JP2831042B2 - Partial discharge monitoring device for oil-immersed transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the harmfulness of partial discharge in oil generated inside an oil-immersed transformer by determining the magnitude and duration of a partial discharge pulse and the presence or absence of an ultrasonic signal. The present invention relates to a partial discharge monitoring device that determines and notifies an abnormality.

[Prior art] When a so-called partial discharge in oil occurs, in which insulating oil is locally broken down in an oil-immersed transformer, a discharge pulse generated at the point where the discharge occurs occurs via a winding or a ground capacitance of the winding. The ultrasonic wave generated when the insulating oil is vaporized by the heat generated by the discharge propagates through the insulating oil and vibrates the tank wall. Therefore, a discharge pulse sensor such as a Rogowski coil is provided on the ground wire of the tank to detect discharge pulses, and an ultrasonic sensor is attached to the tank wall to convert ultrasonic waves into electric signals and detect them (hereinafter referred to as sound signals). It is widely known that when a discharge pulse and a sound signal are detected with a time difference required for propagation of ultrasonic waves, it is determined that a partial discharge in oil has occurred in the oil-immersed transformer. Further, a method has been attempted in which a plurality of ultrasonic sensors are arranged at different positions on a tank wall to determine the position of occurrence of partial discharge in oil based on the detection time difference and the ultrasonic oil-in-propagation transmission rate.

These conventional methods complementarily improve the reliability of detection by treating the partial discharge phenomenon in oil as two types of physical quantities having different properties. However, the detection of discharge pulses suffers from external noise. Therefore, there is a problem that discrimination between a discharge pulse and external noise requires special experience and noise removal technology. Also, since most of the generated ultrasonic waves are reflected on the inner wall of the tank, the acoustic force transmitted through the tank wall and incident on the ultrasonic sensor is small. There is a problem of susceptibility.

[Problems to be solved by the invention]

As the external noise that interferes with the detection of the discharge pulse, a comparison can be made between external noise such as a broadcast wave or communication wave in which a transmission line or the like functions as an antenna and enters a transformer, or commutation noise generated by a thyristor converter. It is considered that external noise at a very low level and switching noise at a high level such as switching surge generated by switching of a circuit breaker, a switch, a vacuum switch, or the like provided in a power system. Focusing on the fact that the former extrinsic noise has a frequency region that is a valley of its frequency components, the detection frequency of the discharge pulse is set to 1.
It has already been proposed by the present applicant that the detection can be greatly reduced by detecting only from 8 MHz to 3.8 MHz, preferably from 2.8 MHz to 3.1 MHz. However, the latter switching noise has a remarkably high noise level, and its occurrence cannot be predicted. Therefore, there is no way to avoid it. There is a problem that high monitoring cannot be performed.

An object of the present invention is to improve the monitoring accuracy by avoiding the influence of a high level switching surge by taking into account the level of a discharge pulse that adversely affects the internal insulation of a transformer and its continuity.

[Means for solving the problem]

In order to solve the above-mentioned problems, according to the present invention, a current pulse and an ultrasonic wave generated by a partial discharge in an oil inside an oil-immersed transformer during operation are detected by a discharge pulse sensor and an ultrasonic sensor, whereby the oil In a monitoring system in which partial discharge is distinguished from noise, when a partial discharge in oil occurs at a frequency of several or more per second, a peak value holding circuit that converts a discharge pulse into a continuous waveform overlapping each other and outputs the converted pulse and a sound. A peak value hold circuit for the signal,
A pair of comparison circuits that receive each output signal via a photocoupler circuit and output only a signal exceeding a threshold determined by an external noise level, and determine the instantaneous values of the output discharge pulse signal and the sound signal of each of the pair of comparison circuits A pair of signals that convert to digital signals every sampling period
An A / D converter; calculating means for determining the duration of the continuous waveform, the accumulated charge value, and the number of sound signal data from the output digital signals of the pair of A / D converters; When the accumulated charge exceeds a predetermined determination level and there is sound signal data of 1 or more, or when there is no sound signal but the accumulated charge value exceeds a predetermined level, the partial discharge in oil reaches a harmful continuous period. Judgment means for judging that a warning has been issued and instructing an alarm output.

