JPH05153725A - Ground fault detector - Google Patents

Abstract

PURPOSE:To prevent erroneous operation due to noise in ground fault detection by charging the storage section in a signal width decision unit with the output signal from a level decision unit and discharging the storage section based on an output signal from a zero-cross detecting circuit. CONSTITUTION:Level decision units 7, 8 compare positive and negative levels of ground fault current, respectively, with thresholds. Signal width decision units 9A, 10A charge capacitors 11, 12, respectively, with output signals from the level decision units 7, 8 and discharge the capacitors 11, 12 based on a reset signal fed from a zero-cross detecting circuit 18. Pulse signals are generated when the terminal voltages of the capacitors 11, 12 exceed thresholds respectively. When the count of the pulse signal exceeds a predetermined value, a switching element 16 and an electromagnetic unit 17 are energized to open a circuit breaker 4 thus interrupting an AC path 1. According to the constitution, ground fault can be detected positively even upon occurrence of noise on the AC path 1.

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 for detecting a ground fault in an AC electric circuit and shutting off the AC electric circuit, and more particularly to a ground fault capable of preventing malfunction due to noise generated in the AC electric circuit. The present invention relates to a detection device.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a conventional ground fault detecting device. In the figure, 1 is an AC electric line, 2 is a load connected to the AC electric line, 3 is a ground fault detection device provided in the AC electric line 1, 4 is a circuit breaker provided in the AC electric line 1, and 5 is an AC electric line 1. A ground fault detector that is provided and detects a ground fault current generated in the AC circuit 1, for example, a zero-phase current transformer (hereinafter, referred to as ZCT), 6 is a waveform shaping circuit that shapes the output signal of the ZCT 5, and 7 is a waveform. A level discriminator connected to the positive output terminal of the shaping circuit 6, the level discriminator 7 having a predetermined threshold value TH ₁ set for the level of the input signal,
When the positive level of the input signal exceeds this threshold value, a rectangular wave output signal having a time width equal to the period of exceeding the threshold value is output. Reference numeral 8 is a level discriminator connected to the negative output terminal of the waveform shaping circuit 6. The level discriminator 8 has a predetermined threshold TH ₂ set for the level of the input signal, When the level of exceeds the threshold, a rectangular wave output signal having a time width equal to the period of exceeding the threshold is output. 9 and 10 are level discriminators 7 and 8 respectively.
A signal width discriminator for discriminating the time width of the output signal of
The capacitors 11 and 12 are connected to each other, and the output signals of the level discriminators 7 and 8, that is, the capacitors 11 and 12 are connected.
When the terminal voltages of the two exceed predetermined threshold values TH ₃ and TH ₄ , respectively, a pulse signal having a time width equal to the period of exceeding the threshold values is generated. Reference numerals 13 and 14 respectively count pulse signals from the signal width discriminators 9 and 10, and generate an output signal when the count value exceeds a predetermined value. 15 is a logical product of the output signals of the count circuits 13 and 14. Is an AND circuit, 16 is a switching element whose ON / OFF operation is controlled by the output signal of the AND circuit 15, and 17 is an electromagnetic device which is energized by the ON of the switching element 16 to drive the circuit breaker 4.

Next, the operation of the conventional ground fault detecting device shown in FIG. 6 will be described with reference to FIG. Now, when a ground fault current having a waveform as shown in FIG. 7A flows in the AC line 1 due to a ground fault, this ground fault current is supplied to the waveform shaping circuit 6 to be waveform shaped, and the output side thereof is shown in FIG. A detection signal having a waveform as shown in (b) is obtained. This detection signal is supplied to the level discriminator 7, and when the level exceeds the threshold value TH ₁ , the output side corresponds to the period in which the level exceeds the threshold value TH ₁ as shown in FIG. 7C. A rectangular wave output signal having a time width (time t1) is obtained. The detection signal from the waveform shaping circuit 6 is supplied to the level discriminator 8, when the level exceeds the threshold value TH _2, to the output side, FIG. 7 (d), the the level of the threshold value TH ₂
A rectangular wave output signal having a time width (t2) corresponding to the period exceeding the above is obtained. The rectangular wave output signal from the level discriminator 7 is supplied to the signal width discriminator 9,
Charges the capacitor 11 for the time t1, and when the terminal voltage thereof exceeds the threshold value TH ₃ as shown in FIG. 7 (e),
A pulse signal as shown in FIG. 7 (g) is generated on the output side. Similarly, the rectangular wave output signal from the level discriminator 8 is supplied to the signal width discriminator 10, the signal width discriminator 10 charges the capacitor 12 for the time t2, and the terminal voltage becomes as shown in FIG. As shown, when the threshold value TH ₄ is exceeded, a pulse signal as shown in FIG. 7 (h) is generated at the output side.
These pulse signals are used for counting circuits 13 and 14 respectively.
When the count value exceeds a predetermined value, a high-level output signal is obtained at the output side thereof.
The gate of the D circuit 15 opens and its output signal is applied as a drive signal to the control electrode of the switching element 16 to turn on the switching element 16.
When the switch is turned on, the electromagnetic device 17 is energized to open the circuit breaker 4 and disconnect the AC circuit 1.

