JPH07108055B2 - Ground fault detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an improvement of a ground fault detection device provided in an AC electric circuit.

[Prior Art] A block diagram of a conventional ground fault detection device is shown in FIG. 7, and waveform diagrams showing its operation are shown in FIGS. 8 (a) to 8 (j). When a current of the waveform shown in FIG. 8 (a) flows in the three-phase electric line P due to a ground fault, the zero-phase current transformer 2 provided in the electric line P detects the current and is shown in FIG. 8 (b). A waveform detection signal is output. The output is input to the waveform shaping circuit 4, and when the level exceeds a predetermined positive threshold value TH ₁₀ ,
As shown in FIG. 8 (c), a pulse signal having a time width corresponding to the period in which the level exceeds the threshold value TH ₁₀ is output. This pulse signal is integrated in the integrating circuit 5 to form a triangular wave shown in FIG.
Entered in. When the level of the triangular wave exceeds the positive threshold value TH ₁₂ of the level discriminating circuit 6, a trapezoidal output having a predetermined time width shown in FIG.

This output is applied to the gate of the thyristor 7 to turn on the thyristor 7, energize the electromagnetic device 8 and activate the opening / closing part 1 connected to the electromagnetic device 8 by a mechanism (not shown) to cut off the electric path P.

On the other hand, when an impulse-shaped current such as a rectangular surge current having a high crest value but a long duration flows in the electric path P, the zero-phase current transformer 2
The current is absorbed by the capacitor 3 connected between the two output terminals, and when the value exceeds the positive threshold value TH ₁₀ , a rectangular wave output having a time width corresponding to the period is generated. However, when the time width of the output waveform of the waveform shaping circuit 4 is quadrature, the peak value when integrated becomes low. Therefore, by properly setting the threshold value of the level discriminating circuit 6, it does not occur as an output of the level discriminating circuit, and the thyristor 7 is not turned on.

[Problems to be Solved by the Invention] For example, when a current with a long negative connection time shown in FIG. 8 (f) flows in the electric path P due to a surge or noise,
The output waveform of the zero-phase current transformer 2 produces a positive level output as shown in FIG. 8 (g) due to its inductance. Then, in the portion of the waveform that exceeds the positive threshold value TH ₁₀ , the output of the waveform shaping circuit 4 produces a rectangular wave shown in FIG. This rectangular wave is integrated in the integrator circuit 5, and the result is shown in FIG.
And the positive threshold value TH ₁₂ of the level discrimination circuit 6 is obtained.
When it exceeds, a rectangular wave output having a predetermined time width shown in FIG. 8 (j) is generated. As a result, this output causes the thyristor 7 and the electromagnetic device 8 to operate to drive the opening / closing unit 1 as in the case of the ground fault current.

The ground fault detection device preferably operates only when a ground fault occurs, and must be a device that does not cause unnecessary operation due to surge or noise.

[Means for Solving the Problem] A ground fault detection device according to a first aspect of the present invention detects a ground fault current of an electric circuit by a zero-phase current transformer, and a positive level of a detection output is a predetermined positive threshold value. A waveform shaping circuit that generates a rectangular wave output at the first output end when it exceeds the threshold value, and generates a rectangular wave output at the second output end when the negative level of the output exceeds a predetermined negative threshold value. The output of the first output terminal is integrated by the first integrating circuit, the output of the second output terminal is integrated by the second integrating circuit, and the output level of the first integrating circuit is a predetermined threshold value. When the output levels of the first pulse generation circuit and the second integration circuit that output a pulse signal having a connection time that exceeds ½ of the cycle of the current flowing through the electric path exceed a predetermined threshold value. A pulse having a duration of more than half the period of the current flowing in the circuit A second pulse generating circuit that outputs a signal is provided, and an AND gate that obtains a logical product of outputs of the first pulse generating circuit and the second pulse generating circuit is provided.