[Action]

The above means is that the partial discharge in AC oil is initially 10 seconds to several tens
An intermittent period in which discharges occur intermittently at long intervals of 0 seconds, a continuous period in which discharges occur at a frequency of several to several tens per second, and eventually the discharge extends into the oil-immersed insulating paper and decomposes The process advances to an erosion period in which the air-immersed insulating paper is eroded while generating a high frequency air discharge pulse in the gas. During this period, the magnitude Q and the frequency N of the discharge pulse sequentially increase, and While the sound wave level was also designed to be higher, the conventional method detected the discharge pulse and the sound signal early in the intermittent period and grasped the detection time difference between the two, etc. In the device of the present invention, the harmfulness of partial discharge in oil can be reduced by grasping the discharge pulse and the sound signal in which the Q value and the N value have increased in the continuous period as a cumulative value within a predetermined time period, for example, within about 1 minute. Based monitoring possible To become, and the discrimination between sporadic switching noise does not penetrate only at a much lower frequency than the discharge pulse can be facilitated.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a signal waveform diagram of a main part of the embodiment, and FIG. 3 is a flowchart showing judgment means of the embodiment. In the figure, a tank 2 of a test oil-filled transformer 1 is provided with, for example, a Rogowski coil as a discharge pulse sensor 4 through which a ground wire 3 penetrates, and an ultrasonic sensor 5 attached in close contact with the tank outer wall. Provided. The discharge pulse 4A detected by the discharge pulse sensor 4 has a specific frequency component tuned and amplified by a narrow-band high-frequency amplifier circuit 11 having a center frequency of, for example, 3 MHz, and becomes a unipolar envelope pulse by a detection and rectification circuit 12, and its peak is obtained. The value is held by the peak value hold circuit 13 and its wave tail is stretched to an attenuation time constant of the order of 100 ms, and V
The current value is converted into a current value suitable for E / O conversion by the / i conversion circuit 14, and transmitted to the monitoring place as an optical signal by the E / O conversion circuit 15A and the optical fiber 15B of the photocoupler unit 15, and the O / E conversion circuit 15C
The discharge pulse 16S is converted to an electric signal by the comparator circuit 16 having the threshold setting unit 17 and exceeding the threshold level 17S.
Only output. The threshold level 17S is, for example, 200
0PC is set to a level corresponding to 0PC, high-frequency noise and commutation noise as external noise reduced to below this level are removed, and the setting of the threshold level 17S is known to the winding of the transformer 1. It is calibrated in advance by injecting a calibration charge.

On the other hand, the sound signal 5A detected by the ultrasonic sensor 5 and converted into an electric pulse is amplified by the sound signal amplifying circuit 31, and then the peak value hold circuit 33, V / i configured similarly to the discharge pulse side.
The signal is sent to the comparison circuit 36 via the conversion circuit 34 and the photocoupler circuit 35, and only the sound signal 36S exceeding the set threshold level 37S of the threshold setting device 37 is output, for example, the ultrasonic noise of the circulating pump of the transformer. Etc. are removed.

Reference numerals 21 and 22 denote a pair of A / D converters arranged on the entrance side of the microprocessor 20, and the A / D converter 21 converts the instantaneous value of the output discharge pulse signal 16S of the comparison circuit 16 into a sampling period of the order of several tens of milliseconds. It is converted into a digital signal 21S once every τ and output, and the A / D converter 22 converts the instantaneous value of the output sound signal 36S of the comparison circuit 36 into a digital signal 22S once every sampling period τ as described above. Output.

FIG. 2 is a time chart showing a state in which the discharge pulse and the sound signal are converted into a digital signal in the embodiment apparatus. The oil corresponding to the continuous period generated in the oil-immersed transformer 1 by the operation of the discharge pulse sensor 4 is shown. It shows a state where a middle partial discharge is detected and a discharge pulse signal 4A is output. Since oil partial discharge during the continuous period repeats discharge at a frequency of about several ten per second several, P ₆ from P ₁ at intervals of about once every several cycles from one cycle of the voltage waveform 1A of the transformer 1 Is detected. Since the discharge pulse signal 4A its wave tail peak value hold circuit 13 is stretched about the decay time constant 100 mS, the pulse P ₁ as output signal 16S FIG comparison circuit 16 having a threshold level 17S, P ₂ , P ₃
... wave tail has overlap with one another, such as, rising at time t _0, the discharge pulse signal 16S has a series of waveforms which falls continuously at t _n to decrease the threshold level 17S. A / D converter 21 time t ₀ the instantaneous value of the discharge pulse signal 16S is
Is converted into a digital signal once every sampling period τ of the order of several tens of milliseconds from the starting point. In the figure, the instantaneous value of a series of signals 16S (actually a voltage value, but Q Can be regarded as values) Q ₁ , Q ₂ ,
Q ₃ … Q ₆ are sampled and held and each is a digital signal
Converted to 21S.

