JPH04207923A - Current limiting method and current limiting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a current limiting method and a current limiting device, that is, a current limiting device that limits the current when a current exceeding a specified value flows through a circuit.

The present invention relates to a current limiting method, current limiting device, and current limiting circuit breaker used to protect a circuit.

[Conventional technology]

A current limiting device using a superconducting current limiting element increases the resistance value and limits overcurrent by transferring the superconducting current limiting element from a superconducting state to a normal conducting state. 63-307635, the configuration of a conventional current limiting device is shown.

In the figure, 3 is a superconducting material, such as Y-Ba-Cu.
- It is a superconducting current limiting element made of ○ series ceramics, and has terminals 1 and 2 at both ends, and the total length of the superconducting current limiting element 3 can provide sufficient current limiting when in a normal conduction state. It has a resistance value and is sized to have a cross-sectional area sufficient to flow the rated current when in a superconducting state.

A measuring transformer 4 for detecting current is attached to the terminal 1, and its signal causes a magnetic field generating coil 6a to be activated.

A control section 5 is provided that causes current to flow through 6b and 6c with a time delay.

When an overcurrent is passed through the conventional current limiting device 15 configured as described above, the control unit 5 receives the signal from the measuring transformer 4 and shifts the time to apply current to the magnetic field generating coils 6a, 6b, 6c. Flow. As a result, the regions 16a, 16b, 16 of the superconducting current limiting element 3 surrounded by the coils 6a, 6b, 6c, respectively
A magnetic field equal to or higher than the critical magnetic field is applied to c, the superconducting state collapses and transitions to a normal conducting state, and resistance is generated in the current-carrying path consisting of the terminals 1, 2 and the superconducting current-limiting element 3 corresponding to each region.

By applying current to each coil at different times, the current is gradually limited.

In this way, by arbitrarily setting the time for applying the current to each coil, it is possible to obtain the optimum current-limiting characteristics for the applied circuit conditions, and to obtain a current-limiting device that does not generate surge voltage. It is.

[Problem to be solved by the invention]

The conventional technology described above requires a measuring transformer for current inspection, a control unit, and a magnetic field generation coil in order to divide the superconducting current-limiting element into many areas and transfer them to each area, making the device configuration complicated. In addition, there was a problem of low operational reliability.

In addition, when one region of a superconducting current limiting element transitions to a normal conducting state, the Joule heat in that region causes other regions to reach a critical temperature, and as a result of the transition to a normal conducting state, the stage There was also the problem that it was difficult to perform effective current limiting.

An object of the present invention is to provide a current limiting device that has high operational reliability and can freely set current limiting characteristics.

[Means to solve the problem]

In order to achieve the above object, the present invention provides that when an overcurrent flows through a main circuit consisting of a superconducting current limiting element through which current flows, the superconducting current limiting element in the main circuit is transferred to a normal conducting state, and the main circuit After limiting the overcurrent flowing through the motor, the current is limited by a current limiting method in which the overcurrent is limited in stages by sequentially commutating the current through a plurality of stages of commutation circuits.

In addition, for this purpose, a main circuit consisting of a superconducting current limiting element,
A current limiting device is constructed from at least one stage of commutation circuit consisting of a superconducting current limiting element and an impedance in series, and a commutation circuit consisting only of impedance.

[Effect]

In the present invention, the superconducting current limiting element of the main circuit is normally kept in a superconducting state, and when an overcurrent flows, it changes to a normal conducting state, limits the overcurrent, and commutates to the commutation circuit.

In the commutation circuit, the commutated current is limited by impedance, and when the current increases further, the superconducting current limiting element in the commutation circuit transitions to a normal conduction state, limiting the current, and starting the next stage of commutation. Commutates into the circuit.

In this way, it has a simple configuration and high operational reliability without using a measuring transformer for current measurement, a control unit, or a magnetic field generation coil, and the impedance can be set for each commutation circuit. , current-limiting characteristics can be set freely.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, 3a is a superconducting material, for example, Y-Ba-Cu-0
This is a superconducting current limiting element made of ceramics, and has terminals 1.2 at both ends. Superconducting current limiting element 3
A has a cross-sectional area sufficient to allow the rated current to flow in a superconducting state, and has a characteristic that its resistance value is sufficiently larger than that of the resistor 7a in a normal conducting state. A commutation circuit consisting of a resistor 7a and a second superconducting current limiting element 3b is connected to the superconducting current limiting element 3a. The superconducting current-limiting element 3b has a cross-sectional area sufficient to flow a current of the limiting current value determined in a superconducting state, and has a characteristic that its resistance value is sufficiently larger than that of the resistor 7b in a normal-conducting state. A commutation circuit consisting of a resistor 7b is connected to both ends of the superconducting current limiting element 3b.

