JPH04212A - Ground fault detector - Google Patents

Abstract

PURPOSE:To prevent unnecessary function upon occurrence of ground fault due to an excessive surge such as a lightning surge by a method wherein a synthesizing means synthesizes an output from a ground fault detector and an output lagged behind by a predetermined time and then the level is judged based on thus synthesized output. CONSTITUTION:Ground fault current flowing through an AC path 1 is detected through a ZCT 6 and amplified through an amplifier 20 and then fed to a level judging unit 21 and a delay circuit 25. The level judging unit 21 produces a pulse signal having time width corresponding to the interval of negative level. The delay circuit 25 produces an output lagged by half period behind the output from the amplifier 20. An adder 27 adds the outputs from the amplifier 20 and the delay circuit 25. A retriggerable one-shot circuit 28 generates a pulse signal having time width corresponding to the interval of positive level. An AND gate 31 performs logical operation on both pulse signals and provides the output to the gate electrode of a switching element 8 thus operating a circuit breaker 5 to interrupt the AC path 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ground fault detection device that detects a ground fault when a ground fault occurs in an AC power line and interrupts the AC power line, and in particular, This invention relates to a ground fault detection device that is unlikely to operate unnecessarily during an intrusion.

[Prior Art] FIG. 7 is a block diagram of a conventional ground fault detection device disclosed in, for example, Japanese Unexamined Patent Publication No. 61-181921, FIG. 8 is a circuit diagram showing a specific configuration of the device shown in FIG. 7, and FIG. FIG. 9 is a waveform diagram illustrating the general operation of the conventional device, and FIGS. 10 and 11 are waveform diagrams illustrating the operation of the conventional device when a surge enters.

In Figure 7, (1) is an AC line, and (2) is an AC line (
(1) is the ground fault detection device installed in the AC line (1).
), (4) is a surge absorber connected to AC line (1) between ground fault detection device (2) and load (3), and (5) is a surge absorber installed on AC line (1). circuit breaker,
(6) is a ground fault detector whose secondary winding is the AC line (1), such as a zero-phase current transformer (hereinafter referred to as ZCT), and (7) is connected so as to trip the circuit breaker (5). The electromagnetic device (8) is a switching element connected in series to the electromagnetic device (7). The circuit breaker (5), the electromagnetic device (7), and the switching element (8) constitute a breaking means. (9) is a level discriminator that receives the output from ZCT (6) as an input, (10) is a first signal width discriminator that discriminates the time width of the output of the level discriminator (9), and (11) is a first signal width discriminator that discriminates the time width of the output of the level discriminator (9). A monostable multivibrator (12) receives the output of the signal width discriminator (10) of No. 1 and generates an output of a predetermined time width (1c.).
(11) is an AND circuit that receives the output of the AND circuit (12) as an input and outputs an output when the logical product is established; (13) is a second signal width discriminator that receives the output of the AND circuit (12) and determines its time width; , its output side is connected to the gate electrode of the switching element (8).

FIG. 8 is a circuit diagram showing a specific circuit example of the ground fault detection device (2). In the same figure, (9'-1) is a level discriminator (
9), outputs a noise level output [H] only when the input signal exceeds a set level, that is, a threshold value. (9-2) is a level judgment! (9) The rL] output terminal outputs a low level output [L] only when the input signal exceeds the dark value, and otherwise outputs an output [H]. (10-1) and (10-2) are respectively [H]
Output terminal (9-1), [L] Output terminal (9-2) [H
] A constant current source that is driven by the output and generates a constant current in the direction shown, (10-3) is a constant current source (10-1), (10
-2), and constitutes the first signal width discriminator (10) together with the constant current sources (10-1) and (10-2). The monostable multivibrator (11) has a constant current source (10-1) and (10
-2). The input side of the AlID circuit (12) is connected to the output side of the monostable multivibrator (11) and also to the [H] output terminal (9-1). (13-1) A JIO circuit that inverts the output of the AND circuit (12), (13-2) is an AND circuit (1
2), and (13-3) is connected to the N07 circuit (1
(13-4) is charged and discharged by the constant current sources (13-2) and (13-3). (13-5) is a level discriminator that discriminates the level of the charging voltage of the capacitor (13-4), and N07
Circuit (13-1), constant current source (13-2), (13-
3) and the capacitor (13-4) constitute a second signal width discriminator (13).

