Excitation inrush current suppression method and system during switching-on of distribution transformer

Abstract

The invention discloses a magnetizing inrush current suppression method and system during closing of a distribution transformer. The method comprises the following steps: acquiring three-phase voltage and current waveform data before and after tripping of a primary side circuit breaker of the distribution transformer; measuring and calculating the residual magnetism of the primary side winding according to the voltage and current data, and determining a closing phase sequence by the minimum residual magnetism in order to avoid dispersive errors of the circuit breaker; determining the specific closing time of the transformer according to the residual magnetism information; only the voltage and current waveform data before and after the primary side circuit breaker is switched on need to be collected, the residual magnetism is measured and calculated, and the switching-on phase sequence and the switching-on time of the circuit breaker are determined, so that the magnetizing inrush current during switching-on of the distribution transformer is inhibited. According to the method, the actual condition of the power distribution network is fully considered, parameters are easy to obtain, the operation is completed within a period after the inherent closing time of the circuit breaker, the speed is high, the principle is deeper, the closing phase sequence and strategy are clear, operability is high, and the method is suitable for various scenes of the power distribution network.

Description

Background Art

[0002] Distribution transformers are one of the most important power equipment in the distribution network. They are directly facing various types of loads, and there are a large number of them distributed along the line with large capacity. When power is restored after the fault is removed, due to the hysteresis and nonlinear saturation characteristics of the transformer core, the core magnetic flux cannot change suddenly. The transient magnetic flux generated by the voltage surge will saturate the transformer core and generate a large current with an amplitude of 6 to 8 times the rated current, which is called the excitation inrush current. The excitation inrush current generated by a large number of distribution transformers overlaps with the load current, which will cause the upstream line protection to malfunction. When a transient fault occurs, it may cause the reclosing failure, seriously affecting the power supply reliability of the distribution network, and may cause significant economic losses and social impacts. Therefore, measures must be taken to suppress the excitation inrush current and reduce the harm caused by the excitation inrush current.

[0003] There are three main methods for suppressing transformer excitation inrush current: (1) Changing the internal structure of the transformer. This mainly involves changing the distribution of the primary and secondary coil windings of the transformer so that the equivalent transient inductance of the transformer coil becomes larger to reduce the transformer excitation inrush current. (2) External devices. Additional components are added to the outside of the transformer to compensate for and suppress the excitation inrush current. For example, series resistors, capacitors on the low-voltage side, external inrush current suppressors, etc. (3) Residual magnetism suppression. The purpose of suppressing the excitation inrush current is achieved by eliminating or offsetting the residual magnetism of the transformer in advance. For example, pre-magnetization method, phase selection closing method, etc. There are a large number of distribution transformers in the distribution network. The first and second methods require a large amount of engineering work for the distribution network transformation, high investment, and cumbersome maintenance, and the suppression effect of this method is limited. The pre-magnetization method also requires external equipment and a long magnetization time, and is usually suitable for a single large transformer. Only the phase selection closing method is flexible and controllable, and can quickly affect the excitation inrush current of many transformers in the distribution network.

[0004] Phase selection closing is a protection control strategy in the power system. It is used to selectively open or close the circuit breaker of a specific phase when a fault or abnormal situation occurs in the power equipment to restore the power supply of the power system and suppress the operation overvoltage, various inrush currents, etc. The basic principle of phase selection closing is to control the circuit breaker to close at a specified voltage (or current) phase angle, so that the residual magnetism of the core at the moment of closing is equal to the pre-induced magnetic flux generated by the system voltage, and the purpose of reducing the core magnetic flux is achieved by weakening the transient magnetic flux. In theory, the phase selection closing technology can completely eliminate the excitation inrush current. The electromagnetic coupling between the phases of the three-phase transformer is very close, and different closing sequences and closing phases will have a huge impact on the excitation current. Therefore, formulating an effective phase selection closing strategy becomes the key to realizing the phase selection closing of the transformer.

[0005] Phase selection closing technology can be used in conjunction with distribution network reclosing technology. At present, the reclosing research of distribution network can identify the type of line fault. When a permanent fault occurs, the circuit breaker does not need to be reclosed; when a transient fault occurs, the circuit breaker will trip due to the existence of excitation inrush current after reclosing. The traditional solution is to increase the setting value of the protection or extend the protection action time to avoid the excitation inrush current, which seriously reduces the sensitivity and speed of the protection. Therefore, a clear optimal closing phase sequence and closing strategy are needed to suppress the excitation inrush current of the distribution network.

