JPH0226449B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an earth leakage detection circuit mainly used for earth leakage and disconnection.

Conventionally, there has been one of this type as shown in FIG. In the figure, reference numeral 16 denotes an electrical circuit having a switch 15 that performs opening and closing operations, and a terminal 16 at one end of the circuit.
a is connected to the AC power supply 17, and the other end terminal 16b is connected to the load 1.
8 respectively. 14 is a zero-phase current transformer provided on the load 18 side of the electric line 16;
This detects the leakage current flowing through the sensor. The voltage across the output of this zero-phase current transformer 14 becomes a detection voltage V ₁ by a resistor 13, which is input to a voltage comparator 1 and compared with a predetermined first threshold voltage V _a .
When the detection voltage V ₁ is larger, the first voltage comparator 1
outputs a first output signal. 2 is capacitor 7
When the charge/discharge control circuit receives the output signal of the voltage comparator 1, it charges the capacitor 7 with the first current value I1, and then charges the capacitor 7 with the first current value _I1 .
is discharged at a second current value _I2 . 27
is a latch circuit, which is activated when the voltage of the capacitor 7 reaches a predetermined second threshold voltage _Vb , and sends an output to the gate circuit 4 at the next stage, and also controls the capacitor 7 to the second current value. Charging is performed using a third current value I ₃ that is larger than I ₂ .

Reference numeral 4 denotes a gate circuit which operates upon receiving the output of the latch circuit 27, and controls the gate of the thyristor 12 serving as a switching means. A trip coil 11 for tripping the switch 15 is connected to the anode side of the thyristor 12, and when the thyristor 12 becomes conductive, the switch 15 performs an opening operation by excitation of the trip coil 11. 8 is a capacitor, 9 is a resistor, and 10 is a diode, which constitute a rectifier circuit. 5 is a stabilized power supply circuit, and this DC constant voltage is supplied to the first voltage comparator 1, charge/discharge control circuit 2, latch circuit 7 and gate circuit 4 through lines 19 and 20.
supplied to

Next, the operation of the above structure will be explained with reference to FIGS. 1 and 2.

Now, when a leakage current occurs in the electric line 16, the detection voltage V ₁ shown in FIG. 2A is input to the voltage comparator circuit 1 through the zero-phase current transformer 14, and is compared with the threshold voltage V _a . At this time, the period when the detection voltage V ₁ is higher,
The charge/discharge control circuit 2 has a constant current value I ₁ and the capacitor 7
is charged as shown in FIG. 2B. but,
When the voltage of the capacitor 7 does not reach the predetermined threshold voltage V _b due to this charging, it is immediately discharged at a constant current value I ₂ , so the latch circuit 27 and gate circuit 4 do not operate, and the thyristor 12 is disabled. Since the trip coil 11 remains in a conductive state and is not excited, the switch 15 remains closed. In other words, when the leakage current does not exceed the current amount until the voltage of the capacitor 7 reaches a predetermined threshold voltage _Vb , that is, the so-called sensitivity current, the switch 15 does not perform the opening operation.

Next, when the voltage of the capacitor 7 reaches the threshold voltage _Vb , that is, when the leakage current shows the second peak in FIG. 2B, which is larger than the sensitivity current, the latch circuit 27 is activated. Therefore, the gate circuit 4 is also activated, and the gate current shown in FIG. cut off

When the electric path 16 is finally cut off, the trip coil 11 is no longer energized.

At this time, when the latch circuit 27 is activated, it will supply a current _I3 larger than the discharge current _I2 to the capacitor 7, so even if the discharge control circuit 2 starts discharging, the voltage of the capacitor 7 will be lower than the threshold voltage.
V _b is maintained to keep the latch circuit 27 in an activated state.

However, in the above circuit, when connecting the AC power source 17 and the load 18 during wiring work, sometimes the AC power source 17 and the load 18 are connected incorrectly, and when such incorrect wiring occurs, the earth leakage detection circuit does not connect the AC power source 17 to the load 18. Since the gate circuit 4 continues to flow the gate current and the thyristor 12 continues to conduct, the trip coil 11 is burnt out.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object of the present invention is to provide an earth leakage detection circuit in which a trip coil will not be burned out even if an AC power source and a load are connected incorrectly.

An embodiment of the present invention will be described below with reference to the drawings.

In the following description, parts that are the same as or equivalent to those of the above-mentioned conventional example are given the same reference numerals, and the description will be omitted.

