JP2505604B2 - Ground fault detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ground fault detection device provided in an AC electric circuit.

[Prior Art] FIG. 6 is a block diagram showing a conventional ground fault detecting device disclosed in, for example, Japanese Patent Application No. 1-189659, in which (1) is a three-phase electric circuit and (2) is an electric circuit ( 1) A ground fault detector provided inside, for example, a zero-phase current transformer (hereinafter referred to as ZCT),
(3) is a capacitor provided on the output side of ZCT (2),
(4) is a waveform shaping circuit connected to ZCT (2), (5)
Is an integrating circuit connected to this waveform shaping circuit (4),
(6) is a level discriminator connected to the integrating circuit (5), (7) is a thyristor having a control electrode connected to the level discriminator (6), and (8) is a main electrode of the thyristor (7). The electromagnetic device (9) provided in the path is provided in the electric path (1) and is controlled by the electromagnetic device (8) to be the electric path (1).
It is a circuit breaker that shuts off.

The conventional ground fault detection device is configured as described above, and is provided in the electric line (1) when a ground fault current having a waveform as shown in FIG. 7 (A) flows in the electric line (1) due to the ground fault, for example. ZCT
(2) detects the ground fault current, and a detection signal having a waveform as shown in FIG. 7 (B) is obtained at the output side. This detection signal is supplied to the waveform shaping circuit (4), and when its level exceeds a predetermined positive threshold value TH _1, as shown in FIG. 7 (C), the period during which the level exceeds the threshold value TH ₁ A rectangular wave output having a time width corresponding to is obtained at the output side of the waveform shaping circuit (4). This rectangular wave output is supplied to the integrator circuit (5), where it is integrated into a triangular wave as shown in FIG. 7 (D), which is then supplied to the level discriminator (6). When the level of the triangular wave exceeds the positive threshold value TH ₂ of the level discriminator (6), the output side of the level discriminator (6) is shown in FIG.
A trapezoidal wave output having a predetermined time width as shown in is obtained. This trapezoidal wave output is applied to the control electrode of the thyristor (7) to turn on the thyristor (7), and when the thyristor (7) is turned on, the electromagnetic device (8) is energized to open the circuit breaker (9). Cut off the electric circuit (1).

On the other hand, for example, when an impulse-shaped current such as a surge current having a high peak value but a short duration flows in the electric circuit (1), the capacitor (3) provided on the output side of the ZCT (2)
The current is absorbed by, but when the value exceeds the positive threshold value TH ₁ , a rectangular wave output having a time width corresponding to the period is obtained at the output side of the waveform shaping circuit (4). However, when the time width of the output waveform of the waveform shaping circuit (4) is short, the peak value when integrated by the integrating circuit (5) becomes low. Therefore, by properly setting the threshold value TH ₂ of the level discriminator (6), the level discriminator (6) does not produce an output and the thyristor (7) is not turned on.

[Problems to be Solved by the Invention] By the way, in the case of the conventional ground fault detection device having the above-described configuration, if the balance characteristic of the ZCT (2) based on the residual current characteristic is poor, for example, the inrush current at the time of starting the motor may be reduced. Such a transient large current may cause the ground fault detection device to perform unnecessary operation. That is, in the state where no ground fault is generated, it is as shown in FIG. 8 (A), but when the motor is started, the rush current causes the secondary winding side of ZCT (2) to move to the side of FIG. 8 (B). A current as shown is generated, and this current exceeds the positive threshold value TH ₁ , and as a result, in the portion of the waveform that exceeds the positive threshold value TH ₁ , the output side of the waveform shaping circuit (4) is shown in FIG. A rectangular wave output as shown in C) is generated. This rectangular wave output is supplied to the integrator circuit (5), where it is integrated and the result is shown in FIG. 8 (D).
It becomes a triangular wave as shown in and is supplied to the level discriminator (6). Since the level of this triangular wave exceeds the positive threshold TH ₂ of the level discriminator (6), the output of the level discriminator (6) has a trapezoidal wave output of a predetermined time width as shown in FIG. 8 (E). Is obtained. As a result, this trapezoidal wave output causes the thyristor (7) and the electromagnetic device (8) to operate in the same manner as in the case of the ground fault current described above, driving the circuit breaker (9), resulting in unnecessary operation.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a ground fault detection device that does not perform an unnecessary operation due to a transient large current such as an inrush current even if the ZCT has poor balance characteristics.