[0006] There are many research results on phase selection and closing to suppress excitation inrush current, but they are only applicable to transmission networks and cannot be applied to distribution networks. On the one hand, the transformers used in the main grid are usually YNy0 or YNd11 transformers, while the distribution network often uses Dyn11 transformers, and the research objects are different; on the other hand, for the suppression of excitation inrush current of large transformers in the main grid, existing studies have avoided measuring residual magnetism by using the strategy of the first closing phase closing angle equal to the circuit breaker opening angle, but this can only be applied to a single transformer. For the distribution network, there are many transformers along the line, and there is only one main circuit breaker. When a line fails, the residual magnetism of each transformer may not be the same. The existing methods are not feasible in the distribution network, and the residual magnetism cannot be directly avoided. Therefore, the research on excitation inrush current suppression for the distribution network requires a set of single Dyn11 transformer closing strategies based on residual magnetism, so as to lay the foundation for the suppression of excitation inrush current of multiple transformers.

[0007] The existing technology has the following defects: (1) Long delay time. After the first two phases are closed, the existing technology needs to delay 2 to 3 cycles before the last phase can be closed. The excitation surge current decays quickly in the distribution network, and the suppression effect of the existing technology is not obvious. At the same time, the excessive delay reduces the speed of protection.

[0008] (2) It is not applicable to multiple transformers with different residual magnetism. In order to avoid the measurement of residual magnetism, the existing technology adopts the strategy of the same closing phase and opening phase, which can only be applied to a single transformer. There is no theoretical basis and clear strategy for suppressing the excitation inrush current of multiple transformers with different residual magnetism due to faults in the distribution network. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a method and system for suppressing the excitation inrush current when closing a distribution transformer in response to the above-mentioned deficiencies in the prior art, and to determine the optimal phase sequence and the optimal target phase angle for phase selection and closing of a Dyn11 type distribution transformer according to the residual magnetism, so as to solve the technical problems that the traditional strategy is not suitable for distribution transformers, is not suitable for multiple transformers with different residual magnetism, and has a long delay time in the closing process, and effectively suppress the transformer no-load closing inrush current.

[0010] The present invention adopts the following technical solutions: A method for suppressing magnetizing inrush current when a distribution transformer is switched on comprises the following steps: Collect three-phase voltage and current waveform data before and after the primary side circuit breaker of the distribution transformer trips; The residual magnetism is estimated using the obtained three-phase voltage and current waveform data, and the residual magnetism of the primary winding is arranged; Determine the first two phases to be closed and the last phase to be closed based on the arrangement order; Determine the closing time of the first two phases based on the first two phases obtained; determine the closing time of the last phase based on the last phase obtained; The control terminal controls the circuit breaker to close according to the obtained closing time of the first two phases to be closed and the closing time of the last phase to be closed.

[0011] Preferably, the Dyn11 type transformer residual magnetism estimation method is used to obtain the phase-to-phase residual magnetism of the primary winding , , , and arrange them in descending order of absolute value.

[0012] Preferably, the remanence with the smallest absolute value is ,definition The phases at both ends of the coil are the first two phases to be closed, and the remaining phases are the unclosed phases.

[0013] Preferably, the closing time of the first two phases to be closed is A and B, and the last phase to be closed is C. for:

[0014] in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases A and B of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

[0015] Preferably, when the first two phases to be closed are phases B and C and the last phase to be closed is phase A, the closing time of the first two phases to be closed is:

[0016] in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases B and C of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

[0017] Preferably, when the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, the closing time of the first two phases to be closed is:

[0018] in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases C and A of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

[0019] Preferably, when the first two phases to be closed are phases B and C and the last phase to be closed is phase A, the closing time of the last phase to be closed is:

[0020] in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases C and A of the transformer, is the residual magnetism of the winding between phases A and B of the transformer, is the angular frequency of the power frequency, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

[0021] Preferably, when the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, the closing time of the last phase to be closed is:

[0022] in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases A and B of the transformer, is the residual magnetism of the winding between phases B and C of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

[0023] Preferably, when the first two phases to be closed are phases A and B and the last phase to be closed is phase C, the closing time of the last phase to be closed is:

[0024] in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases B and C of the transformer, is the residual magnetism of the winding between phases C and A of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

[0025] In a second aspect, an embodiment of the present invention provides a system for suppressing magnetizing inrush current when a distribution transformer is switched on, comprising: The acquisition module collects the three-phase voltage and current waveform data before and after the primary side circuit breaker of the distribution transformer trips; An arrangement module estimates the residual magnetism using the obtained three-phase voltage and current waveform data, and arranges the residual magnetism of the primary winding; A determination module determines the first two phases to be closed and the last phase to be closed based on the obtained arrangement order; A time module determines the closing time of the first two phases based on the first two phases obtained, and determines the closing time of the last phase based on the last phase obtained; The output module and the control terminal control the circuit breaker to close according to the closing time of the first two phases and the closing time of the last phase.

