JPH0634697A - Partial discharge detection method - Google Patents

Abstract

PURPOSE:To reduce noise and detect signal due to partial discharge positively by covering the cable periphery surface of both side regions excluding the area between a power cable connection part and a sensor with a conductor shield material and then connecting it with a shield container. CONSTITUTION:A coupling capacitor is formed between a metal tape 5 which is wound around a power cable 3 and a metal screening layer 3a. Noise which enters the inside of the cable 3 from terminator parts 6a and 6b and is propagated on the screening layer 3a is transmitted to the tape 5 via the coupling capacitor and then flows to the ground via a shield layer 4a. Similarly, noise within air entering the cable 3 flows from the tape 5 to the ground via the layer 4a. Therefore, a sensor 1 does not detect noise. On the other hand, when a partial discharge is generated at a cable connection part 2, pulse signal is propagated within the cable 3 but reaches a sensor installation part and is detected by the sensor 1 and then is output to a measuring instrument via a coaxial cable 4 since no tape is wound around the cable periphery surface between the connection part 2 and the sensor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge (Partia) generated inside an insulator of a power cable and at an insulator-conductor interface.
l Discharge; PD) for detecting partial discharge.

[0002]

2. Description of the Related Art Conventionally, as a partial discharge detection device for detecting a partial discharge generated in a power cable, there have been proposed, for example, a method using a tuned detection method and a method using an AE (acoustic emission) sensor.

As shown in FIG. 2, a tunable detection device using the tuned detection method has a terminating portion 22 of a power cable 21, as shown in FIG.
A coupling content 23 and a detection impedance 24 are connected in series between the inner conductor of a or 22b and the metal shielding layer, and the potential difference generated across the detection impedance 24 is adjusted by the tuning amplifier 25 having a tuning frequency of several hundred kHz. I took it out.

However, this tunable detection device has a problem that it is difficult to detect the signal under the hot line because it is necessary to take out a signal from the inner conductor of the power cable, and a dedicated coupling capacitor is also required. . Further, since the tuning frequency in this device is several hundred kHz, it is easily affected by ambient noise, and although good detection accuracy can be obtained in an experiment in a shielded room, it is difficult to apply it to a cable after installation.

On the other hand, the detection device using the AE sensor is
Although an AE sensor detects elastic waves propagating inside the insulator by partial discharge, this device is not affected by electrical noise, but it is strong because the ultrasonic waves have straightness. It has a directivity and has a drawback that the detection sensitivity is extremely lowered depending on the detection position.

As a method for detecting partial discharges that solves these drawbacks, a metal shield layer is insulated in a connection portion of a power cable, and a potential difference generated between the two metal shield layers sandwiching the insulating portion when a partial discharge occurs is determined by measuring the potential difference between both metal shield layers. A detection method has also been proposed in which detection is performed using a detection impedance connected between shield layers (“Partial discharge test results for the Minamiikegami 275kV CV cable line”; Katsuta et al., Institute of Electrical Engineers, Insulation Material Research Material EIM-90-20). .

However, this method is limited in its application only to the connection portion where the metal shield layer is insulated, and the metal shield layer is in a non-grounded state, resulting in a lack of safety when a short-circuit accident occurs. There is. In addition, there is a drawback that the device becomes large and requires skill in measurement.

Therefore, the inventors of the present invention have proposed a resonance type partial discharge detection device having a sensor composed of an electrode arranged on an insulating coating layer of a power cable and an inductance connected to this electrode ( Japanese Patent Application No. 2-310197).

FIG. 3 is a sectional view showing a sensor portion of this resonance type partial discharge detection device.

On the outer circumference of the power cable 21, an electrode 31 formed of a conductive paint or a metal tape is provided over the entire circumference. The electrode 31 includes an insulating cylinder 33a attached to the power cable 21, a brass cylinder 33b arranged on the outer circumference of the insulating cylinder 33a, and a lead tape 34 covering the outer circumference.
It is housed in a shield container formed by.
A coaxial connector 35 such as a BNC connector is attached to the brass tube 33b.
A coil 32 as an inductance element is connected between the inner conductor of the electrode and the electrode 31. The shield container is connected to the ground wire to which the metal shield layer of the power cable 21 is connected.

The power cable 21 to be detected is, for example, a 275 kV CV cable, and the inner conductor 36, the inner semiconductive layer 37, and the cable insulator (XLPE:
cross-linked polyethylene) 3
8. A metal shielding layer 39 as an outer metal layer and a plastic sheath 40 as a coating layer are coaxially arranged.

