Wind farm step-up transformer protection method and system based on instantaneous differential power time-frequency energy extraction

Abstract

The application provides a wind farm step-up transformer protection method and system based on instantaneous differential power time-frequency energy extraction, which comprises the following steps: obtaining the voltage and current instantaneous values of each side of the transformer in real time; calculating the three-phase differential current amplitude of the transformer according to the current instantaneous value of the periodic wave before the current time; when the three-phase differential current is greater than the set value, sending a transformer internal fault trip signal, otherwise, calculating the instantaneous power and instantaneous differential power of each side of the transformer based on the obtained voltage and current instantaneous values of each side of the transformer; performing time-frequency analysis on the transformer instantaneous differential power before the current time, extracting the time-frequency energy of the instantaneous differential power corresponding to different frequencies; accumulating the time-frequency energy in the set frequency range, and comparing it with the set frequency energy threshold value, if the accumulated time-frequency energy is greater than the set frequency energy threshold value, judging that the transformer internal fault occurs, and sending a transformer internal fault trip signal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system relay protection, and particularly relates to a wind farm step-up transformer protection method and system based on instantaneous differential power time-frequency energy extraction. BACKGROUND

[0002] The statements in this section merely provide background information related to the application and do not necessarily constitute prior art.

[0003] As one of the key devices for connecting wind farms to power grids, the stable operation of step-up transformers directly affects the reliability of system power supply. As the main protection during transformer faults, differential protection cannot distinguish between magnetizing inrush current and internal faults, and usually uses the secondary harmonic content to identify inrush current for blocking.

[0004] Regarding transformer internal faults, it refers to short-circuit faults inside or outside the transformer tank. When an internal fault occurs, the sum of the currents flowing into the transformer from both sides (i.e., differential current) is usually large in value and does not contain secondary harmonic components. If it is not removed quickly, it can easily lead to transformer tank explosion or personal injury. Usually, differential protection is relied on to identify the occurrence of internal faults, and the switches on both sides of the transformer are tripped to remove the fault.

[0005] Regarding magnetizing inrush current, after the transformer is no-load closed or the external fault is removed to restore power supply, a transient overcurrent with nonlinear changes due to transformer core magnetic circuit saturation is generated. It shows certain discontinuous characteristics in waveform, usually with high secondary harmonic content, which decays over time. It is less harmful to transformers or people, and does not need to trip the switches on both sides of the transformer as in internal faults, but it can also increase the differential current and cause the transformer differential protection to malfunction.

[0006] Currently, the secondary harmonic content > 15% (or 20%) is mainly relied on to identify magnetizing inrush current. After meeting the condition, the differential protection is braked, so that the transformer differential protection will not malfunction due to magnetizing inrush current.

[0007] Existing research has proposed many transformer internal fault identification methods that can distinguish magnetizing inrush current, but most of them are based on the external waveform characteristics of differential current or use artificial intelligence / machine learning methods to distinguish. The methods based on waveform characteristics include virtual third harmonic, waveform symmetry, waveform correlation coefficient, morphological gradient, etc. Such methods cannot reflect the essential difference between transformer magnetizing inrush current and internal fault; the artificial intelligence or machine learning methods used include artificial neural network, fuzzy logic, support vector machine, decision tree, etc. Such methods require a large amount of data for training and lack of principle support, which are not suitable for application in the field.

[0008] In addition, a recognition method based on magnetic flux and equivalent excitation inductance is also proposed, but it is difficult to accurately obtain the residual magnetism and excitation inductance. In particular, in terms of the problem of distortion of the differential current waveform caused by the connection of the wind farm to the power grid, after the distortion of the differential current waveform, the second harmonic content increases, which may exceed the set threshold of 15% or 20%, resulting in the misjudgment of internal faults as excitation inrush current, and the protection refuses to act. The existing research lacks targeted solutions, which is one of the technical problems of relay protection in new energy power systems. SUMMARY

[0009] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides a wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction, which uses the time-frequency analysis method of synchronous compression wavelet transform to extract the double-frequency energy of the instantaneous differential power of the transformer, and provides a reliable basis for the recognition of internal faults of the wind farm step-up transformer.

