JPH02265129A - Partial discharge supervisory unit of electric equipment - Google Patents

Abstract

PURPOSE:To surely detect a fine partial discharge with AE(Acoustic Emission) wave by inserting a band pass filter having a specific resonance between a sensor and an amplifier. CONSTITUTION:A signal of an SE sensor 11 installed on the external wall of a closed case is inputted in a signal processing circuit by a cable 16. That is, a signal AE wave from the SE sensor 11 is connected to a band pass filter(BPF) 17 with a center frequency of 27kHz; and its output is amplified by a preamplifier(PA) 12, and amplified a main amplifier(MA) 14 through a high pass and a low pass filters(F) 13 as occasion demands, and thereafter, analog-to- digital(A/D) conversion is carried out by an analog-to-digital converter 15. Thereby, it is possible to detect the AE wave of a fine particle discharge to transfer it to a control board or a computer supervise it and also give an alarm, etc., so that an insulation trouble can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a partial discharge monitoring device for monitoring partial discharge due to insulation deterioration in electrical equipment such as a switchgear.

(Prior Art) In general, a switchgear or the like insulates a main circuit charging part through an insulating material or an insulating medium, and performs stable supply of electric power and opening/closing. As an example of this switchgear, SF6 gas at approximately atmospheric pressure is sealed in a sealed container, and a circuit breaker,
Disconnectors, insulators, busbars, cable heads, connection conductors, etc. are installed.

In such a configuration, if thermal stress is applied to the insulator due to the introduction of foreign matter, poor connection of the main circuit charging section, or temperature change, and the insulation deteriorates, partial discharge occurs. If this partial discharge continues for a long period of time, it may develop into a complete dielectric breakdown and lead to a switchgear insulation failure.

Therefore, as a device for monitoring partial discharges and detecting their occurrence at an early stage, there is a device that detects electromagnetic waves associated with partial discharges or minute discharges, as disclosed in Japanese Patent Publication No. 6349845.

Historically, sound waves caused by partial discharge are called AE (Acoust
In this AE, a sensor is attached to the sealed container, and the output of the sensor is processed by transmitting the signal through a cable.

An example of a conventional partial discharge detection device using this processing method will be described with reference to FIG. 5.

For boat fishing, the signal obtained by the AE sensor 11 is preamplified (
PA) 12 amplifies the signal, and a filter (F) 13 classifies the frequency. This filter 13 has bypass and low-pass functions and distinguishes frequencies from several 1011z to several Mllz. The differentiated signals are further amplified by the main amplifier (MA) 14, converted from analog to digital by the A/D converter 15, and the signals caused by partial discharge are distinguished and transmitted to a control panel or computer (not shown). processing is performed.

Here, the signal output from the main amplifier 14 (point B)
The frequency caused by partial discharge and the frequency passed by the filter, that is, noise are superimposed.

(Problem to be solved by the invention) If the above partial discharge continues for a long time, it will lead to dielectric breakdown, so the signal must be processed appropriately, but it is output to point B in Figure 5. The partial discharge signal and noise are superimposed on the waveform. In addition to the frequencies passed by the filter as described above, noise includes electrostatically and electromagnetically coupled frequencies, especially noise of several 1.00 kHz or more, and noise that enters from the power supply of the detection system. , these are superimposed on the AE wave due to partial discharge. From these facts, in the case of a weak partial discharge, the output voltage of the AE waveform is also small, so the noise may become larger than the AE wave, and the detection sensitivity may decrease. In other words, although large partial discharges such as those immediately before dielectric breakdown can be detected, it is extremely difficult to reliably detect weak partial discharges that begin to cause insulation deterioration.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a partial discharge monitoring device for electrical equipment that can reliably detect weak partial discharges using AE waves.

[Structure of the invention] (Means for solving the problem) An acoustic emission sensor that is attached to a box of an electrical device and converts weak ultrasonic waves transmitted through the box into an electrical signal, and a filter that amplifies the signal of this sensor. The device detects partial discharge by acoustic emission via the sensor, and is characterized in that a bandpass filter having resonance at a center frequency of 27 kHz is inserted between the sensor and the amplifier.

(Function) According to the present invention, when looking at sound waves caused by partial discharge as AE waves, the center frequency is 27 kHz, so a bandpass filter with a center frequency of 27 kHz is connected to signal processing from the AE sensor. This prevents noise having a frequency component whose center frequency is different from 27 kHz from entering, and it becomes easy to distinguish between partial discharge and noise.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

A switchgear as an example of electrical equipment to which the device of the present invention is applied is constructed as 111 (as shown in FIG. 1).

