Method and system for identifying and inhibiting magnetizing inrush current of transformer

Abstract

The invention relates to a method and system for identifying and suppressing magnetizing inrush current of a transformer, and belongs to a part of the technical field of power system application research, the system comprises a transformer main body, and the transformer main body comprises an iron core, a primary winding and a secondary winding; the magnetizing inrush current identification module comprises a current sampling unit and a DSP processing unit. And an adjustable impedance unit. The method has the remarkable advantages that through the microprocessor, the second harmonic content in the magnetizing inrush current of the transformer is recognized, and the value of the adjustable impedance is calculated. Through the implementation of the process, the magnetizing inrush current generated when the transformer is switched on is effectively inhibited, so that the operation safety of the on-site transformer is remarkably improved, and the overall stability of a power system is enhanced.

Description

Technical Field

[0001] The invention belongs to the field of power system application research, and specifically relates to a transformer excitation inrush current identification and suppression method and system. Background Art

[0002] Transformer is one of the indispensable key equipment in the power system. It plays a vital role in the generation, conversion, transmission and final use of electricity. The stable operation of transformer is closely related to the overall stability and safety of the power system. Therefore, ensuring the normal operation of transformer is the basis for maintaining the reliability of the power system.

[0003] When the transformer is in the no-load closing state, the residual magnetism inside the core and its hysteresis characteristics will cause a phenomenon called excitation inrush current. The intensity of this inrush current usually exceeds 5 to 10 times the rated current of the transformer, forming an instantaneous high current state. This strong excitation inrush current will not only affect the transformer's protection equipment, but may even cause it to malfunction, causing the transformer to fail multiple times during startup.

[0004] In addition, the presence of inrush current will cause the electromotive force inside the transformer winding to rise sharply, which will lead to abnormal temperature rise in some areas. This overheating phenomenon may damage the insulation material of the transformer, and even cause deformation or other structural damage to the winding in extreme cases. Therefore, understanding and controlling the characteristics of inrush current is crucial to ensure the safe operation of the transformer and extend its service life.

[0005] In order to effectively deal with the challenges brought by the excitation inrush current, a series of measures need to be taken in the design and operation of the power system, such as reasonably selecting the capacity of the transformer, optimizing the setting of the protection equipment, and monitoring and analyzing the excitation inrush current when necessary. These measures can not only improve the operational reliability of the transformer, but also reduce the risk of failure caused by the excitation inrush current to a certain extent, thereby ensuring the stability and safety of the power system. Summary of the invention

[0006] In order to solve the deficiencies in the prior art, the present invention provides a transformer excitation inrush current identification and suppression method and system, which are used to identify the generation of transformer excitation inrush current, input adjustable impedance, suppress the generated excitation inrush current, stabilize the operation of the power system, and solve the above-mentioned problems existing in the background technology.

[0007] The present invention adopts the following technical solution.

[0008] The present invention provides a method for identifying and suppressing transformer excitation inrush current, which is characterized by comprising:

[0009] Collect transformer primary winding current waveform data and send it to the DSP module;

[0010] The current reference value is set in the DSP module, and the collected current data is compared with the reference value;

[0011] Select the sampling frequency, use the analog-to-digital converter to convert the analog current signal into a digital signal, and store it in the memory of the DSP. When the current is less than the reference value, the transformer is judged to be in normal working state, and the DSP module does not perform FFT analysis on it. When the current is greater than the reference value, the sampled signal is de-DC processed, FFT transformation is performed, the spectrum information of the signal is obtained, and the amplitude of the second harmonic is extracted from it to determine whether there is an excitation inrush current.

[0012] When the presence of an excitation inrush current is detected, the excitation inrush current suppression operation is performed.

[0013] Preferably, the current reference value is 1.5 times the rated current.

[0014] Preferably, the sampling frequency is twice or more of the highest frequency of the signal.

[0015] Preferably, the criterion for determining whether there is an excitation inrush current is that if it is identified that the second harmonic content exceeds 10% of the total current, it is determined that there is an excitation inrush current.

[0016] Preferably, the work of suppressing the excitation inrush current includes:

[0017] When the transformer is in normal working condition, the DSP processing unit calculates the required impedance value to be zero and issues a command to the adjustable impedance module;

[0018] When the DSP processing unit identifies a surge in the second harmonic content, it calculates the impedance value that restores the current to less than 1.5 times the rated current based on the transformer equivalent circuit diagram, and issues a command to the adjustable impedance module;

[0019] After receiving the command, the adjustable impedance module adjusts the impedance value to the specified value to suppress the excitation inrush current;

[0020] The collected current is compared with the reference value again. When the current is greater than the reference value, the adjustable impedance module is still at the specified value. When the current is less than the reference value, the DSP processing unit performs FFT analysis. When the second harmonic content is reduced to within 10% of the total current, the DSP processing unit sends an instruction to the adjustable impedance module to adjust its impedance value to zero.

