JPH0618603A - High frequency partial discharge sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide a high-frequency partial discharge sensor capable of detecting partial discharge occurring in a power cable in a live state and having excellent measurement accuracy. [Structure] An electrode 2 is arranged around the power cable 1, and a coil 6 is connected between the electrode 2 and a connector 5 provided on a shield cover 10. This coil 6 is sealed with resin 3. A waterproof compound 7 is filled in the shield cover 10. [Effect] The electrodes form a coupling capacitance together with the outer conductive layer of the cable, and the coupling capacitance and the coil form a resonance circuit. The resonant circuit selectively detects the high frequency component of the traveling wave generated based on the partial discharge. Also,
Reliable because the waterproof compound is filled in the shield cover.

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 high frequency partial discharge sensor.

[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 connecting 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 high frequency partial discharge sensor capable of simplifying the apparatus and simplifying the measurement.

[0009]

A high frequency partial discharge sensor according to the present invention includes an electrode arranged on a peripheral surface of a power cable, an inductance element connected to the electrode, the electrode and the inductance element. And a filler filled in the shield container.

[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 (which functions 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: strength of resonance) 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 the 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.

It is known that most of the cable accidents are accidents that occur at the connecting part or the terminating part. Therefore, by mounting the partial discharge sensor according to the present invention on the accessory of the connecting portion or the terminating portion of the power cable, it becomes possible to perform quality assurance and maintenance inspection of the power cable.

By the way, as shown in FIG. 6, an electrode 42 is arranged on the peripheral surface of the plastic sheath 40 of the power cable 41, and a coaxial connector attached to a shield container 44 (for example, made of brass) for accommodating the electrode 42. The partial discharge can be detected only by connecting the coil 46 as an inductance element between the inner conductor of 45 and the electrode 42. However, if this is left as it is, it is conceivable that water will enter the shield container and the output of the sensor will change. In addition, since the lead wire of the coil 46 is only connected to and supported by the electrode 42 and the connector 45, there is a possibility that the coil 46 may be deformed and the inductance may change in consideration of long-term use. There is not enough reliability.

Therefore, in the present invention, the filler is filled in the shield container. With this filling material, it is possible to prevent water from entering the shield container, prevent deformation of the coil (inductance element), and ensure the reliability of the sensor.

[0017]

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

FIG. 1 is a sectional view showing a high frequency partial discharge sensor according to an embodiment of the present invention.

The electrode 2 is arranged so as to surround the outer peripheral surface of the power cable 1. The electrode 2 is composed of, for example, a pair of electrode plates in a shape obtained by dividing a metal cylindrical member in half, and both are fixed to each other by bolts and nuts and attached to the electrode cable 1. In addition, a shield cover 10 made of a conductive material is provided on the outer periphery of the power cable 1 so as to surround the electrode 2. The shield cover 10 is connected to the ground wire to which the metal shield layer of the power cable 1 is connected.

The shield cover 10 is provided with a collar portion 10a at both ends in the cable longitudinal direction.
A tape 11a is interposed between 0a and the power cable 1. In addition, the power cable 1 from above the collar portion 10a
The tape 11b is wound around the peripheral surface of the. In this way, the sealing property between the flange portion 10a of the shield cover 10 and the power cable 1 is ensured.

The shield cover 10 has a drip-proof type B
The NC coaxial connector 5 (reception part) is attached.
A coil 6 as an inductance element is connected between the inner conductor of the coaxial connector 5 and the electrode 2.
The coil 6 is connected to the electrode 2 and the coaxial connector 5 by the lead wire 4. The coil 6 is made of resin 3
It is sealed by.

A waterproof compound (resin) 7 is filled in the shield cover 10. The waterproof compound 7 is one which is injected into the shield cover 10 through the resin injection port 8 after the shield cover 10 is arranged on the power cable 1. Is provided with an air hole 9 for discharging.

The shield cover 10 is covered with a heat shrinkable tube 12. This heat shrink tube 1
In the case of 2, the shield cover 10 is filled with the waterproof compound 7 and the resin injection port 8 and the air hole 9 are closed, and then the heat shrinkable tube 12 having a diameter larger than the diameter of the shield cover 10 is inserted into the power cable 1 to heat it. The shield cover 10 is covered by heat-shrinking the heat-shrinkable tube 12. The heat-shrinkable tube 12 has an opening at a portion corresponding to the connector 5.

The sensor thus constructed is connected to a measuring device (not shown) by a coaxial cable 14. A connector plug 13 is attached to the end of the coaxial cable 14, and the connector plug 13 is attached to the connector 5
By engaging with, the sensor and the coaxial cable 14 are electrically connected. This connector connection is cap 15
Is covered with. A caulking material 17 seals between the end of the cap 15 on the shield container side and the heat-shrinkable tube 12, and a tape 18 seals between the end of the coaxial cable 14 and the coaxial cable 14. A caulking material 16 is filled in the cap 15. In this way, the waterproofness of the connector part is ensured.

