JPH08149687A - Ground fault detector - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to prevent the malfunction of the ground fault detection circuit and the change of the detection sensitivity current value due to the influence of the stray capacitance of the lead wire up to the remote test switch, and it is stable regardless of the voltage of the AC circuit. To obtain a ground fault detection device that can operate. A zero-phase current transformer 2 inserted in an AC electric circuit 1, and a ground fault detection circuit 3 for the AC electric circuit which operates when an output from a secondary winding 2a of the zero-phase current transformer exceeds a predetermined value. A rectifier circuit 7 that rectifies the voltage of the AC circuit 1 and supplies power to the ground fault detection circuit 3, and an oscillator circuit 15 that is supplied with power from the rectifier circuit 7 and outputs a pseudo leakage signal to the ground fault detection circuit 3. A test switch 9 for inspecting the operation of the ground fault detection circuit 3, which is connected in series to a power supply circuit from the rectifier circuit 7 to the oscillator circuit 15, is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault detecting device provided with a test circuit for checking operation, and particularly to a lead wire connecting a remote test switch used for operation check and a ground fault detecting device. It is intended to prevent malfunction of the ground fault detection device due to the capacitance of the floating capacitor.

[0002]

2. Description of the Related Art FIGS. 6 and 7 are circuit diagrams showing the structure of a conventional ground fault detecting device. In the figure, 1 is an AC circuit, 2 is a zero-phase current transformer, 2a is a secondary winding thereof, 3 is a ground fault detection circuit connected to the secondary winding 2a, 4 is an output of the ground fault detection circuit 3 A thyristor connected to the end, 5 is driven by conduction of the thyristor 4, for example, an output device such as an electromagnetic relay device, 6 is a voltage drop resistor connected to a power supply circuit to the ground fault detection circuit 3, Reference numeral 7 is a rectifier circuit, 8 is a test terminal for artificially performing a pseudo leakage test, 9 is a remote test switch, 10 is a lead wire connecting the test terminal 8 and the remote test switch 9, 11 is an impedance element, and 12 is the above zero. A test winding wound around the phase current transformer 2 is a capacitor for smoothing the direct current of the rectifier circuit 7. In FIG. 6, the test terminal 8 and the impedance element 11 are
, And in FIG. 7, the test terminal 13, the impedance element 11, and the test winding 12 form a test circuit 13, respectively.

The operation of the conventional ground fault detection device thus configured will be described. When a leakage or a ground fault occurs in the AC circuit 1, the zero-phase current transformer 2 generates a ground fault detection signal in its secondary winding 2a, and this signal is input to the ground fault detection circuit 3. The ground-fault detection circuit 3 determines the magnitude of the ground-fault detection signal, further determines the length of time exceeding a predetermined magnitude and the continuity of the ground-fault detection signal, and then outputs the output of the ground-fault detection circuit 3. Drives the thyristor 4 and operates the output device 5. A contact output or the like is output by the operation of the output device 5.

Here, the rectifier circuit 7 rectifies the voltage of the AC circuit 1 to obtain an operating DC power source for the ground fault detection circuit 3. Further, the voltage drop resistor 6 changes the high voltage of the AC circuit 1 such as 100V, 200V, and 400V to the voltage required for operating the ground fault detection circuit 3, such as 12V and 24V.
It is a series resistance that reduces the partial pressure to V or the like. Further, the capacitor 14 smoothes the pulsating current obtained by the rectifier circuit 7 into a direct current required as a power source of the ground fault detection circuit 3.

In FIG. 6, when the remote test switch 9 is closed, an AC current is drawn from the AC circuit 1, and this is directly applied to the input terminal of the ground fault detection circuit 3 via the remote test switch 9 and the impedance element 11, This alternating current is detected by the ground fault detection circuit 3 as a test signal,
The test is done.

In FIG. 7, the impedance element 11
An alternating current consumption current for supplying power to the ground fault detection circuit 3 is flowing through. When the remote test switch 9 is closed,
Part of the alternating current flowing through the impedance element 11 is shunted to the test winding 12 to excite the zero-phase current transformer 2,
A test signal can be supplied to the ground fault detection circuit 3 to test the operation of the ground fault detection device.

