JP2695722B2 - Ground fault detector - Google Patents

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 which detects a ground fault in an AC circuit and shuts off the AC circuit. The present invention relates to a possible ground fault detecting device.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional ground fault detecting device. In the figure, 1 is an AC circuit, 2 is a load connected to the AC circuit, 3 is a ground fault detecting device provided in the AC circuit 1, 4 is a circuit breaker provided in the AC circuit 1, and 5 is an AC circuit 1. A ground fault detector, for example, a zero-phase current transformer (hereinafter referred to as ZCT), for detecting a ground fault generated in the AC circuit 1;
6 is a waveform shaping circuit for shaping the waveform of the output signal of ZCT5;
7 is a level discriminator connected to the positive output terminal of the waveform shaping circuit 6, the level discriminator 7 is set the first threshold value TH ₁ relative to the level of the input signal, the input signal When the positive level exceeds this threshold, a rectangular wave output signal having a time width equal to the period during which the positive level is exceeded is output. 8 is a negative-coupled level discriminator to the output terminal of the waveform shaping circuit 6, the level discriminator 8 is set for the level of the input signal the second threshold value TH ₂ is the input signal When the negative level exceeds this threshold, a rectangular wave output signal having a time width equal to the period during which the negative level is exceeded is output. Reference numerals 9 and 10 denote signal width discriminators for discriminating the time widths of the output signals of the level discriminators 7 and 8, respectively, to which capacitors 11 and 12 are connected, respectively, and the output signals of the level discriminators 7 and 8; When the terminal voltages of the capacitors 11 and 12 exceed the third threshold value TH ₃ and the fourth threshold value TH ₄ , respectively, a pulse signal having a time width equal to the period during which the threshold value is exceeded is generated. Count circuits 13 and 14 count the pulse signals from the signal width discriminators 9 and 10, respectively, and generate an output signal when the count value exceeds a predetermined value. Reference numeral 15 denotes a logical product of outputs of the count circuits 13 and 14. An AND circuit 16 which is a switching element whose on / off operation is controlled by an output signal of the AND circuit 15;
Reference numeral 17 denotes an electromagnetic device which is energized when the switching element 16 is turned on and drives the circuit breaker 4.

Next, the operation of the conventional ground fault detecting device shown in FIG. 3 will be described with reference to FIG. Now, when a ground fault current having a waveform as shown in FIG. 4A flows through the AC circuit 1 due to a ground fault, the ground fault current is supplied to the waveform shaping circuit 6 and the waveform is shaped. A detection signal having a waveform as shown in FIG. The detection signal is supplied to the level discriminator 7, if the positive level exceeds the threshold value TH _1, at its output, as shown in FIG. 4 (c), the positive level exceeds the threshold value TH ₁ A rectangular wave output signal having a time width (time t1) corresponding to a certain period is obtained.
The detection signal from the waveform shaping circuit 6 is supplied to the level discriminator 8, when the negative level exceeds the threshold value TH _2, to the output side thereof, as shown in FIG. 4 (d), the negative level time width (t but corresponding to a period exceeding the threshold value TH ₂
A square wave output signal having the above condition 2) is obtained. The rectangular wave output signal from the level discriminator 7 is supplied to the signal width discriminator 9,
The signal width discriminator 9 charges the capacitor 11 during the time t1, and when the terminal voltage of the capacitor 11 becomes equal to the threshold T as shown in FIG.
Beyond H _3, it generates a pulse signal as shown in FIG. 4 (g) at its output. Similarly, the rectangular wave output signal from the level discriminator 8 is supplied to the signal width discriminator 10, and the signal width discriminator 10 charges the capacitor 12 during the time t2, and the terminal voltage becomes as shown in FIG. as shown, exceeds the threshold value TH _4, it generates a pulse signal as shown in FIG. 4 (h) at its output. These pulse signals are supplied to count circuits 13 and 14, respectively. When the count value exceeds a predetermined value, a high-level output signal is obtained at the output side, whereby the gate of the AND circuit 15 is opened and the output signal is output. Is applied to the control electrode of the switching element 16 as a drive signal, and the switching element 16 is turned on. When the switching element 16 is turned on, the electromagnetic device 17 is energized, the circuit breaker 4 is opened, and the AC circuit 1 is cut off.

