JPH0769372B2 - Partial discharge monitoring device for gas insulated equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention detects a current pulse generated by partial discharge in a gas inside a gas-insulated equipment during operation by a discharge pulse sensor and discriminates the current pulse from noise. The present invention relates to a partial discharge monitoring device that monitors only partial discharge in gas and gives an alarm.

[Conventional technology]

If the metal conductor of the high voltage part is dislodged or metal dust is present inside the gas insulated equipment such as gas circuit breaker or gas insulated switchgear that is insulated by SF ₆ gas, Electric discharge may occur, and the gas-insulated equipment may cause dielectric breakdown depending on the size and frequency of the discharge. Therefore, in order to prevent accidents, it is important to monitor the partial discharge of the gas-insulated equipment during operation, but at the site where the gas-insulated equipment is operated, radio noise of various frequencies and thyristor commutation noise are observed. Alternatively, there are many noises such as switching noises that hinder the monitoring of the partial discharge pulse, and it is necessary to distinguish the partial discharge pulse from the noise.
However, this discrimination is extremely difficult. For example, an antenna is installed near a gas-insulated device (hereinafter referred to as the EUT), and the signal from the antenna is compared with the signal from the EUT to compare with noise. Attempts have been made to distinguish the discharge from the discharge.

FIG. 4 is a block diagram showing the configuration of a conventional example device. In this figure, the tank 2 of the EUT 1 has a discharge pulse sensor 4 such as a Rogowski coil through which a ground wire 3 penetrates.
And an antenna 100 installed adjacent to the EUT 1
And a detection impedance 104 attached to the. The discharge pulse signal 4A detected by the discharge pulse sensor 4 and the antenna signal 104A detected by the detection impedance 104 are respectively amplified by the high frequency amplifiers 11 and 111, and further converted into envelope pulses by the detection and clearers 12 and 112, respectively, and the judgment circuit 113 is determined. Be transmitted to. When the signal 12A from the EUT 1 and the signal 112A from the antenna 100 are input at the same time and have the same polarity signal, the determination circuit 113 determines that it is the external noise 5 from the air and outputs an alarm. It is set not to output 113A.

When the external noise 5 is generated, the adjacent EUT 1 and antenna 100 receive the noise at the same time, and the respective ground lines 3, 3
Since the noise currents 5A and 5B flow toward 0 to the ground 17, the discharge pulse signal 4A and the antenna signal 104A are generated at the same time and have the same polarity, and the judgment circuit 113 judges the external noise 5. On the other hand, when a partial discharge occurs in the gas of the EUT 1, a discharge pulse current 6A flows through the ground wire 3 of the EUT 1, and at the same time, a discharge pulse current flows through the ground wire 30 on the antenna 100 side via the ground 17. Since 6B flows, the discharge pulse signal 4A and the antenna signal 104A are generated at the same time, but the signals have polarities opposite to each other, and the judgment circuit 113 judges that it is a partial discharge in the gas of the EUT 1, and outputs an alarm signal 113A to the alarm device 20. Output.

[Problems to be Solved by the Invention]

External noise that interferes with the detection of discharge pulses is noise of broadcast waves, communication waves, etc., or relatively low level noise such as commutation noise generated by thyristor converters, etc. There are high-level switching surge noises such as surges caused by opening and closing switches, switches and vacuum switches.

Focusing on the existence of a frequency region where the frequency component of the former noise is a valley, the detection frequency of the discharge pulse is 1.
It has already been proposed by the applicant of the present application that the detection can be significantly reduced by limiting the detection to 8 MHz to 3.8 MHz, preferably 2.8 MHz to 3.1 MHz.

Regarding the latter switching surge noise, its noise level is extremely high, so the level reduction amount is not sufficient only by limiting the frequency as described above, and a noise discriminating device as shown in the conventional example device of FIG. 4 is required. Become. However, the behavior of noise is generally very complicated, and it is impossible to discriminate all kinds of noise by the conventional apparatus shown in FIG. For example, the EUT 1 and the antenna 100 have different ways of receiving noise depending on their shape, size, installation location, noise intrusion direction, and the like. Even with the same external noise 5, the noise current 5A flowing through the EUT 1 is large. ， The noise current 5B flowing in the antenna 100 may be extremely small, and the antenna signal 104A from the antenna 100
Is not detected and it is impossible to discriminate it from the external noise 5, and it is erroneously determined that a partial discharge of the EUT 1 has occurred. Also,
In addition to the external noise 5 entering from the space, there is also a noise current carried on the power transmission line 7 or the grounding line 3 connected to the EUT 1 and propagating. In any case, this kind of noise current flows through the ground wire 3 of the EUT 1 and the output signal 4A of the discharge pulse sensor 4 is output.
However, the current does not always flow to the detection impedance 104 on the antenna 100 side, and it is erroneously determined that a partial discharge of the EUT 1 has occurred.

