JPH04203979A - Insulation diagnostic method and cable supporting device - Google Patents

Abstract

PURPOSE:To enable safety and measuring accuracy to be improved by incorporating a detection means at a cable-supporting device itself for detecting a partial discharge which is generated inside an insulator of a power cable or its accessories and at an interface of one conductor of the insulator. CONSTITUTION:For detecting a discharge of a power cable 1 with termination parts 2a and 2b at a high-voltage power supply line 3, an output from a cleat 6 supporting the cable 1 and incorporating a sensor function is amplified by a wide-band amplifier 7 and is measured by a digitizing oscilloscope 8. The cable 1 is a 275kV CV cable, the cleat 6 consists of a hollow shielded case incorporating a piezoelectric element made of titanic acid zircon acid lead, and it has a filtering characteristic for enabling a high frequency which is equal to 10MHz or higher to pass. An external noise due to a heater, a motor etc., is distributed at 3MHz or below and a noise due to broadcasting electric wave is distributed near 80MHz and 200MHz so that a resonant frequency of a measurement system consisting of the cleat 6 etc., avoids these noise frequency bands, thus achieving an improved measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to reducing partial discharges that occur inside the insulator and at the insulator-conductor interface of power cables or their accessories.
The present invention relates to an insulation diagnosing method for diagnosing the insulation state of a power cable by detecting l Discharge (PD) and a cable support device directly used to implement this method.

[Prior Art] Conventionally, as a partial discharge detection device for detecting partial discharge occurring in a power cable, a tunable detection method and a method using an AE (acoustic emission) sensor have been proposed.

As shown in FIG. 13, the tuned detection device using the tuned detection method has a coupling capacitor 51 and a detection impedance 52 connected in series between the internal conductor of the terminal end 2a or 2b of the power cable 1 and the metal shielding layer. The potential difference generated across the detection impedance 52 is extracted by a tuning amplifier 53 having a tuning frequency of several hundred kHz.

However, this tunable detection device has problems in that it is difficult to measure under live wires because it is necessary to extract the signal directly from the internal conductor, and a dedicated coupling capacitor is also required. In addition, 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 tests in shielded rooms, it is difficult to apply it to cables after installation. is difficult.

Additionally, a device using an AE sensor uses the AE sensor to detect elastic waves propagating inside an insulator due to partial discharge, but while this device does not receive electrical noise, it does not receive ultrasonic waves. Since it has a straight-line property, it has strong directivity, and there is a problem that detection sensitivity is extremely reduced depending on the position.

Therefore, a detection method has also been proposed in which the metal shielding layer is insulated at the connection part of the power cable, and the potential difference that occurs between the two metal shielding layers when a partial discharge occurs is detected by a detection impedance connected between the metal shielding layers. (“Partial discharge test results for the Nikuikegami Line 275kvCV cable line”)
; Katsuta et al., IEEJ Insulating Materials Study Group Materials E IM-9
0-20).

[Problems to be Solved by the Invention] However, the above-mentioned 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 apply the method when a short circuit occurs. There is a problem that it lacks safety. Another disadvantage 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 applied to power cables and connecting parts when laying power cables, has a wide range of application, and has excellent safety and measurement accuracy. Moreover, it is an object of the present invention to provide an insulation diagnosis method that can simplify the device and the measurement, and a cable support device that can be used directly to carry out the method.

[Means for Solving the Problems] The insulation diagnosis method according to the present invention converts high-frequency components of signals generated inside a power cable by partial discharge pulses generated by partial discharge and propagates through the outer conductive layer from the support of the power cable. Detecting the partial discharge by receiving it through a coating layer of the power cable by a detection means built in the device, and processing this detection signal by a processing means built in the support device for the power cable, The present invention is characterized in that insulation diagnosis is performed by observing this processed signal.

Further, the cable support device according to the present invention is a device directly used for carrying out the insulation diagnosis method, and includes a support portion that has a hollow portion forming a shield container and supports the power cable, and a support portion inside the hollow portion. is mounted on a covering layer of the power cable and receives, via the covering layer, a high frequency component of a signal generated inside the power cable by a partial discharge pulse and propagating through an outer metal layer such as a metal sheath or a metal shielding layer. It is characterized by comprising a detection means and a signal processing means provided within the hollow portion and processing the output of the detection means.

