JPH03111775A - Water-tree-current detecting apparatus for cv cable - Google Patents

Abstract

PURPOSE:To make it possible to constitute a detecting apparatus wherein preparation work for diagnosis is simple by providing a step-up transformer in the detecting apparatus, connecting a stabilized AC power source to the primary coil of the transformer, and grounding one end of the secondary coil through a capacitor. CONSTITUTION:A current detecting apparatus 1 is connected between a grounding line 2c which is led out of a shielding copper tape 2b of a cable to be measured 2 and a conductor 2a of the cable 2. A stabilized AC power source 3 and a step-up transformer 4 are provided in the apparatus 1. The power source 3 is connected to a primary coil 4a of the step-up transformer 4. One end of a secondary coil 4b is connected to the conductor 2a. The other end is grounded C through a capacitor 5. A circuit 10 for connecting a part between the capacitor 5 and the step-up transformer 4 to the grounding line 2a at a point B is provided. An AC limiting means (resistor) 11 and a water-tree-current detecting part (detector) 6 are provided in the circuit 10. In this constitution, the water tree current can be measured accurately since AC and stray currents do not flow through the detector 6. Diagnosis preparing work to be performed for the grounding line of GPT which is an electric apparatus can be omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a water tree current detection device for a CV cable that detects water tree current in order to diagnose insulation deterioration of the CV cable.

(Prior Art) In order to diagnose insulation deterioration of a Cv cable, the magnitude of water tree current, which is correlated with insulation deterioration, may be measured.

By the way, since such water tree current is conventionally measured in a live line state, alternating current and stray current flow together with the water tree current in the water tree current measurement circuit, making it difficult to measure accurately. .

Against this background, the inventor of the present application has previously proposed a method for measuring water tree current with high accuracy by interposing a capacitor in the GPT grounding wire to avoid the effects of these alternating currents and stray currents. (Refer to Japanese Patent Application Laid-Open No. 63-281073)
.

(Problem to be Solved by the Invention) By the way, according to this method, water tree current can be measured with high accuracy while avoiding the influence of alternating current and stray current, and insulation deterioration diagnosis of Cv cable can be accurately performed. However, it is necessary to connect a capacitor to the grounding wire of the GPT installed as electrical equipment.

Therefore, when diagnosing the insulation deterioration of the CV cable using this method, it is necessary to request permission from the administrator of the GPT as the facility, making preparation work for the diagnosis troublesome.

Further, the preparation work for the diagnosis is troublesome because it is necessary to perform the work to prepare for the diagnosis at three locations in total: both ends of the cable to be measured and the grounding wire of the GPT.

The present invention was made based on the above circumstances, and an object of the present invention is to provide a Cv cable water tree current detection device that has good water tree current measurement accuracy and is easy to prepare for diagnosis. It is something to do.

(Means for Solving the Problems) For this purpose, the present invention provides a method for connecting a ground wire drawn out from a shielding copper tape of a cable under test in a power outage state and a conductor of the cable under test. The current detection device is provided with a stabilized AC power source and a booster, the AC power source is connected to the primary coil of the booster, and one end of the secondary coil is connected to the booster. A circuit is provided which is connected to the conductor of the cable to be measured and whose other end is grounded via a capacitor, and which connects the capacitor and the booster to a grounding wire extending from the shielding steel tape. It is provided with an alternating current limiting means and a water tree current detecting section.

(Function) According to the present invention, a capacitor is interposed in the grounding wire of the booster that constitutes the measuring device, and the diagnostic preparation work that should be done on the grounding wire of the GPT, which is electrical equipment, can be omitted. It is not necessary to ask permission from the GPT administrator, and the preparation work for diagnosis becomes easier.

Furthermore, it is not necessary to connect the measuring device to the grounding wire of the GPT located at a position separated from the cable to be measured, and the number of work steps is reduced accordingly, making diagnosis preparation easier.

Furthermore, since the measuring device has a stabilized alternating current electromagnetic field, there is less risk of voltage fluctuations occurring unnecessarily, and it is also possible to measure the water tree current more stably and accurately than in the past.

(Example) The present invention will be explained below with reference to embodiments shown in the drawings.

1 indicates a water tree current detection device (hereinafter simply referred to as the detection device), and 2 indicates a cable to be measured consisting of a CV cable (cross-linked polyethylene insulated vinyl sheathed cable), which was disconnected from the power distribution line etc. to create a power outage state. be.

Note that the present invention can be similarly applied to a so-called triplex type CV cable (CVT).

The detection device 1 is provided with contacts A, B, and C, and the contact A is connected to the conductor 2a of the cable under test 2, and the contact B is connected to the conductor 2a of the cable under test 2.
are respectively connected to the ground wires 2c drawn out from the shielding copper tape 2b of the cable to be measured 2, and the contact C is grounded.