[0004]

Since the conventional ground fault detecting device is constructed as described above, it has the following problems. That is, the signal width discriminators 9 and 10 turn on the capacitors 11 and 12 when the output signals of the level discriminators 7 and 8 are at a high level, that is, when the detection signal from the waveform shaping circuit 6 exceeds the thresholds TH ₁ and TH _2. When charged and at a low level, that is, the detection signal from the waveform shaping circuit 6 is the threshold value T
When H ₁ and TH ₂ are not exceeded, the capacitors 11 and 12 are discharged. Therefore, noise is generated in the AC circuit 1 for some reason, and this noise causes the output waveform of the waveform shaping circuit 6 to change. 8 (a), the output signals of the level discriminators 7 and 8 are as shown in FIGS. 8 (b) and 8 (c), respectively, and when the output signals of the level discriminators 7 and 8 are low level. Since the capacitors 11 and 12 are discharged, the terminal voltages of the capacitors 11 and 12 become as shown in FIGS. 8D and 8E, respectively, and the levels thereof may not reach the thresholds TH ₃ and TH _4. As a result, no malfunction occurs because no pulse signal is generated from the signal width discriminators 13 and 14 and the circuit breaker 4 is opened to shut off the AC circuit 1 despite the occurrence of a ground fault in the AC circuit 1. There is a problem that It was.

The present invention has been made in order to solve such a problem, and an object thereof is to obtain a ground fault detecting device capable of preventing malfunction due to noise generated in an AC electric circuit.

[0006]

A ground fault detector according to the present invention includes a ground fault detector for detecting a ground fault current generated in an AC circuit, and a positive level or a negative level of an output signal of the ground fault detector. At least one of the levels is compared with a first threshold value, a level determination means for generating an output signal when the level exceeds the first threshold value, a zero-cross detection circuit for detecting the zero-cross of the ground fault current, and a storage section. And charging the accumulator by the output signal of the level determination means, discharging the charge of the accumulator by the output signal of the zero-cross detection circuit,
A signal width determining means for generating an output signal when the potential of the accumulating portion exceeds a second threshold value, and a disconnecting means for energizing the output signal of the signal width determining means to interrupt the AC circuit. Is.

[0007]

