JPH0519008A - Partial discharge detector - Google Patents

Abstract

PURPOSE:To obtain a partial discharge detector which detects partial discharge occurring on a power cable in an active state with a high S/N and excellent measurement accuracy. CONSTITUTION:Each of partial discharge sensors 1, 2 comprises an electrode placed around a power cable 3 and a coil connected to the electrode. That is, the electrode constitutes coupling capacitor together with an outer conductive layer of the cable 3, while the coupling capacitor and the coil constitutes a resonance circuit. The resonance circuit is used to selectively detect high frequency components of traveling waves generated based on partial discharge. A differential amplifier 5 outputs a differential signal between outputs of the sensors 1, 2.

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) relating to a partial discharge detection device.

[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. 5, a tunable detection device using the tuned detection method has a terminating portion 32 of a power cable 31, as shown in FIG.
The coupling content 33 and the detection impedance 34 are connected in series between the inner conductor of a or 32b and the metal shield layer, and the potential difference generated across the detection impedance 34 is adjusted by the tuning amplifier 35 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 directivity, and there is a problem that the detection sensitivity is extremely lowered depending on the detection position.

Therefore, in the connection portion of the power cable,
A detection method has also been proposed which insulates the metal shield layer and detects the potential difference generated between the two metal shield layers sandwiching the insulating part when a partial discharge occurs by the detection impedance connected between the both metal shield layers (“Minamiikegami”). Line 275kV CV cable line partial discharge test result ”; Katsuta et al., Institute of Electrical Engineers, Insulation Material Research Group EIM-90-20).

[0007]

However, this method is limited in application only to the connection portion where the metal shield layer is insulated, and since the metal shield layer is not grounded, the safety in the event of a short-circuit accident occurs. There is a problem of lack of sex. In addition, there is a drawback that the device becomes large and requires skill in measurement.

The present invention has been made in view of the above problems, and can be easily installed in a power cable and its connection portion after installation, has a wide range of application, and is excellent in safety and measurement accuracy. Moreover, it is an object of the present invention to provide a partial discharge detection device capable of simplifying the device and simplifying the measurement.

[0009]

SUMMARY OF THE INVENTION A partial discharge detection device according to the present invention comprises a plurality of parts each composed of an electrode provided on the surface of an insulating coating layer of a power cable and an inductance connected to the electrode. It is characterized by having a discharge sensor and a noise removing means for comparing output signals from these partial discharge sensors with each other to determine noise commonly applied to each partial discharge sensor and removing the noise.

[0010]

The partial discharge pulse is a wideband signal and becomes a traveling wave propagating in the power cable, which is a distributed constant circuit, between conductors and as a return path through the ground. The inventors of the present application have paid attention to this point, and detected the high-frequency component of the traveling signal wave generated by the partial discharge pulse and propagating in the outer conductive layer of the power cable from the coating layer. That is, an electrode is provided outside the coating layer, an inductance element such as a coil is further connected to the electrode, and a signal is taken out through this inductance element. In this case, a series circuit of the coupling capacitance (functioning as a capacitor as a high-pass filter, that is, a high-pass capacitor) with respect to the outer conductive layers facing each other across the coating layer of the electrode and the inductance element exhibits resonance characteristics, This series resonant circuit resonates with a signal in a desired frequency band at an appropriate Q (quality factor: resonance strength) value, and forms a high frequency resonant circuit capable of selectively amplifying a signal in the required frequency band. ..

According to the present invention, since the high frequency component of the traveling wave traveling from the outer metal layer to the ground when the partial discharge occurs is detected by the high frequency resonant circuit through the coating layer, a power cable or a connection is provided. The setting is completed only by mounting the electrodes and the inductance forming the high frequency resonance circuit on the coating layer of the part. Therefore, the cable can be easily installed on the cable and the connection portion after the installation, and the measurement under the live line condition is also possible.

Further, in the present invention, since the method of detecting the traveling wave propagating through the outer metal layer is used, it is not necessary to bring the outer metal layer into a non-grounded state. For this reason, the present invention can avoid inconveniences such as limited application depending on the type of the connecting portion or the like, and reduced safety.

If the frequency component extracted from the high frequency resonant circuit is 5 MHz or less, it is easily affected by external noise due to mechanical elements such as a motor and a generator, and if it is 60 MHz or more, it is affected by the broadcast band. . Therefore, the frequency component extracted from the high frequency resonance circuit is preferably 5 MHz to 60 MHz. However, the traveling wave generated by partial discharge is a wideband signal, and sufficient sensitivity cannot be obtained even if only a signal in a very narrow band is detected with a high amplification degree, and a signal in a wide band within the frequency range is appropriate. It is desirable to detect with a sufficient amplification degree. In the present invention, the resonance frequency and the Q value can be arbitrarily changed by using a variable inductance as an inductance forming the resonance circuit or connecting a variable resistance in series with the resonance circuit. For example, even if the frequency component included in the partial discharge pulse varies slightly depending on the size of the sample, it can be easily dealt with.