FIG. 4 is a block diagram showing the structure of a partial discharge detecting device using this partial discharge sensor. This apparatus includes a sensor 30 having the above-described structure, a wide band amplifier 41 that amplifies the output of the sensor 30, and a digitizing oscilloscope 42 that performs signal processing such as averaging on the output of the wide band amplifier 41. Has been done.

A plurality of power cables 21 are connected to each other via connecting portions 43a and 43b so as to have a predetermined length, and inner conductors 36 of terminal portions 44a and 44b thereof are connected to a high voltage power supply line 45. In addition, the metal shield layer 39 of the power cable 21 includes the end portions 44a and 44b and the connecting portion 43.
It is properly grounded at a, 43b and the like.

Next, the operation of the resonance type partial discharge detection device configured as described above will be described.

The equivalent circuit of the power cable 21 is generally considered as a circuit as shown in FIG. That is, the ground line of the inner conductor 36, the metal shielding layer 39, the terminal end portions 44a and 44b, and the connection portions 43a and 43b becomes an RL series circuit. The inner conductor 36 and the metal shielding layer 39 are capacitively coupled via a cable insulator 38 interposed therebetween. In addition, the detection unit D includes a coupling capacitance determined by the electrode 31 of the sensor 30 and the plastic sheath 40 of the power cable 21, and a coil 32 provided in series with this coupling capacitance.
And the input impedance of the measuring instrument. The coupling capacitance by the electrode 31 is, for example, the electrode 3
It can be adjusted by the length of the cable in the longitudinal direction.

When a partial discharge occurs in the cable insulator 38, the pulsating current generated by the partial discharge is i2 in the figure.
, I2 ′, ... and the coaxial modes i1 and i1 in FIG.
.., i3, i3 ', ... Propagate separately in the earth return mode. As a result, the detection section D has i1 + i
Since the current indicated by 1'flows, the sensor 30 detects this current.

In the resonance type partial discharge detection device thus constructed, the coupling capacitance formed by the electrode 31 and the metal shielding layer 39 of the power cable 21 and the high frequency resonance circuit formed by the coil 32 are used. , A signal in a predetermined band of a traveling wave of a wide band generated by the partial discharge is detected.

This resonance type partial discharge detection device has the advantages that it can be easily installed on a power cable, has high safety, and can detect partial discharge in a live state.

[0019]

However, the above-mentioned resonance type partial discharge detection device has the following problems. That is, as shown in FIG.
The coaxial cable 47 is connected between the measuring instrument and the measuring instrument, and the shield layer 47a of the coaxial cable 47 is grounded, so that noise hardly mixes between them. However, since the sensor 30 detects the noise propagating through the metal shielding layer 39 of the cable 21 from the cable end portions 44a and 44b and the airborne noise penetrating into the cable, the signal given to the measuring device is , Cable connection 4
In addition to the signal due to the partial discharge generated in 6, a relatively large amount of noise is mixed.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a partial discharge detection method capable of reducing noise and reliably detecting a signal due to partial discharge.

[0021]

SUMMARY OF THE INVENTION A method for detecting partial discharge according to the present invention is directed to an electrode arranged on the peripheral surface of a power cable, an inductance element connected to the electrode, and a shield for housing the electrode and the inductance element. In a partial discharge detection method for detecting a partial discharge generated in a power cable using a sensor configured by a container, the sensor is arranged at a position separated from a power cable connection portion, and the power cable connection portion and the sensor It is characterized in that the peripheral surfaces of the cables in both regions sandwiching the region between are covered with a shield material made of a conductor and the shield material is electrically connected to the shield container.

[0022]

According to the present invention, the cable peripheral surfaces of both regions sandwiching the region between the cable connecting portion and the sensor are covered with a shield material made of a conductor, and the shield material is electrically connected to the shield container of the sensor. Connect to. A large coupling capacity is formed between the shield material covering the cable peripheral surface and the metal shield layer of the power cable. The impedance Z between the shield material and the power cable can be expressed by the following formula 1 where C is the value of the coupling capacitance.

[0023]

## EQU1 ## Z = 1 / (jωC) where j = (− 1) ^1/2 and ω = 2πf.

That is, the impedance between the shield material and the metal shielding layer of the power cable has an extremely low value with respect to a high frequency signal (noise). Therefore, the noise transmitted through the metal shield layer flows to the ground through the shield material, the shield container, and the shield layer of the coaxial cable connecting the sensor and the measuring device. On the other hand, since the shielding material is not provided on the cable peripheral surface in the area between the connection part of the power cable and the sensor, the high-frequency signal due to the partial discharge generated at the connection part is reliably detected by the sensor and measured. Given to the vessel. As a result, a signal with less noise can be obtained.

As the shield material, a metal tape made of copper or aluminum may be wound around the power cable. In this case, there are advantages that the work of attaching the shield material is extremely easy and the material cost is low.