The operation of the ground fault detection device configured as described above will be explained with reference to waveform charts shown in FIGS. 9 to 11. When a ground fault current occurs in the AC line (1), this ground fault current is detected by the ZCT (6), and an output as shown in FIG. 9(a) is obtained on the 8 side. This output is the threshold value T■1 of the level discriminator (9)
If it does not reach, the constant current source (10-2) is driven by the [H] output at the [L] output terminal (9-2),
The capacitor (10-3) is discharged and the voltage across its terminals is kept at zero, and the following circuit does not operate. When the output of ZCT (8) exceeds the threshold value TH of the level discriminator (9),
[)I] output as shown in FIG. 9(b) is obtained at the EH3 output terminal (9-1) of the level discriminator (9), which drives the constant current source (10-1). Capacitor (1
0-3) at the specified speed and the voltage between its terminals is the 9th
It rises as shown in figure (c).

When the terminal voltage of the capacitor (10-3) reaches the threshold value TH of the monostable multi-bi break (11), the mono-stable multi-bi break (11) generates an output as shown in FIG. 9(d). In other words, if the time exceeding the threshold TH of the output level discriminator (9) of the ZCT (6) is short, the voltage across the terminals of the capacitor (10-3) reaches the threshold TH of the monostable multi-vibration break (11). Therefore, the monostable multivibrator (11) does not operate. If the ZCT time is longer than the time width tNA in Figure 9 (C), the voltage across the terminals of the capacitor (to-3) will be monostable Martino)
'The threshold value TH of the oscillator (11) is reached, and the output of the monostable multivibrator (11) is inverted from [L] to [H]. Thereby, the function of the signal width discriminator of the first signal width discriminator (lO) is achieved.

Time width 1 of output of monostable multivibrator (11)
c, [Figure 9(d) E is set longer than the period of the AC line (1), and the 0 circuit (12) is connected to the [H] output of the level discriminator (9) and the monostable multi-bi break. (1
1) is ANDed with the [H] output and output, and the time width of the output of the AND circuit (12) is determined by the second signal width discriminator (13).
) is used for secondary discrimination. The operation of the second signal width discriminator (13) is similar to that of the first signal width discriminator (1G).

That is, in the second discrimination, the time when the output of ZCT (8) [FIG. 9(a)] is greater than the threshold TH of the level discriminator (9) is the discrimination time of the second signal width discriminator (13). t
longer than llB (and monostable multibibreak (11
) when the [H] output terminal (11-1) is [H], the voltage across the terminals of the capacitor (13-4) shown in FIG. 9(e) is level determined! The level discriminator (13-5) in the second signal width discriminator (13) reaches the threshold TH1 of (13-5).
generates an output with a time width t 611 as shown in FIG. 9(f), triggers the switching element (8) to drive the electromagnetic device (7), and operates the interrupter M (5) to disconnect the AC line. (
1) Open the circuit. In this way, the conventional device uses a signal to detect residual signals that do not need to be detected, which occur due to surges and noise components occurring in the AC line (1), and ground fault currents at the frequency of the AC line (1) itself, which should be detected due to an accident. The time width is used to prevent unnecessary operations.

[Problems to be Solved by the Invention] As explained above, conventional ground fault detection devices separate and remove ground faults that do not need to be detected due to surges or noise by focusing on the narrow time width of the signal. , the ground fault current is ZCT
(6), so if a ground fault occurs due to an excessive surge such as a lightning surge, the
As shown in Figure 1, the ZCT (
After the surge current disappears due to the inductance (6), a residual signal with a long time rji width is generated in the opposite direction, although the signal level cannot be said to be excessive. Therefore, as shown in Figure 11, if a residual signal occurs at the opposite polarity to the polarity to be detected, there will be no influence as the level will not exceed the threshold 7B, but as shown in Figure 10, the residual signal will When a signal is generated on the polarity side to be detected, the level thereof exceeds the threshold value TH, which poses a problem that unnecessary operations occur.

The signal width of such a residual signal generated in the opposite direction generally has a length several times the period of the AC circuit, and in the conventional device, the discrimination time width of the first signal width discriminator (10) It was also impossible to solve the problem by adjusting the .

