JPH06213959A - Partial discharge sensor in high-frequency part - Google Patents

Abstract

PURPOSE:To improve the detecting sensitivity in a high-frequency partial discharge sensor, which detects the partial discharge, with a resonance circuit constituted of a signal detecting electrode arranged on the outer surface of a power cable and an inductance element connected to the electrode. CONSTITUTION:Cleats 4a and 4b fix power cables 3 to a rack 2 at both sides of a joint part 1. A coil 5 is connected to a coupling capacitor constituted of one cleat (the cleat 4b) and the metal shield layer of the power cable 3. Thus, a resonance circuit is constituted. The resonance circuit detects the signal having the specified frequency component of the signals in the broad band generated by the partial discharge and outputs the detected signal into a measuring instrument through a coaxial cable 7.

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. 2, a tunable detection device using the tuned detection method has a terminating portion 22 of a power cable 21, as shown in FIG.
The coupling capacitor 23 and the 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 directivity, and there is a problem that the detection sensitivity is extremely lowered depending on the detection position.

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

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

Therefore, the inventors of the present application have proposed a resonance having a sensor (high frequency partial discharge sensor) composed of an electrode arranged on an insulating coating layer (sheath) of a power cable and an inductance connected to this electrode. A type partial discharge detection device was proposed (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 detection device using this high frequency 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 partial discharge detection device constructed 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 lines of the inner conductor 36, the metal shielding layer 39, the terminal ends 44a and 44b, and the connecting portions 43a and 43b form an RL series circuit. The inner conductor 36 and the metal shielding layer 39 are capacitively coupled via a cable insulator 38 interposed therebetween. Further, the detection unit D is composed of the coupling capacitance determined by the electrode 31 of the sensor 30 and the plastic sheath 40 of the power cable 21, the inductance of the coil 32 provided in series with this capacitance, and the input impedance of the measuring instrument. Composed. The coupling capacity of the electrode 31 can be adjusted by, for example, the length of the electrode 31 in the cable 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 partial discharge detection device thus constructed, the metal shield layer 3 of the electrode 31 and the power cable 21 is used.
The coupling capacitance formed by 9 and the high frequency resonance circuit formed by the coil 32 detect a signal in a predetermined band of a traveling wave in a wide band generated by partial discharge.

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

[0019]

However, the above-mentioned resonance type partial discharge detection device has the following problems. That is, the partial discharge is most likely to occur at the connection portion of the power cable. Therefore, it is preferable to install the above sensor near the joint portion of the cable. However, normally, as shown in FIG. 6, the power cable 53 is fixed to the insulating pedestal 52 by cleats (cable retainers) 54 on both sides of the cable joint portion 51. Therefore, conventionally, an electrode 59 is attached to the peripheral surface of the power cable outside the cleat 54, the coil 55 is connected to the electrode 59, and the shield container 56 housing the electrode 59 and the coil 55 is connected to the power cable. It is attached to 53 to form a sensor, and the output of this sensor is sent to the coaxial cable 5
A partial discharge detection system is configured by connecting to the measuring instrument 58 via 7.

Therefore, a space for installing the cleat 54 is required between the cable joint portion 51 and the electrode 59, the distance between the partial discharge occurrence point and the electrode 59 is large, and the sensitivity is lowered. I will end up.

When a partial discharge is generated in the cable joint portion 51, a signal in a predetermined frequency band out of a wide band signal due to this partial discharge is generated in the electrode 59 and the coil 55.
Is detected by the resonance circuit configured by. In this case, since the cleat 54 is grounded, a part of the wideband signal flows to the ground through the cleat 54. Therefore, the output of the signal given to the sensor becomes small.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a high frequency partial discharge sensor having a high detection efficiency of a signal based on a partial discharge generated at a connection portion of a power cable.

[0023]

A high frequency partial discharge sensor according to the present invention comprises a cleat for fixing a power cable to a support member, and a coupling capacitance formed by the cleat and a metal shielding layer of the power cable in series. And an inductance element that is coupled to exhibit resonance.

