JPH03220466A - Grounding detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a ground fault detection device that interrupts an electrical circuit when a ground fault occurs in the electrical circuit, and particularly relates to a ground fault detection device that does not operate unnecessarily during an abnormal surge. It is something.

[Conventional technology]

FIG. 8 is a block diagram of a conventional ground fault detection device disclosed in, for example, Japanese Unexamined Patent Publication No. 61-161921, FIG. 9 is a circuit diagram showing a specific configuration of the device shown in FIG. 8, and FIG. 10 is a conventional ground fault detection device. FIGS. 11 and 12 are waveform diagrams illustrating the general operation of the device. FIGS. 11 and 12 are waveform diagrams illustrating the operation of the conventional device during a surge.

In the figure, (1) is an AC power line, and (b) is an AC power line (1).
), (102) is a surge absorber, (103) is an abnormal surge source such as lightning, (2)
is a breaker installed in the AC line (1), (3) is a zero-phase current transformer whose negative winding is the AC line (1), and (4) is connected to remove the breaker (2). electromagnetic device, (
5) is a switching element connected in series to the electromagnetic device (4), (7) is a level discrimination circuit that receives the output from the zero-phase current transformer (3) as an input, and (8) is a switching element connected in series to the electromagnetic device (4). The first signal width discriminator that discriminates the time width, (9) is the first
A predetermined time width (tc
o) A monostable multivibrator that generates an output, QO
is an AND circuit that inputs the output of the level discrimination circuit (7) and the output of the monostable multivibrator (9), and outputs an output when the logical product is established. This is a second signal width discriminator for discriminating.

In FIG. 9, (7-1) is r of the level discrimination circuit (7).
Only when the input signal exceeds the set level at the HJ output terminal
Output HJ. (7-2) is the rLJ output terminal of the level discrimination circuit (7), which outputs "L" only when the input signal exceeds the set level, and otherwise outputs r)iJ.

(s-t) and (8-2) are the "H" terminals of the rHJ output terminal (7-1) and 1) iJ output terminal 7-2), respectively.
'' output and generates a constant current in the direction shown, (8-3) is a constant current & (8-1) , (8-
2) is a capacitor that is charged and discharged by the IIL source (
8-1) and (8-2) together with the first signal width discriminator (
8). (11-3) is ANL), path αQ
NOT circuit that inverts the output of (11-1) iJ A
A constant current source (11-4) is driven by the output of the N L1 circuit aO and (11-2) is driven from the output of the 01 circuit (11-3) and generates a constant current in the direction shown in the figure.
) are capacitors that are charged and discharged by constant current sources (11-1) and (11-2). (11-5) is the charging WL of the capacitor (11-4)! This is a second level discrimination circuit that discriminates the voltage level, and is a constant current source (nt), (1
1-2) and the capacitor (o-4) constitute a second signal width discriminator.

The operation of the ground fault detection device configured as described above will be explained with reference to FIGS. m to 12. A general ground fault in the AC line (1) is detected by the zero-phase current transformer (3), and its output waveform is
This is shown in (4) in Figure 0. If this output waveform (a) does not reach the judgment level CI4υ of the level discrimination circuit (7), the constant current source (8-2) is driven and the voltage between the terminals of the capacitor (8-3) is kept at zero. The following circuits do not work.

The output waveform (1) is the level judgment circuit (judgment level of 7)
When υ is exceeded, the constant current source (8-1) secretly charges the capacitor (8-3) at a specified speed, and the capacitor (8-3)
) increases as shown by the square in FIG.

This makes the monostable multivibrator (9) the 10th
Generates an output with the waveform shown in the figure. In other words, if the time for which the output waveform (A) exceeds the judgment level 12υ of the level judgment circuit (7) is short, the voltage across the terminals of the capacitor (8-3) will not reach the example judgment level of the monostable multivibrator (9). First, the monostable multivibrator (9) does not operate.

