JPH01277775A - Detecting method of partial discharge - Google Patents

Abstract

PURPOSE:To detect the spot of occurrence of a partial discharge and the degree thereof with high sensitivity, by detecting a frequency component of 100KHz or below the attenuation of which is the least in a sound generated by the partial discharge occurring in an insulator. CONSTITUTION:When a partial discharge occurs in a defective part 5 of an insulator 6, a sound wave generated thereby is collected by a horn 10 while it is attenuated by the insulator 6. The amount of the attenuated frequency component of 100KHz or below in the sound wave is the least. Accordingly, a sound wave detector 12 detects mainly this frequency component of the least attenuation with high sensitivity and outputs a detection signal. The detection signal of a high level is amplified by a preamplifier 13, and after signal components other than the ones of 5-10KHz and a noise signal are removed by a filter 14, said signal is amplified by an amplifier 15 and supplied to a signal processing circuit 16. Therefore, the spot of occurrence of the partial discharge and the degree thereof are detected with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for detecting partial discharge occurring at a connection portion of a power cable or the like.

(Technical background of the invention and its problems) When electrical defects such as voids exist inside an insulator,
When a high voltage is applied to an insulator, the electric field concentrates on the defective part and a partial discharge occurs.

For example, if there is a defect in the insulator of a power cable or its connection to which high voltage is applied, partial discharge will occur at the defective part, deteriorating the insulator, and in the worst case, causing dielectric breakdown. . In order to prevent this, a method is known in which partial discharge occurring in the cable insulator is acoustically detected in advance, and this method is usually referred to as an acoustic emission method.

Now, when a partial discharge occurs in a defective part of a cable insulator, the accompanying discharge sound propagates through the cable insulator as a sound wave. Therefore, conventionally, a sound wave detector is brought into contact with the outer periphery of the cable or the outer periphery of the connection part thereof, and the propagating sound waves are received to detect the location and extent of partial discharge occurrence.

That is, FIG. 3 is a cross-sectional view showing a conventional partial discharge detection method, in which a horn 1 is pressed against the circumferential surface of a cable connection part 4, and a sonic detector 2 such as PZT is attached to the horn 1. . Therefore, when a partial discharge occurs due to a defect 5 inside the insulator 6, a sound wave is generated at this defect, the sound wave propagates through the insulator 6, and is collected by the horn 1, so that the sound wave detected by the sound wave detector 2 By detecting this, it is possible to detect the location and extent of partial discharge occurrence.

Incidentally, the attenuation coefficient α of a sound wave can be expressed as shown in the following equation.

α=Af+Bf2+Cf' where f: frequency of sound wave, A, B, C: constants As is clear from the above equation, it can be seen that high frequency sound waves have a large amount of attenuation.

On the other hand, the insulators that make up the power cables and their connections are mainly made of high-polymer plastic or rubber materials, but these materials have large attenuation coefficients; for example, the attenuation coefficient of 2 MHz sound waves ~100dB/m is also attenuated. For this reason, the sound waves generated by the partial discharge are significantly attenuated by the insulator 6, so the sound wave detector 2 can only obtain a weak detection signal, which may result in a significant reduction in measurement sensitivity. was there.

(Objective of the Invention) An object of the present invention is to provide a partial discharge detection method that can detect sound waves generated by partial discharge with high sensitivity.

(Summary of the Invention) The present invention provides an insulator made of a polymer material with a
It was developed by focusing on the fact that the amount of attenuation of sound waves at frequencies below KHz is relatively small.It detects the frequency components below 100KH2, which have relatively little attenuation, in the sound waves generated by partial discharge, and detects the frequency components with high output levels. It is characterized by obtaining a detection signal.

(Embodiments of the Invention) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the equipment configuration used in the detection method of the present invention, and 10 is a horn. The tip of this horn 10 is pressed against the circumferential surface of the cable connection part 4. A sound wave detector 12 is attached to the upper end of the horn 10. As the sound wave detector 12, a piezoelectric element is used which has particularly excellent response characteristics to sound waves of 5 to 10 KHz. A preamplifier 13 is connected to the sound wave detector 12, and a filter 14 is connected to the output side of the preamplifier 13. The filter 14 has a bandpass filter configuration that passes band signals of 5 to 1 kHz. An amplifier 15 is connected to the output side of the filter 14, and a signal processing circuit 16 is connected to the output side of the amplifier 15.

By the way, when we detected the sound waves generated when partial discharge occurs in an insulator using PZT and amplified the output level of PZT, we investigated the relationship between the output level and the frequency band, and obtained the results shown in Figure 2. It was done. That is, the output level reached its peak when the frequency was IKHz. Also, the frequency is 2
The next highest output level was obtained in the range of KHz to 4KH2, and the output level gradually decreased in the range of 5KH2 to 100KH2. At frequencies above 82 in 100, the output level became extremely low.

From the above, the sound wave generated by partial discharge is 100KH.
The frequency components of , are significantly attenuated by the insulator, and the
It can be seen that the amount of attenuation of frequency components below H2 is relatively small. Therefore, when detecting frequency components of 100KH2 or less in sound waves, a detection signal with a high level can be obtained.

Note that if the frequency component of IKH is detected, the detection signal with the highest level will be obtained, but in this case it will be difficult to distinguish it from external noise such as voice, so from the relationship with the S/N ratio, Most preferably, frequency components of ~10 KHz are detected.

Now, in FIG. 1, when partial discharge occurs at the defective portion 5 of the insulator 6, the resulting sound waves are attenuated by the insulator 6 and collected by the horn 10. In this case, as described above, the frequency components of 100 KH2 or less in the sound wave have the least amount of attenuation. Therefore, the sound wave detector 12 mainly receives the frequency component with the least amount of attenuation with high sensitivity and outputs a detection signal, so the detection signal with a high level is amplified by the preamplifier 13 and sent to the filter 14. After signal components other than 10 KHz and noise signals are removed, the signal is amplified by an amplifier 15 and supplied to a signal processing circuit 16. Therefore, the location where partial discharge occurs and its degree can be detected with high sensitivity.

(Effects of the Invention) According to the present invention, the frequency component of the least attenuated frequency component of l OOK Hz or less in the sound wave generated by the partial discharge generated in the insulator made of the polymeric material of the object to be inspected is detected. , the location and extent of partial discharge can be detected with high sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the equipment configuration used in the method of the present invention;
The figure is a characteristic diagram showing the output level in relation to the frequency band when a sound wave generated by partial discharge is detected, and FIG. 3 is a cross-sectional view showing a conventional detection method. 10-------Horn, 12-----Sound wave detector, 14-----Filter, 16-------- Signal processing circuit. Fig. 3 10 ---------- Horn + 2 - Old wave detector + 4 ------- Filter + 6 ---------- - Signal processing circuit frequency A band □

Claims (1)

[Claims] A partial discharge detection method for detecting a sound wave generated by a partial discharge generated in the insulator in an object to be inspected including an insulator made of a polymeric material, the method comprising:
A partial discharge detection method characterized by detecting only the following frequency components.