JPH0817533B2 - Ground fault detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an undesired operation of a ground fault detection device for shutting off an AC electric circuit when a ground fault occurs in the AC electric circuit, especially for a balance characteristic due to an inrush current. It is related to the ground fault detection which is difficult to do.

[Conventional technology]

FIG. 8 is a block diagram showing the configuration of a conventional ground fault detection device disclosed in, for example, Japanese Patent Laid-Open No. 64-148015, FIG. 9 is a waveform diagram for explaining general operation of the conventional device, and FIG. 10 is a plunge of the conventional device. It is an operation | movement explanatory waveform diagram with respect to the balance characteristic by an electric current.

In the figure, (1) is an AC electric circuit, (3) is a load device such as an electric motor that generates an inrush current, (5) is a circuit breaker installed in the AC electric circuit (1), and (6) is an AC electric circuit (1) A zero-phase current transformer as a winding, (7) a circuit breaker (5) is an electromagnetic device connected so as to be tripped, (8) is a switching element connected in series to the electromagnetic device (7), (10) Is the first level discriminator that receives the output of the zero-phase current transformer (6), (12)
Is a signal width discriminator for discriminating the time width of the output of the first level discriminator (10) from the charging time of the capacitor (11), (9)
Is a second level discriminator which receives the output from the signal width discriminator (12).

The operation of the ground fault detection device configured as described above will be described with reference to the drawings. FIG. 9 shows the case of general ground fault detection. In FIG. 9, (a) shows the ground fault component of the alternating current circuit (1), and (b) shows the output of the zero-phase current transformer (6). The output (b) of the zero-phase current transformer (6) is the determination level (TH) of the first level discriminator (10).
When the value exceeds 1), the constant current source of the first level discriminator (10) outputs a constant current, charges the capacitor (11) at a specified rate, and the terminal voltage of the capacitor (11) becomes the ninth value. It gradually rises as shown in FIG. When a predetermined time (Td) has elapsed after charging, the voltage across the terminals of the capacitor (11) reaches the discriminant value (TH2), and the second level discriminator (9) outputs the output of (e) of FIG. Output to 8),
The switching element (8) is operated to trip the circuit breaker (5) via the electromagnetic device (7) to cut off the AC electric circuit (1). When the output (b) of the zero-phase current transformer (6) exceeds the determination level (TH1) of the first level discriminator (10) for a time shorter than a predetermined time (Td), between the terminals of the capacitor (11) Since the voltage does not reach the discriminant value (TH2), there is no output to the second level discriminator (9) and the switching element (8) does not operate. Further, when the output (b) of the zero-phase current transformer (6) does not reach the determination level (TH1) of the first level discriminator (10), the capacitor (11) is not charged, and naturally, The switching element (8) is inactive.

Next, the operation for the equilibrium characteristic due to the inrush current will be explained.
It will be described with reference to the drawings.

The zero-phase current transformer (6) theoretically cancels the magnetic flux in the iron core by the balanced current flowing through the primary winding and does not generate a secondary output. However, in reality, there is an imbalance in the magnetic characteristics due to the disposition of the primary winding, and a current for canceling this is generated in the secondary winding, and a slight secondary output is generated. This is called the equilibrium characteristic. The switching device (8) does not operate because the secondary output due to this normal balanced characteristic does not reach the determination level (TH1) of the first level discriminator (10). However, the inrush current of the load device (3) such as an electric motor may reach several times the normal current value for a short time (several Hz), and in this case, the output of the zero-phase current transformer (6) The judgment level (TH1) of the first level discriminator (10) may be exceeded, and the ground fault detection device may operate unnecessarily.

[Problems to be Solved by the Invention]

As described above, the conventional ground fault detection device has a problem that the ground fault detection device is unnecessarily operated by the inrush current of the electric motor due to the equilibrium characteristic of the zero-phase current transformer.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a ground fault detection device that is less likely to perform an unnecessary operation due to an inrush current.