[Operation] Generally, it is assumed that the potential of the metal shielding layer of a power cable is at a constant ground potential regardless of the location. Therefore, the conventional measurement method uses the capacitance between the internal conductor and the metal shielding layer and the external detection impedance.In order to extract the signal from the metal shielding layer, the metal shielding layer must be ungrounded. In addition, if the metal shielding layer was grounded, it was necessary to directly detect the signal from the internal conductor via a coupling capacitor (not grounded).

However, the partial discharge pulse is a broadband signal and becomes a traveling wave that propagates through the power cable, which is a distributed constant circuit, between conductors and through the ground as a return path. The inventors of the present invention have focused on this point and have decided to detect the high frequency component of the traveling signal wave generated by the partial discharge pulse and propagating through the outer metal layer from above the coating layer.

In this case, the covering layer essentially acts as a component of a high-frequency filter.

The present invention utilizes a method of detecting the high frequency component of a traveling wave traveling from the outer metal layer toward ground when a partial discharge occurs through a capacitive high frequency filter formed by a coating layer, and has a built-in detection section using this method. In order to detect the power cable using the cable support device of the power cable, the detection means can be mounted on the covering layer of the power cable or the connecting portion by simply supporting and fixing the power cable with the cable support device. Therefore, it can be easily installed on power cables and connecting parts, the detection means can be reliably attached over a long period of time, and measurements can be easily performed under live line conditions. Furthermore, since the present invention is a method for detecting traveling waves propagating through the outer metal layer, there is no need to make the outer metal layer ungrounded, and the application may be limited depending on the type of connection, etc., and safety may be reduced. There will be no problems such as doing so.

Note that the frequency component extracted from the detection means is 5M.
If it is below Hz, it will be easily affected by external noise from mechanical elements such as motors and generators, and if it is above 60 MHz, it will be affected by the broadcast band. Therefore, the frequency components extracted from the detection means range from 5 MHz to 6 MHz.
Preferably, it is broadly distributed in the range of 0 MHz.

Furthermore, it is known that most cable accidents occur at connections or terminations. Therefore, by attaching the detection means to a cable support device such as a cleat used for supporting the connection part or the termination part of the power cable,
It becomes possible to perform quality assurance and maintenance inspections on them.

Furthermore, since the present invention uses a method of detecting traveling waves propagating on the outer metal layer, monitoring over several meters is possible. Therefore, if a plurality of cable support devices each having a built-in detection means according to the present invention are installed at a predetermined interval at a power cable connection, etc., and the outputs from these detection means are centrally monitored, partial discharges can be detected. It is possible to detect the location where a failure occurs, and it is possible to easily prevent accidents from occurring and evaluate the location of the failure.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a partial discharge detection device constructed using a cable support device according to a first embodiment of the present invention.

This partial discharge detection device includes a cleat 6 as a cable support device that supports a power cable 1 for which partial discharge is to be detected and has a built-in sensor function, and a broadband amplifier 7 that amplifies the output of the sensor section of this cleat 6. It is comprised of a digitizing oscilloscope 8 that performs signal processing such as averaging on the output of the broadband amplifier 7.

The power cable 1 to be detected is, for example, a 275 kV Cv cable, and as shown in FIG.
Internal conductor 11, internal semiconducting layer 12, cable insulator (X
It is formed by coaxially arranging LPE (crosslinked polyethylene) 13, a metal shielding layer 14 as an outer conductive layer, and plasti and sheath 15 as a covering layer. As shown in FIG. 1, this power cable 1 is made to a predetermined length.
A plurality of connections are made via the connecting parts 4a and 4b, and the terminal end 2
The internal conductor 11 of a + 2 b is connected to the high voltage power supply line 3 . Moreover, the metal shielding layer 1 of this power cable 1
4 denotes terminal parts 2a', 2b and a connecting part 4a.

4b, etc., as appropriate.

