Test methods for transformer winding deformation

Abstract

This invention discloses a method for testing transformer winding deformation. The method includes: S1, applying a signal to each winding of the transformer, measuring the response signal at both ends of each winding, and extracting the reflected wave of the response signal; and S2, comparing the waveforms of the reflected waves of the three-phase windings. If the reflected wave of a certain winding differs from the other two, then that winding is considered to be deformed. This invention can accurately determine the winding deformation of the transformer with relatively little sampling data. The testing instrument emits a high-frequency sinusoidal signal, which facilitates the elimination of interference signals, has strong anti-interference ability, and the repeatability of the measurement results is easily guaranteed. It also has the advantages of high detection sensitivity and convenient field use.

Description

Technical Field

[0001] This invention relates to the field of power grids, and more specifically to a method for testing transformer winding deformation. Background Technology

[0002] Power transformers are among the most critical components of a power system, directly impacting the safe and stable operation of the grid. Short-circuit faults are a major cause of transformer damage. Post-incident disassembly and analysis of transformers reveal that, in addition to manufacturing and process-related issues, winding deformation is a significant contributing factor to short-circuit damage. Winding deformation has two consequences: one is that the insulation changes or the insulating material is damaged, leading to decreased insulation strength. Under overvoltage or even operating voltage, this can cause partial discharge or breakdown, eventually resulting in sudden damage and burnout. The other consequence is that the winding deviates from its normal position, reducing stability and leading to failure in subsequent short circuits. Therefore, timely analysis and understanding of power transformer winding deformation are crucial.

[0003] Currently, there are two main methods for monitoring transformer winding deformation: the short-circuit impedance method and the frequency response analysis method (FRA). According to the "Standard for Acceptance Testing of Electrical Equipment in Electrical Installation Engineering" (GB 50150-2016) 8.0.12, the transformer winding deformation test should comply with the following provisions: 1. For transformers with voltage levels of 35kV and below, the low-voltage short-circuit impedance method should be used; 2. For transformers with voltage levels of 110(66)kV and above, the frequency response method should be used to measure the winding characteristic spectrum. The short-circuit impedance method measures the short-circuit impedance or leakage reactance of the transformer winding under a 50Hz power frequency voltage. The change in impedance or leakage reactance value is used to determine whether the transformer winding has deformed, such as inter-turn short circuit, open circuit, coil displacement, etc. The short-circuit impedance method mainly uses the change in the lumped parameter of the short-circuit impedance of the transformer winding to determine whether the winding has deformed. However, for windings with less severe deformation or defects only in certain parts of the winding, the change in lumped parameter is not obvious. Using the general method of detecting short-circuit impedance, it is difficult to obtain the necessary detection sensitivity, so the measurement effect is not very good.

[0004] At higher frequencies, a transformer winding is considered a passive linear two-port network composed of distributed parameters such as linear resistance, inductance, mutual inductance, and capacitance. The poles and zeros of the network's transfer function H(ω) are closely related to the parameters of the components within the network. When the winding undergoes localized mechanical deformation, the distributed parameters of its inductance and capacitance will inevitably change relatively, and the winding's transfer function will also change accordingly, meaning the network's frequency response characteristics will change. The frequency response method measures the transformer winding's transfer function over a wide frequency band and analyzes the winding's frequency response characteristics to determine its condition. However, the frequency response method is affected by electric and magnetic fields during field testing. These influences can even alter the measurement results, leading to distorted test results and misjudgments by field personnel.

[0005] Therefore, there is a lack of a testing method in this field that is less affected by the environment and is simpler, more efficient and accurate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for testing transformer winding deformation. This method can accurately determine transformer winding deformation with relatively little sampling data. The testing instrument emits a high-frequency sinusoidal signal, which facilitates the elimination of interference signals, provides strong anti-interference capability, and ensures the repeatability of measurement results. It also has advantages such as high detection sensitivity and ease of on-site use.

[0007] The present invention provides a method for testing transformer winding deformation, the method comprising: S1, applying a signal to each winding of the transformer, measuring the response signal at both ends of each winding, and extracting the reflected wave of the response signal; and S2, comparing the waveforms of the reflected waves of the three-phase windings, and if the reflected wave of a certain winding is different from the other two, then the winding is determined to be deformed.

[0008] In another preferred embodiment, the method further includes: S3, verifying the deformed winding, the verification including: comparing the original data waveform of the winding and the measured reflected wave waveform, and comparing the difference between the two with a threshold.

[0009] In another preferred embodiment, if the difference between the two exceeds a threshold, the verification is correct; otherwise, the verification is incorrect.

