JPH06331691A - Method for measuring partial discharge of power cable and its connection - Google Patents

Abstract

(57) [Summary] [Purpose] It is possible to measure partial discharge with high sensitivity.
Provide a partial discharge measurement method that does not require a power failure during calibration. [Configuration] A calibration pulse is injected from a calibration pulse generator 3 to select a frequency band having a high S / N ratio in a frequency band of 1.6 MHz to 50 MHz. When a partial discharge is generated in the power cable 1 or an intermediate connection portion thereof, a high frequency electric pulse and an ultrasonic pulse are generated by the partial discharge and reach the partial discharge pulse detector 5 and the AE sensor 4. The detected electric pulse is filtered by the bandpass filter in the frequency band in the signal processing unit 8, and is output to the oscilloscope 9 together with the ultrasonic pulse.
Since there is a difference in the propagation speed of the electric pulse and the ultrasonic pulse, the partial discharge and the noise can be distinguished from each other by the time difference, and the place where the partial discharge occurs can be estimated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge measuring method for evaluating the insulation performance and deterioration state of a CV cable and its connecting portion, and in particular, the present invention is used during a field completion test by applying a high voltage after laying a cable. The present invention relates to a partial discharge measuring method suitable for application or as a part of an insulation deterioration monitoring system in a live state.

[0002]

2. Description of the Related Art Conventionally, a method of testing a partial discharge using an ultrasonic pulse (AE wave: Acoustic Emission) and an electric pulse generated with the occurrence of partial discharge has been tried. As these methods, for example, partial discharge generation position locating utilizing the arrival speed difference between the ultrasonic pulse and the electric pulse, and noise discrimination method based on the waveform of the ultrasonic pulse have been proposed (Journal of the Institute of Electrical Engineers of Japan, B, Heisei). October 4 issue, pages 897-90
Page 4, "Detection of partial discharge of CV cable prefabricated junction box by AE sensor").

[0003]

By the way, the conventional method is performed in a relatively low frequency region where the measured frequency of the electric signal is 1 MHz or less, and is applied in a place where the ambient noise is large, such as a cable laying site. Therefore, the detection sensitivity is lowered, which is a problem. Further, unless the partial discharge charge amount is calibrated, the detected partial discharge charge amount cannot be accurately grasped. That is, in principle, it is difficult to estimate the magnitude of the amount of electric charge from the magnitude of the ultrasonic pulse itself, so that the electric pulse is often calibrated and compared with this.

In this case, conventionally, a wire was attached to the high voltage side in advance to inject a pulse for calibration, and thereby the calibration of the measured electric pulse was carried out. For this reason,
The following problems arose. A power outage is required during calibration. Cannot calibrate in a place away from the cable end. That is, it is not possible to calibrate the intermediate connection portion of the long line.

The present invention has been made in view of the above-mentioned problems of the prior art, and is a partial discharge measuring method using both partial discharge measurement by an ultrasonic sensor (hereinafter referred to as AE sensor) and electric partial discharge measurement. In, it is possible to measure the partial discharge with high sensitivity without being relatively affected by the ambient noise, and there is no need to interrupt the power during calibration.
It is another object of the present invention to provide a partial discharge measuring method capable of performing calibration at, for example, an intermediate connecting portion of a long line, which is separated from the cable terminating portion.

[0006]

In order to solve the above-mentioned problems, the invention of claim 1 of the present invention detects an ultrasonic pulse generated at the intermediate connection part or the terminal connection part of a power cable due to the occurrence of partial discharge. The first detecting means and the second detecting means for detecting the electric pulse generated by the occurrence of the partial discharge are provided, and the ultrasonic pulse detected by the first detecting section and the second detecting means are detected. In a partial discharge measuring method for distinguishing a partial discharge signal from noise by comparing electric pulses, a frequency of 1.6 MHz or more and 50 MHz or more is used.
In the following frequency bands, a frequency band having a high S / N ratio is selected, and when partial discharge occurs, the ultrasonic pulse and the electric pulse are compared for the electric pulse in the selected frequency band, and based on the comparison result. It is designed to distinguish between partial discharge and noise.

