JPH04178109A - Eatrh leakage breaker - Google Patents

Abstract

PURPOSE:To stabilize rated current sensitivity by detecting the level of a ground current flowing through an AC feeder line by means of an integrated circuit, processing comparison results with respective reference values through a signal processing circuit every positive and negative half wave of output thereby generating a trip signal. CONSTITUTION:Ground currents flowing through AC feeder lines 1a-1c are detected through a zero-phase current transformer 6 and a voltage Vd across a resistor 7 is detected 5 and fed to an integrated circuit IC2l for detecting leakage. The voltage Vd is amplified 23 to produce a voltage VD while positive and negative half waves are fed to first and second comparators 24, 25 where they are compared with positive and negative reference values E1, E2. Every time when the VD exceeds the reference value, a capacitor 14 is charged through an OR circuit 26. During an interval when the VD is low, the capacitor 14 is discharged to boost the voltage Vc in step and when the operating voltage of a latch circuit 30 is exceeded, a trip signal St is outputted to turn a thyristor 11 ON so as to short-circuit a rectifying circuit 10 thus energizing a coil 9 and opening main contacts 2a-2c. According to the constitution, rated sensitivity current is stabilized even if an offset voltage is present in an IC circuit 21.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an earth leakage breaker that opens a main contact interposed in a load power supply path in response to a ground fault current. In particular, the present invention relates to an earth leakage breaker using an earth leakage detection integrated circuit to determine the presence or absence of a ground fault current.

(Prior Art) FIG. 4 shows a general configuration example of an earth leakage breaker. In FIG. 4, three-phase main circuit conductors 18 to 1c, which are load power supply paths, are connected at one end to power supply side terminals 3a to 3c via main contacts 2a to 2c, and at the other end to the load side. Connected to terminals 4a to 4C. The ground fault current detection circuit 5 as a detection means includes a zero-phase current transformer 6 provided to detect the ground fault current flowing through the main circuit conductors 1a to 1c.
and a current sampling resistor 7 connected between the output terminals of this zero-phase current transformer 6, and the detection voltage Vd obtained from both ends of the resistor 7 is connected to an earth leakage detection integrated circuit (hereinafter referred to as earth leakage I).
(abbreviated as C) 8 between terminals Z1 and 22.

The tripping coil 9, which is the drive source of the tripping device (not shown), performs a tripping operation of opening the main contacts 2a to 2c when a current exceeding the rated value is supplied. It is connected to the circuit conductor 1c, and the other end is connected to one AC input terminal of the full-wave rectifier circuit 10. The other AC input terminal of the aftereffect rectifier circuit 10 is connected to, for example, the main circuit conductor 1a, and the positive polarity line 1 derived from each positive and negative output terminal of the full wave rectifier circuit 10 is connected to the main circuit conductor 1a.
A thyristor 11 of the illustrated polarity is connected between 0a and the negative polarity line 10b, and a series circuit of a current limiting resistor 12 and a smoothing capacitor 13 is also connected.

In this case, in the earth leakage IC 8, the positive polarity line 10a
and the negative polarity line 10b through the current limiting resistor 12 (a configuration in which the power supply terminal Vcc and the ground terminals G to D are connected to both ends of the capacitor 8), and for signal output. Thyristor 11 is connected to terminal P of
cable terminal is connected. Further, a terminal for an external element of the earth leakage IC 8 is connected to a ground terminal GND via an external signal processing capacitor 14.

The internal configuration of such earth leakage IC 8 is as shown in FIG. That is, in FIG. 5, the terminals Vcc and GND
A power supply circuit 15 connected to the power supply circuit 15 serves as a power source for a comparator 16 and a latch circuit 17 made up of operational amplifiers, and is provided to stabilize the power supply voltage.

As shown in FIG. 6, the comparator 16 has terminals Zl,
When the detection voltage Vd applied between 22 and 22 exceeds a predetermined judgment value Ed, the circuit is inverted to a state in which an I\I level signal is output. This comparator 16
A resistor 18 is connected between the output terminal and the terminal, and a series circuit of a diode 19 and a resistor 20 of the polarity shown is connected in parallel with the resistor 18. Latch circuit 1
7 is a voltage signal from the terminal, that is, the capacitor 14
When the terminal voltage Vc exceeds a predetermined operating level Ec, it is inverted to output a high level signal and maintains that state. And such latch circuit 1
The high level signal from 7 is output from the terminal P as a trip signal St.

