JPH10309034A - Current-limiting breaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the steady-state loss of a current limiting breaker caused by a current-limiting element by connecting in series a first switch which is opened at the rise time of a fault current between a power source and a load and a serially connected circuit of a second switch and a capacitor having a prescribed capacitance in parallel with the first switch. SOLUTION: A serially connected circuit is connected in parallel with a first switch 4a by connecting the switch 4a which is connected in series between a power source 1 and a load and a second switch 4b in series with a capacitor 4d which becomes a current-limiting element. Then a current-limiting breaker 4 is constituted by connecting a charger 4e which always charges the capacitor 4d to an arbitrary voltage to the serially connected circuit. Vacuum valves which are suitable for the opening and closing of a high-voltage large current are used for the first and second switches 4a and 4b and an operating device which drives the switches 4a and 4b are additionally provided. Therefore, the breaker 4 can be applied to a high-voltage large-current circuit and the breaker can be constituted in a compact inexpensive breaker, because the steady-state loss of the current-limiting breaker 4 caused by the current-limiting element can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current limiting circuit breaker applicable to a high-voltage and large-current circuit.

[0002]

2. Description of the Related Art When a short circuit or a ground fault occurs in an electric circuit, a fault current of several tens of kA flows, which seriously damages a system and power equipment. A technique for instantaneously detecting and suppressing such a fault current is called a current limiting technique, and techniques based on various principles have been developed so far. 5 and 6 show the configuration of a current limiting device as a typical prior art and an application circuit thereof (Japanese Patent Publication No. 50-4876). In the application circuit of FIG. 5, E is a three-phase power supply, R and X are resistors and inductances provided in a short circuit, B is a circuit breaker, and RG is a current limiting element. In this conventional technology, a PTC (Positive Temperature Coe) made of niobium carbide is used as the current limiting element RG.
fficient) A fault current is limited by using a resistor and utilizing its PTC characteristic. As shown in FIG. 6, niobium carbide has a PTC characteristic in which the specific resistance changes greatly in response to a rise in temperature. Therefore, at a normal current value, the calorific value is small since the specific resistance of the current limiting element RG is small, and the temperature of the current limiting element RG does not rise, the low resistance state is maintained and the circuit is not affected. However, when an accident occurs in the circuit and an excessive current flows, the heat generation of the current limiting element RG increases rapidly and the element temperature rises. As a result, the specific resistance of the current limiting element RG increases and acts to reduce the circuit current. Since the fault current is largely suppressed by such a current limiting action, it is possible to make the circuit breaker compact and reduce damage to the system due to an excessive fault current.

[0003]

As described above, in the conventional current limiting device, by configuring the current limiting element and the circuit breaker in series, an overcurrent having a sharp rise such as a short-circuit current can be prevented. Although it has an excellent feature that the current can be limited from the first wave, since the variation width of the specific resistance is relatively small, the following problems to be solved still remain. Since the load current always flows through the current limiting element, the current carrying capacity is limited. That is, since the temperature of the current limiting element increases in proportion to the load current,
It is necessary to suppress the steady-state temperature (conduction current value) of the current limiting element to such an extent that the circuit and current limiting characteristics are not affected. Since the load current always flows through the current limiting element, Joule heat (power loss) occurs due to the steady conduction current. The specific resistance change width of the current-limitable element at present at room temperature is about 1:
10 is the limit. Therefore, in the conventional configuration in which the current limiting element is connected in series between the power supply and the load, the current limiting effect decreases as the applied circuit voltage increases. That is, the required resistance value (Rm) of the current limiting element at the time of current limiting is as follows: Rm = E / Im (Ω) (1) Here, E: circuit voltage (V), Im: current limiting current value (A). Current-limiting element resistance (R
o) is 1/10 of (Rm), so Ro = Rm /
It becomes 10. Therefore, the continuous conduction current allowable value (I) of the current limiting element is