[0026] In a third aspect, a computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for suppressing magnetizing inrush current when closing the distribution transformer are implemented.

[0027] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, comprising a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for suppressing excitation inrush current when closing the distribution transformer.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects: First of all, in terms of steps, the relevant parameters are easy to obtain, the calculation method is clear, the operation requirements are simple, and the closing phase sequence and strategy are clear; in terms of speed, the closing time can be controlled within one cycle after the inherent closing time, and the speed is relatively fast; in principle, the present invention can derive the traditional suppression strategy of "the phase of the opening moment is consistent with the closing moment" to avoid the measurement of residual magnetism, and can also derive a strategy with a shorter delay, which is suitable for use in distribution networks and lays the foundation for the suppression of excitation inrush currents of multiple transformers. The residual magnetism distribution and corresponding statistical data of multiple transformers when the distribution network fails can be integrated, and the residual magnetism can be considered from an overall perspective. This strategy is used to suppress the excitation inrush current, which has a strong reference for the distribution network.

[0029] Furthermore, it is applicable to instantaneous fault recovery. Traditional suppression methods emphasize that the phase of the opening moment is consistent with the closing moment, so as to avoid the measurement of residual magnetism, but it can only be applied to no-load closing. This method has short delay, high speed, and is based on residual magnetism for calculation. It is convenient to use this method according to the residual magnetism distribution of the transformer when a fault occurs in the distribution network, so it is applicable to instantaneous fault recovery.

[0030] Furthermore, it is convenient to cooperate with the fault identification strategy. The strategy of closing two phases first and then closing one phase leaves room for cooperation with the distribution network phase reclosing fault identification technology, and the fault is removed when a permanent fault occurs. This strategy is used to suppress the excitation inrush current when a transient fault occurs.

[0031] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0032] In summary, the relevant parameters of the present invention are easy to obtain, the speed is fast, the closing phase sequence and strategy are clear, the principle is more profound, and the applicable scenarios are wider. It can be applied to multiple distribution transformers, distribution network scenarios, and instantaneous fault scenarios, and can also be coordinated with the current distribution network fault identification strategy. The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings to be used in the description of the embodiments. Obviously, 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.

[0034] Figure 1 This is a logic diagram of magnetizing inrush current suppression in the distribution network; Figure 2 This is a block diagram of the steps for suppressing magnetizing inrush current in the distribution network; Figure 3 This is the equivalent diagram of two-phase closing of Dyn11 transformer; Figure 4 This is a simulation model diagram of a three-phase distribution transformer; Figure 5 Schematic diagram of magnetizing inrush current when the residual magnetism is (0.7, -0.5, -0.2) and the closing angle is 0; Figure 6 The residual magnetism is (0.7, -0.5, -0.2), and the schematic diagram of the excitation inrush current after adopting the strategy of the present invention; Figure 7 Schematic diagram of magnetizing inrush current when the closing angle is 0 under the condition of zero residual magnetism of UMEC transformer model; Figure 8 Schematic diagram of magnetizing inrush current after adopting the proposed strategy under zero residual magnetism condition of UMEC transformer model; Fig. 9 A schematic diagram of a computer device provided by an embodiment of the present invention; Fig.10 The present invention is a block diagram of an electronic device provided according to an embodiment. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In the description of the present invention, it should be understood that the terms “include” and “comprises” indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0037] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0038] It should be further understood that the term "and / or" used in the present specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects are in an "or" relationship.

[0039] It should be understood that, although the terms first, second, third, etc. may be used to describe preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish preset ranges from each other. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0040] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0041] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0042] The present invention provides a method for suppressing excitation inrush current when a distribution transformer is closed. The method fully considers factors such as the actual situation of the distribution network, the transformer core structure and the winding connection method, and adopts a phase selection closing method for a single Dyn11 three-phase distribution transformer based on residual magnetism to effectively suppress the transformer no-load closing inrush current.