[0024]

According to the present invention, the resonance circuit includes the cleat for fixing the power cable to the support member and the inductance element (coil) connected in series to the coupling capacitance formed by the cleat and the metal shielding layer of the power cable. Make up. That is, the cleat that fixes the power cable to the support member is used as an electrode to form a high frequency partial discharge sensor. Therefore, the distance between the cable joint portion and the sensor can be shortened as compared with the conventional case, and the detection efficiency is improved. Moreover, since the signal component that has conventionally flowed to the ground via the cleat can be effectively used, the detection efficiency is further improved.

[0025]

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

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

Both sides of the joint portion 1 of the power cable 3 are fixed to the insulating base 2 by cleats 4a and 4b. In the present embodiment, the coil 5 is connected to the coupling capacitance formed by the cleat 4b and the metal shielding layer of the power cable 3 to form the high frequency partial discharge sensor 10.
The cleat 4b and the coil 5 are housed in the shield container 6, and the signal output from the sensor 10 is input to the measuring instrument 8 via the coaxial cable 7.

In this embodiment, when a partial discharge occurs in the cable joint section 1, a broadband signal based on this partial discharge propagates through the metal shield layer of the power cable 3. The coil 5 forms a resonance circuit together with the coupling capacitance formed by the cleat 4b and the metal shielding layer of the power cable 3, and detects a signal of a predetermined frequency component in the broadband signal propagating in the power cable 3.

In this embodiment, since the partial discharge sensor is constructed by using the cleat 4b for fixing both sides of the cable joint portion 1 to the frame, the partial discharge sensor should be arranged near the cable joint portion 1. You can Therefore, partial discharge can be detected with high sensitivity as compared with the conventional partial discharge sensor shown in FIG. Also,
Since the signal component that has conventionally flowed to the ground via the cleat can be effectively used, the sensitivity is further improved. Furthermore, since it is not necessary to attach an electrode made of a conductive paint or a metal tape to the peripheral surface of the power cable as in the conventional case, there is an effect that the sensor installation work is easy and the sensor installation cost can be reduced.

[0030]

As described above, the high frequency partial discharge sensor according to the present invention utilizes the coupling capacitance formed by the cleat for fixing the power cable to the support member and the metal shielding layer of the power cable. Since the sensor is configured, it is possible to dispose the sensor in the vicinity of the power cable connecting portion where partial discharge is likely to occur. Therefore, the sensitivity is improved as compared with the conventional case. Further, since the high-frequency partial discharge sensor according to the present invention can effectively utilize the signal component that has conventionally flowed to the ground via the cleat, the sensitivity is further improved. Furthermore, since it is not necessary to form electrodes with conductive paint or metal tape on the peripheral surface of the power cable,
There is an effect that the sensor installation work is easy and the sensor installation cost is reduced.

[Brief description of drawings]

FIG. 1 is a side view showing a high frequency partial discharge sensor 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 conventional resonance type partial discharge detection device.

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

FIG. 6 is a side view showing a conventional high frequency partial discharge sensor.

[Explanation of symbols]

 1, 51; Cable joint part 2, 53; Stand 3, 21, 51; Power cable 4a, 4b, 54; Cleat 5, 32, 55; Coil 7, 56; Coaxial cable 8, 58; Measuring instrument 10, 30; Sensors 31 ;, 59; Electrodes 35; Connectors 36; Inner conductors 38; Cable insulators 39; Metal shielding layers 40; Sheaths

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Tan 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Stock Company (72) Inventor Toshiya Shinozaki 1-1-5, Kiba, Koto-ku, Tokyo Stock Association In Fujikura, Inc. (72) Inventor Watanabe 1-5-1, Kiba, Koto-ku, Tokyo Stock Company In Fujikura

Claims (1)

[Claims] 1. A cleat for fixing a power cable to a support member, and an inductance element which is coupled in series with a coupling capacitance formed by the cleat and a metal shielding layer of the power cable to exhibit resonance. High-frequency partial discharge sensor featuring.