JPH0545404A - Partial discharge sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to obtain a partial discharge sensor capable of detecting a partial discharge generated in a power cable in a live state and having excellent measurement accuracy. [Structure] An electrode 2 is arranged around a plastic sheath 20 of a power cable 1. A coil 6 is connected between the electrode 2 and the connector 5. The electrode 2 and the coil 6 are housed in a metal shield container 3. The shield container 3 is composed of two members that are combined into a substantially cylindrical shape. [Effect] The electrode 2 constitutes a coupling capacitance together with the outer conductive layer of the cable 1, and the coupling capacitance and the coil 6 constitute a resonance circuit. The resonant circuit selectively detects the high frequency component of the traveling wave generated based on the partial discharge.
In this case, since the electrode 2 and the coil 6 are housed in the shield container 3, the noise is small and the durability is high. In addition, it can be easily attached to the power cable 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) relating to a 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, for example, a method using a tuning type detection method and a method using an AE (acoustic emission) sensor has been proposed.

As shown in FIG. 5, a tunable detection device using the tuned detection method has a terminating end 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 at both ends of 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 hundreds of 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 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 its 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. Further, there is a drawback that the device becomes large in size 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 sensor capable of simplifying the device and simplifying the measurement.

[0009]

The partial discharge sensor according to the present invention is a partial discharge sensor attached to a power cable for detecting the partial discharge, and an electrode provided on an insulating coating layer of the power cable. An inductance that exhibits resonance by being connected to a coupling capacitance formed by an electrode and an outer conductive layer of the power cable; and a shield container that is attached to the power cable and that houses the electrode and the coil, The shield container is composed of a plurality of members arranged so as to sandwich the cable.

[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 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, and an inductance element such as a coil is further connected to this 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: 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 resonance circuit through the coating layer, a power cable or a connection is provided. The setting is completed only by disposing the shield container after 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 installation, and the measurement under a 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 only the traveling wave generated by the partial discharge is detected, a sensor having the structure shown in FIG. 6 is conceivable. That is, the electrode 41 made of a conductive paint, a conductive tape, or the like is provided on the peripheral surface of the power cable 1. Then, one end of the coil 42 is connected to the electrode 41, and the other end of the coil 42 is connected to the connector 43. In addition, an insulating cylinder 44 and a shield material 45 are provided around the electrode 41 and the coil 42.
Place a container (eg, a brass tube). Then, a lead tape 46 for reinforcing the shield is wrapped around the container.

With the sensor thus constructed, it is possible to detect the occurrence of partial discharge. However, in this case, the shield material 45 alone is not sufficient for the shield, and the work of winding the lead tape 46 for reinforcing the shield is necessary. Therefore, such a sensor has a drawback that the work of mounting the sensor on the power cable 1 is complicated. Further, when the lead tape 42 has a winding deviation or a difference in thickness, a sufficient shielding effect cannot be obtained, and reliability for long-term use is low.

Therefore, in the present invention, the need for reinforcing the shield with lead tape or the like is eliminated by accommodating the electrodes, coils and the like in a shield container. In this case, in order to facilitate mounting on the power cable, the shield container is composed of a plurality of members, and these members are arranged with the power cable interposed therebetween. As a result, the shield container can be easily attached to the power cable, and a shortage of the shield can be prevented.

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 or the like, it can be easily dealt with.

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

[0018]

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

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

On the outer circumference of the plastic sheath of the power cable 1, an electrode 2 formed of a conductive paint or a metal tape is provided over the entire circumference.

The electrode 2 is housed in a shield container 3 made of metal such as brass. A coaxial connector 5 such as a BNC connector is attached to the shield container 3, and the inner conductor of the coaxial connector 5 and the electrode 2 are attached.
A coil 6 as an inductance element is connected between and. The shield container 3 is made of a substantially cylindrical metal member, and conical taper portions are provided at both ends thereof. Also, this shield container 3
Is configured such that two members are arranged so as to sandwich the power cable 1. Further, the shield container 3 is connected to the ground wire to which the metal shield layer of the power cable 1 is connected.

FIG. 2 is a block diagram showing the structure of a partial discharge detecting apparatus using the partial discharge sensor of this embodiment.

