Method and system for identifying sympathetic inrush current in operation of transformer

Abstract

The invention provides a sympathetic inrush current identification method and system in transformer operation, and belongs to the technical field of transformer protection, and the method comprises the steps: obtaining a three-phase differential current instantaneous value # imgabs0 # of an adjacent no-load transformer T1 and a three-phase differential current instantaneous value # imgabs1 # of an operation transformer T2, and obtaining a difference value # imgabs4 # of # imgabs2 # and # imgabs3 #, and extracting time-frequency energy # imgabs7 # in # imgabs6 # and time-frequency energy # imgabs9 # in # imgabs8 # based on synchronous extrusion wavelet transform, respectively accumulating frequency doubling energy values corresponding to # imgabs10 # and # imgabs11 # in a set frequency interval to obtain # imgabs12 # and # imgabs13 #, comparing # imgabs14 # and # imgabs15 # with a judgment threshold value, and identifying sympathetic inrush current according to a comparison result. According to the method provided by the invention, the occurrence of the sympathetic inrush current can be continuously and reliably identified on the premise of not depending on the second harmonic, and the method is not easily influenced by the current waveform distortion after the new energy is accessed.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer protection, and in particular relates to a method and system for identifying a induced inrush current during transformer operation. Background Art

[0002] The excitation inrush current is the core issue that affects the correct action of transformer protection. When there is an internal fault in the transformer, the current differential protection is relied on to cut off the fault to prevent damage to personnel or equipment, and the excitation inrush current can cause the current differential protection to malfunction when the transformer is not faulty. The action here means that the protection sends a trip signal and can trip the circuit breaker. As a type of excitation inrush current, the response inrush current is not generated on the transformer that is being airdropped, but on the adjacent transformer in operation, so it is concealed; at the same time, because it involves the interaction between transformers running in parallel or cascade, it has a certain complexity. There is no special identification method for the response inrush current on site, but a conventional inrush current identification method based on second harmonics is used. In addition, after the new energy is connected to the system, the current waveforms on both sides of the transformer are distorted, which further increases the difficulty of identifying the response inrush current.

[0003] The various methods for identifying the inrush current proposed in current research mostly rely on the second harmonic, such as the identification method based on the second harmonic phase difference and the differential current positive sequence second harmonic. This method is affected by the failure of the second harmonic braking and its reliability cannot be guaranteed. The methods based on the fundamental amplitude increment and the characteristics of the inrush current first increasing and then decreasing cannot continuously identify its existence during the inrush current. In addition, the method of identifying the inrush current using the instantaneous value of the current is easily affected by the current waveform distortion after the access of new energy, and it is difficult to accurately extract the waveform features to identify the occurrence of the inrush current. Summary of the invention

[0004] In order to solve the problems of inability to continuously identify and low identification accuracy in existing methods for identifying combined inrush current, the present invention provides a method and system for identifying combined inrush current in transformer operation.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for identifying a surge current in transformer operation comprises the following steps:

[0007] Real-time acquisition of the instantaneous value of the three-phase differential current of the adjacent air-drop transformer T1 And the instantaneous value of the three-phase differential current of the running transformer T2 and obtain and The current difference in Indicates the three phases A, B, and C of the transformer;

[0008] Extraction based on synchronous squeezing wavelet transform The time-frequency energy in and The time-frequency energy in Accumulate separately and The corresponding double frequency energy value in the set frequency range is obtained to obtain the time-frequency energy and and time-frequency energy and

[0009] The time-frequency energy and and time-frequency energy and The result is compared with the judgment threshold, and the corresponding inrush current is identified according to the comparison result.

