A method for evaluating the mechanical structure state of a transformer and a computer-readable storage medium

Abstract

The present invention discloses a method for evaluating the mechanical structure state of a transformer and a computer-readable storage medium, comprising the following steps: S1, obtaining a vibration signal on the surface of a transformer box and performing denoising; S2, performing frequency domain analysis on the denoised vibration signal to extract the amplitude of a fundamental frequency component; S3, using the amplitudes of the fundamental frequency components of three measuring points on the surface of the transformer box as three vertices to form a vibration triangle, and using the normal vector of the plane where the vibration triangle is located as the intrinsic feature of the vibration triangle; S4, calculating the angle between the intrinsic feature to be evaluated and the reference intrinsic feature, and evaluating the mechanical structure state of the transformer according to the size of the angle; wherein the size of the angle represents the similarity between the mechanical structure state of the transformer at the moment to be evaluated and the mechanical structure state of the transformer in a normal state, and the smaller the angle, the higher the similarity.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer evaluation, and in particular to a method for evaluating the mechanical structure state of a transformer. Background Art

[0002] Transformers are important electrical equipment in power systems, and the safe and stable operation of transformers is of great significance to ensuring the reliability of power supply in power systems. However, according to the 2023 National Power Reliability Annual Report released by the National Energy Administration and the China Electricity Council, the forced outage rate caused by transformer failures ranks first among the eleven major types of power transmission and transformation facilities, indicating that the management of transformer health status is still in a severe situation, highlighting the necessity and urgency of developing online transformer status assessment and fault diagnosis technology.

[0003] Transformer vibration analysis is a non-invasive condition monitoring and fault diagnosis technology. By measuring and analyzing the vibration signals on the surface of the transformer box, the operating status of the transformer can be evaluated in real time. However, there are still many problems to be solved in transformer vibration analysis. Among them, one of the most prominent problems is that there are many factors affecting transformer vibration, including not only operating conditions such as voltage fluctuations, load and power factor changes, but also non-fault factors such as temperature, moisture content, and material aging. Another potential problem is that the vibration modes on the surface of the transformer box vary greatly, and there is no consensus on how to select the best measurement point. This makes the existing method of evaluating the mechanical structure status of the transformer based on transformer vibration analysis have the problem that the accuracy of the evaluation results is easily affected by factors such as the sensor installation position, operating conditions, and ambient temperature. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a transformer mechanical structure status assessment method in which the accuracy of the assessment result is not affected by operating conditions and non-fault factors.

[0005] According to one aspect of the present invention, a method for evaluating the mechanical structure state of a transformer is proposed, comprising the following steps: S1, obtaining a vibration signal on the surface of a transformer case and performing denoising; S2, performing frequency domain analysis on the denoised vibration signal to extract the amplitude of the fundamental frequency component; S3, using the amplitudes of the fundamental frequency components of three measuring points on the surface of the transformer case as three vertices to form a vibration triangle, and using the normal vector of the plane where the vibration triangle is located as the intrinsic feature of the vibration triangle; S4, calculating the angle between the intrinsic feature to be evaluated and the reference intrinsic feature, and evaluating the mechanical structure state of the transformer according to the size of the angle; wherein the size of the angle represents the degree of similarity between the mechanical structure state of the transformer at the moment to be evaluated and the mechanical structure state of the transformer in a normal state, and the smaller the angle, the higher the degree of similarity.

[0006] Furthermore, in step S1, a low-pass filter is used to filter out high-frequency noise in the vibration signal. Furthermore, in step S1, a 4th-order Butterworth low-pass filter is used to filter out the high-frequency noise, wherein the filter gain G With frequency ω The relationship is as follows:

[0007]

[0008] in, is the cut-off frequency.

[0009] Furthermore, step S2 specifically includes: performing fast Fourier transform on the denoised vibration signal to obtain a corresponding frequency domain signal, and extracting the amplitude of the fundamental frequency component of each measuring point from the frequency domain signal.

[0010] Furthermore, the three measuring points in step S3 are respectively located at x , y , z On the coordinate axis, the amplitudes of the fundamental frequency components of the three measuring points are , , , then the coordinates of the three vertices of the vibration triangle are , , ; The intrinsic characteristics of the vibration triangle for:

[0011] .

[0012] Furthermore, step S4 calculates the angle between the intrinsic feature to be evaluated and the reference intrinsic feature by the following formula: θ :

[0013]

[0014] in, and are respectively the normal vectors of two vibration shape triangles, and the two vibration shape triangles refer to the reference vibration shape triangle of the transformer in normal state and the vibration shape triangle to be evaluated.