[0010] In another preferred embodiment, if the verification is incorrect, it indicates that the windings of the remaining items may be deformed, and step S3 is repeated to verify the windings of the remaining items.

[0011] In another preferred embodiment, S2 includes the sub-steps: S21, the waveform function of the reflected wave from the m-phase winding is f. m (t), the waveform function of the reflected wave delayed x phase of the other n-phase winding is f n(tx), where t is the sampling time and x is the delay phase; the difference amplification function M of the reflected waves from two windings of different phases is calculated by the following formula. mn (x):

[0012]

[0013] Where T is the sampling period.

[0014] In another preferred embodiment, for a three-phase transformer having phases A, B, and C, m is any one of A, B, and C, and n is another one of A, B, and C that is different from m.

[0015] In another preferred embodiment, S2 further includes the sub-step: S22.1, if the following equation holds, it indicates that winding deformation has occurred in phase A:

[0016] [(M BC (x BCmax )-M AC (x ACmax ))>ε]∩[(M BC (x BCmax )-M AB (x ABmax ))>ε]∩[(M AC (x ACmax )-M AB (x ABmax ))<δ];where ε is the first threshold, δ is the second threshold, and x max Let x be the value of the maximum value in M(x).

[0017] In another preferred embodiment, S2 further includes the sub-step: S22.2, if the following equation holds, it indicates that winding deformation has occurred in phase B:

[0018] [(M AC (x ACmax )-M BC (x BCmax ))>ε]∩[(M AC (x ACmax )-M AB (x ABmax ))>ε]∩[(M AB (x ABmax )-M BC (x BCmax ))<δ];where ε is the first threshold, δ is the second threshold, and x max Let x be the value of the maximum value in M(x).

[0019] In another preferred embodiment, S2 further includes the sub-step: S22.3, if the following equation holds, it indicates that winding deformation has occurred in phase C:

[0020] [(M AB (x ABmax )-M AC (x ACmax ))>ε]∩[(M AB (x ABmax )-M BC (x BCmax ))>ε]∩[(M AC (x ACmax )-M BC (x BCmax ))<δ];where ε is the first threshold, δ is the second threshold, and x max Let x be the value of the maximum value in M(x).

[0021] It should be noted that if the formulas in S22.1, S22.2 and S22.3 are not valid, it means that the transformer windings have not been deformed.

[0022] In another preferred embodiment, S3 includes: S31, the waveform function of the reflected wave of a certain phase winding is f i (ty), the waveform function of the reflected wave of the original data of this phase winding is g i (t), where t is the sampling time, y is the delay time, and i represents the number of phases;

[0023] The difference amplification function M between the emitted and reflected waves is calculated using the following formula. i (y):

[0024]

[0025] Where T is the waveform period of the transmitted wave.

[0026] In another preferred embodiment, S3 includes: S32, calculating the difference Δ between the emitted wave and the reflected wave using the following formula. i :

[0027]

[0028] Where k is the correction coefficient.

[0029] In another preferred embodiment, S3 includes: S33, if Δ i If the threshold σ is exceeded, it indicates that the i-th phase winding of the transformer has deformed.

[0030] In another preferred embodiment, S33 further includes if Δ i If the threshold σ is not exceeded, it indicates that deformation may have occurred in the two phase windings of the transformer other than phase i. The above steps are then performed on the other two phase windings to verify whether deformation has occurred.

[0031] In another preferred embodiment, the signal is a high-frequency signal.

[0032] In another preferred embodiment, the frequency of the signal is 1 kHz to 1000 kHz; preferably, 200 kHz to 800 kHz; more preferably, 400 kHz to 600 kHz.

[0033] In another preferred embodiment, f i (ty) is the waveform function of the reflected wave with respect to the time delay y of the emitted wave.

[0034] The main advantages of this invention are:

[0035] This invention accurately determines transformer winding deformation by comparing experimental data with raw data. The testing instrument emits a high-frequency sinusoidal signal, which facilitates the elimination of interference signals, resulting in strong anti-interference capabilities and easily guaranteed repeatability of measurement results. Furthermore, it requires less sampling data, offering advantages such as high detection sensitivity and ease of field use, making it promising for widespread application in modern power systems. This method can serve as a primary means of judging winding deformation, preventing major transformer accidents.

[0036] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of a transformer winding deformation testing method in one embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of a transformer winding deformation testing system in one embodiment of the present invention. Detailed Implementation

[0040] Through extensive and in-depth research and screening, the inventors have developed, for the first time, a testing method for transformer winding deformation. This invention first compares test data between different phase windings to determine if winding deformation has occurred. If deformation is detected, the method then compares the test data with the original data to accurately identify which one or more phases of the transformer are deformed. This method effectively reduces the amount of data collected, offers high detection sensitivity and accuracy, and is convenient for field use. The testing instrument emits a high-frequency sinusoidal signal, which facilitates the elimination of interference signals, provides strong anti-interference capabilities, and ensures the repeatability of measurement results. It has broad application prospects in power systems. This method can serve as a primary means of judging winding deformation, preventing major transformer accidents. This invention was completed based on this foundation.

