JPH04337482A - Partial discharge sensor - Google Patents

Abstract

PURPOSE:To provide a partial discharge sensor 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. A coil and an amplifier 7 are connected between the electrode 2 and a connector 5. The coil 6 and the amplifier 7 are received in a vessel consisting of a brass cylinder 3. The signal outputted from the amplifier 7 is taken out to the outside through the 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 this resonance circuit. This signal is amplified by the amplifier 7 and sent to the outside.

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 sensor 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. 5, a tunable detection device using the tunable detection method described above uses
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 sensor that can simplify the device and the measurement.

[0009]

[Means for Solving the Problems] A partial discharge sensor according to the present invention is a partial discharge sensor that is attached to a power cable to detect partial discharge thereof, and includes an electrode provided on an insulating coating layer of the power cable; an inductance whose one end is connected to a coupling capacitance constituted by the electrode and the outer conductive layer of the power cable and exhibits resonance; an amplifier which amplifies a signal output from the other end of the inductance; The device is characterized by having an output terminal for drawing out the output to the outside.

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.

Furthermore, in the present invention, since the signal output from the resonant circuit is amplified by the amplifier and then sent to the outside via the output terminal, it is possible to suppress the influence of noise and eliminate the need to install an external amplifier. This allows the partial discharge detection system to be downsized.

[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 sensor according to the present invention to an accessory at a connecting portion or a terminal portion 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 partial discharge sensor according to an embodiment of the present invention.

Plastic sheath 20 of power cable 1
An electrode 2 made of conductive paint, metal tape, or the like is provided around the entire circumference.

The electrode 2 includes an insulating tube (not shown) attached to the power cable 1, a brass tube 3 placed on the outer periphery of the insulating tube, and a shielding container formed by a lead tape 4 covering the outer periphery of the insulating tube. is housed within. A coaxial connector 5 such as a BNC connector is attached to the brass cylinder 3, and a broadband amplifier 7 and a coil 6 as an inductance element are connected between the internal conductor of the coaxial connector 5 and the electrode 2. There is. This amplifier 7 and coil 6 are 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. Note that as a driving power source for the amplifier 7, a battery or the like may be provided in the shield container, or
It may also be supplied from outside.

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

This device includes a sensor 10 having the above-described structure, and a digitizing oscilloscope 12 that performs signal processing such as averaging on the output of the sensor 10.
It is composed of.

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. 2, 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 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 partial discharge detection device, a simple and small (approximately 1 cm 3 ) coil 6 and a broadband amplifier 7 are provided inside the sensor 10, instead of using special elements to obtain resonance characteristics. 6 and an amplifier 7 coated on the outer periphery of a plastic sheath 20.
By connecting between the electrode 2 and the internal conductor of the coaxial connector 5, a series resonant circuit is formed between the coupling capacitance of the electrode 2 and the inductance of the coil 6. 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. Also,
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 to cover the entire frequency range with less noise in the frequency range where the broadband partial discharge signal component is distributed. Can be done. 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.

[0027] Furthermore, the partial discharge sensor according to this embodiment has the following features:
Since it has resonance characteristics, it can 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, in this embodiment, since the broadband amplifier 7 is provided within the sensor, it is possible to avoid the complexity of connecting the amplifier and the sensor, and there is no need to install this type of amplifier externally. Space can be reduced. Furthermore, since the signal amplified by the amplifier 7 is sent to the outside, the influence of noise is small, and since the amplifier is housed within the sensor case, there is also the advantage that there is no need to take dust-proof and moisture-proof measures for the amplifier.

[0028]

As explained above, according to the present invention, there is an electrode that forms a coupling capacitance with the outer conductive layer of a power cable, and one end connected to this electrode and the other end connected to an amplifier. Since the power cable has a resonant inductance, it is possible to detect a high frequency component of a signal propagating through the outer conductive layer of the power cable when a partial discharge occurs. Also,
Since the partial discharge sensor according to the present invention has a built-in amplifier, there is no need to install an amplifier externally, and the partial discharge detection system can be made smaller and less susceptible to noise. Further, the partial discharge sensor according to the present invention can be easily installed on installed power cables and connecting parts, and can detect partial discharges with high accuracy under live wires.

[Brief explanation 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 the configuration of a partial discharge detection device using the same partial discharge sensor.

FIG. 3 is a cross-sectional view showing the 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.

[Explanation of symbols]

1,31; power cable 2; Electrode 3; Brass tube 4; Lead tape 5; Coaxial connector 6; coil 7; Wideband amplifier 10; sensor 12; Digitizing oscilloscope 16; Internal conductor 17; Internal semiconducting layer 18; Cable insulation 19; Metal shielding layer 20; plastic sheath

Claims (1)

[Claims] 1. A partial discharge sensor that is attached to a power cable to detect partial discharge thereof, comprising an electrode provided on an insulating coating layer of the power cable, and this electrode and an outer conductive layer of the power cable. an inductance that exhibits resonance by being connected to a coupling capacitor at one end, an amplifier that amplifies a signal output from the other end of this inductance, and an output terminal that draws the output of this amplifier to the outside. Partial discharge sensor.