Three-phase transformer single-phase earth short circuit leakage magnetic field simulation analysis method based on combination of three single-phase transformers

Abstract

The invention discloses a three-phase transformer single-phase grounding short circuit leakage magnetic field simulation analysis method based on a combination of three single-phase transformers, and aims to solve the problem that leakage magnetic field distribution and electromagnetic force conditions of a three-phase transformer formed by the combination of the three single-phase transformers cannot be accurately simulated when a single-phase grounding short circuit fault occurs in the prior art. Constructing a three-dimensional finite element geometric model of the single-phase transformer according to parameters such as the actual size of the transformer; then importing ansys Maxwell software, and adjusting the position to generate a three-dimensional calculation model; setting material attributes of each field domain, creating a winding, and constructing an external circuit matched with different working conditions; then setting a solution domain and boundary conditions, carrying out reasonable mesh generation, and selecting a transient field for simulation solution; and finally, checking simulation results such as short-circuit current and magnetic flux leakage nephograms. The method can accurately analyze the single-phase grounding short circuit fault of the transformer, accurately simulate the fault condition, find hidden dangers in advance, and provide reliable support for fault prevention and scientific design.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer simulation, and in particular to a method for simulating and analyzing a single-phase-to-ground short-circuit leakage magnetic field of a three-phase transformer based on a combination of three single-phase transformers. Background Art

[0002] In modern power systems, as industrial production and social development continue to drive growing electricity demand, large-capacity transformers play a crucial role in the transmission and distribution of electrical energy. Three-phase, large-capacity transformers are widely used in large power plants, substations, and industrially dense areas to convert high-voltage electrical energy into voltage levels suitable for different users and equipment, meeting the needs of long-distance, high-efficiency power transmission and distribution.

[0003] Three-phase, large-capacity transformers typically utilize a monolithic design, resulting in large size and heavy weight. Manufacturing requires high-precision craftsmanship and strict quality control to ensure that their electrical performance and mechanical strength meet design requirements. Transporting and installing these monolithic transformers often present significant challenges due to their size and weight limitations. This is especially true in remote areas or locations with limited access, where transporting these oversized and heavy transformers is virtually impossible.

[0004] In contrast, single-phase transformers offer advantages such as small size, light weight, and ease of manufacturing, making them easier to transport to the installation site. Therefore, in some special environments or remote areas, on-site assembly of three single-phase transformers into a three-phase transformer has become a viable solution. This approach not only reduces transportation costs and risks, but also improves system flexibility and maintainability.

[0005] However, when a three-phase transformer composed of three single-phase transformers experiences an external short-circuit fault, particularly a single-phase ground fault, a large short-circuit current flows through the windings. This leakage magnetic field generates electrodynamic forces on the windings, causing deformation and even relative displacement of the winding coils, which can damage the transformer. Single-phase ground faults are a common and typical asymmetric fault in transformers in power systems. Accurate analysis and simulation of these faults are crucial for ensuring safe transformer operation.

[0006] The existing technology has made some progress in analyzing transformer short-circuit faults. For example, CN107423528B discloses a method and device for analyzing the transient stress of power transformer windings under short-circuit conditions. This method establishes a three-dimensional magnetic-structural coupling model of a three-phase transformer to perform short-circuit transient stress analysis on the windings. However, this technical solution mainly focuses on the stress conditions of the transformer windings under short-circuit transient conditions. Although it can provide a certain basis for the short-circuit resistance design of transformer windings, it still has the following defects and deficiencies in practical applications: Limited model simplification: Although the method in CN107423528B establishes a three-dimensional magnetic-structural coupling model, it may still require some simplification when dealing with complex transformer structures. This can lead to deviations between simulation results and actual results. In particular, when analyzing multi-physics coupling effects, model simplification can overlook key factors, affecting analysis accuracy.

[0007] Limited analysis scope: The patent focuses primarily on the stress on the transformer windings, but provides relatively limited analysis of key parameters such as the internal electromagnetic field distribution and short-circuit current variations. In practical applications, these parameters are crucial for comprehensively evaluating the transformer's performance under short-circuit faults.

[0008] Existing technologies often fail to accurately simulate the leakage field distribution and electromagnetic force under such asymmetric operating conditions when analyzing a single transformer. This is particularly true for three-phase transformers composed of three single-phase transformers. Due to the complex electromagnetic coupling between the phases, traditional single-phase transformer analysis methods struggle to accurately reflect the fault characteristics under actual operating conditions.

[0009] For example, CN117763907A discloses a simulation method for inter-turn short circuits in converter transformers based on bidirectional field-circuit coupling. This method constructs a three-dimensional geometric model of the converter transformer and uses bidirectional field-circuit coupling technology for simulation analysis. However, this technical solution also has the following shortcomings when applied to the analysis of single-phase-to-ground short circuit faults in a three-phase transformer composed of three single-phase transformers: Limited model applicability: The method in CN117763907A primarily simulates and analyzes turn-to-turn short-circuit faults in converter transformers. It is not directly applicable to analyzing single-phase-to-ground short-circuit faults in three-phase transformers combined from three single-phase transformers. Different transformer combinations have different electromagnetic characteristics, so a specific modeling and analysis of three-phase transformers combined from three single-phase transformers is required.

[0010] Simulation Accuracy and Efficiency: While bidirectional field-circuit coupling technology can improve simulation accuracy, it also significantly increases simulation complexity and computation time when dealing with complex transformer structures. This is particularly true when analyzing leakage magnetic field distribution and electromagnetic forces under asymmetric operating conditions. Maintaining simulation accuracy while improving computational efficiency is a major challenge facing existing technologies.

[0011] Lack of comprehensive analysis methods: Existing technologies often focus on single-aspect analysis, such as electromagnetic field distribution, short-circuit current changes, or winding stress conditions, but lack a systematic analysis of the transformer's comprehensive performance under short-circuit faults. This makes it difficult to fully evaluate the transformer's performance under short-circuit faults in actual projects, thus affecting the accuracy of fault diagnosis and prevention.

[0012] In summary, existing technologies for transformer short-circuit fault analysis still have numerous flaws and shortcomings. This is particularly true when dealing with single-phase-to-ground short-circuit faults in three-phase transformers, which are composed of three single-phase transformers. Existing technologies struggle to meet practical engineering requirements. Therefore, it is necessary to develop a simulation and analysis method for single-phase-to-ground short-circuit leakage magnetic fields specifically for three-phase transformers, composed of three single-phase transformers, to address these issues. This approach has important practical significance and application value for accurately evaluating transformer performance under asymmetric faults and guiding transformer design and operation. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a simulation and analysis method for the single-phase to ground short-circuit leakage magnetic field of a three-phase transformer based on a combination of three single-phase transformers, so as to solve the key technical problems in the field of single-phase to ground short-circuit fault analysis of a three-phase transformer composed of three single-phase transformers in a power system. Specifically, the existing technology is relatively mature for the analysis of a single transformer, but in the scenario where three single-phase transformers are combined into a three-phase transformer, due to the complex electromagnetic coupling relationship between the phases, it is difficult to accurately simulate and analyze the leakage magnetic field distribution and electromagnetic force conditions under asymmetric working conditions, which brings great challenges to the fault diagnosis and prevention of the transformer.

