JPH0817532B2 - Ground fault detector - Google Patents

Description

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

[Prior Art] FIG. 4 is a block diagram showing the structure of a conventional ground fault detecting device disclosed in, for example, Japanese Patent Laid-Open No. 64-148015, and FIG. 5 is a general operation explanation waveform diagram of the conventional device. FIG. 6 is a waveform diagram for explaining the operation of the conventional device for the equilibrium characteristic due to the inrush 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), (19) is a second level discriminator for receiving the output from the signal width discriminator (12), (20) ) Is a capacitor.

The operation of the ground fault detection device configured as described above will be described with reference to the drawings. FIG. 5 shows the case of general ground fault detection. In FIG. 5, (a) shows the ground fault component of the AC circuit (1), and (b) shows the output of the zero-phase current transformer (6).

When the output (b) of the zero-phase current transformer (6) exceeds the determination level (TH1) of the first level discriminator (10), the constant current source of the first level discriminator (10) causes a constant current. Is output and the capacitor (20) is charged at a specified rate, and the voltage across the terminals of the capacitor (20) gradually rises as shown in (d) of FIG. After a lapse of a predetermined time (Td), the inter-terminal voltage of the capacitor (20) reaches the discrimination value (TH2), and the second level discriminator (19) outputs the output of (e) of FIG. 5 to the switching element (8). And the switching device (8) is operated to trip the circuit breaker (5) via the electromagnetic device (7) to interrupt the AC electric circuit (1).

Between the terminals of the capacitor (20) when the output (b) of the zero-phase current transformer (6) exceeds the determination level (TH1) of the first level discriminator (10) for less than a predetermined time (Td) Since the voltage does not reach the discriminant value (TH2), the second level discriminator (1
There is no output to 9) and switching element (8) is not triggered. The output (b) of the zero-phase current transformer (6) is the first
If the judgment level (TH1) of the level discriminator (10) is not reached, the capacitor (20) is not charged and the switching element (8) is naturally not activated.

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

The zero-phase current transformer (6) logically 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 arrangement of the primary winding, and a current that cancels this is generated in the secondary winding, causing a slight secondary output, which is called the balanced characteristic. ing. Since the normal secondary output does not meet the determination level (TH1) of the first level discriminator (10), the switching element (8) is not triggered. 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) is exceeded, and the ground fault detection device operates unnecessarily.

[Problems to be Solved by the Invention] As described above, in the conventional ground fault detection device, there is a problem that the ground fault detection device operates unnecessarily due to the inrush current of the electric motor due to the equilibrium characteristic of the zero-phase current transformer. there were.

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 Problems] A ground fault detection device according to the present invention is a positive signal that outputs an output signal when a predetermined magnitude is exceeded for each waveform on the positive side and the negative side of the ground fault component of a zero-phase current transformer. Side and negative side level discriminators, positive side and negative side pulse generators that output a pulse signal by discriminating over a predetermined time width of the output signal of the level discriminator, a capacitor and discharge of this capacitor Positive side and negative side pulse counters that have a resistor and that output the output signal when the voltage of the capacitor reaches the set value by integrating the positive side and negative side pulse signals respectively, the positive side pulse counter and the negative side pulse And an AND circuit that outputs an output for operating the switching element when the logical product of the outputs from the counter is established.

[Operation] In the ground fault detection device according to the present invention, the level discriminator and the signal discriminator each have a predetermined magnitude and a predetermined time width or more separately for the positive side and negative side ground fault components of the zero-phase current transformer. Based on this determination result, the pulse counter integrates the pulse signals output by the pulse generator and outputs an output signal when the capacitor voltage reaches the set value, and the AND circuit outputs the positive side and negative side pulse counters. When the logical product of the outputs is established, an output for activating the switching element is output, and the integrated value of the pulse counter is reset when the discharge resistance of the capacitor has not received a pulse signal input for a predetermined time or longer.

[Embodiment] FIG. 1 is a configuration block diagram 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 an inrush of the embodiment. It is an operation | movement explanatory waveform diagram with respect to the balance characteristic by an electric current.

In the figure, (1) to (8) and (20) are the same as those described in the conventional example.

(9) is a waveform shaping circuit that inputs the output of the zero-phase current transformer (6) in both positive and negative directions, and (10) is one of the outputs of the zero-phase current transformer (6) after the shaped waveform. Is a positive level discriminator that outputs an output signal when the magnitude of the waveform is above a predetermined decision level (TH1), and (11) is the magnitude of the other waveform of the output of the zero-phase current transformer (6) after the shaped waveform. Negative side level discriminator that outputs an output signal when is above a predetermined determination level (TH3),
(12) is a positive side signal width discriminator for discriminating whether or not the time width of the output signal of the positive side level discriminator (10) is a predetermined time or more,
(13) is a negative side signal width discriminator for discriminating whether or not the time width of the output signal of the negative side level discriminator (11) is a predetermined time or more,
(14) and (15) are a positive-side pulse generator and a negative-side pulse generator that output corresponding pulse signals when a predetermined time or longer is determined by the signal width discriminators (12) and (13). . (16) and (17) are pulse generators (14) and (1
5) The pulse signal from the capacitor (16a) second
Is a positive-side and negative-side pulse counter that outputs an output signal when the voltage is accumulated in the capacitor (17a) and reaches a predetermined set voltage. (16b) is the discharge resistance of the capacitor (16a), (17
b) is the discharge resistance of the second capacitor (17a), and these discharge resistances (16b) and (17b) are capacitors (16a) and (17b).
When the electric charge accumulated in a) is gradually discharged and there is no pulse signal for a predetermined time, both pulse counters (16), (1
7) is reset to the initial value. (18) is an AND circuit,
It outputs an output signal for operating the switching element (8) when the logical product of the outputs of both pulse counters (16) and (17) is established.

