CN115435893A - Method for extracting vibration signal of on-load tap-changer of transformer - Google Patents
Method for extracting vibration signal of on-load tap-changer of transformer Download PDFInfo
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- CN115435893A CN115435893A CN202211076470.7A CN202211076470A CN115435893A CN 115435893 A CN115435893 A CN 115435893A CN 202211076470 A CN202211076470 A CN 202211076470A CN 115435893 A CN115435893 A CN 115435893A
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
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Abstract
The embodiment of the invention provides a vibration signal extraction method for a transformer on-load tap-changer, and relates to the technical field of transformer on-load tap-changer state monitoring. The method comprises the steps of monitoring vibration signals on the top cover of the OLTC oil tank or the surface of the shell of the transformer oil tank, firstly, preprocessing, carrying out Fourier transform on each frame of vibration signals to obtain a signal spectrogram, dividing the spectrogram into a plurality of sub-frequency bands, calculating the energy spectrum entropy of each frame of vibration signals, and setting an energy spectrum entropy threshold and a time threshold to obtain the starting point and the ending point of each vibration signal so as to separate millisecond-level OLTC vibration signal segments from the vibration signals with the length of seconds. The method can automatically extract the OLTC vibration signals, facilitates the popularization and the use of an OLTC online monitoring technology, provides a foundation and a support for the evaluation of the OLTC mechanical state, and has good practical value.
Description
Technical Field
The invention relates to the technical field of on-load tap-changer state monitoring of transformers, in particular to a method for extracting vibration signals of an on-load tap-changer of a transformer.
Background
The transformer is a key device of a power system, an on-load tap-changer (OLTC for short) is used as a core component of the transformer which only frequently acts, plays an important role in adjusting reactive power and stabilizing grid voltage, and has important significance for the transformer in terms of operation reliability. Statistics show that the fault caused by the OLTC abnormity accounts for about 30% of the total fault of the transformer, and the OLTC fault mainly comprises a mechanical fault and an electrical fault, wherein the mechanical fault accounts for over 90%. Once mechanical failure occurs in the OLTC, the OLTC causes line tripping and loss of transmission power, and causes the transformer to be burnt out by fire, thereby causing huge economic loss and adverse social influence. Therefore, it is of great significance to detect and diagnose the mechanical state of the OLTC.
At present, an OLTC (online liquid crystal display) generally adopts a power failure maintenance mode, but the mode wastes time and labor and cannot realize online monitoring of the equipment state. The vibration method has the advantages of high sensitivity, convenience in installation, no direct electrical connection with a transformer, easiness in realizing live detection and the like, and is widely applied to power equipment state monitoring in recent years. Mechanical vibration is caused by collision and friction between parts and mechanisms such as a moving contact and a stationary contact when OLTC is switched, and a vibration signal contains a large amount of equipment state information, so that a vibration method gradually becomes a focus of attention for online monitoring of the mechanical state of the OLTC. The existing OLTC mechanical state online monitoring system generally adopts a motor current signal as trigger to synchronously acquire a vibration signal of a plurality of seconds, the time length of the vibration signal caused by the OLTC switching action of a transformer is only millisecond-level, and the OLTC mechanical state diagnosis is carried out on the premise that an OLTC vibration signal segment is extracted from the vibration signal of the plurality of seconds.
Disclosure of Invention
The invention aims to provide a vibration signal extraction method for a transformer on-load tap changer, which can provide a foundation and support for OLTC mechanical state evaluation.
Embodiments of the invention may be implemented as follows:
the invention provides a method for extracting a vibration signal of an on-load tap-changer of a transformer, which comprises the following steps:
s1: monitoring the vibration of the top cover of the OLTC oil tank or the surface of the shell of the transformer oil tank, and acquiring a vibration signal which is several seconds long;
s2: preprocessing the acquired vibration signal to obtain a vibration signal segment;
s3: fourier transform is carried out on each frame of vibration signal in the vibration signal segment to obtain a spectrogram of each frame of vibration signal;
s4: dividing the spectrogram into a plurality of sub-bands, and respectively calculating the energy of each sub-band;
s5: calculating the energy spectrum entropy of each frame of vibration signal based on the energy of each sub-frequency band;
s6: setting an energy spectrum entropy threshold H thres And a duration threshold T thres1 、T thres2 Comparing frame by frame to determine the start position and the end position of the signal;
s7: based on the start and end positions of the signal, the OLTC vibration signal segment is isolated.
In an alternative embodiment, S1 comprises:
when the OLTC performs voltage regulation operation, an OLTC online monitoring system is used for collecting vibration signals of the oil tank top cover of the OLTC or the surface of the transformer oil tank shell, wherein the OLTC online monitoring system is triggered by a motor current signal channel and synchronously collects vibration signals of several seconds.