[0010] To achieve the above object, one or more embodiments of the present application provide the following technical solutions:

[0011] In a first aspect, a wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction is disclosed, comprising:

[0012] Real-time acquisition of voltage and current instantaneous values on both sides of the transformer;

[0013] Setting the current instantaneous value of the periodic wave before the current time, calculating the three-phase differential current amplitude of the transformer;

[0014] When the three-phase differential current is greater than the set value, a transformer internal fault trip signal is sent, otherwise, the instantaneous power and instantaneous differential power of the transformer on both sides are calculated based on the acquired voltage and current instantaneous values on both sides of the transformer;

[0015] Time-frequency analysis of the transformer instantaneous differential power before the current time, extracting the instantaneous differential power time-frequency energy corresponding to different frequencies;

[0016] Cumulative time-frequency energy in the set frequency range is compared with the set frequency energy threshold, if it is greater than the set frequency energy threshold, it is judged that the transformer internal fault occurs, and a transformer internal fault trip signal is sent.

[0017] As a further technical solution, the instantaneous power on both sides of the transformer is the product of the instantaneous voltage and current on both sides of the transformer;

[0018] The instantaneous power on both sides of the transformer is summed up to calculate the instantaneous differential power of the transformer.

[0019] As a further technical solution, based on the synchronous compression wavelet transform, the transformer instantaneous differential power p data time before the current time Tdif (t) is subjected to time-frequency analysis to extract the time-frequency energy T(ω l ) corresponding to different frequencies, and the specific formula is:

[0020] T(ω l ) = f ωl (p dif (t))

[0021] Wherein, T data is the data window size of time-frequency energy extraction, f ωl represents synchronous squeezing wavelet transform with ω l as the center frequency.

[0022] As a further technical solution, based on synchronous squeezing wavelet transform, the transformer instantaneous differential power p data (t) before the current time T dif is subjected to time-frequency analysis, specifically:

[0023] The mother wavelet function is selected to perform continuous wavelet transform on the instantaneous differential power to obtain continuous wavelet coefficients.

[0024] The synchronous squeezing wavelet transform is performed on the signal at the center frequency using the continuous wavelet coefficients to obtain synchronous squeezing wavelet coefficients.

[0025] As a further technical solution, when the three-phase differential current is greater than the set value, wherein the set value is 3 times the rated current of the transformer.

[0026] As a further technical solution, the time-frequency energy T(ω l ) within the range of |ω l -100|<δ is accumulated and compared with the set 100Hz frequency energy threshold E 100 , ω l is the center frequency, and δ is the threshold.

[0027] As a further technical solution, the above method is used to accumulate the threshold of time-frequency energy when the transformer excitation inrush occurs, and the discrimination condition of transformer internal fault is not met, which is used to distinguish the excitation inrush from the transformer internal fault, and the transformer protection is not mis-operated.

[0028] In the second aspect, a wind farm booster protection system based on instantaneous differential power time-frequency energy extraction is disclosed, comprising:

[0029] The data acquisition module is configured to acquire the instantaneous values of voltage and current on both sides of the transformer in real time.

[0030] The data calculation module is configured to calculate the three-phase differential current amplitude of the transformer according to the current instantaneous value of the set periodic wave before the current time.

[0031] The first judging module is configured to send a transformer internal fault tripping signal when the three-phase differential currents are all greater than a set value, and otherwise, to calculate transformer side instantaneous power and instantaneous differential power based on the obtained voltage and current instantaneous values of each side of the transformer;

[0032] The time-frequency energy extraction module is configured to perform time-frequency analysis on the transformer instantaneous differential power before the current time, and extract time-frequency energy of the instantaneous differential power corresponding to different frequencies;

[0033] The second judging module is configured to accumulate time-frequency energy in a set frequency range, and compare the accumulated time-frequency energy with a set frequency energy threshold value, and if the accumulated time-frequency energy is greater than the set frequency energy threshold value, it is determined that an internal fault of the transformer occurs, and a transformer internal fault tripping signal is sent.

[0034] The above one or more technical solutions have the following beneficial effects:

[0035] The method of the present application utilizes the characteristics that the second harmonic component of the instantaneous differential power is higher during an internal fault, and the second harmonic component of the instantaneous differential power is lower during a magnetizing inrush current, performs time-frequency energy extraction on the instantaneous differential power near 100Hz based on synchronous extrusion wavelet transform, has strong anti-noise and anti-spectral aliasing capabilities, can accurately analyze the existence of the second harmonic component in the power, and is used to distinguish internal faults and magnetizing inrush currents.