[0007]

By the way, in the configuration of FIG. 6, when the remote test switch 9 is opened, the line voltage of the AC circuit 1 is directly applied to both ends of the remote test switch 9. The magnitude of the test signal generated by 13 varies depending on the voltage of the AC circuit 1. Therefore, the magnitude of the test signal generated by the test circuit 13 is
It is in direct proportion to the voltage of the AC circuit 1 and is as shown in FIG. That is, in FIG. 8, (a) shows that the voltage of the AC circuit 1 is 400
The magnitude of the test signal when V is shown. Similarly, (b)
Is the magnitude of the test signal when 200V and (c) is 100V. (D) is the detection level of the ground fault detection circuit 3,
When the time during which the ground fault detection signal exceeds this level is longer than the prescribed time T set in the ground fault detection circuit 3,
The ground fault detection signal is counted by the ground fault detection circuit 3. For example, when this count continues three times in the order of negative → positive → negative, the ground fault detection circuit 3 outputs an operation signal to the thyristor 4.
That is, in FIG. 8, T1> T, T2> T, T3> T
At this time, the ground fault detection circuit 3 outputs an operation signal. Note that (e)
Is the reference voltage (positive voltage) determined by the ground fault detection circuit 3.
Is.

In the circuit of FIG. 6, the sizes of T1, T2 and T3 are determined by the ground fault detection level (d) and the voltage of the AC circuit 1. Since the ground fault detection level can be set only in one way, for example, when the ground fault detection level is set in accordance with the voltage of the AC electric line 1 being 100V, the AC electric line 1
When the voltage is 200 V or 400 V, the test signal is too large, and the ground fault detection circuit 3 may be damaged.
On the contrary, when the ground fault detection level is set in accordance with the voltage of the AC electric circuit 1 being 400V, the voltage of the AC electric circuit 1 is 10V.
Since the test signal is too small at 0V and 200V, the ground fault detection circuit 3 may not be able to detect this. These concerns are alleviated to some extent by adjusting the impedance value of the impedance element 11, but the voltage of the AC circuit 1 is still 100V, 200V.
It is difficult to obtain a device that can handle both V and 400V.

Furthermore, there is a problem that the current passing through the stray capacitor capacitance of the lead wire 10 from the test terminal 8 to the remote test switch 9 causes the test circuit to malfunction. This is because, in recent years, the load connected to the AC circuit 1 has a large number of loads including an inverter, and the harmonics generated by the inverter cause the current flowing through the stray capacitor capacitance of the lead wire 10 to increase more than the commercial frequency current. This is because, although the test switch 9 is not closed, an output is produced from the test circuit 13 to cause a malfunction.

On the other hand, in FIG. 7, a small current flows in the test winding 12 due to the influence of the stray capacitance of the lead wire 10 from the test terminal 8 to the remote test switch 9,
Since a small electromotive force is generated in the secondary winding 2a of the zero-phase current transformer 2, there is a problem that the sensitivity current value of the ground fault detection circuit 3 changes.

The present invention has been made to solve the above problems, and malfunctions due to the effect of the stray capacitance of the lead wire 10 from the test terminal 8 to the remote test switch 9 or a change in the sensitivity current value. The purpose of the present invention is to prevent the above-mentioned problems, and further to obtain a ground fault detecting device capable of performing a stable test operation regardless of the voltage of the AC circuit 1.

[0012]

A ground fault detecting device according to the present invention is a zero-phase current transformer inserted in an AC electric circuit, and an output from a secondary winding of the zero-phase current transformer exceeds a predetermined value. The ground fault detection circuit of the AC electric circuit that operates at some time, the rectifier circuit that rectifies the voltage of the AC electric line and supplies power to the ground fault detection circuit, and the power is supplied from this rectifier circuit to generate a pseudo earth leakage signal. An oscillation circuit for outputting to the fault detection circuit, and a test switch which is inserted into a power supply circuit from the rectification circuit to the oscillation circuit and inspects the operation of the ground fault detection circuit.

Further, the oscillating circuit in the above configuration receives power from the rectifier circuit via the light emitting side of the photocoupler and the test switch, and the output side of the oscillating circuit detects the ground fault via the light receiving side of the photocoupler. It is configured to output to a circuit.

The oscillating circuit receives power supply from the rectifying circuit via the switching element and the test switch,
The output side of the oscillation circuit is configured to output to the ground fault detection circuit via the light receiving side of the photocoupler, and the switching element is configured to be controlled by the output of the ground fault detection circuit.