[0010] Preferably, the synchronous squeezing wavelet transform extraction The time-frequency energy in and The time-frequency energy in Specifically include:

[0011] The mother wavelet function Ψ(t) is used to and Perform continuous wavelet transform to obtain continuous wavelet coefficient K I ;

[0012]

[0013] Where m is the scale factor of wavelet transform, n is the translation factor, represents the conjugate of Ψ; i(t) is the function of current changing with time, i(t) represents or t represents time; Indicates the current difference A function that varies with time, Indicates the instantaneous value of the three-phase differential current of the air-drop transformer T1 Functions that vary with time;

[0014] Divide i(t) into different frequency intervals and calculate the center frequency ω l Nearby area The wavelet coefficients are squeezed to obtain the time-frequency energy T after synchronous squeezing wavelet transformation;

[0015]

[0016] Where Δω is the size of the frequency interval, f represents the time-frequency energy T as a function of i(t); m k Represents the value of the kth wavelet transform scale factor, m k-1 Indicates the value of the k-1th wavelet transform scale factor; (Δm)k Represents two adjacent scale factors m k and m k-1 Difference in values, (Δm) k =m k -m k-1 ; and The time-frequency energies after synchronous squeezing wavelet transform are and

[0017] Preferably, the set frequency interval is [2f N -δ, 2f N +δ], where f N represents the rated frequency, and δ represents the frequency deviation to be accumulated;

[0018] The frequency interval of the summation is [2f N -δ, 2f N +δ].

[0019] Preferably, the time-frequency energy and and time-frequency energy and Compared with the judgment threshold, the judgment criteria are as follows:

[0020]

[0021] Where E set1 and E set2 is the threshold in the criterion. When the criterion is met, it is judged that the inrush current occurs and the transformer protection is locked. Otherwise, the differential current of the two transformers is obtained again and the judgment cycle continues.

[0022] The present invention also provides a system for identifying a surge current in transformer operation, comprising:

[0023] The current difference acquisition module is used to obtain the instantaneous value of the three-phase differential current of the adjacent air-drop transformer T1 in real time. And the instantaneous value of the three-phase differential current of the running transformer T2 and obtain and The current difference in Indicates the three phases A, B, and C of the transformer;

[0024] Energy value acquisition module, used for extraction based on synchronous squeezing wavelet transform The time-frequency energy in and The time-frequency energy in Accumulate separately and The corresponding double frequency energy value in the set frequency range is obtained to obtain the time-frequency energy and and time-frequency energy and

[0025] Identification module, used to transform time-frequency energy and and time-frequency energy and The result is compared with the judgment threshold, and the corresponding inrush current is identified according to the comparison result.

[0026] The present invention also provides a computer device, comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement any one of the steps in the method for identifying a surge current in transformer operation.

[0027] The present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is loaded by a processor, the computer program can execute any one of the steps in the method for identifying the inrush current in the operation of the transformer.

[0028] The method for identifying the inrush current in transformer operation provided by the present invention has the following beneficial effects:

[0029] The present invention is implemented based on time-frequency analysis technology. The characteristics of different frequency components changing with time can be continuously used for transformer status discrimination. Therefore, the present invention utilizes the instantaneous value characteristics of the three-phase differential current of the interaction between the air-dropped transformer and the running transformer during the response inrush. This characteristic persists during the response inrush, so the present invention can continuously identify the occurrence of response inrush. On this basis, the present invention distinguishes response inrush based on the time-frequency energy extracted by the synchronous squeezing wavelet transform instead of the second harmonic. The synchronous squeezing wavelet transform has strong anti-noise and anti-spectral aliasing capabilities, and can accurately analyze the double frequency energy in the current. Compared with the instantaneous value form of identification method, it is not easily affected by the current waveform distortion after the access of new energy and the failure of the second harmonic braking, which improves the reliability of response inrush identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiment of the present invention and its design scheme, the following briefly introduces the drawings required for this embodiment. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A flow chart of the method for identifying the inrush current in transformer operation proposed by the present invention;

[0032] Figure 2 This is the embodiment of the present invention in the case of a surge flow. Time-frequency energy distribution diagram;

[0033] Figure 3 This is the embodiment of the present invention in the case of a surge flow. Time-frequency energy distribution diagram;

[0034] Figure 4 This is the embodiment 2 of the present invention in the case of an internal fault in the running transformer Time-frequency energy distribution diagram;

[0035] Figure 5 This is the embodiment 2 of the present invention in the case of an internal fault in the running transformer Time-frequency energy distribution diagram;

[0036] Figure 6 This is a logic block diagram of the surge current identification system in transformer operation proposed by the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the scope of protection of the present invention.