[0014] In order to solve the above technical problems, the present invention adopts the following technical solutions: The simulation analysis method of the single-phase-to-ground short-circuit leakage magnetic field of a three-phase transformer based on a combination of three single-phase transformers is as follows: S1: Geometry model construction In professional modeling software, a precise geometric model for 3D finite element simulation of a single-phase transformer is constructed based on detailed parameters such as the actual physical dimensions, winding structure, and core material of the three-phase single-phase transformer. During the modeling process, all components of the transformer, including the high-voltage winding, low-voltage winding, core, clamps, and fuel tank, are fully considered to ensure the accuracy and completeness of the model. The windings are meticulously modeled based on their actual number of turns, wire diameter, and number of layers to accurately reflect the winding's electrical and mechanical characteristics. The core is modeled according to its actual shape and material properties, including the core's lamination structure and silicon steel sheet material parameters, to accurately simulate the core's magnetic circuit characteristics.

[0015] S2: Model import and position adjustment The geometric model for the single-phase transformer 3D finite element simulation constructed in S1 was imported into ANSYS Maxwell software in three steps. After each single-phase transformer model was imported, the software's move tool was used to precisely adjust the position of two of the single-phase transformers, ensuring a parallel layout of all three transformers. The spacing between each phase met actual installation requirements, ensuring consistency between the simulation results and the actual situation. During the position adjustment process, the electromagnetic coupling between the transformers was fully considered to avoid deviations in the simulation results due to improper positioning.

[0016] S3: Material property setting and 3D computational model generation In Maxwell software, material properties are set for each transformer domain, such as the windings, core, clamps, and fuel tank, based on their actual material properties. For the windings, electrical parameters such as conductivity and resistivity are set; for the core, magnetic parameters such as permeability and saturation magnetic induction are set; and for the clamps and fuel tank, parameters such as conductivity are set to accurately simulate the interaction of these components in the electromagnetic field. Once these settings are completed, the software's relevant functions are used to generate a 3D transformer computational model, which will serve as the basis for subsequent simulation analysis.

[0017] S4: Winding Creation In the generated 3D computational model, the windings are created by selecting the interfaces where current begins and ends. Based on the actual transformer winding connection method (e.g., series or parallel), as well as information such as the polarity and number of turns, the winding parameters are precisely set in the software to ensure that the created windings are consistent with the actual transformer windings. During the winding creation process, the electromagnetic characteristics of the windings, such as inductance and resistance, are fully considered to ensure the accuracy of the simulation results.

[0018] S5: External circuit construction Build corresponding external circuits based on the transformer's different operating conditions, such as normal operation and short-circuit faults. Under normal operation, build an external circuit that meets the transformer's rated voltage, rated current, and other parameters to simulate the transformer's normal operating state. Under short-circuit fault conditions, build an external circuit for a single-phase ground fault, setting parameters such as the fault resistance and fault time to accurately simulate the occurrence of a single-phase ground fault. During the external circuit construction process, fully consider factors such as the circuit's topology and electrical parameters to ensure effective connection and accurate simulation of the external circuit and transformer model.

[0019] S6: Solution domain and boundary condition setting, mesh generation and simulation solution Set the solution domain and boundary conditions. The solution domain should cover the transformer and the space within a certain range around it to ensure accurate simulation of the electromagnetic field distribution around the transformer. Set the boundary conditions according to the actual situation, such as setting an infinite boundary condition to simulate open space, or setting a symmetric boundary condition to simplify the calculation. After the settings are completed, perform the meshing operation, and adopt different meshing strategies according to the different components of the transformer and the characteristics of the electromagnetic field distribution. For areas where the electromagnetic field changes drastically, such as near the winding and the edge of the core, use a finer mesh to improve the calculation accuracy; for areas where the electromagnetic field changes relatively slowly, use a coarser mesh to reduce the amount of calculation. After the meshing is completed, select the transient field for simulation and solution. Using the relevant algorithms and calculation functions of the software, solve the electromagnetic field distribution, current, voltage and other parameters of the transformer at different times.

[0020] S7: Simulation results viewing and analysis View post-processing results in Results to clearly visualize the simulation results of the transformer's short-circuit current over time. By plotting the short-circuit current over time, analyze characteristics such as its amplitude, frequency, and changing trend to assess the transformer's electrical performance under a short-circuit fault. Furthermore, in Field Overlays, visualize the leakage magnetic field distribution and analyze the intensity, distribution range, and changing patterns of the leakage magnetic field to assess the electromagnetic force distribution under a short-circuit fault. Through in-depth analysis of the simulation results, potential transformer problems under short-circuit faults, such as winding deformation and localized overheating, can be identified, providing a basis for transformer fault diagnosis and prevention.

[0021] Through the above series of steps, the present invention realizes the accurate simulation and analysis of the single-phase grounding short-circuit fault of the three-phase transformer composed of three single-phase transformers, and provides a scientific and accurate method for transformer fault analysis and prevention.

[0022] The present invention provides a method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers, which has the following beneficial effects: 1. This invention addresses key technical issues in single-phase ground fault analysis for three-phase transformers formed by combining three single-phase transformers in power systems, filling a gap in the research on simulation analysis of three-phase transformers formed by combining three single-phase transformers. Existing technologies struggle to accurately simulate and analyze the leakage magnetic field distribution and electromagnetic force conditions under asymmetric operating conditions in this scenario, posing significant challenges to transformer fault diagnosis and prevention. This invention addresses the inaccurate and incomplete leakage magnetic field simulation analysis issues through a specific simulation analysis method.

[0023] 2. The present invention can highly accurately simulate the leakage magnetic field distribution and electromagnetic force of a three-phase transformer composed of three single-phase transformers under a single-phase ground short-circuit fault, providing a solid and reliable scientific basis for transformer fault analysis and prevention.

[0024] 3. Through simulation analysis, this invention enables technicians to proactively identify potential fault hazards and take targeted measures during transformer design and operation, effectively reducing the probability of failure and minimizing the economic losses and safety risks caused by such failures. This has been fully validated by establishing a three-dimensional finite element model of three single-phase transformers sharing a common computational domain and performing three-dimensional transient analysis using the field-circuit coupled finite element method.

[0025] 4. The simulation results of the present invention reveal the complex coupling relationship between winding leakage flux and short-circuit circulating current, realize the accurate calculation and characterization of the magnetic field distribution and fault current of the three-phase transformer, and fully demonstrate the practicality and innovation of the present invention.