I = [α · θt / {Ro (1 + β · θt)}] ^1/2 (A) (2) Here, α: heat dissipation coefficient of the current limiting element (W / K),
β: resistance temperature coefficient of the current limiting element, θt: allowable temperature rise value (K) of the current limiting element in a steady state. As can be seen from the above results, when the current limiting current value (Im) is constant,
When the circuit voltage (E) increases, the current-limiting resistance (Rm) of the current-limiting element also needs to be large accordingly, and the steady-state resistance (Ro) increases. The heat dissipation coefficient (α) of the current limiting element and the allowable temperature rise at steady state (θt) are determined by the external shape and characteristics of the current limiting element. The larger the value of Ro), the lower the allowable continuous conduction current value (I). Conversely, if the steady-state resistance value of the current-limiting element is determined by giving priority to the energizing current value, the current-limiting element resistance value at the time of current-limiting rises only about 10 times that of the current-limiting element. As a result, the current limiting current value inevitably increases, and the current limiting effect decreases.

[0004] The present invention has been made in view of the above,
A large current limiting effect can be obtained, the steady-state loss due to the current limiting element can be reduced, and the present invention can be applied to a high-voltage and large-current circuit, and the device can be reduced in size and cost. It is an object to provide a flow blocking device.

[0005]

In order to solve the above-mentioned problems, the invention according to claim 1 is connected between a power supply and a load, detects the rise of the fault current, and limits the current before the fault current rises. A current-limiting circuit breaker for interrupting, wherein a first switch that is normally kept in a closed state and opened when a fault current rises is connected in series between the power supply and a load, and is always kept in an open state. And a series connection circuit of a second switch, which is controlled to be turned on almost simultaneously with the opening of the first switch, and a capacitor having a predetermined capacitance which is constantly charged to an arbitrary voltage, is connected in parallel to the first switch. The gist is to do it. With this configuration, the fault current is rapidly detected at the rise thereof by, for example, an overcurrent detector, and the first switch is opened before the fault current increases to a predetermined amount or more. The switch is turned on. When the second switch is turned on, a resonance current having a frequency corresponding to the residual inductance and the capacitance of the capacitor flows through the circuit of the first switch, and is superimposed on the fault current flowing through the first switch. Since the resonance current frequency from the capacitor is very high with respect to the fault current frequency, a current zero point occurs in the first switch in a short time, and the fault current is cut off. As a result, the fault current is commutated to the capacitor side, and is limited to a required value by the impedance of the capacitor. In addition, since the capacitor, which is a current limiting element, is connected in series with the second switch and connected in parallel with the first switch, there is no steady-state loss due to the current limiting element.

According to a second aspect of the present invention, in the current limiting device according to the first aspect, the first switch and the second switch are formed as vacuum valves. With this configuration, application to a high voltage / high current circuit becomes easy. By making the first switch a vacuum valve,
Even if the switch is opened, the circuit current does not change until the current zero point comes. However, as described above, the second switch is turned on almost simultaneously with the opening of the first switch, and the circuit of the first switch is turned on. The first switch is turned off within a short time because a resonance current very high in frequency with respect to the fault current frequency flows and a current zero point is forcibly created. As a result, the fault current on the first switch side is cut off, commutated to the capacitor side, and the current is limited.

According to a third aspect of the present invention, in the current limiting device according to the first aspect, the first switch is a vacuum valve and the second switch is an air switch. With this configuration, the second switch through which the limited current flows can function as the first switch even if it is an air switch.
At about the same time when the switch is opened, the second switch is controlled to be turned on, so that the current can be limited before the fault current becomes excessive.

