JP2586749B2 - Alarm device for power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alarm device for a power cable, and more particularly to an alarm device for preventing a surge voltage from a secondary side from entering a power supply or an external alarm circuit.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, in order to protect an anticorrosion layer from a surge voltage in a power cable 16,
The metal sheath of the power cable 16 is grounded at one end,
The other piece is provided with a sheath arrester 19. If the sheath arrester 19 is broken, the alarm contact 12 provided on the sheath arrestor is operated as shown in FIG. 14 is a monitoring device (external alarm), 17 is
This is a power cable termination box.

That is, FIG. 4A shows a general power cable alarm device (2 ) used for such a purpose.
0) shows the internal wiring diagram of FIG.
The alarm contact 12 ((a) in FIG. 4 is an example of a normally closed type, but it may be a normally open type) on the secondary side and a relay 9a as shown in (b) of FIG. If it is connected and the alarm contact 12 is opened when the
a is cut off and the contact (b contact) 9b of the relay is closed, as shown in FIG.
An abnormality of the sheath arrester is reported to the monitoring device 14 or the control panel as shown . When the inspection switch 3 is opened, the relay 9a is turned off and the contact 9b is closed, so that the circuit can be inspected.

In this case, a surge absorber 11 is provided to protect components from a surge voltage that enters the alarm device through the alarm contact 12.

[0005] In FIG. 4, the 1-AC power source, 2 is a power switch, the inspection switch 3, 4 fuses, 5 is a power indicator.

[0006]

However, in a power cable system, when a ground fault due to a lightning strike or the like occurs, a sheath arrester may be damaged by a high abnormal voltage induced in a metal sheath of the cable. It is possible. In such an alarm device for a power cable that detects the breakage of the sheath arrester and notifies the abnormality, it is conceivable that a high surge voltage always enters. In some cases, it is sufficiently possible to enter the power supply line through a power supply transformer, enter the monitoring device through another device connected to the same power supply or a contact point of a relay, and damage these devices.

Accordingly, it is an object of the present invention to provide a new alarm device for a power cable which can surely prevent a high surge voltage from an alarm contact from entering a power supply or a relay contact into another device. To provide.

[0008]

SUMMARY OF THE INVENTION A power cable according to the present invention
Alarm device for the power cable, when the sheath arrester for the power cable is damaged by surge voltage ,
An insulation transformer is used in an alarm device that informs the abnormality to the outside by opening (or closing) the accompanying alarm contact .
Connect the alarm contact to the secondary side of this isolation transformer
AC power supply and meter relay on the primary side of the isolation transformer.
To monitor the movable contact of this meter relay.
Connected to, Ru der which the movable contact of the meter <br/> Rire by the primary current of the isolation transformer is configured so as to report the abnormal external by opening (or closing). In addition,
On the secondary side of the edge transformer, a variable resistor, surge absorber
It is good to have a soap bar.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

FIG. 1A is a wiring diagram showing an embodiment of the present invention, in which an insulating transformer 7 is provided, a meter relay 8a is incorporated on a primary side (AC power supply 1 side), and a movable contact 8b of the meter relay 8a. Is connected to the monitoring device 14 as shown in FIG. A variable resistor 10, an inspection switch 3, a surge absorber 11, and an alarm contact 12 are connected to the secondary side of the insulating transformer 7, and the movable contact 8b of the meter relay is always open and the alarm contact 12 is open. Then, the meter relay 8a detects a change in the primary current of the insulating transformer 7, and the movable contact 8b of the meter relay closes to notify the monitoring device 14 of an abnormality.

In the case of a normally open circuit type, a change in the primary current when the alarm contact 12 is closed is detected, and an abnormality is notified by closing the movable contact 8b of the meter relay.

FIG. 2 shows an example of the relationship between the primary current flowing through the current-voltage meter relay at this time. For example, when the power supply voltage is 100 V and the alarm contact 12 is opened, the current flowing through the meter relay 8a becomes 18 mA. If the value of the variable resistor 10 and the value of the shunt resistor 17 are set to the above, the change of the current flowing through the meter relay 8a with respect to the change of the power supply voltage is as shown by a curve 15a when the alarm contact 12 is open. The change in current when the alarm contact 12 is in the open state is as shown by a curve 15b. Therefore, assuming that the fluctuation range of the power supply voltage is about 90 V to 108 V, the operation set value of the movable contact 8b of the meter relay may be set to 30 mA. Also, since the movable contact of the meter relay can be adjusted arbitrarily, if the local power supply voltage fluctuates
If the voltage is 0 V, the operation set value of the movable contact 8b of the meter relay may be set to 35 mV, which can be adjusted to the actual situation of the local voltage fluctuation.

As described above, if the primary current of the insulating transformer 7 is measured by the meter relay 8a and an alarm is issued, a surge voltage that enters through the alarm contact 12 can be blocked by the surge absorber 11 and the insulating transformer 7.

[0014]

As described above, according to the alarm device for a power cable of the present invention, since a change in the primary current is detected by a meter relay by incorporating an insulating transformer, a surge characteristic which enters through the alarm contact can be detected. Voltage can be blocked and other equipment connected to the same power line and the monitoring device to which the contacts of the meter relay are connected can be protected from surge voltage.

[Brief description of the drawings]

FIG. 1A is a wiring diagram showing one embodiment of an alarm device according to the present invention, and FIG. 1B is an enlarged view of a meter relay unit.

FIG. 2 is a diagram showing a relationship between a power supply voltage and a primary current in one embodiment of the present invention.

FIG. 3 is a system diagram of a power cable.

FIG. 4A is a wiring diagram of a conventional power cable alarm device. (B) is an enlarged view of the meter relay section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Power switch 3 Inspection switch 4 Fuse 5 Power indicator lamp 6 Power transformer 7 Insulation transformer 8a Meter relay 8b Meter relay contact 9a Relay 9b Relay movable contact 10 Variable resistor 11 Surge absorber 12 Alarm contact 13 Shunt Resistor 14 Monitoring device (external alarm) 15a Primary current when contact is open 15b Primary current when contact is closed 15c Meter relay set value 16 Power cable

Claims (3)

(57) [Claims] When a sheath arrester for a power cable is damaged by a surge voltage, it is attached to the sheath arrester.
In warning device to inform the external abnormalities by open (or closed) alarm contacts that, using an isolation transformer, this
Connect the alarm contact to the secondary side of the isolation transformer of
Connect an AC power supply and meter relay to the primary side of the edge transformer
And connect the movable contact of this meter relay to the monitoring device.
An alarm device for a power cable, which is configured to report an abnormality to the outside by opening (or closing) a movable contact of a meter relay by a primary current of the insulating transformer . 2. The alarm device for a power cable according to claim 1, further comprising a variable resistor on a secondary side of said insulating transformer. 3. An alarm device for a power cable according to claim 1, wherein a surge absorber is provided on a secondary side of said insulating transformer.