JPH0619415B2 - Water tree current detector for CV cable - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water tree current detection device for a CV cable, which detects a water tree current in order to diagnose insulation deterioration of a CV cable.

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

By the way, since such a water tree current has been conventionally measured in a live state, an AC current or a stray current flows together with the water tree current in the water tree current measuring circuit, which makes it difficult to accurately measure. .

Against this background, the inventor of the present application has previously proposed a method of interposing a capacitor on the grounding wire of the GPT to avoid the influence of these alternating current and stray current and measure the water tree current accurately. (See JP-A-63-281073).

(Problems to be Solved by the Invention) By the way, according to this method, the water tree current can be accurately measured while avoiding the influence of the alternating current and the stray current, and the insulation deterioration of the CV cable can be accurately diagnosed. However, it is necessary to connect a capacitor to the ground wire of the GPT installed as an electric equipment and ground it.

Therefore, when the insulation deterioration diagnosis of the CV cable is performed by this method, it is necessary to ask the manager of the GPT as equipment for permission, and the preparation work for the diagnosis becomes troublesome.

Further, since the work to be performed as the preparation for the diagnosis needs to be performed at a total of three places of both end portions of the cable to be measured and the ground wire of the GPT, the preparation work for the diagnosis is troublesome.

The present invention has been made under such circumstances, and an object of the present invention is to provide a water tree current detection device for a CV cable, which has good measurement accuracy of the water tree current and is easy to perform a preparation work for diagnosis. To do.

(Means for Solving the Problem) To this end, the present invention is connected between a ground wire pulled out from a shielding copper tape of a cable under test in a power failure state and a conductor of the cable under test. A current detecting device, wherein the current detecting device is provided with a stabilized AC power supply and a booster, the AC power supply is connected to a primary coil of the booster, and one end of a secondary coil is A circuit is connected to the conductor of the cable to be measured, and the other end is grounded by a second grounding wire via a capacitor, and a circuit connecting the capacitor and the booster to a grounding wire extending from the shielding copper tape. The circuit is characterized in that an alternating current limiting means and a water tree current detecting section are provided in this circuit.

(Operation) According to the present invention, the capacitor is interposed in the second ground line which is the ground line of the booster which constitutes the measuring device, and the diagnostic preparation work which should be the ground line of the GPT which is the electric equipment is performed. Since it can be omitted, it is not necessary to ask the GPT administrator for permission, and the diagnostic preparation work becomes simple.

Further, since 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, the work man-hours are reduced accordingly, so that the preparation for diagnosis is simplified.

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

(Embodiment) The present invention will be described below with reference to an embodiment shown in the drawings.

Reference numeral 1 denotes a water tree current detection device (hereinafter, simply referred to as a detection device), and 2 denotes a measured cable composed of a CV cable (crosslinked polyethylene insulation vinyl sheath cable).
It was cut from a distribution line to make a power failure.

The present invention can also be applied to a so-called triplex type CV cable (CVT) and the like.

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

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

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

The booster 4 sets the voltage of the current supplied from the AC power source 3 to, for example, 3810 V in ground voltage, but is not limited to this and may be set to 3000 V or 5000 V to detect the water tree current. It is advantageous to increase this voltage in order to facilitate diagnosis of insulation deterioration.

An AC power supply 3 is connected to the primary side coil 4a of the booster 4, a contact A is formed at one end of the secondary side coil 4b, and the other ends of the secondary side coil 4b are parallel circuits 8a, 8b. Is connected to the second ground line 9 and reaches the contact C.

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

The short-circuit fuse 7 opens the circuit 8a in which the capacitor 5 is installed and closes the circuit 8b that is installed in parallel and functions as a bypass, and grounds the current from the contact C when a current of a certain level or more flows. It protects the detection device 1 from damage.

If the booster 4 is composed of a variable transformer, it is possible to measure the water tree current by appropriately adjusting the voltage to be low with respect to the cable 2 to be measured, which is expected from the appearance and the like that insulation deterioration has started. Accordingly, it is possible to reduce the occurrence of dielectric breakdown.

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

A film condenser has a high resistance in terms of direct current and has a small change in direct current resistance even when an alternating current is applied, for example, 1
Some of them have a DC resistance of 1000 mega ohms or more even when a DC voltage of 40 V is applied in the state where AC of about 00 mA is superposed, and it is preferable to use this.

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 the measuring circuit 10.
The other end of the ground wire 2 is pulled out from the shielding copper tape 2b.
It is connected to the contact B on c.

The detector 6 is an ammeter capable of measuring a minute current of, for example, nA with high accuracy, and extracts and measures only a DC component current by a DC filter.

A display 12 such as a recorder is connected to the 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, about 10 kilo ohms to 1 mega ohm, and by installing it, the AC current is almost grounded via the capacitor 5 side, and the detector 6 is not affected.

The detector 6 corresponds to the water tree current detecting section in the present invention, and the resistor 11 corresponds to the AC current limiting means.

In this embodiment, the resistor 11 for limiting the AC charging current is installed in series in front of the detector 6 as described above.
The alternating current limiting means may be configured as shown in FIG.

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

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

Along with the supply of current 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, and the conductor 2a of the cable 2 to be measured passes through the contact A. Flow to.