[0021] Preferably, the criterion for determining whether the second harmonic content increases sharply is that the second harmonic content exceeds 10% of the total current.

[0022] Preferably, the impedance specified value is

[0023]

[0024] Among them, Z o is the specified value of the adjustable impedance module, U 额 is the rated voltage of the transformer, I 额 is the rated current of the transformer, Z 变 is the equivalent impedance of the transformer.

[0025] The present invention also provides a transformer excitation inrush current identification and suppression system, the system is a system used by the aforementioned transformer excitation inrush current identification and suppression method, comprising a transformer body and an excitation inrush current identification module;

[0026] The transformer body comprises an iron core, a primary winding and a secondary winding;

[0027] The excitation inrush current identification module includes a current sampling unit, a DSP processing unit and an adjustable impedance unit;

[0028] The current sampling unit is used to collect the current waveform data of the primary winding of the transformer;

[0029] The DSP processing unit is used to suppress the excitation inrush current;

[0030] The adjustable impedance unit is used to adjust the impedance value.

[0031] The present invention also provides a terminal, including a processor and a storage medium;

[0032] The storage medium is used to store instructions;

[0033] The processor is used to operate according to the instructions to execute the steps of the aforementioned method.

[0034] The present invention also provides a computer-readable storage medium on which a computer program is stored, characterized in that the program implements the steps of the above method when executed by a processor.

[0035] The beneficial effect of the present invention is that, compared with the prior art, the second harmonic content in the transformer excitation inrush current is identified through a microprocessor, and the value of the adjustable impedance is calculated to achieve the suppression of the transformer closing excitation inrush current, which is beneficial to provide the safety of on-site transformer operation and improve the stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of the structure of a transformer excitation inrush current identification and suppression system in the present invention;

[0037] Figure 2 is the transformer equivalent circuit diagram of the present invention;

[0038] Figure 3 The present invention is a flow chart of a transformer excitation inrush current identification and suppression method. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0040] The present invention is based on the same concept and includes two technical solutions, namely, transformer excitation inrush current identification and transformer excitation inrush current suppression method. Both methods use a DSP control system to control an adjustable impedance unit and issue corresponding instructions to achieve the purpose of identifying transformer excitation inrush current and suppressing transformer excitation inrush current.

[0041] like Figure 3 As shown, embodiment 1 of the present invention provides a method for identifying and suppressing transformer excitation inrush current, which is characterized in that DSP uses fast Fourier transform to identify the second harmonic content in the primary winding current of the transformer, including the following steps:

[0042] Step 1, collecting transformer primary winding current waveform data and transmitting it to the DSP processing unit;

[0043] Step 2: a current reference value is set in the DSP processing unit, and the current reference value is set to 1.5 times the rated current, and the collected current data is compared with the reference value;

[0044] Step 3. According to the Nyquist sampling theorem, select an appropriate sampling frequency, which is usually more than twice the highest frequency of the signal to ensure signal integrity. Use an analog-to-digital converter to convert the analog current signal into a digital signal and store it in the memory of the DSP. When the current is less than the reference value, it is assumed to be a normal working state of the transformer, and the DSP processing unit does not perform FFT analysis on it. When the current is greater than the reference value, the sampled signal is de-DC processed to ensure that the center of the signal is near zero to improve the accuracy of the FFT analysis. Apply the window function to reduce spectrum leakage. Perform FFT transformation to obtain the spectrum information of the signal and extract the amplitude of the second harmonic from it. By comparing with the set threshold, determine whether there is an excitation inrush current;

[0045] Step 4: When the existence of the excitation inrush current is detected, the excitation inrush current is suppressed.

[0046] Based on the data of transformer no-load test and short-circuit test, the mathematical model of the transformer is established. The DSP calculates the impedance value required to restore the current to the normal range of the rated current and drives the adjustable impedance unit to change.