This invention was made to solve the above problem, and when a ground fault occurs due to an excessive surge such as a surge, a residual signal with a length several times the period of the AC line. The purpose is to obtain a ground fault detection device that does not operate unnecessarily.

[Means for Solving the Problems] A ground fault detection device according to the present invention includes a ground fault detector that detects a ground fault current occurring in an AC line, and a ground fault detector that is connected to the ground fault detector and amplifies its output. an amplifier, and a charging/discharging signal connected to the amplifier, which is based on a pulse signal formed when the level of the output exceeds a first predetermined threshold; a level discriminator that generates a width output, and is connected to the above amplifier,
a delay means for delaying the output for a predetermined time; a synthesizing means connected to the amplifier and the delay means for synthesizing both outputs;
one-shot means for generating an output according to the time width of the pulse signal formed when the threshold and the fifth threshold are exceeded;
connected to the level discriminator and the one-shot means;
The device includes a gate means for calculating the AND of both outputs, and a cutoff means connected to the gate means and actuated by the output thereof to cut off the alternating current circuit.

Further, a ground fault detection device according to another aspect of the present invention includes a ground fault detector that detects a ground fault current occurring in an AC line, and a first output terminal and a second output terminal connected to the ground fault detector. an amplifier having an output terminal; and an amplifier connected to a first output terminal of the amplifier, which outputs a predetermined width when a pulse signal formed when the output level exceeds a predetermined threshold exceeds a predetermined time width. a first difference generating means connected to the output terminal of the rod 1 and the second output terminal of the amplifier and generating a difference by averaging both outputs; A second difference generation means is connected to the output terminal and the second output terminal, and detects the peak value of both outputs and generates the difference. a first comparator that compares the output with a reference value; a second comparator that is connected to the second difference generating means and that compares its output with the predetermined reference value; A first gate means connected to the second comparator and takes the AND of both outputs; and a second gate means connected to the level discrimination means and the first gate means and takes the AND of the two outputs. and a cutoff means connected to the second gate means and actuated by the output of the second gate means to cut off the alternating current circuit.

[Function] In this invention, the output of the ground fault detection device is amplified by an amplifier, and the output and the output delayed by a predetermined time are synthesized by the synthesizing means, and an output corresponding to the time width of the synthesized output is generated. A one-shot means outputs the output, and a gate means performs an AND operation between this output and the output of a level discriminator which discriminates the level of the output of the amplifier. Therefore, although periodic commercial frequency ground fault signals can be detected, excessive surge signals that arrive irregularly and produce residual signals with a length several times the period of the AC line are removed, causing unnecessary operation. is prevented.

Further, in another aspect of the present invention, the output of the ground fault detector is divided into positive and negative outputs by an amplifier, the first difference generating means averages the two outputs to obtain a difference, and this difference output is used as the first difference output. 1
The second comparator compares the output with a predetermined reference value, the difference generating means of measure 2 detects the peak value of both outputs and calculates the difference, and the second comparator compares this differential output with the predetermined reference value. do.

The logical product of each output of the first comparator and the second comparator is taken by a second data means, and the logical product of the output of the first gate means and the output of the level discrimination means is taken by a second data means. Take it by means of get. Therefore, although periodic commercial frequency ground fault signals can be detected, excessive surge signals that arrive irregularly and produce residual signals with a length several times the period of the AC line are removed, causing unnecessary operation. is prevented.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
(1), (3) to (8) are exactly the same as the conventional device described above. (2) is the ground fault detection device according to the present invention, (20) is an amplifier connected to ZCT (6) and amplifies its output, and (21) is a level discriminator connected to amplifier (2o). For example, cascaded comparators (2
2), consists of a signal width discriminator (23) and a monostable multi-bi break (24). (25) is a delay circuit connected to the amplifier (2o) and delays its output for a predetermined time;
6) is connected to the amplifier (2o) and the delay circuit (25), and in response to the output of the amplifier (20), the delay circuit (25)
This is a phase control circuit that sets the delay time in . Note that the delay circuit (25) and the phase control circuit (26) constitute delay means. (27) is a combining means, such as an adder, which is connected to the amplifier (20) and the delay circuit (25) and adds the outputs of both. A subtracter may be used instead of the adder (27). When an adder is used as (27), the delay circuit (25) delays the output of the amplifier (20) by half a cycle M, and when a subtracter is used, the delay circuit (25) delays the output of the amplifier (20) by M.
0) is set to be delayed by one period. (28
) are one-shot means, for example retriggerable one-shot circuits, connected to the adder (27), for example consisting of a cascaded comparator (29) and a monostable multivibrator. (31) is a gate means, for example, an AND circuit, connected to the output side of the level discriminator (21), that is, the monostable multi-bi break (24), and the output side of the retriggerable one-shot circuit (28), that is, the monostable multi-bi break (30). The output side thereof is connected to the gate electrode of the switching element (8).

