JPH04194762A - Device for monitoring partial discharge of electric apparatus - Google Patents

Abstract

PURPOSE:To prevent an accident of insulation deterioration of an electric apparatus by providing an acoustic emission (AE) sensor detecting an acoustic wave signal generated by partial discharge a means of discriminating the presence or absence of occurrence of partial discharge. CONSTITUTION:An acoustic wave signal detected by an AE sensor 2 is inputted to one input terminal of a discriminator 10 through a signal processing circuit constructed of BPF 4, an amplifier 5 and an A/D converter 6. Besides, a current signal detected by a converter 3 is inputted to the other input terminal of the discriminator 10 through a signal processing circuit constructed of HPF 7, an amplifier 8 and an A/D converter 9. By comparing the detection signals from the sensor 2 and the converter 3 with each other by the discriminator 10, a weak partial discharge in the preceding stage resulting in insulation deterioration which occurs in a switch gear and others can be detected with high precision. By issuing an alarm when the partial discharge is detected, accordingly, an accident of the insulation deterioration of an electric apparatus can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Field of Industrial Application) The present invention relates to a partial discharge monitoring device for electrical equipment such as a switchgear, and particularly for monitoring weak partial discharges in the stage before insulation deterioration. The present invention relates to a partial discharge monitoring device for electrical equipment that easily and reliably detects partial discharge.

(Prior Art) Generally, a switchgear insulates a main circuit charging part through an insulating material or an insulating medium to stably supply electric power and perform opening/closing. A circuit breaker, a disconnector, a tombstone, a bus bar, a cable head, a connecting conductor, and the like are housed inside the switchgear.

In electrical equipment such as switchgears, electrical deterioration tends to occur in insulators due to contamination of foreign matter, poor connection of live parts of the main circuit, high humidity, or thermal stress. If this occurs, a weak partial discharge will occur. If this partial discharge continues for a long time, it will progress to full-scale insulation breakdown, leading to insulation failures in electrical equipment.
For example, this could lead to a power outage.

In contrast, there is a conventional monitoring device that monitors partial discharge and detects its occurrence at an early point in the daytime. ■A method in which the light emitted during partial discharge is detected using a photomultiplier tube; ■A ferrite inserted into the ground wire that generates high-frequency pulses due to partial discharge that are superimposed on the applied commercial frequency current flowing through the ground wire. An electromagnetic coupling method in which detection is performed using a core and a coil wound around the core, ■ A method of applying a pulse voltage to the main circuit and checking the response as disclosed in Japanese Patent Application Laid-Open No. 2-79750, ■
As disclosed in Japanese Patent Publication No. 63-49845, there is a method that detects electromagnetic waves associated with partial discharge or minute discharge, and a method that detects the acoustic emission (hereinafter referred to as AE) itself due to zero partial discharge using an AE sensor. There is a method to do this.

Furthermore, in order to increase the accuracy of detecting the presence or absence of partial discharge,
There is also a method in which two of the above methods are used together, and the detection results of both methods are logically ANDed.

(Problems to be Solved by the Invention) Although any of the conventional monitoring devices described above (■ to ■) can detect a large partial discharge immediately before dielectric breakdown, it is possible to detect a large partial discharge immediately before dielectric breakdown occurs. It is difficult to separate signals caused by the weak partial discharge that has begun to occur from noise, etc., and it is extremely difficult to reliably determine whether a weak partial discharge has occurred. Furthermore, even if an attempt is made to create a logical product using two types of detection means, the discrimination accuracy is low as described above because the signals of each type are processed independently, so it is difficult to significantly improve the discrimination accuracy. Met. For this reason, there has been a problem in that it is difficult to prevent insulation deterioration of electrical equipment.

