JPH0820476B2 - Water tree current detection method for CV cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is suitable for measuring a water tree current generated due to insulation deterioration of a CV cable (crosslinked polyethylene insulated vinyl sheath cable) in a live state. The present invention relates to a water tree current detection method for a CV cable.

(Prior Art) As shown in FIGS. 2 and 3, for example, in a CV cable 1, a conductor 2 is covered with an inner semiconductive layer 3, and an outer semiconductive layer 4 and an inner semiconductive layer 3 are provided. A cross-linked polyethylene 5 as an insulator is interposed between the outer semiconductive layer 4 and the shielding copper tape 6
The shield copper tape 6 is covered with a shielding cloth 7 and the pressing cloth 7 is wrapped around the shielding copper tape 6, and the pressing cloth 7 is insulated with an insulating vinyl sheath 8.
Is formed by coating. As shown in FIG. 4, the CV cable 1 is provided with three structural bodies in which the shielding copper tapes 6 are integrated, and the shielding copper tapes 6 are brought into contact with each other to hold the pressing cloth 7 on the three structural bodies. A CV cable (CV cable of the so-called triplex type) which is a CV cable in which the pressing cloth 7 is covered with an insulating vinyl sheath 8
There is also T). Reference numeral 9 indicates an inclusion.

When the CV cable 1 is insulation deteriorated, a water tree current I _i is generated as shown in FIG. In the example shown in FIG. 5, the shielding copper tape 6 side is + potential, and the conductor 2 side is −.
It is a potential. Further, the water tree current I _i may flow in the direction opposite to the direction shown in the drawing. In order to measure this water tree current I _i, as shown in FIG. 6, the shield copper tape 6 on the other side of the CV cable 1 having one side connected to the high voltage distribution line 10 and the other side connected to a load is grounded. The wire 11 is drawn out, and the water tree current I _i as a quantity related to insulation deterioration is inserted in the middle of the ground wire 11.
The measuring device 12 for measuring is connected. The measuring device 12 includes a detection resistor 13, an amplifier 14 having a filter, and a recording device.
It is composed of 15 and.

However, there is a battery-acting electromotive force E _S between the insulating vinyl sheath 8 and the ground, and a commercial-frequency electromotive force E _AC due to an unbalanced system load between the ground wire 17 of the GPT 16 and the ground, and the ground of the GPT 16 is present. There is a battery action electromotive force E _E in the part. FIG. 7 shows this state by an equivalent circuit. This 7th
In the figure, R _i is the insulation resistance of the cross-linked polyethylene 5 part of the CV cable 1, R _S is the sheath resistance of the insulating vinyl sheath 8, and the electromotive force E _i and the insulation resistance R _i are parallel to the capacitor C _i. It is thought that there is a capacitor C _{S in} parallel with the cell action electromotive force E _S and the sheath resistance R _S.

With these electromotive forces E _S , E _E , and E _AC , the stray currents I _S and I
_E and an alternating current I _AC are generated, and the stray currents I _S and I _E flow into the measuring device 12 as a DC component current together with the water tree current I _i . FIG. 8 shows an equivalent circuit in which the equivalent circuit shown in FIG. 7 is rewritten and expressed by focusing on only the DC component current.

FIG. 8 shows the stray current I _S as a DC component current,
A state where I _E is flowing together with the water tree current I _i is shown, and the symbol I is the total DC component current including the stray currents I _S and I _E and the water tree current I _i . The stray currents I _S and I _E are determined by the resistances R _S and R _E and the electromotive forces E _S and E _E acting on the battery, and the stray current I _E is the ground line 11a between the measuring device 12 and the ground. It can be removed by sharing it with the ground wire 17 of GPT16. Therefore, considering the stray current I _S, the electromotive force E _i water tree current I _i
Is usually several tens of volts or less, and the electromotive force E _S , E _E of the battery is 0.
It is about 5 volts or less. Also, the insulation resistance R _i is several hundred thousand M
Ω, the sheath resistance R _S is usually smaller than the insulation resistance, and if the sheath resistance R _S is 200 MΩ or more, the stray current I _S is 2.5 nanoamps or less, whereas the water tree current I _i is 10 in the deteriorated cable. Since there is about nanoamperes, it is not necessary to consider the stray current I _S under normal conditions, but the sheath resistance R _S fluctuates significantly depending on environmental conditions and other factors, and when the sheath resistance R _S becomes 200 MΩ or less, it becomes relatively stray. The proportion of the current I _S contributing increases. In FIG. 6, 18 is a power source, 19 is a ground wire pulled out from the shielded copper tape 6 on one side of the CV cable 1, and 20 is a switch opened at the time of measurement.