[0036] The method of the present application can effectively identify internal faults, prevent misoperation and refusal of the transformer differential protection, and is not affected by the distortion of the differential current caused by the inverter control of the wind farm.

[0037] The method of the present application utilizes instantaneous power as the identification basis for transformer protection, comprehensively displays the characteristics of the transformer by comprehensively using voltage and current, can fully reflect the essence of the transformer as an energy conversion tool, and is not affected by the low voltage drop degree during three-phase faults, and has no dead zone during three-phase metallic faults.

[0038] The advantages of the additional aspects of the present application will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0039] The drawings accompanying the specification of the present application serve to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof serve to explain the present application, and do not constitute an improper limitation on the present application.

[0040] Figure 1 The flowchart of the present application;

[0041] Figure 2 The connection structure of the wind farm booster transformer in the embodiments 1 and 2 of the present application is shown in the schematic diagram.

[0042] Figure 3 is the instantaneous differential power time-frequency energy diagram in the embodiment 1 of the present application;

[0043] Figure 4 is the instantaneous differential power time-frequency energy diagram in the embodiment 2 of the present application. DETAILED DESCRIPTION

[0044] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0045] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application.

[0046] In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0047] Embodiment One

[0048] The present embodiment discloses a wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction, referring to the accompanying drawings Figure 1 The method comprises the following steps:

[0049] Step one, real-time acquisition of voltage and current instantaneous values u j (t) and i j (t) of each side of the transformer, where j represents the number of end sides of the transformer, t represents the time when the voltage and current are acquired, and the positive direction of the current is the flow direction from the bus to the transformer;

[0050] Step two, calculation of the three-phase differential current amplitude I dif of the transformer according to the current instantaneous values one cycle before the current time, when the three-phase differential currents all meet I dif > I set , then go to step six, otherwise go to step three;

[0051] Step three, calculation of the instantaneous power and the instantaneous differential power of each side of the transformer;

[0052] The instantaneous power p j is the product of the voltage instantaneous value and the current instantaneous value of the transformer, and the calculation formula is:

[0053] p j (t) = u j (t) * i j (t)

[0054] The instantaneous differential power pdif :

[0055]

[0056] Step 4: Apply synchronous squeezing wavelet transform to the current time T data Transformer instantaneous differential power p before time dif (t) Perform time-frequency analysis to extract different frequencies ω l The corresponding instantaneous differential power time-frequency energy, i.e., the synchronous squeeze wavelet coefficients:

[0057]

[0058] Among them, T data This refers to the data window size for time-frequency energy extraction. Indicated by ω l Perform synchronous squeezing wavelet transform on the center frequency;

[0059] In this embodiment, the synchronous squeezing wavelet transform demonstrates strong feature extraction capabilities for transient signals and offers advantages such as noise resistance and spectral aliasing resistance. This method, by squeezing continuous wavelet coefficients along the frequency direction, results in higher accuracy of the extracted frequency components and more concentrated time-frequency energy.

[0060] Step 5, Accumulate |ω l Time-frequency energy T(ω) within the range of -100|<δ l ), and the set 100Hz frequency energy threshold E 100 For comparison, δ is the frequency radius used to calculate the second harmonic energy. When the following formula is satisfied, an internal fault is considered to have occurred, and the process proceeds to step six:

[0061]

[0062] If the conditions are not met, proceed to step one;

[0063] It should be noted that, due to the high frequency of the instantaneous differential power during internal faults and the low frequency of the second harmonic during inrush current, the fundamental frequency is 50Hz and the second harmonic is 100Hz. Therefore, the energy corresponding to the frequency of the instantaneous differential power around 100Hz is extracted, and the energy in the frequency range around 100Hz is used to distinguish the magnitude of the second harmonic component.

[0064] Step 6: Send a trip signal for an internal transformer fault. The process ends here.