According to a second aspect of the present invention, there is provided a first detection means for detecting an ultrasonic pulse generated at the intermediate connection portion or the terminal connection portion of the power cable due to the occurrence of partial discharge,
Second detection of electric pulse generated by partial discharge
In the partial discharge measuring method for locating a partial discharge occurrence point based on the time difference between the ultrasonic pulse detected by the first detecting section and the electric pulse detected by the second detecting section. When a frequency band having a high S / N ratio is selected in the frequency band of not less than 6 MHz and not more than 50 MHz and partial discharge occurs, the time difference between the ultrasonic pulse and the electric pulse of the electric pulse in the selected frequency band is calculated. The position of occurrence of partial discharge is determined based on the obtained time difference.

According to a third aspect of the present invention, in the first or second aspect of the invention, a calibration pulse for injecting a calibration electric pulse from the low potential side into the intermediate connection part or the terminal connection part of the power cable. An injection means is installed, and a calibration pulse is injected from the calibration pulse injection means to select a frequency band having a high S / N ratio in a frequency band of at least 1.6 MHz and not more than 50 MHz.

According to a fourth aspect of the present invention, in the third aspect of the invention, the charge amount of the measurement electric pulse is calibrated by the calibration pulse injected from the low potential side. The invention of claim 5 of the present invention is the invention of claims 1, 2, and 3.
Alternatively, in the invention of claim 4, the ultrasonic pulse signal and the electric pulse signal are both measured, and the partial discharge measurement is performed by averaging the measured values a plurality of times.

[0010]

[Function] Unlike the laboratory, etc., where the cable is laid, it is easily affected by noise. Especially when the measurement frequency is low, 1.
It is easily affected by the AM radio area below 6 MHz. Also, other noise often propagates to the measurement system without being attenuated. Therefore, one of the conventional methods is, for example, 4
There is also a method in which the measurement frequency band is around 00 kHz, but in this case, the detection sensitivity may be about several hundred pC, which is not suitable for practical use.

Further, the broadcasting frequency of FM is 60 MHz or more, and this frequency band is also unfavorable in terms of noise characteristics. On the other hand, it is well known that the frequency characteristic of the actual partial discharge shows a relatively flat characteristic, although it tends to decrease slightly up to a band of 100 MHz or more. Therefore, in order to improve the detection sensitivity of the partial discharge measurement, it is advantageous to perform the measurement within the range of 1.6 MHz to 60 MHz, which is the region where the S / N ratio is large. Actually, it is practically 50 MHz or less because it is affected by the measurement line for attaching the detector to the outside of the sheath or the case.

Further, as mentioned above, from 1.6 MHz to 6
By detecting the electric pulse of partial discharge in the frequency band of 0 MHz, the influence of noise can be relatively avoided, but noise may be mixed in the frequency band depending on the installation site. Therefore, for example, a calibration pulse is injected by a calibration pulse generator, an electric pulse is measured to obtain an S / N ratio, and a band having a large S / N ratio is selected from the frequency bands and selected. The detection sensitivity can be further improved by detecting the electric pulse in the frequency band.

In the partial discharge measuring method using the partial discharge measurement by the AE sensor and the electric partial discharge measurement in combination,
By improving the detection sensitivity of the electric pulse as described above, it becomes easier to trigger by the electric pulse,
Since the trigger is applied with a low charge amount, the time difference from the subsequent ultrasonic pulse can be measured efficiently.

Here, in the case of partial discharge, the ultrasonic pulse and the electric pulse are detected with a certain time difference, and in the case of mechanical noise, only the ultrasonic wave is detected, and in the case of only electric noise, only the electric pulse is detected. A noise waveform appears at. That is, if the ultrasonic pulse and the electric pulse are detected with a certain time difference, it can be identified as partial discharge rather than noise.

Therefore, by making it possible to efficiently measure the electric pulse and the ultrasonic pulse that appear with a certain time difference as described above, it becomes possible to easily distinguish the partial discharge signal from the noise. Further, if the above-mentioned time difference is known, it is possible to estimate the partial discharge occurrence location based on the propagation speed of the ultrasonic pulse and the propagation speed of the electric pulse.