On the other hand, the ultrasonic wave generated simultaneously with the discharge pulse signal 4A is detected by the ultrasonic sensor 5 with a delay of propagation time Δt in oil, and the waveform of the output sound signal 36S of the comparison circuit 36 is the number of sampling periods τ as shown in the figure. About twice the threshold level
Exhibits the following become waveform 37S, the A / D converter 22 is the instantaneous value V _1, V _2, V ₃ is converted into a digital signal 22S.

Digital signal 21S is _{Q 1, Q 2, Q 3} ... Q 6 like the amount of charge accumulated value continuously by the operation unit 23 at a predetermined time, for example several tens of seconds is digitally converted sampled discharge charge shown in Figure 1
The product τ (ΣQ _i ) of the sum of the Q _i values ΣQ _{i and the} sampling period τ is determined as the cumulative value of the continuous partial discharge Q in the oil. Further, the cumulative time calculating means 24 calculates the product N · τ of the number N of the digital signals 21S continuously sampled within one minute and the sampling period τ as the cumulative duration of the continuous partial discharge in oil. . Further, the sound signal counting means 25
Sound signal sampled and converted digitally for 22 minutes
The number n of S is counted.

The judging means 26 judges the harmfulness of the partial discharge in the continuous oil with a judging cycle of several tens of seconds. As shown in the flowchart of FIG.
Q _i ) The value exceeds a predetermined level A, the N · τ value obtained by the arithmetic means 24 exceeds the predetermined level B, and the sound signal counting means 25
When the sound signal count value is 1 or more, it is determined that partial discharge in oil has occurred continuously in the oil-immersed transformer, and the output of an abnormality alarm is commanded to the alarm 27, and the determination data is output. Output to the recording device 28. Further, when the τ (ΣQ _i ) value reaches a higher C level even without a sound signal, it is determined that there is a possibility that the erosion period has progressed with bubble discharge, and an abnormality is notified. Furthermore, τ (Σ
Q _i ) value exceeds the A level but the N · τ value is less than the B level, and if there is a sound signal, it is determined that this is due to partial discharge in oil and an abnormality is notified. in this case,
Since the magnitude (Q value) of the spontaneous switching noise is significantly large and the wave tail is elongated, τ (ΣQ _i )
Although the value may exceed the A level, the switching noise does not accompany the sound signal, and thus the switching noise and the harmful discharge can be determined by the above determination. Note that τ
(ΣQ _i ) The value is in the range from A level to C level,
If the N · τ value exceeds the B level but there is no sound signal, re-determination is instructed, and the above determination is repeated based on new data for several tens of seconds.

Judgment levels A, B, C, etc. vary depending on the magnitude of external noise or switching noise that enters the test transformer,
The A level is about twice or more the threshold signal 17S, the B level is about 10 times or more the sampling period τ, and the C level is about 5 to 10 times the threshold level 17S.
That is, if the level of the threshold signal 17S is set to the equivalent of the apparent discharge charge of 2000PC by injection charge calibration of the known charge, the true discharge charge inside the transformer is generally considered to be about 5 times the order of 10,000 PC. ing. Therefore, in the determination of the A level, the determination can be made by capturing the state of the initial stage of the continuous period in which about several to ten partial discharges in oil of the order of 10,000 to 20,000 PCs occur every second. Also, C
In the level judgment, partial discharges in oil of the order of tens of thousands of PCs per second
The determination is made by capturing a state further advanced in a continuous period in which about 10 occurrences occur, and in this state, the duration N
-Since the τ value becomes longer, it is possible to discriminate the switching noise with high accuracy without the aid of the sound signal. At the stage where the sound signal is detected without the accumulated time N · τ having reached the B level, if it is considered that there is still room for the harmfulness judgment, a re-judgment is instructed, and the progress of the subsequent discharge It may be configured to determine the abnormality depending on the situation.