The cleat 6 is attached to the outer periphery of the plastic sheath 15 in order to support the power cable 1 and to fix the connection box and the like when the power cable 1 is laid. This cleat 6
An example of the configuration of the internal sensor section is shown in FIG. That is, the hollow part 21 formed inside the cleat 6 made of conductive metal
is a part that serves as a shield case that houses the sensor section, and an opening is formed on the side that contacts the power cable 1. This opening is closed by an insulating plate 22 made of alumina or the like. A piezoelectric element 23 having an electrode 24 formed on one side by vapor deposition is housed inside the hollow part 21 . The surface of the piezoelectric element 23 opposite to the surface on which the electrode 24 is formed is closely fixed to the insulating plate 22. This piezoelectric element 23 is made of, for example, lead zirconate titanate (PZT), and together with the plastic sheath 15 of the electric cable 1, has a capacitance of about 500 pF and exhibits high frequency filter characteristics that allow signals in a frequency band of 10 MHz or higher to pass. It is configured as follows. The electrode 24 of this piezoelectric element 23 is
It is connected via a lead wire 25 to an internal conductor of a coaxial connector 26 attached to the hollow portion 21 . Cleat 6
is grounded, so the hollow portion 21 functions as a shield case.

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

Now, it is common to think that the equivalent circuit of the power cable 1 is as shown in FIG. That is, the inner conductor 11,
Metal shielding layer 14 and termination portion 2a.

The grounding wires of 2b and connecting portions 4a+4b form an RL series circuit. The inner conductor 11 and the metal shielding layer 14 are coupled through the capacitance of the cable insulator 13 interposed therebetween. Further, the detection section is composed of a combined capacitance of the sensor section of the cleat 6 and the plastic sheath 15, and the input impedance of the measuring device.

When a partial discharge occurs in the cable insulator 13, the resulting pulsed current is 12°12' in the figure.
The coaxial mode indicated by . . . and il in the same figure.

tt', . . . + 131 13'l . . . As a result, a current shown as il+il' flows through the detection section, and the sensor section of the cleat 6 detects this current.

Characteristic A shown in FIG. 5 shows the frequency response result of a measurement system using the cleat 6 incorporating the sensor of this embodiment.

However, the power cable 1 was assumed to be 20 m long, and the distances from the discharge point and the grounding point to the cleat 6 were assumed to be 2 m and 4 m, respectively. Further, for comparison, the frequency response of the conventional tuning type measurement method is shown as characteristic B in FIG. As can be seen from the figure, the high frequency component can be detected even from above the plastic sheath 15. For example, when a partial discharge occurs with a true discharge charge amount of 100 pC, the high frequency component can be detected for about 20 m only with the 50 MHz component.
I was able to get V. The resonant frequency of the measurement system when using the cleat 6 of this embodiment varies slightly depending on the power cable 1, the distance to the grounding point, etc., but can be set in the range of 30 MHz to eOMHz.

On the other hand, considering external noise, as shown in Figure 5, the airborne noise area N due to heaters, motors, etc.
1 is distributed below 3 MHz, and the noise region N2 due to broadcast radio waves is distributed around 80 MHz and 200 MHz. Therefore, in the conventional tuning method (characteristic B), the detection signal was completely included in the noise region Nl, but the resonant frequency of the measurement system using the cleat 6 of this embodiment is 30
to eOMHz exists in the region with the least noise,
Good S/N ratio can be measured.

Incidentally, the inventors of the present application used the partial discharge detection device using the cleat 6 of this embodiment to detect the AC of the power cable 1.
A destructive test was conducted. As a result, until the breakdown voltage is reached,
As shown in Figure 6 (a), no pulses were observed, but a partial discharge pulse waveform as shown in Figure 6 (b) was observed immediately after the voltage rose to the breakdown voltage, and breakdown occurred approximately 2 minutes later. did.

As described above, it is clear that the device of this example has sufficient performance as a failure prediction ability.

Note that in this test, the breaking point was 3 m away from the cleat 6 containing the sensor, and since the output voltage obtained this time was sufficiently large, it is thought that monitoring over a longer distance is possible.

Therefore, in the partial discharge detection device using a cleat with a built-in sensor according to this embodiment, when installing the power cable, the sensor can be attached to the power cable by simply supporting and fixing the power cable with the cleat inside a manhole or the like. It is possible to detect partial discharges in live lines and in frequency ranges with little external noise. Therefore, it is easy to install the partial discharge detection device, the sensor can be mounted reliably, and it can withstand long-term use.

FIG. 7 is a schematic block diagram of a partial discharge detection device according to a second embodiment of the present invention.

This part number N@ output device is for each connection part 4 of the power cable 1.
A cleat 6a has sensors similar to those of the cleatro shown in FIG. 1 built into each of a, 4b, . . . +4c.

By providing cleats 6b, . . . +6c and centrally monitoring the output from the sensor portion of each cleat 6a to 6C, it is possible to detect a faulty section in a long-distance cable.