The ground fault detecting device of the second invention of the present invention detects the ground fault current of the electric circuit by the zero-phase current transformer, and when the positive level of the detection output exceeds a predetermined positive threshold value, A rectangular wave output is generated at the output end, and a waveform shaping circuit that generates a rectangular wave output at the second output end when the negative level of the output exceeds a predetermined negative threshold value is provided. The output of the first
And the output of the second output terminal is integrated by the second integrator circuit, and when the output level of the first integrator circuit exceeds a predetermined threshold value, about 4 times the cycle of the current flowing through the electric circuit When the output level of the first pulse generating circuit and the second integrating circuit, which output a pulse signal having a duration of one-half, exceeds a predetermined threshold value, about one-fourth of the cycle of the current flowing through the electric line. A second pulse generating circuit that outputs a pulse signal of a duration is provided, and the output pulse of the first pulse generating circuit is delayed by a time delay circuit that exceeds ½ of the cycle of the current flowing through the electric circuit, A gate for obtaining a logical product of the outputs of the pulse generation circuit and the delay circuit is provided.

[Operation] In the present invention, the detection signal of the zero-phase current transformer is separated into the positive and negative components, and when the signal obtained by integrating the respective components exceeds the respective predetermined threshold values, each pulse having a predetermined duration Since the signals are generated and the two signals are synchronized to obtain the logical product of the two pulse signals, the ground fault detection device operates only when both components exceed a predetermined threshold value and have a predetermined time difference.

[Embodiment] A block diagram of a ground fault detection apparatus according to the first invention of the present invention is shown in FIG. 1, and waveform diagrams showing its operation are shown in FIGS. 2 (a) to 2 (r). When a current of the waveform shown in FIG. 2 (a) flows in the three-phase electric line due to a ground fault, the zero-phase current transformer 2 provided in the electric line P detects the electric current and is shown in FIG. 2 (b). A waveform detection signal is output. This detection signal is input to the waveform shaping circuit 9. The waveform shaping circuit 9 is set with a positive threshold TH ₁ and a negative threshold TH ₂ with respect to the level of the input signal, and when the positive or negative level of the input signal exceeds these thresholds, the threshold is exceeded. The pulse output having a time width equal to the current period is individually output to the positive or negative terminal. The output waveform of the positive terminal of the waveform shaping circuit 9 is shown in FIG. 2 (c), and the output waveform of the negative terminal is shown in FIG. 2 (f).

The outputs of the positive terminal 9a and the negative terminal 9b of the waveform shaping circuit 9 are input to the integrating circuits 5a and 5b, respectively, and are integrated. FIG. 2 (d) shows the output waveform of the integrating circuit 5a, and FIG. 2 (g) shows the output waveform of the integrating circuit 5b.

Next, the outputs of the integration circuits 5a and 5b are pulse generation circuits, respectively.
Input to 10a and 10b. Pulse generation circuit 10a and 10b are respectively set predetermined threshold value TH _3, TH ₄ with respect to the input level, the input level is adapted to produce an output exceeds a respective threshold. Pulse generator circuit 10a
The duration of the outputs of 10 and 10b is set to a time slightly longer than one half of the period of the ground fault current of the circuit P to which the ground fault detector is applied. The waveforms are shown in FIGS. 2 (e) and 2 (h), respectively.

These outputs are input to the AND circuit 12, but both are output during the period of time t as shown in FIGS. 2 (e) and 2 (h), so that the AND circuit 12 produces an output. This output is applied to the gate of thyristor 7 to turn it on. As a result, power is applied to the electromagnetic device 8 from a power source (not shown), and the circuit breaker switch 1 is opened via a mechanism (not shown).

On the other hand, when a lightning surge current as shown in FIG. 2 (j) flows in the electric path P, the zero-phase current transformer 2 produces an output having the waveform shown in FIG. 2 (k). This output is shaped by the waveform shaping circuit 9 as in the case of the ground fault current, and the positive terminal 9a
2 (l), and the signal having the waveform shown in FIG. 2 (o) is output to the negative terminal 9b.