If the time for which the output waveform - exceeds the judgment level 2υ of the level discrimination circuit (7) is longer than the iM person in Figure 10, the voltage across the terminals of the capacitor (8-3) will be at the judgment level of the monostable multivibrator (9). - and inverts the output of the monostable multivibrator (9J). This achieves the function of the first signal width discriminator (3). The output time width tco of the monostable multivibrator (9) is It is set longer than the period of (1), and is output in the AND circuit GO which takes the logical product of the rHJ output of the level discrimination circuit (7) and the output of the monostable multivibrator (9),
The second signal width discriminator qυ discriminates the one-circuit α circuit high Q time width as a second discrimination.

The operation of the second signal width discriminator αυ is similar to that of the first signal width discriminator (8
).

That is, in the second judgment BIl, the time during which the output waveform - is longer than the judgment level υ of the level discrimination circuit (7) is longer than the judgment time tMB of the second signal width discriminator IJIJ, and the monostable multivibrator When the "H" output terminal (9-1) of (9) is rHJ, the voltage across the terminals of the capacitor (11-4) shown by waveform (7) is the level discriminator (11).
-5) level (waveform @) is reached, and the second level discriminator circuit (11-5) in the second signal width discriminator (11/) generates an output of the waveform (to) shown in Fig. 10, and the switching Trigger the element (5) to drive the electromagnetic device fi! (4J,
The circuit breaker (2) is operated to open the AC line (1).

In this way, in the conventional device, there is no need to detect surges and noise components generated in the AC line (1).
The ground fault current at the frequency of the AC line (1) itself to be detected due to an accident is distinguished by the time width of the signal, thereby preventing unnecessary operations.

[Problems to be Solved by the Invention] As explained above, in conventional devices, ground faults that do not need to be detected due to surges or noise are removed by focusing on the narrow time width of the signal. is a zero-phase current transformer (3)
If a ground fault occurs due to an excessive surge such as a lightning surge, a zero-phase current transformer (
After the surge current disappears due to the inductance (3), a residual signal with a long time width is generated in the opposite direction, although the signal level cannot be said to be excessive. Therefore, as shown in Figure 12, if the residual signal occurs on the opposite polarity to the detected polarity, there will be no effect, but as shown in Figure 11, if the residual signal occurs on the detected polarity side, unnecessary operation will occur. There were issues such as the occurrence of

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 (8) It was also impossible to solve the problem by adjusting the

This invention was made to solve the above-mentioned problems.When a ground fault occurs due to an excessive surge such as a lightning surge, a residual current with a length several times the period of the AC line, The purpose of this invention is to provide a ground fault detection device that does not operate unnecessarily due to signals.

[Means for solving problems]

The ground fault detection device according to the present invention includes a level discriminator that generates an output signal of a predetermined time width when a ground fault component detected by a zero-phase current transformer has a predetermined magnitude or more and exists for a predetermined time or more. , a zero-cross detector that outputs a signal for a predetermined time or less each time a zero-volt point of the ground fault component is detected, and a switching element that operates when the logical product of the output signal of the level discriminator and the signal of the zero-cross detector is established. It is equipped with a trigger circuit to

[Effect]

The ground fault detection device according to the present invention detects surges, whereas the output signal of the zero-phase current transformer that detects a ground fault is a repetitive signal based on the commercial frequency of the AC line and is an AC signal that crosses between zero and Focusing on the fact that the output signal of the zero-phase current transformer is a DC signal that does not cross zero V or is a single asynchronous signal, the difference between the output signal of the level discriminator and the signal of the zero-cross detector is calculated by using the output signal of the level discriminator and the signal of the zero-cross detector in the trigger circuit. The determination is made by the logical product of an AND circuit.

[Embodiment] Fig. 1 is a block diagram of a configuration for ground fault detection showing an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining general operation of the embodiment, and Figs. A waveform diagram explaining the operation at the time of an excessive surge according to the embodiment, FIG. 5 is a block diagram of the configuration of a ground fault detection device showing another embodiment of the present invention, and FIG. 6 is a waveform diagram explaining the general operation of another embodiment. , FIG. 7 is a waveform diagram illustrating the operation at the time of an excessive surge in another embodiment.