Moreover, FIG. 8 is a sectional view showing details of the connecting portion 4a of this device. The inner conductors 11 are connected by a conductor connecting tube 36 . An insulating tape 37 is wrapped around the part of the joint where the cable insulator 13 has been peeled off, and a metal shielding layer 14 and a plastic sheath 15 are further covered thereon. The sensor 6a connects to this connection part 4a.
attached to the accessories that make up the Other connection parts 4b~
4c also has a similar configuration.

Now, in FIG. 7, the output of the sensor of each cleat 6a to 6c is output to a broadband amplifier 31a131b.

..., 31c, and subjected to electrical-to-optical conversion by Elo (electro-optical) converters 32a, 32b, ..., 32c, and then connected to optical fiber cables 33a, 33b.

..., transmitted at 33c. The transmitted signal is 0
/E (optical-electrical) converters 34a, 34b, . . .

The light is subjected to optical-to-electrical conversion at 34c and is supplied to the central monitoring device 35.

In this embodiment, the sensor section is built into the cleats 6a to 6C that support and fix the power cable 1 when the power cable 1 is installed, so the sensor can be installed extremely easily and securely. , each connection part 4
It is also extremely easy to install the cleaners 6a to 6C each having a built-in sensor in a to 4C.

In this embodiment, the wideband amplifiers 31a, 311), -
, 31c and E10 converter 32 a + 32 b +
..., 32c are provided near the cleats 6a to 6C, and the main signal transmission is performed using the optical fiber cables 33a+, 33b+-, and 33c, thereby further reducing the influence of noise on the lead wires.

In general, most cable accidents occur at connections or terminations, so each connection 4a to 4
If a sensor is installed at the end portions 2a and 2b, good detection sensitivity can be obtained, and quality assurance and maintenance inspection can be facilitated. In this case, since the level of the signal wave detected by each sensor 6a to 6C differs depending on the position where the partial discharge occurs, the failure section can be easily evaluated based on this level difference.

Note that, although an example has been described above in which a resonance sensor using a piezoelectric element such as lead zirconate titanate is used as a partial discharge detection means, the detection means is not particularly limited to a resonance sensor.

9 to 11 show an example in which an electrode capacitively coupled to the outer conductor of the cable is used as the detection means.

That is, on the outer periphery of the plastic sheath 15 of the power cable 1, an electrode 40 formed of metal tape or the like is attached in an annular or cylindrical shape over the entire outer periphery of the plastic sheath 15. This electrode 40 is connected to a support member 41 made of conductive metal that forms a cleat that supports the power cable 1.
They are located in hollow portions 42a and 42b formed in. The hollow portions 42a and 42b are composed of an annular portion 42a surrounding a portion where the electrode 40 is arranged, and a recess 42b formed at one location on the circumference of the annular portion 42a. A conductive member 45 such as a semiconductive sheet or aluminum mesh is inserted into the gap between the support member 41 and the outer peripheral surface of the plastic sheath 15 of the power cable 1. The electrode 40 provided on the outer periphery of the plastic sheath 15 is connected to the support member 41
and the conductive member 45, the hollow parts 42a and 4
The cleat formed by the support member 41 is used while being grounded. That is, the electrode 40
is shielded by a support member 41 and a conductive member 45. A coaxial connector 43 is attached to the recess 42b of the support member 41, and the internal conductor of this coaxial connector 43 and the electrode 40 are connected via a lead wire 44. The support member 41 constituting the cleat is composed of two parts, an upper half and a lower half as shown in the figure, and a conductive member 45 is inserted between the plastic sheath 15 and the power cable is connected to the two parts. 1 to support and fix the power cable 1.

In this embodiment as well, the metal shielding layer 14 of the power cable 1
Since the electrode 40, which is capacitively coupled to the sensor and constitutes a high-pass filter sensor, is shielded, a broadband partial discharge pulse can be detected without being affected by surrounding noise.

Further, FIG. 12 shows an example in which an inductance element is provided in series with the coupling capacitance between the outer conductor of the cable and the electrode to give the detection means resonance characteristics.