[0015] Further, in step S4, if the angle exceeds a preset threshold, it is determined that the mechanical structure state of the transformer is abnormal; if the angle does not exceed the preset threshold, it is determined that the mechanical structure state of the transformer is normal.

[0016] Further, in step S4, when the calculated angle θ satisfy When , it is judged that the mechanical structure of the transformer at the time to be evaluated is normal; when When , the transformer mechanical structure state at the time to be evaluated is judged to be slightly defective; when , it is judged that the mechanical structure state of the transformer at the time to be evaluated is a fault.

[0017] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the aforementioned transformer mechanical structure status assessment method can be implemented.

[0018] The beneficial effects of the technical solution of the present invention are embodied in that the transformer mechanical structure state evaluation method of the present invention extracts intrinsic features that are only related to the transformer mechanical structure state and are independent of the operating conditions, non-fault factors, and sensor installation positions from the transformer vibration signal. The intrinsic features can accurately reflect the mechanical structure state of the transformer, so that the evaluation method of the present invention improves the accuracy, reliability, and generalization of the transformer state analysis results; at the same time, the transformer mechanical structure state evaluation can be achieved by simply comparing the similarity between the intrinsic features to be evaluated and the benchmark intrinsic features, and the method has excellent operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 4 is a flow chart of a method for evaluating the mechanical structure status of a transformer according to an embodiment of the present invention.

[0020] Figure 2 It is a flow chart of frequency domain information extraction of vibration signals according to an embodiment of the present invention.

[0021] Figure 3 It is a typical vibration triangle schematic diagram of an embodiment of the present invention.

[0022] Figure 4 It is a trend chart of load fundamental amplitude variation of the test transformer within 24 hours.

[0023] Figure 5 It is a comparison diagram of vibration triangles at 5 optional moments.

[0024] Figure 6 It is a comparison diagram of vibration triangles of different fault states. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods and examples. It should be noted that the purpose of providing the examples is only for illustration, and does not limit the scope of protection of the present invention in any way.

[0026] At present, the main problems in transformer vibration analysis include:

[0027] 1. Transformer vibration is affected by many factors, including operating conditions (such as voltage fluctuations, load and power factor changes, etc.) and non-fault factors (such as temperature, moisture content, material aging, etc.);

[0028] 2. The vibration modes on the surface of the transformer box vary greatly, and the selection of the best measurement point has not yet been determined;

[0029] 3. Lack of intrinsic characteristics that are only related to the mechanical structure state of the transformer and have nothing to do with other factors.

[0030] To this end, the embodiment of the present invention provides a transformer mechanical structure state assessment method, referring to Figure 1 First, three vibration measurement points are selected from the surface of the transformer box, and the frequency domain analysis is used to obtain the spectrum information of the vibration signal. The vibration triangle is constructed based on the amplitude of the 100Hz fundamental frequency component of the vibration signal, and the normal vector of the plane where the triangle is located is used as the intrinsic feature describing the vibration shape of the fundamental frequency component; then the similarity between the intrinsic features is used to quantify the similarity of the mechanical structure state of the transformer, and the purpose of evaluating the mechanical structure state of the transformer is achieved by comparing the similarity between the intrinsic features to be evaluated and the benchmark intrinsic features. Specifically, the evaluation method includes the following steps S1 to S4:

[0031] S1. Obtain the vibration signal on the surface of the transformer box and perform denoising.

[0032] In this step, firstly, the vibration signal of the transformer box surface obtained by measurement is imported; then, the vibration signal is denoised, and the specific denoising refers to filtering out high-frequency noise using a low-pass filter.

[0033] In some specific implementations, a 4th-order Butterworth low-pass filter can be used to filter out high-frequency noise in the vibration signal, where the filter gain is G With frequency ω The relationship is as follows:

[0034]

[0035] in, is the cut-off frequency, generally set to 1kHz.

[0036] S2. Perform fast Fourier transform on the denoised vibration signal to obtain the corresponding frequency domain signal, and extract the amplitude of the fundamental frequency component of each measuring point from the frequency domain signal.

[0037] Please refer to Figure 2 , the denoised vibration signal is subjected to fast Fourier transform to obtain the spectrum distribution of the vibration signal. FFT is an algorithm for efficient calculation of Fourier transform. Its mathematical principle is based on discrete Fourier transform, that is, assuming that N The signal sequence of sampling points , then its discrete Fourier transform It can be expressed as:

[0038]

[0039] in, j is an imaginary unit, k is the frequency index, n is the time series index.

