JPH02285269A - Partial discharge monitor apparatus of gas insulated machinery - Google Patents

Abstract

PURPOSE:To output an alarm signal by selecting a discharge pulse equal to or more than a threshold value level and judging abnormality on the basis of the number of discharge pulses at every predetermined sampling cycle and the accumulated charge quantity during the discharge period of pulses. CONSTITUTION:In the earthed tank 2 of a device 1 tested, a discharge pulse sensor 4 through which an earth wire 3 passes is provided and the discharge pulse signal 4A detected by the sensor 4 is amplified by a narrow-band high frequency amplifier 11 and detected and rectified by a detection rectifier 12 to be converted to an envelope pulse of positive polarity. A comparing circuit 13 having a threshold value setting device 14 outputs only a discharge pulse signal 13A exceeding a threshold value level 14S and a digital counter 18 counts the number N of discharge pulses at every predetermined sampling cycle to input the same to a judge means 19. An integration circuit 15 integrates the peak values of respective discharge pulses at every same sampling cycle and the accumulated charge quantity thereof is converted by an A/D converter 16 to be inputted to the means 19. The means 19 judges abnormal partial discharge when the number N of pulses and the accumulated charge quantity exceed a predetermined level to make it possible to output an alarm signal 19A.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention detects current pulses caused by partial discharge in gas inside gas insulated equipment during operation using a discharge pulse sensor, distinguishes the current pulses from noise, and A partial discharge lid that monitors only partial discharges in gas and alerts you to abnormalities? j! Regarding equipment.

(Conventional technology) Metal conductors of high voltage parts are about to come off during operation inside gas-insulated equipment such as gas circuit breakers and gas-insulated switchgear, and metal dust is present inside. If the equipment is in operation, partial discharge may occur, and depending on its size and degree of occurrence, it may lead to dielectric breakdown of gas-insulated equipment.Therefore, to prevent accidents, it is necessary to monitor partial discharges in gas-insulated equipment during operation. Although it is considered important, radio noise of various frequencies is generated at sites where gas-insulated equipment is operated.
There are many noises that interfere with partial discharge pulse monitoring, such as thyristor commutation noise or switching noise.
It is necessary to distinguish between partial discharge pulses and noise. However, this discrimination is very difficult; for example, an antenna is installed near a gas-insulated device (hereinafter referred to as the device under test), and the signal from the antenna is compared with the signal from the device under test. Attempts have been made to distinguish between partial discharge and other methods.

FIG. 4 is a block diagram showing the configuration of a conventional device. In this figure, the tank 2 of the device under test 1 has its ground vA3
A discharge pulse sensor 4 such as a Rogowski coil penetrated by
and an antenna 10 installed near and adjacent to the device under test 1.
A detection impedance 104 is provided, which is attached to the sensor impedance 104 . The discharge pulse signal 4^ detected by the discharge pulse sensor 4 and the antenna signal 104A detected by the detection impedance 104 are respectively connected to the high frequency amplifier 11.
, 111, and are further amplified by detection rectifiers 12., 111, respectively.
At step 112, the signal is converted into an envelope pulse and transmitted to a judgment circuit 113.

If the signal 12^ from the device under test 1 and the signal 112A from the antenna 100 are input at the same time and have the same polarity, the judgment circuit 113 judges that it is external noise 5 from the air and issues an alarm. The output 113A is set not to be output.

When external noise 5 occurs, the adjacent device under test 1 and antenna 100 receive the noise at the same time, and noise currents 54 and 58 flow through their respective ground wires 3 and 30 toward ground 17, so that discharge pulse signal 4A and antenna signal 1
04A are generated simultaneously and have the same polarity, and the determination circuit 113 determines that it is external noise 5.

On the other hand, when a partial discharge occurs in the gas of the device under test 1, a discharge pulse current of 6 A flows through the ground wire 3 of the device under test 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. 6B flows, the discharge pulse signal 4^ and the antenna signal 104A are generated at the same time, but the signals have opposite polarities, and the judgment circuit 113 judges that it is a partial discharge in the gas of the device under test 1, and sends the alarm signal 113 to the alarm 20. Outputs ^.

[Problem to be solved by the invention]

External noises that can interfere with the detection of discharge pulses include relatively low-level noise such as noise from broadcast waves and communication waves, commutation noise generated by thyristor converters, etc., and interruptions installed in the power system. There are high-level switching surge noises such as surges caused by the opening and closing of equipment, switches, vacuum switches, etc.

