JPH01144313A - Over voltage protecting circuit - Google Patents

Abstract

PURPOSE:To enable re-execution of protective operation without requiring replacement of components, by temporarily shortcircuiting the load side of a circuitbreaker through contacts of an electromagnetic relay for detecting over-voltage and operating the circuitbreaker. CONSTITUTION:An over-voltage protection circuit 2 comprises an earth leakage breaker 6 servable for ground protection and over-voltage protection, an electromagnetic relay 20 and a variable resistor 22. Upon application of excessive voltage onto the electromagnetic relay 20, the electromagnetic relay 20 detects over-voltage and closes ite contacts 20b. Consequently, load side of the earth leakage circuitbreaker 6 is shortcircuited temporarily so as to break the circuit through operation based on the shortcircuit current of the circuitbreaker 6.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to an overvoltage protection circuit.

(Conventional technology) FIG. 2 is a circuit diagram showing a conventional overvoltage protection circuit.

The conventional overvoltage protection circuit 2 includes a fuse 28 and a varistor 3.
It consists of a series circuit with 0.

Two terminals 5a, 5b of the plug 4 are connected to power supply side terminals 8a, 8b of the earth leakage breaker 6, respectively. One load side terminal 12a of this earth leakage breaker 6 is connected to one end of the fuse 28, and the other end of this fuse is connected to the other negative (1; j side terminal) of the earth leakage breaker 6 via the varistor 30. 12b.One power supply side terminal 26a of the protected circuit 24 is connected to the connection point between the fuse 28 and the varistor 30, and the other power supply side terminal 28a of the protected circuit 24 is connected to the connection point between the fuse 28 and the varistor 30.
b is connected to one load side terminal 12b of the earth leakage breaker 6. Note that when the protected circuit 24 is configured as a 100V circuit, the varistor 30 has a voltage of 10V to itself.
A type that conducts when a voltage higher than 0V is applied is selected, and for convenience of mounting, it is mounted on a printed circuit board together with other electronic components.

Both terminals 5a and 5b of the plug 4 are normally connected to a 100V AC power source. At this time, one terminal 5 of the plug 4
a to the power supply side terminal 8a of the earth leakage breaker 6 and the load side terminal 1
2a and the fuse 28 in order to reach one power supply side terminal 26a of the protected circuit 24, and from the other power supply side terminal 26b of the protected circuit 24, the load side terminal 12b and the power supply side terminal 8b of the earth leakage breaker 6 are connected. A circuit is constructed in which the terminals 5b and 5b are connected to the other terminal 5b of the plug 4, and a voltage of 100 V is applied between the source-side terminals 2Ga and 26b of the protected circuit 24. At this time, since a voltage of 100V is also applied to the varistor 30, this varistor 30 will not become conductive. Therefore, power can be supplied to the protected circuit 24 at a voltage of 100V.

Now, due to a mistake in the wiring work, both terminals 5a of the plug 4,
5b may be accidentally connected to a 200v AC power source. In this case, the varistor 30 to which an excessive voltage of 200V is applied becomes conductive and short-circuits the source side terminals 26a and 2Bb of the protected circuit 24.

Therefore, an excessive voltage is not applied to the protected circuit 24. Furthermore, when the varistor 30 becomes conductive, a short-circuit current flows through the fuse 28.
fuses and interrupts the circuit.

It should be noted that when a short circuit failure occurs in the protected circuit 24, the fuse 28 blows to interrupt the circuit, and when a ground fault occurs, the earth leakage breaker 6 interrupts the circuit.

(Problems to be Solved by the Invention) As explained above, in the conventional overvoltage protection circuit 2,
The circuit was protected by conduction of the varistor 30.

Now, due to its operating principle, the varistor 30 becomes permanently conductive when an excessive voltage is applied to it.