In the figure, (100) to (103), (1) to
(5), (7) to (9) are the same as those explained in the conventional example above. (6) is a waveform shaping circuit that shapes the output waveform from the zero-phase current transformer (3) and outputs it to the level discriminator (7) and zero-cross detection circuit 4 (described later); CIG is the level discriminator; It consists of a discriminator circuit (7), a first signal width discriminator (8) and a monostable multivibrator (9). It consists of a zero cross detection circuit (6) that outputs a signal at the zero crossing point, and a second monostable multivibrator □ that outputs an output signal with a predetermined time width based on this signal. - is a trigger circuit; An AND circuit α4 that outputs a signal when the AND of the output signals of both the monostable multivibrator (9) and the second monostable multivibrator is established, and a trigger that receives this signal and operates the switching element (5). It consists of a third monostable multivibrator that outputs a signal.

Figure 2 shows the operation of the ground fault detection device configured as above.
This will be explained using FIG. In case of general ground fault,
The output waveform of a ground fault in the AC line (1) detected by the zero-phase current transformer (3) is shown in 4 of FIG. In this case, as in the operation description of the conventional example above, when the output waveform edge exceeds the judgment level υ of the level discriminator (7), the capacitor (8- The voltage across the terminals of 3) rises as shown in the circle in FIG. 2, and the monostable multivibrator (9) generates an output with the waveform shown in FIG.

On the other hand, in the zero cross detector ση, the output waveform end of the ground fault of the zero phase current transformer (3) with the waveform shaping circuit (6) red and white is input to the zero cross detection circuit □□□, and this output waveform - is zero
A signal edge with a time width (tx) is output from the second monostable multi-pie break at the position where it intersects with .

This signal end is continuously output at a timing of 1/2 of the period (τ) of the AC line (1) while the zero-phase current transformer (3 output waveform 4 exists).Trigger circuit (to) Then, when the AND circuit Q41 establishes the logical product of waveform 4 and the signal end, it outputs the trigger signal 6 from the third monostable multivibrator (to).
Output υ. This trigger signal C + old causes the switching element (5) to actuate and drive the electromagnetic device (4), actuating the circuit breaker (2) and opening the AC line (1). At this time, in order to prevent interference between the output waveform of the level discriminator (e) and the zero-cross detector α force signal (g), the time width (tx) of the signal edge is set to tx((τ/2-tco )/2 is required.

In addition, if the output waveform □□□ of the ground fault of the zero-phase current transformer (3) does not reach the judgment level υ of the level discrimination circuit (7), and if the output waveform (a) If the time exceeding level 4 is short, the monostable multivibrator (9) does not operate. Therefore, there is no output from the ANL) circuit (141) and the ground fault detection device does not operate.

Next, the operation at the time of an excessive surge will be explained with reference to FIG. If a ground fault occurs due to excessive surge, connect the zero-phase current transformer (
After the surge current disappears due to the inductance of 3), the third
An output signal □□□ with a long time width shown by ■ in the figure is generated. ) is the judgment level G of the level judgment circuit (7)! 1
Monostable multivibrator (
9) outputs the waveform shown in FIG. 3) to the AND circuit cI4. The zero cross detector port connects the signal end from the output signal ■ to AN
Output to D circuit C141. In the AND circuit Q41, the output waveform (to) of the signal end and the monostable multivibrator (9)
Since the logical product is not established at the timing of , the ground fault detection device does not operate unnecessarily.

However, when the surge of reverse polarity as shown in Fig. 3 is shown in Fig. 4,
The peak side of the output signal due to the surge is the level discrimination circuit (7
), the monostable multivibrator (9) outputs the output waveform shown in FIG. Also, the output signal from zero cross detector αη! The signal end is output by the zero crossing when the signal transitions from the peak side to the residual side. This output signal (7) and signal (6) are connected to an AND circuit α
4 is the timing at which the logical product is established, which may cause the ground fault detection device to operate unnecessarily.