[Means for Solving the Problem] In the ground fault detection device according to the present invention, when the positive level of the output of the ground fault detector exceeds a predetermined first threshold value, the time corresponding to the period in which the positive level is exceeded. The rectangular wave output having the width is output to the first output terminal, and when the negative level of the output exceeds a predetermined negative threshold value, the rectangular wave output having the time width corresponding to the exceeding period is output to the second output terminal. , A triangular wave generating means for generating a triangular wave according to the rectangular wave output, and a pulse signal having a predetermined time width when the level of the triangular wave exceeds a predetermined third threshold value. A pulse generation circuit, an integration circuit that integrates the pulse signal, and a level discriminator that outputs an output signal that shuts off the electric path when the output level of the integration circuit exceeds a predetermined fourth threshold value are provided. It is a thing.

[Operation] In the present invention, the detection signal of the ground fault detector is separated into the positive and negative components, and when the triangular wave formed according to each component exceeds the predetermined third threshold value, A pulse signal is generated and integrated, and an output signal that interrupts the electric path when the integrated output does not exceed a predetermined fourth threshold value is not generated to prevent unnecessary operation.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention, in which (1) to (3) and (5) to (9) are exactly the same as the above-mentioned conventional apparatus. (4A) is a waveform shaping circuit connected to the ZCT (2), and has a positive first threshold value such as threshold TH ₃ and a negative first threshold value such as threshold TH ₄ for the level of the input signal. , When the positive or negative level of the input signal exceeds these thresholds, a rectangular wave output having a time width equal to the period in which the thresholds are exceeded is output to the first output terminal such as the positive output terminal (4A ₁ ) or The second output terminal, for example, the negative output terminal (4A ₂ ) is individually output. (10) is connected to a waveform shaping circuit (4A), and a triangular wave generating means for discriminating the time width of its output, for example, a signal width discrimination circuit, (11) is connected to a signal width discrimination circuit (10), and its output is It is a pulse generation circuit that generates a pulse signal of a predetermined time width when the threshold value exceeds three threshold values, for example, the threshold value TH ₅ .

In the ground fault detection device configured as described above, when the ground fault does not occur in the electric circuit (1), the ZCT (2) does not detect the ground fault current, so the circuit breaker (9) does not operate.

When a ground fault occurs in the electric line (1), a ground fault current with a waveform as shown in FIG. 2 (A) flows in the electric line (1), and this ground fault current is detected by the ZCT (2) and its output Figure 2 (B) on the side
A detection signal having a waveform as shown in is obtained. This detection signal is supplied to the waveform shaping circuit (4A), and when its level exceeds the positive threshold value TH ₃ and the negative threshold value TH ₄ , respectively, as shown in FIGS. 2 (C) and (D), respectively. A square wave output having a time width corresponding to the period when the level exceeds the thresholds TH ₃ and TH ₄ , respectively, is applied to the positive output terminal (4A ₁ ) and the negative output terminal (4A ₂ ) of the waveform shaping circuit (4A). Obtained respectively. These rectangular wave outputs are supplied to the signal width determination circuit (10),
The time width is determined, and a plurality of triangular waves as shown in FIG. 2 (E) are obtained at the output side of the signal width determination circuit (10).

The signal width determination circuit (10) is composed of a pair of constant current circuits (10a) and (10b) and a capacitor (10c) as shown in FIG. 4, and when the input signal is positive, the constant current circuit (10a) A current i ₁ is supplied to (10c), and when the input signal is negative, the current i ₂ is pulled from the capacitor (10c) into the constant current circuit (10b).

Returning to FIG. 1 again, the plurality of triangular waves from the signal width determination circuit (10) are supplied to the pulse generation circuit (11), and when the level of the triangular wave exceeds the threshold value TH ₅ , a predetermined time is output to the output side. A plurality of pulse signals having a width shown in FIG. 2 (F) are generated. These pulse signals are supplied to an integrating circuit (5), where they are sequentially added and integrated, and an output having a waveform as shown in FIG. 2 (G) is obtained at the output side thereof. This output is supplied to the level detector (6), and when the level exceeds a positive fourth threshold value of the level discriminator (6), for example, the threshold TH ₆ , the output of the level discriminator (6) is shown in FIG. A waveform output as shown in H) is obtained. This output is applied to the control electrode of the thyristor (7) to turn on the thyristor (7), and the electromagnetic device (8) is turned on by turning on the thyristor (7).
Is urged to open the circuit breaker (9) to cut off the electric circuit (11).