In an alternative embodiment, S2 comprises:
and carrying out zero-mean value, windowing and frame preprocessing on the acquired vibration signals.
In an alternative embodiment, S2 comprises:
carrying out zero-mean processing on the acquired vibration signals, and removing direct-current components in the signals, wherein the method comprises the following steps:
in the formula:
to remove the averaged vibration signal, N represents the number of sampling points of the vibration signal x.
In an alternative embodiment, S2 comprises:
performing windowing and framing preprocessing on the vibration signal to obtain a vibration signal segment, wherein a frame of vibration signal at the nth moment is as follows:
x n ＝x*h(n) (2)
in the formula: x is a radical of a fluorine atom n For a sequence of x samples of the signal, h (n) is a window function.
In an alternative embodiment, in S4, the energy of each sub-band is calculated as follows:
in the formula: s. the i For the sum of the energy of the ith sub-band of each frame of vibration signal, M is the number of divided sub-bands, f j Is the amplitude of the jth frequency component in the corresponding sub-band, and K is the number of frequency components in each sub-band.
In an alternative embodiment, in S5, the calculation formula of the energy spectrum entropy of each frame of vibration signal is as follows:
in the formula, p i Probability density function for i-th sub-band of vibration signal per frame, p k And H is the energy spectrum entropy of each frame of vibration signal.
In an alternative embodiment, S6 comprises:
when the energy spectrum entropy of a certain frame signal is larger than H thres And the signal duration exceeds T thres1 Then, it is determined that the current frame is the start position of the OLTC vibration signal.
In an alternative embodiment, S6 comprises:
when the energy spectrum entropy of a certain frame signal after the signal start is detected to be less than H thres And the duration exceeds T thres2 There is still no energy spectrum entropy greater than H thres When the signal of (2) is present, it is determined that the current frame is the end position of the OLTC vibration signal.
In an alternative embodiment, in S6, H thres Set to 0.5,T thres1 Set to 5ms thres2 Set to 5ms.
The method for extracting the vibration signal of the on-load tap-changer of the transformer provided by the embodiment of the invention has the beneficial effects that:
monitoring vibration signals on the top cover of an OLTC (on-line analytical test) oil tank or the surface of a shell of a transformer oil tank, firstly carrying out preprocessing such as zero mean processing, windowing, framing and the like, carrying out Fourier transform on each frame of vibration signals to obtain a signal spectrogram, dividing the spectrogram into a plurality of sub-frequency bands, calculating the energy spectrum entropy of each frame of signals, and setting an energy spectrum entropy threshold and a time threshold to obtain the starting point and the ending point of the signals so as to separate millisecond-level OLTC vibration signal segments from the vibration signals with the length of seconds. The method can automatically extract the OLTC vibration signals, facilitates the popularization and the use of an OLTC online monitoring technology, provides a foundation and a support for the evaluation of the OLTC mechanical state, and has good practical value.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is a flowchart of a method for extracting a vibration signal of an on-load tap-changer of a transformer according to an embodiment of the present invention;
FIG. 2 is a time domain waveform diagram of the vibration signal collected in the present embodiment;
FIG. 3 (a) is a frequency spectrum diagram of a vibration signal of the transformer body in the present embodiment;
FIG. 3 (b) is a spectrum diagram of the OLTC vibration signal in this embodiment;
FIG. 4 is an energy spectrum entropy of the vibration signal in the present embodiment;
fig. 5 is an OLTC vibration signal automatically extracted in the present embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the description of the present invention, it should be noted that, if the terms "upper", "lower", "inner", "outer", etc. are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which the product of the present invention is used to usually place, it is only for convenience of description and simplification of the description, but it is not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
Furthermore, the appearances of the terms "first," "second," and the like, if any, are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.
It should be noted that the features of the embodiments of the present invention may be combined with each other without conflict.
Referring to fig. 1, the present embodiment provides a method for extracting a vibration signal of an on-load tap changer of a transformer, including the following steps:
s1: the method comprises the steps of monitoring vibration of the top cover of the OLTC oil tank or the surface of the shell of the transformer oil tank, and collecting a vibration signal which is several seconds long.
Specifically, when the OLTC performs the voltage regulation operation, the OLTC online monitoring system collects the vibration signal of the top cover of the oil tank of the OLTC or the surface of the outer shell of the oil tank of the transformer, and the OLTC online monitoring system is triggered by a motor current signal channel to synchronously collect the vibration signal x = (x =) with the length of several seconds 1 ,x 2 ,···,x N ) The vibration signal includes an OLTC vibration signal segment and a transformer body vibration signal segment.