The earth leakage breaker configured as described above operates as follows.

That is, the earth leakage IC 8 is supplied with power from between the main circuit conductors 1a and lc via the tripping coil 9, the full-wave rectifier circuit 10, and the current limiting resistor 12, and becomes operational. In this case, since a current exceeding the rated value is not supplied to the tripping coil 9, the tripping operation of the main contacts 2a to 2c is not performed. On the other hand, the main circuit conductor 18~IC
When a ground fault current flows through the ground fault current, it is detected by the zero-phase current transformer 6, and is converted by the resistor 7 into a detection voltage Vd of a level corresponding to the ground fault current, and this detection voltage is applied to the terminal of the IA electric IC 8. Given between Z1.22.

In this case, in the earth leakage IC8, the comparator 16
starts to compare the level of the detection voltage Vd with the judgment level -Ed, and the comparison output is inverted to a high level signal every time the relationship Vd<-Ed (Fig. 6(a), (b)
)reference). In this case, during the period when the comparator 16 outputs the 7 During the output period, the charge in the capacitor 14 is discharged via the resistor 18 with a relatively long time constant, and accordingly, the terminal voltage Vc of the capacitor 14 increases as shown in FIG. 6(c). It begins to rise in a stair-like manner.

In this way, when the terminal voltage VC of the capacitor 14 exceeds the operating voltage Ec of the latch circuit 17, as shown in FIG.
), the latch circuit 17 maintains the state in which it outputs the high level signal, and the high level signal is output from the terminal P as the trip signal St.

Then, the thyristor 11 is turned on and the positive and negative output terminals of the full-wave rectifier circuit 10 are short-circuited, so that a current exceeding the rated value is supplied to the tripping coil 9. Then, a tripping operation is performed in which the main contacts 2a to 2C are opened.

(Problem to be solved by the invention) In this type of earth leakage breaker, the level of the detection voltage Vd is relatively low at about 10 mV in the tripping operation, and therefore,
It is necessary to make a level judgment of about 10 mV using the comparator 16 in the earth leakage IC 8. However, there is generally an offset voltage in the comparator 16 made of an operational amplifier, and this offset voltage
6, which causes a level determination error, that is, an error in the rated sensitivity current of the earth leakage breaker.

That is, when a positive offset voltage exists in the comparator 16, for example, the relationship between the detection voltage Vd and the determination level -Ed changes, as shown in FIGS. The period during which a high level signal is output is shortened, and in this case, the capacitor 14
The terminal voltage Vc of the latch circuit 17 no longer reaches the operating voltage Ec of the latch circuit 17 (see FIG. 7(c) 2). Therefore, in such a case, as shown in FIG. 7(d), the child circuit 17 continues to output the low level signal and the above-mentioned tripping operation is not performed, resulting in a decrease in sensitivity. This causes an increase in current. On the other hand, if a negative offset voltage exists in the comparator 16, the sensitivity current will decrease.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a B-type breaker that can stabilize the rated sensitivity current even when an offset voltage exists in the earth leakage detection integrated circuit. is to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for tripping when a detected voltage indicating a ground fault current flowing through an AC load supply path exceeds a set level. In an earth leakage breaker comprising an earth leakage detection integrated circuit that outputs a signal, and a tripping device that opens a main contact interposed in the load power supply path when the tripping signal is output, the earth leakage detection integrated circuit The circuit includes a first comparator that outputs a judgment signal when the positive half wave of the detected voltage is at a predetermined level or higher, and a second comparator that outputs a judgment signal when the negative half wave of the detected voltage is at a predetermined level or higher. , and a signal processing circuit that generates the trip signal based on determination signals from the first and second comparators.