In the embodiment, the output signals of the comparison circuits 16 and 36 are A / D
Although an example in which the signal is converted and processed by the microprocessor 20 is shown, it is assumed that the test transformer 1 is installed in an unmanned substation, for example, and that the monitoring is performed in a distant substation or power station. However, it is configured to facilitate data transmission, and needless to say, it may be configured to perform analog signal processing when unnecessary.

〔The invention's effect〕

As described above, according to the present invention, the analog signal circuit portion is configured so that the peak value of the discharge pulse signal and the sound signal is held by the peak value hold circuit, the wave tail length is extended, and a threshold value is provided in the comparison circuit to remove external noise. Configured. As a result, during the continuous period of partial discharge in oil refueling, in which several to several tens of discharges occur per second, a series of waveforms in which the tails of the discharge pulse signals overlap each other, preventing switching noise that intrudes sporadically Since the duration is much longer than that, it is possible to discriminate the switching pulse from the switching noise which cannot be avoided conventionally because of the high noise level. Therefore, the instantaneous values of the discharge pulse signal and the sound signal are converted into digital signals at a sampling period τ of several tens of milliseconds, and the time product τ (Q _i ) of the accumulated charge N 累積 τ and the count value of the sound signal are calculated as By determining the harmfulness of partial discharge in continuous oil by determining seconds as a determination cycle, high-level switching noise that could not be avoided conventionally can be discriminated by the accumulated time N · τ and the presence or absence of a sound signal, It is possible to provide a partial discharge monitoring device for an oil-immersed transformer that can perform abnormality monitoring based on the harmfulness of partial discharge in oil based on the time product of the accumulated charges and the accumulated time. Compared to the conventional method of detecting partial discharges in oil during intermittent periods and calculating the detection time difference from the sound signal, etc., detection is performed in a continuous period in which the amount of discharge charge and the frequency of occurrence are high, so detection of discharge pulses and sound signals In addition to the sensitivity, there is an advantage that discrimination from external noise is facilitated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a time chart of the main part showing the operation of the embodiment, and FIG. 3 is a flowchart showing the procedure for determining the embodiment. 1: oil-filled transformer, 4: discharge pulse sensor, 5: ultrasonic sensor,
11,31: amplifier circuit, 13,33: peak value hold circuit, 15,35:
Photocoupler block diagram, 16, 36: comparison circuit, 20: microprocessor, 21, 22: A / D converter, 23, 24, 25: arithmetic means, 2
6: judgment means, 4A: discharge pulse, 16S, 36S: output signal of comparison circuit, 17S, 37S: threshold level, 21S, 22S: digital signal, τ: sampling period.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Kawajiri 1-1-1, Tanabe-shinda, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. Examiner Yoshiyuki Shimonaka (56) References JP-A-2-227657 (JP) JP-A-2-22569 (JP, A) JP-A-62-194475 (JP, A) JP-A-60-69570 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) G01R 31/12 G01R 31/00

Claims (1)

(57) [Claims] 1. A discharge pulse sensor and an ultrasonic sensor detect a current pulse and an ultrasonic wave generated by a partial discharge in oil inside an oil-immersed transformer during operation to monitor the partial discharge in oil from noise. In the thing, when the partial discharge in oil occurs at a frequency of several or more occurrences per second, a peak value hold circuit and a peak value hold circuit of a sound signal that convert and output a discharge pulse into a continuous waveform having an overlap with each other, and And a pair of comparison circuits that receive only the signal exceeding a threshold determined by the external noise level via a photocoupler circuit, and output instantaneous values of the output discharge pulse signal and the sound signal of each of the pair of comparison circuits to a predetermined value. A pair of A / D converters that convert to digital signals at each sampling period, and a pair of A / D converter output digital signals Calculating means for calculating the duration of the continuous waveform, the accumulated charge value, and the number of sound signal data, respectively, and determining whether the duration value and the accumulated charge amount of the calculating means exceed a predetermined determination level and there is one or more sound signal data. Or a judgment means for judging that the partial discharge in oil has reached a harmful continuous period when there is no sound signal but the accumulated charge value exceeds a higher predetermined level, and instructing an alarm output. A partial discharge monitoring device for an oil-filled transformer.