In any of the above configurations, the rectifier circuit is of constant voltage output type.

[0016]

In the ground fault detecting device of the present invention, a pseudo leak current is generated in the test circuit by the oscillation circuit using the rectifier circuit for the power supply of the ground fault detection circuit as a power source, and the test circuit is tested in series with the power circuit of the oscillation circuit. By providing a switch,
When the lead wire of the test switch is extended to form a remote test switch, the voltage applied between the lead wires is lowered,
Leakage current due to the stray capacitor capacity of the lead wire is suppressed,
Prevents malfunction of the oscillator circuit.

Further, by inserting the light emitting side into the power source input side of the oscillator circuit and providing the photo coupler in which the output side of the oscillator circuit is connected to the ground fault detection circuit via the light receiving side, it is possible to open the test switch. The ground current detection current is prevented from flowing into the oscillation circuit to prevent the sensitivity current value from changing.

Further, by inserting a switching element in series with the power source input side of the oscillation circuit and controlling the control terminal of this switching element with the output of the ground fault detection circuit, the oscillation circuit and The current flowing through the voltage drop resistor is suppressed to prevent burning of the oscillation circuit and the voltage drop resistor.

Further, by forming the rectifier circuit as a constant voltage circuit, the oscillation circuit can be stably operated and the oscillation circuit can be protected regardless of the value of the AC circuit voltage.

[0020]

【Example】

Example 1. Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1 to 10 and 14 are the same as those described in the conventional device. Reference numeral 19 denotes the AC circuit 1 together with the rectifier circuit 7, the voltage drop resistor 6, and the capacitor 14.
This is an impedance element for obtaining a constant DC voltage from the voltage of, and in this example, a DC voltage of 24 V is obtained at the output side of the voltage drop resistor 6 regardless of the voltage of the AC circuit 1. Reference numeral 15 is an oscillator circuit, which is supplied with power from the rectifier circuit 7 through the test terminal 8 and the remote test switch 9,
A rectangular wave voltage is output to the ground fault detection circuit 3. The oscillator circuit 15 is controlled in power supply by the remote test switch 9. When the remote test switch 9 is closed, power is supplied to operate the oscillator circuit 15 and the rectangular wave is sent to the ground fault detection circuit 3. The pseudo leakage output of is added. A rectangular wave voltage, which is a pseudo-leakage output generated in the oscillator circuit 15, is transmitted to the input stage of the ground fault detection circuit 3 as a test signal. Therefore, by properly setting the output voltage of the oscillation circuit 15 as shown in FIG. 2, it is possible to test the operation of the ground fault detection device. 2A shows the magnitude of the test signal, FIG. 2B shows the detection level of the ground fault detection circuit 3, and FIG. 2C shows the reference voltage of the ground fault detection circuit 3.

Next, the operation will be described. In FIG.
The operation from the detection of the ground fault current in the case of occurrence of the electric leakage or the ground fault to the operation of the output device 5 is the same as the conventional device. Also,
The operation of supplying power to the ground fault detection circuit 3 by the voltage drop resistor 6, the rectifier circuit 7, and the capacitor 14 is also the same as the conventional one, and at the same time, the test circuit 13 is also supplied with power.

The power supply of the oscillation circuit 15 includes a ground fault detection circuit 3
Since the same voltage as the voltage supplied to the oscillator, that is, a constant voltage is used, the voltage drop resistor 6 supplies a constant voltage to the power supply of the oscillation circuit 15 regardless of the voltage of the AC circuit 1. Is given. Therefore, the magnitude of the test signal is constant regardless of the voltage of the AC circuit 1, and if the oscillator circuit 15 in which the values of T1 and T2 in FIG. It enables stable operation test of the ground fault detection device.

In general, the lead wire 10 extending from the test terminal 8 to the remote test switch 9 has a floating capacitor capacity, but in the configuration of the present invention, a low voltage on the output side of the rectifier circuit 7 is applied to the lead wire 10. Therefore, when the remote test switch 9 is open, a minute current flows through the capacitance of the floating capacitor, but its magnitude does not cause the oscillation circuit 15 to operate. Therefore, a malfunction due to the capacitance of the stray capacitor of the lead wire 10 or a change in the sensitivity current value does not occur.

