JPH1028322A - Safety device for ground-fault protection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage of an element in electric equipment by breaking the power source circuit of another system when a ground-fault occurs in one system by connecting a serial circuit of a discharge tube and a resistor between the class-2 ground of a power source circuit to be protected and the frame ground of the electric equipment. SOLUTION: A safety device X for ground-fault protection is composed of a serial circuit in a discharge tube AR which discharges at a fixed voltage and a resistor R, and connected between the class-2 ground E2' of the power source circuit of electric equipment 2b to be protected and the frame ground E3' of the equipment 2b. Therefore, when a ground-fault occurs in a power system A, the overvoltage between the voltage phase and ground E of the system A drops lower than the operating voltage of a varistor VR and the breakage of the equipment 2b can be prevented, because the discharge tube AR discharges and the resistor R short-circuits, when the voltage across the class-2 ground E2' of another system B and the frame ground E3' of the equipment 2b becomes higher than the discharge-starting voltage of the tube AR. In addition, the occurrence of a power failure due to the unprepared operation of an earth leakage breaker ELB can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit of a different system in which a transformer is used in a low-voltage distribution line. This is related to a protective device for ground fault protection.

[0002]

2. Description of the Related Art In a power supply circuit of a plurality of systems, when one system causes a ground fault, a potential gradient occurs due to the ground fault current, and a voltage generated between two types of grounds of another system and a chassis ground. Is superimposed on the supply voltage, overvoltage is applied between the voltage phase and the ground, and the lightning arrester for lightning surge protection connected between the power line and the ground of the electrical equipment may be damaged or installed on the power side of the electrical equipment. There was a concern that the leaked circuit breaker that had been inadvertently operated and power supply to electrical equipment was stopped, but no special measures have been taken so far. For example, in a tollgate on a toll road, a power supply circuit for a lighting lamp and a power supply circuit for an electric device for toll collection in a booth are provided separately. When an accident occurs, there is a concern that a lightning arrester provided in a toll collection electric device may be damaged, an earth leakage breaker may be operated to cut off a power supply, and a toll collection function may be paralyzed, resulting in great confusion.

[0003]

FIG. 1 is a diagram for explaining the occurrence of a ground fault in the power supply circuits of the A system and the B system. In the drawings, reference numerals 1a and 1b denote transformers, 2a and 2b denote electric devices, and E
2, E2 'denotes two types of grounding, E3 and E3' denote housing grounds (three types of grounding) of electric equipment, VR denotes a varistor, and ELB denotes an earth leakage breaker.

As shown in the figure, when a ground fault occurs in the system A, a voltage V2 due to a ground fault current is generated between the type B ground E2 'and the housing ground E3' in the system B, and the power supply voltage VB is reduced to V.
2 is superimposed, and an overvoltage V3 is generated between the voltage phase L of the electric device 2b and the ground E3 '. If the overvoltage V3 exceeds the operating voltage of the varistor VR of the electric device 2b, an overcurrent flows through the varistor VR and the varistor VR is damaged. To avoid this, it is necessary to increase the operating voltage of the varistor VR, but there is a problem that the lightning arrester performance deteriorates. In addition, when the earth leakage breaker ELB is provided on the power supply side of the electric device 2b, there is a possibility that the power supply to the electric device 2b may be stopped by operating together with the operation of the varistor VR.

FIG. 2 is a diagram showing the principle of generation of an overvoltage due to the ground fault of FIG.
The potential gradient between the grounds E2 'and E3' in the system, RE is the ground resistance (E2 + E3), and VB is the power supply voltage of the B system.

According to the present invention, in such a plurality of power supply circuits, when one of the power supply circuits causes a ground fault, the power supply circuit of the other system is cut off or the elements in the electric equipment are destroyed. The purpose is to prevent the problem.

[0007]

In order to achieve the above object, according to the present invention, a power supply circuit for protecting a series circuit of a discharge tube and a resistor is connected between two kinds of grounds and a housing ground. It is based on limiting the voltage.

That is, according to the present invention, a series circuit of a discharge tube and a resistor is connected between two kinds of grounds of a power supply circuit to be protected from a ground fault in a power supply circuit of another system and a ground of an electric equipment housing. It constitutes a protection device for short circuit protection.

