JPH01185128A - Self-reset current limiter - Google Patents

Abstract

PURPOSE:To provide self-reset function and to simplify the structure, by employing a superconductor as a current limit element and connecting a switch in parallel or series therewith. CONSTITUTION:A current limit element 1 comprises an oxide superconductor. A switch 4 is connected in parallel with the current limit element 1 through a terminal 2. The current limit element 1 is cooled through liquid nitrogen and the like. When current having magnitude exceeding over a critical level flows, the current limit element 1 is quenched instantaneously to exhibit high resistance thus suppressing overcurrent immediately. Consequently, only small current flows through the current limit element 1 and small amount of heat thus produced is absorbed by the liquid nitrogen and the like, and the current limit element 1 is protected from breakdown. Upon reset from abnormality, the switch 4 is closed and load current flows through the switch 4 thus stopping generation of heat from the current limit element 1 and resetting to superconducting state. The switch 4 is opened under this state.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a self-recovering current limiting device.

(Prior Art) As is well known, current limiting devices are used to protect power equipment from short circuits, etc., and conventional current limiting devices of this type are configured with power fuses or circuit breakers. is considered normal.

However, although the former has a simple structure, it does not have a self-recovery function because it melts and therefore needs to be replaced every time it is operated. Although the latter has a self-restoring function, it has a complicated and expensive structure and has drawbacks such as a limited number of short-circuit interruptions.

(Problems to be Solved by the Invention) An object of the present invention is to propose a current limiting device having a self-resetting function and having a simple configuration.

(Means for Solving the Problems) This invention uses an oxide superconductor whose resistivity becomes high enough to have a current limiting function at a current exceeding a critical current as a current limiting element, and connects the oxide superconductor in parallel or in series with this current limiting element. It is characterized by being connected to a switch.

(Example) An example of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a current limiting element, which is made of an oxide superconductor. The oxide superconductor used here has a characteristic that when an overcurrent exceeding the critical current flows, the resistance value becomes high due to a quenching effect.

The high resistance value at this time is set to a value that provides the required current limiting function, and is set to an appropriate length so that the current limiting element 1 does not generate excessive heat. In addition, this current density is selected so as to be, for example, approximately half of the critical current in normal conditions, taking into account load fluctuations on the line.

As each oxide superconductor used here, for example, ceramics made of oxides of strontium, barium, or yttrium-based elements and copper are suitable.

Terminals 2 are connected to both ends of the current-limiting element 1 and are made of a normal conductor such as copper. Terminal 2 and current limiting element 1
is sealed in a tank (not shown) together with a cooling medium such as liquid nitrogen.

3 is a conductor connected to the line to be protected, 4 is a current limiting element 1
This is a switch connected in parallel to the two terminals, specifically between two terminals. In the example of FIG. 1, it is assumed that the switch 3 is always open.

In the above configuration, the current-limiting element 1 is normally cooled by liquid nitrogen, so that it exhibits characteristics as a superconductor, and therefore its resistance value is zero. Therefore, the current from the line 3 continues to flow through the current limiting element 1 without any loss.

Next, if an overcurrent exceeding the critical current of the superconductor flows, the current limiting element 1 instantly quenches and becomes high in resistance. Therefore, this overcurrent is immediately suppressed. The current flowing through the current limiting element 1 after current limiting is minute, and even if some heat is generated, it is absorbed by the heat of vaporization of the liquid nitrogen, so it will not be damaged due to overheating.

The switch 4 is closed when the fault in the line is restored. Then, since all the load current from this point on flows through the switch 4, the current limiting element 1 is cooled by liquid nitrogen and returns to the state of a superconductor by itself again.

Therefore, the entire load current also flows through the current limiting element 1. At this time, the switch 4 is opened.

This opening occurs without current.

The embodiment shown in FIG. 2 has a configuration in which the switch 4 is connected to the current limiting element 1 in series. In this case, the switch 4 is normally closed.

Even in the case of overcurrent, if an overcurrent flows, the current limiting element 1 quenches and limits the overcurrent. After this, the switch 4 is opened, and the interrupting current at that time may be extremely small. Therefore, the switch can be of a simple and compact structure as in the case of FIG. 1.

When the switch 4 is opened as described above, the current flowing through the current limiting element 1 becomes zero, so no heat is generated thereafter. This causes the current limiting element 1 to self-return to a superconductor. If the switch 4 is closed after the fault has been recovered, the load current will return to the current limiting element 1.
flows to In other words, it functions as a current limiting device.

(Effects of the Invention) As detailed above, according to the present invention, since it is constructed using a current limiting element made of a superconductor that exhibits a high resistance value against overcurrent, it has a self-resetting function and , the configuration can be made extremely simple, and the number of operations is not limited in any way.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram showing an embodiment of the invention, and FIG. 2 is a wiring diagram showing another embodiment of the invention.

Claims (1)

[Claims] The current-limiting element is an oxide superconductor whose specific resistance becomes high enough to have a current-limiting function when the current exceeds the critical current, and when an overcurrent flows through the current-limiting element, the current-limiting function is exhibited by a quenching action. And as soon as the line failure is recovered,
A self-recovering current limiting device comprising: a switch for interrupting current flowing through the current limiting element; connected in parallel or series to the current limiting element in order to restore superconducting function to the current limiting element.