Therefore, in order to supply power to the protected circuit 24, it was necessary to replace not only the fuse 28 but also the varistor 30, and then reconnect the plug 4 to the regular 100cm AC power source. However, as mentioned above, since the varistor 30 is usually mounted on a printed circuit board together with other electronic components, conventionally there was a problem in that the printed circuit board on which the varistor 30 was mounted had to be replaced. Ta.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an overvoltage protection circuit that can re-execute the protection operation without requiring replacement of components.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention detects overvoltage using an electromagnetic relay, and temporarily closes the load side of the circuit breaker using the contacts of the electromagnetic relay. By short-circuiting the circuit breaker, the circuit breaker is operated to interrupt the circuit.

(Function) According to the present invention, when an excessive voltage is applied to the electromagnetic relay, the relay detects the overvoltage and closes the contacts. When this contact closes, the load side of the circuit breaker is temporarily shorted. Then, a short-circuit current flows through the circuit breaker whose load side is short-circuited, and the circuit is interrupted by the operation of this circuit breaker. Moreover, the electromagnetic relay and circuit breaker that constitute the overvoltage protection circuit according to the present invention do not need to be replaced even after the overvoltage protection is activated.

(Embodiment) FIG. 1 is a circuit diagram showing an overvoltage protection circuit according to an embodiment of the present invention.

The overvoltage protection circuit 2 shown in the figure has an earth leakage breaker 6 for earth fault protection also used for overvoltage protection, and includes an electromagnetic relay 20 and a variable resistor 22 in addition to this breaker.

The earth leakage breaker 6 has power supply side terminals 8a, 8 inside.
b are connected to load side terminals 12a and 12b via contacts 10a and 10b, respectively. Contactor 10a
, 10b and the load-side terminals 12a, 12b, a zero-phase current transformer 14 is arranged between both contacts 10a, lOb.
Detects the difference in current passing through the terminals and applies this difference to relay 1B. The relay 16 opens both contacts 10a and 1Ob when the input current difference becomes larger than a certain value.

Between the load side terminals 12a and 12b of the earth leakage breaker 6,
A series circuit of the coil 20a of the electromagnetic relay 20 and the variable resistor 22 is connected. A contact 201 of electromagnetic relay 20)
One end is connected to one power supply side terminal 8b of the earth leakage breaker 6, and the other end of this a contact 20b is connected to one side of the earth leakage breaker 6 via a current limiting resistor 18 in the earth leakage breaker 6. is connected to the load side terminal 12a.

Overvoltage protection circuit 2 according to the embodiment of the present invention described above
The plug 4 is connected to the power supply side terminals 8a and 8b of the earth leakage breaker 6.
The two terminals 5a and 5b of the earth leakage circuit breaker 6 are connected to the load side terminals 12a and L2b of the protected circuit 2, respectively.
The four power supply side terminals 26a and 26b are connected and used, respectively.

When the protected circuit 24 is configured as a 100V circuit, the electromagnetic relay 20 closes the a contact 20b when the voltage applied to the coil 20a is higher than a certain voltage within the range of 100 to 200V. For example, the overvoltage protection circuit 2 will not shut off when the voltage applied between both terminals 5a and 5b of the plug 4 is less than 130V, and if this voltage becomes 160V or more, the contactor 10a,
10b is adjusted to be open.

Both terminals 5a and 5b of the plug 4 are connected to a regular 100V AC power source, and the contact 10a of the earth leakage breaker 6.

10b is closed, one terminal 5a of the plug 4 passes through the power supply side terminal 8as contact 10a of the earth leakage breaker 6 and the load side terminal 12a in order, and reaches one power supply side terminal 26a of the protected circuit 24. A circuit is constructed from the other power supply side terminal 26b of the protected circuit 24 to the other terminal 5b of the plug 4 through the load side terminal 12b of the earth leakage breaker 6, the contact 10b and the power supply side terminal 8b in order. circuit 24
A voltage of 100V is applied between the power supply side terminals 26a and 26b. At this time, a voltage obtained by dividing a voltage of 100 V by this coil and the variable resistor 22 is applied to the coil 20a of the electromagnetic device 20. At this time, the electromagnetic relay 20 does not operate, and the a contact 20b remains open. Therefore, no current flows through the current limiting resistor 18 and the solid contact 10a.

