JPH04337481A - Partial discharge detecting device - Google Patents

Abstract

PURPOSE:To provide a partial discharge detecting device capable of detecting a partial discharge generated in a power cable in hot-line state and excellent in measuring precision. CONSTITUTION:An electrode 2 is disposed around the plastic sheath 20 of a power cable 1. The electrode 2 is formed of a pair of electrode plates 1 forming nearly a cylinder by the combination thereof, and the two electrode plates press the cable 1 at a determined contact pressure by a bolt, a nut and a spring. A coil 6 is connected between the electrode 2 and a connector 5. The electrode 2 forms a coupling capacity together with the outside conductive layer of the cable 1, and the coupling capacity and the coil 6 form a resonance circuit. The high frequency component of a progressive wave generated on the basis of a partial discharge is selectively detected by the resonance circuit.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to partial discharge (Par
The present invention relates to a partial discharge detection device that detects partial discharge (PD).

0002

2. Description of the Related Art Hitherto, partial discharge detection devices for detecting partial discharge occurring in power cables have been proposed, for example, using a tunable detection method and a method using an AE (acoustic emission) sensor.

As shown in FIG. 7, a tunable detection device using the tunable detection method is a
A coupling capacitor 33 and a detection impedance 34 are connected in series between the internal conductor of a or 32b and the metal shielding layer, and the potential difference generated across the detection impedance 34 is transmitted by a tuned amplifier 35 with a tuning frequency of several hundred kHz. It was designed to be taken out.

However, this tunable detection device has problems in that it is difficult to detect under live wires because it is necessary to extract the signal from the internal conductor of the power cable, and a dedicated coupling capacitor is also required. . Furthermore, since the tuning frequency of this device is several hundred kHz, it is easily affected by surrounding noise, and although good detection accuracy can be obtained in experiments in a shielded room, it is difficult to apply it to cables after installation.

On the other hand, a detection device using an AE sensor is
An AE sensor is used to detect elastic waves propagating inside an insulator due to partial discharge, but while this device is not affected by electrical noise, it is highly sensitive to ultrasonic waves because they travel in a straight line. There is a problem that the detection sensitivity is extremely low depending on the detection position due to the directivity.

[0006] Therefore, at the connection part of the power cable,
A detection method has also been proposed in which the metal shielding layer is insulated and the potential difference generated between the two metal shielding layers sandwiching the insulating part when a partial discharge occurs is detected by a detection impedance connected between the two metal shielding layers. Line 275kV CV
"Partial discharge test results for cable lines"; Katsuta et al., Institute of Electrical Engineers of Japan Insulating Materials Study Group material EIM-90-20).

[0007]

[Problems to be Solved by the Invention] However, this method is limited to application only to connections where the metal shielding layer is insulated, and since the metal shielding layer is in an ungrounded state, it is difficult to ensure safety in the event of a short circuit accident. The problem is that it lacks sex. Another drawback is that the device is large and measurement requires skill.

The present invention has been made in view of these problems, and can be easily installed on power cables and their connections after installation, has a wide range of application, and has excellent safety and measurement accuracy. Moreover, it is an object of the present invention to provide a partial discharge detection device that can simplify the device and simplify the measurement.

[0009]

[Means for Solving the Problems] A partial discharge detection device according to the present invention includes an electrode provided on an insulating coating layer of a power cable, and a coupling capacitor constituted by this electrode and an outer conductive layer of the power cable. The power cable is characterized by comprising an inductance that is coupled in series with the power cable to exhibit resonance, and support means that supports the electrode in a state where it is elastically pressed against the power cable.

0010

[Operation] A partial discharge pulse is a broadband signal, and becomes a traveling wave that propagates between conductors in a power cable, which is a distributed constant circuit, and uses the earth as a return path. The inventors of the present application have focused on this point and have attempted to detect the high frequency component of the traveling signal wave generated by the partial discharge pulse and propagating through the outer conductive layer of the power cable from above the coating layer. That is, an electrode is provided outside the coating layer, an inductance element such as a coil is further connected to this electrode, and a signal is extracted through this inductance element. In this case, a series circuit of the inductance element and a coupling capacitance (functioning as a capacitor as a high-pass filter, that is, a high-pass capacitor) to the outer conductive layer facing each other with the coating layer in between of the electrodes exhibits resonance characteristics; This series resonant circuit resonates with signals in a desired frequency band at an appropriate Q (quality factor: strength of resonance), forming a high frequency resonant circuit that can selectively amplify signals in the desired frequency band. .

According to the present invention, since the high frequency component of the traveling wave traveling from the outer metal layer toward the ground is detected by the high frequency resonant circuit through the coating layer when a partial discharge occurs, the power cable or connection The setting is completed simply by mounting the electrodes and inductance constituting the high frequency resonant circuit on the coating layer of the section. Therefore, it can be easily installed on cables and connections after installation, and measurements can be taken even under live wire conditions.

