JPH0894682A - Apparatus for diagnosing insulation deterioration - Google Patents

Abstract

PURPOSE: To detect a minute partial discharge with high accuracy and estimate the time till a break down by attenuating a pulse signal detected by a high frequency current transformer at an attenuator, detecting a peak of the signal through a BPF of a high gain, and averaging the signal. CONSTITUTION: A partially discharging pulse current is inputted to a point A and output to an input terminal of a matching resistor 21 connected by means of a coaxial cord. The pulse current output from the matching resistor 21 is divided by an attenuator 22 of 0-several tens dB in accordance with the size of noises of a set switch gear so as not to exceed a maximum input value of a BPF23, and input to the BPF23 matching the frequency component. The output is amplified by an amplifier 24 to several tens dB and sent to a terminal B and a peak detection circuit 25. The peak detection circuit 25 holds a peak at a time constant of several ms under a decimal point. Passing through an averaging circuit 26 averaging by a time interval of several 100ms and a voltage/current conversion circuit 27, an output current, of DC4mA-20mA is outputted from a terminal C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation deterioration diagnosing device for detecting a partial discharge generated in a switchgear or the like.

[0002]

2. Description of the Related Art In FIG. 6 showing a metal closed type switchgear to which a partial discharge detector is attached, a partition 1a is vertically provided at a rear portion of a metal box 1 whose outer periphery is surrounded by a mild steel plate. . A spacer 2 is provided on the ceiling at the rear of the upper end of the partition 1a, and a conductor 3a for receiving power is connected to the lower end of the conductor penetrating the axial center of the spacer 2.

The lower end of the conductor 3a is curved in a U shape,
At the end, the lower end of the conductor 3b penetrating the pair of current transformers 4 attached to the rear surface of the partition 1a and the substantially L-shaped conductor 3c.
The upper end of is connected. Of these, the upper end of the upper conductor 3b is connected to the lower pole of the vacuum circuit breaker 5 housed in the circuit breaker chamber 1b, and the upper pole of the vacuum circuit breaker 5 is connected to the lower end of the conductor 3d. The upper end of the conductor 3d is attached to the busbar chamber 1c, and is connected to the busbar 6 arranged on the lower surface of the ceiling of the box body 1 in the direction orthogonal to the plane of the drawing.

On the other hand, an instrument transformer 7 is housed in the instrument transformer chamber 1d provided below the circuit breaker chamber 1b, and the primary side of the instrument transformer 7 is connected to the lower end of the conductor 3e. ing. Further, a lightning arrester 8 is housed in a lightning arrester chamber 1e provided below the instrument transformer room 1d, and a conductor 3f supported by a partition 1f via an insulator (not shown) is provided in the lightning arrester 8.
One side of the conductor 3f is connected, and the other side of the conductor 3f is connected to the lower end of the conductor 3d.

A ground busbar 9 is provided in the rear portion of the lower end of the box body 1 in a direction orthogonal to the plane of the drawing. One side of a ground conductor 10 is connected to the ground busbar 9, and the other end of the ground conductor 10 is a ground rod of the box body 1. It is connected to the. A high-frequency current transformer 11 (hereinafter referred to as a high-frequency CT) is loosely fitted in the ground conductor 10 in advance, and
The coaxial cord wire 12 on the secondary side of 11 is connected to a detection device (not shown). Further, an AE sensor 13 is attached to the upper end of the front surface of the instrument transformer room 1d, and the coaxial cord wire 14 on the output side of the AE sensor 13 is also connected to an ultrasonic detecting device (not shown).

In the metal-closed switch gear constructed as described above, as a result of long-term operation, the insulators and insulators constituting the transformer 7 for the instrument and the vacuum circuit breaker are deteriorated, and the switch gear adheres to the surface of the conductor. When a partial discharge is generated between the ground and between the phases due to dust or the like, ultrasonic waves are generated and a pulse current due to the partial discharge flows through the ground bus 9,
It is discharged from the ground conductor 10 to the ground through the ground rod.