[0047] Step 4.1, when the transformer is in normal working state, the DSP calculates the required impedance value to be zero and sends a command to the adjustable impedance unit;

[0048] Step 4.2: When the DSP identifies that the second harmonic content surges, that is, the second harmonic content exceeds 10% of the total current, the DSP calculates the impedance value that restores the current to less than 1.5 times the rated current based on the transformer equivalent circuit diagram, and issues a command to the adjustable impedance unit;

[0049] Step 4.3, after receiving the instruction, the adjustable impedance unit adjusts the impedance value to the specified value to suppress the excitation inrush current;

[0050] Step 4.4, compare the collected current with the reference value again. When the current is greater than the reference value, the adjustable impedance unit is still at the specified value. When the current is less than the reference value, the DSP performs FFT analysis, in which the second harmonic content is reduced to within the normal range. The DSP issues a command to the adjustable impedance unit to adjust its impedance value to zero. First, based on the no-load test and short-circuit test in the factory experiment of the transformer, a mathematical model of the transformer is established, Z = R + jX, where j is an imaginary unit. Provide a basis for the subsequent calculation of the adjustable impedance unit.

[0051] The DSP in this method is responsible for receiving and processing the transformer primary current data collected from the current sampling unit. By performing a fast Fourier transform (FFT), the DSP is able to analyze the frequency components in the current signal, especially the critical second harmonic, to determine whether an excitation inrush current occurs. Once an inrush current is identified, the DSP will calculate the required impedance value and instruct the adjustable impedance unit to adjust to that value to effectively suppress the inrush current and protect the system. In addition, the DSP continuously monitors the current state and harmonic level to ensure that the adjustable impedance unit is instructed to return to its original state after the current returns to normal.

[0052] Set up the DSP processing unit, install the necessary software and hardware interfaces, and load the algorithms for magnetizing inrush current detection, including FFT and harmonic analysis functions.

[0053] The current sampling unit and the adjustable impedance unit are connected in series to the primary winding of the transformer to ensure the accuracy and real-time performance of data collection.

[0054] When the transformer is closed, the current waveform data on the primary side is collected and sent to the DSP processing unit, and the system is set to work in a continuous monitoring mode.

[0055] When the current exceeds the preset reference value, the DSP processing unit performs FFT analysis to convert the sampled data into frequency domain data, thereby detecting and quantifying the various frequency components in the signal. The second harmonic content is used to determine whether there is an excitation inrush current. If a second harmonic higher than 10% of the total current is identified, it is determined that the current state is an excitation inrush current.

[0056] The current signal of the transformer can be expressed as:

[0057] i(t)=I1 sin(2πft)+I2 sin(4πft)+…+I n sin(2nπft)+ε(t)

[0058] where I1,I2,…,I n is the amplitude of the harmonics of different frequencies, f is the fundamental frequency, ε(t) is the noise term, and the size of I2 is extracted.

[0059] According to the severity of the excitation inrush current, that is, the proportion of the second harmonic in the total current, the DSP calculates the necessary impedance adjustment value.

[0060]

[0061] Among them, Z o is the specified value of the adjustable impedance unit, U 额 is the rated voltage of the transformer, I 额 is the rated current of the transformer, Z 变 is the equivalent impedance of the transformer.

[0062] The DSP sends a control signal to the adjustable impedance unit, instructing it to adjust to the calculated impedance value to reduce the inrush current effect.

[0063] The adjustable impedance unit adjusts the impedance according to the instruction of the DSP and feeds the result back to the DSP, and the DSP continues to fine-tune the impedance value according to the feedback result.

[0064] When the current returns to below the reference value and the second harmonic returns to normal level, the DSP instructs the adjustable impedance unit to adjust the impedance value back to the initial (usually zero) state.

[0065] This embodiment describes a method for identifying and suppressing transformer excitation inrush current, which effectively improves the safety of transformer closing operation and the stability of the system. By adopting advanced digital signal processing technology (DSP), the current sampling unit and fast Fourier transform (FFT) technology are used to accurately identify the second harmonic in the primary side current and accurately determine the existence of excitation inrush current. Subsequently, based on the identification results, the DSP calculates the required adjustment impedance value and adjusts it in real time through an adjustable impedance unit, thereby effectively suppressing the excitation inrush current.

[0066] like Figure 1 , 2 As shown, embodiment 2 of the present invention provides a transformer excitation inrush current identification and suppression system, the system is a system used by the aforementioned transformer excitation inrush current identification and suppression method, including a transformer body and an excitation inrush current identification module;

[0067] The transformer body comprises an iron core, a primary winding and a secondary winding;

[0068] The excitation inrush current identification module includes a current sampling unit, a DSP processing unit and an adjustable impedance unit;

[0069] The current sampling unit is used to collect the current waveform data of the primary winding of the transformer;

[0070] The DSP processing unit is used to suppress the excitation inrush current;

[0071] The adjustable impedance unit is used to adjust the impedance value.

