Vibration signal extraction method for transformer on-load tap changer

Abstract

The embodiment of the present invention provides a method for extracting vibration signals of an on-load tap changer of a transformer, and relates to the technical field of transformer on-load tap changer status monitoring. The method monitors the vibration signals on the top cover of the OLTC oil tank or the surface of the transformer oil tank shell. First, through preprocessing, a Fourier transform is performed on each frame of the vibration signal to obtain a signal spectrum diagram, and the spectrum diagram is divided into multiple sub-bands and the energy spectrum entropy of each frame of the signal is calculated. The starting point and end point of the signal are obtained by setting the energy spectrum entropy threshold and the time threshold, so as to separate the millisecond-level OLTC vibration signal fragments from the vibration signal of several seconds. The method can automatically realize the extraction of OLTC vibration signals, facilitate the promotion and use of OLTC online monitoring technology, provide a basis and support for OLTC mechanical status assessment, and has good practical value.

Description

Technical Field

[0001] The invention relates to the technical field of transformer on-load tap changer state monitoring, and in particular to a method for extracting a vibration signal of a transformer on-load tap changer. Background Art

[0002] Transformers are key equipment in power systems. On-load tap-changers (OLTCs) are the only core components in transformers that frequently operate. They play an important role in regulating reactive power and stabilizing grid voltage. Their operational reliability is of great significance to transformers. Statistics show that faults caused by OLTC anomalies account for about 30% of total transformer faults. OLTC faults mainly include mechanical faults and electrical faults, of which mechanical faults account for more than 90%. Once a mechanical fault occurs in OLTC, it may cause line tripping and loss of transmission power at the least, or even cause the transformer to catch fire and burn, causing huge economic losses and adverse social impacts. Therefore, it is of great significance to detect and diagnose the mechanical status of OLTCs.

[0003] At present, OLTC generally adopts the method of power outage maintenance, but this method is time-consuming and labor-intensive and cannot realize online monitoring of equipment status. The vibration method has the advantages of high sensitivity, easy installation, no direct electrical connection with the transformer, and easy to realize live detection. It has been widely used in power equipment status monitoring in recent years. When OLTC switches, the collision and friction between the moving and static contacts and other components will cause mechanical vibration, and the vibration signal contains a large amount of equipment status information. Therefore, the vibration method has gradually become a hot topic for online monitoring of OLTC mechanical status. The existing OLTC mechanical status online monitoring system generally uses the motor current signal as a trigger and synchronously collects vibration signals of several seconds. The vibration signal caused by the transformer OLTC switching action is only in the millisecond level. The premise of OLTC mechanical status diagnosis is to extract OLTC vibration signal segments from the vibration signal of several seconds. The manual extraction method is time-consuming and labor-intensive, and requires professionals to complete, which is not convenient for the promotion and use of this technology. However, there are few reports on the method of locating and extracting OLTC vibration signals. Summary of the invention

[0004] The purpose of the present invention includes providing a method for extracting vibration signals of an on-load tap changer of a transformer, which can provide a basis and support for OLTC mechanical condition assessment.

[0005] The embodiments of the present invention can be implemented as follows:

[0006] The present invention provides a method for extracting a vibration signal of an on-load tap changer of a transformer, and the method for extracting a vibration signal of an on-load tap changer of a transformer comprises:

[0007] S1: Monitor the vibration of the OLTC tank top cover or transformer tank shell surface and collect a vibration signal of several seconds;

[0008] S2: preprocessing the collected vibration signal to obtain a vibration signal segment;

[0009] S3: performing Fourier transform on each frame of the vibration signal in the vibration signal segment to obtain a frequency spectrum of each frame of the vibration signal;

[0010] S4: Divide the spectrum graph into multiple sub-bands and calculate the energy of each sub-band respectively;

[0011] S5: Calculate the energy spectrum entropy of each frame of vibration signal based on the energy of each sub-frequency band;

[0012] S6: Set the energy spectrum entropy threshold H thres And duration threshold T thres1 , T thres2 , compare frame by frame to determine the start and end positions of the signal;

[0013] S7: Separate the OLTC vibration signal segment based on the start position and the end position of the signal.

