JPH04181177A - Partial discharge detector - Google Patents

Abstract

PURPOSE:To widen an adaptation range, to enhance measuring accuracy and to simplify the title apparatus and measurement by providing the electrode mounted on the coating layer of a power cable and providing an inductance element between the conductor in a coaxial connector and the electrode. CONSTITUTION:A sensor 6 is mounted on the outer periphery of the plastic sheath of a power cable 1 and an electrode 21 formed from conductive paint or a metal tape is provided on the entire outer periphery of the sheath 15. The electrode 21 is received in a shield container formed from the insulating cylinder 22 mounted on the cable 1, a brass cylinder 23 and the lead tape 24 covering the outer peripheries of both cylinders. A coaxial connector 25 is attached to the brass cylinder 23 and a coil 26 as an inductance element showing resonance characteristics is connected to the internal conductor of the coaxial connector 25 and the electrode 21. The shield container is connected to the earth wire to which the metal shield layer 14 of the cable 1 is connected. By this constitution, the adaptation range of the apparatus is widened and safety and measuring accuracy can be enhanced and the apparatus and measurement can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to the prevention of partial discharges that occur inside an insulator and at the insulator-conductor interface of a power cable.
Partial discharge detection device (
(hereinafter referred to as a "PD detection device").

[Prior art] Conventionally, a P
As the D detection device, for example, a tunable detection method and a method using an AE (acoustic emission) sensor have been proposed.

As shown in FIG. 10, the tunable detection device using the tunable detection method includes a coupling capacitor 51 and a detection impedance 52 between the internal conductor of the terminal end 2a or 2b of the power cable 1 and the metal shielding layer. are connected in series, and 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 detect under live wires because it is necessary to extract the signal from the internal conductor, and a dedicated coupling capacitor is also required. Moreover, the tuning frequency in this device is several hundred kilometres.
Hz, it is easily affected by surrounding noise, and although good detection accuracy can be obtained in experiments in shielded rooms, it is difficult to apply to cables after installation.

In addition, a detection 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 is not affected by electrical noise, it is Since it has a straight-travel property, it has strong directivity, and there is a problem that detection sensitivity is extremely reduced depending on the detection position.

Therefore, there is a detection method in which a metal shielding layer is insulated at the connection part of a power cable, and when a partial discharge occurs, the potential difference generated between the two metal shielding layers sandwiching the insulating part is detected by a detection impedance connected between the two metal shielding layers. has also been proposed (``Results of partial discharge test on Nanko Kami Line 275kV CV cable line''; Katsuta et al., Institute of Electrical Engineers of Japan Insulating Materials Study Group Material EIM-90-20).

[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 disadvantage is that the device is large and measurement requires skill.

The present invention has been made in view of the above problems, and can be easily installed on power cables and connection parts after installation, has a wide range of application, has excellent safety and measurement accuracy, and is an excellent device. An object of the present invention is to provide a PDM output device that can simplify the process and the measurement.

[Means for Solving the Problems] The PD detection device according to the present invention is mounted on an insulating coating layer such as an anti-corrosion layer or a plastic sheath of a power cable, and is configured to detect the inside of the power cable by a partial discharge pulse. a detection means for receiving, via the covering layer, a high frequency component of a signal generated and propagating through an outer conductive layer such as a metal sheath or a metal shielding layer of the power cable; and a signal processing means for processing the output of the detection means. In the PDM output device, the detection means includes an electrode mounted on the covering layer of the power cable, and an inductance element that is coupled in series with a coupling capacitance of this electrode to the outer conductive layer and exhibits resonance characteristics. It is characterized by containing.

[Operation] Generally, it is assumed that the potential of the metal shielding layer, which is the outer conductive layer of a power cable, is at a constant ground potential regardless of location. For this reason, the conventional measurement method uses the capacitance between the internal conductor and the metal shielding layer and the external detection impedance.In principle, in order to extract the signal from the metal shielding layer, must be ungrounded.