[0072] The above description is for the convenience of illustrating the basic method of the present invention, taking a single-phase transformer as an example. The method is also applicable to a three-phase transformer. For a three-phase transformer, it is only necessary to set the respective adjustable impedance units in different phases.

[0073] This embodiment is carried out by taking a single-phase transformer as an example. This method is also applicable to a three-phase transformer. For a three-phase transformer, it is only necessary to set respective adjustable impedance units in different phases.

[0074] Combined with the above discussion, the technical solution of the present invention not only demonstrates innovation in the field of magnetizing inrush current identification and suppression, but also provides a reliable and practical solution. Although the above embodiments provide specific implementation methods, the present invention is not limited to these examples. Those skilled in the art may also make various appropriate modifications and layouts to the present invention without departing from the purpose and scope of the present invention, which all belong to the protection scope of the present invention.

[0075] The beneficial effect of the present invention is that, compared with the prior art, the second harmonic content in the transformer excitation inrush current is identified through a microprocessor, and the value of the adjustable impedance is calculated to achieve the suppression of the transformer closing excitation inrush current, which is beneficial to provide the safety of on-site transformer operation and improve the stability of the power system.

[0076] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0077] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0078] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0079] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for identifying and suppressing transformer excitation inrush current, characterized in that: include: Collect transformer primary winding current waveform data and send it to the DSP module; The current reference value is set in the DSP module, and the collected current data is compared with the reference value; Select the sampling frequency, use the analog-to-digital converter to convert the analog current signal into a digital signal, and store it in the memory of the DSP. When the current is less than the reference value, the transformer is judged to be in normal working state, and the DSP module does not perform FFT analysis on it. When the current is greater than the reference value, the sampled signal is de-DC processed, FFT transformation is performed, the spectrum information of the signal is obtained, and the amplitude of the second harmonic is extracted from it to determine whether there is an excitation inrush current. When the presence of an excitation inrush current is detected, the excitation inrush current suppression operation is performed.

2. A method for identifying and suppressing transformer excitation inrush current according to claim 1, characterized in that: The current reference value is 1.5 times the rated current.

3. A method for identifying and suppressing transformer excitation inrush current according to claim 2, characterized in that: The sampling frequency is twice or more of the highest frequency of the signal.

4. A method for identifying and suppressing transformer excitation inrush current according to claim 3, characterized in that: The criterion for determining whether there is an excitation inrush current is that if it is identified that the second harmonic content exceeds 10% of the total current, it is determined that there is an excitation inrush current.

5. A method for identifying and suppressing transformer excitation inrush current according to claim 4, characterized in that: The suppression work of the excitation inrush current includes: When the transformer is in normal working condition, the DSP processing unit calculates the required impedance value to be zero and issues a command to the adjustable impedance module; When the DSP processing unit identifies a surge in the second harmonic content, it calculates the impedance value that restores the current to less than 1.5 times the rated current based on the transformer equivalent circuit diagram, and issues a command to the adjustable impedance module; After receiving the command, the adjustable impedance module adjusts the impedance value to the specified value to suppress the excitation inrush current; The collected current is compared with the reference value again. When the current is greater than the reference value, the adjustable impedance module is still at the specified value. When the current is less than the reference value, the DSP processing unit performs FFT analysis. When the second harmonic content is reduced to within 10% of the total current, the DSP processing unit sends an instruction to the adjustable impedance module to adjust its impedance value to zero.

6. A method for identifying and suppressing transformer excitation inrush current according to claim 5, characterized in that: The criterion for determining whether the second harmonic content surges is that the second harmonic content exceeds 10% of the total current.

7. A method for identifying and suppressing transformer excitation inrush current according to claim 6, characterized in that: The impedance is specified as Among them, Z o is the specified value of the adjustable impedance module, U 额 is the rated voltage of the transformer, I 额 is the rated current of the transformer, Z 变 is the equivalent impedance of the transformer.

8. A transformer excitation inrush current identification and suppression system, the system being a system used in a transformer excitation inrush current identification and suppression method as claimed in any one of claims 1 to 7, characterized in that: It includes a transformer body and an excitation inrush current identification module; The transformer body comprises an iron core, a primary winding and a secondary winding; The excitation inrush current identification module includes a current sampling unit, a DSP processing unit and an adjustable impedance unit; The current sampling unit is used to collect the current waveform data of the primary winding of the transformer; The DSP processing unit is used to suppress the excitation inrush current; The adjustable impedance unit is used to adjust the impedance value.

9. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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