JPS62298778A - Insulation abnormality detection for cable line - Google Patents

Abstract

PURPOSE:To always detect insulation abnormality without fetching a signal from a high voltage section, by comparing ground currents on both sides of an insulating connection part of a cable to judge abnormality in the insulation when either thereof increases relatively. CONSTITUTION:Ground currents flow to leads 9A and 9B linked to an insulating connection part 3C as measuring point from cables 1C and 3D on both sides thereof and then, to first and second coils 12A and 12B respectively. An insulation abnormality detector 10 is adjusted with a tap changer 13 beforehand so that a magnetic flux in a circular core 11 is zero when a cable line 4 is normal. A charge current Ic of the ground currents depends on the electrostatic capacitance of the cables while the effective current IR thereof depends on the insulation resistance thereof. If a change is caused in the dielectric constant insulation resistance of one cable 1C or 1D, current flows to a third coil 13C and an alarm 15 sounds as it exceeds a specified level normal.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a cable line insulation abnormality detection method for detecting insulation abnormality of a cable line.

(Prior art) As shown in FIG. 3, in a cable line 4 in which a cable 1 is connected by a normal connection part 2 and an insulated connection part 3, tan δ is one of the indicators of abnormality in the cable 1. Due to the increasing phenomenon, t is periodically increased on real lines.
An δ is being measured. In this case, conventionally, the charging is temporarily stopped, the standard capacitor 5 is connected to the high voltage part of the cable head 6, and the ground current of the standard capacitor 5 and the cable 1 is compared with the tan δ measuring device 7. was being measured. In this case, the insulating connection part 3 is insulated from ground by the axter 8.

(Problems to be Solved by the Invention) However, with such a cable line insulation abnormality detection method, tan δ cannot be constantly monitored, and tan δ
There was a problem in that it was necessary to temporarily stop charging the cable line 4 during measurement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting an insulation abnormality in a cable line that can detect an insulation abnormality in a cable line in a live line state.

(Means for Solving the Problems) In order to achieve the above object, the means of the present invention will be explained with reference to FIGS. 1 and 2 corresponding to the embodiments. Insulated connection part 3A.

3B, 3C, . . . are provided to form the cable line 4, the insulation connection portions 3B and 3D on both sides of a certain insulation connection portion 3C are grounded with an arrester 8.8. and cable ICs on both sides of the insulated connection portion 3C.

The feature is that the 1D ground currents are compared, and if either ground current increases relatively, it is determined that there is an insulation abnormality.

(Function) When detection is performed in this manner, no signal is extracted from the high-voltage section, so insulation abnormalities can be detected at all times in the energized state.

(Example) Examples of the present invention will be described in detail below with reference to FIGS. 1 and 2. As shown, cable 1A, IB, IC
. . . are insulated connection parts 3A, 3B, and 3C.

... to form the cable line 4, the insulation abnormality can be detected by checking the cables 1A and IB in each section.
...When detecting every other insulation connection part 3B
, 3D, . . . are insulated from ground using an arrester 8. Insulated connection parts 3A, 3C, 3 to which arrester 8 is not connected
E,... have cables IA, IB, and IC on both sides.
, ID, IE, and IF, connect the lead wires 9A and 9B, and connect these lead wires 9A and 9B.
is connected to the insulation abnormality detector 10. Insulation abnormality detector 10
has an annular iron core 11, and the annular iron core 11 has first to third coils 12A each having a number of turns of N1, N2, and Nd.

12B and 12C are wound respectively, and the lead l119A
is connected to one end of the first coil 12A via the tap changer 13, the other end of the first coil 12A is grounded, the lead wire 9B is connected to one end of the second coil 12B, and the second The other end of the coil 1B is grounded, and the third coil 12C
is connected to an amplifier 14, and the amplifier 14 is connected to an alarm 15. In addition, 16A and 16B are
Insulation connection parts 3A and 3C to which the insulation abnormality detector 10 is connected.

This is the capacitance on both sides of 3E.

In this case, the ground current from the cables IC and 1D on both sides flows through the leads 119A and 9B connected to the insulated connection portion 3C at the location to be measured. This ground current is connected to the cable IC.