The detection device 1 includes a stabilized AC power supply 3, a booster 4, a capacitor 5, and a detector 6 as main components.

The AC power supply 3 supplies current from a power supply with little fluctuation to the booster 4 via a stabilizing device.

The booster 4 makes the voltage of the current supplied from the AC power supply 3, for example, 3810V to ground voltage, but it is not limited to this and may be made to 3000V or 5000V, and the voltage of the water tree current is In order to facilitate detection and diagnosis of insulation deterioration, it is advantageous to increase this voltage.

The AC power supply 3 is connected to the primary coil 4a of the booster 4, a contact A is formed at one end of the secondary coil 4b, and the other end of the secondary coil 4b is connected to parallel circuits 8a and 8b. It is connected to the grounding wire 9 through the contact point C.

The secondary coil 4b is normally connected to the capacitor 5 by a circuit 8a via a short-circuit fuse 7 as a protection device, and the circuit 8b is open.

When a current exceeding a certain level flows, the short circuit fuse 7 opens the circuit 8a in which the capacitor 5 is installed, closes the circuit 8b installed in parallel and functions as a bypass, and grounds the current from the contact C. This protects the detection device 1 from damage.

If the booster 4 is configured with a variable transformer, the water tree current can be measured by adjusting the voltage to a low level as appropriate for the cable 2 to be measured whose insulation is expected to have begun to deteriorate from its appearance etc. Accordingly, it is possible to reduce the occurrence of dielectric breakdown.

The capacitor 5 has a low impedance (for example, 50 ohms) for AC and a high resistance for DC (for example, 1
0 to 200 megohms).

Film capacitors have high resistance in terms of direct current, and the change in direct current resistance is small even when alternating current is applied, such as 1.
There are some that exhibit a DC resistance of 1000 megaohms or more even when a DC voltage of 40 volts is applied with a superimposed alternating current of about 00 mA, and it is preferable to use these.

A measuring circuit 10 is branched from between the short-circuit fuse 7 and the capacitor 5, and a detector 6 and a resistor 11 are connected in series to this measuring circuit 10.
The other end is a grounding wire 2 drawn out from the shielding steel tape 2b.
It is connected to contact B on c.

The detector 6 is an ammeter that can measure a minute current of nA order with high precision, for example, and extracts and measures only the DC component current using a DC filter.

A display 12 such as a recorder is connected to this detector 6, and the detected current value is displayed on the display 12 such as a recorder.

The resistor 11 has a high resistance of, for example, 10 kilohms to 1 megaohm, and by installing this resistor 11, most of the alternating current is grounded through the capacitor 5 side, so that the detector 6 is not affected.

Note that the detector 6 corresponds to a water tree current detecting section in the present invention, and the resistor 11 corresponds to an alternating current limiting means.

In this embodiment, a resistor 11 is installed in series upstream of the detector 6 to limit the AC charging current.
The alternating current limiting means may also be constructed as shown in FIG.

That is, the alternating current limiting means shown in FIG.
An opening/closing switch 6b is provided in series with the bypass capacitor 6a which is normally installed in the detector, and by opening the opening/closing switch 6b, the action of the bypass capacitor 6a is eliminated. In FIG. 2, 6c is the detector. 6 shows the internal resistance.

Next, the operation of the detection device 1 shown in FIG. 1 will be explained.

As current is supplied from the AC power supply 3 to the primary coil 4a of the booster 4, a stable high-voltage AC is generated in the secondary coil 4b, which flows through the contact A to the conductor 2a of the cable under test 2. flows to

In this way, the cable to be measured 2, which had been disconnected from the live line and was in a power outage state due to the high-voltage alternating current flowing through the conductor 2a of the cable to be measured 2, is now set to a stable energized state by the booster 4. As a result, alternating current, stray current, and water tree current are generated, similar to when the line is used as a power distribution line.

First, to explain the flow of alternating current, alternating current flows between the grounding wire 2c and the secondary coil 4b.

The grounding wire 2c and the secondary coil 4b are each grounded, and a resistor 11 is connected to the measuring circuit 10 connecting between them.
is arranged, the alternating current is grounded through the capacitor 5 and is difficult to flow into the measuring circuit 10.

Of the DC component currents of the stray current, the most problematic ones are the electromotive force generated by the battery action due to the grounding of the grounding wire 2C drawn out from the shielding steel tape 2b, and the battery action caused by the grounding of the grounding wire 9 from the detection device 1. This is the electromotive force generated by

However, the electromotive force due to the grounding of the grounding wire 9 is such that the capacitor 5 of the circuit 8a exhibits a large resistance value, and the electromotive force generated by the grounding of the grounding line 9
is opened by the short-circuit fuse 7, so virtually no current flows.