[0004]

Since the conventional ground fault detecting device is constructed as described above, for example, the capacitors 11, 1 connected to the signal width discriminators 9, 10 respectively.
When the capacitance value of the capacitor 2 varies and becomes larger than the standard value, the rise of the charging characteristic becomes slower, and in some cases, the terminal voltage does not reach the threshold values TH ₃ and TH _4. Since this is no longer generated, a malfunction occurs that it cannot be detected despite the occurrence of a ground fault in the AC circuit, and a pair of signal width discriminators and capacitors are used for the positive and negative levels of the ground fault detection signal. Therefore, there is a problem that the configuration is complicated and expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is possible to reduce a malfunction caused by a variation in the capacitance value of a capacitor connected to a signal width discriminator and to realize a simple and inexpensive ground fault. It is intended to obtain a detection device.

[0006]

A ground fault detecting apparatus according to the present invention includes a ground fault detecting means for detecting a ground fault current generated in an AC circuit, a positive level of an output signal of the ground fault detecting means and a first level.
And a first level discriminator that generates an output signal when the level exceeds the first threshold value, and compares a negative level of the output signal of the ground fault detection means with a second threshold value. ,
A second level discriminator for generating an output signal when the level exceeds the second threshold, a synthesizing means for synthesizing output signals of the first and second level discriminators, and the synthesized output signal A signal width discriminator for generating an output signal when the level exceeds the third threshold, a sign discriminator for discriminating the sign of the ground fault current, and a sign discriminator. When the output signal of the detector is high level, the above signal width is determined.
Select the high-level output signal of the
When the output signal is low level,
Of the signal width discriminator based on the output signal of
A selection means for selecting an output signal of a level , and a cutoff means which is energized by the output signal of the selection means and cuts off the AC electric circuit.

[0007]

In the present invention, the first and second synthesizing means are used.
, And the signal width discriminator compares the level of the combined output signal with a third threshold value.
When this level exceeds a third threshold, an output signal is generated,
This output signal is selected by the selection means in accordance with the polarity of the output signal from the positive / negative discriminator, and the cutoff means is activated by the output signal of the selection means to cut off the AC electric circuit. As a result, the number of signal width discriminators conventionally used two and the number of capacitors connected thereto can be reduced to one.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention.
Parts corresponding to those in FIG. 3 are denoted by the same reference numerals, and redundant description thereof will be omitted. 3A is a ground fault detecting device, 18 is a positive / negative discriminator for discriminating the positive / negative of the output signal of ZCT5, and 19 is O as a synthesizing means for taking a logical sum of the output signals of the level discriminators 7 and 8.
R circuits 20, 21 are AND circuits as selection means for obtaining a logical product of the output signal of the signal width discriminator 9 and the output signal of the positive / negative discriminator 18, and the output signals of the ANDs 20, 21 are respectively counted by the count circuit 13 , 14.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be described with reference to FIG. Now, when a ground fault current having a waveform as shown in FIG. 2A flows through the AC circuit 1 due to a ground fault, the ground fault current is supplied to the waveform shaping circuit 6 to be waveform-shaped and output to the output side as shown in FIG. A detection signal having a waveform as shown in FIG. The detection signal is supplied to the level discriminator 7, if the positive level exceeds the threshold value TH _1, at its output, as shown in FIG. 2 (c), the positive level exceeds the threshold value TH ₁ A rectangular wave output signal having a time width (t1) corresponding to a certain period is obtained. or,
Detection signals from the waveform shaping circuit 6 is supplied to the level discriminator 8, when the negative level exceeds the threshold value TH _2, to the output side thereof, as shown in FIG. 2 (d), the negative level threshold square wave output signal having a time width (t2) corresponding to a period exceeding the TH ₂ is obtained. The OR output of the square wave output signals from the level discriminators 7 and 8 is obtained by an OR circuit 19, and an output signal as shown in FIG. You. Signal width discriminator 9 the output signal of the OR circuit 19 to charge between capacitor 11 of the time at a high level, the terminal voltage, as shown in FIG. 2 (f), exceeds the threshold value TH _3, the output Figure 2 on the side
A pulse signal as shown in (g) is generated. The pulse signals from the signal width discriminator 9 are AND20,
21. AND20 and 21 have ZCT5.
2 (h) of the positive / negative discriminator 18 for discriminating the output signal of FIG. When the output signal of the positive / negative discriminator 18 is high when the output signal of the ZCT 5 is positive (high level), and the output signal of the positive / negative discriminator 18 is low when the output signal of the ZCT 5 is negative (low level), A high-level output signal from the positive / negative discriminator 18 is combined with a pulse signal (high-level) from the signal width discriminator 9 by AN
The gate of the AND circuit 20 is opened at the time when the signal is supplied to the D20, and a pulse signal as shown in FIG. 2 (i) is obtained on the output side. Is inverted and input, the gate is not opened and no pulse signal is generated at the output side. Also, when the low level output signal from the positive / negative discriminator 18 is supplied to the AND 21 together with the pulse signal (high level) from the signal width discriminator 9, the AND circuit 2
2 is opened, and a pulse signal as shown in FIG. 2 (j) is obtained at the output side.
Since the low-level output signal of the positive / negative discriminator 18 is input to the gate, the gate is not opened and no pulse signal is generated at the output side. The pulse signals thus obtained from the AND circuits 20 and 21 are respectively counted by the count circuit 1
When the count value exceeds a predetermined value, a high-level output signal is obtained at the output side, whereby the gate of the AND circuit 15 is opened and the output signal is used as a drive signal of the switching element 16. The switching element 16 is turned on by being applied to the control electrode. When the switching element 16 is turned on, the electromagnetic device 17 is energized, the circuit breaker 4 is opened, and the AC circuit 1 is cut off.