[0014] In an optional embodiment, S1 includes:

[0015] When the OLTC is performing voltage regulation operation, the OLTC online monitoring system is used to collect vibration signals on the OLTC oil tank top cover or the surface of the transformer oil tank shell. The OLTC online monitoring system is triggered by the motor current signal channel and synchronously collects vibration signals of several seconds in length.

[0016] In an optional embodiment, S2 includes:

[0017] The collected vibration signal is preprocessed by zero mean, windowing and framing.

[0018] In an optional embodiment, S2 includes:

[0019] The collected vibration signal is processed with zero mean to remove the DC component in the signal. The method is as follows:

[0020]

[0021] Where: is the vibration signal after removing the mean, and N represents the number of sampling points of the vibration signal x.

[0022] In an optional embodiment, S2 includes:

[0023] The vibration signal is preprocessed by windowing and framing to obtain vibration signal segments, where a frame of vibration signal at the nth moment is:

[0024] x n =x*h(n) (2)

[0025] Where: x n is the sampling sequence of signal x, and h(n) is the window function.

[0026] In an optional implementation manner, in S4, the energy of each sub-band is calculated as follows:

[0027]

[0028] Where: S i is the energy sum of the ith sub-band of each frame of vibration signal, M is the number of sub-bands, and 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.

[0029] In an optional implementation, in S5, the energy spectrum entropy of each frame of vibration signal is calculated as follows:

[0030]

[0031]

[0032] In the formula, p i is the probability density function of the ith sub-band of each frame vibration signal, p k is the probability density function of the kth sub-band of each frame of vibration signal, and H is the energy spectrum entropy of each frame of vibration signal.

[0033] In an optional embodiment, S6 includes:

[0034] When the energy spectrum entropy of a frame signal is greater than H thres , and the signal duration exceeds T thres1 , it is determined that the current frame is the starting position of the OLTC vibration signal.

[0035] In an optional embodiment, S6 includes:

[0036] When the energy spectrum entropy of a frame signal after the signal starts 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 appears, it is determined that the current frame is the end position of the OLTC vibration signal.

[0037] In an optional embodiment, in S6, H thres Set to 0.5, Tthres1 Set to 5ms, T thres2 Set to 5ms.

[0038] The beneficial effects of the transformer on-load tap changer vibration signal extraction method provided by the embodiment of the present invention include:

[0039] By monitoring the vibration signal of the OLTC oil tank top cover or the transformer oil tank shell surface, firstly, through zero mean processing, windowing and framing and other preprocessing, the Fourier transform of each frame of vibration signal is obtained, the spectrum is divided into multiple sub-bands and the energy spectrum entropy of each frame signal is calculated. By setting the energy spectrum entropy threshold and time threshold to obtain the starting point and end point of the signal, the millisecond-level OLTC vibration signal fragment is separated from the vibration signal of several seconds. This method can automatically realize the extraction of OLTC vibration signals, facilitate the promotion and use of OLTC online monitoring technology, provide the basis and support for OLTC mechanical condition assessment, and has good practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 A flow chart of a method for extracting vibration signals of an on-load tap changer of a transformer provided in an embodiment of the present invention;

[0042] Figure 2 is a time domain waveform diagram of the vibration signal collected in this embodiment;

[0043] FIG3( a) is a spectrum diagram of the transformer body vibration signal in this embodiment;

[0044] FIG3( b ) is a spectrum diagram of the OLTC vibration signal in this embodiment;

[0045] Figure 4 is the energy spectrum entropy of the vibration signal in this embodiment;

[0046] Figure 5 It is the OLTC vibration signal automatically extracted in this embodiment. DETAILED DESCRIPTION

[0047] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0048] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0050] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0051] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0052] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0053] Please refer to Figure 1 This embodiment provides a method for extracting a vibration signal of an on-load tap changer of a transformer, comprising the following steps:

[0054] S1: Monitor the vibration of the OLTC tank top cover or transformer tank shell surface and collect a vibration signal of several seconds.

[0055] Specifically, when the OLTC performs voltage regulation, the OLTC online monitoring system collects vibration signals from the oil tank cover of the OLTC or the surface of the transformer oil tank shell. The OLTC online monitoring system is triggered by the motor current signal channel and synchronously collects vibration signals x=(x 1 ,x 2 ,···,x N), the vibration signal includes an OLTC vibration signal segment and a transformer body vibration signal segment.