[0026] 5. The present invention models a three-phase transformer composed of three single-phase transformers to obtain a three-dimensional geometric model, uses finite element method to perform a three-dimensional transient magnetic field solver, analyzes the field-circuit bidirectional coupling mechanism and solves it, and obtains accurate and reliable simulation calculation results.

[0027] 6. The present invention can serve as an effective alternative to dangerous, expensive, and impractical field tests of real converter transformer short circuits, and as a reliable technical means for fault mechanism research and theoretical analysis. It can achieve accurate calculation and characterization of the magnetic field distribution and fault current of three-phase transformers after a single-phase ground short circuit fault, and provide an effective simulation method for the simulation of asymmetric short circuit faults of three-phase transformers composed of three single-phase transformers.

[0028] 7. The present invention establishes a three-dimensional finite element model in which three single-phase transformers share a common computational domain, so that the three single-phase transformers have both electrical and magnetic field connections. The model is subjected to three-dimensional transient analysis using the field-circuit coupling finite element method, and the short-circuit current, winding leakage magnetic field, and electromagnetic force distribution when the high-voltage winding is single-phase grounded are calculated. This is of great significance for studying the calculation of single-phase grounding short-circuit problems of three-phase double-winding transformers with three single-phase power transformers connected in combination.

[0029] 8. The present invention simulates transformer asymmetric faults by establishing a three-phase transformer single-phase grounding short-circuit fault model in which three single-phase transformers share one calculation domain.

[0030] 9. The present invention tailors the simulation analysis process according to the characteristics of the three-single-phase transformer combination, fully considering the particularity of the combination in every link from model establishment to external circuit construction. Compared with general simulation methods, it is more targeted and practical.

[0031] 10. When establishing the three-dimensional geometric model of the transformer, the present invention simplifies the low-voltage spiral and high-voltage inner-screen continuous windings and replaces them with circular ring columns. While ensuring the simulation accuracy, it reduces the complexity of the model and improves the calculation efficiency.

[0032] 11. Based on the single-phase ground short-circuit operating condition of the three-phase transformer, the present invention builds a practical external circuit model, clarifies the connection relationship between each winding and the external circuit, and takes into account the phase difference between each phase.

[0033] 12. In the grid division of the calculation model, the present invention adopts a strategy of refining the grid in areas where the magnetic field changes significantly and coarsening the grid in areas where the magnetic field changes relatively slowly. This strategy is more targeted and reasonable and can better balance the calculation accuracy and efficiency.

[0034] 13. The present invention sets a reasonable stop time and step size for the transient field solver of three single-phase transformers and retains the solution results of each step, thereby improving the efficiency and accuracy of simulation calculations.

[0035] 14. The simulation analysis results of the present invention can provide a more accurate basis for the fault assessment and design optimization of the three-phase transformer of the three-single-phase transformer combination in actual engineering.

[0036] 15. The present invention can comprehensively understand the electromagnetic characteristics of the transformer under a single-phase-to-ground short-circuit fault by analyzing the simulation results in multiple dimensions, providing richer information and contributing to a deeper understanding of the transformer's fault mechanism and performance.

[0037] 16. The present invention retains the solution results of each step in the solver setting, which is convenient for subsequent viewing of the leakage magnetic field distribution at each moment, so that the dynamic process of the transformer after a short-circuit fault occurs can be analyzed in detail, and the formation, development and change of the leakage magnetic field can be observed, providing a deeper perspective for transformer fault diagnosis and prevention, and helping to formulate more effective protection strategies.

[0038] 17. The present invention adopts simplified winding modeling, optimized mesh partitioning strategy and solver parameter optimization measures to improve the calculation efficiency and reduce the consumption of computing resources while ensuring the simulation accuracy, providing a feasible solution for large-scale simulation analysis.

[0039] 18. Through simulation analysis, the present invention can discover problems in transformer design or operation in advance and take corresponding measures to improve them, thereby improving the reliability and safety of the transformer and reducing engineering risks.

[0040] 19. The research results of this invention are helpful to promote the development of transformer technology and provide new ideas and methods for the design and manufacture of transformers. By continuously optimizing the simulation analysis process and model, the performance and efficiency of the transformer can be further improved, and the stable operation and development of the power system can be promoted. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A flow chart of a simulation method for a single-phase to ground short circuit of a three-phase transformer in a wiring combination of three single-phase double-winding transformers according to the present invention; Figure 2 A front view of a three-dimensional model for simulating single-phase-to-ground short-circuit current in a three-phase transformer in a combination of three single-phase double-winding transformers in embodiments 4 and 5 of the present invention; Figure 3 A side view of a three-dimensional model for simulating single-phase-to-ground short-circuit current in a three-phase transformer in a wiring combination of three single-phase double-winding transformers according to embodiments 4 and 5 of the present invention; Figure 4 A top view of a three-dimensional model for simulating single-phase-to-ground short-circuit current in a three-phase transformer in a combination of three single-phase double-winding transformers in embodiments 4 and 5 of the present invention; Figure 5 This is a high-voltage side external circuit diagram of the high-voltage single-phase-to-ground short-circuit simulation of embodiments 4 and 5 of the present invention; Figure 6 This is a low-voltage side external circuit diagram of the high-voltage single-phase-to-ground short-circuit simulation of Examples 4 and 5 of the present invention; Figure 7 This is a short-circuit current simulation waveform diagram of Examples 4 and 5 of the present invention; Figure 8 Magnetic flux density distribution cloud diagrams of Examples 4 and 5 of the present invention; Figure 9 The current density distribution cloud diagrams of Examples 4 and 5 of the present invention are shown; In the figure: magnetic shield 1, lobe shield 2, iron core 3, high voltage II winding 4, high voltage I winding 5, low voltage winding 6. DETAILED DESCRIPTION

[0042] The technical solutions of the present invention are further described below with reference to the accompanying drawings and embodiments: Example 1 like Figure 1 As shown, this embodiment provides a specific implementation process of a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field simulation analysis method based on a combination of three single-phase transformers, including the following steps: Step 1: Establish a geometric model for 3D finite element simulation In professional 3D modeling software (such as SolidWorks), a three-phase single-phase transformer was modeled based on its actual physical dimensions. Taking all components of the transformer into consideration, the high-voltage winding was modeled in detail based on its known number of turns (1200), wire diameter (2.5mm), and number of layers (10). The low-voltage winding was also modeled in detail, with 240 turns, wire diameter (5mm), and 5 layers (240 turns). The core was constructed using high-quality silicon steel sheets with a three-column structure and a lamination thickness of 0.3mm, consistent with its actual shape. Material parameters, including the magnetic permeability curve (derived from experimental measurements) and saturation magnetic induction (1.8T), were set to accurately simulate the core's magnetic circuit characteristics. The clamps and oil tank were also modeled according to their actual dimensions and structure, completing the geometric model for the single-phase transformer 3D finite element simulation.