[Means for solving the problem]

The ground fault detection device according to the present invention is a level discriminator that outputs an output signal of a time width corresponding to a portion where the ground fault component of the zero-phase current transformer exceeds a predetermined magnitude, and a predetermined time of this output signal. The signal width discriminator that discriminates the width or more and outputs a pulse signal when the output signal falls, and inverts the phase of the ground fault component in response to the control signal from the flip-flop that inverts the control signal by this pulse signal. It is provided with a phase switch for outputting to the level discriminator and a continuous signal discriminator for outputting an output for activating the switching element when the output signal from the level discriminator continues for a predetermined period.

[Action]

The ground fault detection device according to the present invention discriminates a predetermined time width or more of the output signal of the level discriminator, and the phase switching device completely eliminates the ground fault component of the zero-phase current transformer at the timing when the output signal falls. The continuous signal discriminator determines that the output signal of the level discriminator of the waveform after the wave conversion and full-wave conversion is continuous for a predetermined period, and operates the switching element.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a ground fault detection apparatus according to an embodiment of the present invention, FIG. 2 is a general operational explanation waveform diagram of the embodiment, and FIG. 3 is a balance characteristic by an inrush current of the embodiment. 4 is a block diagram of another embodiment of the continuous signal discriminator, and FIGS. 5 and 6 are operation waveform diagrams of another embodiment of the configuration of FIG. 4, FIG. FIG. 6 is a block diagram of another embodiment of the phase switch.

In the figure, (1), (3) to (8), (10), (11)
Is the same as that described in the above conventional example.

(13) is a signal width discriminator, which discriminates the time width of the output signal from the level discriminator (10) from the charging time of the capacitor (11), and outputs the level discriminator (10) when the time width exceeds a predetermined time width. A pulse signal is output when the signal falls. Reference numeral (14) is a flip-flop, which inverts the output control signal every time the pulse signal of the signal width discriminator (13) is received.

(20) is a phase switch that inputs the output of the zero-phase current transformer (6) and outputs the waveform to the level discriminator (10), (21)
Is the switching element (8) when the continuity of the output signal from the level discriminator (10) is discriminated
It is a continuous signal discriminator which outputs an operation signal to.

Here, the detailed configuration of the phase switch (20) will be described.
(20-1) is a resistor for converting the output current of the zero-phase current transformer (6) into voltage, and (20-2) and (20-3) are second and third switching elements which are flip-flops (14 ON / OFF is inversely controlled by the control signal from). (20-5) is an inverting amplifier, which inverts the positive and negative voltage waveform of the resistor (20-1) and outputs the inverted voltage waveform to the third switching element (20-3).
The flip-flop (14) inverts H (High) and L (Low) of the control signal (20-6) by the signal from the signal width discriminator (13). When the control signal (20-6) is H, the second switching element (20-2) is ON and the output (20-6) is L.
At this time, the third switching element (20-3) is turned on.

Next, the detailed configuration of the continuous signal discriminator (21) will be described.
(21-1) is the first monostable multivibrator,
In this embodiment, when the output signal from the level discriminator (10) is received, the commercial frequency of the AC electric circuit (1) is risen at each rising edge.
An H (High) pulse having a predetermined time width (ts = about 10 milliseconds) slightly longer than 1/2 cycle is output. Reference numeral (21-2) denotes a second monostable multivibrator, which is normally an H output and, when receiving an output signal from the level discriminator (10), has a predetermined time width (th) longer than one cycle of the commercial frequency. = (About 25 milliseconds) L (Low) pulse is output. (21-3) is an operation signal of the switching element (8) when the logical product of the pulses from the first monostable multivibrator (21-1) and the second monostable multivibrator (21-2) is established. It is an AND circuit to issue.