In the case of injecting the above calibration pulse, the foil electrodes are attached to both sides of the high frequency impedance connected between the sheaths in the prefabricated type connection part, and the insulation connection is used in the insulation connection part. Attach to both sides of the insulation part of the section, connect the calibration pulse generator to the foil electrode, and inject the calibration electric pulse from the low potential side of the sheath side to cause a power failure as described above. It is possible to inject the calibration pulse without using the calibration pulse, and it is possible to perform the calibration at a position away from the cable end portion.

Further, in order to make the detection of the ultrasonic pulse and the electric pulse more reliable, the following method can be used. That is, the partial discharge in which both the ultrasonic pulse and the electric pulse are detected has reproducibility. Therefore, if the ultrasonic pulse and the electric pulse are reproduced plural times with a certain time difference, the probability of partial discharge rather than noise is extremely high. Become higher.

As one specific method therefor, there is a method in which an electric pulse is triggered to measure an electric pulse and an ultrasonic pulse a plurality of times, and the averaging process is performed. By using this method, the partial discharge and the noise can be more reliably identified, and the accuracy of the time difference measurement between the ultrasonic pulse and the electric pulse can be improved and the estimation accuracy of the partial discharge occurrence position can be improved. Can be made.

In the invention of claim 1 of the present invention, as described above, in the frequency band of 1.6 MHz or more and 50 MHz or less, a frequency band having a high S / N ratio is selected, and the electric power of the selected frequency band is selected. Since the pulse is measured, the measurement sensitivity of the electric pulse can be improved without being affected by noise, and the partial discharge and the noise can be easily distinguished.

In the second aspect of the present invention, as described above, the partial discharge is performed based on the time difference between the ultrasonic pulse detected by the first detecting section and the electric pulse detected by the second detecting means. In the partial discharge measuring method for locating the generation location, a frequency band having a high S / N ratio is selected in a frequency band of 1.6 MHz or more and 50 MHz or less, and when partial discharge occurs, an electric pulse of the selected frequency band is selected. Regarding, regarding the time difference between the ultrasonic pulse and the electric pulse, the position where the partial discharge is generated is determined based on the calculated time difference, so the measurement sensitivity of the electric pulse is improved, and the time difference between the ultrasonic pulse and the electric pulse is improved. Can be obtained with high accuracy, and the location accuracy of the location where the partial discharge occurs can be improved.

According to a third aspect of the present invention, in the first or second aspect of the invention, the calibration is performed by injecting an electrical pulse for calibration from the low potential side into the intermediate connection portion or the termination connection portion of the power cable. A pulse injection means is installed, a calibration pulse is injected from the calibration pulse injection means, and a frequency band having a high S / N ratio is selected in a frequency band of at least 1.6 MHz and 50 MHz or less. The sensitivity can be improved. Also,
Since the electric pulse for calibration is injected from the low potential side,
The calibration pulse can be injected without causing a power failure, and the calibration pulse can be injected at a place distant from the cable end portion.

According to a fourth aspect of the present invention, in the third aspect of the invention, the charge amount of the measurement electric pulse is calibrated by the calibration pulse injected from the low potential side. It is possible to obtain the same effect as the above, and it is possible to accurately estimate the partial discharge charge amount. According to the invention of claim 5 of the present invention,
In the inventions of claims 2 and 3 or 4, the ultrasonic pulse signal and the electric pulse signal are both measured and the averaging process is performed a plurality of times, so that the partial discharge and the noise can be reliably identified. At the same time, the position where the partial discharge occurs can be accurately estimated.