Next, the operation of this circuit will be explained. Normally, current flows through the superconducting current limiting element 3a. At this time, since the superconducting current-limiting element 3a is in a superconducting state, the circuit current flowing through the terminal 1 to the superconducting current-limiting element 38 to the terminal 2 as a conduction path is not subjected to any resistance. Next, when an overcurrent corresponding to the critical current of the superconducting current limiting element 3a flows through this current path, the superconducting state of the superconducting current limiting element 3a collapses and transitions to a normal conducting state. As a result, the overcurrent flowing through the current-carrying path is limited, and the resistance of the superconducting current-limiting element 3a becomes sufficiently larger than the resistance of the resistor 7a, so that the current is commutated between the resistor 7a and the superconducting current-limiting element 3b. The current is commutated to the circuit, and the current is limited by the resistor 7a. At this time, the current mainly flows through the second current path consisting of terminal 1 - resistor 7a - superconducting current limiting element 3b - terminal 2. Also,
At this point, the superconducting current limiting element 3b is in a superconducting state, so it does not affect the circuit at all. Next, the current flowing through the second current-carrying path gradually increases, and when it reaches the critical current of the superconducting current-limiting element 3b, the superconducting state of the superconducting current-limiting element 3b collapses, transitions to a normal conducting state, and the resistance value rises. the result,
The current flowing through the second current-carrying path is limited, and the resistance value of the superconducting current-limiting element 3b becomes sufficiently larger than the resistance value of the resistor 7b, so the current is commutated to the resistor 7b, and at this time, The current mainly flows from terminal 1 to resistor 78 to resistor 7b to terminal 2.
The current flows through the third current-carrying path.

As the resistance value of the current-carrying path increases in this way, the overcurrent is gradually limited, and the electric circuit is opened by the operation of a circuit breaker (not shown), the current is interrupted, and the superconducting current-limiting elements 3a and 3b It transitions to a superconducting state and the circuit returns to its initial state.

FIG. 7 shows an example of a change in the conduction current of the circuit of FIG. 1 showing such a change, with the vertical axis representing the conduction current and the horizontal axis representing time. In FIG. 7, the dashed line 10 indicates the overcurrent flowing in the absence of a current limiting device, Icl.

(2) c2 indicates the critical current of the superconducting current limiting elements 3a and 3b.

In addition, tl and t2 on the horizontal axis are superconducting current limiting elements 3a, respectively.
, 3b shows the transition time.

Corresponding to FIG. 7, FIG. 8 shows an example of a change in current-carrying path resistance of the circuit shown in FIG. 1, with the vertical axis representing the current-carrying path resistance and the horizontal axis representing time. Curve 12 in the figure is the current path resistance characteristic, tl,
t2 indicates the time during which the superconducting current limiting elements 3a and 3b transition, corresponding to FIG.

In this way, the superconducting current limiting element first limits the overcurrent, and then the current is commutated to the commutation circuit, and the resistance in the commutation circuit performs the main current limiting, which improves operational reliability with a simple configuration. By appropriately selecting the resistance value of each resistor, it is possible to realize current-limiting characteristics that are optimal for the applied circuit conditions, and to obtain a current-limiting device that does not generate surge voltage.

In this embodiment, the superconducting current-limiting element 3b can also be provided with a function of transitioning to a normal conductive state by causing Joule heat generated in the resistor 7a to act on the superconducting current-limiting element 3b.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. This has switches 17a and 17b connected in series with the superconducting current limiting element in the circuit shown in FIG. The operation of this circuit is as follows. Start, switch 17
a and 17b are inserted. The current flowing through the first energizing path, that is, terminal 1 - switch 17a - superconducting current limiting element 38 - terminal 2 is not subjected to any resistance because superconducting current limiting element 3a is in a superconducting state. Next, superconducting current limiting element 3
When an overcurrent corresponding to the critical current a flows through the first current path, the superconducting current limiting element 3a transitions to a normal conductive state and its resistance increases. As a result, the overcurrent flowing through the current-carrying path is limited,
In addition, since the resistance of the superconducting current-limiting element 3a becomes sufficiently larger than the resistance of the resistor 7a, the current is diverted to the second current-carrying path consisting of the resistor 7a, the switch 17b, and the superconducting current-limiting element 3b, and the current is passed through the resistor. The current is limited by 7a. When the switch 17a is opened at the same time, the current flowing through the superconducting current-limiting element 3a that has transitioned to the normal conductive state is cut off, and the current flows only through the second current-carrying path, thereby preventing damage to the superconducting current-limiting element 3a. be able to. Next, when the current flowing through the second current-carrying path gradually increases and reaches the critical current of the superconducting current-limiting element 3b, the superconducting current-limiting element 3b transitions to a normal conductive state and its resistance value increases. As a result, the current flowing through the superconducting current-limiting element 3b is restricted, and the resistance of the superconducting current-limiting element 3b becomes sufficiently larger than the resistance of the resistor 7b, so that the current is commutated to the resistor 7b. At the same time, when the switch 17b in the second current-carrying path is opened, the current flowing through the superconducting current-limiting element 3b that has transitioned to the normal conductive state is cut off, and the limited current flows only through the resistor 7b. Damage to the superconducting current limiting element 3b that has transitioned to a conductive state can be prevented.