Therefore, the present invention provides a partial discharge monitoring device for electrical equipment that can reliably detect weak partial discharges before insulation deterioration, thereby preventing insulation deterioration accidents in electrical equipment. The purpose is to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the invention corresponding to claim 1 is attached to an electrical device for monitoring partial discharge,
an acoustic emissive sensor that detects a sound wave signal due to a partial discharge generated in the electrical equipment, a current sensor that detects a current flowing through a grounding wire of the electrical equipment, and signals based on the sensor and the current sensor, respectively; The time delay between these two signals is measured during one cycle,
The device is equipped with a discrimination means that compares the continuity of time delays in at least two cycles or more to determine whether or not a partial discharge has occurred.

The invention corresponding to claim 2 includes: a first acoustic emission sensor that is attached to an electrical device whose partial discharge is to be monitored and detects a sound wave signal due to partial discharge generated in the electrical device; and a vibration system that is the same as that of the electrical device. a second acoustic emission sensor that is attached to a structure that is not affected by sound waves caused by partial discharge of electrical equipment and detects sound wave signals caused by vibrations generated in the structure;
The apparatus is equipped with a comparison means for inputting the sensor and a detection signal from the sensor, comparing the two detection signals, and determining from the result whether or not partial discharge has occurred in the electrical equipment.

(Operation) According to the invention corresponding to claim 1, the following operation is achieved. Random external noise and signals due to partial discharge are always superimposed on the AE sensor and current sensor attached to electrical equipment that is to monitor partial discharge. here,
A signal due to partial discharge always occurs at a fixed phase within one voltage cycle.

On the other hand, with respect to external noise, although the phase of ignition noise of a thyristor or the like is determined by the ground wire, the detection output of the AE sensor is a sound wave signal, and the phase is not determined. For this reason,
Compare the phases of the detection signals of the AE sensor and current sensor,
If the signals with the same phase are continuous over several cycles, it can be determined that it is a partial discharge. Therefore, it is possible to prevent insulation deterioration accidents in electrical equipment based on this detection result.

According to the invention corresponding to claim 2, the first AE sensor detects a sound wave signal caused by a partial discharge generated in an electrical device, but this includes external noise caused by mechanical vibration that has entered the electrical device from the outside. It is included. In order to separate partial discharge and external noise, a second AE sensor is attached to a structure that is not affected by sound waves caused by partial discharge, and this sensor outputs a signal that detects only external noise without including acoustic waves. By determining the difference between the output signal of the first AE sensor, that is, a signal containing partial discharge and noise, and reducing noise having the same vibration frequency, partial discharge occurring in the electrical equipment can be reliably detected. , accidents caused by deterioration of insulators can be prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the present invention. An AE sensor 2 for detecting a sound wave signal due to partial discharge is attached to a metal box 1 of an electrical device whose partial discharge is to be monitored, such as a switchgear, and a current sensor, e.g., is attached to the ground wire of the box 1. A current transformer 3 with a coil wound around a ferrite core is installed.

Here, the sound wave signal detected by the AE sensor 2 is passed through a band pass filter 4 (BPF) and an amplifier 5 (AMP).
The signal is input to one input terminal of the discriminator 10 via a signal processing circuit consisting of an analog-to-digital converter 6 (A/D). Although the frequency of partial discharge itself is as high as several 10 M) lz, when it propagates as a sound wave, it becomes several tens of kHz in gases such as air and SF6 gas, which are the insulating media of switchgear, so BPF4 detects components of several tens of kHz. It is allowed to pass.

Further, the current signal detected by the current transformer 3 is sent to the discriminator 10 via a signal processing circuit consisting of a bypass filter 7 (HPF), an amplifier 8 (AMP), and an analog-digital converter 9 (A/D). It is configured to be input to the other input terminal. Since the partial discharge current signal directly flows through the grounding wire, it becomes a signal of several tens of MHz. Since such high frequency signals are detected by a ferrite core with good frequency characteristics, BPF7 is a filter that passes components of several tens of MHz or more. be.