In the ground fault detection device (2A) configured as described above, if there is no ground fault in the AC line (1), ZCT (
Since the circuit breaker (5) does not detect the ground fault current, the circuit breaker (5) does not operate.

Next, connect the AC line (1) to ground l? When i current is generated, it is detected by ZCT (6), and the detection signal is sent to amplifier (2o
) and is amplified, and an output as shown in FIG. 2(a) is obtained on the output side. The way this comes out is the comparator (22)
When the negative level exceeds a first threshold, for example, the negative threshold TH, the negative level corresponds to a period in which the negative level exceeds the negative threshold TH, as shown in FIG. 2(b). A pulse signal of &'ll is generated.

This pulse signal is supplied to the signal width discriminator (23), and a capacitor (not shown) provided inside the 21N
Charge as shown in (c). Then, during the charging process, when the terminal voltage of the capacitor reaches a second threshold value, for example, the threshold value TH, it rises, and during the discharging process, the terminal voltage of the capacitor rises to 3.
It rises when a threshold value, for example, threshold value TH3 is reached. Figure 2 (d
) A pulse signal having a predetermined time width t am as shown in FIG. (21) is obtained on the output side. This pulse signal is supplied to one input terminal of an AND circuit (31).

Further, the output of the amplifier (20) is supplied to a delay circuit (25), a phase control circuit (26) and an adder (27).
) and the amplifier ( ) supplied to the delay circuit (25).
20) is output to the amplifier (20) for a predetermined period of time under the control of the phase control circuit (26), for example, as shown in FIG. 2(e).
The output is delayed by half a period with respect to the output of . This delayed output is supplied to an adder (27) and an amplifier (20
) is added to the output of Fig. 2 (f
) will produce the output shown. This output is the comparator (2
g), the positive and negative levels of which are compared with a fourth threshold, such as a positive threshold TH, and a fifth threshold, such as a negative threshold TH, respectively. In this case, the positive level of the adder (27) exceeds the positive threshold TH, so the comparator (29)
On the output side of , there is a pulse signal with a time width corresponding to the period in which the positive level exceeds the positive threshold TH, as shown in Figure 2 (g).
It is generated as shown in . This pulse signal is supplied to the monostable multivibrator (30), which instantaneously discharges a capacitor (not shown) installed inside the monostable multivibrator (30). As shown in FIG. The terminal voltage of the capacitor of the stable multivibrator (30) becomes low level (L) at the same time as it reaches O volts, and after a predetermined time after the output of the comparator (29) becomes low level, the terminal voltage of the capacitor reaches the threshold value THs. An output that becomes a high level (H) is generated when the value exceeds the level discriminator (21). .As a result, AND circuit (31)
A high level output with a predetermined width as shown in FIG. 2 (D) is obtained on the output side of the switching element (8).
is applied to the gate electrode of to turn on the switching element,
By turning on this switching element (8), the electromagnetic device (7)
) is energized, the circuit breaker (5) operates, and the AC line (1)
cut off.

Next, if an excessive surge appears on the AC line (1),
This is detected by the ZCT (6), and the detection signal is supplied to the amplifier (20) and amplified, and the output side is shown in Fig. 3 (
The output shown in a) is obtained. This output is the comparator (
22) and its residual signal (oversheet portion)
exceeds the negative threshold TH, the residual signal reaches the negative threshold TH, as shown in FIG. 3(b).

A pulse signal with a time width corresponding to the period exceeding . This pulse signal is supplied to the signal width discriminator (23) and charges a capacitor (not shown) provided therein as shown in FIG. 3(c).