[0043] Step 2: Import the geometry model into ANSYS Maxwell The constructed single-phase transformer 3D finite element simulation geometry model was imported into ANSYS Maxwell software in three steps. After importing, the software's move tool was used to precisely adjust the positions of two of the single-phase transformers. The spacing between adjacent transformers was set to 600 mm, ensuring a parallel layout of the three transformers. The spacing between each phase transformer met actual installation requirements, generating a 3D transformer calculation model.

[0044] Step 3: Set material properties and generate a three-dimensional calculation model of the transformer In Maxwell, select the transformer transient field and set the material properties. For the winding, set the conductivity to S / m. The windings are created by selecting the interface where current starts and ends. In this embodiment, the high-voltage windings of the three single-phase transformers are connected in series, and the low-voltage windings are also connected in series. Based on the series connection method and information such as the winding polarity and number of turns, the winding parameters are accurately set in the software to ensure that the created windings are consistent with the actual transformer windings, thereby generating a three-dimensional calculation model of the transformer.

[0045] Step 4: Build the external circuit of the model Normal operation: Build an external circuit that meets the transformer's rated voltage, rated current, and other parameters. Assume the transformer's rated high voltage is 120kV, rated low voltage is 11kV, and rated capacity is 12MVA. Based on these parameters, calculate that the rated current on the high-voltage side is approximately 57.7A, and the rated current on the low-voltage side is approximately 629.9A. Set the corresponding voltage source and load resistance in the external circuit to simulate the transformer's normal operating state. Short-circuit fault scenario: Build an external circuit for a single-phase-to-ground short-circuit fault. Set a fault resistor between a phase on the high-voltage side (for example, phase B) and the ground. The fault resistor is set to 0.2Ω, and the fault time is set to 0.03s after the start of the simulation to accurately simulate the occurrence process of a single-phase-to-ground short-circuit fault.

[0046] Step 5: Establish the solution domain, set boundary conditions, add meshing, and set the solver Establish a solution domain: The solution domain covers the transformer and the space within a certain range around it. For example, set the solution domain to a cube with a side length of 6 meters to ensure that the electromagnetic field distribution around the transformer can be accurately simulated; Set boundary conditions: Set the boundary conditions to infinite boundary conditions to reduce the impact of boundary effects on simulation results; Meshing: Different meshing strategies are used based on the different components of the transformer and the electromagnetic field distribution characteristics. For areas with drastic electromagnetic field changes, such as near the windings and the core edge, a finer mesh is used, with a mesh size of 12 mm. For areas with relatively gentle electromagnetic field changes, such as the outer surface of the fuel tank, a coarser mesh is used, with a mesh size of 60 mm. Set the solver: Select the transient field solver for simulation.

[0047] Step 6: View the simulated current distribution and cloud distribution of each winding View winding current distribution: View post-processing results in the Results section to obtain simulation results showing the transformer's short-circuit current over time. By plotting the short-circuit current over time, you can clearly see that after the fault occurs, the short-circuit current rises rapidly, reaching a large amplitude, and then gradually stabilizes over time. Analyze the short-circuit current's amplitude, frequency, and variation trends to assess the transformer's electrical performance under a short-circuit fault. Viewing the distribution of magnetic flux cloud maps: View the distribution of magnetic flux leakage cloud maps in Field Overlays and analyze information such as the intensity, distribution range, and variation patterns of the leakage magnetic field. You can see that when a short-circuit fault occurs, the leakage magnetic field undergoes significant changes around the transformer windings and core, with leakage magnetic field intensity significantly increasing in some areas. This information can be used to assess the electromagnetic force distribution of the transformer during a short-circuit fault, providing a basis for transformer fault diagnosis and prevention.

[0048] Example 2 In another preferred embodiment, based on the above-mentioned embodiment 1, this embodiment differs from embodiment 1 mainly in the winding connection method. In this embodiment, the high-voltage windings of three single-phase transformers are connected in parallel, and the low-voltage windings are also connected in parallel.

[0049] Step 1 to Step 3: Same as Example 1, operate according to the method of Example 1, and when establishing the geometric model, importing the model, and setting the material properties to generate the calculation model, fully consider the characteristics of the parallel connection and make corresponding settings.

[0050] Step 4: Build the external circuit of the model Normal operation: Recalculate the rated current based on the rated voltage and rated capacity of the transformer after parallel connection. Assume that the rated high voltage remains at 120kV, the rated low voltage remains at 11kV, and the rated capacity is 12MVA. Due to the parallel connection, the rated current on the high voltage side is approximately 173.1A (three branches in parallel), and the rated current on the low voltage side is approximately 1889.7A. Set the corresponding voltage source and load resistance in the external circuit to simulate the normal operation of the transformer. Short-circuit fault condition: Similar to Example 1, a fault resistance of 0.2Ω is set between a phase on the high-voltage side and the ground, and the fault time is set to 0.03s after the start of the simulation to simulate the occurrence process of a single-phase ground short-circuit fault.

[0051] Step 5: Same as Example 1, establish the solution domain, set boundary conditions, add meshing, and set the solver.

[0052] Step 6: As in Example 1, examine the simulated current distribution and cloud map distribution of each winding. By examining the short-circuit current variation curve over time and the leakage magnetic field cloud map distribution, it can be found that due to the different winding connection methods, the short-circuit current amplitude, change trend, and leakage magnetic field distribution are different from those in Example 1. For example, when connected in parallel, the short-circuit current may rise faster and have a larger amplitude, and the distribution range and intensity of the leakage magnetic field will also change accordingly. By analyzing these simulation results, we can further study the impact of different winding connection methods on the performance of the transformer under single-phase ground short-circuit faults.

[0053] Example 3 In another preferred embodiment, based on the above-mentioned embodiment 1, this embodiment differs from embodiment 1 mainly in the different fault resistance settings. In this embodiment, the fault resistance for a single-phase ground short circuit fault is set to 2Ω, and the other steps are basically the same as those in embodiment 1.

[0054] Step 1 to Step 3: Same as Example 1, operate according to the method of Example 1.

[0055] Step 4: Build the external circuit of the model Normal operation: As in Example 1, an external circuit that meets the transformer's rated voltage, rated current and other parameters is built to simulate the transformer's normal operating state; Short-circuit fault condition: The fault resistance between a phase on the high-voltage side and the ground is set to 2Ω, and the fault time is set to 0.03s after the start of the simulation to simulate the occurrence process of a single-phase ground short-circuit fault.

[0056] Step 5: Same as Example 1, establish the solution domain, set boundary conditions, add meshing, and set the solver.