[0065] To better illustrate the technical solution of the method described above in this disclosure, the following is in conjunction with the appendix. Figure 2 Specific embodiments of the present invention will be further described below. (See appendix) Figure 2The schematic diagram of the connection structure of the wind farm connected to the 155kV power system through a step-up transformer is shown in the figure. The ratio of the step-up transformer of the wind farm is 155kV / 34.5 / 34.5kV, and the rated capacity S N is 200MVA.

[0066] When the switches CB2 and CB3 on the low-voltage side of the transformer are disconnected, at t=1s, the closing operation is performed on CB1 to generate the magnetizing inrush current. The specific embodiment of the method is shown in the figure below:

[0067] Step one, the voltage and current instantaneous values u1(t), u2(t), u3(t) and i1(t), i2(t), i3(t) on each side of the transformer are obtained, where t represents the time when the voltage and current are obtained, and the reference direction of the current is shown in the figure below: Figure 2

[0068] Step two, the three-phase differential current amplitude I dif of the transformer is calculated according to the current instantaneous value one cycle before the current time. dif Since none of the three-phase differential currents meets I set , step three is entered, where I set =3I N , I N is the rated current of the transformer. For the selected empirical value in this example, when the three-phase short-circuit fault occurs in the step-up transformer of the wind farm, the differential current level is about 3I N when internal fault occurs. The above step is mainly for such faults.

[0069] Step three, the instantaneous power on each side of the transformer and the instantaneous differential power are calculated.

[0070] The instantaneous powers p1, p2, p3 are the products of the voltage instantaneous values and the current instantaneous values on each side of the transformer. The sum of p1, p2, p3 is calculated to obtain the instantaneous differential power p dif :

[0071] p dif (t) = u1(t)i1(t) + u2(t)i2(t) + u3(t)i3(t)

[0072] Step four, the time-frequency analysis is performed on the transformer instantaneous differential power p data (t) before the current time T dif based on the synchronous squeezed wavelet transform, and the instantaneous differential power time-frequency energy corresponding to different frequencies ω l is extracted, i.e., the synchronous squeezed wavelet coefficients:

[0073]

[0074] where T data ​The data window size for time-frequency energy extraction is 2 cycle values, i.e. 40 ms. ωl The synchronous squeezing wavelet transform is performed with ω l as the center frequency. Figure 3 The time-frequency analysis result of the instantaneous differential power is shown in the figure, and the lighter the color, the more concentrated the time-frequency energy is. It can be seen that the time-frequency energy of the example is mainly concentrated at 50 Hz.

[0075] Step five, accumulate |ω l -100|<δ range of time-frequency energy T(ω l ), and compare it with the set 100 Hz frequency energy threshold E 100 , take δ=10, E 100 =2S N , since the accumulated time-frequency energy does not meet , go to step one.

[0076] After the closing of the transformer CB1, the above steps are repeated, and the threshold of the accumulated time-frequency energy is not met, i.e. the discrimination condition of the internal fault of the transformer is not met. As can be seen from the above example, the method can effectively distinguish the magnetizing inrush current from the internal fault, and ensure that the transformer protection does not malfunction.

[0077] The synchronous squeezing wavelet transform process of step three is as follows:

[0078] The mother wavelet function Ψ(t) is selected as Morlet wavelet, and the continuous wavelet transform is performed on the instantaneous differential power p dif (t) to obtain the continuous wavelet coefficient W f (a,b):

[0079]

[0080] Where a is the scale factor of the continuous wavelet transform, and b is the translation factor of the continuous wavelet transform. The instantaneous frequency corresponding to the continuous wavelet coefficient is:

[0081]

[0082] Since Morlet wavelet has good balance between localization in time and frequency, it contains rich vibration information and is generally used for real signal analysis, i.e. real signals that can be measured in reality.

[0083] Let the number of sampling points in p dif (t) signal n=2L+1, the sampling time interval Δt, n v =32, let n a =Ln v , ω0=1 / (nΔt), ω l =2 lΔωω0, where the frequency interval of the signal l=0,1,…,n a -1, the frequency range of the signal is divided into different intervals

[0084] At the center frequency ω l The signal is synchronously squeezed wavelet transformed using continuous wavelet coefficients, and synchronous squeezed wavelet coefficients are obtained:

[0085]

[0086] Where (Δa) k =a k -a k-1 .