In the above example, the output voltage waveform of the oscillating circuit 15 is a rectangular wave, but since the power supply voltage of the oscillating circuit 15 is constant, the output voltage of
The same effect can be expected by using a voltage waveform such as a sine wave or a triangular wave. That is, in the case of a triangular wave, as shown in FIG.
If the amplitude, frequency, etc. are set so that T1> T, T2> T (where T is a specified time determined by the ground fault detection circuit 3), the same effect as described above is obtained. In FIG. 3, (a) shows the magnitude of the test signal, (b) shows the detection level of the ground fault detection circuit 3, and (c) shows the reference voltage of the ground fault detection circuit 3.

Example 2. When a ground fault occurs, an electromotive force is generated in the secondary winding 2a of the zero-phase current transformer 2, and a current flows between the secondary winding 2a and the ground fault detection circuit 3. This current is the oscillation circuit 15 Flowing out through, the sensitivity current value of the ground fault detection circuit 3 changes. The second embodiment is intended to obtain a ground fault detection device capable of preventing the change in the sensitivity current value.

FIG. 4 is a circuit configuration diagram showing a ground fault detection apparatus according to the second embodiment of the present invention. In the figure, 1 to 11 and 13 to 15 are the same as those in the first embodiment. 1
Reference numeral 6 is a photocoupler such as a phototransistor coupler. The light emitting side 16a is inserted between the test terminal 8 and the power supply side of the oscillation circuit 15, and the light receiving side 16b is the output of the oscillation circuit 15 and the input of the ground fault detection circuit 3. It is inserted between the steps. These test terminal 8, photo coupler 16, and oscillator circuit 1
5 constitutes the test circuit 13. Reference numeral 18 denotes a diode, which enables the output of the pseudo leakage signal from the oscillation circuit 15 to the ground fault detection circuit 3, and the secondary winding 2 a of the zero-phase current transformer 2.
To prevent the ground fault signal from flowing into the oscillation circuit 15.

Next, the operation will be described. When the remote test switch 9 is pressed to close the circuit, the oscillation circuit 15 outputs a pseudo leakage current. At this time, since the power supply current to the oscillation circuit 15 is supplied to the light emitting side 16a of the photocoupler 16, the light receiving side 16b of the photocoupler 16 is in the conductive state, and the pseudo leakage current is output to the ground fault detection circuit 3. An operation test of the ground fault detection device can be performed. When a ground fault occurs in the actual use of the ground fault detection device, the remote test switch 9 is in an open state, the light emitting side 16a of the photocoupler 16 is not energized, and the light receiving side 16b of the photocoupler 16 is non-conductive. There is continuity. Therefore, due to the actual ground fault, the output of the secondary winding 2a of the zero-phase current transformer 2 tries to flow to the ground fault detection circuit 3 and the oscillation circuit 15, but the photocoupler 1
Since the light receiving side 16b of 6 is non-conducting, the oscillation circuit 15
Is prevented from flowing into.

In this way, the light receiving side 1 of the photocoupler 16
By connecting 6b between the oscillation circuit 15 and the ground fault detection circuit 3, it is possible to prevent the current from flowing into the oscillation circuit 15, and thus it is possible to prevent the sensitivity current value of the ground fault detection circuit 3 from changing. When the remote test switch 9 is open,
The potential of the output stage of the oscillation circuit 15 is set lower than the potential of the input stage of the ground fault detection circuit 3, and the diode 18 blocks the flow of current into the ground fault detection circuit 3.

In the above example, the transmission control between the oscillation circuit 15 and the ground fault detection circuit 3 is performed by the photocoupler 16 and the diode 18, but this may be replaced by a transmission element such as a phototriac coupler. A similar operation can be performed (the diode 18 is often omitted in this case).

Example 3. In the second embodiment, when the remote test switch 9 is kept closed, the remote test switch 9 → the light emitting side 16a of the photocoupler 16 →
A closed circuit of the oscillator circuit 15 is formed, and current continues to flow.
Since this closed circuit has a small resistance, the oscillation circuit 15 or the voltage drop resistor 6 may be burned out due to the heat generation thereof. The third embodiment relates to a ground fault detection device which does not cause the oscillating circuit and the voltage drop resistor to burn even if the remote test switch is kept closed.

