voltage power source 5° and the current limiting cable 51. First, a steady current of 60 A is applied from the DC constant voltage power supply 50. Next, switch 52 in the circuit is opened to cause a short circuit.

The current value at this time is determined as allJ.

For comparison, the critical current and short-circuit peak current of only the draining cord were similarly investigated without using the superconducting magnetic shield tube. The results are also listed in Table 1 below.

As is clear from Table 1 of ff51, the current limiting rope of the present invention (experimental example) shows a large critical current value regardless of the presence or absence of a magnetic field,
Moreover, the short circuit peak current value was small. On the other hand, in the conventional current limiting device (comparative example), the critical current value decreased due to the application of a magnetic field, and the short circuit peak current value was large.

[Effects of the Invention] As explained above, the current limiting device of the present invention is capable of blocking external and self-generated magnetic fields, exhibiting a highly reliable current limiting effect against short-circuit accidents in power systems, and is small in size. It is possible to change the

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of the current limiting device of the present invention;
The figure is a plan view of a non-inductive wiring type current limiting element, and FIG. 5 is a short circuit peak current measurement circuit diagram. DESCRIPTION OF SYMBOLS 10... Current limiting cable, 11... Bus cable, 12°22.32... Cryostat, 13... Refrigerant chamber, 14... Heat insulation layer, 15.21... Oxide superconductor Material layer, 20... Superconducting magnetic shield tube, 30...
Flat plate... support.

Claims (1)

[Claims] 1. A current limiting device comprising: a current limiting element made of an oxide superconductor; and a superconducting magnetic shield member disposed to enclose the current limiting element.