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, and FIG. 2 (b) shows the output of the zero-phase current transformer (6) after the shaping waveform. When this output exceeds the determination level (TH1) of the positive side level discriminator and the determination level (TH3) of the negative side level discriminator (11), the signal outputs of (c) and (f) of FIG. 2 are obtained. The output (c) and the output (f) are output from the capacitor (2) in the respective signal width discriminators (12) and (13).
When the inter-terminal voltage of (0) reaches the discriminant values (TH2) and (TH4), the pulse signals of (e) and (h) in the figure are output from the pulse generators (14) and (15). Both pulse counters (1
6) and (17), the pulse signals input to them are respectively integrated into the capacitor (16a) and secondly to the capacitor (17a), and when the set voltages (TH5) and (TH6) are reached, (j) in the figure,
It becomes the output of (l). The outputs (j) and (l) are input to the AND circuit (18), and when the logical product is established, the output (m) in the figure is output, and the output (m) activates the switching element (8). Then, the circuit breaker (5) is pulled out via the electromagnetic device (7) to interrupt the AC electric circuit (1).

Next, the operation at the time of the balance characteristic due to the inrush current will be described with reference to FIG.

In this case, it is not a ground fault or an electric leakage, so the AC circuit (1)
There is no ground fault component (a).

Due to the inrush current, the zero-phase current transformer (6) has the output shown in FIG. 3 (b). This output (b) generally has a high level at first, but it decays quickly, and the output of the zero-phase current transformer (6) exceeding the level (TH1) and (TH3) of the level discriminators (10) and (11) is It is several Hz, and the signal width discriminators (12) and (13) have a third
It becomes the input of (c) and (c) 'in the figure.

A signal width discriminator (12) based on these inputs (c) and (c) ',
The internal waveform of (13) becomes (d) and (f) of FIG. 3, the pulse generator (14) outputs the pulse signal of (e) of FIG. 3, and the pulse generator (15) outputs the pulse signal (g). ) Is output. This is the pulse counter (16), (17) capacitor (16
The states in which a) and (17a) are integrated are (h) and (k) in Fig. 3, respectively, and the capacitor (16a) is set to the set voltage (T
H5), but the second capacitor (17a) does not reach the set voltage (TH6), and the AND circuit (18) has only one input, so that it does not output an output for activating the switching element (8). Therefore, it becomes difficult to perform unnecessary operation due to the inrush current due to the balance characteristic.

In the above explanation, the waveforms that exceed the determination levels (TH1) and (TH3) of the level discriminators (10) and (11) are three times (1.5H).
Although the case of z) is shown, it can be set to an arbitrary number of times by appropriately setting the set voltages (TH5) and (TH6) of the capacitors (16a) and (17a).

[Effects of the Invention] As described above, according to the present invention, the positive-side and negative-side levels that output an output signal when the positive and negative waveforms of the ground fault component of the zero-phase current transformer exceed a predetermined magnitude. The positive side and negative side pulse generators that output a pulse signal by discriminating with the signal discriminator a predetermined time width or more of the output signal of the discriminator, a capacitor and a discharge resistance of this capacitor Switching when the logical product of the positive side and negative side pulse counters that output the output signal when the voltage of the capacitor reaches the set value by integrating the pulse signals and the output from the positive side pulse counter and the negative side pulse counter is established. By including an AND circuit that outputs an output for operating the element, it is possible to provide a ground fault detection device that is less likely to perform an unnecessary operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of a ground fault detecting device according to an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams for explaining the operation of the embodiment, and FIG. 4 is a structure of a conventional ground fault detecting device. Block diagrams, FIGS. 5 and 6 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) is a switching element, (9) is a waveform shaping circuit,
(10) and (11) are level discriminators, (12) and (13) are signal width discriminators, (14) and (15) are pulse generators, (16),
(17) is a pulse counter, (16a) and (17a) are capacitors, (16b) and (17b) are discharge resistors, and (18) is an AND circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A ground fault detection device that operates a switching element when a ground fault component of a zero-phase AC device that is electromagnetically coupled to an AC power line and detects a ground fault of the AC power line has a predetermined magnitude or more. A positive side level discriminator and a negative side level discriminator that output an output signal when the positive side and negative side waveforms of the ground fault component that is the output exceed a predetermined magnitude for each of the output signals of the positive side level discriminator. Positive side signal discriminator that discriminates a predetermined time width or more, positive side pulse generator that outputs a pulse signal by discrimination of the positive side signal discriminator, a capacitor and a discharge resistance of this capacitor, and integrates the above pulse signal. Positive side pulse counter that outputs an output signal when the voltage of the capacitor reaches a set value, a negative side signal discriminator that discriminates a predetermined time width of the output signal of the negative side level generator, and this negative side signal Discriminator discrimination When a negative side pulse generator that outputs a more pulse signal, a second capacitor, and a discharge resistance of the second capacitor are provided and the pulse signals are integrated and the voltage of the second capacitor reaches a set value A ground fault characterized by comprising a negative pulse counter that outputs an output signal, and an AND circuit that outputs an output that operates the switching element when the logical product of the outputs of the negative pulse counter and the positive pulse counter is established. Detection device.