Fig. 2 shows a time domain waveform diagram of the vibration signal acquired in this embodiment, and it can be seen that the time duration of the vibration signal acquired by the OLTC online monitoring system is 8s, the amplitude of the vibration signal is obviously increased in a time period of 5.9 to 6.1s, a cluster of impact vibration signals appears, the time period signal is an OLTC vibration signal, and the remaining time period signals are vibration signals of the transformer body.
S2: and preprocessing the acquired vibration signals to obtain vibration signal fragments.
Specifically, preprocessing such as zero mean value, windowing and framing is performed on the acquired vibration signals.
Carrying out zero-mean processing on the acquired vibration signals, and removing direct-current components in the signals, wherein the specific method comprises the following steps:
in the formula:
to remove the averaged vibration signal, N represents the number of sampling points of the vibration signal x.
Performing windowing and framing preprocessing on the vibration signal to obtain a vibration signal segment of one frame and one frame, wherein the vibration signal of one frame at the nth moment is as follows:
x n ＝x*h(n) (2)
in the formula: x is a radical of a fluorine atom n For a sequence of x samples of the signal, h (n) is a window function.
In this embodiment, the window length is 10ms, and the frame shift length is 5ms, so as to obtain the windowed and framed vibration signal segment.
S3: and carrying out Fourier transform on each frame of vibration signal in the vibration signal segment to obtain a spectrogram of each frame of vibration signal.
In the present embodiment, the frequency spectrums of the transformer body vibration signal and the OLTC vibration signal are shown in fig. 3 (a) and fig. 3 (b), respectively. It can be seen that the vibration signals of the transformer body are concentrated within 2kHz, the frequency distribution of the OLTC vibration signals is wide, a large amount of energy is distributed within the frequency range of 10 kHz-50 kHz, and the amplitude of each frequency component is larger than that of the vibration signals of the transformer body.
S4: the spectrogram is divided into a plurality of sub-bands, and the energy of each sub-band is calculated respectively.
Specifically, the calculation formula of the energy of each sub-band is as follows:
in the formula: s i For the sum of the energy of the ith sub-band of each frame of vibration signal, M is the number of divided sub-bands, f j Is the amplitude of the jth frequency component in the corresponding sub-band, and K is the number of frequency components in each sub-band.
In this embodiment, the frequency spectrum is divided into 10 sub-bands, and the energy of each sub-band of each frame of the vibration signal is obtained through formula (3).
S5: and calculating the energy spectrum entropy of each frame of vibration signal based on the energy of each sub-frequency band.
Specifically, the calculation formula of the energy spectrum entropy of each frame of vibration signal is as follows:
in the formula: p is a radical of i Probability density function for i-th sub-band of vibration signal per frame, p k H is the energy spectrum entropy of each frame vibration signal as a probability density function of the kth sub-band of each frame vibration signal.
The energy spectrum entropy of the vibration signal in this embodiment is shown in fig. 4, and it can be seen that the energy spectrum entropy of the bulk vibration signal is small, the energy spectrum entropy of the OLTC vibration signal is large, and the difference between the two is obvious.
S6: setting an energy spectrum entropy threshold H thres And a duration threshold T thres1 、T thres2 And comparing frame by frame to determine the starting position and the ending position of the signal.
Specifically, when the entropy of the energy spectrum of a certain frame signal is greater than H thres The current frame may then be the start position of the signal. Since the noise is usually sudden and not long in duration, a signal duration threshold T is set thres1 When the signal duration exceeds T thres1 When so, the OLTC vibration signal is considered to start. Energy spectrum entropy threshold H in this embodiment thres Set to 0.5, signal duration threshold T thres1 Set to 5ms.
When the energy spectrum entropy of a certain frame signal after the signal start is detected to be less than H thres The current frame may be the end position of the signal. Since the OLTC vibration signal has a plurality of impact sections, the time threshold T is set based on the duration between the impact sections thres2 When the duration exceeds T thres2 No energy spectrum entropy is larger than H within time thres If the signal of (2) appears, the OLTC vibration signal is considered to be ended. Time threshold T in this embodiment thres2 Set to 5ms.
S7: based on the start and end positions of the signal, the OLTC vibration signal segment is isolated.
Fig. 5 shows that the OLTC vibration signal is automatically extracted in this embodiment, and it can be seen that the OLTC vibration signal can be accurately and effectively extracted by the method.
