JPH02162266A - Method for detecting water tree current in cv cable - Google Patents

Abstract

PURPOSE:To accurately measure a water tree current even when a stray current flows by interposing a capacitor on the earth side of the GPT drawn out from a high voltage distribution line to be earthed and allowing the same to bypass a measuring device to reflux the stray current. CONSTITUTION:A capacitor C is interposed on the earth side of the GPT 16 drawn out from a high voltage distribution line 10 to be earthed. A measuring device 12 for detecting a DC component current containing a water tree current and a stray current is connected on the way of the earth line 11, which is drawn out from the shield copper of a CV cable to be earthed, on the side of one terminal thereof and connected to the midway between the GPT 16 and a capacitor C' on the side of the other terminal thereof. The stray current flowing to the capacitor C' from the earth line 11 through the earth is allowed to bypass the measuring device to be reflexed to the earth line 11 and the water tree current is measured in a live wire state by the measuring device 12.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention is suitable for measuring water tree current generated due to insulation deterioration of a CV cable (cross-linked polyethylene insulated vinyl sheathed cable) in a live line state. The present invention relates to a water tree current detection method for a CV cable.

(Prior Art) As shown in FIGS. 4 and 5, for example, a CV cable 1 includes a conductor 2 covered with an inner semiconducting layer 3, an outer semiconducting layer 4 and an inner semiconducting layer 3. A cross-linked polyethylene 5 as an insulator is interposed between the external semiconducting layer 4 and the shielding copper tape 6 to cover and shield the shielding steel tape 6, and the shielding steel 16 is wrapped with a presser cloth 7, and the presser cloth is 7 is covered with an insulating vinyl sheath 8. Note that, as shown in FIG. 6, the CV cable 1 is provided with three structures in which up to the shielding copper tape 6 are integrated, and the shielding copper tapes 6 are brought into contact with each other, and a pressing cloth 7 is attached to the three structures. The CV is made by wrapping the pressing cloth 7 and covering it with an insulating vinyl sheath 8.
There is also a so-called triplex type CV cable (CV T '').

Reference numeral 9 indicates an inclusion.

When the insulation of this CV cable 1 deteriorates, a water tree current breakage 1 occurs as shown in FIG.

In the example shown in FIG. 7, the side of the shielding copper tape 6 has a positive potential.
The conductor 2 side is at one potential. Further, the water tree-current works 1 may flow in a direction opposite to that shown in the drawings. This water tree current! -, as shown in Figure 8,
A grounding wire 11 is pulled out from the shielding steel tape 6 on the other side of the CV cable 1, which is connected to the high-voltage distribution line 10 on one side and the load on the other side, and a water droplet is inserted in the middle of the grounding wire 11 as a quantity related to insulation deterioration. - connect a measuring device 12 for measuring the electric current 1; This measuring device 12 is generally composed of a detection resistor 13, an amplifier 14 having a filter, and a recording device 15.

However, there is a battery action electromotive force E$ between the insulating vinyl sheath 8 and the earth, and a commercial frequency electromotive force Esc between the grounding wire 17 of the G P T 16 and the earth due to the unbalanced system load. There is a battery action electromotive force EE at the ground portion of P T 16. FIG. 9 shows this state using an equivalent circuit. In this figure, R1 is the insulation resistance of the cross-linked polyethylene 5 part of the CV cable 1, R$ is the sheath resistance of the insulating vinyl sheath 8 part, and there is a capacitor C1 in parallel with the electromotive force E+ and the insulation resistance R+. It is considered that there is a capacitor C$ in parallel with the battery action electromotive force E$ and the sheath resistance R1. With these electromotive forces E-5EE and E^C, the stray currents $ and XE
, an alternating current flow ^C is generated, and a stray current II, IC flows as a DC current component into the measurement@12 together with the water tree current flow 1. The equivalent circuit shown in Figure 9 is the DC current component! FIG. 10 shows an equivalent circuit rewritten and expressed by focusing only on the above.