Furthermore, since the present invention uses a method of detecting traveling waves propagating through the outer metal layer, there is no need to bring the outer metal layer into a non-grounded state. Therefore, the present invention can avoid inconveniences such as application being limited depending on the type of the connection portion, etc., and safety being reduced.

[0013] As the electrode, for example, a conductive paint or a metal tape may be disposed so as to cover the entire outer periphery of the power cable. However, in this case, the cable undergoes repeated thermal expansion and contraction, which causes cracks or the like to occur in the conductive paint or metal tape, shifting the resonance frequency and making the cable susceptible to external noise. Therefore,
The electrode needs to be able to follow changes in the outer diameter of the power cable due to changes in temperature and the like. For this purpose, in the present invention, the electrode is elastically pressed against the power cable by a support means. This results in
Regardless of changes in the outer diameter of the power cable, changes in the resonant frequency of the resonant circuit constituted by the electrodes and inductance can be avoided.

[0014] If the frequency component extracted from the high frequency resonant circuit is 5 MHz or less, it will be easily affected by external noise from mechanical elements such as motors and generators, and if it is 60 MHz or more, it will be affected by the broadcast band. . Therefore, the frequency component extracted from the high frequency resonant 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 by detecting only a very narrow band signal with high amplification. It is desirable to detect with a high degree of amplification. In the present invention, the resonant frequency and Q value can be changed arbitrarily by using a variable inductance as the inductance constituting the resonant circuit or by connecting a variable resistor in series with the resonant circuit. For example, even if there is slight variation in the frequency components included in the partial discharge pulse due to the size of the sample, etc., it can be easily accommodated.

[0015] Furthermore, it is known that most cable accidents occur at connections or terminations. Therefore, by attaching the partial discharge detection device according to the present invention to an accessory of a connecting part or a terminal part of a power cable, quality assurance and maintenance inspection of the power cable becomes possible.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

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

Plastic sheath 20 of power cable 1
A metal electrode 2 is disposed around the outer periphery of the sheath 20 so as to surround the sheath 20.

The electrode 2 is housed in a shielding container formed by an insulating tube (not shown) attached to the power cable 1, a brass tube 3 placed around the outer periphery of the insulating tube, and a lead tape 4 covering the outer periphery. is housed in. In the brass tube 3,
For example, a coaxial connector 5 such as a BNC connector is attached, and a coil 6 as an inductance element is connected between the internal conductor of this coaxial connector 5 and the electrode 2. This coil 6 is also housed within the shield container. The shielding container is connected to a ground wire to which the metal shielding layer of the power cable 1 is connected.

FIGS. 2(a) and 2(b) are a front view and a side view showing the electrode 2, respectively.

[0021] The electrode 2 is composed of a pair of electrode plates 2a and 2b each having a shape obtained by dividing a cylindrical member in half, and flanges 7a and 7b are provided at the ends of each electrode plate 2a and 2b. It is being These two electrode plates 2a, 2b have flange portions 7a, 7b.
are arranged to face each other, the bolt 8a and the nut 8b
and is attached to the outer periphery of the power cable 1 by a spring 9. That is, holes slightly larger than the diameter of the bolt 8a are provided in the flanges 7a and 7b, and after placing the electrode plates 2a and 2b across the power cable 1, the bolt 8a is
are inserted into the holes in the flanges 7a and 7b, a spring 9 is passed through the bolt 8a, and a nut 8b is screwed onto the tip of the bolt 8a. When the electrode 2 is attached to the power cable 1, a slight gap is provided between the flange 7a and the flange 7b. Therefore, the electrode plates 2a and 2b always press the power cable 1 with a substantially constant pressing force due to the elastic force of the spring 9.

FIG. 3 is a block diagram showing the configuration of a partial discharge detection device using the above-described sensor.

This device includes a sensor 10 attached to a power cable 1 to detect partial discharge, and a sensor 10 that is attached to a power cable 1 to detect partial discharge.
It is composed of a wideband amplifier 11 that amplifies the output of 0, and a digitizing oscilloscope 12 that performs signal processing such as averaging on the output of the wideband amplifier 11.

The power cable 1 to be detected is, for example, a 275 kV CV cable, and as shown in FIG.
lythylene (crosslinked polyethylene) 18, a metal shielding layer 19 as an outer metal layer, and a plastic sheath 20 as a covering layer, which are coaxially arranged. As shown in FIG. 3, this power cable 1 is connected to a plurality of terminals via connecting portions 13a and 13b so as to have a predetermined length, and the internal conductor 16 of the terminal portions 14a and 14b is connected to the high-voltage power line 15. connected to. Also, this power cable 1
The metal shielding layer 19 is appropriately grounded at the terminal ends 14a, 14b, the connecting parts 13a, 13b, etc.

Next, the operation of the partial discharge detection device according to this embodiment configured as described above will be explained.