(Problems to be solved by the invention) Therefore, in order to prevent a dielectric breakdown accident due to insulation deterioration of the CV cable 1 by using the conventional measuring device 12, the water tree current I _i based on the insulation deterioration of the CV cable 1 is prevented. Detect
Method for detecting water tree current in CV cable
59-202075), it becomes impossible to distinguish whether the stray current I _S is being measured or the water tree current I _i is being measured.

In such a case, it is preferable to have a method capable of measuring the water tree current I _i without being affected by the stray current I _S.

The present invention has been made from the above viewpoint, and it is an object of the present invention to provide a water tree current detection method for a CV cable, which can accurately measure the water tree current even when a stray current flows.

(Means for Solving the Problem) The water tree current detection method for a CV cable according to the present invention is a GP
T is pulled out from the high-voltage distribution line and grounded, and the CV cable is grounded through the grounding wire pulled out from the shielded copper, and the water tree current and the stray current are inserted by interposing a measuring instrument in the middle of the grounding wire. After measuring the total DC component current including
A measuring instrument for detecting a stray current in the middle of the ground wire that is pulled out from the high voltage distribution line and grounded to the ground side of the GPT and that is pulled out from the shielded copper of the CV cable and grounded. While connecting the one terminal side of
One terminal side of the measuring device is connected between the capacitor and the GPT, the ground side of the capacitor is connected to the other terminal side of the measuring device, and a stray current is caused to flow through the measuring device. Is measured and the stray current is subtracted from the total DC component current to measure the water tree current.

(Example) Below, the water tree current detection method of the CV cable which concerns on this invention is demonstrated, referring drawings.

FIG. 1 is a diagram showing an embodiment of a method for detecting a water tree current of a CV cable according to the present invention, which is a ground of a GPT 16 which is grounded through a ground wire 17 which is drawn from a high voltage electric wire 10 and connected to the ground. A capacitor C'is interposed in the middle of the wire 17, and is drawn out from the shielding copper 6 of the CV cable 1 and grounded to the ground. In the middle of the ground wire 11, one terminal 12 of a measuring device 12 'for detecting a stray current is provided. While connecting the'a side, one terminal 12'a side of this measuring device 12 'is connected between the capacitor C'and the GPT 16 via a connection line 50, and the ground side of the capacitor C'is connected to a connection line 51. It is connected to the other terminal 12'b side of the measuring device 12 'via the.

If the measuring device 12 'and the capacitor C'are connected in this way, only the stray current I _S flows through the measuring device 12', and the water tree current I _i bypasses the measuring device 12 'and the high voltage distribution line 10 Reflux to. Therefore, interpose the measuring device 12 in the middle of the ground wire 11,
Total DC component current I including stray current I _S and water tree current I _i
Then, as shown in FIG. 1, a measuring device 12 'and a capacitor C'are connected to change the total DC component current I to the stray current.
By subtracting I _S , the water tree current I _i can be accurately measured.

(Effects of the Invention) As described above, the method for detecting the water tree current of the CV cable of the present invention makes it possible to cause only a stray current to flow in the measuring instrument by interposing a capacitor in the middle of the ground wire of the GPT. By subtracting the stray current from the total DC component current including the tree current and the stray current, the water tree current itself can be accurately measured even in a live state.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining a method for detecting a water tree current of a CV cable according to the present invention, FIG. 2 is a sectional view of a CV cable according to the present invention, FIG. 3 is a side view thereof, and FIG. FIG. 5 is a sectional view of another CV cable according to the invention, FIG. 5 is an explanatory view of a water tree current generation mechanism according to the invention, and FIG. 6 is a connection diagram of a conventional measuring instrument to a CV cable, FIG. 7, FIG. FIG. 8 is an equivalent circuit of the connection diagram shown in FIG. 1 …… CV cable, 10 …… High-voltage distribution line 11 …… Grounding wire, 12,12 ′ …… Measuring instrument 16 …… GPT, 17 …… Grounding wire 51 …… Connecting wire, C ′ …… Capacitor I _i … … Water tree current, I _S …… Stray current I …… Total DC component current

Claims (1)

[Claims] 1. A GPT is pulled out from a high-voltage distribution line and grounded, a CV cable is grounded via a grounding line pulled out from its shielding copper, and a water tree current is provided by interposing a measuring device in the middle of the grounding line. After measuring the total DC component current including the stray current and the stray current, insert a capacitor on the ground side of the GPT that is pulled out from the high-voltage distribution line and grounded, and that is pulled out from the shielded copper of the CV cable and grounded. In the middle of the line, one terminal side of the measuring device for detecting the stray current is connected, while one terminal side of the measuring device is connected between the capacitor and the GPT, and the ground side of the capacitor is It is connected to the other terminal side of the measuring device, a stray current is passed through the measuring device to measure the stray current, and the water tree current is measured by subtracting the stray current from the total DC component current. CV Water tree current detection method of Buru.