(Function) When a ground fault current flows through the load power supply path, a detection voltage having a level corresponding to the ground fault current is outputted from the detection means and applied to the j2i voltage ratio detection product circuit. In the earth leakage detection integrated circuit, when the positive half-wave of the input detection voltage is at a predetermined level or higher, a judgment signal is output from the first humparator, and when the negative half-wave of the detection voltage is at a predetermined level or higher, a judgment signal is output. A determination signal is output from the second comparator. Then, when a determination signal is output from at least one of the first and second comparators, the signal processing circuit generates a tripping signal, thereby performing a tripping operation. In this case, since the determination signal is obtained by separately determining the levels of the positive half-wave side and the negative half-wave side of the detection voltage, even if there is an offset voltage in each comparator, the offset voltage is canceled out. The sensitivity current becomes stable.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3. However, since there are parts in FIG. 1 that are the same as those in FIG. 4, the description thereof will be omitted by giving the same reference numerals as in FIG. 4.

In the earth leakage detection integrated circuit (hereinafter referred to as leakage 4IC) 21 shown in FIG. 1, a power supply circuit 22 connected to terminals vCC and GND supplies stable power to each internal circuit element described below. It is set in.

That is, the amplifier circuit 23 is provided to amplify the detection voltage Vd applied between the terminals Zl and 22, and the amplified output is sent to the non-inverting input terminal (+) of the first comparator 24 and the second is applied to the inverting input terminal (-) of the comparator 25. Each of the comparators 24 and 25 is composed of an operational amplifier, and the first reference voltage E1 at a positive level is applied to the inverting input terminal (-) of the first conoparator 24, and the non-inverting input terminal of the second comparator 25 Terminal (
+) is given a second reference voltage E2 of a negative level.

Incidentally, the reference voltages El and E2 are set to have substantially equal absolute values.

Each output terminal of the comparators 24 and 25 is connected to the OR circuit 2.
A resistor 27 is connected between the output terminal and the terminal of the OR circuit 26, and a diode 28 with the polarity shown and a resistor 29 are connected in series in parallel with the resistor 27. The circuit is connected. The latch circuit 30, which is a signal processing circuit, receives the terminal voltage Vc of the capacitor 14 through a terminal, and when the terminal voltage VC exceeds a predetermined operating level Ec, the latch circuit 30 is inverted to output a high-level signal. At the same time, the state is maintained. And such a latch circuit 30
The high level No. 15 from the terminal P is output from the terminal P as the trip signal St.

In the above configuration, when a ground fault current flows through the main circuit conductor 1a to IC, a detection voltage Vd of a level corresponding to the ground fault current is applied between the terminals Zl and 22 of the earth leakage IC 20, and the detection voltage Vd is amplified by the amplifier circuit 23 and output as a detection voltage VD.

Here, in FIG. 2, the amplifier circuit 23, each comparator 2
Earth leakage I when there is no offset voltage in 4 and 25
The output voltage waveforms of each part in the IC 20 are shown, and FIG. 3 shows the output voltage waveforms of each part in the leakage IC 20 when there is an offset voltage in the amplifier circuit 23 and each comparator 24, 25.

Therefore, in the earth leakage IC 20, the first comparator 24 compares the level of the detection voltage VD with the first reference voltage El having a positive level, and the comparison output (and thus the output of the OR circuit 26) is VD >El, the signal is inverted to a high level, and the second comparator 25 starts to compare the level of the detection voltage VD with the second reference voltage E2 of negative level, and the comparison output (as well as O
The output of the R circuit 26) is inverted to a high level signal every time the relationship VD<E2 (Fig. 2(a),
(b), see FIGS. 3(a) and (b)).

In this case, during the period when a high level signal is output from each comparator 24%, the resistor 27 is connected to the capacitor 14.
．． During the period when a low level signal is output from the comparators 24 and 25, the charge in the capacitor 14 is charged via the resistor 27 with a relatively short time constant. Accordingly, the terminal voltage VC of the capacitor 14 becomes the second voltage.
As shown in Figure (c) or Figure 3 <c>, it rises in a stepwise manner.

In this way, when the terminal voltage Vc of the capacitor 14 exceeds the operating voltage Ec of the latch circuit 30, as shown in FIG.
) or as shown in FIG. 3(d), the latch circuit 30
The output state of the high-level signal is maintained, and the high-level signal is output to the terminal P as the trip signal St.
is output from.