[0041] the term

[0042] As used in this article, the term "winding deformation" refers to the axial or radial dimensional changes of the windings of a power transformer under the action of mechanical or electrodynamic forces, which are usually manifested as local twisting, bulging or displacement of the windings.

[0043] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, the accompanying drawings are schematic diagrams, and therefore the apparatus and device of the present invention are not limited to the size or scale of the schematic diagrams.

[0044] It should be noted that in the claims and specification of this patent, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0045] Example

[0046] The transformer winding deformation test method in this embodiment is shown in Figure 1, which is achieved through the following... Figure 2 The transformer winding deformation test system shown is implemented.

[0047] Under high-frequency voltage, each winding of a transformer can be considered a passive linear two-terminal network composed of distributed parameters such as linear resistance, inductance (mutual inductance), and capacitance. If the winding deforms, the distributed inductance, capacitance, and other parameters inside the winding will inevitably change, leading to a change in the characteristics of the reflected wave of the input voltage signal. The transformer winding deformation test method mentioned in this invention is based on traveling wave theory. A specific pulse signal is applied to each winding of the transformer, and the response signal at its port is measured to extract the reflected wave of the response signal. The reflected waves of the three-phase windings are then used to calculate the function value M for each pair using waveform functions. AB M BC and M AC To determine the degree of winding deformation.

[0048] For example, M in formula (1) AB This calculates the waveform similarity function value between the reflected waves of phase A and phase B. This embodiment utilizes the changes in the component distribution parameters inside the transformer caused by transformer winding deformation, resulting in differences in the reflected waves, to identify faults.

[0049]

[0050] In the formula f A (t)---Waveform of the reflected wave from phase A winding;

[0051] f B (tx)---The waveform of the reflected wave from phase B winding delayed by x time;

[0052] T --- Sampling period.

[0053] Similarly, we can derive M BC (x) and M AC The formula for (x).

[0054] If the function values ​​of the three phases have the relationship of formula (2), the winding of phase A will be deformed.

[0055] [(M BC (x BCmax )-M AC (x ACmax ))>ε]∩[(M BC (x BCmax )-M AB (x ABmax ))>ε]∩[(M AC (x ACmax )-M AB (x ABmax Equation (2) < δ

[0056] In the formula, ε is the threshold, δ is the threshold, and x is the threshold value. max —The value of x corresponding to the maximum value in M(x).

[0057] If the function values ​​of the three phases have the relationship of formula (3), the winding of phase B will be deformed.

[0058] [(M AC (x ACmax )-M BC (x BCmax ))>ε]∩[(M AC (x ACmax )-M AB (x ABmax ))>ε]∩[(M AB (x ABmax )-M BC (x BCmax Equation (3) < δ

[0059] In the formula, ε is the threshold, δ is the threshold, and x is the threshold value. max —The value of x corresponding to the maximum value in M(x).

[0060] If the function values ​​of the three phases have the relationship of formula (4), the winding of phase C will be deformed.

[0061] [(M AB (x ABmax )-M AC (x ACmax ))>ε]∩[(M AB (x ABmax )-M BC (x BCmax ))>ε]∩[(M AC (x ACmax )-M BC (x BCmax Equation (4) < δ

[0062] In the formula, ε is the threshold, δ is the threshold, and x is the threshold value. max —The value of x corresponding to the maximum value in M(x).

[0063] In transformer deformation, the probability of single-phase deformation is very high, the probability of two phases deforming simultaneously is low, and the probability of three-phase deformation occurring simultaneously is almost non-existent. Therefore, the simple method described above can accurately detect single-phase deformation with relatively small amounts of collected data. This can then be supplemented by the methods described below to verify or determine whether two phases of deformation are occurring simultaneously.

[0064] The waveform function of the reflected wave from a certain phase winding is f i (ty), the waveform function of the reflected wave of the original data of this phase winding is g i (t), where t is the sampling time, y is the delay time, and i represents the number of phases, which can be phase A, phase B, or phase C;

[0065] The difference amplification function M between the emitted and reflected waves is calculated using the following formula. i (y):

[0066]

[0067] Where T is the waveform period of the transmitted wave.

[0068] The difference Δ between the emitted and reflected waves is calculated using the following formula. i :

[0069]

[0070] Where k is the correction coefficient.