FIG. 3 is an explanatory view of the operation. In the event that a ground fault occurs, the discharge tube AR performs a discharge operation by connecting a discharge tube AR and a resistor R connected in series to the ground E2 'and the ground E3'. As a result, a current I flows, and V2 in FIG. 2 is reduced to V2 '= IR, thereby limiting V3' to an operating voltage of the varistor VR.

As described above, if the discharge tube AR operates,
The voltage is reduced, and the electric equipment can be protected from a ground fault. However, a switch is provided in parallel with the series circuit of the discharge tube and the resistor to prevent damage / deterioration of the electrodes of the discharge tube, and the ground E2 , E3 'may be short-circuited to stop the operation of the discharge tube.

That is, a switch capable of externally controlling the opening and closing is connected in parallel with the series circuit of the discharge tube and the resistor, and the switch is energized when a voltage is detected between the grounds E2 'and E3' or when the discharge tube is operated. If closed when current is detected, ground E
Since the 2 'and E3' are short-circuited, deterioration of the discharge tube can be prevented.

It is conceivable that another electrical device connected to the power supply circuit of the B system may cause a ground fault and cause the discharge tube to perform a discharging operation. In this case, the switch is operated in conjunction with this operation. If closed, the short circuit between the grounds E2 'and E3' has the disadvantage that the ground fault current of the electric equipment increases. In order to solve this, a series circuit of a discharge tube and a resistor may be separately incorporated. That is, in a protective device for ground fault protection, in which a switch SW1 whose opening and closing can be controlled externally is connected in parallel with the series circuit of the discharge tube AR1 and the resistor R1, the voltage phase L of the power supply circuit and the housing ground E3 'of the electric equipment are further connected. A discharge tube AR2 and a resistor R2 are connected in series between them, and if any one of the voltage between the voltage phase L and the housing ground E3 'and the current passed through the discharge tube AR2 is monitored and detected, the switch is opened and closed. Instrument SW1
Is to close.

In connection with the protector, the connection to the two kinds of grounds E2 'is often difficult in the case of existing facilities,
There is a need for a ground fault protector that can be easily connected to a distribution board near electrical equipment. In response to this, a ground fault protection protector that performs a desired function in the event of a ground fault accident is configured as follows.

That is, a series circuit of a discharge tube AR1 and a resistor R1 connected between a ground phase N of a power supply circuit to be protected from a ground fault in a power supply circuit of another system and a ground E3 'of a housing of an electric device. In parallel, a switch SW1 whose opening and closing can be externally controlled is connected, and further, a discharge tube AR2 and a resistor R2 are connected in series between a voltage phase L of a power supply circuit and a housing ground E3 'of an electric device, and a voltage phase L and a housing are connected. The switch SW1 is closed when one of the voltage between the body ground E3 'and the current passed through the operation of the discharge tube AR2 is monitored and detected, and a series circuit of the discharge tube AR1 and the resistor R1 is connected. An externally controllable switch SW2 is provided in series, a current flowing through the discharge tube AR1 discharged between the ground phase N of the power supply circuit and the housing ground E3 'of the electric device is detected, and a switch is provided after a predetermined time by a delay circuit. Open SW2 It was a ground fault protection for the security device.

[0015]

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

Embodiment 1 FIG. 4 shows two types of power supply circuits of A system and B system.
The parts equivalent to are denoted by the same reference numerals. That is, 1a,
1b is a transformer, 2a and 2b are electrical devices, E2 and E2 'are two types of grounds, E3 and E3' are electrical device housing grounds (three types of grounds), VR is a lightning arrester, and ELB is an earth leakage breaker. is there. ZCT indicates a ground fault alarm, and X indicates a ground fault protection protector of the present invention in this example.