Then, during the charging process, the terminal voltage of the capacitor increases to the threshold value TBt.
It rises when the voltage reaches the threshold value TH, and falls when the terminal voltage of the capacitor reaches the threshold value TH during the charging process. A pulse signal having a predetermined time width tag as shown in FIG. 3(d) is obtained at the output side of the monostable multivibrator (24), that is, the output side of the level discriminator (21). This pulse signal is supplied to one input terminal of an AND circuit (31).

Further, the output of the amplifier (20) is supplied to a delay circuit (25), a phase control circuit (26) and an adder! ! (27
) and the amplifier ( ) supplied to the delay circuit (25).
20) is outputted to the amplifier (2o) for a predetermined period of time under the control of the phase control circuit (26), for example, as shown in FIG. 3(e).
The output is delayed by half a period with respect to the output of . This delayed output is supplied to an adder (27) and an amplifier (20
) is added to the output of Fig. 3 (f
) will produce the output shown. This output is the comparator (2
9), and its positive and negative levels are compared with a positive threshold TH and a negative threshold Tf15, respectively. In this case, the positive level and negative level of the adder (27) are a positive threshold MTH and a negative threshold TH.

, so the comparator (29) outputs a pulse signal with a time width corresponding to the period in which the positive level and negative level exceed the positive threshold TH and the negative lower threshold H. The signal is generated as shown in FIG. 3(g). This pulse signal is supplied to a monostable multi-by-break (30),
A capacitor (not shown) provided inside the capacitor is instantaneously discharged, and when this pulse signal disappears, the capacitor is gradually charged again as shown in FIG. 3(h). Here, as can be seen from Fig. 3(f) to (h), the residual signal of the surge has a long period, so the pulse signal from the comparator (29) formed based on this residual signal has a wide width. As a result, the time during which the terminal voltage of the capacitor of the monostable multi-pipe rake (30) is held at O volts becomes longer.Therefore, the output side of the monostable multivibrator (30), that is, the zotrigable one-shot circuit (28) On the output side, as shown in Figure 3 (i), the terminal voltage of the capacitor of the monostable multi-bi break (30) becomes low level (L) at the same time as it reaches 0 port, and then after holding the low level for a long time. When the terminal voltage of the capacitor exceeds the threshold value TH after a predetermined time t0 after the output of the comparator (29) finally becomes low level, it becomes high level (H).
The output will be generated. This output is an AND circuit (31
), and is ANDed with the pulse signal from the level discriminator (21).

Here, when the pulse signal from the level discriminator (21) is at high level, the output of the AND circuit (26) is at low level, so the gate of the AND circuit (3X) does not open, so that the output side A low level output is obtained as shown in FIG. 3(j). As a result, switching element (8)
is not turned on, the electromagnetic device (7) is not energized and the circuit breaker (5) is not activated, thereby preventing unnecessary operation.

In the above embodiment, the level discriminator (2I) discriminates the level based on the positive output of the amplifier (20), but the level discriminator (2I) discriminates the level based on the negative output of the amplifier (2o). You can do it like this.

FIG. 4 is a block diagram showing another embodiment of the present invention, in which (1), (3) to (8) are completely the same as the conventional device described above. (40) is a ground fault detection device according to the present invention, and (40) is an amplifier connected to ZCT (6), which has a first output terminal, for example, a positive output terminal, and a second output terminal, for example, a negative output terminal. It has an output e.g. -.

(41) is a level discriminator connected to the positive output terminal + of the amplifier (40), which includes the level discriminator (9) and the first signal width discriminator (1o) shown in FIG. , a monostable multivibrator (11), an AND circuit (12), and a second signal width discriminator (13). (42-1) is a positive-side average value conversion circuit connected to the positive output terminal of the amplifier (40) and averages its output, and (42-2) is the negative output terminal of the amplifier (40). The average value conversion circuit (43-1) is connected to the amplifier (43-1) and averages the output thereof.
(43-2) is an amplifier (40) that is connected to the positive output terminal of 0) and detects its peak value.
(44-1) is the average value conversion circuit (44-1) connected to the negative output terminal of
2-1) and (42-2), the differential amplifier takes the difference between both outputs, and (44-2) is a peak value conversion circuit (
43-1) and (43-2), and is a differential amplifier that takes the difference between both outputs. Average value conversion circuit (42-1
) and (42-2) and the differential amplifier (44-1) are the first
The peak value conversion circuit (43-1
) and (43-2) and the differential amplifier (44-2) are the second
constitutes a difference generation means. (45=1) is a first comparator that is connected to the differential amplifier (44-1) and compares its output with a predetermined reference value; (45-2) is a first comparator that is connected to the differential amplifier (44-1);
-2) and compares its output with a predetermined reference value, the second comparator (46) is connected to the comparator (45-1) and (
45-2) and calculates the AND of both outputs.
The gate means (47), for example, an AND circuit, is connected to the level discrimination means (41) and the AND circuit (46), and the second gate means, for example, an AND circuit, is connected to the level discrimination means (41) and the AND circuit (46), and
The output side of the AND circuit (47) is connected to the gate electrode of the switching element (8).