[0038] The present invention proposes a method for identifying the inrush current in transformer operation, specifically a method for identifying the inrush current based on synchronous squeezing wavelet transform. After obtaining the differential current of the operating transformer and the air-dropped transformer in real time, the difference between the two differential currents is calculated. The difference current exhibits significant double frequency energy characteristics due to the alternating appearance of the inrush current and the initial inrush current, which can be used to identify the inrush current. Then, based on the synchronous squeezing wavelet transform, the difference between the differential currents of the two transformers and the double frequency energy in the differential current of the operating transformer are accurately extracted. When the double frequency energy values ​​of both meet the threshold requirements, it is determined that the inrush current occurs, providing a reliable basis for preventing the protection malfunction caused by the inrush current.

[0039] Specifically, Figure 1 As shown, the implementation of the method for identifying the inrush current in transformer operation provided by the present invention includes the following steps:

[0040] 1) Real-time acquisition of the instantaneous value of the three-phase differential current of the adjacent air-drop transformer T1 And the instantaneous value of the three-phase differential current of the running transformer T2 in Indicates the three phases A, B, and C of the transformer.

[0041] 2) Calculate the instantaneous value of the three-phase differential current of the air-drop transformer T1 And the instantaneous value of the three-phase differential current of the running transformer T2 The current difference The details are as follows:

[0042]

[0043] 3) Extracting current difference based on synchronous squeezing wavelet transform And the instantaneous value of the three-phase differential current of the air-drop transformer T1 The time-frequency energy T(ω l ), where the time-frequency energy T(ω l )include Time-frequency energy after synchronous squeezing wavelet transform and Time-frequency energy after synchronous squeezing wavelet transform Get the time-frequency energy T(ω l ) specifically includes the following steps:

[0044] First, select the mother wavelet function Ψ(t) and Perform continuous wavelet transform and obtain the continuous wavelet coefficient K according to formula (2): I :

[0045]

[0046] Where m is the scale factor of wavelet transform, n is the translation factor, represents the conjugate of Ψ. i(t) is the function of current changing with time, i(t) is the function of current changing with time. or t represents time; Indicates the current difference A function that varies with time, Indicates the instantaneous value of the three-phase differential current of the air-drop transformer T1 A function that varies with time.

[0047] Secondly, i(t) is divided into different frequency intervals, and the center frequency ω l Nearby area The wavelet coefficients of are squeezed to obtain the time-frequency energy T after synchronous squeezing wavelet transform, as shown in formula (3):

[0048]

[0049] Where Δω is the size of the frequency interval, f represents the time-frequency energy T as a function of i(t); m k Represents the value of the kth wavelet transform scale factor, m k-1 Indicates the value of the k-1th wavelet transform scale factor; (Δm) k Represents two adjacent scale factors m k and m k-1Difference in values, (Δm) k =m k -m k-1 ; and The time-frequency energies after synchronous squeezing wavelet transform are and

[0050] 4) Accumulate separately and At the frequency [2f N -δ, 2f N +δ], the corresponding double frequency energy value in the interval is obtained, and the time-frequency energy and and time-frequency energy and where f N represents the rated frequency, δ represents the frequency deviation to be accumulated; f N Typically 50Hz, 2f N Usually 100Hz.

[0051] 5) According to formula (4), the existence of the surge flow is determined, where E set1 and E set2 is the threshold in the judgment criterion. When equation (4) is satisfied, it is judged that the inrush current occurs and the transformer protection is locked. Otherwise, the differential current of the two transformers is obtained again and the judgment cycle continues.