In the present invention, the storage section of the signal width determination means is charged by the output signal of the level determination means, and the charge of the storage section of the signal width determination means is discharged by the output signal of the zero cross detection circuit. As a result, even when noise is superimposed on the ground fault current generated in the AC circuit, it is possible to generate a signal that interrupts the AC circuit by maintaining the potential of the storage unit to exceed the second threshold value whenever a ground fault occurs. A malfunction that prevents the ground fault from being detected due to noise is prevented.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention,
Portions corresponding to those in FIG. 4 are designated by the same reference numerals, and duplicate description thereof will be omitted. 3A is a ground fault detection device, 9A and 10A are signal width discriminators for discriminating the time widths of the outputs of the level discriminators 7 and 8, respectively, and capacitors 11 and 12 as accumulators are connected, respectively. When the output signals of the discriminators 7 and 8 are high level, the capacitors 11 and 1
2 is charged, the charging is stopped at a low level and the potential at that time is held, and when the terminal voltages of the capacitors 11 and 12 exceed predetermined thresholds TH ₃ and TH ₄ , respectively, the threshold is exceeded. A pulse signal having a time width equal to the current period is generated. Reference numeral 18 is a zero-cross detection circuit that detects the zero-cross of the output signal of the ZCT 5 and resets the signal width discriminators 9A and 10A.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described with reference to FIGS.
First, the normal operation will be described with reference to FIG. Now, when a ground fault current having a waveform as shown in FIG. 2A flows in the AC line 1 due to a ground fault, this ground fault current is supplied to the waveform shaping circuit 6 to be waveform shaped, and the output side thereof has the waveform shown in FIG. A detection signal having a waveform as shown in (b) is obtained. This detection signal is supplied to the level discriminator 7, and when the level exceeds the threshold TH ₁ , the output side thereof corresponds to the period in which the level exceeds the threshold TH ₁ as shown in FIG. A rectangular wave output signal having a time width (time t1) is obtained. The detection signal from the waveform shaping circuit 6 is supplied to the level discriminator 8, when the level exceeds the threshold value TH _2, to the output side, FIG. 2 (d), the the level of the threshold value TH ₂
A rectangular wave output signal having a time width (t2) corresponding to the period exceeding the above is obtained. The rectangular wave output signal from the level discriminator 7 is supplied to the signal width discriminator 9A, and the signal width discriminator 9A charges the capacitor 11 during the time t1 when the rectangular wave output signal of the level discriminator 7 is at a high level, When the rectangular wave output of the level discriminator 7 becomes low level, charging is stopped and the potential at that time is held, and this held state is released by the reset signal from the zero cross detection circuit 18 as shown in FIG. , The capacitor 11 is forcibly discharged. Then, when the terminal voltage of the capacitor 11 exceeds the threshold value TH ₃ as shown in FIG. 2 (e), the signal width discriminator 9A generates a pulse signal as shown in FIG. 2 (g) at the output side thereof. .. Similarly, the rectangular wave output signal from the level discriminator 8 is supplied to the signal width discriminator 10A, and the signal width discriminator 1
0A charges the capacitor 12 during the time t2 when the rectangular wave output signal of the level discriminator 8 is high level, and when the rectangular wave output signal of the level discriminator 8 becomes low level, the charging is stopped and the potential at that time is changed. The held state is released, and the held state is released by the reset signal from the zero-cross detection circuit 18 as shown in FIG. 2 (i), and the capacitor 12 is forcibly discharged. The signal width discriminator 10A is the capacitor 1
2 has a threshold voltage TH ₄ as shown in FIG.
When it exceeds, a pulse signal as shown in FIG. 2 (h) is generated on the output side. Then, the signal width discriminators 9A and 10A
The pulse signals from are supplied to the count circuits 13 and 14, respectively, and when the count value exceeds a predetermined value, a high-level output signal is obtained at the output side thereof.
The gate of the circuit 15 is opened and its output signal is applied as a drive signal to the control electrode of the switching element 16 to turn on the switching element 16. By turning on the switching element 16, the electromagnetic device 17 is energized and the circuit breaker 4 is turned on. Open,
The AC circuit 1 is cut off.

Next, the operation when noise occurs in the AC electric circuit 1 will be described with reference to FIG. Now, when noise is generated in the AC circuit 1 for some reason, and the output waveform of the waveform shaping circuit 6 becomes as shown in FIG. 3A due to this noise, the output signals of the level discriminators 7 and 8 are respectively shown in FIG. As shown in b) and (c). Then, when such an output is supplied, the signal width discriminators 9A and 10A cause the output signals of the level discriminators 7 and 8 to be at the high level for times t3 and t.
5, the capacitors 11 and 12 are charged respectively, and the charging is stopped until the reset signal is applied after the time t4 and the time t5 when the level of the output signals of the level discriminators 7 and 8 is low level and immediately before that. Of the capacitors 11 and 12 when the zero cross detection circuit 18 applies a reset signal as shown in FIG.
Discharges the electric charge stored in. As a result, the terminal voltages of the capacitors 11 and 12 have waveforms having levels exceeding the thresholds TH ₃ and TH ₄ as shown in FIGS. 3D and 3E, respectively. After that, the capacitor 11,
When the terminal voltages of 12 exceed the threshold values TH ₃ and TH ₃ , respectively, the signal width discriminators 9A and 10A generate pulse signals on their output sides. These pulse signals are supplied to the count circuits 13 and 14, respectively, and when the count value exceeds a predetermined value, a high level output is obtained at the output side thereof, whereby the gate of the AND circuit 15 is opened and its output signal is changed. As a drive signal, it is applied to the control electrode of the switching element 16 to turn on the switching element 16, and when the switching element 16 is turned on, the electromagnetic device 17 is energized to open the circuit breaker 4 to cut off the AC circuit 1.

FIG. 4 is a block diagram showing an example of a concrete circuit configuration of the signal width discriminator 9A as a representative. Of course, the signal width discriminator 10A can also have the same circuit configuration. In the figure, 20 is a constant current source, one side of which is connected to the power supply Vcc, and the other side is connected to the capacitor 11 via the switch 21. The switch 22 is connected between the connection point A of the switch 21 and the capacitor 11 and the ground (GRD). The switch 21 is turned on by the output signal of the level discriminator 7 (FIG. 1) through the buffer 23,
The switch 22 is controlled to be off, and the switch 22 is the zero-cross detection circuit 1
ON / OFF is controlled by a reset signal from 8 (FIG. 1). The switch 21 is turned on when the output signal of the level discriminator 7 is high level and turned off when it is low level, and the switch 22 is turned on when the reset signal is high level and turned off when the reset signal is low level. Reference numeral 24 denotes a comparator, the non-inverting input terminal of which is connected to the connection point A, and the inverting input terminal of which is connected to the DC power source having the threshold value TH ₃ .