FIG. 2(a) shows the information detected by the AE sensor 2, for example, the number 1
A waveform diagram of a 0 MHz sound wave signal is shown, and Fig. 2 (b
) shows a waveform diagram of a current signal of several tens of MHz, for example, detected by the current transformer 3.

Here, the current signal from the current transformer 3 corresponds to the current of partial discharge, and only the first wave is formed, but due to the reactance and stray capacitance comprised in the measurement system, it has a fast decay characteristic. This becomes a signal that causes vibration.

The signals detected by the AE sensor 1 and the current transformer 3 are input to the discriminator 10 via the signal processing circuits as described above, where the following processing is performed. Figure 3(a)
is an example of a signal from the AE sensor 2, and FIG. 3(b) is an example of a signal from the current transformer 3. The dotted line indicates the voltage e, and each signal is converted into a constant voltage or current corresponding to the peak value of the vibration waveform that exceeds the threshold after A/D conversion, and the peak value is formed only for the duration of time. That is, each signal has a time width that exceeds the threshold value, and between the AE sensor 2 and the current transformer 3, the former has a wider signal width in terms of frequency components.

Here, in the current transformer 3, there is almost no time delay in the phase of each signal with respect to the occurrence of partial discharge, but in the AE sensor 2, there is a delay due to the propagation of the speed of sound. The speed of the AE sensor 2 is approximately 350 s/s in the air - approximately 135 s/s in Fe gas.For example, the time from the point where partial discharge occurs in the switchgear to the AE sensor 2 can be determined. In the air, if you are 1.0m away, it will take about 2.8ms.
There will be a delay. From these facts, it is possible to measure the time delay t between the detection signal of the AE sensor 2 and the detection signal of the current transformer 3 in one cycle of voltage e, and check whether there is a signal with the same time delay t in the next cycle. By comparing, it is possible to determine whether a partial discharge has occurred. In other words, the time delay t between the AE sensor signal Sa and the current transformer signal sb is measured, and if the same time delay t occurs in the next cycle, it can be determined that this is due to the occurrence of partial discharge. Note that a signal whose time delay t is not in the next cycle is a random signal and therefore becomes noise Sn. In this way, partial discharge can be determined by performing at least two or more cycles of measurement. The accuracy of partial discharge detection can be further improved by increasing the number of measurement cycles depending on the storage capacity of the measuring device.

Here, the time delay t changes because the location where the partial discharge occurs is not constant.
At 50Hz, a partial discharge signal occurs within 2(]+s).

As described above, according to the partial discharge monitoring device for electrical equipment of the first embodiment, by comparing the detection signals from the AE sensor 2 and the current transformer 3 with the discriminator 10, it is possible to detect the It is possible to accurately detect weak partial discharges before insulation deterioration. Therefore, by configuring the system to issue a warning such as an alarm when partial discharge is detected, it is possible to prevent insulation deterioration accidents in electrical equipment such as switch gears.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a block diagram showing the second embodiment. Reference numeral 11 is a metal box for electrical equipment to be monitored for partial discharge, such as a switch gear. A sensor 12 is attached.

A structure that has the same vibration system as the switchgear and is not affected by the sound waves caused by the partial discharge of the switchgear, for example, the monitoring panel 1.
3 is a structure with the same vibration system as the switch gear 11 installed near the switch gear 11, and an AE sensor 14 for detecting external vibration is attached to the outer wall of the metal box of the monitoring panel 13. When a weak partial discharge occurs in the switchgear due to insulation deterioration, a sound wave (
The acoustic wave is transmitted to the metal box 11, detected by the AE sensor 12, and converted into an electrical signal.

Here, since the switchgear 11 is installed on the floor 15, external vibrations enter through the floor 15 and are detected by the AE sensor 12 like partial discharge. Then, the output of the AE sensor 12 includes sound waves due to partial discharge and noise.

Therefore, if only the noise that enters the switchgear box 11 is detected and processed and removed, only the partial discharge will remain.