[0057] Step 6: Similar to Example 1, the simulated current distribution and cloud distribution of each winding are examined. The short-circuit current variation curve and the leakage magnetic field cloud distribution are examined. It can be found that due to the increase in fault resistance, the short-circuit current amplitude decreases significantly, and the rate of increase of the short-circuit current also slows down. At the same time, the distribution range and intensity of the leakage magnetic field are also different from those in Example 1, with the leakage magnetic field intensity in some areas being reduced. By analyzing these simulation results, the impact of different fault resistances on the electromagnetic characteristics of the transformer under single-phase ground faults can be studied, providing a more comprehensive basis for transformer fault analysis and protection design.

[0058] Example 4 In another preferred embodiment, based on the above embodiment 1, Figure 2 As shown, this embodiment provides a three-phase transformer single-phase to ground short-circuit leakage magnetic field simulation analysis method based on a combination of three single-phase transformers. The basic process is as follows: Figure 1 As shown, the simulation calculation process of this embodiment is described in detail below. In this example, the simulation analysis of the single-phase-to-ground short-circuit leakage magnetic field of a three-phase transformer with a 375MVA / 500kV / 24kV single-phase transformer connection combination is used as an example for explanation: First, based on the geometric parameters of the sample transformer, the three-dimensional geometric model of the transformer is established using solidworks software. The low-voltage spiral and high-voltage internal screen continuous windings are simplified and replaced with circular rings. The core is modeled according to the stacking level, and magnetic shielding and lobe shielding are considered. The schematic diagram of the calculation model of the three-phase single-phase transformer is shown in the figure. Figures 2 to 4 shown.

[0059] Export the established 3D transformer model to .step format. Open ANSYS Maxwell and use Modeler > Import to import the exported step file. Repeat this process three times, shifting two transformers left and right, with a spacing of 200 mm between each transformer. Then, select the Transformer Transient Field domain in ANSYS Maxwell and set the material properties. Set the core 3, magnetic shield 1, and lobe shield 2 to B27R085. Set the windings (HV Winding II 4, HV Winding I 5, and LV Winding 6) to copper. Generate the 3D transformer model. Create and segment the windings. Use the resulting cross-section as the surface to add excitation. Select one side of each winding and use Assign Excitation > Coil Terminal... to set the number of turns and generate the coils. Next, add Winding and set it to External Circuit.

[0060] According to the single-phase ground short circuit operating condition of the three-phase transformer, the external circuit of the model is built. Through ExternalCircuit-Edit External Circuit.-Create Circuit (External Circuit Edit External Circuit.-Create Circuit), the external circuit settings are as follows Figure 5 、 6 As shown, L is the winding, AL (Phase A Low-voltage Side, A phase winding low-voltage side), BL (Phase B Low-voltage Side, B phase winding low-voltage side), CL (Phase C Low-voltage Side, C phase winding low-voltage side) winding are the transformer low-voltage side winding, AH (Phase A High-voltage Side, A phase winding high-voltage side), BH (Phase B High-voltage Side, B phase winding high-voltage side), CH (Phase C High-voltage Side, C phase winding high-voltage side) winding are the transformer high-voltage side. Normal operation is low voltage plus excitation, each phase difference is 120°, and high voltage loading.

[0061] Create a solution domain. Use the Create region (module to add constraints) to select a volume of appropriate size as the solution domain for the transformer finite element calculation. Select vacuum as the material for the solution domain. The boundary conditions for the solution domain surface are determined by the spatial relationship between the magnetic field lines and the surface. If the magnetic field lines are perpendicular to the surface, set the perpendicular boundary condition. If the magnetic field lines are parallel to the surface, set the parallel boundary condition. In this example, the parallel boundary condition is set.

[0062] The mesh of the computational model needs to be refined in areas with significant magnetic field variations. In this example, the windings are meshed finely, while the core and solution domain are meshed coarsely.

[0063] Solver settings: For the transient field solver of three single-phase transformers, set the stop time and step size, retain the solution results of each step to facilitate subsequent viewing of the leakage magnetic distribution at each moment, and keep the rest as default to ensure the accuracy of the solution.

[0064] After solving, check the current distribution of each winding in the Results-Create Transient Report-Rectangular Plot interface, such as Figure 7 As shown, in Field Overlays-Fields, view the distribution of magnetic flux density and current density, as shown in the figure. Figure 8 、 9 As shown; Figure 7 In the figure, the horizontal axis time represents time, and the vertical axis Y1 represents current; the blue line is the high-voltage side A phase winding current, the red line is the high-voltage side B phase winding current, and the green line is the high-voltage side C phase winding current; Winding plot 2 represents the winding Figure 2 ; Curve Info indicates curve information; Current indicates current; BH2 Winding 1, CH2 Winding 1, AH2 Winding 1 indicate BH2 winding 1, CH2 winding 1, AH2 winding 1 respectively; Setup1: Transient indicates configuration 1: using transient response simulation; Imported indicates import; max indicates maximum value.

[0065] Example 5 In another preferred embodiment, based on the above-mentioned embodiment 4, this embodiment further refines the specific implementation process of the embodiment providing a method for simulating and analyzing single-phase-to-ground short-circuit leakage magnetic field of a three-phase transformer based on a combination of three single-phase transformers: In power system operation, single-phase-to-ground short-circuit faults in three-phase transformers are one of the most common and potentially harmful fault types. To accurately evaluate the transformer's leakage magnetic field distribution and electrical performance during a single-phase-to-ground short-circuit, this example uses a three-phase transformer consisting of a 375MVA / 500kV / 24kV single-phase transformer connection as the research object. A simulation analysis method for single-phase-to-ground short-circuit leakage magnetic fields in a three-phase transformer based on a three-single-phase transformer combination is employed. Through a detailed simulation calculation process, key simulation data is obtained, providing a basis for transformer fault analysis, optimized design, and protection strategy formulation.

[0066] The simulation calculation process is as follows: 1. Establishing a 3D geometric model of the transformer 1. Geometric parameter acquisition By consulting the technical documents, design drawings, and other materials of the 375MVA / 500kV / 24kV single-phase transformer, the detailed geometric parameters of the transformer were obtained, including the height, width, and depth of the transformer; the inner diameter, outer diameter, and height of the windings; the dimensions of the core (such as the core leg diameter and yoke height); and the shapes and dimensions of the magnetic shield and lobe shield.

[0067] 2. Modeling software operation SolidWorks software was used to establish a three-dimensional geometric model of the transformer based on the acquired geometric parameters. Considering the efficiency and feasibility of the simulation calculation, the low-voltage spiral and high-voltage inner-screen continuous windings were simplified and replaced with circular cylinders. The size of the circular cylinders was set according to the actual average diameter and height of the windings to ensure that the simplified model had electromagnetic characteristics similar to those of the actual windings.