As a method of discriminating against external noise other than the conventional apparatus shown in FIG. 4, a method of attaching an ultrasonic sensor to the outer wall of the tank 2 of the test device 1 to detect ultrasonic waves due to partial discharge has been considered. In the case of an insulating device, the amount of attenuation during sound wave propagation in gas is so large that detection sensitivity is poor and there is a practical problem.

An object of the present invention is to avoid high-level switching surge noise and improve monitoring accuracy by considering the level of the discharge pulse that adversely affects the internal insulation of the gas-insulated equipment and the frequency of the pulse generation.

[Means for Solving the Problems]

In order to solve the above problems, according to the present invention, a current pulse generated by a partial discharge in a gas inside a gas-insulated device during operation is detected by a discharge pulse sensor, and the current pulse is discriminated from noise in the gas. For monitoring only the partial discharge of, a comparison circuit for outputting only a signal exceeding a predetermined threshold among discharge pulse signals generated by the partial discharge in the gas, and a predetermined sampling period for receiving the output signal of the comparison circuit. A digital counter for outputting the number of discharge pulses for each period, an integrating circuit for receiving the output signal of the comparison circuit and outputting a cumulative charge value for each cycle, and an A / D converter for converting the cumulative charge value into a digital signal. , Abnormal when the accumulated charge value of this digital signal exceeds a predetermined judgment level and the number of discharge pulses exceeds a predetermined number. It is determined that there shall become comprise determination means for instructing the alarm output.

[Action]

The above means is a condition that there is a partial discharge in the gas when there is a contact failure in the high voltage conductor part or when there is metallic dust in the tank, and the level and frequency of occurrence of the gas insulated device in the operating gas. Paying attention to the possibility that dielectric breakdown will increase when the voltage exceeds the limit, the switching surge at the local level is tens of thousands to hundreds of thousands at a single charge level at the charge conversion level.
Although it is very high at pC, the frequency of occurrence is several to several tens per minute, so even if the discharge pulse sensor detects partial discharge of the test device and switching surge noise, the test A predetermined condition for the device to report an abnormality, that is, 20 or more discharge pulses N occur every sampling period τ of 1 second and the accumulated charge value ΣQ _i is 50,000 pC per second.
Compared with the above conditions, the number of partial discharge pulses generated in an abnormal case is an order of magnitude larger than that of switching surge noise, and is within the error range. Discharge can be discriminated from noise and an alarm signal can be output.

〔Example〕

 The present invention will be described below based on examples.

FIG. 1 is a block diagram showing an apparatus according to an embodiment of the present invention, and FIG.
FIG. 3 is a signal waveform diagram of a main part of the embodiment apparatus, and FIG. 3 is a flow chart showing a judging means of the embodiment apparatus. The same parts as those of the prior art apparatus are designated by the same reference numerals and detailed description thereof will be omitted. .

In FIG. 1, the tank 2 of the EUT 1 has its ground wire 3
For example, a Rogowski coil is provided as the discharge pulse sensor 4 through which the discharge pulse signal 4A detected by the discharge pulse sensor 4 is tuned and amplified for a specific frequency component by a narrow band high frequency amplifier 11 having a center frequency of 3 MHz, for example. The detection rectifier 12 converts the envelope pulse having a positive polarity and a pulse width of several tens of ms, and the comparator circuit 13 having the threshold value setter 14 outputs only the discharge pulse signal 13A exceeding the threshold level 14S. . As the threshold level 14S,
A value less than that is set to a level that does not relate to the determination of whether there is an abnormality, for example, a level equivalent to 1,000 pC, and high-frequency noise, commutation noise, etc. as noise reduced to below this level are removed, and The threshold level 14S is set in advance by injecting a known calibration charge into the EUT 1.