On the other hand, a grounding wire 2c drawn out from the shielding copper tape 2b
The electromotive force caused by the grounding flows through the surface of the sheath 2d through the grounding wire 2C and the shielding steel tape 2b, and flows through a circuit through the contact point between the cable and the earth.

Along with this, a circuit is also formed from contact B through the measurement circuit 10 to the capacitor 5 side or the secondary coil 4b, but the resistance of these circuits is extremely large compared to the above circuit, so in reality Almost no flow.

In other words, stray current flows between the grounding wire 2c and the shielding copper tape 2.
Since it flows only on the surface of the water tree b and the sheath 2d, it hardly affects the measurement of the water tree current by the detector 6.

In addition, in order to further reduce these stray currents,
As shown in FIG. 3, a line 13 connects the grounding line 9 and the grounding line 2c, and an open/close switch 14 is provided on the ground side from the connection point of the line 13 to the grounding line 2c, and is opened/closed. It may be a state.

As a result, the electromotive force due to the grounding of the grounding wire 9 and the grounding wire 2
It is possible to fundamentally prevent the generation of stray current due to the difference between the electromotive force caused by grounding of c and the electromotive force caused by grounding.

On the other hand, the water tree current flows between the shielding copper tape 2b and the conductor 2a.
Since the current flows through the insulating layer 2e between the grounding wire 2
The water tree current flows between C and the secondary coil 4b, but since a capacitor 5 with high DC resistance is installed, the water tree current is not grounded through contact C, and all water tree current flows through the measurement circuit 10. Become.

Therefore, all of the water tree current generated in the cable 2 to be measured can be measured by the detector 6, and since no alternating current or stray current flows through the detector 6 as described above, the water tree current can be accurately measured. can be measured.

This embodiment has the following advantages.

When measuring this water tree current, the detection device l
An AC power source 3 and a voltage booster 4 are installed in the AC power source 3, and a capacitor 5 is interposed in the secondary coil 4b of the voltage booster 4, and the capacitor 5 is connected to the ground. This may be done with the permission of.

Furthermore, since a stable power source is used, there is less noise, etc. than when measuring in a live line state, and the measurement accuracy is improved.

Furthermore, since it is only necessary to ground the contact C of the detection device 1,
In general, the measurement preparation work at the GPT grounding wire, which is a separate location, can be omitted, and the number of work points is reduced, making it possible to reduce the preparation work.

In addition, stray current can be completely cut using capacitor 5, etc., so measurement accuracy can be maintained well.Since the principle is different from the currently widely used DC leakage current method, this method can be used in combination with the present application. This makes it possible to diagnose insulation deterioration with significantly improved reliability.

(Effects of the Invention) Since the present invention is configured as described above, a capacitor is interposed in the grounding wire of the booster that constitutes the measuring device, and the grounding wire of the GPT, which is an electrical equipment, is prepared for diagnosis. Since the work can be omitted, it is not necessary to ask for permission from the GPT administrator, and the preparation work for diagnosis is simplified.

Furthermore, it is not necessary to connect the measuring device to the grounding wire of the GPT located at a position separated from the cable to be measured, and the number of work steps is reduced accordingly, making diagnosis preparation easier.

Furthermore, since the measuring device has a stabilized AC power source, there is less risk of voltage fluctuations occurring unnecessarily, and it is also possible to measure the water tree current more stably and accurately than in the past.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the embodiment, FIG. 2 is an explanatory diagram of a modified example of the alternating current limiting means, and FIG. 3 is an explanatory diagram of a modified example that further prevents stray current. Current detection device, cable to be measured, a; conductor, b; shielding copper tape, C; grounding wire/AC power supply, booster, a; - secondary coil, b; secondary coil, capacitor, water tree current detection section 0: Measuring circuit, 1: AC current limiting means (detector), (resistor). Diagram

Claims (2)

[Claims] (1) A current detection device connected between the grounding wire drawn out from the shielding copper tape of the cable under test in a power outage state and the conductor of the cable under test, wherein the current detection device includes a stabilizing device. An AC power source and a booster are provided, the AC power source is connected to the primary coil of the booster, one end of the secondary coil is connected to the conductor of the cable under test, and the other end is connected via a capacitor. and ground it.
Furthermore, a circuit is provided for connecting the capacitor and the booster to a grounding wire extending from the shielding copper tape, and this circuit is provided with an alternating current limiting means and a water tree current detecting section. CV cable water tree current detection device. (2) In the water tree current detection device according to claim 1, a line is provided between the grounding wire drawn out from the shielding copper tape and the grounding wire connected to the secondary coil of the booster via a capacitor. A water tree current detection device for a CV cable, characterized in that the grounding side of a grounding wire drawn out from a shielding copper tape is opened from the connection point with the line.