The operation of the ground fault detection device configured as described above is shown in FIG.
This will be described with reference to FIG. FIG. 2 shows the case of general ground fault detection. In FIG. 2, (a) shows the voltage waveform across the resistor (20-1), and this voltage waveform (a) shows the second switching element (20-2). ) Is entered. In the figure, (b) shows the resistance (20−
1) It is a voltage waveform after passing the voltage waveform of both ends through the inverting amplifier (20-5), and the third switching element (20-
Input to 3). Second and third switching elements (20-
The voltage waveforms input to 2) and (20-3) are inverted and controlled by the control signal from the flip-flop (14) and converted into the output waveform of the solid line in FIG. 2 (c), and the level discriminator (1
It is output to 0). The level discriminator (10) outputs the output signal (d) to the continuous signal discriminator (21) and the signal width discriminator (13) corresponding to the portion exceeding the determination level (TH1) shown in FIG. 2 (d). . The signal width discriminator (13) discriminates when the time width of the output signal (d) is equal to or longer than a predetermined time (Td) from the charging time of the capacitor (11) and flips the pulse output shown in (e) of FIG. (14). The flip-flop (14) is designed to be set to either polarity when the ground fault detection device is connected to the alternating current circuit (1) and is energized, and the pulse signal (from the signal width discriminator (13) ( The polarity of the control signal is switched every e), and switching control of the second and third switching elements (20-2) and (20-3) is performed.

On the other hand, in the continuous signal discriminator (21), the first monostable multivibrator (21-1) receives the output signal (d) from the level discriminator (10) for a predetermined time width (ts = about 10 milliseconds). ) Output the first pulse, and if the output waveform in FIG. 2 (c) continuously exceeds the determination level (TH1), it becomes a pulse with a seemingly long time width as shown in (f) in the same figure. . Further, the second monostable multivibrator (21-2) outputs a second pulse having a predetermined time width (ts = about 25 milliseconds) as shown in (g) of the same figure, and during this pulse, The output signal (d) from the level discriminator (10) is ignored. AND circuit (2
In 1-3), when the logical product of these two pulses (f) and (g) is established, the operation signal (h) of the switching element (8) is output to cut off the ground fault.

FIG. 3 shows the case of equilibrium characteristics due to inrush current, and FIG. 3 (a) shows the voltage waveform across the resistor (20-1). Third
The operation up to the pulse output from the signal width discriminator (13) shown in (e) of the figure is the same as in the case of the general ground fault detection.
Generally, the inrush current is at a high level at first, but it decays quickly, and the level discriminator (10) continuously determines the level (TH1).
Exceeds a few Hz, and the first pulse (f) of the continuous time width of the first monostable multivibrator (21-1) has a second frequency as shown in (f) of FIG. It becomes shorter than the second pulse (g) of the predetermined time width (th) of the monostable multivibrator (21-2), and in the AND circuit (21-3), the logical product of these two pulses (f) and (g) Not satisfied.

Therefore, the ground fault detection device does not operate unnecessarily in the equilibrium characteristic due to the inrush current.

Although the time width (th) of the output pulse of the second monostable multivibrator (21-2) is set to about 25 milliseconds in the above-mentioned one embodiment, this time width setting is set to a longer value. By doing so, it is possible to provide a ground fault detection device that does not perform unnecessary operation even when the output signal (d) from the level discriminator (10) is three times or more.

Next, another embodiment of the continuous signal discriminator of the present invention will be described.
This will be described with reference to FIGS. 5, 5 and 6. In FIG.
(21-3) is the same as that described in the above embodiment. Reference numeral (23-1) is a monostable multipiperator which does not retrigger, and outputs a pulse having a predetermined time width by a signal from the level discriminator (10). (23) is a continuous signal discriminator, (23-2) is a second AND circuit, and the output signal (d) from the level discriminator (10) and the first monostable multivibrator (23-1) are used. When the logical product of the pulse output (e) of the above is established, the signal of the output (f) is output to the second monostable multivibrator (23-3). When the second monostable multivibrator (23-3) receives the output (f), it has a predetermined time width (th = about 25 milliseconds) longer than one cycle of the commercial frequency.
The H pulse (g) is output.