[0023]

FIG. 1 is a diagram showing the system configuration of an embodiment of the present invention. In the figure, 1 is a power cable, 2 is an intermediate connection part of the power cable 1, and 3 is a calibration pulse generating means for injecting a calibration pulse from the low potential side of the intermediate connection part. As described above, the pulse attaches the foil electrodes to both sides of the high-frequency impedance connected between the sheaths in the prefabricated type connection portion, or, in the insulation connection portion, to both sides of the insulation portion of the insulation connection portion. It can be attached and a calibration pulse generator can be connected to the foil electrode to inject from the low potential side of the sheath side (a prefabricated type connection will be described in the embodiment shown in FIG. 2).

Reference numeral 4 denotes an AE sensor. The AE sensor 4 is embedded in the intermediate connection portion 2 or attached to the outside of the intermediate connection portion and detects an ultrasonic pulse generated due to partial discharge. Reference numeral 5 is a partial discharge pulse detector for detecting an electric pulse generated by partial discharge. The partial discharge pulse is detected by connecting a high frequency impedance between the sheaths in the prefabricated type connection portion, as will be described later. Alternatively, in the insulated connection portion, a method of attaching and detecting a foil electrode on both sides of the insulated connection portion sandwiching the insulating portion can be used.

Reference numeral 6 is a preamplifier for amplifying the output of the AE sensor 4, 7 is a main amplifier for amplifying the output of the preamplifier 6, 8 is a signal processing section, and the signal processing section 8 is detected by the partial discharge pulse detector 5. The high-frequency electric pulse is filtered and frequency-converted to facilitate output to the oscilloscope, and the processed electric pulse is output to the oscilloscope 9 together with the detected ultrasonic pulse. Reference numeral 9 is an oscilloscope for observing the waveforms of the electric pulse and the ultrasonic pulse processed by the signal processing unit.

FIG. 2 is a view showing a mounting structure of the AE sensor, the partial discharge pulse detector, and the calibration pulse generator when the system shown in FIG. 1 is applied to a prefabricated intermediate connection portion. Indicates a 154 kV class prefabricated connection. In the figure, 1 is a power cable such as a CV cable, 11 is a cable conductor, and 12 is a cable 1.
Main shielding layer, 2 is a prefabricated intermediate connecting portion, 21 is a conductor connecting tube, 22 is an electric field relaxation electrode for controlling the electric field distribution, 23 is an epoxy resin insulator, 24 is a premold insulator, and 25 is a premold. Insulator push fitting, 26
Is a compressing device, and the compressing device 26 pushes the premolded insulator 24 toward the epoxy resin insulator 23 through the premolded insulator pressing metal fitting 25, and the interface between the epoxy resin insulator 23 and the premolded insulator 24. , And the insulation resistance property of the interface between the insulator surface of the cable 1 and the premolded insulator 24.

Further, 27 is a protective copper tube, 28 is a shielding tape, 29 is a flange, and the AE sensor 4 is embedded in the flange 29 as shown in FIG. The measurement frequency range of the AE sensor 4 is 20 Hz to 100 KHz, and although the AE sensor 4 is embedded in the inside of the connection portion in this embodiment, the sensitivity is somewhat lowered, but the AE sensor 4 contacts the outside of the connection portion as necessary. You can also attach it.

Reference numeral 51 is a high frequency impedance, and the high frequency impedance 51 is connected between the protective conduit 27, which is the main shielding layer of the connecting portion, and the shielding layer 12 of the CV cable 1. Then, when the partial discharge occurs, the electric pulse propagating through the main shielding layer 12 of the cable 1 is taken out from both ends of the high frequency impedance 51 and given to the detection impedance 53 via the insulating connector 52.
Reference numeral 54 is a bandpass filter, which filters the detected electric pulse pulses.

Reference numeral 3 is a calibration pulse generator, and the calibration pulse generated from the calibration pulse generator 3 is placed on the anticorrosion layer of the protective copper tube 27 and the anticorrosion layer of the cable 1 so as to electrically sandwich the high frequency impedance 51. It is injected from the attached foil electrode 31. In this example, an aluminum foil was used as the detection foil electrode, and its size was such that the capacitance with the sheath was about 500 pC.

