A method for calculating the losses of end structure components and end coils in a large generator.

Abstract

This invention relates to a method for calculating the losses of end-strument components and end-coil coils in a large generator, belonging to the technical field of electromagnetic field calculation methods for generator components. The method includes: Step 1, establishing a realistic three-dimensional model of the end-strument component, which includes the stator end-strument component, stator end coils, and rotor structure; Step 2, establishing a virtual three-phase model of the rotor end coils within the realistic three-dimensional model, which includes three-phase coils staggered circumferentially by 120°; Step 3, performing time-harmonic traveling wave field analysis on the complete end-strument model constructed from Steps 1 and 2 to calculate the end electromagnetic field and eddy current loss distribution. Specifically, alternating currents with a phase difference of 120° are applied to the three-phase coils to form a rotating rotor magnetic field, thereby converting the nonlinear transient rotation analysis into a linear time-harmonic analysis. This invention significantly shortens the calculation time, reduces hardware requirements, and improves calculation stability and fault tolerance while ensuring calculation accuracy.

Description

Technical Field

[0001] This invention relates to a numerical calculation method for studying the losses of end structural components and end coils of large synchronous steam turbine generators. It can be used in the study of eddy current losses and structural design of stator end structural components and end coils of large steam turbine generators, and belongs to the technical field of electromagnetic field calculation methods for generator components. Background Technology

[0002] In the research of large synchronous steam turbine generators, the losses of the stator core end structure and end coils affect the generator's end heating, and also limit the generator's maximum capacity and leading-phase operation capability. Analyzing the end heating problem requires studying and analyzing the losses of its end structural components and end coils. Typically, the study of end losses in large synchronous steam turbine generators uses transient field electromagnetic simulation analysis. Transient field analysis requires treating the rotor and its coils as rotating components, necessitating extensive calculations of the magnetic field within one rotation cycle to ensure the reliability of the results. Furthermore, the calculation step size and mesh generation need to be carefully coordinated, resulting in high hardware requirements, long computation time, and a high risk of convergence failure. Therefore, the study of end losses in large synchronous steam turbine generators introduces resource constraints and inaccuracies in the results.

[0003] Existing computational methods typically employ finite element method (FEM) software to perform transient simulations of generator end-point models, with the boundary condition set as a parallel magnetic field. However, for steel end-point structures, due to their high permeability and extremely small skin depth, the simulation involves nonlinear magnetic materials, ultimately leading to problems such as excessively long computation times, high hardware requirements, and non-convergence of transient simulations. Summary of the Invention

[0004] The purpose of this invention is to provide a calculation method for studying the losses of end structures and end coils of large synchronous steam turbine generators, which uses three-phase windings to simulate the rotor's rotating magnetic field, has a shorter calculation time, and lower hardware requirements.

[0005] To achieve the above objectives, the present invention provides a method for calculating the losses of end structural components and end coils of a large generator, comprising the following steps:

[0006] Step 1: Establish a realistic 3D model of the end section. The realistic 3D model of the end section includes the stator end structural components, stator end coils, and rotor structure. Step 2: Establish a virtual rotor end coil three-phase model in the real end three-dimensional model. The virtual rotor end coil includes three-phase coils that are staggered by 120° in the circumferential position. Step 3: Perform time-harmonic traveling wave field analysis on the complete end model composed of Step 1 and Step 2 to calculate the end electromagnetic field and eddy current loss distribution; wherein, apply alternating current with a phase difference of 120° between each pair of three-phase coils to form a rotating rotor magnetic field, thereby converting the nonlinear transient rotation analysis into a linear time-harmonic analysis.

[0007] Preferably, the actual end three-dimensional model in step 1 includes part of the iron core, stepped iron core, pressure ring, tooth pressure plate, stator end coil and rotor shaft structure, which are accurately created according to the actual drawings using CAD computer-aided design software.

[0008] Preferably, in step 2, the three-phase coils of the virtual rotor coil are evenly distributed circumferentially in space, with each phase coil spaced 120° apart, thus laying the foundation for generating a rotating magnetic field electrically.

[0009] Preferably, the time-harmonic traveling wave field analysis in step 3 further includes: setting corresponding material properties for the end bars, end structural components, iron core, rotor coil and shaft structure according to the actual materials used, including resistivity, relative permeability or BH magnetization curve.

[0010] Preferably, step 3, the harmonic traveling wave field analysis, further includes: performing finite element mesh generation on the complete end model, discretizing the generator end structure model into a numerical model, wherein local mesh refinement is implemented for the steel end structure with high magnetic permeability and the end coil region with large eddy current loss.

[0011] Preferably, step 3, the harmonic traveling wave field analysis, further includes: applying a parallel boundary condition of magnetic field lines to the iron core end face and the outer boundary of free space, in order to simulate the effective limit of the magnetic field and avoid numerical distortion caused by boundary reflection.