[0071] If Δ i If the threshold σ is exceeded, it indicates that the i-th phase winding of the transformer has deformed.

[0072] If Δ i If the threshold σ is not exceeded, it indicates that deformation may have occurred in the two phase windings of the transformer other than phase i. The above steps are then performed on the other two phase windings to verify whether deformation has occurred.

[0073] Points to note during testing:

[0074] (1) Before the test, the terminals of the transformer under test should be discharged to ground to prevent static electricity or induced electricity from damaging the instrument;

[0075] (2) After the test cable is laid out, short-circuit the cable to check the continuity and insulation of the cable.

[0076] (3) The waveform characteristics of the transformer windings are related to the tap changer position. The results vary significantly depending on the tap changer position. The tap changer position must be recorded during testing.

[0077] (4) Grounding Requirements. The grounding system is crucial during the testing process. The test instrument housing, transformer core, and casing must be reliably grounded. The measurement system must have one and only one grounding point, i.e., the test instrument housing, transformer core, and casing must all be reliably grounded at the same point.

[0078] (5) All leads connected to the transformer bushing should be removed and kept as far away from the transformer bushing as possible; surrounding grounding bodies and suspended metal objects should be at least 20cm away from the transformer bushing to reduce the impact of stray capacitance.

[0079] step:

[0080] (1) First, check whether the transformer grounding condition is good. All bushing leads should be disconnected and kept as far away from the transformer bushing as possible.

[0081] (2) The test winding lead-out terminal of the transformer under test is effectively connected to the three ports of the tester through three dedicated test leads. Two of the test leads are power supply lines for the tester to apply voltage excitation signals, and one test lead is for the response signal, so that the tester can extract the reflected wave of the excitation signal.

[0082] (3) The tester applies a specific high-frequency signal to the transformer winding and uses the collected response signal to extract the reflected wave and transmit it to the data processing center (CPU).

[0083] (4) The data processing center (CPU) uses waveform functions to calculate the waveform similarity function of each phase reflected wave and compares the differences between them, as well as arbitrarily comparing the difference between the reflected wave similarity function and the original data to determine the degree of winding deformation.

[0084] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for testing transformer winding deformation, characterized in that, The method includes: S1. Connect the lead-out end of the tested winding of the transformer under test to the three ports of the tester through three test leads. Two of the test leads are power lines for the tester to apply voltage excitation signals to the tested winding, and the other test lead is a signal line for the tester to collect response signals. The tester applies signals to the A-phase, B-phase and C-phase windings of the transformer respectively, measures the response signals at both ends of each winding, and extracts the reflected waves of the response signals. S2. Compare the waveforms of the reflected waves from each of the three-phase windings pairwise, where the waveform function of the reflected wave from the m-phase winding is: The waveform function of the reflected wave delayed x phase of the other n-phase winding is as follows: , where t is the sampling time and x is the delay phase; The difference amplification function of the reflected waves from two different phase windings is calculated using the following formula. : Where T is the sampling period, m is any one of A, B, and C, and n is another one of A, B, and C that is different from m; Obtain the waveform similarity function values ​​M for the reflected waves of phase A and phase B respectively. AB (x), Waveform similarity function value M of phase B and phase C reflected waves BC (x), Waveform similarity function value M of phase A and phase C reflected waves AC (x), and: If the following formula holds true, it indicates that winding deformation has occurred in phase A: If the following formula holds true, it indicates that winding deformation has occurred in phase B: If the following formula holds true, it indicates that winding deformation has occurred in phase C: Where ε is the first threshold, The second threshold, for The value of x corresponding to the maximum value in the range; S3. For the deformed i-th phase winding, compare the reflected wave waveform measured by the i-th phase winding with the original data waveform, wherein the waveform function of the reflected wave of the i-th phase winding is: The waveform function of the reflected wave of the original data of this phase winding is: The difference amplification function between the transmitted and reflected waves is calculated using the following formula. : The difference between the transmitted and reflected waves is calculated using the following formula. : Where t is the sampling time, y is the delay time, i represents the number of phases, and k is the correction coefficient; like Exceeding the threshold This indicates that the i-th phase winding of the transformer has been deformed. like No threshold exceeded This indicates that the two phase windings of the transformer other than phase i may have been deformed. Step S3 is repeated on the other two phase windings to verify whether they have been deformed.

2. The method as described in claim 1, characterized in that, The frequency of the signal is 1kHz to 1000kHz.

3. The method as described in claim 1, characterized in that, The frequency of the signal is 200kHz to 800kHz.

4. The method as described in claim 1, characterized in that, The frequency of the signal is 400kHz to 600kHz.

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