This earth fault protection protector is constituted by a series circuit of a discharge tube AR discharging at a constant voltage and a resistor R,
It is connected between two types of ground E2 'of the power supply circuit of the electric device 2b to be protected and the housing ground E3' of the electric device. Therefore,
When a ground fault occurs in the power supply A system, the grounding E2 of the system B
When the discharge start voltage of the discharge tube AR is equal to or higher than the discharge start voltage of the discharge tube AR between the discharge tube AR and the housing ground E3 'of the electric device 2b, the discharge tube AR discharges and short-circuits with the resistor R.
Can be reduced below the operating voltage of the varistor VR to prevent damage to the varistor VR and to prevent power failure due to careless operation of the earth leakage breaker ELB. Embodiment 2 FIG. 5 shows an example in which means for preventing damage / deterioration of the electrodes of the discharge tube AR is added. The voltage reducing means at the time of occurrence of a ground fault is the same as in the first embodiment. That is,
A series circuit of a discharge tube AR and a resistor R that discharges at a constant voltage,
It is connected between the two types of ground E2 'of the power supply circuit of the electric device 2b to be protected and the housing ground E3' of the electric device. In this example, as means for protecting the discharge tube AR, a switch SW1 that can be externally controlled is connected in parallel with a series circuit of the discharge tube AR and the resistor R, and the switch SW1 is connected to a voltage between both grounds E2 'and E3'. By closing at the time of detection or at the time of detection of an energizing current at the time of operation of the discharge tube AR, the grounds E2 'and E3' are short-circuited. In the figure, VD is a voltage detection circuit, CD is a current detection circuit, and CT is a current transformer attached to a discharge tube circuit. In the ground fault protection protector X configured as described above, when a ground fault occurs, after the discharge tube AR discharges,
The switch SW1 is closed to short-circuit the grounds E2 'and E3' by detecting either the current value or the voltage between the grounds E2 'and E3', and the discharge operation of the discharge tube AR is stopped. Of the electrodes can be prevented from being deteriorated. It is preferable that the switch SW1 be closed after a certain period of time by a delay circuit in consideration of a malfunction.

Embodiment 3 When a series circuit of a discharge tube AR1 and a resistor R1 is connected between two types of ground E2 'of the power supply circuit of the electric equipment 2b and the housing ground E3' of the electric equipment, the other electric circuits of the power supply B system are connected. In some cases, the discharge tube AR1 performs a discharging operation due to a ground fault in the device 3b. When the switch SW1 is closed as in the second embodiment, the ground resistance is short-circuited, and the ground fault current in the electric device 3b increases. The earth fault protection protector X of the present embodiment shown in FIG. 6 takes such a case into consideration. That is, in this example, the detection of overvoltage due to the ground fault current of the A system, which is the original function of the protector, is performed by connecting the discharge tube AR2 and the resistor R2 in series between the voltage phase L of the power supply circuit and the housing ground E3 '. Discharge tube A due to overvoltage
The discharge current of R2 and the voltage between the voltage phase L and the ground E3 'are monitored, and when a certain voltage or more is detected or the current is detected, the switch SW1 is closed to stop the discharge of the discharge tube AR1 to prevent deterioration. Things. This focuses on the point that the voltage between the voltage phase L and the ground E3 'does not change even when the ground fault of the electric device 3b occurs. In this way, even if a ground fault occurs in the electric device 2b, the switch SW1 does not operate and the ground fault current does not increase. In the figure, VD is a voltage detection circuit, CD is a current detection circuit, and CT is a current transformer attached to the circuit of the discharge tube AR2.

Embodiment 4 In the case of existing equipment, the connection to the ground E2 'is often difficult, but the connection of the protector is connected to the voltage phase L, the ground phase N, and the housing ground E3' of the electric equipment. With this method, it can be easily grounded to the distribution board near the electrical equipment to be protected. The earth fault protection protector X shown in FIG. 7 shows an example thereof, and is capable of coping with a ground fault accident of the electric device 3b as in the third embodiment.

That is, in this example, a switch whose opening and closing can be externally controlled is connected in parallel with the series circuit of the discharge tube AR1 and the resistor R1 connected between the ground phase N of the power supply circuit and the housing ground E3 'of the electric equipment. SW1 is connected. Further, a discharge tube AR2 and a resistor R2 are connected in series between a voltage phase L of the power supply circuit and a housing ground E3 'of the electric device, and a voltage between the voltage phase L and the housing ground E3' and the discharge tube are connected. The switch SW1 is closed when one of the currents supplied through the operation of the AR2 is monitored and detected, and the switch SW2 which can be externally controlled is connected in series with the series circuit of the discharge tube AR1 and the resistor R1. A ground fault protection circuit for detecting a current flowing through the discharge tube AR1 between the ground phase N of the power supply circuit and the housing ground E3 'of the electric device and opening the switch SW2 after a predetermined time by a delay circuit. Protector X
And

When the discharge tube AR1 performs a discharge operation due to a ground fault of the electric equipment 2b of the power supply B system, when the connection of the protector to the ground E2 'is on the load side of the system ground fault alarm ZCT as shown in the figure, The alarm may be disabled, but the discharge tube AR1
If the switch SW2 is opened after a predetermined time of the discharge operation, the deterioration of the discharge tube AR1 can be prevented and the ground fault alarm device ZCT can be operated. In this way, in this example, the wiring can be easily attached to the distribution board near the electric equipment, and the ground fault alarm ZCT can be operated even when a ground fault occurs in another electric equipment of the same power supply circuit. And the deterioration of the discharge tube can be prevented. In the figure, VD is a voltage detection circuit, CD is a current detection circuit, and CT is
1, CT2 is a current transformer.