[0087] It should be noted that the synchronous squeezed wavelet transform has strong feature extraction capability for transient signals, and has the advantages of anti-noise and anti-spectrum aliasing. The method squeezes the continuous wavelet coefficients in the frequency direction, so that the extracted frequency component has high precision and the time-frequency energy is more concentrated.

[0088] In another embodiment, when the transformer low-voltage side switches CB1, CB2 and CB3 are all closed, at t=1.5s, an internal A-phase ground fault occurs at the high-voltage side of the transformer, and the specific implementation process of the method is repeated from the above steps one to five until the cumulative frequency exceeds the set value at t=1.504s, and a trip signal is sent. Figure 4 The time-frequency analysis result of the transient differential power in this embodiment.

[0089] The above method of the application solves the problem of identifying internal faults of the booster transformer in the wind farm. The method calculates the differential current and the transient differential power according to the voltage and current of each side of the transformer, and extracts the time-frequency energy of the transient differential power using the synchronous compression wavelet transform. The time-frequency energy near the double frequency is accumulated and compared with the set threshold, and step five is to select the frequency radius for accumulation, and the time-frequency energy in the frequency radius is summed (T(ω l ), and the time-frequency energy near the double frequency is accumulated. When the accumulated time-frequency energy exceeds the threshold or the three-phase differential current simultaneously exceeds the set threshold, the internal fault is judged to occur. The application can effectively identify the internal fault on the basis of accurately analyzing the double frequency component of the transient differential power, prevent the misoperation and refusal of the transformer differential protection, and is not affected by the distortion of the differential current caused by the wind farm inverter control. There is no dead zone when the three-phase metallic fault occurs.

[0090] Example two

[0091] The embodiment aims to provide a computer device, comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0092] Embodiment three

[0093] The embodiment aims to provide a computer readable storage medium.

[0094] A computer readable storage medium, on which a computer program is stored, the program being executable by a processor to perform the steps of the above method.

[0095] Embodiment four

[0096] The embodiment aims to provide a wind farm booster protection system based on instantaneous differential power time-frequency energy extraction, comprising:

[0097] A data acquisition module configured to acquire voltage and current instantaneous values of each side of the transformer in real time;

[0098] A data calculation module configured to calculate three-phase differential current amplitudes of the transformer according to current instantaneous values of a periodic wave before the current time;

[0099] A first judgment module configured to send a transformer internal fault tripping signal when the three-phase differential currents are all greater than a set value, otherwise, calculate instantaneous power and instantaneous differential power of each side of the transformer based on the acquired voltage and current instantaneous values of each side of the transformer;

[0100] A time-frequency energy extraction module configured to perform time-frequency analysis on the transformer instantaneous differential power before the current time, and extract time-frequency energy of the instantaneous differential power corresponding to different frequencies;

[0101] A second judgment module configured to accumulate time-frequency energy in a set frequency range, and compare the accumulated time-frequency energy with a set frequency energy threshold, if the accumulated time-frequency energy is greater than the set frequency energy threshold, it is determined that a transformer internal fault occurs, and a transformer internal fault tripping signal is sent.

[0102] The steps and methods of the above embodiments two, three and four correspond to the first method embodiment, and the specific implementation can refer to the related description part of the first embodiment. The term "computer readable storage medium" should be understood as including a single medium or multiple media of one or more instruction sets; it should also be understood as including any medium capable of storing, encoding or carrying instruction sets for execution by a processor and causing the processor to perform any method in the present application.

[0103] Those skilled in the art should understand that the modules or steps of the present application described above can be realized by general computer devices, or alternatively, they can be realized by program codes executable by the computer devices, so that they can be stored in the storage devices and executed by the computer devices, or they can be respectively manufactured into individual integrated circuit modules, or a plurality of modules or steps among them can be manufactured into a single integrated circuit module. The present application is not limited to any specific combination of hardware and software.