3, the difference from the conventional example shown in FIG. 1 is that a second voltage comparator 3 is provided instead of the latch circuit 27, and a line 6
The charge/discharge control circuit 2 is controlled via the charge/discharge control circuit 2. That is, when the charge/discharge control circuit 2 receives the output signal from the second voltage comparator 3, the delay characteristic of the capacitor 7 is utilized by discharging the capacitor ₇ with a current _I4 smaller than the discharge current I2. The purpose is to invert the output of the second voltage comparator 3 after a certain period of time.

Next, the operation will be explained with reference to FIGS. 3 and 4.

When the leakage current is smaller than the sensitivity current, the voltage of the capacitor 7 does not reach the threshold voltage V _b of the second voltage comparator 3, as shown in FIG. 2B.
There is no output from the second voltage comparator 3, and the operation of the charge _/ discharge control circuit 2 is similar to the conventional example, with the discharge current _I2 flowing after the charging current I1. However, at this time, the discharging current _I2 is set larger than the charging current _I1 ,
This prevents the first voltage comparator 1 from operating under the influence of external noise or surges and increasing the voltage of the capacitor 7.

On the other hand, if the magnitude of the leakage current is larger than the sensitivity current, the output of the second voltage comparator 3 is inverted when the voltage of the capacitor 7 reaches the threshold voltage V _b , and this output drives the gate circuit 4. By making the thyristor 12 conductive, the trip coil 11 is energized and the switch 15 is opened.

However, the output of the second voltage comparator 3 is also sent to the charge/discharge control circuit 2 via the line 6, and the charge/discharge control circuit 2 is switched to the constant discharge current _I4 .
As a result, as shown in FIG. 4B, the voltage of the capacitor 7 is discharged by a discharge current I4 smaller than the discharge current _I2 , so the voltage of the capacitor ₇ gradually decreases, and the voltage of the capacitor 7 gradually decreases.
When the threshold voltage V _c of the voltage comparator 3 is reached, the voltage is reversed and the operation of the gate circuit 4 is stopped. Therefore,
The thyristor 12 is turned off and the trip coil 11
Power is cut off. That is, the period during which the trip coil 11 is energized to open the switch 15 is the period from when the voltage of the capacitor 7 reaches the threshold voltage V _b until it reaches the threshold voltage V _c , as shown in FIG. 2C. It will be limited to the period ΔT.

The above operation is the same even when the AC power source 17 and the load 18 are wired incorrectly, and the energization time to the trip coil 11 is limited to ΔT.
This cannot be burned out.

As described above, according to the present invention, it is possible to provide an earth leakage detection circuit in which the trip coil will not be burned out even if an AC power source and a load are connected by mistake.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional earth leakage detection circuit, FIGS. 2A to C are waveform diagrams showing the operation of the circuit in FIG. 1, and FIG. 3 is a circuit diagram showing an earth leakage detection circuit according to an embodiment of the present invention. 4A to 4C are waveform diagrams showing the operation of the same embodiment. DESCRIPTION OF SYMBOLS 1... First voltage comparator, 2... Charge/discharge control circuit, 3... Second voltage comparator, 11... Trip coil, 12... Switch means (thyristor),
14... Zero-phase current transformer, 15... Switch, 16...
Electrical circuit, 17... AC power source, V _a , V _b , V _c ... first, second, third threshold voltages, I ₁ , I ₂ , I ₄ ... charging/discharging current. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An earth leakage detection circuit that detects earth leakage in an electric line connecting an AC power source and a load via a switch, comprising terminals provided at both ends of the electric line and connected to the AC power source and the load, respectively; A zero-phase current transformer that is installed in the electrical circuit and detects the leakage current on the load side receives the output of the zero-phase current transformer, and compares the detected voltage according to this output with a predetermined first threshold voltage. a first comparator that outputs a first output signal when the detected voltage is greater than a first threshold voltage; and a charge/discharge control that operates upon receiving the first output signal to charge and discharge the capacitor. a second comparison circuit that delivers a second output signal when the charging voltage of the capacitor reaches a second threshold voltage and inverts at a third threshold voltage that is lower than said second threshold voltage; a switch, a switch means that operates to close in response to the second output signal, and a trip coil connected in series with the switch means and connected to the electric circuit to trip the switch, The charging/discharging control circuit charges the capacitor with a first current value when receiving the first output signal, and when the charging voltage does not reach the second threshold voltage, the charging/discharging control circuit charges the capacitor with a first current value. Discharging the capacitor with a second larger current value, and discharging the capacitor with a third current value smaller than the second current value when receiving the second output signal from the second voltage comparator. 2. An earth leakage detection circuit configured to limit the current supply time to the trip coil to a predetermined time in the event of an erroneous connection.