[0043] The present invention provides a method for suppressing excitation inrush current when a distribution transformer is switched on, comprising the following steps: S1. Collect basic data; When the transformer is running, the data acquisition device collects the three-phase voltage and current waveforms before and after the primary side circuit breaker of the distribution transformer trips.

[0044] S2, estimate the residual magnetism and arrange the residual magnetism of the primary winding; Using the data in step S1, the existing Dyn11 transformer residual magnetism estimation method is used to obtain the phase-to-phase residual magnetism of the primary winding, which are respectively , , , and arrange them in descending order according to their absolute values.

[0045] S3, determine the first two phases to be closed and the last phase to be closed; Assume the minimum absolute value of residual magnetism is ,definition The phases at both ends of the coil are the first two phases to be closed, and the remaining phase is the last phase to be closed. For example, the residual magnetism with the smallest absolute value is , the first two phases to be closed are phases A and B, and the last phase to be closed is phase C.

[0046] S4, determine the closing time of the first two phases; The following closing phases all take the zero crossing point of phase A voltage with positive slope as the reference time point , the inherent closing time of the circuit breaker is .

[0047] If the first two phases to be closed are phases A and B, and the last phase to be closed is phase C, then the first closing phase angle is: (1) The corresponding closing time is: (2) Among them, T is the power frequency period 0.02s, .

[0048] If the first two phases to be closed are phases B and C, and the last phase to be closed is phase A, then the first closing phase angle is: (3) The corresponding closing time is: (4) Among them, T is the power frequency period 0.02s, .

[0049] If the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, then the first closing phase angle is (5) The corresponding closing time is: (6) Among them, T is the power frequency period 0.02s, .

[0050] S5, determining the closing time of the last closed phase; The following closing phases all take the zero crossing point of phase A voltage with positive slope as the reference time point , the inherent closing time of the circuit breaker is .

[0051] If the first two phases to be closed are phases B and C, and the last phase to be closed is phase A, the last phase angle is: (7) The corresponding closing time is: (8) If the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, the last phase angle is: (9) The corresponding closing time is: (10) If the first two phases to be closed are phases A and B, and the last phase to be closed is phase C, the last phase angle is: (11) The corresponding closing time is: (12) S6. The control terminal controls the circuit breaker to close according to the closing time of the first two phases to be closed and the last phase to be closed.

[0052] The overall phase selection and closing technology control logic is as follows: Figure 1 , the specific excitation inrush current suppression steps flow chart is as follows Figure 2 .

[0053] It will be appreciated by those skilled in the art that various aspects of the present invention may be implemented as systems, methods or program products. Therefore, various aspects of the present invention may be specifically implemented in the following forms, namely: complete hardware implementation, complete software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, which may be collectively referred to herein as "circuits", "modules" or "platforms".

[0054] In another embodiment of the present invention, a system for suppressing excitation inrush current when a distribution transformer is closed is provided. The system can be used to implement the above-mentioned method for suppressing excitation inrush current when a distribution transformer is closed. Specifically, the system for suppressing excitation inrush current when a distribution transformer is closed includes an acquisition module, an arrangement module, a determination module, a time module and an output module.

[0055] Among them, the acquisition module collects the three-phase voltage and current waveform data before and after the primary side circuit breaker of the distribution transformer trips; An arrangement module estimates the residual magnetism using the obtained three-phase voltage and current waveform data, and arranges the residual magnetism of the primary winding; A determination module determines the first two phases to be closed and the last phase to be closed based on the obtained arrangement order; A time module determines the closing time of the first two phases based on the first two phases obtained, and determines the closing time of the last phase based on the last phase obtained; The output module and the control terminal control the circuit breaker to close according to the closing time of the first two phases and the closing time of the last phase.

[0056] In another embodiment of the present invention, a terminal device is provided, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the excitation inrush current suppression method when the distribution transformer is closed, including: Collect three-phase voltage and current waveform data before and after the primary-side circuit breaker of the distribution transformer trips; use the obtained three-phase voltage and current waveform data to estimate the residual magnetism, and arrange the residual magnetism of the primary-side winding; determine the first two phases to be closed and the last phase to be closed based on the arrangement order; determine the closing time of the first two phases to be closed based on the obtained first two phases to be closed; determine the closing time of the last phase to be closed based on the obtained last phase to be closed; the control terminal controls the circuit breaker to close according to the obtained closing time of the first two phases to be closed and the closing time of the last phase to be closed.