Then, the thyristor 11 is turned on and the positive and negative output terminals of the full-wave rectifier circuit 10 are short-circuited, so that a current exceeding the rated value is supplied to the tripping coil 9, and accordingly A tripping operation is performed in which the main contacts 2a to 2c are opened.

Therefore, during the above-described tripping operation, if there is no offset voltage in the amplifier circuit 23 and each comparator 24.25, the respective times tl and t2 at which a high level signal is output from the comparator 24.25 are as follows. Figure 2(b)
As shown in FIG. The difference will be shown in b). However, in this case, the time t
1. Since the total time t2 is approximately equal, the rising speed of the terminal voltage Vc of the capacitor 14 is approximately equal, and as a result, the timing at which the latch circuit 30 outputs the trip signal St is determined by the offset in the amplifier circuit 23, etc. Regardless of the presence or absence of voltage, the sensitivity current of the iA interrupter is stabilized because it is approximately the same.

In this case, since the amplifier circuit 23 is configured to amplify the detected voltage with alternating current, the sensitivity current characteristics are further stabilized. That is, the voltage detected by the ground fault current detection circuit 5 is 10 m
Assuming that the offset voltages of the Vs amplifier circuit 23 and the comparators 24 and 25 are 5 mV, and the amplification degree of the amplifier circuit 23 is 50 times, the amplifier circuit 23 detects the detection voltage Vd, which is an alternating current component.
Since only the detected voltage VD will be amplified, the signal component in the detection voltage VD to be outputted from now on will be 500 mV, and the offset component will be 5 mV. Furthermore, after this detection voltage VD is level-determined by the comparator 24.25 with an offset voltage of 5 mV, the signal component becomes 500 mV, the offset component becomes 10 mV, and the determination error becomes 2%.

[Effects of the Invention] As is clear from the above description, according to the present invention, when the detection voltage indicating the ground fault current flowing through the AC load supply line exceeds a set level, a tripping signal is output and the main In an earth leakage breaker equipped with an earth leakage detection integrated circuit that opens a contact, the earth leakage detection integrated circuit is activated when the positive half wave of the detection voltage is at a predetermined level or higher, and when the negative half wave of the detection voltage is at a predetermined level or higher. first and second comparators each outputting a determination signal at a certain time;
Since the configuration includes a signal processing circuit that generates the trip signal based on the judgment signal from the comparator, the rated sensitivity current can be stabilized even if an offset voltage exists in the earth leakage detection integrated circuit. It has excellent effects.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention, in which FIG. 1 is an overall circuit configuration diagram, and FIGS. 2 and 3 are voltage waveform diagrams for explaining the operation. Furthermore, FIGS. 4 to 7 are for explaining the conventional configuration. FIG. 4 is an overall schematic circuit configuration diagram, FIG. 5 is a circuit diagram of main parts, and FIGS. 6 and 7 are FIG. 4 is a voltage waveform diagram for explaining the action. In the figure, 1a to 1c are main circuit conductors (load supply path), 5 is a ground fault current detection circuit (detection means), 6 is a zero-phase current transformer, 9 is a tripping coil, 1o is a full-wave rectifier circuit, 14 21 is a capacitor, 21 is a leakage detection integrated circuit, 22 is a power supply circuit, 23 is an amplifier circuit, 24 is a first comparator, 25 is a second comparator, and 30 is a latch circuit (signal processing circuit). Agent Patent Attorney Sato Ignition 2 Figure 3 Figure 6

Claims (1)

[Claims] 1. A main contact interposed in an AC load power supply path, a detection means for generating a detection voltage at a level corresponding to the ground fault current flowing through the load power supply path, and when the detection voltage exceeds a set level. In an earth leakage breaker comprising an earth leakage detection integrated circuit that outputs a trip signal and a trip device that opens the main contact when the trip signal is output, the earth leakage detection integrated circuit A first circuit that outputs a judgment signal when the positive half wave of the detection voltage is at a predetermined level or higher.
a second comparator that outputs a determination signal when the negative half wave of the detected voltage is at a predetermined level or higher, and generates the trip signal based on the determination signals from the first and second comparators. An earth leakage breaker comprising: a signal processing circuit that performs a signal processing circuit;