In the ground fault detection device (40) configured as described above, if there is no ground fault in the AC line (D), the ZCT (6
) does not detect a ground fault current, so the circuit breaker (5) does not operate.

Next, when a ground fault occurs in the AC line (1), this ground fault current is detected by the ZCT (6), and a detection signal having a waveform as shown in FIG. 5(a) is obtained at its output side. This detection signal is supplied to the amplifier (40), and its positive output terminal outputs a waveform as shown in FIG. ) The waveform output shown in ) is obtained. The output obtained at the positive output terminal of the amplifier (40) is supplied to the level determining means (41) and processed as described above, so that the output side has a waveform as shown in FIG. 5(b). The output is obtained.

Further, the output obtained at the positive output terminal of the amplifier (40) is supplied to the average value conversion circuit (42-1) and also to the peak value conversion circuit (43-1). 42-1'') averages its output, so that an output with a waveform as shown in Figure 5(e) is obtained on its output side, and the peak value conversion circuit (43-1) averages its output. By detecting the peak value of , an output with a waveform as shown in FIG.
) The output obtained at the negative output terminal - of the average value conversion circuit (
42-2) and the peak value conversion circuit (43
-2), and the average value conversion circuit (42-2) averages the output, so that the output side is
) is obtained, and the peak value conversion circuit (43-2) detects the peak value of the output, and the output side has a waveform as shown in Figure 5 (h). I get the output.

The respective outputs of the average value conversion circuits (42-1) and (42-2) are supplied to the differential amplifier (44-1), where the difference between the two outputs is taken, and thus the differential amplifier (44-1) On the output side, an output having a waveform as shown in FIG. 5(i) is obtained.

This output is supplied to the first comparator (45-1) and compared with its positive reference value Rrl and negative reference value RF2. The first comparator (45-1) is a differential amplifier (45-1).
When the output of 1) is between the reference values RFI and RP2, a high level (H) is generated; It generates a level (L) output.In this case, as can be seen from Figure 5(i), the differential amplifier (44-
The output of 1) is the reference value RPI and I? Since the voltage is between F2, the first comparator (45-1) generates a high level a as shown in FIG. 5(k). At the same time, each output of the peak value conversion circuits (43-1) and (43-2) is supplied to a differential amplifier (44-2), where the difference between the two outputs is taken, and then the differential amplifier (24-2) is On the output side of 2), there is a fifth
Eight waveforms as shown in rgJ(j) are obtained. This output is supplied to the second comparator (45-2) and compared with its positive reference value RF3 and negative reference value RF4.

The second comparator (45-2) is the first comparator (45-1)
It works in the same way, and the reference value is RF3=RFI, 1l
There is a relationship of F4=RF2. Therefore, the differential amplifier (4
Since the output of 4-1) is between the reference values RF3 and RF4, the second comparator (45-2) generates an output at the NO level as shown in FIG. 5 (&). Comparison i (45
The respective outputs of -1) and (45-2) are supplied to the first AND circuit (46), and the output side thereof is shown in FIG.
It is possible to obtain the output of the level shown in (Japan). 1st
The output of the AND circuit (46) is the level determination means (41)
is supplied to the second AlID circuit (47) together with the output of
As a result, a high level output with a predetermined width as shown in FIG. 5(n) is obtained on the output side. This output is applied to the gate electrode of the switching element (8) to turn on the switching element (8), and by turning on the switching element (8), the electromagnetic device (7) is energized and the circuit breaker (5) is activated. and cut off the alternating current (1).