[0104] The specific embodiments of the present application described above in conjunction with the accompanying drawings are not intended to limit the protection scope of the present application. Those skilled in the art should understand that various modifications or changes made on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction, characterized in that, The method comprises the following steps: Real-time acquisition of voltage and current instantaneous values on both sides of the transformer; Calculation of three-phase differential current amplitude of the transformer according to the current instantaneous value of the periodic wave at the current time; When the three-phase differential currents are all greater than a set value, the set value being 3 times the rated current of the transformer, a transformer internal fault trip signal is sent, otherwise, instantaneous power and instantaneous differential power on both sides of the transformer are calculated based on the acquired voltage and current instantaneous values on both sides of the transformer; Time-frequency analysis of the transformer instantaneous differential power before the current time, extraction of time-frequency energy of the transformer instantaneous differential power corresponding to different frequencies; Accumulation of time-frequency energy in a set frequency range, comparison with a set frequency energy threshold value, and if the time-frequency energy is greater than the set frequency energy threshold value, it is determined that a transformer internal fault occurs, and a transformer internal fault trip signal is sent. Wherein, based on the synchronous extrusion wavelet transform to the current time T data Transformer transient differential power before time p dif ( t ) time-frequency analysis, extract the corresponding instantaneous differential power time-frequency energy of different frequency Time, the specific formula is: wherein, T data a data window size for time-frequency energy extraction, representing a synchronous synchrosqueezing wavelet transform with ω l a center frequency; where the accumulation ω l -100| δ time-frequency energy in the range and compared to a set 100 Hz frequency energy threshold E 100 , ω l is the center frequency, δ is the threshold.

2. The wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction as claimed in claim 1, characterized in that the transformer The instantaneous power on both sides of the transformer is the product of the voltage instantaneous value and the current instantaneous value on both sides of the transformer; Summation of the instantaneous power on both sides of the transformer, calculation of the instantaneous differential power of the transformer.

3. The wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction as claimed in claim 1, characterized in that, Based on synchronous extrusion wavelet transform to the current time T data Transformer transient differential power before time p dif t Time-frequency analysis is performed, specifically:​ When the three-phase differential currents are all greater than a set value, the set value being 3 times the rated current of the transformer, a transformer internal fault trip signal is sent, otherwise, instantaneous power and instantaneous differential power on both sides of the transformer are calculated based on the acquired voltage and current instantaneous values on both sides of the transformer. The above method is used to distinguish the magnetizing inrush current from the transformer internal fault when the magnetizing inrush current of the transformer occurs, and the transformer protection is not mis-operated.

4. The wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction as claimed in claim 1, characterized in that, The method comprises the following steps:

5. The wind farm step-up transformer protection method based on instantaneous differential power time-frequency energy extraction according to any of claims 1-4, characterized in that, The data acquisition module is configured to acquire real-time voltage and current instantaneous values on both sides of the transformer; 6. A wind farm step-up transformer protection system based on instantaneous differential power time-frequency energy extraction, characterized in that, The data calculation module is configured to calculate three-phase differential current amplitude of the transformer according to the current instantaneous value of the periodic wave at the current time; The first judgment module is configured to send a transformer internal fault trip signal when the three-phase differential currents are all greater than a set value, otherwise, instantaneous power and instantaneous differential power on both sides of the transformer are calculated based on the acquired voltage and current instantaneous values on both sides of the transformer; The time-frequency energy extraction module is configured to perform time-frequency analysis on the transformer instantaneous differential power before the current time, and extract time-frequency energy of the transformer instantaneous differential power corresponding to different frequencies; The second judgment module is configured to accumulate time-frequency energy in a set frequency range, compare with a set frequency energy threshold value, and if the time-frequency energy is greater than the set frequency energy threshold value, it is determined that a transformer internal fault occurs, and a transformer internal fault trip signal is sent. ω ω Wherein, based on the synchronous extrusion wavelet transform to the current time T data Transformer transient differential power before time p dif ( t ) time-frequency analysis, extract the corresponding instantaneous differential power time-frequency energy of different frequencies , the specific formula is: wherein, T data a data window size for time-frequency energy extraction, denotes a synchronization squeeze wavelet transform with δ l a center frequency; wherein the cumulative ω l -100| δ time-frequency energy in the range and compared to a set 100 Hz frequency energy threshold E 100 , The processor implements the steps of the method of any one of claims 1-5 when executing the program. l is the center frequency, The program is executed by the processor to perform the steps of the method of any one of claims 1-5. is the threshold.

7. A computer apparatus comprising a memory, a processor, and a computer program stored on the memory and loadable on the processor, characterized in that, ​ 8. A computer-readable storage medium having stored thereon a computer program, characterized in that, ​

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