Furthermore, when the metal shielding layer is grounded, it is necessary to directly detect a signal from the internal conductor via an ungrounded coupling capacitor.

However, the partial discharge pulse is a broadband signal;
It 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 application 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 conductive layer 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, the coupling capacitance of the electrode to the outer conductive layer facing each other across the coating layer (functions as a high-pass filter capacitor, that is, a bypass capacitor)
A series circuit of the inductance element and the above-mentioned inductance element exhibits resonance characteristics, and this series resonant circuit resonates with a signal in a desired frequency band at an appropriate Q (quality factor: strength of resonance), and generates a signal in the desired frequency band. A high frequency resonant circuit is formed that can selectively amplify signals.

According to the present invention, the high frequency component of the traveling wave traveling from the outer metal layer toward the ground when a partial discharge occurs is detected by a high frequency resonant circuit through the coating layer, so the coating layer of the power cable or the connection part Setting is completed simply by attaching the detection means on top. Therefore, it can be easily installed on the cable and the connection part after it has been laid, and it is also possible to easily perform measurements under live line 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. For this reason, the present invention does not have problems such as being limited in its application or being reduced in safety depending on the type of the connecting portion or the like.

Note that the frequency component extracted from the detection means is 5MHz.
If it is below, it will be easily affected by external noise due to mechanical elements such as motors and generators, and if it is above BOMHz, it will be affected by the broadcast band.

Therefore, the frequency components extracted from the detection means are:
5MHz to 60MH2 is preferred. However, partial discharge is a broadband signal, and detecting only a very narrow band signal with high amplification will not provide sufficient sensitivity; detecting a wide band signal within the above frequency range with appropriate amplification. It is desirable to do so. In this regard, the capacitance (capacitor) of the present invention
In a series resonant circuit consisting of an inductance and an inductance, the resonant frequency and Q value can be arbitrarily changed by using a variable inductance or by connecting a variable resistor in series.

For example, even if there are slight variations in the frequency components included in the partial discharge pulse due to the size of the sample, etc., this can be accommodated.

Furthermore, it is known that most cable accidents occur at connections or terminations.

Therefore, by attaching the detection means to an accessory of a connecting part or a terminal part of a power cable, quality assurance and maintenance inspection thereof becomes possible.

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 multiple detection means are installed at predetermined intervals, such as at power cable connections, and the outputs from these detection means are centrally monitored, it is possible to detect the location where partial discharge occurs. It is possible to easily prevent accidents from occurring and identify failure locations.

[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 PD detection device according to a first embodiment of the present invention.

This device includes a sensor 6 attached to a power cable 1 that is to detect partial discharge, a wideband amplifier 7 that amplifies the output of this sensor 6, and signal processing such as averaging for the output of this wideband amplifier 7. It is composed of a digitizing oscilloscope 8 that performs

The power cable 1 to be detected is, for example, a 275kV CV cable, and as shown in FIG.
Internal conductor 11, internal semiconducting layer 12, cable insulator (X
LPE: cross-1 inked poly
ethylene (crosslinked polyethylene) 13, a metal shielding layer 14 as an outer metal layer, and a plastic sheath 15 as a covering layer, which are coaxially arranged. As shown in FIG. 1, this power cable 1 is connected to a connecting portion 4a so as to have a predetermined length.

4b, and the internal conductors 11 at the terminal ends 2a, 2b are connected to the high voltage power supply line 3.

Further, the metal shielding layer 14 of the power cable 1 is appropriately grounded at the terminal ends 2 a + 2 b, the connecting parts 4 a and 4 b, and the like.

The sensor 6 is connected to the plastic sheath 15 of the power cable 1
attached to the outer periphery of the

3 and 4, an example of the sensor 6 is connected to the power cable 1.
FIG. 2 is a cross-sectional view and a perspective view, respectively, showing a portion attached to the device.