[0056] The time domain waveform of the vibration signal collected in this embodiment is as follows: Figure 2 As shown, it can be seen that the vibration signal collected by the OLTC online monitoring system lasts for 8 seconds. The amplitude of the vibration signal increases significantly in the time period of 5.9 to 6.1 seconds, and a cluster of impact vibration signals appears. The signal in this time period is the OLTC vibration signal, and the signals in the remaining time periods are the transformer body vibration signals.

[0057] S2: Preprocess the collected vibration signal to obtain vibration signal segments.

[0058] Specifically, the collected vibration signal is preprocessed by zero mean, windowing and frame division.

[0059] The collected vibration signal is processed with zero mean to remove the DC component in the signal. The specific method is as follows:

[0060]

[0061] Where: is the vibration signal after removing the mean, and N represents the number of sampling points of the vibration signal x.

[0062] The vibration signal is preprocessed by windowing and framing to obtain vibration signal fragments frame by frame. The vibration signal of a frame at the nth moment is:

[0063] x n =x*h(n) (2)

[0064] Where: x n is the sampling sequence of signal x, and h(n) is the window function.

[0065] In this embodiment, the window length is 10 ms, the frame shift length is 5 ms, and the vibration signal segments after windowing and framing are obtained.

[0066] S3: Perform Fourier transform on each frame of the vibration signal in the vibration signal segment to obtain a frequency spectrum diagram of each frame of the vibration signal.

[0067] In this embodiment, the spectrum diagrams of the transformer body vibration signal and the OLTC vibration signal are shown in Figure 3(a) and Figure 3(b) respectively. It can be seen that the transformer body vibration signal is concentrated within 2kHz, while the frequency distribution of the OLTC vibration signal is wider, with a large amount of energy distributed in the frequency range of 10kHz to 50kHz, and the amplitude of each frequency component is greater than that of the transformer body vibration signal.

[0068] S4: Divide the spectrum graph into multiple sub-bands, and calculate the energy of each sub-band respectively.

[0069] Specifically, the energy calculation formula for each sub-band is as follows:

[0070]

[0071] Where: S i is the energy sum of the ith sub-band of each frame of vibration signal, M is the number of sub-bands, and 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.

[0072] In this embodiment, the spectrum is divided into 10 sub-bands, and the energy of each sub-band of each frame of vibration signal is obtained by formula (3).

[0073] S5: Based on the energy of each sub-frequency band, calculate the energy spectrum entropy of each frame of the vibration signal.

[0074] Specifically, the calculation formula of the energy spectrum entropy of each frame of vibration signal is as follows:

[0075]

[0076]

[0077] Where: p i is the probability density function of the ith sub-band of each frame vibration signal, p k is the probability density function of the kth sub-band of each frame of vibration signal, and H is the energy spectrum entropy of each frame of vibration signal.

[0078] The energy spectrum entropy of the vibration signal in this embodiment is as follows: Figure 4 As shown, it can be seen that the energy spectrum entropy value of the body vibration signal is small, and the energy spectrum entropy of the OLTC vibration signal is large, and the difference between the two is obvious.

[0079] S6: Set the energy spectrum entropy threshold H thres And duration threshold T thres1 , T thres2 , compare frame by frame to determine the start and end positions of the signal.

[0080] Specifically, when the energy spectrum entropy of a frame signal is greater than H thres When , the current frame may be the start position of the signal. Since noise is usually sudden and does not last long, the signal duration threshold T is set. thres1 , when the signal duration exceeds T thres1 When , it is considered that the OLTC vibration signal starts. In this embodiment, the energy spectrum entropy threshold H thres Set to 0.5, signal duration threshold T thres1 Set to 5ms.

[0081] When the energy spectrum entropy of a frame signal after the signal starts is detected to be less than H thres When , the current frame may be the end position of the signal. Since the OLTC vibration signal has multiple impact segments, the time threshold T is set based on the duration between the impact segments. thres2 , when the duration exceeds T thres2 There is still no energy spectrum entropy greater than H within this time. thres When the signal appears, it is considered that the OLTC vibration signal ends. thres2 Set to 5ms.

[0082] S7: Separate the OLTC vibration signal segment based on the start position and the end position of the signal.