This apparatus has a sensor 10 having the above-described structure, a wide band amplifier 11 for amplifying the output of the sensor 10, and a digitizing oscilloscope 12 for performing signal processing such as averaging on the output of the wide band amplifier 11. It is composed of and.

The power cable 1 to be detected is, for example,
With a 275 kV CV cable, as shown in FIG. 3, an inner conductor 16, an inner semiconductive layer 17, a cable insulator (XLPE: cross-linked polyethylene) 18, and a metal shield as an outer metal layer are sequentially provided from the center. Layer 19
And a plastic sheath 20 as a coating layer is coaxially arranged. As shown in FIG. 2, the power cable 1 has a connection portion 13a, 1 so that the power cable 1 has a predetermined length.
3b, and a plurality of terminal portions 14a and 14b are connected.
The inner conductor 16 of is connected to the high-voltage power supply line 15. In addition, the metal shield layer 19 of the power cable 1 is
4a, 14b and connecting portions 13a, 13b, etc. are properly grounded.

Next, the operation of the partial discharge detection device constructed as described above 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 1
6. The metal shield layer 19, the ground lines of the terminal portions 14a and 14b, and the connection portions 13a and 13b form an RL series circuit. The inner conductor 16 and the metal shielding layer 19 are capacitively coupled via a cable insulator 18 interposed therebetween. Further, the detection unit D includes the electrode 2 of the sensor 10 and the power cable 1
It is composed of a coupling capacitance determined by the plastic sheath 20, 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 18, 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 ', .. As a result, i1 + i
Since the current indicated by 1 ′ flows, the sensor 10 detects this current.

In this partial discharge detecting device, a simple and small coil (volume: about 1 cm ³ ) 6 is provided inside the sensor 10 without using a special element for obtaining the resonance characteristic. The plastic sheath 20
By connecting between the electrode 2 attached to the outer periphery of the electrode and the internal conductor of the coaxial connector 5, a series resonance circuit of the coupling capacitance of 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. Therefore, only the Q value can be appropriately adjusted by selecting the capacitance C and the inductance L. Further, if the resistance value of the resistance component is appropriately selected, the detection frequency band can be made to have a certain width, and it is possible to cover the entire region of low noise in the frequency region where 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, the partial discharge sensor according to this embodiment is
Since it has a resonance characteristic, a high frequency component of an 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, since the shield container is constructed by combining two members, it is only necessary to dispose the two members so as to sandwich the power cable when mounting on the power cable. The sensor can be installed easily without the need for winding, and there is no fear that a gap will be provided between the sensor and the power cable. Therefore, the process for filling the gap is unnecessary, and it has sufficient durability even for long-term use.

[0030]

As described above, according to the present invention, an electrode forming a coupling capacitance with the outer conductive layer of a power cable, an inductance connected to this coupling capacitance and exhibiting resonance, and mounted on the power cable are described. Since the shield container for accommodating the electrodes and the coil is provided, the high frequency component of the signal propagating through the outer conductive layer of the power cable can be detected when the partial discharge occurs. It is easy to attach to the power cable, is not easily affected by noise, etc. and has high durability.

[Brief description of drawings]

FIG. 1 is a perspective view showing a 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 partial discharge sensor.

FIG. 3 is a cross-sectional view showing a configuration of 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 cross-sectional view showing an example of a resonance type partial discharge sensor.

[Explanation of symbols]

 1, 31; Power cable 2, 41; Electrode 3; Shield container 5, 43; Connector 6, 42; Coil 10; Sensor 11; Broadband amplifier 12; Digitizing oscilloscope 16; Inner conductor 17; Inner semiconductive layer 18; Cable Insulator 19; Metal shielding layer 20; Plastic sheath

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

Claims (1)

[Claims] 1. A partial discharge sensor attached to a power cable for detecting a partial discharge thereof, comprising: an electrode provided on an insulating coating layer of the power cable; and the electrode and an outer conductive layer of the power cable. Having a resonance connected to a coupling capacitance, and a shield container attached to the power cable to accommodate the electrode and the coil, the shield container having a plurality of shield containers sandwiching the cable. A partial discharge sensor comprising a member.