Next, when an excessive surge appears in the AC line (1), a current as shown in FIG. 6(a) is generated on the secondary winding side of the ZCT (6). This current signal is supplied to the amplifier (40), and its positive output terminal + has a pressure waveform as shown in FIG. 5(c), and its negative pressure terminal - has a pressure waveform as shown in FIG. ) The waveform output shown in ) is obtained. Amplifier (4
The output obtained at the positive output terminal of 0) is supplied to the level discrimination means (41) and processed as described above, so that the output side has a waveform as shown in FIG. 5(b). is obtained.

Further, the output obtained at the positive output terminal of the amplifier (40) is supplied to the average value conversion circuit (42-1) and also to the peak value conversion circuit (43-1). 42-1) averages the output, so that an output with a waveform as shown in FIG. 6(e) is obtained on the output side, and the peak value conversion circuit (43-1) averages the output. The peak value is detected, and an output having a waveform as shown in FIG. 6(g) is obtained on the output side.

On the other hand, the output obtained at the negative output terminal of the amplifier (40) is supplied to the average value conversion circuit (42-2), and is also supplied to the peak value conversion circuit (43-2).
2-2) averages the output, so that an output with a waveform as shown in FIG. 6(f) is obtained on the output side, and the peak value conversion circuit (43-2) averages the output. The peak value is detected, and an output having a waveform as shown in FIG. 6(h) is obtained on the output side.

The respective outputs of the average value conversion circuits (42-1) and (42-2) are supplied to the differential amplifier (44-1), where the difference between the two river forces is taken, and thus the differential amplifier (44-1) On the output side, an output having a waveform as shown in FIG. 6(i) is obtained.

This output is supplied to the first comparator (45-1) and compared with its positive reference value RFI and negative reference value RF2. In this case, as can be seen from FIG. 6(i), the output of the differential amplifier (44-1) is the reference (iRFl and R
Since it is between F2, the first comparator (45-1)
As shown in Figure (k), a high level output is generated. At the same time, peak value conversion circuits (43-1) and (43-2)
The respective outputs of are supplied to the differential amplifier (44-2), where the difference between the two river forces is taken, and the output side of the differential amplifier (44-2) has a voltage as shown in Fig. 6 (j). Waveform output is obtained.

This output is supplied to the second comparator (45-2), which has a positive reference value RF3 and a negative reference value 1? Compared with F4.

In this case, as can be seen from Fig. 6 (j), the output of the differential amplifier (44-2) exceeds the reference value RF3, so the second comparator (45-2) An output as shown in FIG. 6 (&) which is at a low level for a period is output. Each output of comparators (45-1) and (45-2) is A
The signal is supplied to the ND circuit (46), and an output as shown in FIG. 6(m) is obtained on its output side. First AlI
The output of the D circuit (46) is supplied to the second AND circuit (47) together with the output of the level determining means (41). When the output of the level determining means (41) is high level, the first A
ND times! Since the output of (48) is at a low level, the gate of the second AND circuit (47) is not opened, so that a low level output is obtained on its output side as shown in Figure 6(n). . As a result, the switching element (8) is not turned on, so the electromagnetic device (7) is not energized, and the circuit breaker (5) is not energized.
) also does not operate, thereby preventing unnecessary operation.

In addition, in the above-mentioned embodiment, the level determination means (41)
Although the level is determined based on the positive output of the amplifier (40), the level may be determined based on the negative output of the amplifier (40).

[Effects of the Invention] As explained above, the present invention includes a ground fault detector for detecting ground fault current occurring in alternating current electricity, an amplifier connected to the ground fault detector and amplifying its output, and a ground fault detector connected to the ground fault detector to amplify its output. is connected, and generates an output of a predetermined width when the level of a charge/discharge signal based on a pulse signal formed when the output level exceeds a predetermined first threshold value reaches a predetermined second threshold value and a third threshold value. connected to the level discriminator and the above amplifier,
a delay means for delaying the output for a predetermined time; a synthesizing means connected to the amplifier and the delay means for synthesizing both outputs;
one-shot means for generating an output according to the time width of the pulse signal formed when the threshold and the fifth threshold are exceeded;
connected to the level discriminator and the one-shot means;
Since it is equipped with a gate means that takes the logical product of both outputs, and a cutoff means that is connected to this gate means and is actuated by the output of the gate means and cuts off the above-mentioned alternating current circuit, This has the effect of eliminating unnecessary operations and preventing unnecessary operations.