[0040] The vibration sources of the transformer mainly come from two aspects: one is the electromagnetic force of the winding related to the current, and the other is the magnetostrictive force of the core related to the magnetic flux density (indirectly related to the voltage). According to electromagnetic theory, the main components of these two forces are proportional to the square of the current and the magnetic flux density, respectively. Therefore, under the industrial frequency AC power supply, the fundamental frequency of the vibration is theoretically twice the fundamental frequency of the power grid, that is, 100Hz in a 50Hz power grid. The embodiment of the present invention only focuses on the vibration mode of the fundamental frequency component of the vibration signal on the surface of the box, so it is only necessary to extract the amplitude of the 100Hz vibration component of each measuring point from the spectrum for subsequent intrinsic feature extraction and transformer mechanical structure state analysis.

[0041] S3. The amplitudes of the fundamental frequency components at three measuring points on the surface of the transformer box are used as the three vertices to form a vibration triangle, and the normal vector of the plane where the vibration triangle is located is used as the eigenvalue of the vibration triangle.

[0042] According to the mathematical principle of "three non-collinear points determine a plane", the amplitude of the fundamental frequency component of three non-collinear measurement points on the surface of the transformer box is used as the three vertices of the vibration triangle, and the three vertices are located at x , y , z On the coordinate axis, Figure 3 As shown, it is assumed that the amplitudes of the fundamental frequency components of the three measuring points are , , , then the coordinates of the three vertices of the vibration triangle are , ,

[0043] ; The intrinsic characteristics of the vibration triangle for:

[0044] .

[0045] S4. Calculate the angle between the intrinsic feature to be evaluated and the reference intrinsic feature, and evaluate the mechanical structure state of the transformer according to the size of the angle. The size of the angle between the intrinsic feature to be evaluated and the reference intrinsic feature characterizes the similarity between the mechanical structure state of the transformer at the time of evaluation and the mechanical structure state of the transformer under normal state. The smaller the angle, the higher the similarity. The higher the similarity, the closer the mechanical structure state of the transformer at the time of evaluation is to the normal state. On the contrary, if the larger the angle, the lower the similarity, the more the mechanical structure state of the transformer at the time of evaluation deviates from the normal state, and a fault is likely to occur.

[0046] The triangular eigencharacteristics of two vibration modes with the same mechanical structure but different operating conditions are similar. The similarity between the two mechanical structure states can be calculated by quantifying the similarity between the triangular eigencharacteristics of the two vibration modes.

[0047] The angle between the two triangular eigenvalues ​​of the vibration mode θ for:

[0048]

[0049] in, and are the normal vectors of the two vibration shape triangles respectively. The two vibration shape triangles here refer to the reference vibration shape triangle of the transformer in normal state and the vibration shape triangle to be evaluated.

[0050] The smaller the angle between the two vibration triangle eigenfeatures, the higher the similarity between the two, and the closer the corresponding mechanical structure state of the transformer. Therefore, a mechanical structure state evaluation rule table as shown in Table 1 can be constructed, and the thresholds in the table are empirical values. So far, the transformer winding mechanical structure state evaluation based on the intrinsic characteristics of the vibration shape of the transformer box surface has been realized.

[0051] Table 1 Transformer mechanical structure status assessment rules based on the similarity of vibration triangle intrinsic characteristics

[0052]

[0053] In order to verify the effectiveness of the method of the present invention, 30928 vibration monitoring data samples with a time span of 6 months were collected from an operating dry-type distribution transformer with rated parameters as shown in Table 2. The measurement data included vibration time domain signals at three measuring points on the surface of the transformer box.

[0054] Table 2 Rated parameters of test transformer

[0055]

[0056] The load of the test transformer is mainly nonlinear loads such as motors and power electronic equipment. Figure 4 The change of the amplitude of the three-phase current fundamental wave (50Hz) within 24 hours is shown. It can be seen that the test transformer is in an operating environment with complex working conditions and a periodic load change trend, which provides a condition for the effectiveness verification of the method in a multi-working operating environment.

[0057] Five moments are randomly selected from the vibration data with a time span of 6 months. The vibration signal frequency domain analysis and intrinsic feature extraction proposed by the method of the present invention can be used to draw the vibration triangle of each moment, such as Figure 5 The angles between the eigenvalues ​​of the triangular vibration modes are shown in Table 3, where the largest angle is 21.7°, indicating that the mechanical structure states of the transformers are highly similar at the five selected moments, which is consistent with the actual results. During the six-month vibration monitoring, no abnormalities occurred in the tested transformers, and the mechanical structure of the transformers was always in normal condition.