However, the frequency characteristic of the partial discharge sensor consisting of the electrodes and the inductance which constitute the high frequency resonance circuit has a certain width depending on the Q value of LC, and external noise other than the resonance frequency is also detected. In the actual state, there is noise other than that due to partial discharge even in the frequency band of 5 MHz to 60 MHz. Therefore,
In the present invention, a plurality of partial discharge sensors are used,
The output signals from these sensors are compared with each other, and the noise commonly given to each partial discharge sensor is discriminated and removed. That is, since the signal due to the partial discharge is a high frequency signal, the attenuation due to the propagation distance is large. For this reason, the amplitudes of the output signals of the plurality of partial discharge sensors rarely become the same. On the other hand, since the external noise has a relatively small attenuation when propagating through the power cable, the amplitudes of the output signals of the plurality of partial discharge sensors are substantially the same. Therefore, the noise removal unit can remove the noise commonly given to each partial discharge sensor by subtracting the output signals of the plurality of partial discharge sensors, for example. Thereby, the S / N ratio can be improved.

[0015]

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

FIG. 1 is a schematic diagram showing a partial discharge detection device according to a first embodiment of the present invention. Partial discharge sensors 1 and 2
Are arranged at appropriate intervals on the power cable 3 for detecting partial discharge. The outputs from the partial discharge sensors 1 and 2 are output to the differential amplifier 5 via the lead wires 1a and 2a.
To be given to. This differential amplifier 5 is
It outputs a signal based on the difference between the outputs of the two sensors 1 and 2. This signal is applied to a measuring device 6 equipped with an oscilloscope and a recording device.

A plurality of power cables 3 are connected via a connecting portion, and the inner conductors of the terminal portions 3a and 3b are high-voltage power supply lines 4.
Connected to. Further, the metal shielding layer of the power cable 1 is properly grounded at the end portions 3a and 3b and the connecting portion.

FIG. 2 is a sectional view showing the sensors 1 and 2 of the partial discharge detecting apparatus according to this embodiment.

The plastic sheath 14 of the power cable 3
A metal electrode 15 is provided on the outer periphery of the so as to surround the sheath 14.

The electrode 15 is housed in a shield container formed by an insulating cylinder 18 mounted on the power cable 3, a brass cylinder 17 arranged on the outer circumference of the insulating cylinder 18, and a lead tape 19 covering the outer circumference. ing. A coaxial connector 20 such as a BNC connector is attached to the brass cylinder 17, and a coil 16 as an inductance element is provided between an internal conductor of the coaxial connector 20 and the electrode 15.
Are connected. This coil 16 is also housed in the shield container. The shield container is connected to a ground wire to which the metal shield layer of the power cable 3 is connected.

The power cable 3 to be detected is, for example,
275kV CV cable, inner conductor 1 sequentially from the center
0, inner semiconductive layer 11, cable insulator (XLPE: cr
oss-linked polyethylene, 12,
A metal shield layer 13 as an outer metal layer and a plastic sheath 14 as a coating layer are coaxially arranged.

Next, the operation of the partial discharge detection device according to this embodiment having the above-mentioned structure will be described.

The equivalent circuit of the power cable 3 is generally considered as a circuit as shown in FIG. That is, the inner conductor 1
0, the metal shielding layer 13, the terminal portions 3a and 3b, and the ground wire of the connection portion form an RL series circuit. The inner conductor 10 and the metal shield layer 13 are capacitively coupled via the cable insulator 12 interposed therebetween. Further, the detection unit D has a coupling capacitance determined by the electrode 15 of the sensor 1 (or the sensor 2) and the plastic sheath 14 of the power cable 3,
It is composed of the inductance of the coil 16 provided in series with this capacitance and the input impedance of the measuring instrument.
The coupling capacity of the electrode 15 can be adjusted by, for example, the length of the electrode 15 in the cable longitudinal direction.

When a partial discharge occurs in the cable insulator 12, 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 1 (or the sensor 2) detects this current.

Usually, the partial discharge is a weak point of the power cable,
That is, it is likely to occur in various accessories such as connection parts. For example, assume that the position indicated by A in FIG. 1 is the connection portion of the power cable. Further, the sensor 1 is installed within 5 m from the connecting portion A, and the sensor 2 is 20 m from the connecting portion A.
It is assumed that they are attached at positions separated from each other. And
It is assumed that a partial discharge has occurred in the connection portion A. Then, since the sensor 1 is arranged at a position near the partial discharge occurrence point, the sensor 1 outputs a signal with a large amplitude. On the other hand, since the sensor 2 is far from the partial discharge occurrence point, the sensor 2 outputs a signal with a small amplitude. The signal output from the sensor 1 is V _PD1 ,
If the output signal from the sensor 2 is V _PD2 , the differential amplifier 5
Outputs a difference signal V _PD1 −V _PD2 of the two signals. The measuring device 6 can detect the partial discharge based on this difference signal.

