JP2000222998A - Earth leakage breaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an earth leakage breaker from burning by preventing short circuit and breakage of a varistor when excess surge exceeding surge- resisting amount enters the varistor (surge absorber) for protecting a leak detecting circuit. SOLUTION: A power source circuit 8 for a leak detection circuit 6 is connected to between phases of a main circuit, a trip coil 7 is operated on the basis of a leak detecting signal detected with the leak detecting circuit 6 to open a switching breaking part of the main circuit to operate an earth leakage breaker, and the trip coil 7 and a varistor 11 are connected to the power source circuit 8, the trip coil 7 is positioned near to the main circuit (power source) than the surge absorber, and when excess current flows in the varistor 11 by the entry of excess surge from the main circuit side through the power source circuit, the trip coil 7 is instantaneously operated to open the switching breaking part of the main circuit to prevent abnormal heat generation and burning of the breaker caused by excess surge before the varistor 11 causes shirt circuit and breakage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an earth leakage circuit breaker, and more particularly to a protection circuit against an external surge.

[0002]

2. Description of the Related Art FIG. 2 shows a basic circuit of an earth leakage circuit breaker. In the figure, reference numeral 1 denotes an open / close interrupting portion of the main circuit 2, 3 denotes a zero-phase current transformer having the main circuit 2 as a primary conductor, 4 denotes a main terminal (R, S, T) on the power supply side of the main circuit 2, and 5 denotes a load. Side main terminals (U,
V, W), 6 is a leakage detection circuit connected to the secondary coil of the zero-phase current transformer 3, 7 is a trip coil of the cutoff unit 1, 8 is a power supply circuit for the leakage detection circuit 6, and the power supply circuit 8 is It is connected between the phases of the main circuit 2 (U-W phase) to supply power to the leakage detection circuit 6.

[0003] The operation of such earth leakage breakers is well known,
When a leakage occurs on the load side, a voltage is induced in the secondary coil of the zero-phase current transformer 3, and the trip coil 7 is excited by an output signal of the leakage detection circuit 6 that detects this voltage, and the switching circuit 2 is opened.
Is opened.

In the conventional earth leakage breaker, a varistor is provided as a surge absorber in the power supply circuit 8 in order to protect the earth leakage detection circuit 6 from an external surge such as an induced lightning surge that enters from the main circuit 2 side through the power supply circuit 8. Connected to absorb surge voltage and current.

Next, examples of a conventional control power supply circuit are shown in FIGS. In each of the figures, reference numeral 9 denotes a power supply circuit 8.
Diode bridge for AC / DC conversion connected to
Reference numeral 0 denotes a thyristor that is turned ON by an output signal of the leakage detection circuit 6. In the circuit shown in FIG. 3, a trip coil 7 is connected to the AC side of the power supply circuit 8, and a varistor 11 is connected in parallel as a surge absorber to the main circuit (power supply) side of the trip coil 7. The varistor 11 absorbs an external surge intruding from the main circuit side through 8 so as to prevent a failure of the leakage detection circuit 6 connected to the subsequent stage.

In the circuit of FIG. 3, the current flowing through the trip coil 7 is represented by i ₁ , and the current flowing through the leakage detecting circuit 6 is represented by i.
₂ , the current flowing through the thyristor 10 is assumed to be i ₃ , and in a steady state (thyristor 10 is OFF), only a very small current of i ₁ = i ₂ flows through the leakage detecting circuit 6 and the trip coil 7, and the thyristor 10 is not energized. (I ₃ = 0), and the trip coil 7 does not trip the opening / closing block 1 (see FIG. 2) of the main circuit. On the other hand, when the leakage detection circuit 6 detects the occurrence of leakage and turns on the thyristor 10, the current flowing through the trip coil 7 in this state is i ₁
= I ₂ + i ₃ , and the trip coil 7
Operates to open the opening / closing shut-off unit 1.

On the other hand, in the example of the circuit shown in FIG. 4, a trip coil 7 is connected in series with a thyristor 10 so that a control power supply circuit 8 is connected.
And a fuse 12 for protecting the varistor 11 is connected in series with the varistor 11. In this circuit, the thyristor 10 is turned off during normal operation.
Therefore, no current flows through the trip coil 7, and when a leakage occurs, the thyristor 10 is turned on, and an exciting current flows through the trip coil 7 to open the switching section 1.

[0008]

The above-mentioned conventional circuit has the following problems in terms of reliability.
That is, a varistor made of a sintered body containing SiC powder or the like as a main component may be short-circuited or destroyed when an excessive surge that greatly exceeds the surge resistance enters. In addition, if an excessive current flows in this short-circuit state, it is overheated by Joule heat, which may cause a varistor to ignite and cause a fire.

In order to prevent the abnormal overheating due to the short circuit and the destruction as described above, a method of connecting and protecting the fuse 12 in series with the varistor 11 as shown in FIG. 4 is known. Since the function of the varistor 11 connected in series is also lost, if a surge enters again during the use of the earth leakage breaker, the earth leakage detection circuit 6 fails and the earth leakage detection circuit 6 fails and the earth leakage detection circuit does not operate. Will be disabled, and the leakage breaker will not function properly when a leakage occurs. In addition, the normal fuse cannot be checked for fusing from the outside of the earth leakage breaker, so that early detection of an abnormality in maintenance is difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve the above-mentioned problems. Therefore, when an external surge enters and an excessive current exceeding a surge withstand current flows into a varistor (surge absorber). An object of the present invention is to provide an earth leakage breaker improved so that a main circuit is cut off before a varistor is short-circuited or broken to prevent burning of equipment.