[0022]

As described above, according to the protector for ground fault protection of the present invention, when a ground fault occurs in one of a plurality of power supply circuits, the power supply circuit of another system is cut off, It can effectively prevent the blockage of the toll from being destroyed, and is most suitable for protecting toll collection electric equipment from a ground fault in a power circuit of a lighting lamp at a tollgate on a toll road or the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram when a ground fault occurs in a power supply circuit of AB2 system.

FIG. 2 is a diagram showing the principle of overvoltage generation due to the ground fault in FIG.

FIG. 3 is an explanatory view of the principle of overvoltage reduction of the earth fault protection protector according to the present invention.

FIG. 4 is a connection diagram showing an embodiment of a ground fault protection protector according to the present invention.

FIG. 5 is a connection diagram showing a second embodiment of the present invention.

FIG. 6 is a connection diagram showing a third embodiment of the present invention.

FIG. 7 is a connection diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

A: Power supply circuit of A system B: Power supply circuit of B system 1a, 1b: Transformer 2a, 2b, 2c: Electrical equipment E2, E2 ': Two types of grounding E3, E3': Housing of electrical equipment (3 types) VR: Varistor ELB: earth leakage breaker AR, AR1, AR2: discharge tube R, R
1, R2: Resistance SW1, SW2: Switch ZCT: Ground fault alarm X
... Protector for ground fault protection VD ... Voltage detection circuit CD ... Current detection circuit CT, CT1, CT2 ... Current transformer N ... Ground phase of power line L ... Voltage phase of power line

Continued on the front page (72) Inventor Hiroaki Shikata 3-2-6 Honcho, Chuo-ku, Osaka-shi Inside Osaka Fuse Co., Ltd. (72) Inventor Yoshishin Fujii 3-2-6 Honcho, Chuo-ku, Osaka-shi Osaka Huse Inside the corporation

Claims (4)

[Claims] 1. A series circuit of a discharge tube AR and a resistor R is connected between two kinds of grounds E2 'and a ground E3' of an electric equipment housing of a power supply circuit to be protected from a ground fault in a power supply circuit of another system. A protector for ground fault protection, characterized in that: 2. A switch SW1 whose switching can be externally controlled is connected in parallel with the series circuit of the discharge tube AR and the resistor R, and this switch is used when detecting a voltage between the grounds E2 'and E3' or when the discharge tube operates. 2. The protective device for ground fault protection according to claim 1, wherein the protective device is closed when an energizing current is detected. 3. A switch SW1 that can be externally controlled for opening and closing is connected in parallel with the series circuit of the discharge tube AR1 and the resistor R1, and further, the discharge tube is connected between the voltage phase L of the power supply circuit and the housing ground E3 'of the electric device. AR2 and the resistor R2 are connected in series, and one of the voltage between the voltage phase L and the housing ground E3 'and the current passed through the operation of the discharge tube AR2 is monitored. The earth fault protection protector according to claim 1, wherein the safety ground is closed. 4. A series circuit of a discharge tube AR1 and a resistor R1 connected between a ground phase N of a power supply circuit to be protected from a ground fault in a power supply circuit of another system and a housing ground E3 'of an electric device. Switch SW1 that can externally control the opening and closing in parallel
The discharge tube AR2 and the resistor R2 are connected in series between the voltage phase L of the power supply circuit and the housing ground E3 'of the electric device, and the voltage between the voltage phase L and the housing ground E3' and the discharge tube AR2
Operates to detect and detect one of the supplied currents, closes the switch SW1, and provides an externally controllable switch SW2 in series with the series circuit of the discharge tube AR1 and the resistor R1. , The current flowing through the discharge tube AR1 between the ground phase N of the power supply circuit and the housing ground E3 'of the electric equipment is detected, and the switch SW2 is turned on after a predetermined time by the delay circuit.
A protective device for ground fault protection, characterized in that it is opened.