[0068] The core is modeled according to the lamination hierarchy to accurately simulate the core's lamination structure. The core geometry is created in SolidWorks based on parameters such as the actual lamination thickness and lamination factor to accurately reflect the core's magnetic circuit characteristics. Furthermore, the effects of magnetic shielding and lobe shielding are fully considered, and the modeling is based on the actual shape and size to ensure that the model accurately simulates the electromagnetic environment of the transformer during actual operation.

[0069] 3. Model schematic display The schematic diagram of the calculation model of three single-phase transformers is as follows Figures 2 to 4 These schematic diagrams clearly show the layout of the three single-phase transformers, the structure of the windings and cores, and the positions of the magnetic shields and lobe shields, providing an intuitive reference for subsequent simulation analysis.

[0070] 2. Import the model into ANSYS Maxwell and set up the calculation model 1. Model export and import Export the established 3D transformer model to step format. Open ANSYS Maxwell and select Import from the Modeler menu to import the step file exported in the previous step. Repeat this process three times to import the models of the three single-phase transformers into ANSYS Maxwell.

[0071] 2. Transformer position adjustment In ANSYS Maxwell, using the software's move tool, two of the transformers were moved left and right, adjusting their positions so that the spacing between them was 200 mm. This spacing setting meets actual installation requirements and ensures that the simulation results are consistent with the actual situation.

[0072] 3. Select the field and set the material properties In ANSYS Maxwell, select the transformer transient field and set the material properties. The material for the core 3, magnetic shield 1, and lobe shield 2 is B27R085. This material is found in the software's material library, and its corresponding electromagnetic parameters, such as magnetic permeability and saturation magnetic induction, are set. The windings, including high-voltage winding II 4, high-voltage winding I 5, and low-voltage winding 6, are set to copper. Similarly, parameters such as conductivity are selected and set in the material library.

[0073] 4. Winding creation and excitation setting To create the windings, first split the windings and use the resulting sections as the surfaces for adding excitation. Select one side of each winding and use the Assign Excitation-Coil Terminal... command in the software. Set the number of turns for each winding based on the actual number of turns of the transformer to generate the coils. Next, add Winding and set it to external circuit form so that it can be connected to the external circuit later.

[0074] 3. Build the external circuit of the model 1. External circuit setting interface operation According to the single-phase ground short-circuit operating condition of the three-phase transformer, the external circuit of the model is built; in ANSYS Maxwell, the external circuit setting interface is opened through the External Circuit - Edit External Circuit... - Create Circuit command.

[0075] 2. Connection setting between winding and external circuit In the external circuit setting interface, the connection relationship between each winding and the external circuit is clearly defined. The windings of AL, BL, and CL are the low-voltage side of the transformer, and the windings of AH, BH, and CH are the high-voltage side of the transformer. Normal operation is low voltage plus excitation, with each phase difference of 120° and high voltage loading. By setting appropriate voltage sources, current sources, resistors, inductors and other components, an external circuit model that meets the actual operating conditions is constructed, such as Figure 5 shown.

[0076] 4. Establishing the solution domain and setting boundary conditions 1. Solution domain creation Use the Create region command to select an appropriately sized volume as the solution domain for the transformer finite element calculation. The solution domain should encompass the transformer and a certain range of surrounding space to ensure accurate simulation of the electromagnetic field distribution around the transformer. In this example, a cube with a side length of 8 meters is selected as the solution domain based on the transformer's size and actual operating environment.

[0077] 2. Assignment of solution domain materials Select vacuum as the material assignment for the solution domain to simulate the free space environment around the transformer.

[0078] 3. Boundary condition setting The boundary condition setting needs to be determined based on the spatial relationship between the magnetic lines of force and the surface. If the magnetic lines of force are perpendicular to the surface, a perpendicular boundary condition should be set; if the magnetic lines of force are parallel to the surface, a parallel boundary condition should be set. In this embodiment, after analysis, the parallel boundary condition was set to reduce the impact of boundary effects on the simulation results.

[0079] 5. Meshing of the computational model 1. Meshing principles The meshing of the computational model has a significant impact on the accuracy and computational efficiency of the simulation results. Regions with significant magnetic field variations require a finer mesh to improve computational accuracy. Regions with relatively gentle magnetic field variations require a coarser mesh to reduce computational effort.

[0080] 2. Specific segmentation operations In this example, the windings are finely meshed. Due to the dramatic changes in the electromagnetic field near the windings, a smaller mesh size of 8 mm is used. The core and solution domain are coarsely meshed, with a mesh size of 40 mm at the core and 60 mm in the solution domain. This rational meshing strategy improves computational efficiency while maintaining accuracy.

[0081] 6. Solver Settings 1. Solver type selection The transient field solver for three single-phase transformers is set up accordingly in ANSYS Maxwell.

[0082] 2. Stop time and step size settings Set the stop time and step size to accurately simulate the dynamic process of the transformer after a single-phase-to-ground short-circuit fault occurs. Based on actual needs and computing resources, set the stop time to 0.1s and the step size to 0.0001s. Retain the solution results at each step to facilitate subsequent review of the leakage flux distribution at each moment.

[0083] 3. Other parameter settings The accuracy of the solution can be guaranteed by keeping the other parameters as default, such as the iterative accuracy and convergence conditions of the solver.

[0084] 7. Simulation Results Viewing and Analysis 1. Check the winding current distribution After solving, view the simulated current distribution in each winding in the Results - Create Transient Report - Rectangular Plot interface. By plotting the short-circuit current over time, you can clearly see the rise, amplitude, and trend of the short-circuit current after the fault occurs. Analyzing these characteristics allows you to assess the transformer's electrical performance under a short-circuit fault, such as whether the short-circuit current exceeds the transformer's tolerance and whether it will cause damage.

[0085] 2. Check the magnetic flux density and current density distribution View the distribution of magnetic flux density and current density in Field Overlays - Fields. This cloud diagram displays the distribution of magnetic flux density and current density within the transformer, analyzing information such as the strength, distribution range, and variation patterns of the leakage magnetic field. This information can be used to assess the distribution of electromagnetic force during a short-circuit fault and identify areas of high electromagnetic force, providing a basis for transformer fault diagnosis and prevention. For example, if excessive electromagnetic force is detected in a specific area, it may cause deformation or damage to the winding or core in that area, requiring appropriate measures to address the problem.

[0086] Through the detailed simulation calculation process of this example, a simulation analysis of the single-phase short-circuit leakage magnetic field of a three-phase transformer with a 375MVA / 500kV / 24kV single-phase transformer connection was conducted. Key simulation data, such as winding current distribution, magnetic flux density, and current density distribution, were obtained, providing an important reference for transformer fault analysis, optimized design, and protection strategy formulation. In practical applications, these simulation results can be used to implement targeted improvements and optimizations to enhance transformer reliability and safety.