[0011]

In order to achieve the above object, according to the present invention, a power supply circuit for a leakage detection circuit is connected between phases of a main circuit, and a leakage detection signal detected by the leakage detection circuit is used based on the leakage detection signal. An earth leakage circuit breaker that opens and closes an opening and closing part of a main circuit by operating a trip coil, and a surge absorber is connected in parallel to the power supply circuit to protect an earth leakage detection circuit from a surge entering from the main circuit side. In this device, the trip coil is inserted and connected to a power supply circuit, and the trip coil is connected to the main circuit side with respect to the surge absorber (claim 1). A varistor is used for the surge absorber (claim 2). .

With this configuration, when an excessive surge enters the main circuit through the power supply circuit and an excessive current flows through the varistor, the trip coil immediately operates before the varistor is short-circuited or destroyed, and the main circuit is activated. Open and close the opening / closing part of. As a result, it is possible to avoid abnormal heat generation of the varistor and burnout of equipment due to excessive surge.

[0013]

FIG. 1 is a block diagram showing an embodiment of the present invention.
A description will be given based on the embodiment. Note that FIG.
The same reference numerals are given to the same members corresponding to and the description thereof is omitted. That is, in this embodiment, as in FIG. 3, the trip coil 7 is connected to the AC side of the power supply circuit 8 that supplies power to the leakage detection circuit 6, and the power supply circuit 8 is connected in parallel with a varistor 11 as a surge absorber. However, the connection order is opposite to that of FIG. 3, and when viewed from the main circuit 2 (see FIG. 2), the trip coil 7 is connected to the main circuit (power supply) side.
The varistor 11 is connected to the rear side of the trip coil 7.

In such a circuit configuration, the current flowing through the trip coil 7 is i ₁ , the current flowing through the leakage detecting circuit 6 is i ₂ , the current flowing through the thyristor 10 is i ₃ , and the varistor 11
Assuming that the energizing current of i is i ₄ , in the steady state (thyristor 10 is OFF), the leakage current detecting circuit 6 and the trip coil 7 have i ₁
= I ₂ , the thyristor 10,
The varistor 11 is not energized (i ₃ = 0, i ₄ = 0),
The trip coil 7 does not trip the opening / closing shut-off unit 1 (see FIG. 2) of the main circuit. When the leakage detection circuit 6 turns on the thyristor 10 by detecting the occurrence of leakage, the current flowing through the trip coil 7 in this state increases to i ₁ = i ₂ + i ₃ , and the trip coil 7 operates with this current. To open the switching breaker 1 to cut off the leakage current and protect the load.

On the other hand, the surge that enters from the main circuit side through the power supply circuit 8 while the earth leakage circuit breaker is energized is absorbed by the varistor 11, and in this case, when an excessive surge exceeding the rated capacity of the varistor 11 enters, the varistor 11 , A large current i ₄ flows, and at the same time, a current i ₁ = i ₂ + i ₄ including the current i ₄ flows through the trip coil 7. Moreover, the current i ₁ in this case is more than the current value required for the trip operation of the breaker. As a result, the trip coil 7 operates instantaneously to open the opening / closing cutoff portion of the circuit breaker.

As a result, current flowing through the varistor 11 is also eliminated, so that abnormal heat generation and flaming of the varistor 11 can be prevented. Even if the varistor 11 is short-circuited, a large current (i ₁ = i ₂ + i) is applied to the trip coil 7 when the earth leakage breaker is reset and turned on again.
_{Since 4} ) flows, the opening / closing shut-off section 1 is instantaneously opened, so that it is possible to determine that the varistor 11 has failed.

[0017]

As described above, according to the configuration of the present invention, short-circuit and destruction due to excessive surge of a varistor (surge absorber) can be prevented, and abnormal heat generation, flaming, and earth leakage due to the varistor failure can be prevented. The failure-safety function can be secured by preventing the damage to the burnout of the vessel.
Moreover, as compared with the conventional configuration, it can be dealt with only by changing the connection position of the trip coil, and there is no increase in cost.

[Brief description of the drawings]

FIG. 1 is a power supply circuit diagram for a leakage detection circuit of a leakage breaker according to an embodiment of the present invention.

FIG. 2 is a basic circuit diagram of an earth leakage breaker to which the present invention is applied;

FIG. 3 is a power supply circuit diagram of a conventional example for a leakage detection circuit of a leakage breaker.

4 is a power supply circuit diagram of a conventional example different from FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Opening / closing interrupt part 2 Main circuit 3 Zero-phase current transformer 6 Leakage detection circuit 7 Trip coil 8 Power supply circuit 11 Varistor (surge absorber)

Claims (2)

[Claims] A power supply circuit for a leakage detection circuit is connected between phases of a main circuit, and a trip coil is operated based on a leakage detection signal detected by the leakage detection circuit to open / close a switching part of the main circuit. Wherein a surge absorber is connected in parallel to the power supply circuit to protect the leakage detection circuit from surges entering from the main circuit side.
An earth leakage circuit breaker characterized in that a trip coil is connected to a power supply circuit and a trip coil is connected to a main circuit side of the surge absorber. 2. The earth leakage circuit breaker according to claim 1, wherein the surge absorber is a varistor.