Since there is no difference in the current passing through 10b, there is no output from the current transformer 14 when it reaches zero, and the relay 16 is a solid contact 10a.

10b will not be opened. Therefore, power can be continuously supplied to the protected circuit 24 at a voltage of 100V.

On the other hand, due to a mistake in the wiring of the power supply, both terminals 5a of the plug 4,
When an excessive voltage of 200V is applied across 5b, this overvoltage is detected by the electromagnetic relay 20, and the a contact 20b is closed. When the a contact 20b is closed, the load side of the earth leakage breaker 6 is temporarily short-circuited as follows. That is, when the a contact 20b is closed, the short circuit current flowing through one terminal 5a of the plug 4 flows out through the power supply side terminal 8a, the contact 10a and the load side terminal 12a of the earth leakage breaker 6, but this current , flows through the series circuit of the a contact 20b and the current limiting resistor 18 without passing through the contact 10b, and returns to the power source from the other terminal 5b of the plug 4. Therefore, a difference occurs in the current passing through the solid contact 10a, fob, this difference in current is detected by the relay 16, and the operation of the relay 16 causes the solid contact 10a,
lOb is released. As a result, the protected circuit 24
The circuit containing the will be automatically cut off.

Moreover, after changing the voltage applied to both terminals 5a and 5b of the plug 4 from 200V to 100V, if the earth leakage breaker 6 that was previously shut off is turned on again, the voltage applied to the protected circuit 24 will be 100V.
It can supply power at the regular voltage.

The overvoltage protection circuit 2 according to the present embodiment described above connects the electromagnetic relay 20, which closes the a contact 20b when an overvoltage is applied to the coil 20a, to the load side terminal 12a of the earth leakage breaker 6.
, ljb, and a series circuit consisting of the A contact 20b of this electromagnetic relay 20 and the current limiting resistor 18 is connected between one wire on the power supply side of earth leakage breaker B and the other wire on the load side. Therefore, the earth leakage breaker 6 for earth fault protection can also be used for overvoltage protection, and the number of parts can be reduced.

In the embodiment described above, since the series circuit of the coil 20a of the electromagnetic relay 20 and the variable resistor 22 is connected between the load side terminals 12a and 12b of the earth leakage breaker 6, this variable resistor 2'' : By adjusting the resistance value of I22, variations in the characteristics of the electromagnetic relay 20 can be compensated for, and predetermined operating and non-operating voltages can be easily achieved.

In addition, in the above explanation, the current limiting resistor 18 in the earth leakage breaker 6
Although the current limiting resistor is connected in series with the a contact 20a, it goes without saying that another current limiting resistor may be used.

[Effects of the Invention] As detailed above, the overvoltage protection circuit according to the present invention detects overvoltage using an electromagnetic relay, and temporarily shorts the load side of the breaker using the contacts of the electromagnetic relay, thereby interrupting the circuit breaker. According to the present invention, the electromagnetic relay and circuit breaker that make up this circuit do not need to be replaced even after the overvoltage protection is activated.
It is possible to provide an overvoltage protection circuit that can re-execute a protection operation without requiring replacement of components.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an overvoltage protection circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional overvoltage protection circuit. Explanation of symbols 2... Overvoltage protection circuit, 6... Earth leakage breaker, 18.
...Current limiting resistor, 20...Electromagnetic relay, 20a...
Coil, 20b... A contact, 22... Variable resistor,
24...Protected circuit.

Claims (1)

[Claims] 1. An overvoltage protection circuit characterized in that an overvoltage is detected by an electromagnetic relay, and the contacts of the electromagnetic relay temporarily short-circuit the load side of the circuit breaker to operate the circuit breaker and interrupt the circuit.