[0057] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and the extended storage medium supported by the terminal device, and can be any tangible medium containing or storing a program, which can be used by an instruction execution system, device or device or used in combination with it. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that more specific examples (non-exhaustive list) of the computer-readable storage medium here include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0058] Computer readable storage media also include data signals propagated in baseband or as part of a carrier wave, which carry readable program codes. Such propagated data signals can take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. The readable storage medium can also be any readable medium other than a readable storage medium, which can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, device, or device. The program code contained on the readable storage medium can be transmitted using any appropriate medium, including but not limited to wireless, wired, optical cable, RF, etc., or any suitable combination of the above.

[0059] Program code for performing the operations of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, etc., and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user device, as a separate software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server. In the case of a remote computing device, the remote computing device may be connected to the user computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., through the Internet using an Internet service provider).

[0060] The processor may load and execute one or more instructions stored in a computer-readable storage medium to implement the corresponding steps of the method for suppressing magnetizing inrush current when the distribution transformer is closed in the above embodiment; the processor may load and execute the following steps of one or more instructions in the computer-readable storage medium: Collect three-phase voltage and current waveform data before and after the primary-side circuit breaker of the distribution transformer trips; use the obtained three-phase voltage and current waveform data to estimate the residual magnetism, and arrange the residual magnetism of the primary-side winding; determine the first two phases to be closed and the last phase to be closed based on the arrangement order; determine the closing time of the first two phases to be closed based on the obtained first two phases to be closed; determine the closing time of the last phase to be closed based on the obtained last phase to be closed; the control terminal controls the circuit breaker to close according to the obtained closing time of the first two phases to be closed and the closing time of the last phase to be closed.

[0061] See also Fig. 9 , the terminal device is a computer device, and the computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When the computer program 63 is executed by the processor 61, the method for suppressing the excitation inrush current when the distribution transformer is closed in the embodiment is implemented. To avoid repetition, it is not described one by one here. Alternatively, when the computer program 63 is executed by the processor 61, the functions of each model / unit in the system for suppressing the excitation inrush current when the distribution transformer is closed in the embodiment are implemented. To avoid repetition, it is not described one by one here.

[0062] The computer device 60 may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will appreciate that Fig. 9 This is only an example of the computer device 60 and does not constitute a limitation of the computer device 60. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0063] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, central processing units, graphics processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, data processing logic based on quantum computing, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may be any conventional processor, etc.

[0064] The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc., equipped on the computer device 60.

[0065] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.

[0066] Any reference to a memory, database or other medium used in the embodiments provided in the present application may include at least one of a non-volatile and a volatile memory. Non-volatile memory may include a read-only memory (ROM), a magnetic tape, a floppy disk, a flash memory, an optical memory, a high-density embedded non-volatile memory, a resistive random access memory (ReRAM), a magnetic random access memory (MRAM), a ferroelectric random access memory (FRAM), a phase change memory (PCM), a graphene memory, etc. Volatile memory may include a random access memory (RAM) or an external cache memory, etc. As an illustration and not limitation, RAM may be in various forms, such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), etc.

[0067] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0068] See also Fig.10 The terminal device 600 is an electronic device, and the electronic device is in the form of a general computing device. The components of the electronic device may include but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including the storage unit 620 and the processing unit 610), a display unit 640, etc.

[0069] The storage unit stores program codes, which can be executed by the processing unit 610, so that the processing unit 610 performs the steps according to various exemplary embodiments of the present invention described in the above method section of this specification. For example, the processing unit 610 can perform the following steps: Figure 2 Follow the steps shown in .

[0070] The storage unit 620 may include a readable medium in the form of a volatile storage unit, such as a random access memory unit (RAM) 6201 and / or a cache memory unit 6202 , and may further include a read-only memory unit (ROM) 6203 .

[0071] The storage unit 620 may also include a program / utility 6204 having a set (at least one) of program modules 6205, such program modules 6205 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0072] Bus 630 may represent one or more of several types of bus structures, including a memory unit bus or memory unit controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.

[0073] The electronic device 600 may also communicate with one or more external devices 700 (e.g., keyboards, pointing devices, Bluetooth devices, etc.), may also communicate with one or more devices that enable a user to interact with the electronic device 600, and / or communicate with any device that enables the electronic device 600 to communicate with one or more other computing devices (e.g., routers, modems, etc.). Such communication may be performed via an input / output (I / O) interface 650. Furthermore, the electronic device 600 may also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter 660. The network adapter 660 may communicate with other modules of the electronic device 600 via a bus 630. It should be understood that, although not shown in the figure, other hardware and / or software modules may be used in conjunction with the electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms, etc.