The output signal 13A of the comparison circuit 13 is transmitted to a digital counter 18 for counting the number of discharge pulses and an integrating circuit 15 for accumulating the amount of discharged charges. Digital counter
Reference numeral 18 counts the number N of discharge pulses for each predetermined sampling period τ, for example, for each second, and notifies the number to the judgment means 19 in the microprocessor 22. On the other hand, the integration circuit 15 integrates the peak value of each discharge pulse at the same sampling cycle as that of the digital counter 18 and transmits the accumulated charge value ΣQ _i to the A / D converter 16 in the microprocessor 22, and the A / D converter 16 The converter 16 converts the accumulated charge value for each sampling period τ into a digital signal 16A and sends it to the judging means 19.

The appearance of the partial discharge pulse in the gas-insulated equipment differs depending on the abnormal situation in the EUT. For example, if the metal shield of the high-voltage part is disengaged and contact failure occurs with the high-voltage bus bar, a breakdown discharge in the gas occurs between the metal shield with a floating potential and the high-voltage bus bar. 4 detects. When this kind of partial discharge occurs, SF ₆ gas and the metal conductor may overheat and chemically decompose, which may lead to a short-circuit accident, which is extremely dangerous. According to the experiments, in many cases, several tens to tens of thousands of pC level discharge pulses are always generated at every several cycles of the applied commercial frequency voltage, and the number N of discharge pulses per second is 1,000.
The accumulated charge value ΣQ _i of about several pieces per second is several million pC or more.

If wire-like metal dust is present in the test device 1, the metal dust randomly moves in the tank 2 due to the high voltage application. That is, when the metal dust attracted to the high voltage bus bar side by the electrostatic force due to the electric field floats up to near the high voltage bus bar, the charges of the metal dust are discharged toward the high voltage bus bar through the SF ₆ gas gap. As a result, the metal dust loses its charge and falls due to gravity, but when it comes into contact with the lower tank wall, it again receives the charge and begins to levitate again. The discharge pulse sensor 4 detects a partial discharge pulse when the metal dust discharges electric charges toward the high-voltage bus. If the frequency or level of partial discharge in this case is too large, this triggers a short-circuit accident. It may reach. In general, since metal dust moves randomly, the generation of discharge pulses is not stable, the magnitude of the amount of discharge charge constantly fluctuates, and the aspect of pulse generation stops or occurs again for a certain period of time. However, the number N of discharge pulses above the level of about 1,000 pC is 1 due to experiments using actual equipment.
20 or more are generated per second, and the accumulated charge value ΣQ _i during that time is
If it is over 50,000pC, it will lead to a short circuit accident, which is extremely dangerous.

FIG. 2 is a time chart showing a conversion state into a digital signal for an example of generation of a discharge pulse when metal dust is mixed in the apparatus of the embodiment, and the discharge pulse sensor 4 is generated in the DUT 1 in operation. In this example, a partial discharge pulse is detected and a discharge pulse signal 4A is output. The discharge pulse signal 4A is converted into a positive-polarity envelope pulse 12A by the detection rectifier 12, and the threshold value 1 of 1,000 pC, for example, is obtained by the comparison circuit 13.
The discharge pulse of 4S or less is removed. One of the output signals 13A of the comparison circuit 13 is transmitted to the digital counter 18, and counts the number N of discharge pulses per second as a predetermined sampling period τ, for example.

On the other hand, the output signal 13A of the comparison circuit 13 is also transmitted to the integration circuit 15, and the peak value of each discharge pulse is accumulated every 1 second as a predetermined sampling period τ. This accumulated charge value ΣQ _i value is converted by the A / D converter 16 into a digital signal 16 every second.
It is converted into A and transmitted to the judging means 19.

The judging means 19 determines the number N of discharge pulses for each sampling period τ.
And the accumulated charge value ΣQ _i between them and both exceed a predetermined level, it is judged as an abnormal partial discharge and an alarm signal 19
As shown in FIG. 3, the accumulated charge value ΣQ _i obtained by the A / D converter 16 for each sampling period τ exceeds a predetermined level A, and the digital counter 18 outputs When the number N of discharge pulses for each sampling period τ obtained in step 3 is B or more, it is determined that an abnormal partial discharge has occurred inside the EUT, and an alarm output signal 19A is issued to the alarm device 20. Together with the judgment data 19B
Is output to the recording device 21.