Therefore, in this metal closed switchgear, the pulse current discharged to the ground by the high frequency CT11 is detected at a specific center frequency and is input to an amplifier circuit (not shown). This frequency has a low frequency range of several 100 kHz and several MHz as shown in FIG. 7, and is used depending on the application. The detection method using the high frequency CT11 is also disclosed in, for example, Japanese Patent Publication No. 2-43409.

On the other hand, the AE sensor 13 detects an ultrasonic wave of several tens of kHz due to partial discharge, converts the ultrasonic wave into an electric signal, and inputs the electric signal to the amplification circuit of the detection device via the coaxial cord 14.

[0009]

However, noise may be mixed into the pulse current and ultrasonic waves detected by the metal-closed switchgear. As noise mixed in the pulse current, the pulse voltage of the high-frequency component that enters and is superimposed on the power supply system to which the switch gear is connected,
There is a surge voltage generated by opening and closing a vacuum circuit breaker, a disconnector, etc. housed in the switch gear and the adjacent switch gear and a voltage of a harmonic component of the power receiving transformer. In the high frequency region, the broadcast frequency is electrostatically coupled and enters.

On the other hand, noise detected by the AE sensor includes mechanical vibration due to electromagnetic force generated by current flowing through the conductor of the metal-closed switchgear, sound waves due to discharge of electric equipment installed in the vicinity, and There are sound waves generated from a wireless communication device.

When noise enters the high frequency CT or AE sensor as described above, the detection accuracy of the partial discharge deteriorates. Therefore, in order to reduce the influence of noise, a frequency band is selected or a noise removing circuit is used together. There is. However, if the pulse current flowing in the ground line is tuned to the measurement circuit at several 100 kHz, the detection sensitivity can be increased, but the frequency does not correspond to the rise time of partial discharge, so the pulse current associated with partial discharge cannot be detected. . Further, in the frequency band of FIG. 7, although the pulse current accompanying the partial discharge via the high frequency CT is detected, the gain at about 1 MHz is about 18
Only dB can be reduced, and large noise including broadcast frequency cannot be suppressed. Furthermore, when the noise is large and the signal is over, the magnitude of the peak is distorted and the frequency of the signal changes. Therefore, partial discharge cannot be detected at the frequency of the bandpass filter.

Further, although the ultrasonic waves detect several tens of kHz, the noise of the partial discharge is detected, so that the noise easily enters and the detection accuracy deteriorates. Therefore, in the conventional partial discharge detection device in which the detection accuracy decreases due to the intrusion of noise, the partial discharge cannot be detected in the early stage of insulation deterioration when the discharge charge amount of the partial discharge is weak, and the insulation deterioration progresses. Partial discharge cannot be detected unless the amount of discharged electric charge becomes large. Further, the detected discharge charge amount is also the maximum value, and not all are captured. Also, it is not possible to estimate the dielectric breakdown due to the magnitude of the discharge charge amount and the shape of the discharge,
It was not possible to judge whether or not the operation could be continued. The purpose of the present invention is to
An object of the present invention is to provide an insulation deterioration diagnosing device capable of detecting a weak partial discharge with high accuracy and estimating a time until dielectric breakdown.

[0013]

In order to achieve the above object, the present invention is to penetrate a ground wire of a switchgear with a high frequency CT, and first reduce a pulse signal detected by the high frequency CT with an attenuator. It is characterized in that averaging processing is performed after peak detection through a bandpass filter having a large gain.

[0014]

In these configurations, when partial discharge occurs inside the switchgear, the frequency of several MHz becomes high frequency CT.
The pulse current of the partial discharge can be accurately captured by filtering only the pulse current of this frequency component that is detected by. In this case, the band of the broadcast frequency and the band of the partial discharge overlap, so make a distinction with a filter with a large gain and make sure that the frequency of the original wave does not change due to various signals being attenuated by the attenuator. The effect of the filter is improved.