For details of the structure of the prefabricated type connecting portion and the structure of the partial discharge pulse detecting portion, see, for example, Japanese Patent Application No. 4-71217. For details of the type and mounting position of the AE sensor, see, for example, the Institute of Electrical Engineers of Japan B, October 1992, pp. 897-904, "A.
See Partial Discharge Detection of Prefabricated Junction Box for CV Cable by E-Sensor.

In FIG. 1 and FIG. 2, in order to measure the partial discharge, the calibration pulse generator 3 previously measures 1.6 MHz to 5 MHz.
The partial discharge pulse detector 5 (51, 52, 53 in FIG. 2) by injecting the calibration pulse in the frequency band of 0 MHz
The electric pulse detected by the oscilloscope 9 is observed. Then, a frequency band having a high S / N ratio is selected in the frequency band, and the frequency band of the bandpass filter of the signal processing unit 8 is set to the band having a high S / N ratio.
In this embodiment, the frequency band is set to the band from 29 MHz to 31 MHz.

When a partial discharge is generated in the power cable 1 or an intermediate connection portion thereof, a high frequency electric pulse and an ultrasonic pulse are generated by the partial discharge, and the high frequency electric pulse and the ultrasonic pulse propagate through the power cable 1. , The partial discharge pulse detector 5 and the AE sensor 4 provided in the intermediate connection portion 2
(34 in FIG. 2) is reached. In the present embodiment, the high-frequency electric pulse detected as described above is applied to the signal processing unit 8
In the above, it was filtered by a band pass filter of 29 MHz to 31 MHz and amplified by an amplifier of 40 dBm. Then, the amplified high frequency electric pulse is
Furthermore, in order to make it easier to output to the oscilloscope 9, 20
The frequency was converted to kHz and output to the oscilloscope 9 together with the ultrasonic pulse detected by the AE sensor 4. Further, the pulses detected as described above were averaged every 10 times, and the partial discharge was identified and the generation position was estimated based on the result of the averaging process.

FIG. 3 is a diagram showing the observed waveforms of the ultrasonic pulse detected by the AE sensor 4 and the electrical pulse detected by the partial discharge pulse detector 5 when the partial discharge occurs. In FIG. 3, the horizontal axis represents time. Is shown. Since there is a difference between the propagation speed of the electric pulse and the propagation speed of the ultrasonic pulse,
As shown in the figure, when a partial discharge occurs, an electric pulse is first observed in the intermediate connection portion 2, and an ultrasonic pulse is observed after a predetermined time Δt corresponding to the partial discharge occurrence position.

Therefore, a predetermined time Δt has passed after the electric pulse having a level higher than the trigger position shown in FIG.
When the ultrasonic pulse is detected within the range, it can be identified that the partial discharge has occurred, as described above.
Further, the partial discharge occurrence point can be estimated based on the time from the observation of the electric pulse to the observation of the ultrasonic pulse and the propagation time difference between the electric pulse and the ultrasonic pulse.

As a result of measuring the partial discharge as described above, the measurement sensitivity is several hundreds p
From C to 20pC, and in the laboratory, the conventional 20pC
To 5 pC, and the probability of failing to locate the partial discharge generation position also decreased. In the above embodiment, an example in which the present invention is applied to the prefabricated intermediate connecting portion has been shown, but the present invention is not limited to the above-mentioned prefabricated intermediate connecting portion, but the sensitivity is slightly lowered, but other intermediate connecting portions are used. It is also possible to apply to parts and terminal connection parts.

[0036]

As described above, according to the present invention, in the partial discharge measuring method using the partial discharge measurement by the AE sensor and the electric partial discharge measurement together, 1.6 MH
In the frequency band from z to 50 MHz, a frequency band with a high S / N ratio is selected and the electric pulse in the selected frequency band is measured. Therefore, the measurement sensitivity of the electric pulse is not affected by noise. Therefore, it is possible to accurately distinguish between partial discharge and noise, estimate a partial discharge occurrence location, and the like.