On the other hand, when the ground fault does not occur, it is as shown in Fig. 3 (A). However, for example, when the motor is started, the inrush current causes the secondary winding side of the ZCT (2) to move to the side of Fig. 3 (B). It is assumed that a current as shown occurs. Approximately 1 cycle unit of this current exceeds the thresholds TH ₃ and TH ₄ , respectively.
Waveform shaping circuit (4A) in the area beyond TH ₃ and TH ₄
Output terminals (4A ₁ ) and (4A ₂ ) of Fig. 3 (C), respectively.
And a rectangular wave output as shown in (D) is generated. These rectangular wave outputs are supplied to the signal width discriminating circuit (10) and discriminated on the time width side, and a plurality of triangular waves as shown in FIG. Is obtained. These triangular waves are supplied to the pulse generating circuit (11), and when the level of the triangular waves exceeds the threshold value TH ₅ , a plurality of pulse signals as shown in FIG. 3 (F) are generated at the output side thereof. . These pulse signals are supplied to the integrating circuit (5),
Here, the signals are sequentially added and integrated, and the output having the waveform as shown in FIG. 3 (G) is obtained. This output is fed to the level detector (6), where it is compared with a positive threshold TH ₆ . However, as can be seen from FIG. 3 (G), the level of the final output of the integrating circuit (5) is a positive threshold value TH ₆
Since it is lower, nothing is output from the level detector (6) as shown in FIG. 3 (H). As a result, since the thyristor (7) is not turned on, the electromagnetic device (8) is not energized, the circuit breaker (9) is not opened, and unnecessary operation is prevented.

In the above embodiment, the signal width discriminating circuit (10) is provided after the waveform shaping circuit (4A). Instead of this, as shown in FIG. 5, an integrating circuit (12) as a triangular wave generating means is provided. ) May be provided, and thus, the same operation and effect as those of the above-described embodiment can be obtained.

As described above, according to the present invention, when the positive level of the output of the ground fault detector exceeds the predetermined first threshold value, the rectangular waveform output of the time width corresponding to the period of the excess is output. When output to the first output terminal and the negative level of the output exceeds a predetermined negative threshold value, a rectangular wave output having a time width corresponding to the period of the output is output to the second output terminal. A waveform shaping circuit, a triangular wave generating means for generating a triangular wave according to a rectangular wave output, a pulse generating circuit for generating a pulse signal having a predetermined time width when the level of the triangular wave exceeds a predetermined third threshold value, and a pulse The equilibrium characteristic of ZCT is provided because it has an integrator circuit that integrates a signal and a level discriminator that outputs an output signal that shuts off the electric path when the output level of this integrator circuit exceeds a predetermined fourth threshold value. Transient high voltage such as inrush current at worst This has the effect of preventing unnecessary operation due to flow.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams for explaining the operation of FIG. 1, and FIG. 4 is a block showing an example of a main part of the present invention. Figure,
FIG. 5 is a block diagram showing another embodiment of the present invention, and FIG.
FIG. 7 is a block diagram showing an example of a conventional ground fault detection device.
FIG. 8 and FIG. 8 are waveform diagrams for explaining the operation of FIG. In the figure, (1) is a three-phase electric circuit, (2) is a zero-phase current transformer,
(4A) is a waveform shaping circuit, (5) and (12) are integrating circuits,
(6) is a level discriminator, (10) is a signal width discrimination circuit, (1
1) is a pulse generation circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A ground-fault detector for detecting a ground-fault current generated in an electric circuit, and a ground-fault detector connected to the ground-fault detector, when the positive level of its output exceeds a predetermined positive first threshold value. A rectangular wave output with a time width corresponding to the exceeding period is output to the first output terminal, and when the negative level of the output exceeds a predetermined negative second threshold value, the corresponding period is exceeded. Connected to the first output terminal and the second output terminal, and a waveform shaping circuit for outputting a rectangular wave output of a time width to the second output terminal,
Triangular wave generating means for generating a triangular wave according to the rectangular wave output, and a pulse which is connected to the triangular wave generating means and generates a pulse signal of a predetermined time width when the level of the triangular wave exceeds a predetermined third threshold value. A generating circuit, an integrating circuit connected to the pulse generating circuit to integrate the pulse signal, and an output connected to the integrating circuit to cut off the electric path when the output level exceeds a predetermined fourth threshold value. A ground fault detection device comprising: a level discriminator that outputs a signal.