For the former noise, we focused on the fact that there is a frequency region where the frequency component has a valley, and set the detection frequency of the discharge pulse to 1.
, 8M11z to 3.8MHz, preferably 2.8M
The applicant of the present application has already proposed that it can be significantly reduced by restricting the detection from I(Z to 3.IMI(z).

Regarding the latter switching surge noise, the noise level is extremely high, so limiting the frequency as described above is not enough to reduce the level, and a device for discriminating from noise as shown in the conventional example device in Figure 4 is required. Become. However, the behavior of noise is generally very complex, and the conventional example shown in Fig. 4'! It is not possible to discriminate all types of noise by position. For example, test equipment 1 and 7 antenna 10
0 differs in how they receive noise depending on their shape, size 1 installation location, noise intrusion direction, etc.
Even with the same external noise 5, the noise current flowing through the EUT 1 is 5A.
is large, but the noise current 5B flowing through the antenna 100 may become extremely small, and the antenna signal 104A from the antenna 100 is not detected, making it impossible to distinguish it from the external noise 5 and causing partial discharge in the device under test L. This will result in a misjudgment. In addition to the external noise 5 that enters from the space, there is also noise current that propagates on the power transmission line 7 and grounding line 3 connected to the device under test 1. In any case, this type of noise current flows through the grounding wire 3 of the device under test 1 and becomes the output signal 4^ of the discharge pulse sensor 4, but it does not necessarily flow through the antenna 10.
This does not necessarily mean that the current flows through the detection impedance 104 in the case of zero, and it will be erroneously determined that a partial discharge has occurred in the device under test 1.

In addition to the conventional device shown in Fig. 4, a method of detecting ultrasonic waves caused by partial discharge by attaching an ultrasonic sensor to the outer wall of the tank 2 of the test device 1 has also been considered as a method for distinguishing from external noise. In the case of gas-insulated equipment, the amount of attenuation during propagation of sound waves in gas is very large, resulting in poor configuration sensitivity and a practical problem.

The purpose of this invention is to avoid high-level switching/notching surge noise and improve monitoring accuracy by considering the level of discharge pulses that adversely affect the internal insulation of gas-insulated equipment and the frequency of their pulse occurrence. It is in.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, a discharge pulse sensor detects a current pulse caused by a partial discharge in gas inside gas insulated equipment during operation, and distinguishes the current pulse from noise to A device that monitors only partial discharges in the gas includes a comparator circuit that outputs only signals exceeding a predetermined threshold among the discharge pulse signals generated by the partial discharges in the gas, and a comparator circuit that outputs only signals exceeding a predetermined threshold value from among the discharge pulse signals generated by the partial discharges in the gas, and a comparator circuit that receives the output signal of the comparator circuit and outputs a predetermined sample. a digital counter that outputs the number of discharge pulses per cycle; an integrating circuit that receives the output signal of the comparison circuit and outputs the accumulated charge value for each cycle; and an A/D converter that converts the accumulated charge value into a digital signal. and determining means for determining that the accumulation of digital signals is abnormal when the load value exceeds a predetermined judgment level and the number of discharge pulses exceeds a predetermined number, and instructs an alarm output. do.

[Effect]

The above measures apply to gas insulated equipment in gas during operation, when partial discharge occurs in the gas when there is a poor contact in the high voltage conductor or when there is metal dust in the tank, and the level and frequency of occurrence are certain. Focusing on the fact that the possibility of dielectric breakdown increases when the switching surge exceeds The number of pulses per minute ranges from several to several dozen, so even if the discharge pulse sensor detects both partial discharge and switching surge noise in the device under test, the device under test will report an abnormality under certain conditions, that is, discharge The number of pulses N is 20 or more generated per sampling period τ of 1 second, and the cumulative charge value ΣQ.

Compared to the condition that the voltage is 50,0OOpC or more per second, the number of partial discharge pulses that occur during an abnormality is an order of magnitude higher than that of switching surge noise, which is within the margin of error, so gas insulated equipment It is possible to distinguish partial discharges that adversely affect internal insulation from noise and output an alarm signal.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a signal waveform diagram of the main part of the embodiment device, and FIG. 3 is a flowchart showing the determination means of the embodiment device. The same reference numerals are used for the same parts as in the conventional device, and detailed explanation will be omitted. .