The case of general ground fault detection in the continuous signal discriminator (23) will be described with reference to FIG. The pulse output (e) of the first monostable multivibrator (23-1) by the output signal (d) from the level discriminator (10) is a predetermined value slightly longer than 1/2 cycle of the commercial frequency of the AC electric circuit (1). Since it is the time width (ts), the second AND circuit (23-2) outputs the signal of the output (f) to the second monostable multivibrator (d) when it overlaps with the next output signal (d). Send to 23-3). Output (f)
The second monostable multivibrator (23-3) which has received the AND circuit (21-3) receives the pulse (g) having a predetermined time width (th).
Send out. In the AND circuit (21-3), the H of the pulse (g) is approximately one cycle of the commercial frequency, and the next output signal (f) is input during this period to establish a logical product and the operating signal of the switching element (8). By issuing (h), the ground fault detection is cut off. FIG. 6 shows the case of an inrush current. When the output signal (d) from the level discriminator (10) is three times or more, the AND circuit (21-3) outputs a pulse (g) and an output signal (d). The ground fault detection device does not operate unnecessarily in the equilibrium characteristic due to the inrush current because the logical product of d) is not established.

Next, another embodiment of the phase switch will be described with reference to FIG. In this phase switch (22), four switching elements are combined in a bridge to convert the ground fault component of the zero-phase current transformer (6) into a full-wave converter, and the switching element from the flip-flop (14) of the switching element on the opposite side is combined. The configuration is such that the control signals are the same and the inversion control is performed, and the same operation as that of the phase switch of the above-described embodiment is performed.

〔The invention's effect〕

As described above, the present invention provides a level discriminator that outputs an output signal having a time width corresponding to a portion where the ground fault component of a zero-phase current transformer exceeds a predetermined magnitude, and a predetermined time width of this output signal. The phase switching device that discriminates the above and outputs the signal to the level discriminator by inverting the phase of the ground fault component at the falling phase of this output signal, and the switching element when the output signal from the level discriminator continues for a predetermined period. By providing a continuous signal discriminator that outputs an output to be operated, it is possible to provide a ground fault detection device in which the ground fault detection device is less likely to perform unnecessary operation due to an inrush current of a motor or the like due to the equilibrium characteristic of the zero-phase current transformer.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a ground fault detecting device according to an embodiment of the present invention, and FIGS. 2 and 3 are waveform diagrams for explaining the operation of the embodiment.
FIG. 4 is a block diagram of another embodiment of the continuous signal discriminator, FIGS. 5 and 6 are waveform diagrams for explaining the operation of the configuration of FIG. 4, and FIG. 7 is a block of another embodiment of the phase switch. FIG. 8 is a block diagram showing the structure of a conventional ground fault detecting device, and FIGS. 9 and 10 are waveform diagrams for explaining the operation of the conventional device. In the figure, (1) is an AC circuit, (6) is a zero-phase current transformer,
(8), (20-2), (20-3) are switching elements,
(10) is a level discriminator, (12) and (13) are signal width discriminators, (14) is a flip-flop, (20) and (22) are phase selectors, and (21) and (23) are continuous signals. Discriminator, (21−
1), (21-2) and (23-3) are monostable multivibrators, and (21-3) and (23-2) are AND circuits. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A ground fault detecting device which operates a switching element when a ground fault component of a zero-phase current transformer that is electromagnetically coupled to an AC electric line and detects a ground fault of the AC electric line has a predetermined magnitude or more, A level discriminator that outputs an output signal with a time width corresponding to the portion where the ground fault component exceeds a predetermined magnitude, and discriminates a predetermined time width or more of the output signal of this level discriminator and outputs a pulse when the output signal falls. A signal width discriminator that outputs a signal, a flip-flop that inverts a control signal by a pulse signal of this signal width discriminator, and a full-wave conversion of the ground fault component of the zero-phase current transformer corresponding to the control signal from this flip-flop And a continuous signal discriminator which outputs an output for activating the switching element when the output signal from the level discriminator continues for a predetermined period. Ground fault sensing device to.