As described above, according to the present embodiment, the number of capacitors causing a malfunction can be reduced to one, so that the occurrence rate of the malfunction can be reduced to half of that of the prior art. Can be reduced to one, so that the configuration is simpler and less expensive than in the past.

[0011]

As described above, according to the present invention, the ground fault detecting means for detecting the ground fault current generated in the AC circuit, and the positive level of the output signal of the ground fault detecting means are compared with the first threshold value. When the level exceeds the first threshold, a first level discriminator that generates an output signal is compared with a negative level of an output signal of the ground fault detecting unit and a second threshold, and the level is compared. A second level discriminator for generating an output signal when the second threshold value is exceeded, synthesizing means for synthesizing output signals of the first and second level discriminators, and a level of the synthesized output signal; A signal width discriminator for comparing a third threshold value and generating an output signal when the level exceeds the third threshold value, a sign discriminator discriminating whether the ground fault current is positive or negative, and an output of the sign discriminator. When the signal is high level, the signal level
Select the output signal of the
High level output when the low level is inverted
High level output of the signal width discriminator based on the force signal
Since there is provided a selection means for selecting a signal and a cutoff means which is energized by the output signal of the selection means and cuts off the AC circuit, the number of capacitors which may cause a malfunction can be reduced to one. Compared to the past, the occurrence rate of malfunction can be reduced by half, and the number of signal width discriminators together with the capacitor is one.
Since it can be made into individual pieces, there is an effect that the configuration is simple and inexpensive as compared with the related art.

[Brief description of the drawings]

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

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

FIG. 3 is a configuration diagram illustrating a conventional ground fault detection device.

FIG. 4 is a signal waveform diagram for describing the operation of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC electric circuit 3A Ground fault detection device 4 Circuit breaker 5 Zero phase current transformer 6 Waveform shaping circuit 7, 8 Level discriminator 9 Signal width discriminator 11 Capacitor 13, 14 Count circuit 15, 20, 21 AND circuit 16 Switching element 17 Electromagnetic device 18 Zero cross detection circuit 19 OR circuit

Claims (1)

(57) [Claims] 1. A ground fault detecting means for detecting a ground fault current generated in an AC circuit, and comparing a positive level of an output signal of the ground fault detecting means with a first threshold value, wherein the level is equal to the first threshold value. A first level discriminator that generates an output signal when the output signal exceeds the threshold value, and compares a negative level of the output signal of the ground fault detection means with a second threshold value. When the level exceeds the second threshold value, the output signal A second level discriminator that generates a signal; a combining unit that combines output signals of the first and second level discriminators; and comparing the level of the combined output signal with a third threshold value,
A signal width discriminator for generating an output signal when the level exceeds the third threshold value; a sign discriminator for discriminating the sign of the ground fault current; and a signal when the output signal of the sign discriminator is at a high level. width
Select the high level output signal of the discriminator
Inverts the low level when the output signal of the
Based on the high-level output signal
A ground fault detecting device comprising: a selection unit that selects a high-level output signal ; and a cutoff unit that is energized by the output signal of the selection unit and cuts off the AC circuit.