[0058] Table 3 Angles between the triangular eigenvalues ​​of vibration modes at five optional moments

[0059]

[0060] In order to further verify the effectiveness of the proposed method in identifying abnormal mechanical structure status of transformers, three measuring points were randomly selected from the surface of a transformer with a turn-to-turn short-circuit fault, and the corresponding vibration triangles were drawn as shown in Figure 2. Figure 6 As shown in the figure, the number of short-circuit turns corresponding to each vibration triangle is different. The angles between the eigenvalues ​​of each vibration triangle are shown in Table 4. It can be found that all the angles exceed 30°. The state assessment result is that the mechanical structure of the transformer is abnormal. The assessment result is consistent with the actual situation, which verifies the effectiveness of the method of the present invention in identifying the abnormal state of the mechanical structure of the transformer.

[0061] Table 4 Angles between the eigenvalues ​​of the vibration triangle under different fault conditions

[0062]

[0063] No. 1: Short circuit 5 turns No. 2: Short circuit 14 turns No. 3: Short circuit 19 turns No. 4: Short circuit 22 turns

[0064] In summary, the method of the present invention innovatively extracts the intrinsic features related to the mechanical structure state of the transformer, effectively solves the problem that the accuracy of transformer vibration analysis is easily affected by operating conditions and measurement point locations, and improves the accuracy and reliability of transformer state assessment.

[0065] In addition, another embodiment of the present invention further proposes a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the transformer mechanical structure state assessment method of the previous embodiment can be implemented. Based on such an understanding, the technical solution of the present invention can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.), including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the various steps of the method of the present invention, thereby realizing the function of the method of the present invention.

[0066] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, several equivalent substitutions or obvious variations can be made without departing from the concept of the present invention, and the performance or use is the same, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for evaluating the mechanical structure status of a transformer, characterized in that: The steps include: S1, obtaining the vibration signal on the surface of the transformer box and performing denoising; S2, performing frequency domain analysis on the denoised vibration signal to extract the amplitude of the fundamental frequency component; S3. The amplitudes of the fundamental frequency components at three measuring points on the surface of the transformer box are used as the three vertices to form a vibration triangle, and the normal vector of the plane where the vibration triangle is located is used as the eigenvalue of the vibration triangle; S4. Calculate the angle between the intrinsic feature to be evaluated and the reference intrinsic feature, and evaluate the mechanical structure state of the transformer according to the size of the angle; wherein the size of the angle represents the degree of similarity between the mechanical structure state of the transformer at the moment to be evaluated and the mechanical structure state of the transformer in a normal state, and the smaller the angle, the higher the degree of similarity.

2. The transformer mechanical structure status assessment method according to claim 1, characterized in that: In step S1, a low-pass filter is used to filter out high-frequency noise in the vibration signal.

3. The transformer mechanical structure status assessment method according to claim 2, characterized in that: In step S1, a 4th-order Butterworth low-pass filter is used to filter out the high-frequency noise, wherein the filter gain G With frequency ω The relationship is as follows: ； in, is the cut-off frequency.

4. The transformer mechanical structure status assessment method according to claim 1, characterized in that: Step S2 specifically includes: performing fast Fourier transform on the denoised vibration signal to obtain a corresponding frequency domain signal, and extracting the amplitude of the fundamental frequency component of each measuring point from the frequency domain signal.

5. The transformer mechanical structure status assessment method according to claim 1, characterized in that: The three measuring points in step S3 are respectively located at x , y , z On the coordinate axis, the amplitudes of the fundamental frequency components of the three measuring points are , , , then the coordinates of the three vertices of the vibration triangle are , , ; The intrinsic characteristics of the triangular mode shape for: 。 6. The transformer mechanical structure status assessment method according to claim 1, characterized in that: Step S4 calculates the angle between the intrinsic feature to be evaluated and the reference intrinsic feature by the following formula: θ : ； in, and are respectively the normal vectors of two vibration shape triangles, and the two vibration shape triangles refer to the reference vibration shape triangle of the transformer in normal state and the vibration shape triangle to be evaluated.

7. The transformer mechanical structure status assessment method according to claim 1, characterized in that: In step S4, if the angle exceeds the preset threshold, it is determined that the mechanical structure state of the transformer is abnormal; if the angle does not exceed the preset threshold, it is determined that the mechanical structure state of the transformer is normal.

8. The transformer mechanical structure status assessment method according to claim 1, characterized in that: In step S4, when the calculated angle θ satisfy When , it is judged that the mechanical structure of the transformer at the time to be evaluated is normal; when When , the transformer mechanical structure state at the time to be evaluated is judged to be slightly defective; when , it is judged that the mechanical structure state of the transformer at the time to be evaluated is a fault.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the transformer mechanical structure status assessment method according to any one of claims 1 to 8 can be implemented.

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