According to a fourth aspect of the present invention, in the current limiting device of the first aspect, the first switch is a vacuum valve, and the second switch is a trigger gap. With this configuration, when the second switch through which the limited current flows has a trigger gap with a very fast response, the second switch is turned on more quickly after the opening of the first switch, so that a shorter time is required. It is possible to limit the fault current to a required value within a time.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 to FIG. 3 are views showing a first embodiment of the present invention. First, the configuration and operation of the current limiting device will be described with reference to FIG. In the figure, 1 is a power supply, 2
Is a circuit breaker, 3 is an overcurrent detector, and 4 is a current limiting device. The current limiting device 4 includes a first switch 4a and a second switch 4b connected in series between the power supply 1 and the load. And a capacitor 4d serving as a current limiting element are connected in series and are connected in series to the first switch 4a, and a charger 4e for constantly charging the capacitor 4d to an arbitrary voltage. . Both the first switch 4a and the second switch 4b use a vacuum valve suitable for opening and closing a high voltage and a large current, and drive the first switch 4a and the second switch 4b, respectively. An operating device (not shown) is provided.

The current limiting device is configured as described above, and operates as follows. That is, the overcurrent detector 3 detects and detects a fault current generated in the circuit at a high speed, opens the first switch 4a before the fault current increases, and simultaneously opens the first switch 4a. Second switch 4
Input b. The capacitor 4d is always charged to a predetermined voltage by the charger 4e. When the second switch 4b is turned on, an LC resonance current having a frequency corresponding to the residual inductance flows through the circuit of the first switch 4a, and The first switch 4a is superimposed on the fault current flowing. Since the resonance current frequency from the capacitor 4d is very high with respect to the fault current frequency, a current zero point occurs in the first switch 4a within a short time, and the fault current is cut off. As a result, the fault current is commutated to the capacitor 4d side and is limited by the impedance of the capacitor 4d.

Next, the operation of the current limiting device will be described in more detail with reference to the current limiting test circuit shown in FIG. In FIG. 2, a 6 kV-50 Hz AC power supply is provided by using a capacitor 11 and a reactor 12 instead of the power supply 1.
That is, the power supply resonance frequency is set to 50 Hz by setting the capacitance of the capacitor 11 to 500 μF and the inductance of the reactor 12 to 20 mH, and the surge impedance of the LC series circuit is 6.3Ω. Therefore, in the circuit of FIG. 2, the circuit breaker 2 is turned on and the first switch 4a is turned on.
Is closed, a current 952A, which is obtained by dividing the charging voltage 6000V of the power supply capacitor 11 by the surge impedance 6.3Ω, flows through the circuit. The capacitance of the current limiting capacitor 4d is 500 μF, and the voltage
It is charged to 00V. In the current limiting test circuit of FIG. 2, first, the first switch 4a is closed, and then the circuit breaker 2 is turned on to supply a short-circuit current of 952A peak. At the moment when the short-circuit current reached a peak, the second switch 4b was closed, and the operation of the current limiting device in the above-described current limiting device was confirmed.

FIG. 3 is an oscillogram showing an example of the operation characteristics of the current limiting device in the circuit of FIG. In the figure, I ₁ is circuit total current, I ₂ is the current through the second switch 4b, I _sw is the current flowing through the first switch 4a. As can be seen from FIG. 3, when the circuit breaker 2 was turned on and the first wave peak of the short-circuit current flowed, the first switch 4a was opened, and the second switch 4b was turned on almost simultaneously. Since the first switch 4a is a vacuum valve, even if the first switch 4a is opened, the circuit current I
₁ does not change. However, when the second switch 4b is turned on, a high-frequency current flows from the capacitor 4d to the first switch 4a in a superimposed manner, and the current of the first switch 4a is forced to have a current zero point. Therefore, the short-circuit current flowing through the first switch 4a is interrupted and commutated to the capacitor 4d, which is a parallel circuit, and to the second switch 4b. Capacitor 4d is 1 / jωC for 50Hz AC
(6.4Ω), the short-circuit current is limited according to the impedance. The short-circuit current thus limited is interrupted by the circuit breaker 2. In this embodiment, both the first switch 4a and the second switch 4b use a vacuum valve. However, only the first switch 4a through which the entire circuit current flows is a vacuum valve, and the current is limited. Second switch 4 through which current flows
An air switch may be used for b. The use of the air switch eliminates the need for an operating device.