In FIG. 10, stray current Xs as a DC current component is shown.
, xi are shown in a state where they are stagnant together with the water tree-electrical work 1. The stray current Iε is determined by the resistance R$, RE and the battery action electromotive force Es, E.
This can be eliminated by sharing a with the grounding line 17 of the GPT 16. Therefore, considering the stray electric current worker 1, the electromotive force E1 of the water tree electric current worker 1 is usually about several tens of volts or less, and the battery action electromotive forces Es and EE are about 0.5 volt or less. In addition, the insulation resistance R is several tens of MΩ, the sheath resistance R$ is smaller than the normal insulation resistance, and the sheath resistance R$
When is 200MΩ or more, the stray current is less than 2.5 nanoamperes, whereas in a deteriorated cable, the water-trimmed current 1 is about 10 nanoamperes.
Under normal conditions, there is no need to consider stray current flow, but sheath resistance R$ fluctuates greatly depending on environmental conditions and other factors, and when sheath resistance R$ becomes 200 MΩ or less, the relative contribution of stray current flow increases. becomes larger. In addition, the 8th
In the figure, 18 is a power supply, 19 is a grounding wire drawn out from the shielding copper tape 6 on one side of the CV cable 1, and 20 is a switch that is opened during measurement.

(Problem to be solved by the invention [) Therefore, in order to prevent insulation breakdown accidents due to insulation deterioration of the CV cable 1 using the conventional measuring instrument 12,
In the CV cable water tree current detection method (for example, Japanese Patent Application Laid-Open No. 59-202075) that detects the water tree current I+ based on the insulation deterioration of the V cable 1, it is difficult to determine whether stray electric current is being measured or not. It becomes impossible to identify whether the tree current work 1 is being measured.

In such a case, it is preferable if there is a method that can measure the water tree current I+ without being affected by the stray current wire 9.

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

(Means for Solving the Problems) A method for detecting a water tree current in a CV cable according to claim 1 of the present invention includes interposing a capacitor on the ground side of a GPT that is drawn out from a high-voltage distribution line and grounded, and ,CV
One terminal of a measuring device for detecting DC component current including water tree current and stray current is connected to the middle of the grounding wire that is pulled out from the shielding collar of the cable and grounded. The other terminal side is connected between the GPT and the capacitor, and stray current flowing from the ground wire to the capacitor via the earth is allowed to bypass the measuring device and return to the ground wire; The water tree current is measured using the measuring device.

The CV cable water tree current detection method according to claim 2 of the present invention includes interposing a capacitor on the ground side of the GPT which is drawn out from the high voltage distribution line and grounded, and
One terminal side of a measuring device for detecting stray current is connected to the middle of the grounding wire pulled out from the shielding collar of the cable and grounded, while one terminal side of the measuring device is connected to 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 to measure the stray current. The water tree current is measured by subtracting the stray current from the total DC component current including.

(Example) Hereinafter, a method for detecting a water tree current of a CV cable according to the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the water tree current detection method of a CV cable according to claim 1, in which C' is a capacitor, and this capacitor C' is connected to a high voltage distribution line. GP pulled out from 10 and grounded to the earth
It is interposed in the middle of the grounding wire 17 of T16. Then, a connecting wire 50 is drawn out from this grounding wire 17, and the connecting wire 50 is connected to the other terminal 12b side of the measuring instrument 12. One terminal 12a side of the measurement 1112 is connected to a grounding wire 11 drawn out from the shielding copper tape 6 of the C2 cable 1 and grounded as before, and also connected to the grounding side of the capacitor C' via a connecting wire 51.

Considering the grounding relay and grounding resistance of G P T 16, the capacitor C' should have low AC resistance (for example, impedance at commercial frequency is 50 ohms, and capacitance is 50 μF) and DC resistance. uses a high-resistance capacitor, such as a film capacitor. Film capacitors have a high resistance in terms of direct current and the change in DC resistance is small even when alternating current is applied. For example, when an alternating current of about 100 mA is superimposed,
Some exhibit a direct current resistance of 1000 MΩ or more when a voltage is applied.

When the capacitor C' measuring device 12 is connected in this way, the stray current flowing from the grounding wire 11 to the capacitor C- via the ground will flow toward the measuring device 12 through the capacitor C'. The stray current flow bypasses the measuring device 12 and flows back to the grounding wire 11. Using the measuring device 12, the water current I+
can only be measured.