[0074] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0075] At present, the distribution transformer generally adopts Dyn11 three-phase transformer, whose primary neutral point is not grounded. For the three-phase transformer with ungrounded neutral point, when only one phase of the three-phase circuit breaker is closed, the power supply and the transformer windings cannot form a current path. Therefore, for the first closing of the transformer with ungrounded neutral point, at least two phases must be closed at the same time, such as Figure 3 shown.

[0076] The following gives the flux derivation process for closing two phases, the flux derivation process for closing three phases, and the specific closing phase and closing time determination strategy.

[0077] (1) Derivation of the magnetic flux after any two phases are closed For three-phase power supply (13) in, is the primary side voltage amplitude, is the angular frequency of the power frequency, is the initial phase angle of the system power supply. The reference time points of the following derivation process are all zero-crossing points where the slope of phase A voltage is positive. , the inherent closing time of the circuit breaker is .

[0078] Close the B and C phases and write the circuit voltage equation. Then (14) in, , , is the magnetic flux corresponding to the primary side (delta side) of the transformer, is the primary side resistance, is the number of turns of the primary winding.

[0079] The equation is three-phase coupled. If the primary side resistance is ignored, combining equation (13) and equation (14), the sum-difference-product formula is used to simplify it to obtain (15) Integrate at both ends to get (16) make , is the flux amplitude, then the steady-state flux expression after phases B and C are closed is (17) Similarly, the steady-state flux expression after phases A and B are closed is: (18) The steady-state flux expression after phase C and phase A are closed is: (19) Assume that before closing the circuit, the residual magnetism of the primary winding is , , .

[0080] When closing the B and C phases, in order to make the magnetic flux enter the steady state directly after closing, the closing moment needs to meet (20) When closing the A and B phases, in order to make the magnetic flux enter the steady state directly after closing, the closing moment needs to meet (twenty one) When closing the C and A phases, in order to make the magnetic flux enter the steady state directly after closing, the closing moment needs to meet (twenty two) (2) Derivation of magnetic flux after three-phase closing For all three phases closed, write the circuit voltage equation (twenty three) Combining equation (13) and equation (23), we can use the sum-difference-product formula to get (twenty four) Ignore the internal resistance of the primary side and integrate the two ends, then the flux expression is: (25) make ,but (26) (3) Specific closing strategy ① Determine the first two phases to be closed and the last phase to be closed: According to formulas (17), (18) and (19), when the two phases are first closed, the residual magnetism between the two phases should be as small as possible. In this way, even if there is a phase error of the circuit breaker, the excitation inrush current will be reduced to a minimum.

[0081] Given that the residual magnetism between phases of the primary winding is , , , and arrange them in descending order according to their absolute values. If the remanence with the smallest absolute value is ,definition The phases at both ends of the coil are the first two phases to be closed, and the remaining phase is the last phase to be closed. For example, the flux with the smallest absolute value is , the first two phases to be closed are phases A and B, and the last phase to be closed is phase C.

[0082] ② Determine the closing time of the first two phases: According to equations (20), (21), and (22), we can obtain: If the first two phases to be closed are phases A and B, and the last phase to be closed is phase C, then the first closing phase angle is (27) The corresponding closing time is (28) Among them, T is the power frequency period 0.02s, , is the reference time point, i.e. the zero-crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker.

[0083] If the first two phases to be closed are phases B and C, and the last phase to be closed is phase A, then the first closing phase angle is (29) The corresponding closing time is (30) Among them, T is the power frequency period 0.02s, .

[0084] If the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, then the first closing phase angle is (31) The corresponding closing time is (32) Among them, T is the power frequency period 0.02s, .

[0085] ③ Determine the closing time of the last closed phase If the first two phases to be closed are phases B and C, and the last phase to be closed is phase A, according to equation (26), in order to make the magnetic flux directly enter the steady state after closing, the last phase to be closed needs to satisfy (33) in, It is the closing phase of the last closing phase.

[0086] Subtracting

[0087] Right now

[0088] Therefore, the closing phase of the last phase is (34) The corresponding closing time is (35) in, is the reference time point, i.e. the zero-crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker.