When a switch is connected in series with a superconducting current-limiting element in this way, it prevents damage to the superconducting current-limiting element by cutting off the current flowing through the superconducting current-limiting element that has transitioned to a normal conducting state.
In addition, it is possible to reliably limit the current in stages.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

This is the resistor 7a in the circuit shown in FIG.

7b is replaced with coils 6a and 6b, and due to the inductance of the coils, it exhibits the same effect as the circuit shown in FIG. 1.

Needless to illustrate again, it is also possible to connect a resistor in series to the coil 6a and limit the current with both the coil and the resistor, and it is also possible to select the impedance by replacing only the coil 6a with a resistor. Conceivable. That is,
Each current-limiting impedance may be composed of at least one of a resistor and a coil.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

In this embodiment, the magnetic field generated in the coils 6a, 6b is applied to the superconducting current limiting elements 3b, 3c to exceed the critical magnetic field, thereby making it possible to transition to the normal conductive state.
This is an example in which commutation and current limiting are performed in three stages, and a series switch is provided to prevent damage to the superconducting current limiting element. According to this configuration, the superconducting current limiting element can be transferred by two means, a critical magnetic field and a critical current, so the degree of freedom in setting the current limiting characteristics is greatly increased.

Next, FIG. 5 shows a fifth other embodiment of the present invention.

In this case, whereas the embodiment shown in Fig. 1 performs current limiting and commutation in two stages, current limiting and commutation are performed in three stages, and the resistance change characteristics of the current carrying path are changed in the first stage. Compared to the circuit shown in FIG. 1, more detailed settings can be made.

Next, FIG. 6 shows a sixth other embodiment of the present invention.

In this case, current limiting and commutation are performed in four stages, and the sixth
The circuit shown in the figure allows the resistance change characteristics to be set more finely than the circuit shown in FIG.

〔Effect of the invention〕

The present invention is comprised of a main circuit consisting of a superconducting current-limiting element that constantly conducts current, at least one stage of commutation circuit consisting of the superconducting current-limiting element and an impedance in series, and a commutation circuit consisting only of impedance. Therefore, after the overcurrent is limited at one end by the superconducting current limiting element, it is commutated to the commutation circuit and is limited by the impedance in the commutation circuit, but since the commutation circuit is connected in several stages, it gradually Current is limited. Also.

Current-limiting characteristics can be changed by appropriately selecting the impedance of each commutation circuit.

As a result, it is possible to realize a current limiting device that has a simple configuration, has high operational reliability, and can freely set current limiting characteristics without using a measuring transformer for current measurement, a control unit, or a magnetic field generating coil.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the invention, FIG. 3 is a circuit diagram showing a third embodiment of the invention, and FIG. FIG. 4 is a circuit diagram showing a fourth embodiment of the invention, FIG. 5 is a circuit diagram showing a fifth embodiment of the invention, and FIG. 6 is a circuit diagram showing a sixth other embodiment of the invention. 7 is a current characteristic diagram of the embodiment of the present invention shown in FIG. 1, FIG. 8 is a current conduction path resistance characteristic diagram of the embodiment of the present invention shown in FIG. 1, and FIG. 9 is a superconducting current characteristic diagram. It is a block diagram of the conventional current limiting device using a current limiting element. 1.2-=terminal, 3a, 3b, 3c, 3d=superconducting current limiting element, 6a, 6b-coil, 7a, 7b. 7c, 7d - resistor, 17 a, 17 b, 1
7 c - Figure 1 Figure 2 @ Figure 3 Jα Figure 4 @ Figure 5 Figure 6 Wa d J Out Figure 7 Figure 8 Figure 9

Claims (1)

[Scope of Claims] 1. In a current limiting method that increases the resistance of a superconducting current limiting element by transferring it from a superconducting state to a normal conducting state to limit the current, an overcurrent flows in the main circuit through which the current always flows. When the superconducting element in the main circuit transitions to normal conductivity and limits the overcurrent flowing through the main circuit, the overcurrent is gradually reduced by commutating the current through multiple stages of commutation circuits. A current limiting method characterized by current limiting. 2. In a current limiting device comprising a current-carrying path including a superconducting current-limiting element whose resistance increases upon transition from a superconducting state to a normal-conducting state and limits current, a main circuit consisting of the superconducting current-limiting element; A current limiting device comprising: a commutation circuit made up of the superconducting current limiting element and an impedance in series; and a commutation circuit made up of only the impedance.