[0087] Through the above five embodiments, the specific implementation process of the three-phase transformer single-phase-to-ground short-circuit leakage magnetic field simulation analysis method based on the combination of three single-phase transformers of the present invention is demonstrated from different angles, fully reflecting the diversity and practicality of the method.

[0088] In a preferred embodiment, in Step 1, when constructing a geometric model for a three-dimensional finite element simulation of a single-phase transformer in professional modeling software, the various components of the transformer, including the high-voltage winding, low-voltage winding, core, clamps, and fuel tank, are fully considered. The windings are meticulously modeled based on their actual number of turns, wire diameter, and number of layers. This ensures a highly accurate simulation model. Furthermore, in Step 2, when meshing the model, an adaptive algorithm is used to optimize the mesh density, particularly in the area where the windings contact the core, to improve computational efficiency and the accuracy of the simulation results.

[0089] In the preferred solution, the core is modeled according to its actual shape and material properties, including the core's lamination structure and silicon steel sheet material parameters, to accurately simulate the core's magnetic circuit characteristics. This setup significantly improves the accuracy of simulation analysis, thereby optimizing the performance design of electromagnetic devices. Furthermore, core losses and temperature effects are considered, and iterative calculations are performed to ensure the design's efficiency and stability in actual operation.

[0090] In the preferred solution, the specific steps of Step 2 are to import the constructed single-phase transformer three-dimensional finite element simulation geometric model into the ansys Maxwell software three times, and accurately adjust the positions of two of the single-phase transformers so that the three transformers are arranged in parallel to generate a three-dimensional calculation model of the transformer; the above settings ensure that the electromagnetic fields between the transformers do not interfere with each other and are convenient for subsequent analysis; then, apply corresponding boundary conditions and excitation sources to the model, set solution parameters, and start simulation calculations to obtain the electromagnetic performance parameters of each transformer.

[0091] In the preferred solution, when adjusting the positions of two of the single-phase transformers, the spacing between the phase transformers meets the actual installation requirements, ensuring the consistency of the simulation results with the actual situation; the above settings can significantly improve the operating efficiency and safety of the power system; at the same time, the transformers are regularly inspected and maintained to promptly detect and eliminate potential faults and ensure stable power supply to the power grid.

[0092] In the preferred solution, in Step 3, when setting material properties and generating a three-dimensional calculation model of the transformer, the current starting current-carrying interface and the current ending current-carrying interface are selected to create the winding, and according to the actual winding connection mode of the transformer, such as series connection, parallel connection, etc., as well as the polarity, number of turns and other information of the winding, the winding parameters are accurately set in the software to ensure that the created winding is consistent with the actual transformer winding; the above settings also need to consider the insulation material and thickness of the winding to simulate the electrical isolation between the windings; at the same time, according to the actual working conditions, the parameters such as the winding temperature rise and heat dissipation conditions are set, and the model is optimized through iterative calculation until its key indicators such as electrical performance and thermal performance are highly consistent with those of the real transformer.

[0093] In the preferred solution, the Step 4 is to build a corresponding external circuit according to the different working conditions of the transformer, specifically including: under normal operating conditions, building an external circuit that meets the transformer's rated voltage, rated current and other parameters to simulate the normal working state of the transformer; under short-circuit fault conditions, building an external circuit for a single-phase ground short-circuit fault, setting parameters such as fault resistance and fault time to accurately simulate the occurrence process of a single-phase ground short-circuit fault; the above settings also need to consider the overload condition, build an overload external circuit, set the current value and duration exceeding the rated load of the transformer, and simulate the impact of the overload state on the transformer; at the same time, for open-circuit faults, design an open-circuit external circuit to study the behavioral characteristics of the transformer under no-load conditions.

[0094] In the preferred solution, when setting the solution domain in Step 5, the solution domain covers the transformer and the space within a certain range around it to ensure that the electromagnetic field distribution around the transformer can be accurately simulated; the above setting can fully capture the electromagnetic field changes generated by the transformer during operation, and provide accurate data support for subsequent electromagnetic field analysis and optimization design, thereby improving the safety and reliability of transformer operation.

[0095] In the preferred solution, in the meshing operation of Step 5, different meshing strategies are adopted according to the different components of the transformer and the electromagnetic field distribution characteristics. For areas where the electromagnetic field changes dramatically, such as near the winding and the edge of the core, a finer mesh is used for meshing to improve the calculation accuracy; for areas where the electromagnetic field changes relatively slowly, a coarser mesh is used for meshing to reduce the amount of calculation; the above settings effectively improve the calculation efficiency while ensuring the calculation accuracy; at the same time, the meshing process also takes into account the heterogeneity of material properties, and performs special treatment on the material interface to ensure the accuracy and reliability of the electromagnetic field simulation results.

[0096] In the preferred solution, when checking the simulated current distribution of each winding in Step 6, the short-circuit current is plotted over time to analyze the amplitude, frequency, change trend and other characteristics of the short-circuit current to evaluate the electrical performance of the transformer under a short-circuit fault. The above settings can comprehensively monitor and warn of potential electrical anomalies to ensure that the transformer can maintain stable operation in sudden short-circuit events. In addition, combined with real-time monitoring data, the winding design can be further optimized to improve the overall tolerance and reliability of the transformer.

[0097] In the preferred solution, when viewing the cloud map distribution in Step 6, the intensity, distribution range, and variation pattern of the leakage magnetic field are analyzed to evaluate the electromagnetic force distribution of the transformer under a short-circuit fault, providing a basis for transformer fault diagnosis and prevention. The above settings can accurately locate potential fault points and improve diagnostic efficiency and accuracy. At the same time, by combining historical data with real-time monitoring, the analysis algorithm is continuously optimized to ensure safe and reliable operation of the transformer and extend the service life of the equipment.

[0098] In summary, the present invention focuses on the field of single-phase to ground short-circuit fault analysis of three-phase transformers formed by a combination of three single-phase transformers in power systems, and proposes an innovative simulation analysis method for single-phase to ground short-circuit leakage magnetic field of three-phase transformers based on the combination of three single-phase transformers. In the prior art, the analysis of a single transformer is relatively mature. However, for the case where three single-phase transformers are combined into a three-phase transformer, due to the complex electromagnetic coupling relationship between the phases, it is difficult to accurately simulate and analyze the leakage magnetic field distribution and electromagnetic force conditions under asymmetric working conditions, which brings great challenges to the diagnosis and prevention of transformer faults. The present invention specifically carries out simulation analysis for the three-phase transformer formed by the combination of three single-phase transformers, which has a wide range of practical applications but relatively few simulation studies. It fills the research gap in this field and provides an accurate basis for the fault assessment and design optimization of such transformers in actual engineering.