In Figure 1, the tank 2 of the device under test 1 has its ground wire 3.
For example, a Rogowski coil is provided as the discharge pulse sensor 4 through which the discharge pulse sensor 4 passes, and the discharge pulse signal 4A detected by the discharge pulse sensor 4 is tuned to a specific frequency component by a narrow band high frequency amplifier 11 having a center frequency of, for example, 3 MHz. It is amplified and converted by the detection rectifier 12 into an envelope pulse with positive polarity and a pulse width of several tens of m5, and a comparator circuit 13 having a threshold setter 14 outputs only the discharge pulse signal 13A exceeding the threshold level 14s. be done. In addition,
As for the threshold level 14S, a value lower than that is a level that is irrelevant to determining whether there is an abnormality or not, for example, 1.0O
The threshold level 14S is set to a level corresponding to OpC, and high-frequency noise, commutation noise, etc. are removed as noises reduced below this level, and the threshold level 14S is set to apply a known calibration charge to the device under test It is calibrated in advance by injection.

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 discharge 1tif.

The digital counter 18 is configured to calculate a value for each predetermined sampling period τ.
For example, the number N of discharge pulses per second is counted and the number is transmitted to the determining means 19 in the microprocessor 22. On the other hand, the integrating circuit 15 is connected to the digital counter 18 mentioned above.
The microprocessor 2 integrates the peak value of each discharge pulse at the same sampling period as , and calculates the cumulative charge value ΣQ.
2, and the A/D converter 16 converts the cumulative charge value for each sampling period τ into a digital signal 16A.
, and then conveys it to the judgment means 19.

The appearance of partial discharge pulses in gas-insulated equipment differs depending on the abnormal situation inside the equipment under test. For example, if the metal shield of a high voltage section comes off and causes a poor contact with the high voltage bus, a destructive discharge in the gas will occur between the floating metal shield and the high voltage bus, and this will be detected as a partial discharge by the discharge pulse sensor. 4 is detected. When this type of partial discharge occurs, it is extremely dangerous as it may cause overheating or chemical decomposition of the SF, gas, or metal conductor, leading to a short circuit accident. According to experiments, in many cases, several dozen discharge pulses of several thousand to nearly PC level occur continuously for each cycle of the applied commercial frequency voltage, and the number N of discharge pulses per second is 1.
, 000, and the cumulative charge value ΣQ4 per second is several million 9 C or more.

Further, if wire-shaped metal dust is present in the test device 1, the metal dust moves randomly within the tank 2 due to the application of high voltage. In other words, when the metal dust is attracted to the high-voltage bus by electrostatic force caused by the electric field and floats up close to the high-voltage bus, the electric charge held by the metal dust becomes SF! Discharge towards the high voltage bus through the gas gap. As a result, the metal dust loses its charge and falls due to gravity, but when it comes into contact with the tank wall at the bottom, it receives a new charge and begins to float again. When metal dust releases charge toward the high-voltage bus, the discharge pulse sensor 4 detects it as a partial discharge pulse, but if the frequency or level of partial discharge in this case is too large, this can act as a trigger and cause a short circuit accident. In some cases, this may occur. -In fact, since metal dust moves randomly, the generation of discharge pulses is not stable, and the amount of discharge charge fluctuates constantly, and the appearance of pulse generation may stop for a certain period of time and then occur again. do. However, experiments using actual equipment have shown that if the number N of discharge pulses at a level of about 1.0OOpC or more occurs 20 or more per second, and the cumulative charge value ΣQt during that time exceeds 50,000pC, it is likely to lead to a short circuit accident. This will result in an extremely dangerous situation.

FIG. 2 is a time chart showing the conversion state into a digital signal for an example of the generation of discharge pulses when metal dust is mixed in the device of the embodiment, and shows the state of conversion into digital signals when the discharge pulse sensor 4 generates in the test device 1 during operation. This is an example in which a partial discharge pulse is detected and a discharge pulse signal 4A is output. Discharge pulse signal 4
A is a positive envelope pulse 12 by a shear wave rectifier 12.
A, for example, 1.0O by the comparison circuit 13.
Discharge pulses below the OpC threshold 143 are removed. One of the output signals 13A of the comparison circuit 13 is transmitted to a digital counter 18, which counts discharge pulses @N every 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 second as a predetermined sampling period τ.

The A/D converter 16 converts this accumulated charge value ΣQt value to 1
Converted into digital signal 16A per second and judgment means 19
transmitted to.