However, if another AE sensor is attached to the switchgear box 11, even if an attempt is made to detect only noise, it will be affected by the AE waves due to partial discharge. Noise is detected by the AE sensor 14 attached to the AE sensor 14, and this detection signal is input to the signal processing device 16, which is comprised of various devices as described below. here,
Electrical signals from AE sensors 12 and 14 are input and noise is removed.

The signal processing device [16 is an amplifier 17, a bandpass filter 18
, a computing unit 19. AE sensor 12,1
After the output signal of No. 4 is amplified by an amplifier 17, it is extracted by a bandpass filter 18 as a signal narrowed down to a frequency range having a center frequency optimal for capturing AE waves due to partial discharge.

FIG. 5 shows the AE waveforms in FIGS. 4A, B, and C. The AE waveform of A includes parts due to partial discharge and noise, and it is not clear which part of the AE waveform is due to partial discharge. The AE waveform of B is only noise. These two AE waves are input to the calculator 19,
The waveform of B is subtracted from the waveform of A.

However, the phases of the waveforms of A and B are different because the distance of the AE sensor from the noise source is different, so the phase of the AE wave of B is shifted by a delay circuit, and the phase of the AE wave of A is matched with the phase of the AE wave of A before subtraction. It is carried out.

Next, the output signal of the arithmetic unit 19 is amplified by an amplifier 17, and a low-pass filter 20 removes high frequency noise. By doing this, the AE waveform of FIG. 1C is signal-processed as the AE waveform of C shown in FIG. 5, and the AE wave caused by partial discharge can be accurately captured. Note that 21 is a comparison section.

As described above, according to the partial discharge monitoring device for electrical equipment of the second embodiment, weak partial discharges caused by insulation deterioration occurring in switchgear etc. can be detected without using other sensor methods.
The detection outputs of the E-sensors 12 and 14 can be detected with high precision through relatively simple arithmetic processing, and insulation deterioration accidents of electrical equipment such as switch gears can be prevented.

[Effects of the Invention] According to the present invention described above, it is possible to determine whether or not a partial discharge has occurred in an electrical device to be monitored, and it is possible to reliably detect the occurrence of a weak partial discharge due to insulation deterioration. It is possible to provide a partial discharge monitoring device for electric appliances that can prevent accidents caused by insulation deterioration of the appliance.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the partial discharge monitoring device for electrical equipment of the present invention, FIG. 2 is an example of a signal due to partial discharge from the AE sensor and current transformer in FIG. 1, and FIG. 1 is an explanatory diagram of the operation of FIG. 1, FIG. 4 is a block diagram showing a second embodiment of the partial discharge monitoring device for electrical equipment of the present invention, and FIG.
FIG. 1.11...Electrical equipment such as switchgear, 2...
AE sensor, 3-current transformer, 10... discriminator, 11...
・Switch gear, 12.14...AE sensor, 13.
,. Monitoring panel, 16...signal processing device. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) Attached to electrical equipment to monitor partial discharge,
an acoustic emission sensor that detects a sound wave signal due to a partial discharge generated in the electrical equipment; a current sensor that detects a current flowing through a grounding wire of the electrical equipment; signals based on the sensor and the current sensor are respectively input; Partial discharge monitoring of electrical equipment, comprising a discriminator that measures the time delay of both signals during one cycle and compares the continuity of the time delay over at least two cycles to determine the presence or absence of partial discharge. Device. (2) Attached to electrical equipment to monitor partial discharge,
a first acoustic emission sensor for detecting a sound wave signal due to a partial discharge generated in the electric device; A second acoustic emission sensor detects a sound wave signal caused by vibrations generated in an object, and the detection signals from this sensor and the sensor are input, and the two detection signals are compared. Based on the results, it is possible to detect the occurrence of partial discharge in the electrical equipment. A partial discharge monitoring device for electrical equipment, comprising comparison means for determining presence/absence.