That is, on the outer periphery of the plastic sheath 15 of the power cable 1, an electrode 2 formed of conductive paint, metal tape, etc.
1 is provided all around the circumference. This electrode 21 is
It is housed in a shield container formed by an insulating tube 22 attached to the power cable 1, a brass tube 23, and a lead tape 24 covering the outer periphery thereof. A coaxial connector 25 such as a BNC connector is attached to the brass tube 23, and a coil 26 as an inductance element is connected between the internal conductor of the coaxial connector 25 and the electrode 21. This coil 26 is also housed within the shield container. The shielding container is connected to a ground wire to which the metal shielding layer 14 of the power cable 1 is connected.

Next, the operation of the PD 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 internal conductor 11, the metal shielding layer 14, the termination portions 2a, 2b, and the ground wires of the connection portions 4a, 4b form an RL series circuit. The inner conductor 11 and the metal shielding layer 14 are separated by a cable insulator 13 interposed between them.
capacitively coupled via. In addition, the detection part is determined by the coupling capacitance determined by the electrode 21 of the sensor 6 and the plastic sheath 15 of the power cable 1, the inductance of the coil 26 installed in series with this capacitance, and the input impedance of the measuring device. It consists of

The coupling capacity of the electrode 21 can be adjusted, for example, by adjusting the length of the electrode 21 in the longitudinal direction of the cable.

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.

it', . . . + i3, 13'+ . . . As a result, a current shown as il+il' flows through the detection section, and the sensor 6 detects this current.

In this embodiment, instead of using a special element to obtain resonance characteristics, a simple and small (1
By connecting the coil 26 between the electrode 21 attached to the outer periphery of the plastic connector 15 and the internal conductor of the coaxial connector 25 and the electrode 21, the coupling capacitance due to the electrode 21 and the coil 26 can be reduced. A series resonant circuit is formed with 26 inductances. In this way, in the case of series resonance, the resonance point does not change due to a change in the resistance component of the detection section, so the capacitance C and inductance L
By selecting , only the Q value can be adjusted appropriately. 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 less 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.

In order to examine the characteristics of the sensor 6 according to this embodiment in more detail, we roughly calculated the resonance frequency and Q value when the inductance of the coil 26 and the coupling capacitance C of the electrode 21 were selected from various values. Capacity C is 2
．． In the case of 8pF, the resonance frequency is 95.1μH2, the Q value is 11.9, the inductance L is 1μH, and the capacitance C is 12.
In the case of 5pF, the resonance frequency is 45.0μH2 and the Q value is 5.
．． 65, inductance L is 1μH and capacitance C is 20pF
In the case of , the resonant frequency is 35. EiMH2 has a Q value of 4.4
7. If the inductance L is 1 μH and the capacitance C is 50 pF, the resonance frequency is 22.5 μH2 and the Q value is 2.82, and the inductance L is 20 μH and the capacitance C is 50 pl'i.
”, the resonance frequency is 5.0MHz and the Q value is 2.6 months.
The value was obtained. In addition, in order to confirm the frequency characteristics of the signal component of the partial discharge pulse, we enlarged the time axis of the single pulse using a digital oscilloscope and determined the frequency of the damped oscillation waveform, which was confirmed to almost match the resonance frequency. . Therefore, it is clear that partial discharge pulses can be effectively measured by the resonance effect of this embodiment.

In addition, for the above-mentioned combination of inductance L and coupling capacitance C, the number of observed pulses at an applied voltage of 4 kV was measured experimentally, and the balanced bridge method (similar to the tuning method described earlier, is used for live wires). When the inductance L is 1 μH and the capacitance C is 2.81) F (resonance frequency 95
．． 1μH2) is 10 cycles (4Si output limit 8.'7o
p C), inductance L is 1 μH and capacity C is 2 months.
．． In the case of 5pF (resonance frequency 45.0μHz), it is 26
Cycle (detection limit 1.50pc), inductance L
is 1 μH and the capacitance C is 20 pF (resonant frequency 35.
6 μH2) for 28 cycles (detection limit 1.98 pC)
, when the inductance L is 1 μH and the capacitance C is 50 pF (resonance frequency 22.5 MHz), the I5 cycle (detection limit is 3.301 C), and the inductance L is 20
When the capacitance C is 50 pF at μH (resonant frequency 5.0 μH
For z), a value of 8 cycles (detection limit 15.01)C) was obtained.