[0052]

[0053] Therefore, the method for identifying the inrush current in transformer operation provided by the present invention has the following advantages:

[0054] (1) The present invention distinguishes the inrush current based on the time-frequency energy extracted by synchronous squeezing wavelet transform, rather than the second harmonic used in the field and some existing technologies, and is not affected by the second harmonic braking failure.

[0055] (2) The present invention is implemented based on time-frequency analysis technology. The characteristics of different frequency components changing with time can be continuously used to distinguish the state of the transformer. The present invention also utilizes the characteristics of the interaction between the unattended transformer and the running transformer during the response inrush. This characteristic persists during the response inrush. Therefore, the present invention can continuously identify the occurrence of response inrush.

[0056] (3) The synchronous squeezed wavelet transform used in the present invention has strong anti-noise and anti-spectral aliasing capabilities, and can accurately analyze the double frequency energy in the current. Compared with the instantaneous value form of identification method, it is not easily affected by the current waveform distortion after the access of new energy.

[0057] Embodiment 1:

[0058] When the transformer is inrush current, obtain and like Figure 2 and Figure 3 As shown. The horizontal axis is time, the vertical axis is frequency, and the higher the color brightness, the greater the value of the point. In this embodiment, after t = 1s, and At 100Hz, larger values ​​appear. The criterion of formula (4) is met, and the inrush current occurs, and the transformer protection is locked.

[0059] Embodiment 2:

[0060] An internal fault occurs in the running transformer. and like Figure 4 and Figure 5 As shown. The horizontal axis is time, the vertical axis is frequency, and the higher the color brightness, the greater the value of the point. In this embodiment, after t = 1.7s, and Large values ​​appear at 50Hz, but not at 100Hz. The criterion of formula (4) is not satisfied, and the transformer protection is not locked. The period with higher brightness at 50Hz corresponds to the period when the fault occurs.

[0061] Based on the same inventive concept, the present invention also provides a system for identifying the inrush current in transformer operation, such as Figure 6 As shown, it includes a current difference acquisition module 101 , an energy value acquisition module 102 and an identification module 103 .

[0062] The current difference acquisition module 101 is used to obtain the instantaneous value of the three-phase differential current of the adjacent air-drop transformer T1 in real time. And the instantaneous value of the three-phase differential current of the running transformer T2 and obtain and The current difference in Indicates the three phases A, B, and C of the transformer.

[0063] The energy value acquisition module 102 is used to extract the energy value based on synchronous squeezing wavelet transform. The time-frequency energy in and The time-frequency energy in Accumulate separately and The corresponding double frequency energy value in the set frequency range is obtained to obtain the time-frequency energy and and time-frequency energy and

[0064] The identification module 102 is used to and The result is compared with the judgment threshold, and the corresponding inrush current is identified according to the comparison result.

[0065] Each module in the above transformer operation and inrush current identification system can be implemented in whole or in part by software, hardware and their combination. Each module can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to each module above.

[0066] The present invention also provides a computer device, including a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps in the embodiment of the method for identifying the inrush current in transformer operation. The specific implementation method can be found in the method embodiment, which will not be described in detail here.

[0067] Furthermore, the present invention also provides a non-temporary computer-readable storage medium containing instructions, and a computer program is stored on the storage medium. For example, a memory containing instructions, the above instructions can be executed by a processor of a computer device to complete the above method. For example, the non-temporary computer-readable storage medium can be a ROM, a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. When the computer program is executed by the processor, the steps in the embodiment of the method for identifying the inrush current in the operation of the transformer can be implemented. The specific implementation method can be found in the method embodiment, which will not be repeated here.

[0068] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0069] The present invention is described with reference to flowcharts and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as a combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0070] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0071] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0072] It should be pointed out that the specific implementation methods described above can enable those skilled in the art to understand the invention more comprehensively, but do not limit the invention in any way. Therefore, although the invention has been described in detail in this specification and embodiments, those skilled in the art should understand that the invention can still be modified or replaced by equivalents; and all technical solutions and improvements that do not deviate from the spirit and scope of the invention are included in the protection scope of the patent for the invention. Any figure mark in the claims should not be regarded as limiting the claims involved. Any simple change or equivalent replacement of the technical solution that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention belongs to the protection scope of the present invention.