The method for extracting the vibration signal of the on-load tap-changer of the transformer has the beneficial effects that:
the OLTC online monitoring system monitors vibration signals on the top cover of an OLTC oil tank or the surface of a shell of a transformer oil tank, firstly carries out preprocessing such as zero mean processing, windowing and framing to carry out Fourier transform on each frame of vibration signals to obtain a signal spectrogram, divides the spectrogram into a plurality of sub-frequency bands, calculates the energy spectrum entropy of each frame of vibration signals, and obtains the starting point and the ending point of the signals by setting an energy spectrum entropy threshold and a time threshold to realize separation of millisecond-level OLTC vibration signal segments from the vibration signals with the length of several seconds. The method can automatically extract OLTC vibration signals, facilitates popularization and use of an OLTC online monitoring technology, provides basis and support for OLTC mechanical state evaluation, and has good practical value.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A transformer on-load tap-changer vibration signal extraction method is characterized by comprising the following steps:
s1: monitoring the vibration of the top cover of the OLTC oil tank or the surface of the shell of the transformer oil tank, and acquiring a vibration signal which is several seconds long;
s2: preprocessing the acquired vibration signal to obtain a vibration signal segment;
s3: fourier transform is carried out on each frame of vibration signal in the vibration signal segment to obtain a spectrogram of each frame of vibration signal;
s4: dividing the spectrogram into a plurality of sub-frequency bands, and respectively calculating the energy of each sub-frequency band;
s5: calculating the energy spectrum entropy of each frame of vibration signal based on the energy of each sub-frequency band;
s6: setting an energy spectrum entropy threshold H thres And a duration threshold T thres1 、T thres2 Comparing frame by frame, and determining the starting position and the ending position of the signal;
s7: based on the start position and the end position of the signal, an OLTC vibration signal segment is isolated.
2. The method for extracting the vibration signal of the on-load tap-changer of the transformer according to claim 1, wherein the step S1 comprises the following steps:
when OLTC carries out the pressure regulating operation, utilize OLTC on-line monitoring system to gather the vibration signal on OLTC's oil tank top cap or transformer tank shell surface, wherein, OLTC on-line monitoring system is triggered by motor current signal passageway, gathers the long vibration signal of several seconds in step.
3. The method for extracting the vibration signal of the on-load tap-changer of the transformer according to claim 1, wherein the step S2 comprises the following steps:
and carrying out zero-mean value, windowing and frame preprocessing on the acquired vibration signals.
4. The method for extracting the vibration signal of the on-load tap-changer of the transformer according to claim 3, wherein S2 comprises:
carrying out zero-mean processing on the acquired vibration signals, and removing direct-current components in the signals, wherein the method comprises the following steps:
in the formula:
to remove the averaged vibration signal, N represents the number of sampling points of the vibration signal x.
5. The method for extracting the vibration signal of the on-load tap-changer of the transformer according to claim 3, wherein S2 comprises:
performing windowing and framing preprocessing on the vibration signal to obtain the vibration signal segment, wherein a frame of vibration signal at the nth moment is as follows:
x n ＝x*h(n) (2)
in the formula: x is the number of n For a sequence of x samples of the signal, h (n) is a window function.
6. The method for extracting vibration signal of on-load tap-changer of transformer according to claim 3, characterized in that in S4, the energy of each sub-band is calculated as follows:
in the formula: s. the i For the sum of the energy of the ith sub-band of each frame of vibration signal, M is the number of divided sub-bands, f j Is the amplitude of the jth frequency component in the corresponding sub-band, and K is the number of frequency components in each sub-band.
7. The method for extracting vibration signals of on-load tap-changer of transformer according to claim 1, wherein in S5, the calculation formula of the energy spectrum entropy of each frame of vibration signals is as follows:
in the formula: p is a radical of i Probability density function for i-th sub-band of vibration signal per frame, p k And H is the energy spectrum entropy of each frame of vibration signal.
8. The method for extracting the vibration signal of the on-load tap-changer of the transformer according to claim 1, wherein S6 comprises:
when the energy spectrum entropy of a certain frame signal is larger than H thres And the signal duration exceeds T thres1 Then, the current frame is determined to be the start position of the OLTC vibration signal.
9. The method for extracting the vibration signal of the on-load tap-changer of the transformer according to claim 8, wherein S6 comprises:
when the energy spectrum entropy of a certain frame signal after the signal start is detected to be less than H thres And the duration exceeds T thres2 There is still no energy spectrum entropy greater than H thres When the signal of (2) is present, it is determined that the current frame is the end position of the OLTC vibration signal.
10. The method of claim 8, wherein in S6, H is H thres Set to 0.5,T thres1 Set at 5ms thres2 Set to 5ms.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117110587A (en) * | 2023-10-25 | 2023-11-24 | 国网四川省电力公司超高压分公司 | Method and system for on-line monitoring abnormality alarm of dissolved gas in oil |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117110587A (en) * | 2023-10-25 | 2023-11-24 | 国网四川省电力公司超高压分公司 | Method and system for on-line monitoring abnormality alarm of dissolved gas in oil |
| CN117110587B (en) * | 2023-10-25 | 2024-01-23 | 国网四川省电力公司超高压分公司 | Method and system for on-line monitoring abnormality alarm of dissolved gas in oil |
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