FIG. 2 is a block diagram showing the structure of a partial discharge detection device using the above-mentioned sensor.

This device comprises a sensor 20 attached to a power cable 1 for detecting a partial discharge, and a sensor 20.
It is composed of a wide band amplifier 21 for amplifying the output of 0 and a digitizing oscilloscope 22 for performing signal processing such as averaging on the output of the wide band amplifier 21.

The power cable 1 to be detected is, for example,
With a 275 kV CV cable, as shown in FIG. 3, an inner conductor 26, an inner semiconductive layer 27, a cable insulator (XLPE: cross-linked polyethylene) 28, and a metal shield as an outer metal layer, in order from the center. Layer 29
And a plastic sheath 30 as a covering layer is coaxially arranged. As shown in FIG. 2, the power cable 1 has a connecting portion 23a,
A plurality of terminals are connected via 3b, and their end portions 24a and 24b are connected.
The inner conductor 26 of is connected to the high-voltage power supply line 25. In addition, the metal shielding layer 29 of the power cable 1 has the end portion 2
4a, 24b and connecting portions 23a, 23b, etc. are properly grounded.

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

The equivalent circuit of the power cable 1 is generally considered as a circuit as shown in FIG. That is, the inner conductor 2
6. The metal shield layer 29, and the ground lines of the end portions 24a and 24b and the connecting portions 23a and 23b form an RL series circuit.
The inner conductor 26 and the metal shield layer 29 are capacitively coupled via a cable insulator 28 interposed therebetween. Further, the detection unit D includes the electrode 2 of the sensor 20 and the power cable 1
It is composed of the coupling capacitance determined by the plastic sheath 30 of FIG. 1, the inductance of the coil 6 provided in series with this capacitance, and the input impedance of the measuring instrument. The coupling capacity of the electrode 2 can be adjusted by, for example, the length of the electrode 2 in the cable longitudinal direction.

When a partial discharge occurs in the cable insulator 28, the pulsed current generated by it 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 20 detects this current.

In the present embodiment, a simple and small coil (about 1 cm ³ ) is provided inside the sensor 20 without using a special element for obtaining the resonance characteristic, and this coil 6 is connected to the plastic sheath 30. By connecting between the electrode 2 arranged on the outer periphery and the inner conductor of the coaxial connector 5, a series resonance circuit of the coupling capacitance by the electrode 2 and the inductance of the coil 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. Also,
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 where the noise is low in the frequency region in which the partial discharge signal component of the wide band is distributed. You can 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 this embodiment has the resonance characteristic, the high frequency component of the arbitrary frequency of the partial discharge pulse can be effectively amplified. Further, since the Q value is relatively low, the observation frequency band can be widened. Furthermore, in this embodiment,
Since the waterproof compound and the caulking material are respectively filled in the shield cover and the cap covering the coaxial connector, it is possible to avoid a change in characteristics due to a change in humidity. Furthermore, since the coil is fixed by the resin and the waterproof compound, the inductance of the coil can be prevented from changing and the reliability of the sensor is high.

[0033]

As described above, according to the present invention, the electrode arranged on the peripheral surface of the power cable and the inductance element connected to the electrode are housed in the shield container, and the shield container is housed in the shield container. Is filled with the filling material, it is possible to detect high frequency components of the signal propagating in the outer conductive layer when partial discharge occurs, avoid the influence of humidity, and maintain reliability for a long period of time. . Further, the partial discharge detection sensor according to the present invention can be easily installed in 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 sectional view showing a high frequency partial discharge sensor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a partial discharge detection device using the same sensor.

FIG. 3 is a cross-sectional view showing a power cable.

FIG. 4 is an equivalent circuit diagram of a power cable and a detection system.

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

FIG. 6 is a perspective view showing an example of a high frequency partial discharge sensor.

[Explanation of symbols]

 1, 41; power cable 2, 42; electrode 5, 45; connector 6, 46; coil 7; waterproof compound 10; shield cover 12; heat shrink tube 13; connector plug 14; coaxial cable 15; cap 16; caulking material 26 Inner conductor 27; inner semiconductor layer 28; cable insulator 29; metal shielding layer 30, 40; sheath

Front Page Continuation (72) Inventor Yasuhiro Takahashi 1-5-1, Kiba, Koto-ku, Tokyo Within Fujikura Electric Line Co., Ltd. (72) Inventor Watanabe 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Line Co., Ltd. In the company

Claims (1)

[Claims] 1. An electrode arranged on a peripheral surface of a power cable, an inductance element connected to the electrode, a shield container for housing the electrode and the inductance element, and a filling filled in the shield container. And a high frequency partial discharge sensor.