Claims

1. A method for identifying the inrush current in transformer operation. It is characterized in that The following steps are involved: Real-time acquisition of the instantaneous value of the three-phase differential current of the adjacent air-drop transformer T1 And the instantaneous value of the three-phase differential current of the running transformer T2 and obtain and The current difference in Indicates the three phases A, B, and C of the transformer; Extraction based on synchronous squeezing wavelet transform The time-frequency energy in and The time-frequency energy in Accumulate separately and The corresponding double frequency energy value in the set frequency range is obtained to obtain the time-frequency energy and and time-frequency energy and The time-frequency energy and and time-frequency energy and The result is compared with the judgment threshold, and the corresponding inrush current is identified according to the comparison result.

2. The method for identifying the inrush current in transformer operation according to claim 1, It is characterized in that The synchronous squeezing wavelet transform extraction The time-frequency energy in and The time-frequency energy in Specifically include: The mother wavelet function Ψ(t) is used to and Perform continuous wavelet transform to obtain continuous wavelet coefficient K I ; Where m is the scale factor of wavelet transform, n is the translation factor, represents the conjugate of Ψ; i(t) is the function of current changing with time, i(t) represents or t represents time; Indicates the current difference A function that varies with time, Indicates the instantaneous value of the three-phase differential current of the air-drop transformer T1 Functions that vary with time; Divide i(t) into different frequency intervals and calculate the center frequency ω l Nearby area The wavelet coefficients are squeezed to obtain the time-frequency energy T after synchronous squeezing wavelet transformation; Where Δω is the size of the frequency interval, f represents the time-frequency energy T as a function of i(t); m k Represents the value of the kth wavelet transform scale factor, m k-1 Indicates the value of the k-1th wavelet transform scale factor; (Δm) k Represents two adjacent scale factors m k and m k-1 Difference in values, (Δm) k =m k -m k-1 ; and The time-frequency energies after synchronous squeezing wavelet transform are and 3. The method for identifying the inrush current in transformer operation according to claim 1, It is characterized in that The set frequency interval is [2f N -δ, 2f N +δ], where f N represents the rated frequency, and δ represents the frequency deviation to be accumulated; The frequency interval of the summation is [2f N -δ, 2f N +δ].

4. The method for identifying the inrush current in transformer operation according to claim 1, It is characterized in that The time-frequency energy and and time-frequency energy and Compared with the judgment threshold, the judgment criteria are as follows: Where E set1 and E set2 is the threshold in the criterion. When the criterion is met, it is judged that the inrush current occurs and the transformer protection is locked. Otherwise, the differential current of the two transformers is obtained again and the judgment cycle continues.

5. A system for identifying the inrush current in transformer operation. It is characterized in that include: The current difference acquisition module is used to obtain the instantaneous value of the three-phase differential current of the adjacent air-drop transformer T1 in real time. And the instantaneous value of the three-phase differential current of the running transformer T2 and obtain and The current difference in Indicates the three phases A, B, and C of the transformer; Energy value acquisition module, used for extracting based on synchronous squeezing wavelet transform The time-frequency energy in and The time-frequency energy in Accumulate separately and The corresponding double frequency energy value in the set frequency range is obtained to obtain the time-frequency energy and and time-frequency energy and Identification module, used to transform time-frequency energy and and time-frequency energy and The result is compared with the judgment threshold, and the corresponding inrush current is identified according to the comparison result.

6. A computer device comprising a memory, a processor and a computer program stored in the memory, It is characterized in that The processor executes the computer program to implement the steps of the method for identifying the inrush current in transformer operation according to any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, It is characterized in that When the computer program is loaded by a processor, it is capable of executing the steps of the method for identifying the inrush current in transformer operation as described in any one of claims 1 to 4.

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