FIG. 5 is a circuit configuration diagram showing a ground fault detection device according to a third embodiment of the present invention. In the figure, 1 to 11 and 13 to 16 are the same as in the second embodiment. 17 is, for example, F
A switching element such as ET, the input terminal of which is connected to the DC low-voltage power supply voltage via the remote test switch 9, and the output terminal of which is connected to the voltage input section of the oscillation circuit 15 via the light emitting side 16a of the photocoupler 16. Has been done. The control terminal 17a of the switching element 17 is set to an intermediate potential between the output device 5 and the thyristor 4.

Next, the operation will be described. Immediately after the remote test switch 9 is closed, the thyristor 4 is in the inoperative state, and the control terminal 17a is at high potential. Therefore,
Switching element 1 by closing the remote test switch 9
Reference numeral 7 denotes the light emitting side 16a of the photocoupler 16 and the oscillation circuit 15
The ground fault detection circuit 3 is operated by the pseudo leakage current of the oscillation circuit 15 by making the thyristor 4 conductive and the output device 5 is operated, and the ground fault detection test is completed. After that, when the remote test switch 9 is still closed, the potential of the control terminal 17a changes to a low potential due to the conduction of the thyristor 4, so that the switching element 17 causes the current flowing from the light emitting side 16a of the photocoupler 16 to the oscillation circuit 15. Can be reduced to a value at which the oscillation circuit 15 and the voltage drop resistor 6 are not burned out.

In each of the above embodiments, the lead wire 1
Although the example in which the remote switch 9 is provided via 0 has been described, it is clear that the same effect can be obtained when the test switch is directly provided to the test terminal 8.

[0034]

As described above, according to the present invention, the malfunction due to the influence of the stray capacitance of the lead wire to the remote test switch and the change in the detection sensitivity current value are small,
A ground fault detection device with high detection accuracy can be obtained.

Further, it is possible to obtain the ground fault detection device in which the circuit element is not burned even if the test circuit is kept closed.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a ground fault detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of an output waveform of the oscillation circuit of the first embodiment.

FIG. 3 is a diagram showing another example of the output waveform of the oscillation circuit of the first embodiment.

FIG. 4 is a circuit configuration diagram showing a ground fault detection device according to a second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing a ground fault detection device according to a third embodiment of the present invention.

FIG. 6 is a circuit configuration diagram showing a conventional ground fault detection device.

FIG. 7 is a circuit configuration diagram showing a conventional ground fault detection device.

FIG. 8 is a diagram illustrating an operation of a test circuit of a conventional ground fault detection device.

[Explanation of symbols]

1 AC line, 2 zero-phase current transformer, 2a secondary winding, 3
Ground fault detection circuit, 4 thyristor, 5 output device, 6 voltage drop resistor, 7 rectifier circuit, 8 test terminal, 9 remote test switch, 10 lead wire, 11 impedance element, 13 test circuit, 14 capacitor, 15
Oscillation circuit, 16 Photo coupler, 16a Photo coupler light emitting section, 16b Photo coupler light receiving section, 17 Switching element, 17a Control terminal, 18 Diode.

Claims (4)

[Claims] 1. A zero-phase current transformer inserted in an AC electric circuit, a ground fault detection circuit for the AC electric circuit, which operates when an output from a secondary winding of the zero-phase current transformer exceeds a predetermined value. A rectifier circuit that rectifies the voltage of the AC circuit and supplies power to the ground fault detection circuit, an oscillator circuit that is supplied with power from the rectifier circuit and outputs a pseudo-leakage signal to the ground fault detection circuit, and the rectifier circuit described above. A ground fault detection device comprising a test switch which is inserted into a power supply circuit for an oscillation circuit and inspects the operation of the ground fault detection circuit. 2. The oscillation circuit receives power supply from the rectification circuit via the light emitting side of the photocoupler and the test switch,
The ground fault detection device according to claim 1, wherein the output side of the oscillation circuit is configured to output to the ground fault detection circuit via the light receiving side of the photocoupler. 3. The oscillation circuit receives power supply from the rectifier circuit via the switching element and the test switch, and the output side of the oscillation circuit outputs to the ground fault detection circuit via the light receiving side of the photocoupler. The ground fault detection device according to claim 1 or 2, wherein the switching element is configured to be controlled by an output of the ground fault detection circuit. 4. The ground fault detection device according to claim 1, wherein the rectifier circuit is of a constant voltage output type.