That is, SF6 gas at approximately atmospheric pressure is sealed in a closed container 1, and a circuit breaker 2 is installed in the closed container, a disconnect switch 3 connected to the circuit breaker 2, and a switch 4 is connected to one of the disconnect switches 3. The other disconnector 3 is connected to a busbar 5 fixed to the busbar 5, and the other disconnector 3 is connected to a cable 2'6, and these devices are connected by a connecting conductor 7. A door 1a is provided at the front opening of the closed container 1.

In order to detect corona discharge, an AE sensor 11 is attached to the outer wall of the closed container 1, and a signal from the AE sensor 11 is inputted to a signal processing circuit described below via a cable 16. That is, the signal from the AE sensor 11, that is, the AE wave, is connected to a band pass filter (BPF) 17 having a center frequency of 27 kHz. Then, the output of the bandpass filter 17 is amplified by a preamplifier (PA) 12 as in the conventional device, passed through a noi-pass and low-pass filter (F) 13 as necessary, and amplified by a main amplifier (MA) 14. The A/D converter 15 performs analog-to-digital conversion (A/D), detects the AE wave of partial discharge, and transfers it to a control panel or computer (not shown) for monitoring and issuing alarms, etc., to prevent insulation. It prevents decimals.

Here, the frequency characteristics of the bandpass filter 17 will be explained with reference to FIG. 3, and the center frequency is 27kHz.
It has the function of passing frequencies with a width of ±3 kHz in z, and attenuating other frequency regions by a maximum of 120 dB. Further, a relatively high frequency as external noise has an attenuation characteristic of 90 dB in IMIIz.

FIG. 4 shows the AE wave passing through such a byte-pass filter 17, and the AE wave V is a signal at point A on the output side of the main amplifier 14 in FIG.

The AE wave V appears after a small noise when the partial discharge pulse PD occurs, that is, after the propagation time T (ms) of the sound wave due to the partial discharge, has a frequency of 27 kHz, and has a preset threshold value. If it exceeds Vl), it can be detected as partial discharge.

The magnitude of the AE wave V varies depending on the magnitude and degree of occurrence of the partial discharge, and the propagation time T varies depending on the insulating medium (here S
F6 gas, To-135III/sec・20℃
The frequency of the AE wave does not change, noise is suppressed by the band pass filter 17, and only the frequency of 2 7 kllZ due to partial discharge is passed through and amplified, so even a weak partial discharge can be detected. Detection is possible reliably.This is because the AE wave V 2 appears more easily because the noise is small, and the detection sensitivity is improved because the threshold value Vb can be lowered.

In this way, by improving the detection sensitivity of partial discharges, it is possible to detect weak partial discharges before insulation deterioration.
It is possible to prevent insulation breakdown accidents by issuing an alarm etc. before GL. In addition, the simple circuit configuration is not complicated, and detection is possible with high sensitivity without being affected by external noise.

[Effects of the Invention] According to the partial discharge monitoring device for electrical equipment according to the present invention, by connecting a bandpass filter having a center frequency of 27 kHz, which is equivalent to the frequency of sound waves propagated by partial discharge, to the AE sensor, the external suppresses the influence of noise from the source, and can reliably detect weak partial discharges as AE waves.
It is possible to prevent insulation deterioration accidents in electrical equipment such as switch gears.

[Brief explanation of drawings]

FIG. 1 is a side view showing an example of a switchgear equipped with a partial discharge detecting device according to the present invention, FIG. 2 is a block diagram showing an example of a partial discharge detecting device for electrical equipment according to the present invention, and FIG. A frequency characteristic diagram of a bandpass filter according to an embodiment of the present invention, FIG. 4 is an oscillogram of a partial discharge pulse and an AE wave according to an embodiment of the present invention, and FIG. 5 is a block diagram showing an example of a conventional partial discharge detection device. It is a diagram. 1... Airtight container, 2... Circuit breaker, 3... Disconnector,
4... Insulator, 5... Bus bar, 6... Cable head, 7... Connection conductor, 8... Sensor, 9... Cable, ]1... AE sensor, ]2...・Preamplifier,
13... Filter 14... Main amplifier, 15
...A/D converter, 17...Bypass filter Patent attorney Takehiko Suzue

Claims (1)

[Claims] Acoustic emission sensors are attached to the box of electrical equipment and convert weak ultrasonic waves transmitted through the box into electrical signals, and sensors amplify the sensor signal and detect partial discharge through a filter using acoustic emission. A partial discharge monitoring device for electrical equipment, characterized in that a bandpass filter having resonance at a center frequency of 27 kHz is inserted between the sensor and the amplifier.