On the other hand, the atmospheric corona generated at the cable end portions 3a and 3b and the external noise due to the electric motor and the broadcast wave are detected by the sensors 1 and 2 in substantially the same manner, and the amplitudes of the output signals of the sensors 1 and 2 are It will be almost the same. Therefore, these signals are canceled and no signal is output from the differential amplifier 5. As described above, if the distance between the partial discharge occurrence point and the partial discharge sensor 1 is 5 m or less and the distance between the partial discharge occurrence point and the partial discharge sensor 2 is 20 m or more, the output of the differential amplifier 5 is the sensor 2 Sensor 1 not affected by
Will be the same as the output of. In this way, in this embodiment, the signal due to the partial discharge can be detected at a high S / N ratio.

In this embodiment, a simple and small coil 16 (having a volume of about 1 cm ³ ) is provided inside the sensors 1 and 2 instead of using a special element to obtain the resonance characteristic.
By connecting this coil 16 between the electrode 15 arranged on the outer periphery of the plastic sheath 14 and the internal conductor of the coaxial connector 20, the coupling capacitance by the electrode 15 and the coil 1 are connected.
A series resonance circuit with the inductance of 6 is formed.
In the case of such series resonance, the resonance point does not change due to the change in the resistance component of the detection unit D, so that only the Q value can be appropriately adjusted by selecting the capacitance C and the inductance L. Further, by appropriately selecting the resistance value of the resistance component, the detection frequency band can be made to have a certain width, and it is possible to cover the entire region in which the noise is small in the frequency region in which the partial discharge signal component of the wide band is distributed. can do. That is, the partial discharge signal can be detected with high sensitivity by utilizing the resonance characteristic in a wide frequency range with less noise. Therefore, it is possible to easily obtain a good S / N ratio with a simple configuration.

Further, since the resonance type partial discharge detection apparatus according to the present embodiment has the resonance characteristic, it can effectively amplify the high frequency component of the arbitrary frequency of the partial discharge pulse. Further, since the Q value is relatively low, the observation frequency band can be widened.

FIG. 4 is a schematic view showing a partial discharge detection device according to the second embodiment of the present invention.

In the present embodiment, a plurality of partial discharge sensors 22a, 22b, ..., 22c are provided on the power cable 21 at appropriate intervals. Each of these sensors 22a, 22b, ..., 22c has the structure shown in FIG. These sensors 22a, 22b, ..., 2
The output of 2c is supplied to E / O converters (electric-optical converters) 24a, 24b, 24a, 24b, via amplifiers 23a, 23b, ..., 23c, respectively.
, 24c, and converted into an optical signal. These optical signals are O / E converters (optical-electrical converters) 26a, 26b, via optical fibers 25a, 25b, ..., 25c.
, 26c, and converted into an electric signal. The centralized monitoring device 27 is equipped with a computer or the like. The centralized monitoring device 27 includes O / E converters 26a, 26b, ..., 26.
The signal given by c is digitally processed and stored in a storage device. Then, the difference between these signals is calculated, and the signals commonly input to the partial discharge sensors 22a, 22b, ..., 22c are removed as noise.

When a large number of partial discharge sensors are arranged on the power cable, signal processing by hardware such as a differential amplifier is difficult as in the first embodiment. However, as in the present embodiment, the output signals of the partial discharge sensors are digitized and input to the storage device, and then these signals are processed by the computer, whereby the signals due to the partial discharge are output at a high S / N ratio. Can be detected.

Generally, most of the cable accidents are accidents at the connecting portion or the terminating portion. Therefore, by installing a sensor near each connecting portion and the terminating portion, quality assurance over the entire cable and Easy maintenance and inspection.

[0033]

As described above, the partial discharge detection device according to the present invention is provided with a plurality of partial discharge sensors composed of electrodes and inductances arranged on the surface of the insulating coating layer of the power cable, and these. Since the output signals from the sensors are compared with each other to determine noise and remove the noise, the high frequency component of the signal propagating through the outer conductive layer when the partial discharge occurs has a high S / N ratio. Can be detected with. Further, the partial discharge detection device according to the present invention can be easily installed on the power cable and the connection portion after the installation, has a wide application range, and is excellent in safety.

[Brief description of drawings]

FIG. 1 is a schematic view showing a partial discharge detection device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a sensor of the partial discharge detection device according to the first exemplary embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a power cable and a detection system.

FIG. 4 is a schematic diagram showing a partial discharge detection device according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional tunable partial discharge detection device.

[Explanation of symbols]

 1, 2, 22a to 22c; Sensors 3 and 21; Power cables 3a and 3b; Termination part 4; High-voltage power supply line 5; Differential amplifier 6; Measuring device 10; Inner conductor 11; Inner semiconductive layer 12; Cable insulator 13; Metal shielding layer 14; Plastic sheath 15; Electrode 16; Coil 17; Brass tube 18; Insulation tube 19; Lead tape 20; Coaxial connector 23a-23c; Amplifier 24a-24c; E / O converter 25; Optical fiber 26a- 26c; O / E converter 27; Centralized monitoring device

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

Claims (1)

Claim: What is claimed is: 1. A plurality of partial discharge sensors composed of an electrode provided on a surface of an insulating coating layer of a power cable and an inductance connected to the electrode, and partial discharges of these sensors. 2. A partial discharge detection device, comprising: noise removal means for comparing output signals from the sensors with each other to determine noise commonly applied to each partial discharge sensor and removing the noise.