Next, the operation of the signal width discriminator 9A will be described with reference to FIG. From the level discriminator 7, FIG.
When the rectangular wave output signal as shown in (a) is supplied through the buffer 23, the switch 21 is turned on during the high level of the rectangular wave output signal, the capacitor 11 is charged by the power source Vcc, and its terminal voltage, that is, the connection point. Fig. 5 shows the potential of A
As shown in (b), the voltage gradually rises, and when the rectangular wave output signal becomes low level, the switch 21 is turned off. During this time, the switch 22 is also turned off. Therefore, the potential at the connection point A is at the time when the switch 21 is turned off. The potential is maintained. Then, when the zero-cross detection circuit 18 detects the zero-cross of the ground fault current and generates the reset signal as shown in FIG. 5C, the switch 22 is turned on, which causes the capacitor 11
The electric charge accumulated at the point A is discharged, the potential at the connection point A becomes zero volt, and as a result, a signal having a waveform as shown in FIG. 5B is obtained at the connection point A. This signal is supplied to the comparator 24 and compared with the threshold value TH _3, and when the level of the input signal exceeds the threshold value TH ₃ , the comparator 24 outputs a pulse signal as shown in FIG. Occur.

As described above, in this embodiment, even if the noise generated in the AC circuit at the time of the ground fault detection is superposed on the ground fault current, the ground fault current detection function can be achieved without being affected by the noise and malfunction due to the noise. Is prevented.

In the above embodiment, the ground fault is detected by discriminating both the positive and negative levels of the ground fault detection signal, but the positive or negative level of the ground fault detection signal is discriminated. It can be similarly applied to the case where the detection is performed, and the same effect can be obtained.

[0015]

As described above, according to the present invention, a ground fault detector for detecting a ground fault current generated in an AC circuit and at least one of a positive level and a negative level of an output signal of the ground fault detector. And a first threshold value, and has a level determination means for generating an output signal when the level exceeds the first threshold value, a zero-crossing detection circuit for detecting the zero-crossing of the ground fault current, and a storage section, The storage section is charged by the output signal of the level discriminating means, the charge of the storage section is discharged by the output signal of the zero-cross detection circuit, and an output signal is generated when the potential of the storage section exceeds a second threshold value. Since the signal width discriminating means and the breaking means which is energized by the output signal of the signal width discriminating means and shuts off the AC electric circuit, the noise generated in the AC electric circuit at the time of the ground fault detection causes a ground fault current. Even if it is superposed To be able to achieve a ground fault detection function without an effect that malfunction due to noise can be prevented.

[Brief description of drawings]

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

FIG. 2 is a signal waveform diagram for explaining the operation of FIG.

FIG. 3 is a signal waveform diagram for explaining the operation of FIG.

FIG. 4 is a configuration diagram showing a main part of the present invention.

5 is a signal waveform diagram for explaining the operation of FIG.

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

7 is a signal waveform diagram for explaining the operation of FIG.

FIG. 8 is a signal waveform diagram for explaining the operation of FIG.

[Explanation of symbols]

 1 AC line 3A Ground fault detector 4 Circuit breaker 5 Zero-phase current transformer (ZCT) 6 Waveform shaping circuit 7, 8 Level discriminator 9A, 10A Signal width discriminator 13, 14 Count circuit 15 AND circuit 16 Switching element 17 Electromagnetic Device 18 Zero cross detection circuit

Claims (1)

[Claims] 1. A ground fault detector for detecting a ground fault current generated in an AC circuit, and a first threshold value is compared with at least one of a positive level and a negative level of an output signal of the ground fault detector, It has a level discriminating means for generating an output signal when the level exceeds the first threshold value, a zero-crossing detecting circuit for detecting a zero-crossing of the ground fault current, and an accumulating portion, and the accumulating portion according to the output signal of the level discriminating means. And a signal width discriminating means for discharging the electric charge of the accumulating section by the output signal of the zero-cross detection circuit and generating an output signal when the potential of the accumulating section exceeds a second threshold, and the signal width discriminating section. A ground fault detection device, comprising: a breaking unit that is energized by an output signal of the unit to cut off the AC electric circuit.