JPS619120A - Leakage detecting circuit - 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 [Technical Field of the Invention] The present invention relates to an earth leakage detection circuit constituting an earth leakage breaker, an earth leakage alarm, etc.

[Prior art]

FIG. 1 shows a conventional earth leakage detection circuit. In Figure 1,
1 is an earth leakage detection circuit, 2 is a zero-phase current transformer that outputs the detected leakage current as a low-voltage secondary output signal, 3 is the load resistance of the zero-phase current transformer 2, and 4 and 5 are zero-phase transformers. An input terminal for inputting the secondary side output signal (hereinafter simply referred to as "secondary side output signal") output from the flowmeter 2, and 6 compares the level of the secondary side output signal with the threshold voltage. 7 is a capacitor, 8 is a charging/discharging control circuit that controls charging and discharging of capacitor 7, 9 is a terminal voltage of capacitor 7 and the first voltage comparison circuit.
1o is an output circuit that outputs a cutoff signal for driving an external circuit; II is a constant voltage circuit;
2 is an output terminal for sending a cutoff signal from the output circuit 10 to the outside, and 13 and 14 are input terminals for inputting the power supply voltage supplied to the constant voltage circuit 11.

15 is an AC power supply, 16 is a contact for electrical circuit breaking, and 17a.

17b is an electric circuit; 18 is a load circuit for the AC power supply 15;
20 is a tripping coil for driving the circuit breaking contact 16, 21 is a thyristor for driving the tripping coil 20, and 22, 23, and 24 are diodes, resistors, and capacitors forming a rectifying and smoothing circuit. The above components constitute an external circuit for the earth leakage detection circuit.

Next, the operation of the leakage detection circuit configured as described above will be explained. Electrical line 17a or 17. When a leakage current occurs in b, the leakage current is detected by the zero-phase current transformer 2, and the secondary side output signal 51 shown in FIG.
, 5. The first voltage comparator circuit 6 is shown in FIG.
A comparison signal between the threshold voltage 52 and the secondary output signal 51 shown at 1 is output to the charge/discharge control circuit 8. The charge/discharge control circuit 8 operates during a period during which the secondary side ratio signal 51 is greater than the threshold voltage 52 (hereinafter referred to as the "charging period").
As shown in FIG. 2(b), the capacitor terminal voltage 53 is increased by charging the capacitor 7 with a constant current. During this charging period, the capacitor terminal voltage 53 increases to the first threshold voltage 5 of the second voltage comparator circuit 9 shown in FIG.
4, the accumulated charge in the capacitor 7 is discharged with a discharge current larger than the charging current. If the leakage current is large (and the capacitor terminal voltage 53 reaches the first threshold voltage 54 within the charging period), the state signal 56 of the second voltage comparator circuit 9 changes as shown in FIG. 2(C). It becomes "1".

This state signal "1" causes the charge/discharge control circuit 8 to discharge the accumulated charge in the capacitor 7 with a discharge current smaller than the charging current. When the capacitor terminal voltage 53 reaches the second threshold voltage 55 shown in FIG.
'', and the charge/discharge control circuit 8 rapidly discharges the accumulated charge in the capacitor 7 with a discharge current larger than the charging current. The output circuit 10 controlled by the state signal 56 turns on the thyristor 21 by applying a cutoff signal to the gate of the thyristor 21 (a) through the output terminal 12 while the state signal 56 is "1". 20 is impressed and pulls out the electrical circuit breaker contact 16 to cut off the electrical circuit.

The earth leakage detection circuit 1 as described above always performs a cutoff operation if the leakage current is an undistorted sine wave current with a value equal to or higher than the rated sensitivity current value. When the waveform distortion increases, even if the leakage current value is constant, the comparison signal output from the first voltage comparator circuit 6 changes depending on the shape of the waveform, resulting in a leakage current value, that is, a sensitivity current value that allows a cutoff operation. There was a problem with the change in That is, there is a problem in that even if the leakage current value is greater than the rated sensitivity current value, the cutoff operation is not performed, and even if the leakage current value is less than the rated sensitivity current value, the cutoff operation is performed.

[Summary of the invention]

The present invention has been made in view of the above points, and its purpose is to determine the secondary side output by comparing the DC voltage corresponding to the effective value of the secondary side output signal with the threshold voltage. An object of the present invention is to provide an earth leakage detection circuit in which changes in sensitivity current due to signal waveform distortion are negligible.

In order to achieve such an object, the present invention provides an effective value conversion circuit that outputs a DC voltage corresponding to the effective value of a secondary side output signal to an earth leakage detection circuit, and a capacitor control circuit that switches the connection of a capacitor.

A voltage comparison circuit is provided that compares a DC voltage corresponding to the effective value of the secondary side output signal with a first threshold voltage and compares a capacitor terminal voltage with a second threshold voltage.