Comparing the measurement sensitivity based on the output characteristics when the same applied voltage is applied as described above, it is found that the inductance L is 1 μH, the capacitance C is 2
．． 51) The combination of F (45 MHz) seems to be the best, but there was almost no difference when the inductance L was 1 μH and the capacitance C was 20 pF (35.6 μHz). Since the resonance Q value is proportional to L12 and inversely proportional to C1'', if the inductance L is the same, the capacitance C is C
The smaller the value, the narrower the band. Strictly speaking, it is desirable to take this point into account and calculate the optimum value according to the power cable, and also consider the influence of the inductance L of the lead wire, etc. However, since good measurements can be made with almost no difference in the vicinity of 30 to 50 μH2, and the size of the partial discharge itself varies, it is not necessary to strictly calculate the optimum value.

In order to examine the characteristics of the sensor 6 of this example in more detail,
The applied voltage characteristics of partial discharge were measured using the above-mentioned balanced bridge method and the sensor 6 according to this example. Figure 6 (a
) is the characteristic of the discharge charge per pulse Δq (average value during one cycle) and the frequency of occurrence n per cycle with respect to the applied voltage in the balanced bridge method, Figure 6 (b)
are the characteristics of the output signal voltage Δv per pulse (average value during one cycle) and the frequency of occurrence n per cycle with respect to the applied voltage in the sensor 6 according to this embodiment, and the seventh
Figure (a) shows the characteristics of the total number of charges Σq per cycle in the balanced bridge method with respect to the applied voltage, and the seventh
Figure (b) shows the characteristics of the total voltage ΣV of output signals per cycle in the sensor 6 according to this embodiment and the frequency n of occurrence per cycle with respect to the applied voltage. From these measurement results, the total number of electrical charges per cycle Σq or the total output signal voltage ΣV increases in proportion to the increase in applied voltage (the discharged charge per pulse Δq or the output signal voltage ΔV slightly increases) It was confirmed that the tendency peculiar to internal partial discharges, that is, the occurrence frequency n per cycle decreases, and the frequency n of occurrence per cycle increases), almost corresponds to each other.

Of course, in the device of this embodiment, since the electrode 21 is shielded by the shield container, a broadband partial discharge pulse can be detected without being affected by surrounding noise.

The inventors of the present application conducted an AC breakdown test on the power cable 1 using the apparatus of this example. As a result, no pulses were observed until the breakdown voltage was reached, but
A partial discharge pulse waveform was observed immediately after the voltage was increased to the breakdown voltage, and breakdown occurred about 2 minutes later. In this way, the device of this embodiment has sufficient failure prediction performance. In this test, the breaking point was 3 m away from the sensor 6, and since the output voltage obtained this time was sufficiently large, it is thought that monitoring over a longer distance is possible.

As mentioned above, the detection section of the resonant PD detection device according to the present example is an extremely excellent detection section according to the experimental results. It has the characteristics of being able to effectively amplify high frequency components, and (2) having a relatively low Q value, allowing for a wide observation frequency band.

FIG. 8 is a block diagram of a PD detection device according to a second embodiment of the present invention.

This device includes each connection portion 4a of the power cable 1.

4b, . . . +4c are provided with sensors 6a t (3b + . This system is designed to detect faulty sections in distance power cables.

Further, FIG. 9 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.
It is attached to the accessories (not shown) that make up the.

The other connecting portions 4b to 4c also have the same configuration as in FIG. 9.