The determining means 19 receives the number N of discharge pulses per sampling period τ and the pre-s accumulation value ΣQ during that period, and if both exceed a predetermined level, it determines that it is an abnormal partial discharge and outputs an alarm signal 19A. As shown in FIG. 3, the flowchart is as shown in FIG. When the number N of discharge pulses per 1l is output to recording device 2].

The determining means 19 determines that the test device is normal if N is less than or equal to B even if ΣQ exceeds A. A is 50,000ρC
, B is 20 as a guide, so for example, if a pulse from the PC enters as a switching surge noise, ΣQl
Even if exceeds A, the frequency of switching surge noise is from several to several dozen per minute, so unless a partial discharge occurs in the device under test 1, N will not exceed B and is considered normal. Partial discharge and switching surge noise can be distinguished.

In the example device, an output signal 13A of a comparison circuit 13 and an output signal 15A of an integration circuit 15 are converted into digital signals by a digital counter 18 and an A/D converter 16, respectively, and the signals are processed by a microprocessor 22. This is designed to facilitate data transmission, assuming that the device under test 1 is installed at, for example, an unmanned substation and its monitoring is performed at a distant substation or power station. However, if this is not necessary, it goes without saying that the configuration may be configured to perform analog signal processing.

〔Effect of the invention〕

As described above, in this invention, a comparator circuit selects discharge pulses exceeding a threshold value for the output signal of a discharge pulse sensor, and calculates the number N of discharge pulses in each predetermined sampling period and the cumulative charge value ΣQ during that period.

When this exceeds a predetermined level, it is determined that there is an abnormality in the equipment under test and an alarm is output.

As a result, conventional equipment incorrectly judges when switching surge noise at the level of several hundred thousand pC enters.
Conventionally, it was impossible to automatically monitor partial discharges, but by focusing on the fact that switching surge noise occurs at a frequency of several to several tens of pulses per minute, the number of abnormal partial discharge pulses was 20 per second. By determining the cumulative MA value as above and at 50,000 pC or more, it is possible to provide a partial discharge monitoring device that eliminates erroneous determination and can discriminate from external switching surge noise.

Furthermore, since erroneous determinations due to noise are eliminated, there is an advantage that automatic monitoring of partial discharges in unmanned substations, which was previously impossible, is possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a signal waveform diagram of the main part of the apparatus according to the embodiment of the present invention, FIG. 3 is a flowchart showing the determination means of the apparatus according to the embodiment, and FIG. 4 is a block diagram showing the conventional apparatus. 1: Gas insulated switchgear (test equipment) 2: Grounded tank,
3.30jI ground wire, 4: discharge pulse sensor, 4A: discharge pulse signal, 5: external noise, 5A, 5B: noise current, 6A, 6B: discharge pulse current, 7: power transmission line,
100: antenna, 104: detection impedance, 10
4A: antenna signal, 11.111 + high frequency amplifier, 12.112: detection rectifier, 12A, 112A: output signal of detection rectifier, 13; comparison circuit, 113: judgment circuit, output signal of 13A comparison circuit, 15: integration circuit , 15
Aj integration circuit output signal, 16: A/D converter, 16A
: Output signal of A/D converter, 17; Ground, 14 Niji threshold setter, 14S Niji threshold level, 18+digital counter, 18A: Output of digital counter, 19:
Judgment means, 19A, 113A: Alarm output signal, 19B
: Judgment data output signal, 20: Alarm, 21: Recording device, 22: Microprocessor. Figure 2 Time (SeC) → Figure 3

Claims (1)

[Claims] 1) A discharge pulse sensor detects a current pulse caused by a partial discharge in the gas inside the gas insulated equipment during operation, and monitors only the partial discharge in the gas by distinguishing the current pulse from noise. a comparator circuit that outputs only a signal that exceeds a predetermined threshold value among discharge pulse signals generated by a partial discharge in the battery; a digital counter that receives the output signal of the comparator circuit and outputs the number of discharge pulses for each predetermined sample period; an integrating circuit that receives the output signal of the comparison circuit and outputs the cumulative charge value for each cycle; an A/D converter that converts the cumulative charge value into a digital signal; and a determination device that determines the cumulative charge value of the digital signal in advance. 1. A partial discharge monitoring device for gas insulated equipment, characterized in that the device comprises determining means for determining that an abnormality is occurring when the discharge pulse number exceeds a predetermined number and outputting an alarm.