Charging current 1c (-ωC■) to 1D and effective current IR (
=V/R). Here, ω is the frequency of the applied voltage,
C is the capacitance of the cable, and ■ is the applied voltage R is the insulation resistance of the cable. Each ground current passes through lead wires 9A and 9B to the first. Flows into the second] files 12A and 12B. The insulation abnormality detector 10 detects the first one so that the magnetic flux in the annular iron core 11 becomes zero when the cable line 4 is normal. second coil 12
The ratio of the number of turns N1 and N2 of A and 12B is adjusted in advance by a tap changer 13. In this state, the current flowing through the third coil 12G is constantly monitored. Of the ground currents, the charging current 1c depends on the capacitance (or dielectric constant) of the cable, and the effective current In depends on the insulation resistance of the cable. If the dielectric constant or insulation resistance of the cable IC or ID on one side changes for some reason, the first cable wound around the annular core 11 may change. The ground current flowing through the second coils 12A, 12B changes, thereby generating magnetic flux in the annular iron core 11, and current flows through the third coil 12G. This current is amplified by an amplifier 14, and when the level exceeds a certain level, an alarm is issued from an alarm device 15.

Here, tan δ of the cable is expressed as tan δ - IR/Ic = 1/ωcR - (1), so the fact that the alarm 15 issues an alarm means tan
This means that an abnormality has occurred in the value of δ, and tan δ can be constantly monitored. Since the insulation abnormality detector 10 used in the present invention cannot determine the absolute value of the change in tan δ, after an alarm is issued, a tan δ measuring device can be brought to the site and tan δ can be precisely measured.

Next, an example of measurement data will be explained. The cable used (
The capacitance of the cable (66 KV) is 200 pF/m, and the cable length is approximately 1000 m between connections. Therefore, lc-ωCV = 2.4A Also, since tanδ is 0.0001 as a normal value, 1
R=tan δx l c = O, 0O024A.

Therefore, the ground current is (Ic 2 + IR2) Φ2.4A = [c. t
Since the main cause of the and[delta] change is due to an abnormality in insulation resistance, Ic remains almost constant and In increases. Therefore, if the tanb difference between cable IC and ID (
-8 tan δ) is o, oo.

In order to issue an alarm when the temperature exceeds 5, the sensitivity of the third coil 12C is determined by the increase in IR, △IR, from formula (1), ΔIR=Δtanδ×IC −〇, 0005 x 2.4= 0.0012Φ1(a
mA). Therefore, an experiment was conducted using an insulation abnormality detector 10 with a sensitivity of about 0.11111A. When the grounding current on the cable 1B side was increased by 0.1 mA or more in a simulated manner, the alarm 15 issued an alarm.

Note that if this is carried out in a energized state, there is a risk of malfunction due to induction due to changes in the energized current, so the insulation abnormality detector 10
must be placed in a shield box or at least 1 m away from the cable line 4.

In this embodiment, a current transformer type amparator is used as the insulation abnormality detector 10, but the problem of induction can be solved by using an optical magnetic field sensor instead.

(Effects of the Invention) As described above, according to the present invention, since a signal is not extracted from the high voltage section, insulation abnormality can be detected at all times while the power is being applied. Therefore, it is possible to prevent a ground fault of the power cable.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of a cable line in which the method of the present invention is implemented, Fig. 2 is a wiring diagram showing an example of an insulation abnormality detector used in the present invention, and Fig. 3 is a diagram showing an example of a conventional method. FIG. 2 is an explanatory diagram of a cable line implementing the 1A to 1F...Cable, 3A to 3E...Insulated connection part, 4...Cable line, 8...Arrester, 9A
. 9B... Lead wire, 10... Insulation abnormality detector.

Claims (1)

[Claims] In a method for detecting an insulation abnormality in a cable line in which insulated connection parts are provided at appropriate intervals to constitute a cable line, the insulated connection parts on both sides of a certain insulated connection part are respectively insulated from ground to ground using an arrester, and the certain insulation A method for detecting an insulation abnormality in a cable line, comprising comparing ground currents of cables on both sides of a connection part, and determining an insulation abnormality when either ground current increases relatively.