The equivalent circuit of the power cable 1 is generally considered to be a circuit as shown in FIG. That is, the inner conductor 1
6. The metal shielding layer 19, the termination portions 14a, 14b, and the grounding wires of the connection portions 13a, 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. In addition, the detection unit D is based on the coupling capacitance determined by the electrode 2 of the sensor 10 and the plastic sheath 20 of the power cable 1, the inductance of the coil 6 provided in series with this capacitance, and the input impedance of the measuring device. configured. The coupling capacity of the electrode 2 can be adjusted, for example, by adjusting the length of the electrode 2 in the longitudinal direction of the cable.

When a partial discharge occurs in the cable insulator 18, the resulting pulsed current is i2 in the figure.
, i2 ′, ... and i1 , in the same figure.
It propagates separately from the earth return mode shown by i1',...,i3,i3',.... As a result, the detection unit D has
Since a current shown as i1 +i1' flows, the sensor 10 detects this current.

In this embodiment, instead of using a special element to obtain resonance characteristics, a simple and small (about 1 cm 3 ) coil 6 is provided inside the sensor 10, and this coil 6 is connected to the outer periphery of the plastic sheath 20. By connecting between the electrode 2 disposed in and the internal conductor of the coaxial connector 5, a series resonant 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, since the resonance point does not change due to a change in the resistance component of the detection section D, only the Q value can be appropriately adjusted by selecting the capacitance C and the inductance L. In addition, by appropriately selecting the resistance value of the resistance component, it is possible to provide a certain degree of width to the detection frequency band, and it is possible to cover the entire frequency range with little noise in the frequency range where the broadband partial discharge signal component is distributed. can do. That is, the partial discharge signal can be detected with high sensitivity by utilizing resonance characteristics over a wide frequency range with little noise. Therefore, a good S/N ratio can be easily obtained with a simple configuration.

Furthermore, since the resonant partial discharge detection device according to this embodiment has resonance characteristics, it is possible to effectively amplify the high frequency component of any frequency of the partial discharge pulse. Furthermore, since the Q value is relatively low, the observation frequency band can be widened. Furthermore, since the two electrode plates 2a and 2b constituting the electrode 2 always press the power cable 1 with a substantially constant contact pressure by the spring 9, the electrode plate 2a and 2b that constitute the electrode 2 always press the power cable 1 with a substantially constant contact pressure, so that the electrode 2 and the power cable 1 can be avoided, and partial discharge can always be detected with high accuracy.

FIG. 6 is a schematic cross-sectional view showing an electrode of a partial discharge sensor according to a second embodiment of the present invention. In this embodiment, the electrode 21 is constituted by a substantially ring-shaped metal member having a notch 21a in a portion thereof.

In the partial discharge detection device according to this embodiment, the electrode 21 is disposed so as to fit around the outer circumference of the power cable 1. Then, the electrode 21 presses the cable 1 with a predetermined contact pressure due to its elasticity. As in the first embodiment, a partial discharge sensor is constructed by providing a coil in series with the capacitor formed by the electrode 21 and the metal shielding layer of the power cable 1.

In this embodiment, the inner diameter of the electrode 21 changes in accordance with the change in the outer diameter of the cable 1 due to temperature, and the electrode 21 always presses the cable 1 with a substantially uniform contact pressure. In this embodiment as well, the same effects as in the first embodiment can be obtained.

[0033]

As explained above, according to the present invention, an inductance is added to the coupling capacitance formed by the electrode elastically pressed against the power cable by the supporting means and the outer conductive layer of the power cable. Since they are coupled in series, it is possible to detect the high frequency component of the signal propagating through the outer conductive layer when a partial discharge occurs while avoiding changes in detection sensitivity due to temperature or the like. Further, the partial discharge detection device according to the present invention can be easily installed on the installed power cable and the connecting portion, has a wide range of application, and is excellent in safety.

[Brief explanation of drawings]

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

FIGS. 2(a) and 2(b) are a front view and a side view showing electrodes, respectively.

FIG. 3 is a block diagram of a partial discharge detection device according to a first embodiment of the present invention.

FIG. 4 is a sectional view showing the configuration of a power cable.

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

FIG. 6 is a schematic cross-sectional view showing an electrode of a partial discharge detection device according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a conventional tunable partial discharge detection device.

[Explanation of symbols]

1,31; power cable 2, 21; electrode 2a, 2b; electrode plate 3; Brass tube 4; Lead tape 5; Coaxial connector 6; coil 8a; bolt 8b; nut 9; Spring 10; sensor 11; Wideband amplifier 12; Digitizing oscilloscope 16; Internal conductor 17; Internal semiconducting layer 18; Cable insulation 19; Metal shielding layer 20; plastic sheath

Claims (1)

[Claims] 1. An inductance that exhibits resonance by being coupled in series with a coupling capacitance formed by an electrode provided on an insulating coating layer of a power cable and an outer conductive layer of the power cable; A partial discharge detection device comprising: support means for supporting an electrode in a state where it is elastically pressed against the power cable.