JPH05164811A - Measurement of partial discharge - Google Patents

Abstract

PURPOSE:To provide partial discharge measurement by which a pre-discharge breaking test is performed surely by carrying out inter-slit processing easily and detecting partial discharge generated in the slit of a power cable. CONSTITUTION:A slit is made in a shielding layer 14 of a power cable 10 and a piezoelectric element film 16 is installed in the slit in the case of a partial discharge measurement in a pre-discharge breaking test for locating partial discharge. When partial discharge is generated in the power cable 10, the piezoelectric element film 16 detects sound waves generated from partial discharge for conversing them into an electric signal. Installation of the piezoelectric element film 16 in the slit 15 makes it possible to detect generation of partial discharge in the slit 15 and perform the power cable test surely without failing the pre-discharge breaking test due to dielectric breakdown of the slit 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring partial discharge in a pre-breaking test conducted for evaluating the performance of a power cable, and in particular, dielectric breakdown at a slit portion provided in the power cable for the pre-breaking test. The present invention relates to a partial discharge measuring method capable of reliably performing a pre-breaking test by preventing the above.

[0002]

2. Description of the Related Art Conventionally, in order to confirm the performance of a power cable that has been used and removed during the development of the power cable or for a long period of time, a commercial frequency AC voltage is applied to the power cable to remove power. A pre-breaking test is performed to detect a partial discharge and stop the voltage applying device before the cable causes insulation breakdown. In particular, the extraction of defective parts before dielectric breakdown is a very important test for understanding the characteristics of power cables.

Positioning at the time of the conventional pre-interruption test has been performed as shown in FIG. In the figure, 100 is a power cable, 101 is a conductor, 102 is a shield layer, and 103.
Is an external conductive layer, 103 'is an insulator, 104 is a slit provided in the shield layer, and 105 is a commercial frequency AC power supply for testing. In FIG. 4, when the test of the power cable 100 is performed, slits are provided at both ends of the power cable 100 and the shield layer in the central portion, and the detectors 106, By connecting 107, the difference between the partial discharge charge amounts captured by the detectors 106 and 107 is obtained. Then, the position of the partial discharge is repeatedly determined while determining which side the larger partial discharge has occurred, and finally the position of the part where the partial discharge is generated is determined within about 4 cm.

By the way, in the above test, the slit 1
When a partial discharge occurs in 04, the partial discharge generated between the slits causes no difference in the partial discharge charge amount in the detectors provided at both ends A and B of the slit. Therefore, the slit 10
There was a very high probability that the occurrence of partial discharge could not be detected in No. 4, and dielectric breakdown was caused at the slit part, thus failing the precursor interruption test.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned drawbacks of the prior art. It is possible to easily perform slit-to-slit treatment, and moreover, the slits of the power cable are generated. It is an object of the present invention to provide a partial discharge measuring method capable of surely completing a precursor interruption test by making it possible to detect partial discharge.

[0006]

In order to solve the above problems, the present invention provides a slit in the shielding layer 14 of the power cable 10 and obtains the difference in the partial discharge charge amount at both ends of the slit to determine the position of the partial discharge. In the partial discharge measuring method in the pre-breaking test for performing the orientation, the piezoelectric element film 16 is attached between the slits. Then, the partial discharge generated between the slits is detected by detecting the vibration wave generated when the partial discharge is generated by the piezoelectric element film 16.

[0007]

When a partial discharge is generated in the power cable 10, a sound wave is generated due to the void or the rapid expansion of the gas in the electric tree tube. The piezoelectric element film 16 detects a sound wave generated by the partial discharge and converts it into an electric signal. Since the piezoelectric element film 16 is provided in the slit portion 15, it is possible to detect that partial discharge has occurred in the slit portion 15, and the slit portion 15 may cause dielectric breakdown and fail the precursor interruption test. Without, the power cable can be reliably tested.

[0008]

FIG. 1 is a diagram showing an embodiment of the present invention. In FIG. 1, FIG. 1A is an external view of a power cable that has been slit according to the present invention, and FIG. 1B is a sectional view of the slit portion 14 in FIG. In FIGS. 1A and 1B, 10 is a power cable such as a cross-linked polyethylene cable, 11 is a conductor, 12 is an insulator, 13 is an outer conductive layer, 14 is a shield layer, 15 is a slit portion, and 16 is piezoelectric. Polyvinylidene chloride resin film (hereinafter PV
(Abbreviated as DF film), 17 is a polyethylene film, 18 is an insulating tape, and 19 is a measurement lead wire.