As described above, the high voltage AC flows through the conductor 2a of the cable to be measured 2, and the cable 2 to be measured, which has been disconnected from the live line and is in a power failure state, is set by the booster 4 and is in a stable energized state. Therefore, AC current, stray current and water tree current are generated as in the case of using as distribution line.

First, the flow of the alternating current will be described. The alternating current flows between the ground wire 2c and the secondary coil 4b.

The ground wire 2c and the secondary coil 4b are grounded, and the measuring circuit 10 connecting them has a resistor 11
Is arranged, the alternating current is grounded through the capacitor 5 and hardly flows into the measuring circuit 10.

The most problematic part of the DC component current of the stray current is the electromotive force generated by the battery action due to the grounding of the ground wire 2c drawn from the shielding copper tape 2b, and the second from the detection device 1.
This is the electromotive force generated by the battery action due to the grounding of the ground wire 9 of FIG.

However, the electromotive force generated by the grounding of the second ground wire 9 causes
Since the capacitor 5 of a shows a large resistance value and the circuit 8b is opened by the short-circuit fuse 7, there is practically no flow.

On the other hand, the ground wire 2c pulled out from the shielding copper tape 2b
The electromotive force due to the grounding flows through the ground wire 2c, the shielding copper tape 2b, the surface of the sheath 2d, and the circuit through the contact point between the cable and the ground.

Along with this, a circuit from the contact B to the capacitor 5 side or the secondary coil 4b via the measuring circuit 10 is also formed. However, the resistance of these circuits is extremely large compared to the above circuit, so that it is practically practical. Hardly flows.

That is, the stray current is applied to the ground wire 2c and the shielding copper tape 2
Since it flows only on the surface of b and the sheath 2d, it has little influence on the measurement of the water tree current by the detector 6.

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

As a result, it is possible to fundamentally prevent the generation of a stray current due to the difference between the electromotive force due to the grounding of the second ground line 9 and the electromotive force due to the grounding of the ground line 2c.

On the other hand, the water tree current is generated by the shielding copper tape 2b and the conductor 2a.
Since it flows into the insulating layer 2e between the ground line 2e and
Although it flows between c and the secondary coil 4b, since the capacitor 5 having a high DC resistance is installed, it is not grounded via the contact C and all the water tree current flows through the measurement circuit 10. Become.

Therefore, all the water tree current generated in the cable 2 to be measured can be measured by the detector 6, and since the AC current and the stray current do not flow in 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 detecting device 1 is used without using the ground wire of the GPT, which is an electric facility, unlike the conventional case.
Since the AC power supply 3 and the booster 4 are provided in the secondary coil, and the secondary coil 4b of the booster 4 is grounded by interposing the capacitor 5, the administrator of the electrical equipment is required to diagnose the insulation deterioration of the CV cable. It can be performed without permission of.

Further, since a stable power source is used, noise and the like are less than in the measurement in the live line state, and the measurement accuracy is good.

Furthermore, since the contact C of the detection device 1 may be grounded,
Generally, it is possible to omit the measurement preparatory work at the grounding wire of the GPT, which is another position, and the number of working places can be reduced to reduce the preparatory work.

Moreover, the stray current can be completely cut off by using the capacitor 5 and the like, so that the measurement accuracy can be maintained well, and the principle is different from the DC leakage current method which is widely used at present. By doing so, it is possible to perform insulation deterioration diagnosis with significantly improved reliability.

(Effects of the Invention) Since the present invention is configured as described above, a capacitor is interposed in the second ground line, which is the ground line of the booster that constitutes the measurement device, and the GPT of the electrical equipment is installed. Since the diagnostic preparation work to be done on the ground wire can be omitted,
It is not necessary to ask the administrator of the GPT for permission, which simplifies the preparation work for diagnosis.

Further, since 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, the work man-hours are reduced accordingly, so that the preparation for diagnosis is simplified.

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

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the embodiment, FIG. 2 is an explanatory diagram of a modified example of the AC current limiting means, and FIG. 3 is an explanatory diagram of a modified example in which a stray current is further prevented. DESCRIPTION OF SYMBOLS 1; Current detection device, 2; Cable to be measured, 2a; Conductor, 2b; Shielding copper tape, 2c; Ground wire, 3; AC power supply, 4; Booster, 4a; Primary coil, 4b; Secondary coil, 5: Capacitor, 6; Water tree current detection part (detector), 9: Second ground wire, 10: Measuring circuit, 11: AC current limiting means (resistor).

Claims (2)

[Claims] 1. A current detecting device connected between a ground wire drawn from a shielding copper tape of a cable to be measured in a power failure state and a conductor of the cable to be measured, the current detecting device comprising: A stabilized AC power supply and a booster are provided, the AC power supply is connected to the primary coil of the booster, one end of the secondary coil is connected to the conductor of the cable to be measured, and the other end is a capacitor. Grounded by a second grounding line through the capacitor, and a circuit connecting the capacitor and the booster to a grounding line extending from the shielding copper tape is provided with an AC current limiting means and a water tree. A water tree current detecting device for a CV cable, which is provided with a current detecting portion. 2. The water tree current detection device according to claim 1, wherein the ground wire drawn from the shielding copper tape and the second coil connected to the secondary coil of the booster via a capacitor. The water of the CV cable is characterized in that a line is connected between the ground wire and the ground side of the capacitor, and the ground side is opened from a connection point of the ground wire drawn out from the shielding copper tape with the line. Tree current detector.