[0089] Similarly, if the first two phases to be closed are phases A and C, and the last phase to be closed is phase B, then the last phase to be closed is (36) The corresponding closing time is (37) If the first two phases to be closed are phases A and B, and the last phase to be closed is phase C, then the last phase to be closed is (38) The corresponding closing time is (39) In order to verify the effectiveness of the above method for suppressing the magnetizing inrush current of the Dyn11 type distribution transformer under no-load closing, a simulation model was built using the electromagnetic transient simulation software PSCAD / EMTDC. Figure 4 The main simulation model is a three-phase double-winding Dyn11 distribution transformer with a rated voltage of 10kV / 0.4kV, a rated capacity of 1MVA, an active load of 0.005MW per phase (approximately no-load, to ensure the normal operation of the model), a system frequency of 50Hz, and a reference time point of 0.1ms.

[0090] Since it is difficult to simulate residual magnetism in a transformer with a triangle connection on the primary side, the traditional DC source simulation method and the dual AC source simulation method proposed by some scholars cannot reasonably set the residual magnetism. The transformer with a triangle connection group satisfies that the sum of the three-phase flux is 0. To facilitate the setting of residual magnetism, the PSCAD classic transformer model is used here, and the zero residual magnetism of the unified magnetic circuit equivalent model (UMEC) model is used to assist in verification. By setting the residual magnetism in the transformer and observing the excitation current waveform on the primary side of the transformer, the suppression effect is tested.

[0091] Here, we take (0.7, -0.5, -0.2) as an example to explain the steps of the invention content. First, (0.7, -0.5, -0.2) means that after calculation, , , are 0.7pu, -0.5pu, -0.2pu respectively, then The absolute value is the smallest in the residual magnetism, so the first two phases to be closed are phases C and A, and the last phase to be closed is phase B.

[0092] Using formulas (30) and (35), it is calculated that the closing time of phase C and phase A is 0.1ms-0.0040ms, and the closing time of phase B is 0.1ms+0.0092ms. Here, the three-phase closing time is all 0.1ms and compared with this strategy. The closing suppression effect is as follows: Figure 5 and Figure 6 It can be seen that the current after closing the circuit breaker using the patent solution is close to the no-load current and almost completely enters the steady state. From the numerical point of view, the closing strategy of this paper has a significant suppression effect, and the current peak is suppressed to less than 1% of the original, and it only needs to be closed within one cycle without excessive delay.

[0093] Since there is no good residual magnetism simulation method for the Dyn11 transformer of the unified magnetic circuit equivalent model (UMEC), the zero residual magnetism case is used here to further assist in verification. (0,0,0) indicates that the , , They are 0p.u., 0p.u., and 0p.u. respectively. Any two phases can be selected as the first two phases to be closed. Here, phases A and B are used as the first two phases to be closed, and phase C is the last phase to be closed. According to formulas (28) and (39), the closing time of phases A and B is 0.1ms+0.0033ms, and the closing time of phase C is 0.1ms+0.0183ms. The closing suppression effect is as follows: Figure 7 and Figure 8 It can be seen that the current after closing the circuit breaker using the patent solution is close to the no-load current and almost completely enters the steady state. From the numerical point of view, the suppression effect of the closing strategy in this paper is significant, the current peak is suppressed to 1% of the original, and it only needs to be closed within one cycle without excessive delay.

[0094] In summary, the method and system for suppressing magnetizing inrush current when a distribution transformer is switched on in the present invention have the following advantages: The closing time can be controlled within one cycle, which has the advantages of faster speed, higher efficiency, simple operation requirements and strong operability, providing an effective strategy for suppressing the excitation inrush current of the distribution transformer.

[0095] The suppression of the excitation inrush current of the distribution transformer based on residual magnetism is beneficial for use in the distribution network and can be applied to a large number of small distribution transformers. Specifically, the residual magnetism distribution and corresponding statistical data of multiple transformers when the distribution network fails can be integrated, and the residual magnetism can be considered from an overall perspective to suppress the excitation inrush current. It has a strong reference for the distribution network, and the relevant parameters are simple and convenient to obtain, and it is easy to put into use.

[0096] It is convenient to cooperate with the fault identification strategy. The strategy of closing two phases first and then closing one phase leaves room for cooperation with the distribution network phase reclosing fault identification technology, and cuts off the fault when a permanent fault occurs. This strategy is used to suppress the excitation inrush current when a transient fault occurs.

[0097] Applicable to instantaneous fault recovery. Traditional suppression methods emphasize that the phase of the opening moment is consistent with the closing moment, so as to avoid the measurement of residual magnetism, but it can only be applied to no-load closing purposes. This method has short delay, fast speed, emphasizes the importance of residual magnetism, and is convenient to use according to the residual magnetism distribution of the transformer when a fault occurs in the distribution network, so it is suitable for instantaneous fault recovery.