According to the current limiting device of the present embodiment described above, it is possible to perform the current limiting and interrupting before the fault current rises, so that the power equipment can be used without considering the influence of the fault current. it can. Therefore, it is possible to prevent deterioration of the power equipment, and to economically select the size and cost.

FIG. 4 shows a second embodiment. In the present embodiment, the second switch 4c is replaced with a trigger gap instead of a vacuum valve. The trigger gap is a switch that conducts between terminals when a predetermined voltage is applied to the control terminal. The trigger gap can be turned on without requiring an operating device such as a vacuum valve, and the response is very fast. This has a great effect on a current having a / dt value. Therefore, by turning on the trigger gap immediately after the first switch 4a is opened, the first switch current is cut off, and at the moment of the cut off, the fault current is diverted to the capacitor 4d side and the fault current is limited by the impedance of the capacitor 4d. It is.

[0016]

As described above, according to the first aspect of the present invention, the first switch which is normally kept closed and opened when the fault current rises is connected in series between the power supply and the load. A series connection circuit comprising a second switch connected and normally kept in an open state and controlled to be turned on substantially simultaneously with the opening of the first switch, and a capacitor having a predetermined capacitance constantly charged to an arbitrary voltage. Is connected in parallel to the first switch, the fault current is limited to a required value by a capacitor having a predetermined capacitance before the fault current rises to a predetermined value or more, so that a large current limiting effect can be obtained. In addition, since the capacitor, which is a current limiting element, is connected in series with the second switch that is always open, and is connected in parallel with the first switch, there is no steady loss due to the current limiting element. Therefore, the present invention can be applied to a high-voltage / large-current circuit, and can reduce the size and cost of the device.

According to the second aspect of the present invention, since the first switch and the second switch are vacuum valves, easiness of application to a high voltage / high current circuit can be obtained.

According to the third aspect of the present invention, since the first switch is a vacuum valve and the second switch is an air switch, the second switch through which a limited current flows is an air switch. By doing so, the operation device when using the vacuum valve becomes unnecessary, and the cost can be further reduced.

According to the fourth aspect of the present invention, the first switch is a vacuum valve and the second switch is a trigger gap. Therefore, the second switch through which a limited current flows is very responsive. By setting the fast trigger gap, the second switch is turned on more quickly after the first switch is opened, and the fault current can be limited to a required value in a shorter time. Therefore, in addition to the effect of the third aspect of the invention, an even greater current limiting effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a current limiting device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a current limiting test circuit according to the first embodiment.

FIG. 3 is a timing chart showing an operation test result of the first embodiment by the current limiting test circuit of FIG. 2;

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

FIG. 5 is a circuit diagram of a conventional current limiting device.

FIG. 6 is a characteristic diagram showing the temperature dependence of the specific resistance of the current limiting element in the conventional current limiting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 2 Circuit breaker 3 Overcurrent detector 4 Current limiting circuit breaker 4a 1st switch 4b 2nd switch (vacuum valve) 4c 2nd switch (trigger gap) 4d Capacitor 4e Charger

Claims (4)

[Claims] 1. A current limiting device which is connected between a power supply and a load, detects a rise of an accident current, and limits and interrupts the current before the accident current rises. A first switch, which is opened when the power supply rises, is connected in series between the power supply and the load, and is normally kept in the open state, and is controlled to be turned on almost simultaneously with the opening of the first switch. And a series connection circuit comprising a capacitor having a predetermined capacitance constantly charged to an arbitrary voltage and connected in parallel to the first switch. 2. The apparatus according to claim 1, wherein said first switch and said second switch are vacuum valves.
The current limiting device according to claim 1. 3. The first switch is a vacuum valve,
2. The current limiting device according to claim 1, wherein the second switch is an air switch. 4. The first switch is a vacuum valve,
The current limiting device according to claim 1, wherein the second switch is used as a trigger gap.