[0083] The OLTC vibration signal automatically extracted in this embodiment is as follows Figure 5 As shown, it can be seen that this method can accurately and effectively extract the OLTC vibration signal.

[0084] The beneficial effects of the transformer on-load tap changer vibration signal extraction method provided in this embodiment include:

[0085] The OLTC online monitoring system monitors the vibration signal of the OLTC tank top cover or the transformer tank shell surface. First, through zero mean processing, windowing and framing and other pre-processing, the Fourier transform of each frame of vibration signal is obtained, and the spectrum is divided into multiple sub-bands and the energy spectrum entropy of each frame signal is calculated. The starting point and end point of the signal are obtained by setting the energy spectrum entropy threshold and time threshold, and the millisecond-level OLTC vibration signal fragments are separated from the vibration signal of several seconds. This method can automatically realize the extraction of OLTC vibration signals, facilitate the promotion and use of OLTC online monitoring technology, provide a basis and support for OLTC mechanical condition assessment, and has good practical value.

[0086] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for extracting vibration signals of transformer on-load tap changer, It is characterized in that The transformer on-load tap changer vibration signal extraction method comprises: S1: Monitor the vibration of the OLTC tank top cover or transformer tank shell surface and collect a vibration signal of several seconds; S2: preprocessing the collected vibration signal to obtain a vibration signal segment; S3: performing Fourier transform on each frame of the vibration signal in the vibration signal segment to obtain a frequency spectrum of each frame of the vibration signal; S4: Divide the spectrum graph into a plurality of sub-bands, and calculate the energy of each of the sub-bands respectively; S5: Calculating the energy spectrum entropy of each frame of the vibration signal based on the energy of each sub-frequency band; S6: Setting the energy spectrum entropy threshold H thres and duration threshold T thres1 , T thres2 , compare frame by frame to determine the start and end positions of the signal, including: when the energy spectrum entropy of a frame signal is greater than H thres , and the signal duration exceeds T thres1 When the energy spectrum entropy of a frame signal after the start of the signal is detected to be less than H thres , and lasts longer than T thres2 There is still no energy spectrum entropy greater than H thres When the signal appears, it is determined that the current frame is the end position of the OLTC vibration signal; S7: Separate the OLTC vibration signal segment based on the start position and the end position of the signal.

2. The method for extracting vibration signals of transformer on-load tap changer according to claim 1, It is characterized in that S1 includes: When the OLTC performs voltage regulation operation, the vibration signal of the oil tank top cover of the OLTC or the surface of the transformer oil tank shell is collected by the OLTC online monitoring system, wherein the OLTC online monitoring system is triggered by the motor current signal channel and synchronously collects vibration signals of several seconds in length.

3. The method for extracting vibration signals of transformer on-load tap changer according to claim 1, It is characterized in that S2 includes: The collected vibration signal is preprocessed by zero mean, windowing and framing.

4. The method for extracting vibration signals of transformer on-load tap changer according to claim 3, It is characterized in that S2 include: The collected vibration signal is processed with zero mean value to remove the DC component in the signal. The method is as follows: (1) Where: is the vibration signal after removing the mean, N represents the vibration signal The number of sampling points.

5. The method for extracting vibration signals of transformer on-load tap changer according to claim 3, It is characterized in that S2 include: The vibration signal is subjected to windowing and frame preprocessing to obtain the vibration signal segments, wherein a frame of vibration signal at the nth moment is: （2） Where: x n For signal Sampling sequence, h(n) is the window function.

6. The method for extracting vibration signals of transformer on-load tap changer according to claim 3, It is characterized in that In S4, the energy of each sub-band is calculated as follows: ( )(3) Where: S i is the energy sum of the ith sub-band of each frame of vibration signal, M is the number of sub-bands, and 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 transformer on-load tap changer according to claim 1, It is characterized in that In S5, the calculation formula of the energy spectrum entropy of each frame of vibration signal is as follows: ( )(4) (5) Where: p i is the probability density function of the ith sub-band of each frame vibration signal, p k is the probability density function of the kth sub-band of each frame of vibration signal, and H is the energy spectrum entropy of each frame of vibration signal.

8. The method for extracting vibration signals of transformer on-load tap changer according to claim 1, It is characterized in that In S6, H thres Set to 0.5, T thres1 Set to 5ms, T thres2 Set to 5ms.

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