Now, in FIG. 8, the output of each sensor 6a to 6c is amplified by broadband amplifiers 31a, 31b, .
..., 32c, and then transmitted through optical fiber cables 33a, 33b, ..., 33c. The transmitted signals are optical-to-electrical converted by O/E converters (optical-to-electrical converters) 34a, 34b, .

In this embodiment, since it is extremely easy to attach the sensors 6a to 6c, each connection part 4a to 6c is
It is also possible to install the sensors 6a to 6C on each of the sensors 4c with little effort.

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, the level of the signal wave detected by each of the sensors 6a to 6C differs depending on the position where the partial discharge occurs, so the failure section can be easily detected based on this level difference.

In addition, instead of providing the coil 26 as the above-mentioned inductance element, a lead wire may be wound into a coil shape, etc.
Any configuration may be used as long as it exhibits an appropriate inductance. Further, the power cable to be monitored is not limited to the above-mentioned type. For example, in the embodiment described above, the metal shield J-14 is used as the outer metal layer.
Although the power cable 1 has been described in which the plastic sheath 15 is provided as a coating layer, the present invention can also be applied to the monitoring of power cables provided with a metal sheath as an outer metal layer and a plastic anti-corrosion layer as a coating layer. Needless to say.

[Effects of the Invention] As described above, according to the present invention, the high frequency component of a signal propagating through the outer metal layer when a partial discharge occurs is transmitted from the coating layer by connecting the coupling capacitance formed by the electrode and the inductance element formed by the coil in series. Since it was detected by a resonant circuit,
It can be easily installed on installed power cables and connections, has a wide range of applications, is highly safe, and can amplify and detect partial discharge pulses as high-frequency components in any wide frequency band. A PD detection device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a PD detection device according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view of a power cable in the device, and FIG. Figure 4 is a perspective view of the sensor part in the same device, Figure 5 is an equivalent circuit diagram of the power cable and detection system in the same device, and Figures 6 and 7 are the applied voltage characteristics of the balanced bridge method and partial discharge using the same device. FIG. 8 is a block diagram of a PD detection device according to a second embodiment of the present invention, FIG. 9 is a sectional view of a connection part in the same device, and FIG. 10 is a conventional tunable PD detection device. It is a block diagram of 1; power cable, 2a, 2b; termination part, 3; voltage power supply line, 4a, 4b+4c: connection part, 6,
6a-6c; sensor, 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, 21; Electrode, 22; Insulating tube, 23; Brass tube, 24; Lead tape, 2
5; Coaxial connector, 26; Coil, 32a to 32c; Electrical-to-optical converter, 33a to 33c; Optical fiber cable,
34a to 34c; Optical-electrical converter, 35; Central monitoring device, 36; Conductor connection tube, 37; Insulating tape Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 8 Applied tEE (KV) ( a) 6th Applied Voltage (KV) 11th Intoguchi (KV) (b) Figure (b) 7 Figure

Claims (3)

[Claims] (1) Provided on an insulating coating layer of a power cable, the high-frequency component of a signal generated inside the power cable by a partial discharge pulse and propagating through the outer conductive layer of the power cable is passed through the coating layer. In a partial discharge detection device having a detecting means for receiving and a signal processing means for processing the output of the detecting means, the detecting means includes an electrode mounted on a coating layer of the power cable and the outer side of the electrode. 1. A partial discharge detection device comprising: an inductance element that is coupled in series with a coupling capacitance to a conductive layer and exhibits resonance characteristics. (2) The partial discharge detection device according to claim 1, wherein the detection means is attached to an attached part attached to the power cable. (3) A plurality of the detection means are provided at predetermined intervals on the power cable, and the signal processing means intensively monitors a partial discharge occurrence point of the power cable based on the output of the plurality of detection means. 3. The partial discharge detection device according to claim 1, further comprising a centralized monitoring means for monitoring the partial discharge.