Further, as described above, another invention of the present invention includes a ground fault detector for detecting a ground fault current occurring in an AC line, and a first output terminal and a second output terminal connected to the ground fault detector. and an amplifier connected to the first output terminal of the amplifier, which generates an output with a predetermined width when the pulse signal formed when the level of the output exceeds a predetermined threshold exceeds a predetermined time width. a level determining means; a first difference generating means connected to a first output terminal and a second output terminal of the amplifier and generating a difference by averaging both outputs; and a first output terminal of the amplifier; and a second difference generating means connected to the second output terminal to detect the peak value of both outputs and generate a difference therebetween; a second comparator connected to the second difference generating means and comparing its output with the predetermined reference value; a first gate means connected to the second comparator and takes an AND of both outputs; a second gate means connected to the level discrimination means and the first gate means and takes an AND of both outputs; Since it is equipped with a cutoff means connected to the second gate means and actuated by the output of the second gate means to cut off the alternating current circuit, excessive surges arriving irregularly are removed and unnecessary operations are prevented. It has the effect that it can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
l! J and FIG. 3 are waveform diagrams for explaining the operation of FIG. 1, FIG. 4 is a block diagram showing another embodiment of the invention, and FIGS. 5 and 6 are for explaining the operation of FIG. 4. 7 is a block diagram showing an example of a conventional ground fault detection device, FIG. 8 is a circuit diagram showing an example of the specific circuit configuration of FIG. 7, and FIGS. 9 to 11 are 9 is a waveform diagram for explaining the operation of FIG. 8. FIG. In the figure, (1) is an AC power line, (2 people) is a ground fault detection device, (5) is a circuit breaker, (6) is a zero-phase detector, (7) is an electromagnetic device, (8) is a switching element, ( 2o) ~ (4o)
is an amplifier, (21) is a level discriminator, (25) is a delay circuit, (26) is a phase control circuit, (27) is an adder, (2
8) is a retriggerable one-on-one circuit, (41) is a level determination means, (42-1) and (42-2) are average value conversion circuits, and (43-1). (43-2) is a peak value conversion circuit, (44-1), (
44-2) is a differential amplifier, (45-1), (45-2
) is a comparator, and (46) and (47) are AND circuits. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A ground fault detector that detects ground fault current that occurs in an AC power line; An amplifier that is connected to this ground fault detector and amplifies its output; and 1
a level discriminator that generates an output with a predetermined width when the level of the charge/discharge signal based on the pulse signal formed when the threshold is exceeded reaches a predetermined second threshold and a third threshold; a delay means for delaying the output for a predetermined time; a combining means connected to the amplifier and the delay means for combining both outputs; and a combining means connected to the combining means, the output of which exceeds a predetermined fourth threshold and a fifth threshold. one-shot means for generating an output according to the time width of a pulse signal formed when the level discriminator is connected to the one-shot means;
1. A ground fault detection device comprising: gate means for taking a logical product of both outputs; and cutoff means connected to the gate means and actuated by the output of the gate means to cut off the alternating current circuit. (2) a ground fault detector that detects a ground fault current occurring in an AC line; an amplifier connected to the ground fault detector and having a first output terminal and a second output terminal; a level determining means connected to the output terminal of the amplifier and generating an output having a predetermined width when a pulse signal formed when the level of the output exceeds a predetermined threshold exceeds a predetermined time width; a first difference generating means connected to the output terminal and the second output terminal of the amplifier, for averaging both outputs and generating a difference thereof; and connected to the first output terminal and the second output terminal of the amplifier; a second difference generation means that detects the peak value of both outputs and generates the difference; and a first comparator connected to the first difference generation means and that compares the output with a predetermined reference value. , a second comparator connected to the second difference generating means and for comparing its output with the predetermined reference value; and a second comparator connected to the first comparator and the second comparator, and having both outputs. a first gate means that is connected to the level determination means and the first gate means, and a second gate means that takes the AND of both outputs, and a second gate means that is connected to the second gate means, A ground fault detection device comprising: a cutoff means that is activated by the output of the cutoff means to cut off the AC power line.