Further, by averaging the peak value and the occurrence frequency of the pulse current, it is possible to capture the discharge energy within a fixed time. In the signal after the band pass filter, the discharge pulse rises from the phase of the discharge pulse to the right at the beginning of discharge.
Since it is sloping down right before the dielectric breakdown, it is possible to estimate the time until the dielectric breakdown to some extent in combination with the magnitude of the discharge charge amount.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the insulation deterioration diagnosing device of the present invention will be described below with reference to the drawings. However, the same parts as those of the conventional device are designated by the same reference numerals. FIG. 1 is a block diagram of an insulation deterioration diagnosing device showing an embodiment of the present invention. In the same figure, as in FIG. 6, point A is penetrated by the ground wire, and is composed of, for example, a ferrite core, and is several MHz to several tens of MHz.
It is connected to the output terminal of the high frequency CT11 having the frequency characteristic of.

A partial discharge pulse current is input to this point A, and is output to the input terminal of the matching resistor 21 connected by the coaxial cord line. The pulse current output from the matching resistor 21 is
0 to 0 depending on the noise level of the installed switchgear
The signal is divided by the attenuator 22 of several tens of dB so as not to exceed the maximum input value of the bandpass filter 23, and is input to the bandpass filter 23 adapted to the frequency component. This output is amplified to several tens of dB by the amplifier 24 and sent to the terminal B and the peak detection circuit 25. In the peak detection circuit 25, 0. A few meters
The peak is held with the time constant of s, and the voltage is passed through the averaging circuit 26 that performs the averaging process in the time width of several 100 ms.
An output current of 4 mA to 20 mA DC is output from the terminal C via the current conversion circuit 27.

With these circuits, the partial discharge pulse flowing in the high frequency CT11 has a steep rise of several to several tens of ns, and when converted to frequency, several MHz to several tens of MH.
z. Further, noises of different magnitudes are superimposed on various kinds of frequencies. These signals are attenuated by the attenuator 22 to the extent that the input voltage of the bandpass filter 23 is not exceeded in accordance with the noise level around the switch gear. In addition, when it exceeds, the peak value is distorted and the frequency component becomes different. This input voltage is several tens of mV, and it is not necessary to attenuate it with noise that does not exceed this value. The partial discharge pulse signal and the noise original wave are input to the band pass filter 23, and the partial discharge signal is extracted by the low pass filter shown in FIG. 2 and the high pass filter shown in FIG. The frequency of partial discharge obtained by experiments by the present inventor was about 3 MHz for air discharge and creeping discharge, and about 3 MHz for void discharge.
It was 30 MHz.

Here, in the broadcast frequency band, the component at about 1 MHz is large and overlaps with the partial discharge, so that the gain at 1 MHz is about 35 dB in the low-pass filter. As a result, noise below about 1 MHz is greatly attenuated. In the conventional frequency characteristics, it was difficult to distinguish from partial discharge due to large noise, but it became possible to distinguish by increasing the gain. In addition, the high-pass filter provides a gain of 100 MHz or more from the conventional level of approximately 30 dB to approximately
The attenuation is 55 dB, and noise in the VHF broadcast frequency band is also greatly attenuated.

The signal that has passed through the bandpass filter 23 is amplified by the amplifier 24, output at point B as the original waveform of the partial discharge, and also input to the peak detection circuit 25. In the peak detection circuit 25, 0. The peak is held with a time constant of several ms,
The individual pulse currents are similarly peak-detected. afterwards,
The averaging circuit 26 accumulates the magnitude and frequency in a time width of about 330 ms and then divides by the frequency to obtain an average value. This is 0 .. when measuring pulse current on a 50 Hz basis.
If peak detection is performed for several ms, it is decomposed into about 30 lines per cycle, and the total number with respect to the frequency of partial discharges can be almost measured. Further, if the averaging is performed in about 330 ms, it is possible to catch the partial discharge that continuously occurs. Note that the peak value of noise generated suddenly is attenuated by averaging.