[Embodiments of the invention]

The present invention will be explained in detail based on examples. FIG. 3 shows an embodiment of the earth leakage detection circuit according to the present invention. In FIG. 3, 32 is an effective value conversion circuit that outputs a DC voltage corresponding to the effective value of the secondary side output signal, 33 is a capacitor, and 3
4 is a capacitor control circuit that switches the connection of the capacitor 33; 35 is a capacitor control circuit that compares a DC voltage corresponding to the effective value of the secondary output signal with a first threshold voltage and compares the capacitor terminal voltage with a second threshold voltage; Voltage comparison circuits 41 to 44 are lines. In FIG. 3, the same or equivalent parts as in FIG. 1 are given the same reference numerals.

The operation of the leakage detection circuit configured in this way will be explained. First, the output from the voltage comparator circuit 35 is shown in FIG.
) The operation before the status signal 66 becomes "1" will be explained. When no leakage current is generated in the electrical circuits 17'a and 17b, the state signal 6 is as shown in FIG. 4(d).
6 is rOJ, and the signal on line 44 becomes rOJ.

When the signal on line 44 is "0", capacitor control circuit 34 connects capacitor 33 to line 42. At this time, the capacitor 33 generates a DC voltage ( (hereinafter referred to as "rRMs DC voltage")
Acts as an averaging capacitor when creating Electric line 17
a.

゛ When a leakage current occurs in 17b and a secondary side output signal 51 as shown in FIG. An 8MS DC voltage 62 as shown in Figure fbl is applied to line 4.
1 is output. This 8MS DC voltage 62 is compared in the voltage comparison circuit 35 with a first threshold voltage 63 shown in FIG. 4 fbl. When the 8MS DC voltage 62 reaches the threshold voltage 63, the status signal 6G becomes "1" and the signal on the line 44 becomes "1".The signal on the line 44 becomes "1".
1'', the capacitor 33 discharges the charge already charged by the capacitor control circuit 34 at a constant current.

FIG. 4 (The capacitor terminal voltage 64 shown in C1 is line 4
3 to the voltage comparator circuit 35 and compared with a second threshold voltage 65 shown in FIG. 4(C). When the capacitor terminal voltage 64 reaches the second threshold voltage 65, the status signal 66 returns to "0".

While the status signal 66 is "1", the output circuit 10 applies a cutoff signal to the gate of the thyristor 21 to turn on the rethyristor 21 and cause the tripping coil 20 to move. As a result, the tripping coil 20 trips the electric circuit breaking contact 16 and interrupts the electric circuit. The leakage current when the DC voltage 62 matches the first threshold voltage 63 becomes the sensitivity current of this earth leakage detection circuit. R.M.
Since the S DC voltage is not susceptible to changes due to waveform distortion of the secondary output signal, this circuit can make changes in the sensitivity current negligible. In addition, this circuit has an averaging capacitor used in the effective value conversion circuit 32 and a state signal 66.
Since it also serves as a timing capacitor that determines the period of 1", it also has the effect of preventing an increase in the number of parts.

〔Effect of the invention〕

As described above, the present invention generates an RMS DC voltage corresponding to the effective value of the secondary output signal by calculating the square root of the square of the secondary output signal and taking the time average. Since changes in the sensitivity current due to waveform distortion of the next-side output signal can be ignored, there is an effect that the value of the leakage current to be cut off can be made constant regardless of the waveform distortion.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a conventional earth leakage detection circuit, FIG. 2 is an explanatory diagram of its operation, FIG. 3 is a circuit diagram of an earth leakage detection circuit according to the present invention, and FIG. 4 is an illustration of its operation. 1...Earth leakage detection circuit, 2...Zero phase current transformer, 3...
Load resistance, 4, 5, 13.14 Input terminal, 10 Output circuit, 11 Constant voltage circuit, 1
2... Output terminal, 32... Effective value conversion times! ,3
3... Capacitor, 34... Capacitor control circuit, 35... Voltage comparison circuit, 41-44...
Line, 51...Secondary side output signal, 62...R
MS DC voltage, 63.65...Threshold voltage, 64
...Capacitor terminal voltage, 6G...Status signal.

Claims (1)

[Claims] In an earth leakage detection circuit that uses as an input signal a secondary side output signal output from a zero-phase current transformer that detects leakage current in an AC power line and outputs a cutoff signal for touching a tripping coil, the zero-phase current transformer an effective value conversion circuit that outputs a DC voltage corresponding to the effective value of the secondary side output signal output from the
A capacitor control circuit that switches the connection of the capacitor to make the capacitor work as an averager for the effective value conversion circuit or to discharge the accumulated charge in the capacitor with a constant current, and a capacitor control circuit that controls the output from the effective value conversion circuit. A state signal is outputted to output the cutoff signal when the DC voltage becomes equal to or higher than a first threshold voltage, and a state signal is outputted to output the cutoff signal when the terminal voltage of the capacitor becomes equal to or less than the second threshold voltage. and a voltage comparison circuit that stops the status signal in order to stop the current leakage detection circuit.