[0098] Based on residual magnetism, the excitation inrush current of distribution transformers is suppressed. This lays the foundation for further suppressing the excitation inrush current of multiple transformers. Combined with the distribution law of transformer residual magnetism when a fault occurs, the excitation inrush current of multiple transformers can be suppressed.

[0099] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0100] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0101] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the present invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0102] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0103] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0104] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0105] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0106] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes 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 generate 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.

[0107] 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.

[0108] 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. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0109] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for suppressing magnetizing inrush current when a distribution transformer is switched on, characterized in that: The following steps are involved: Collect three-phase voltage and current waveform data before and after the primary side circuit breaker of the distribution transformer trips; The residual magnetism is estimated using the obtained three-phase voltage and current waveform data, and the residual magnetism of the primary winding is arranged; Determine the first two phases to be closed and the last phase to be closed based on the arrangement order; Determine the closing time of the first two phases based on the obtained first two phases; Determine the closing time of the last closed phase based on the obtained last closed phase; The control terminal controls the circuit breaker to close according to the obtained closing time of the first two phases to be closed and the closing time of the last phase to be closed.

2. The method for suppressing magnetizing inrush current when the distribution transformer is closed according to claim 1, characterized in that: The residual magnetism estimation method of Dyn11 transformer is used to obtain the phase-to-phase residual magnetism of the primary winding , , , and arrange them in descending order of absolute value.

3. The method for suppressing magnetizing inrush current when the distribution transformer is closed according to claim 1, characterized in that: Assume the minimum absolute value of residual magnetism is ,definition The phases at both ends of the coil are the first two phases to be closed, and the remaining phases are the unclosed phases.

4. The method for suppressing magnetizing inrush current when the distribution transformer is closed according to claim 1, characterized in that: The closing time of the first two phases when the first two phases to be closed are phases A and B and the last phase to be closed is phase C for: in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases A and B of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

5. The method for suppressing magnetizing inrush current when the distribution transformer is closed according to claim 1, characterized in that: When the first two phases to be closed are phases B and C, and the last phase to be closed is phase A, the closing time of the first two phases to be closed is: in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases B and C of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

6. The method for suppressing magnetizing inrush current when the distribution transformer is switched on according to claim 1, characterized in that: When the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, the closing time of the first two phases to be closed is: in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases C and A of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

7. The method for suppressing magnetizing inrush current when the distribution transformer is switched on according to claim 1, characterized in that: When the first two phases to be closed are phases B and C, and the last phase to be closed is phase A, the closing time of the last phase to be closed is: in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases C and A of the transformer, is the residual magnetism of the winding between phases A and B of the transformer, is the angular frequency of the power frequency, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

8. The method for suppressing magnetizing inrush current when the distribution transformer is switched on according to claim 1, characterized in that: When the first two phases to be closed are phases C and A, and the last phase to be closed is phase B, the closing time of the last phase to be closed is: in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases A and B of the transformer, is the residual magnetism of the winding between phases B and C of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

9. The method for suppressing magnetizing inrush current when the distribution transformer is switched on according to claim 1, characterized in that: When the first two phases to be closed are phases A and B, and the last phase to be closed is phase C, the closing time of the last phase to be closed is: in, The reference time point is the zero crossing point where the slope of phase A voltage is positive. is the inherent closing time of the circuit breaker, is the residual magnetism of the winding between phases B and C of the transformer, is the residual magnetism of the winding between phases C and A of the transformer, is the angular frequency of the power frequency, is the power frequency period, is the magnetic flux amplitude, is the transformer primary side phase voltage amplitude, N is the number of turns of the primary winding of the transformer.

10. A system for suppressing magnetizing inrush current when a distribution transformer is switched on, characterized in that: include: The acquisition module collects the three-phase voltage and current waveform data before and after the primary side circuit breaker of the distribution transformer trips; An arrangement module estimates the residual magnetism using the obtained three-phase voltage and current waveform data, and arranges the residual magnetism of the primary winding; A determination module determines the first two phases to be closed and the last phase to be closed based on the obtained arrangement order; A time module determines the closing time of the first two phases based on the first two phases obtained, and determines the closing time of the last phase based on the last phase obtained; The output module and the control terminal control the circuit breaker to close according to the closing time of the first two phases and the closing time of the last phase.

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