That is, in the configuration shown in FIG. 12, the electrode 40 and the coaxial connector 4
Instead of simply connecting the electrode 40 and the coaxial connector 43 with a lead wire 44 as shown in FIG. 9, the electrode 40 and the coaxial connector 43 are connected with a coil 46 as an inductance element. In this case, a coil 4e as an inductance element is provided in series with the coupling capacitance between the metal shielding layer 14 as an external conductor of the power cable 1 and the electrode 40, and a resonance characteristic due to the circuit including the coupling capacitance and the inductance element is provided. Therefore, partial discharge can be detected with high sensitivity and reliability. The series circuit of the coupling capacitance and the inductance element has a resonance Q of
Due to the resonance characteristics in which the (quality factor) is suppressed to an appropriate value, signals in a wide frequency band can be detected with high sensitivity. Therefore, by using a cleat having such a configuration, it is possible to detect signals in a frequency range that is not affected by noise among signals based on partial discharge in a wide frequency band.

Note that the power cable to be monitored is not limited to the type described above. For example, in each of the above embodiments, the metal shielding layer 14 as the outer metal layer and the plastic sheath 15 as the coating layer were used, but a power cable provided with the metal sheath as the outer metal layer and the plastic anti-corrosion layer as the coating layer It goes without saying that the present invention can also be applied to monitoring. Of course, the present invention is not limited to the above-mentioned cleat, but can also be applied to other cable support devices that directly support power cables.

[Effects of the Invention] As described above, according to the present invention, the cable support device itself that supports the power cable has a detection system that detects the high frequency component of the signal propagating through the outer metal layer from above the coating layer when a partial discharge occurs. Since the means is built-in, when installing the power cable, the power cable can be easily installed on the power cable and the connecting part by simply supporting and fixing the power cable with the cable support device according to the device of the present invention, and the scope of application is wide. This enables widespread partial discharge detection with excellent safety, durability, and measurement accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the configuration of a partial discharge detection device according to a first embodiment of the present invention, FIG. 2 is a sectional view showing the configuration of a power cable support part in the device, and FIG.
The figure is a cross-sectional view showing the configuration of the sensor section in the same device.
The figure is an equivalent circuit diagram of the power cable and detection system in the same device, Figure 5 is a graph showing the frequency response characteristics of the detection system in the same device, and Figure 6 is partial discharge pulse detection in a destructive test using the same device. A graph diagram showing an example, FIG. 7 is a block diagram schematically showing the configuration of a partial discharge detection device according to a second embodiment of the present invention, and FIG. 8 is a cross-sectional view showing the configuration of a connection part in the device. FIG. 9 is a cross-sectional view showing the vertical cross-sectional configuration of a power cable support portion in a partial discharge detection device according to the third embodiment of the present invention, and FIG. 10 is a cross-sectional view showing the cross-sectional configuration of the same portion. Figure 11 is a side view of the same part;
FIG. 12 is a sectional view showing the configuration of a power cable support portion in a partial discharge detection device according to a fourth embodiment of the present invention, and FIG. 13 is a block diagram of a conventional tunable partial discharge detection device. 1; Power cable, 2a, 2b; Termination part, 3; Voltage power line, 4 a + 4 b, 4 c; Connection part, 6, 6
a-6c; cleat, 7.31a-31c; broadband amplifier, 8; digitizing oscilloscope, 11; internal conductor, 12; internal semiconducting layer, 13; cable insulator, 1
4; Metal shielding layer, 15; Plastic sheath, 32a~
32c; Electrical-optical converter, 33a-33c: Optical fiber cable, 34a-34c; Optical-electrical converter, 35; Central monitoring device, 36; Conductor connecting tube, 37; Insulating tape, 4
0; electrode, 41; support member, 42a, 42b; hollow part,
43; coaxial connector, 44; lead wire, 45; conductive member, 46; coil

Claims (2)

[Claims] (1) The high-frequency component of a signal generated inside the power cable by a partial discharge pulse generated by partial discharge and propagating through the outer conductive layer is detected by the detection means built in the power cable support device to detect the coating layer of the power cable. Detecting the partial discharge by receiving the partial discharge through the power cable, processing this detection signal by a processing means built in the power cable support device, and performing insulation diagnosis by observing the processed signal. An insulation diagnostic method characterized by: (2) A cable support device that supports a power cable, which includes a support portion that has a hollow portion that forms a shield container and supports the power cable, and a support portion that is installed on a coating layer of the power cable in the hollow portion and is disposed on a partial discharge layer. a detection means for receiving, via the coating layer, a high frequency component of a signal generated inside the power cable by a pulse and propagating through an outer metal layer such as a metal sheath or a metal shielding layer; A cable support device comprising: signal processing means for processing the output of the cable support device.