JPH04255418A - Alarm for power cable - Google Patents

Abstract

PURPOSE:To block a surge voltage entering through an alarm contact by incorporating an insulating transformer and detecting variation of primary current through a meter relay. CONSTITUTION:An insulating transformer 7 is arranged in an alarm unit and a meter relay 8a having movable contact 8b connected with a monitor 14 is built in on the primary. Variation of the primary current of the insulating transformer 7 is detected through the meter relay 8a and an abnormality is notified to the monitor 14 by opening or closing the movable contact 8b while furthermore a surge voltage entering through an alarm contact 12 is blocked by means of a surge absorber 11 and the insulating transformer 7. According to the invention, other machines connected with same power supply line and a monitor connected with the contact of meter relay can be protected against surge voltage.

Description

[Detailed description of the invention]

0001

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

0002

2. Description of the Related Art Generally, as shown in FIG. 3, in order to protect the anti-corrosion layer from surge voltage in a power cable 16
The metal sheath of the power cable 16 has one end grounded 18;
A sheath arrester 19 is installed on the other piece. In the event that the sheath arrester 19 is damaged, the alarm contact 12 provided on the sheath arrester operates as shown in FIG. 3, thereby causing the power cable alarm device 20 to display the abnormality.

That is, FIG. 4(a) shows an internal wiring diagram of a general power cable alarm device used for this purpose, and shows an alarm contact on the secondary side of the power transformer 6. 12 ((a) in FIG. 4 is an example of a normally closed type, but there is no problem even if it is a normally open type) and a relay 9a as shown in (b) in FIG. 4 is connected,
When the alarm contact 12 is opened in the event of an abnormality, the relay 9a is disconnected and the relay contact (b contact) 9b is closed to notify other monitoring devices or a control panel of the abnormality of the sheath arrester. Further, when the inspection switch 3 is opened, the relay 9a is disconnected and the contact 9b is closed, so that the circuit can be inspected.

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

[0005] The symbols shown in the above and subsequent drawings are 1 for AC power supply, 2 for power switch, 3 for inspection switch, 4 for fuse, 5 for power indicator, 6 for power transformer, and 7 for insulation. Transformer, 8a is meter relay,
8b is a meter relay contact, 9a is a relay, 9b is a movable contact of the relay, 10 is a variable resistor, 11 is a surge absorber, 12 is an alarm contact, 13 is a shunt resistor, 14
is a monitoring device (external alarm), 15a is the primary current when the contact is open, 15b is the primary current when the contact is closed, 15c is the setting value of the meter relay, 16 is the power cable, 17 is the termination box for the power cable, 18 19 is a sheath arrester, and 20 is a power cable alarm device.

[0006]

[Problem to be Solved by the Invention] However, in power cable systems, when a ground fault occurs due to a lightning strike, the sheath arrester may be damaged by the high abnormal voltage induced in the metal sheath of the cable. It is possible that In such a power cable warning device that detects damage to the sheath arrester and notifies the user of an abnormality, it is possible that high surge voltage will always enter the system. In some cases, it may enter the power line through the power transformer, enter the monitoring device through the contacts of other devices or relays connected to the same power source, and may even damage these devices.

Therefore, an object of the present invention is to provide a novel power cable alarm device that can reliably prevent high surge voltage from the alarm contact side from entering other equipment through the power supply or relay contacts. It's there to provide.

[0008]

[Means for Solving the Problems] Firstly, when a power cable sheath arrester is damaged by surge voltage, the present invention provides insulation in an alarm device that notifies the outside of an abnormality by opening (or closing) its contacts. Has a transformer,
The load current on the primary side opens (or closes) a movable contact of a meter relay, for example, so that an abnormality can be reported to the outside.Secondly, the secondary side of the isolation transformer A variable resistor is provided in the transformer. Thirdly, a surge absorber is provided on the secondary side of the isolation transformer.

[0009]

EXAMPLES The present invention will be described in detail below with reference to Examples.

FIG. 1A is a wiring diagram showing an embodiment of the present invention, in which an insulating transformer 7 is provided, and a meter relay 8a is installed on the primary side (AC power supply 1 side), and a movable contact 8b of the meter relay 8a is installed. is connected to the monitoring device 14 as shown in FIG. 1(b). Also, 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 isolation transformer 7, and the movable contact 8b of the meter relay is normally open and the alarm contact 12 is open. At this time, 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 the abnormality.

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

FIG. 2 is an example showing 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 values of the variable resistor 10 and the shunt resistor 13 are set so that the alarm contact 7 is open, the change in the power flowing to the meter relay 8a in response to a change in the power supply voltage will be as shown by a curve 15a. Further, when the alarm contact 7 is in a closed state, the current changes as shown by a curve 15b. Therefore, the fluctuation range of the power supply voltage is
Considering that the voltage is about 0V to 108V, the operating setting value of the movable contact 8b of the meter relay should be 30mA. In addition, the movable contact of the meter relay can be adjusted arbitrarily, so if the local power supply voltage fluctuation range is 95V to 110V.
In this case, the operating setting value of the movable contact 8b of the meter relay may be set to 35 mA, and this can be adjusted to the actual situation of local voltage fluctuations.

If the primary current of the insulating transformer is measured by the meter relay and an alarm is issued in this way, the alarm contact 7
The surge voltage that enters through the surge absorber 11
This can be prevented by the isolation transformer 7.

[0014]

[Effects of the Invention] As explained above, according to the power cable alarm device of the present invention, since an insulating transformer is incorporated and changes in the primary current are detected by a meter relay, surges entering through the alarm contact are detected. The voltage can be blocked, and other equipment connected to the same power line and the monitoring device to which the meter relay contacts are connected can be protected from surge voltage.

[Brief explanation of the drawing]

FIG. 1 (a) is a wiring diagram showing one embodiment of an alarm device according to the present invention, and (b) is an enlarged view of a meter relay section.

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

FIG. 3 is a power cable system diagram.

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

[Explanation of symbols]

1 AC power supply 2 Power switch 3 Inspection switch 4 Fuse 5 Power indicator light 6 Power transformer 7 Isolation 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 the contact is open 15b Primary current when the contact is closed 15c Meter relay setting value 16 Power cable

Claims (3)

[Claims] Claim 1: When a power cable sheath arrester is damaged by surge voltage, its contacts open (or close).
An alarm device that notifies the outside of an abnormality by having an isolation transformer, and is configured to be able to notify the outside of an abnormality by, for example, opening (or closing) a movable contact of a meter relay due to the load current on the primary side of the transformer. A warning device for power cables. 2. The power cable alarm device according to claim 1, further comprising a variable resistor on the secondary side of said isolation transformer. 3. The power cable alarm device according to claim 1, further comprising a surge absorber provided on the secondary side of the insulation transformer.