Both signals are integrated by the respective integrating circuit 5a or 5b,
Outputs of the waveforms shown in FIGS. 2 (m) and 2 (p) are obtained, respectively. These outputs are inputted to the respective pulse generating circuits 10a and 10b, but since the input level of the pulse generating circuit 10a has not reached the threshold value TH ₃ thereof, the pulse generating circuit 10a is set as shown in FIG. 2 (n). No output is produced. On the other hand, the pulse generating circuit 10b produces the output shown in FIG. These outputs are input to the AND circuit 12, but since the pulse generation circuit 10a does not generate an output, the AND circuit 12
Does not produce an output and therefore the thyristor 7 does not turn on.

That is, the ground fault detector of the present invention does not operate due to a lightning surge having a waveform as shown in FIG. 2 (j).

FIG. 3 shows an actual circuit example of the waveform shaping circuit 9. In the figure, transistors 12-1 and 12-2 and a constant current source 12-3 constitute a general differential amplifier.
Both ends of the zero-phase current transformer 2 are connected between the bases −1 and 12-2. The collectors of the transistors 12-1 and 12-2 are connected to the input terminals of the level discriminating circuits 13 and 14, respectively. As the level discrimination circuits 13 and 14, for example, an amplifier circuit or the like to which a predetermined emitter bias voltage is applied is used.

FIG. 4A is a circuit diagram showing another specific example of the waveform shaping circuit 9. In the figure, the positive level output of the zero-phase current transformer 2 is the transistors 21-1, 21-2 and 21-3, the diode.
It is amplified and shaped by the high-gain amplifier 21 composed of 21-4 and the constant current source 21-5, and the output of the waveform shown in FIG. 2 (c) is obtained from the collector of the transistor 21-2.

Also, the negative level output of the zero-phase current transformer 2 is the transistor
22-1, 22-2, 22-3, diode 22-4 and constant current source
It is amplified and shaped by the high-gain amplifier 22 composed of 22-5, and the output of the waveform shown in FIG. 2 (f) is obtained from the collector of the transistor 22-2.

In the waveform shaping circuit 9 shown in FIG.
The thresholds TH ₁ and T are set by resistors 23 and 24 that set the bias of the base of 21-1 and resistor 25 that uses the input offset voltage
H ₂ is set.

A block diagram of the ground fault detection apparatus of the second invention of the present invention is shown in FIG. 5, and waveform diagrams showing its operation are shown in FIGS. 6 (a) to 6 (t). In the figure, the waveform shaping circuit 9, the integrating circuits 5a and 5b, and the AND circuit 12 are equivalent to those of the first invention. In the present invention, the pulse generation circuits 10a and 10b have their input levels respectively set to the threshold value TH
_{When 3} and TH ₄ are exceeded, a rectangular wave signal having a duration of about ¼ of the cycle of the current in the electric path P is output regardless of the magnitude of the input level. This waveform is shown in FIGS. 6 (e) and 6 (i).

Next, the output of the pulse generation circuit 10a is input to the delay circuit 11. In the delay circuit 11, as shown in FIG.
The output of the pulse generation circuit 10a (FIG. 6 (e)) is delayed by a time t _d which is one half of the cycle of the current in the electric path P. As a result, the timing of the output of the delay circuit 11 (Fig. 6 (f)) and the timing of the output of the pulse generation circuit 10b (Fig. 6 (i)) are matched and applied to the AND circuit 12 to generate an AND output. The subsequent operation is equivalent to that of the first invention.

In the ground fault detector of the second invention, when the impulse due to the lightning surge shown in FIG. 6 (k) is input, the zero-phase current transformer 2 produces the output of the waveform shown in FIG. 6 (l). This output is input to the waveform shaping circuit 9, and the output of the waveform shown in FIG. 6 (m) and FIG. 6 (q) is obtained. These outputs are integrated by respective integrating circuits 5a and 5b to generate outputs having the waveforms shown in FIGS. 6 (n) and 6 (r). The outputs of the integration circuits 5a and 5b are the pulse generation circuits 10a and 10b, respectively.
To the output of the waveforms shown in FIGS. 6 (o) and 6 (s) for the duration of the quarter cycle.