The judging means 19 judges that the EUT is normal if N is B or less even if ΣQ _i exceeds A. Since A is 50,000 pC and B is 20, 20 is a standard, so even if a pulse of tens of thousands of pC enters as switching surge noise and ΣQ _i exceeds A,
The frequency of occurrence of switching surge noise is about several to several tens of minutes per minute. Therefore, unless partial discharge occurs in the EUT 1, it is judged that N does not exceed B and is normal, and partial discharge and switching surge noise are separated. Can be discriminated.

In the apparatus of the embodiment, the output signal 13A of the comparison circuit 13 and the output signal 15A of the integration circuit 15 are supplied to the digital counters 18 and A, respectively.
An example in which a digital signal is converted by the / D converter 16 and processed by the microprocessor 22 is shown. This is because the EUT 1 is installed in, for example, an unmanned substation,
Assuming that monitoring is performed at a distant substation or power station,
It is configured to facilitate the transmission of data,
It goes without saying that the configuration may be such that analog signal processing is performed when there is no need for this.

〔The invention's effect〕

As described above, the present invention selects a discharge pulse of a threshold value or more, which is a comparison circuit, for the output signal of the discharge pulse sensor, and determines the number N of discharge pulses for each predetermined sampling cycle and the accumulated charge value ΣQ _{i for} that period. When is above a predetermined level, it is judged that the EUT is abnormal and an alarm is output.

As a result, the conventional device erroneously determined that switching surge noise of the level of tens of thousands to hundreds of thousands of pC would enter, and it was impossible to automatically monitor partial discharge in the past. Paying attention to the fact that the number of pulses per minute is several to several tens, and the number of pulses of abnormal partial discharge is 20 or more per second and the accumulated charge value is determined to be 50,000 pC or more. It is possible to provide a partial discharge monitoring device capable of discriminating from surge noise.

Further, since there is no erroneous determination due to noise, there is an advantage that it becomes possible to automatically monitor partial discharge in an unmanned substation, which has been impossible in the past.

[Brief description of drawings]

FIG. 1 is a block diagram showing an apparatus according to an embodiment of the present invention, and FIG.
FIG. 4 is a signal waveform diagram of the essential part of the embodiment apparatus of the present invention, FIG. 3 is a flow chart showing the judging means of the embodiment apparatus, and FIG. 4 is a block diagram showing the conventional apparatus. 1: Gas insulated switchgear (test equipment), 2: Ground tank, 3,30:
Ground wire, 4: Discharge pulse sensor, 4A: Discharge pulse signal, 5:
External noise, 5A, 5B: Noise current, 6A, 6B: Discharge pulse current, 7: Transmission line, 100: Antenna, 104: Detection impedance, 104A: Antenna signal, 11,111: High frequency amplifier, 12,11
2: Detection rectifier, 12A, 112A: Output signal of detection rectifier, 13: Comparison circuit, 113: Judgment circuit, 13A: Output signal of comparison circuit, 15:
Integrator circuit, 15A: Output signal of integrator circuit, 16: A / D converter, 16
A: A / D converter output signal, 17: Ground, 14: Threshold setter, 14S: Threshold level, 18: Digital counter, 18
A: Digital counter output, 19: Judgment means, 19A, 113A:
Alarm output signal, 19B: Judgment data output signal, 20: Alarm device, 2
1: recording device, 22: microprocessor.

Claims (1)

[Claims] 1. A discharge pulse sensor for detecting a current pulse generated by a partial discharge in a gas inside a gas-insulated equipment during operation, and discriminating the current pulse from noise to monitor only the partial discharge in the gas. A comparison circuit for outputting only a signal exceeding a predetermined threshold value among discharge pulse signals generated by the partial discharge in the gas, and a digital circuit for receiving the output signal of the comparison circuit and outputting the number of discharge pulses for each predetermined sampling period. A counter, an integrating circuit that receives the output signal of the comparison circuit and outputs a cumulative charge value for each cycle, and converts the cumulative charge value into a digital signal.
An A / D converter and a judgment means for judging an abnormality and issuing an alarm output when the accumulated charge value of the digital signal exceeds a predetermined judgment level and the number of discharge pulses exceeds a predetermined number. Partial discharge monitoring device for gas-insulated equipment characterized by the following.