FIG. 2 shows a connection example in which a plurality of GPTs 16 are connected to the high-voltage distribution line 10. In this case, a capacitor C''C is installed in the middle of the grounding wire 17 of each GPT 16. ', and connect the ground sides of the capacitors C=C'' to each other using a connecting wire 52.

FIG. 3 is a diagram showing an embodiment of the water tree current detection method for a CV cable according to claim 2, in which the cable is grounded via a grounding wire 17 drawn out from the high-voltage electric wire 10 and connected to the ground. A capacitor C is placed in the middle of the ground wire 17 of GPT16.
', and one terminal 12a side of the measuring device 12'' for detecting stray current is connected to the middle of the grounding wire 11 which is pulled out from the shielding collar 6 of the CV cable 1 and grounded to the earth. , one terminal 12'a side of this measuring instrument 12' is connected between the capacitor C' and the GPT 16 via a connecting wire 50, and the ground side of the capacitor C' is connected to the measuring instrument 12- through a connecting wire 51. It is connected to the other terminal !2'b side.

If the measuring device 12' and the capacitor C' are connected in this way, only the stray current flows through the measuring device 12', and the water tree current X+ bypasses the measuring device @12' and the high voltage distribution line lO Therefore, the water tree current 1 can be accurately measured by subtracting the stray electric current 1 from the total DC component including the stray type MI I s and the water tree current 1+.

(Effects of the Invention) As explained above, the method for detecting the water tree current of a CV cable according to claim 1 of the present invention is as follows.
Since the measuring device is interposed in the middle of the grounding wire of the T and the stray current is circulated by bypassing the measuring device, there is an effect that the water tree current itself can be accurately measured even in a live line state.

The water tree current detection method for a CV cable according to claim 2 of the present invention, as explained above,
Since the T is interposed in the middle of the grounding wire so that only stray current flows through the measuring device, the stray current can be subtracted from the total DC component including the water triage current and the stray current. - It has the effect of accurately measuring the current itself.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining the water tree current detection method of the CV cable according to claim 1 of the present invention, and FIG. 2 is a circuit diagram for explaining the water tree current detection method of the CV cable according to claim 1 of the present invention. A circuit diagram for explaining another example of the detection method, FIG. 3 is a circuit diagram for explaining the water tree current detection method of a CV cable according to claim 2 of the present invention, and FIG. 5 is a side view thereof, FIG. 6 is a sectional view of another CV cable according to the present invention, and FIG.
The figure is an explanatory diagram of the generation mechanism of water tree current according to the present invention,
Figure 8 is a connection diagram of the conventional measuring instrument to the CV cable, Figure 9
10 is an equivalent circuit of the connection diagram shown in FIG. 8. 1...CV cable, 11...ground wire, 16...GPT. 51...Connection line, 11...Water tri-electricity box, lO...High voltage distribution line 12.12-...Measuring instrument 17...Grounding wire C'...Capacitor 8... Stray current Fig. 1 Fig. 3 s Fig. 2 Fig. Fig. Fig. A

Claims (2)

[Claims] (1) A capacitor is interposed on the grounding side of the GPT, which is drawn out from the high-voltage distribution line and grounded to the earth, and a water tree current One terminal side of a measuring device for detecting DC component current including stray current and stray current is connected, and the ground side of the capacitor is connected, and the other terminal side of the measuring device is connected between the GPT and the capacitor. connection, the stray current flowing from the ground wire to the capacitor via the earth bypasses the measuring device and returns to the grounding wire, and the water tree current is measured using the measuring device. A water tree current detection method for a CV cable, characterized in that: (2) GPT pulled out from the high voltage distribution line and grounded
A capacitor is interposed on the grounding side of the CV cable, and one terminal side of the measuring device for detecting stray current is connected to the middle of the grounding wire that is drawn out from the shielding copper of the CV cable and grounded. One terminal side of the 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 to measure the stray current. A water tree current detection method for a CV cable, characterized in that the water tree current is measured by subtracting the stray current from the total DC component current including the water tree current and the stray current.