Therefore, by incorporating the present invention into a test conducted at the initial stage of track construction or a continuous monitoring system, an abnormality can be detected before dielectric breakdown occurs, and in particular, a prefabricated type connecting portion assembled and assembled on site. When applied to, it becomes possible to detect the abnormality with high sensitivity. In addition, a calibration pulse injection means for injecting a calibration electric pulse from the low potential side is installed at the intermediate connection portion or the termination connection portion of the power cable, and the calibration pulse is injected to S / N.
By selecting a frequency band with a high ratio, it is possible to improve the measurement sensitivity of electric pulses, and it is possible to calibrate the partial discharge charge amount, so that the calibration pulse can be injected without a power failure. It is possible to inject the calibration pulse at a place distant from the part.

Further, by measuring both the ultrasonic pulse signal and the electric pulse signal and performing the averaging process a plurality of times, the partial discharge and the noise can be discriminated and the position where the partial discharge is generated can be more accurately estimated. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment in which the present invention is applied to a prefabricated type connecting portion.

FIG. 3 is a diagram showing observed waveforms of ultrasonic pulses and electric pulses.

[Explanation of symbols]

 1 Power Cable 2 Intermediate Connection Section 3 Calibration Pulse Generator 4 AE Sensor 5 Partial Discharge Pulse Detector 6 Preamplifier 7 Main Amplifier 8 Signal Processing Section 9 Oscilloscope 11 Cable Conductor 12 Main Shield Layer 21 Conductor Connection Tube 22 Electric Field Mitigating Electrode 23 Epoxy Resin Insulator 24 Pre-mold Insulator 25 Pre-mold Insulator Clamp 26 Compressor 27 Protective Copper Tube 28 Shield Tape 29 Flange 31 Foil Electrode 51 High Frequency Impedance 52 Insulation Connector 53 Detection Impedance 54 Bandpass Filter

Claims (5)

[Claims] 1. A first detecting means for detecting an ultrasonic pulse generated by the occurrence of partial discharge, and a second detecting means for detecting an electric pulse generated by the occurrence of partial discharge at an intermediate connection portion or a terminal connection portion of a power cable. A partial discharge measuring method for identifying a partial discharge signal and noise by comparing the ultrasonic pulse detected by the first detecting unit with the electric pulse detected by the second detecting unit by providing a detecting unit. In the frequency band of 1.6 MHz or more and 50 MHz or less, a frequency band having a high S / N ratio is selected, and when partial discharge occurs, an ultrasonic pulse and an electric pulse are selected for the electric pulse of the selected frequency band. A method for measuring partial discharge of a power cable and its connection, characterized by comparing and comparing partial discharge and noise based on the comparison result. 2. A first detecting means for detecting an ultrasonic pulse generated by the occurrence of partial discharge, and a second detecting means for detecting an electric pulse generated by the occurrence of partial discharge at an intermediate connection portion or a terminal connection portion of the power cable. In the partial discharge measuring method, which is provided with a detecting means, and which locates a partial discharge occurrence location based on a time difference between the ultrasonic pulse detected by the first detecting portion and the electric pulse detected by the second detecting means, When a frequency band with a high S / N ratio is selected in the frequency band of 6 MHz or more and 50 MHz or less and the partial discharge occurs, the time difference between the ultrasonic pulse and the electric pulse is calculated for the electric pulse of the selected frequency band. A method for measuring partial discharge of a power cable and its connection, characterized by locating a partial discharge occurrence position based on the obtained time difference. 3. A calibration pulse injecting means for injecting a calibration electric pulse from the low potential side is installed at an intermediate connection portion or a termination connection portion of the power cable, and a calibration pulse is injected from the calibration pulse injection means, 3. The method for measuring partial discharge of a power cable according to claim 1 or 2, wherein a frequency band having a high S / N ratio is selected in a frequency band of at least 1.6 MHz and 50 MHz or less. 4. The method for measuring partial discharge of a power cable and its connecting portion according to claim 3, wherein the charge amount of the measurement electric pulse is calibrated by the calibration pulse injected from the low potential side. 5. The partial discharge measurement is performed by measuring both the ultrasonic pulse signal and the electric pulse signal, averaging the measured values a plurality of times, and performing partial discharge measurement. Method for measuring partial discharge of power cables and their connections.