[0099] The present invention fully considers the particularity of the three-single-phase transformer combination and tailors the simulation analysis process. From model establishment to external circuit construction, each link reflects pertinence and practicality. In the modeling process, the low-voltage spiral and high-voltage internal screen continuous windings are simplified and replaced with circular columns. While ensuring the simulation accuracy, the model complexity is reduced and the calculation efficiency is improved, providing a feasible solution for large-scale simulation analysis. In terms of parameter setting, the materials are accurately selected and the corresponding electromagnetic parameters are set, and the boundary conditions are reasonably determined to make the simulation environment closer to reality, providing reliable data support for transformer performance evaluation and fault analysis.

[0100] In terms of result analysis, this method examines not only the winding current distribution but also the magnetic flux density and current density distributions. This multi-dimensional analysis of simulation results provides a comprehensive understanding of the transformer's electromagnetic characteristics under a single-phase-to-ground short-circuit fault, providing rich information for a deeper understanding of transformer failure mechanisms and performance. Furthermore, the solver settings retain the results of each step, facilitating subsequent review of the leakage flux distribution at each moment. This allows for a detailed analysis of the dynamic process after a transformer short-circuit fault occurs, providing a deeper perspective for fault diagnosis and prevention, and contributing to the development of more effective protection strategies.

[0101] From the perspective of methodological innovation, this invention integrates technologies from multiple fields, including three-dimensional modeling, electromagnetic field simulation, and external circuit construction, to form a complete simulation and analysis process. This process can more comprehensively and accurately simulate the electromagnetic characteristics of the transformer during actual operation, providing a more effective means for transformer fault analysis and design optimization. In terms of external circuit construction, a realistic external circuit model is constructed based on the single-phase ground short-circuit operating conditions of a three-phase transformer. The connection relationship between each winding and the external circuit is clarified, and the phase difference between the phases is taken into account. This innovative external circuit construction method ensures the accuracy of the simulation results.

[0102] In terms of technical implementation, the computational model meshing strategy employs a finer mesh in areas with significant magnetic field variations and a coarser mesh in areas with relatively gentle variations, balancing computational accuracy and efficiency for a more targeted and rational approach. Optimizing parameters such as the stop time and step size for the transient field solver for three-phase single-phase transformers improves simulation efficiency and accuracy, providing more detailed data support for transformer fault analysis and performance evaluation.

[0103] From the perspective of engineering application value, the simulation analysis results of this invention can provide an accurate basis for fault analysis, optimized design, and protection strategy formulation of three-phase transformers in a combination of three single-phase transformers in actual projects. This allows for early detection of problems in transformer design or operation and the implementation of corrective measures, thereby improving transformer reliability and safety and reducing engineering risks. Furthermore, the research results of this invention will help promote the development of transformer technology, provide new ideas and methods for transformer design and manufacturing, and further improve transformer performance and efficiency by continuously optimizing simulation analysis processes and models, thereby promoting the stable operation and development of power systems.

Claims

1. A simulation and analysis method for a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers, characterized in that: The following steps are involved: Step 1: Create a three-dimensional finite element simulation geometric model based on the actual size of the three single-phase transformers in professional modeling software; Step 2: Import the geometric model into ANSYS Maxwell; Step 3: Select the transformer transient field in Maxwell, set the material properties, and generate a three-dimensional calculation model of the transformer; Step 4: Build the external circuit of the model according to the single-phase ground short circuit operating condition of the three-phase transformer; Step 5: Establish the solution domain, set boundary conditions, add meshing, and set the solver; Step 6: View the simulated current distribution of each winding in Results, and view the cloud distribution in Fields of Field Overlays.

2. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 1, characterized in that: In Step 1, when constructing a geometric model for three-dimensional finite element simulation of a single-phase transformer in professional modeling software, full consideration is given to various components of the transformer, including high-voltage winding, low-voltage winding, iron core, clamps, and oil tank. The winding part is carefully modeled based on its actual number of turns, wire diameter, and number of layers.

3. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 2, characterized in that: The core part is modeled according to its actual shape and material properties, including the core's laminated structure and silicon steel sheet material parameters, so as to accurately simulate the core's magnetic circuit characteristics.

4. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 3, characterized in that: The specific steps of Step 2 are to import the constructed single-phase transformer three-dimensional finite element simulation geometric model into ANSYS Maxwell software three times, and accurately adjust the positions of two of the single-phase transformers so that the three transformers are arranged in parallel to generate a three-dimensional calculation model of the transformer.

5. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 4, characterized in that: When adjusting the positions of two of the single-phase transformers, the spacing between the transformers of each phase is made to meet the actual installation requirements, thereby ensuring the consistency between the simulation results and the actual situation.

6. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 5, characterized in that: In Step 3, when setting material properties and generating a three-dimensional calculation model of the transformer, the starting current-carrying interface and the ending current-carrying interface of the current outflow are selected to create the winding. According to the actual winding connection method of the transformer, as well as the polarity and number of turns of the winding, the winding parameters are accurately set in the software to ensure that the created winding is consistent with the actual transformer winding.

7. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 6, characterized in that: The Step 4 is to build a corresponding external circuit according to different working conditions of the transformer, specifically including: under normal operating conditions, building an external circuit that meets the transformer's rated voltage, rated current and other parameters to simulate the normal working state of the transformer; under short-circuit fault conditions, building an external circuit for a single-phase ground short-circuit fault, setting parameters such as fault resistance and fault time to accurately simulate the occurrence process of a single-phase ground short-circuit fault.

8. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 7, characterized in that: When setting the solution domain in Step 5, the solution domain covers the transformer and the space within a certain range around it to ensure that the electromagnetic field distribution around the transformer can be accurately simulated.

9. The method for simulating and analyzing a three-phase transformer single-phase-to-ground short-circuit leakage magnetic field based on a combination of three single-phase transformers according to claim 8, characterized in that: In the meshing operation of Step 5, different meshing strategies are adopted according to the different components of the transformer and the electromagnetic field distribution characteristics. For areas where the electromagnetic field changes drastically, a finer mesh is used for meshing to improve the calculation accuracy; for areas where the electromagnetic field changes relatively slowly, a coarser mesh is used for meshing to reduce the amount of calculation.

10. The method for simulating and analyzing single-phase-to-ground short-circuit leakage magnetic field of a three-phase transformer based on a combination of three single-phase transformers according to claim 9, characterized in that: When viewing the simulated current distribution of each winding in Step 6, a curve of the short-circuit current changing with time is drawn to analyze the amplitude, frequency, change trend and other characteristics of the short-circuit current to evaluate the electrical performance of the transformer under a short-circuit fault; when viewing the cloud map distribution, the intensity, distribution range and change pattern of the leakage magnetic field are analyzed to evaluate the electromagnetic force distribution of the transformer under a short-circuit fault, providing a basis for transformer fault diagnosis and prevention.

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