[0026]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a partial discharge detection method according to an embodiment of the present invention.

First, the resonance type partial discharge sensor 1 is arranged in the vicinity of the connecting portion 2 of the power cable 3. This sensor 1
It is composed of an electrode attached to the peripheral surface of the power cable 3, a coil connected to the electrode, a shield container that houses the electrode and the coil (see FIG. 3).
Usually, the sensor 1 is installed at a position within 5 m from the cable connecting portion 2. In addition, between this sensor 1 and the measuring device,
Connection is made by a coaxial cable 4 having a shield layer 4a.

Next, a metal tape 5 made of copper or aluminum is provided on the cable peripheral surface on both sides of the area between the sensor 1 and the connecting portion 2 over a range of at least several meters.
Wrap it tightly so that there are no gaps. Then, the metal tape 5 and the shield container of the sensor 1 are electrically connected. No metal tape is wrapped around the peripheral surface of the power cable 3 between the sensor 1 and the connecting portion 2.

After disposing the sensor 1 and the metal tape 5 on the electrode cable 3 in this manner, detection of partial discharge is started.

A coupling capacitance is formed between the metal tape 5 wound around the power cable 3 and the metal shielding layer 3a (wire shield, Al shield, SUS sheath, etc.) of the power cable 3. Since the capacitance value of this coupling capacitance is extremely large, the impedance for a high frequency signal is extremely small. Therefore, the terminal portions 6a, 6 of the electrode cable 3 are
The noise penetrating the power cable 3 from b and propagating through the metal shield layer 3a is transmitted to the metal tape 5 through this coupling capacitance, and the metal tape 5 causes the shield container of the sensor 1 and the shield layer 4a of the coaxial cable 4 to pass through. It flows to the ground. Similarly, the airborne noise that has entered the power cable 3 also flows to the ground through the metal tape 5, the shield container of the sensor 1, and the shield layer 4a of the coaxial cable 4.
Therefore, the sensor 1 does not detect these noises.

On the other hand, when a partial discharge is generated in the cable connecting portion 2, a pulsed signal propagates in the cable 3 with this partial discharge. In this case, since the metal tape is not wound around the cable peripheral surface between the cable connecting portion 2 and the sensor 1, the signal generated due to the partial discharge reaches the sensor installation portion. The sensor 1 detects this signal and outputs it to the measuring instrument via the coaxial cable 4.

In the present embodiment, as described above, the signal due to the partial discharge can be reliably detected, and the noise propagating through the metal shielding layer of the power cable flows to the ground through the metal tape or the like, so that it is output from the sensor. The noise of the generated signal can be significantly reduced. Further, in the present embodiment, since it is only necessary to wind the metal tape around the power cable, the attachment work is easy, the operation is completed in a short time, and the cost required for noise reduction is low. Further, even in a live state, the sensor and the metal tape can be attached and detached.

[0034]

As described above, according to the present invention, the cable peripheral surfaces of the regions on both sides of the region between the connection portion of the power cable and the sensor are covered with a shield material, and the shield material and the sensor. Since it is electrically connected to the shield container, the signal generated by the partial discharge can be surely detected, and the noise and airborne noise that have entered the cable from the cable end can be removed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a partial discharge detection method according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional tunable partial discharge detection device.

FIG. 3 is a cross-sectional view showing a sensor section of a resonance type partial discharge detection device.

FIG. 4 is a block diagram showing a configuration of a partial discharge detection device using the partial discharge sensor.

FIG. 5 is an equivalent circuit diagram of a power cable and a detection system.

FIG. 6 is a schematic diagram showing a problem of a conventional partial discharge detection method.

[Explanation of symbols]

 1, 30; Resonant partial discharge sensor 2, 43a, 43b, 46; Connection part 3, 21; Power cable 3a, 39; Metal shielding layer 4, 47; Coaxial cable 4a, 47a; Shield layer 5; Metal tape 31; Electrode 32; coil 35; coaxial connector 40; plastic sheath

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Watanabe 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd.

Claims (2)

[Claims] 1. An electrode disposed on a peripheral surface of a power cable,
In a partial discharge detection method for detecting a partial discharge generated in a power cable using a sensor composed of an inductance element connected to the electrode and a shield container housing the electrode and the inductance element, the sensor is connected to the power cable. Is disposed at a position apart from the power cable connection portion, and the cable peripheral surfaces of the regions on both sides of the region between the power cable connection portion and the sensor are covered with a shield material made of a conductor, and the shield material is used as the shield container. A partial discharge detection method characterized in that the partial discharge is electrically connected to the. 2. The partial discharge detection method according to claim 1, wherein the shield material is a metal tape wound around the peripheral surface of the power cable.