In order to cope with this, a configuration of a ground fault detection device shown in another embodiment shown in FIG. 5 is proposed. In Figure 5, (100)
~(103), (1) ~(6), Q4~Q5
, αη, (g) are the same as those explained in the above embodiment. α9 is a level discriminator, which includes a level discriminator circuit (7), a first signal width discriminator (8), a monostable multivibrator (9), and an AND circuit α cylinder 2.
The signal width discriminator αυ is the same as that explained in the above conventional example.

The operation in the case of a general ground fault will be explained with reference to FIG. When the output waveform of the zero-phase current transformer (3) exceeds the judgment level 91J of the level discrimination circuit (7) in output waveform 4 within the predetermined time width (tco) of the monostable multivibrator (9), Only then, the output (to) of the level discriminator o9 is inputted to the ANL) circuit α of the trigger circuit (g). This output (to) is the judgment level G! of the level judgment circuit (7). It is output with a delay of about one cycle (τ) from the first output exceeding υ, and the timing at which the logical product is established with the signal (support) from the zero cross detector αη in the AND circuit Q (about one cycle from the first output) The trigger signal Cυ is output with a delay of (τ). This trigger signal Cυ causes the switching element (
5) operates to drive the electromagnetic device (4), and the circuit breaker (2)
is activated to open the AC circuit (1).

The operation at the time of a reverse polarity surge that causes the ground fault detection device of the above embodiment to operate unnecessarily will be explained with reference to FIG.

The peak side of the output signal due to the surge is the level discrimination circuit (7
), the monostable multivibrator (9) outputs an output waveform (transformation) if the time exceeding the determination level Qη is long.

However, since there is no output exceeding the judgment level Gυ of the next level discriminator (7), there is no output from the second signal width discriminator (6) and the trigger circuit (G) does not operate, causing the ground fault to occur. The detection device will not operate unnecessarily.

〔Effect of the invention〕

The ground fault detection device in this invention is a commercial frequency AC signal that crosses zero when the output signal of a zero-phase current transformer is in the event of a ground fault, and that the output signal due to a surge is a DC signal that does not cross zero Since it is asynchronous, there is a level discriminator that generates an output signal when the detected ground fault component exceeds a predetermined magnitude and exists for a predetermined time, and a zero cross detector that outputs a signal every time a zero volt point is detected. By providing a ground fault detector and an AND circuit that makes a determination based on the logical product of these signals, it is possible to provide a ground fault detection device that does not operate unnecessarily due to an excessive surge.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram of a ground fault detection device showing an embodiment of the present invention, FIGS. 2, 3, and 4 are waveform diagrams for explaining the operation of the embodiment, and FIG. 6 and 7 are waveform diagrams for explaining the operation of other embodiments. FIG. 8 is a block diagram of the configuration of a conventional ground fault detection device. FIG. 9 8 is a circuit diagram showing a specific configuration of the device shown in FIG. 8, and FIG. 1θ, FIG. 11, and FIG. In the figure, (1) is an AC line, (a zero-phase current transformer,
(May switching element, (7) level discrimination 91 circuit, (8) first signal width discriminator, (September monostable multivibrator, (b) zero cross detection circuit, (141
is an AND circuit, αQ is a level discriminator, qη is a zero cross detector, and (to) is a trigger circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) In a ground fault detection device that is electromagnetically coupled to an AC line and is activated via a switching element when a ground fault component of a zero-phase current transformer that detects a ground fault in the AC line is greater than or equal to a predetermined size, a level discriminator that generates an output signal with a predetermined time width when the ground fault component has a predetermined magnitude or more and exists for a predetermined time; a zero-cross detector that outputs a signal;
A ground fault detection device comprising: a trigger circuit that operates the switching element when the logical product of the output signal of the level discriminator and the signal of the zero-cross detector is established.