The averaging-processed signal is converted into a DC current of 4 to 20 mA by the voltage-current conversion circuit 27 and input to a monitoring device (not shown) from the point C so that partial discharge can be constantly monitored. FIG. 4 shows a characteristic example in which the output current at the point C is converted into the discharge charge. When the applied voltage is raised, partial discharge begins,
A discharge charge of about 6000 pC is continuously generated. And about
The discharge of 10,000 pC is repeated, and when it reaches about 20000 pC, dielectric breakdown occurs. As a result, there is a discharge charge of several thousand pC immediately before the dielectric breakdown, and this value serves as a standard for estimating the size of the dielectric breakdown.

When the relationship between the voltage phase and the partial discharge pulse is obtained by a waveform observing device having a synchroscope or the like connected to the point B, different shapes are shown near the start of partial discharge and immediately before dielectric breakdown. A measurement example is shown in FIG. 5, but in the vicinity of the start of partial discharge, as shown in FIG.
Immediately before dielectric breakdown, it rises to the right as shown in (b). In other words, it is considered that the downward-discharging partial discharge does not lead to dielectric breakdown in a short time in the initial stage of insulation deterioration, and the upward-sloping partial discharge leads to dielectric breakdown at the final stage of insulation deterioration.

From the above, it is possible to estimate the dielectric breakdown to some extent by combining the magnitude of the discharge charge and the discharge pattern. In other words, if the discharge charge rises to several thousand pC and the discharge pulse is falling to the right with respect to the voltage phase,
This will result in dielectric breakdown in a short time, so the operation of the switchgear cannot be continued. If this condition is not satisfied, and the discharge pulse has a small discharge charge and rises to the right, dielectric breakdown will not occur in a short time.

[0024]

As described above, according to the present invention, the attenuator for attenuating the output signal from the harmonic current transformer which is penetrated through the ground wire of the switchgear, and the partial discharge from the signal attenuated by the attenuator are provided. A bandpass filter that extracts the pulse signal,
Since it has a peak detector that detects peaks from the output signal of the bandpass filter and an averaging processing circuit that performs averaging processing on the output signal of the peak detector, even a weak partial discharge can be detected with high accuracy and dielectric breakdown. The time to can be estimated.

[Brief description of drawings]

FIG. 1 is a block diagram of an insulation deterioration diagnosing device showing an embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram of a low pass filter included in the band pass filter 23 of FIG.

FIG. 3 is a frequency characteristic diagram of a high pass filter included in the band pass filter 23 of FIG.

FIG. 4 is a diagram for explaining the relationship between discharge charge and voltage until dielectric breakdown.

FIG. 5 is a diagram for explaining a relationship between a voltage phase and a partial discharge pulse.

FIG. 6 is a side view showing the configuration of a typical metal-closed switchgear.

FIG. 7 is a frequency characteristic diagram of a conventional bandpass filter.

[Explanation of symbols]

11 ... High-frequency current transformer, 22 ... Attenuator, 23 ... Bandpass filter, 25 ... Peak detection circuit, 26 ... Averaging processing circuit.

Claims (4)

[Claims] 1. An attenuator for attenuating an output signal from a high frequency current transformer, which penetrates a ground wire of a switchgear, a bandpass filter for extracting a partial discharge pulse signal from the signal attenuated by the attenuator, and An insulation deterioration diagnosing device having a peak detector for detecting a peak from an output signal of a bandpass filter, and an averaging processing circuit for averaging the output signal of the peak detector. 2. An amplifier for amplifying the partial discharge pulse signal is provided between the bandpass filter and the peak detector, and waveform observing means for obtaining a relationship between the voltage phase and the partial discharge pulse signal from the output signal of the amplifier. The insulation deterioration diagnosing device according to claim 1, wherein 3. A voltage-current conversion circuit for converting an output signal of the averaging processing circuit into a current signal is provided, and the magnitude of partial discharge converted into discharge charge obtained from the output signal of the voltage-current conversion circuit, and The insulation deterioration diagnostic device according to claim 2, wherein the time until the dielectric breakdown is estimated from the discharge pattern obtained from the waveform observing means. 4. The insulation deterioration diagnostic device according to claim 1, wherein the low-pass filter included in the band-pass filter has a gain of 30 dB or more at a frequency of 1 MHz or less.