Next, the output of the pulse generation circuit 10a is delayed by the delay circuit 11 for a time t _{d of} about a half cycle. The output waveform of the delay circuit 11 is shown in FIG. As is apparent from the figure, the output of the delay circuit 11 (FIG. 6 (p)) and the pulse generation circuit 10b.
Since the output of the above (FIG. 6 (s)) does not coincide in timing, the AND output does not occur even when both outputs are applied to the AND circuit 12. As described above, also in the present invention, the ground fault detection device does not operate due to the irregular impulse input as shown in FIG. 6 (k).

[Advantages of the Invention] In the first and second aspects of the present invention, a signal based on the positive and negative components of the signal detected by the zero-phase current transformer (2) is output by a waveform shaping circuit having a predetermined threshold value. It is judged individually that the ground fault has occurred only when the integrated output of both signals is above a predetermined level and the timings match, so if the positive and negative levels such as impulse due to lightning surge are significantly different, the ground fault will occur. The circuit breaker is not activated without judging that

[Brief description of drawings]

FIG. 1 is a block diagram of the first invention, FIGS. 2 (a) to 2 (r) are waveform diagrams showing the operation of the first invention, and FIG. 3 is a concrete circuit diagram of a waveform shaping circuit. FIG. 4 is another specific circuit diagram of the waveform shaping circuit, FIG. 5 is a block diagram of the second invention, and FIGS. 6 (a) to 6 (t) show the operation of the second invention. The waveform diagram shown in FIG. 7 is a block diagram of a conventional ground fault detection device, and FIG. 8 (a).
~ Fig.8 (j) is a waveform diagram which shows operation | movement of the conventional ground fault detection apparatus. In the figure, 2 is a zero-phase current transformer, 9 is a waveform shaping circuit, 5a and 5b are integrating circuits, 10a and 10b are pulse generating circuits, and 11 is a delay circuit.

Claims (2)

[Claims] 1. A zero-phase current transformer for detecting a ground-fault current in an electric circuit, and when the output of the zero-phase current transformer is input and the positive level of the output exceeds a predetermined positive threshold value, it exceeds the threshold value. When a rectangular wave output having a time width corresponding to a certain period is output to the first output terminal and the negative level of the output exceeds a predetermined negative threshold value, the time corresponding to the exceeding period. A waveform shaping circuit for outputting a rectangular wave output having a width to a second output end; a first for connecting to the first output end and integrating the rectangular wave output
Second integrating circuit, which is connected to the second output terminal and integrates the rectangular wave output
An output circuit of the first integrating circuit, and outputs a pulse signal having a duration exceeding ½ of the cycle of the current flowing through the electric circuit when the output level of the first integrating circuit exceeds a predetermined threshold value.
A pulse generating circuit of the second integrating circuit, and when the output level of the second integrating circuit exceeds a predetermined threshold value, outputs a pulse signal having a duration exceeding one half of the cycle of the current flowing through the electric circuit. Two
And a AND gate that obtains a logical product of the outputs of the first pulse generating circuit and the second pulse generating circuit. 2. A zero-phase current transformer for detecting a ground fault current in an electric circuit, and when the output of the zero-phase current transformer is input and the positive level of the output exceeds a predetermined positive threshold value, the voltage exceeds the threshold value. When a rectangular wave output having a time width corresponding to a certain period is output to the first output terminal and the negative level of the output exceeds a predetermined negative threshold value, the time corresponding to the exceeding period. A waveform shaping circuit for outputting a rectangular wave output having a width to a second output end; a first for connecting to the first output end and integrating the rectangular wave output
Second integrating circuit, which is connected to the second output terminal and integrates the rectangular wave output
And an output of the first integrator circuit is input, and when the output level exceeds a predetermined threshold value, the first integrator circuit outputs a pulse signal having a duration of about one quarter of the cycle of the current flowing through the electric circuit. The pulse generator circuit, the second integrator circuit output is input, and when the output level exceeds a predetermined threshold value, a second pulse signal having a duration of about one quarter of the cycle of the current flowing through the electric circuit is output. A pulse generating circuit, a delay circuit delaying the output pulse of the first pulse generating circuit for more than half the cycle of the current flowing through the electric path, and a logical product of the outputs of the second pulse generator and the delay circuit Ground fault detection circuit including AND gate.