In FIG. 1B, the shield layer 14 is provided with slits of 1 cm to 1.5 cm.
A thickness of 10 μm and a width of 1.
An insulating polyethylene film 17 of 5 cm to 2.0 cm is wrapped around one layer, and a thickness of 10 μm is formed on the insulating polyethylene film 17.
PVDF film 16 with piezoelectric characteristics of nickel vapor-deposited on both sides of 1 to 100 cm in width and 1 cm to 1.5 cm in width
(Nickel deposition thickness of about 0.5 μm) is further wound. Then, a lead wire 19 is attached to the PVDF film 16 and is fixed with an insulating tape 18. Since the PVDF film is thin and has excellent flexibility, the power cable can be easily and easily wound in the circumferential direction. Further, the insulating polyethylene film 17 is formed on the outer conductive layer 13 and PVDF.
It is for insulating the film 16.

FIG. 2 is a diagram showing a system configuration for detecting a partial discharge between the slits in the power cable subjected to the slit-to-slit process as described above. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals, 21 is a terminal to which a commercial frequency AC voltage for testing is connected, 31 is a preamplifier, 32 is a main amplifier, and 33 is a digital memory. , 34 is a data processing device, 35 is an oscilloscope, and 36 is a printer. In the figure, a preamplifier 31 and a main amplifier 32 are PVDs having piezoelectric characteristics.
The digital memory 33 is means for amplifying the output of the F film 16, and the digital memory 33 is means for storing the output waveform of the main amplifier 32. The data processor 34 is a digital memory 3
3 is a means for taking out the partial discharge signal by averaging the output waveform stored in 3 to remove the noise signal, and the processing result is printed out by the printer 36. The output waveform stored in the digital memory 33 is observed by the oscilloscope 35.

Next, a method of detecting partial discharge between the slits 15 in this embodiment will be described with reference to FIGS. 1 and 2. In FIG. 2, when a commercial frequency AC voltage for testing is applied from the terminal 21, when a partial discharge occurs due to a void and an electrical tree between the slits 15, a void due to the partial discharge and a rapid expansion of gas in the electrical tree tube occur. ,
Sound waves are generated. PVDF film 16 with piezoelectric properties
Detects the sound wave and converts it into an electric signal. This electric signal is amplified by the preamplifier 31 and the main amplifier 32 and stored in the digital memory 33.

FIG. 3A is a diagram showing a waveform of a signal detected by the PVDF film 16 and stored in the digital memory 33 when a partial discharge occurs between the slits 15. As shown in the figure, the signal stored in the digital memory 33 contains random noise, and the data processing device 34 synchronously adds the signal containing the random noise a plurality of times (averaging process), -Remove noise. FIG. 3B is a diagram showing a signal waveform after the averaging process is performed by the data processing device 34,
As shown in the figure, the random noise is removed, and the vibration waveform generated by the sound wave generated by the partial discharge is detected. The waveform of the signal stored in the digital memory 33 can be observed by the oscilloscope 35.

In the above embodiments, the PVDF film is used as the piezoelectric element. However, the piezoelectric element in the present invention is not limited to the PVDF film and has a small thickness and excellent flexibility. Any other element can be used. Further, in the above embodiment, as the means for measuring partial discharge, an example using a digital memory, a data processing device and an oscilloscope was shown, but the measurement means of the present invention is not limited to the above embodiment, For example, various other means such as removing random noise with an analog filter can be used.

[0014]

As is apparent from the above description, in the present invention, the piezoelectric element is attached between the slits provided in the power cable so that the partial discharge generated between the slits can be detected. Partial discharge generated between slits can be detected and insulation breakdown between slits can be prevented.
In addition, it is possible to reliably investigate the cause of destruction of the removed cable that has been actually used for many years.

[Brief description of drawings]

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

FIG. 2 is a system configuration diagram for detecting partial discharge between slits.

FIG. 3 is a diagram showing detected signal waveforms.

FIG. 4 is a diagram showing a conventional example.

[Explanation of symbols]

10 power cable 11 conductor 12 insulator 13 outer conductive layer 14 shield layer 15 slit part 16 polyvinylidene chloride resin film (PVDF
17) Polyethylene film 18 Insulating tape 19 Measurement lead wire 31 Preamplifier 32 Main amplifier 33 Digital memory 34 Data processing device 35 Oscilloscope

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Muto 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A partial discharge measurement in a pre-interruption test for locating a partial discharge by providing a slit in the shielding layer (14) of the power cable (10) and determining the difference in the partial discharge charge amount at both ends of the slit. In the method, the piezoelectric element film (16) is attached between the slits, and the partial discharge generated between the slits is detected by detecting the vibration wave generated when the partial discharge is generated by the piezoelectric element film (16). Characteristic partial discharge measurement method.