[0012] Preferably, step 3, the harmonic traveling wave field analysis, further includes: dividing the stator windings into three phases, and applying specific current excitation to each stator coil conductor of phases A, B, and C in the model according to the actual working load conditions. The current excitation of the stator windings and the current excitation of the rotor three-phase coils form a spatial superposition relationship.

[0013] Preferably, the nonlinear transient rotational analysis is equivalent to the linear time-harmonic analysis as follows: the electrical rotating magnetic field of the three-phase coil of the virtual rotor is used to replace the mechanical rotation of the real rotor, and the nonlinear transient electromagnetic field analysis of the generator end model is transformed into a linear time-harmonic field analysis. By setting impedance boundary conditions and magnetic field equivalence, the eddy current losses of the end structure and the end coil are calculated.

[0014] Preferably, step 3 is followed by step 4: post-processing the calculation results of the time-harmonic traveling wave field analysis to obtain specific magnetic flux density distribution and eddy current loss distribution data on the end structure, and using the data for end heating assessment and structural optimization design.

[0015] Preferably, NX software is used to establish a three-dimensional model of the real end and a three-phase model of the virtual rotor end coil, and finite element CAE software is used to perform time-harmonic traveling wave field analysis, wherein the virtual rotor end coil and the real end structure form a complete electromagnetic calculation domain.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention employs a three-phase virtual rotor winding with a circumferential offset of 120° and applies three-phase alternating current with a phase difference of 120° between each pair of windings to electrically synthesize a rotating magnetic field. This replaces the traditional method of applying direct current to a rotating rotor to form a mechanical rotating magnetic field. This successfully transforms the complex nonlinear transient field analysis in the study of end losses of large synchronous steam turbine generators into a linear time-harmonic field analysis. This equivalent method fundamentally avoids the numerous time-step iterations caused by rotor rotation in transient field calculations, significantly shortening the computation time and greatly improving computational efficiency. Furthermore, due to the use of time-harmonic field solutions, the convergence during calculation is better, effectively improving the fault tolerance and stability of the calculation method.

[0017] Compared to the high hardware requirements of existing transient field simulation technologies, the calculation method of this invention significantly reduces the demand for computer memory and processor performance. Eddy current loss calculations for the end structures and coils of large steam turbine generators can be efficiently completed on conventional workstations, reducing reliance on high-performance computing resources and lowering computational costs. Furthermore, by avoiding the complex coordination and adjustment of step size and mesh generation in transient field calculations, this invention simplifies the preprocessing setup process while maintaining computational accuracy, reducing the technical skill requirements for operators and improving the convenience of engineering applications.

[0018] The calculation method of this invention can accurately capture the skin effect and eddy current distribution of steel end structures under high magnetic permeability conditions, providing a reliable numerical basis for generator end heating assessment and structural optimization design. By using an equivalent modeling method with a virtual rotating magnetic field, the method preserves the authenticity of the physical distribution of the end magnetic field while achieving fast and stable numerical solutions. It is particularly suitable for end loss research and serial design development of large synchronous steam turbine generators under different operating conditions, demonstrating significant engineering practical value and promising prospects for widespread application. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the rotor coil model in the calculation method of end coil loss of a large generator end structure component of the present invention; Figure 2 This is a flowchart illustrating a method for calculating the end structure component and end coil loss of a large generator according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a method for calculating the end structure components and end coil losses of a large synchronous steam turbine generator. This method uses an equivalent calculation approach, which converts the nonlinear transient analysis of the generator end model into a linear time-harmonic analysis. By setting impedance boundary conditions and magnetic field equivalence, the calculation time for eddy current losses is effectively reduced, and the stability and accuracy of the calculation are improved.

[0022] The calculation method provided by this invention specifically includes the following steps: Step 1, Create a realistic end model Based on the actual drawings of the end structures of the large synchronous steam turbine generator, a three-dimensional model (real end model) of the steel end structure of the large generator was created using the CAD computer-aided design software NX. This model includes a portion of the core, stepped core sections, pressure rings, toothed pressure plates, stator end coils, and a three-dimensional model of the rotor structure. The stator end coils include three-phase coils. This step accurately recreates the geometric features of the generator end, providing realistic physical boundary conditions for subsequent electromagnetic field calculations and ensuring structural consistency between the calculation model and the actual equipment.

[0023] Step 2: Establish a three-phase model of the virtual rotor end coils. Based on the preliminary model formed in step 1, the rotor coil is drawn using CAD computer-aided design software NX, such as... Figure 1 As shown, the rotor coil is divided into three phase coils, which are staggered by 120° in the circumferential position. This three-phase distribution structure lays the geometric foundation for the subsequent generation of a rotating magnetic field by electrical means rather than mechanical rotation. When the complete three-dimensional model is imported into the CAE computer-aided analysis software, the real end structure and the virtual rotor coil model form a complete electromagnetic calculation domain. The synergistic effect of the geometric arrangement of the virtual rotor coil and the real rotor structure ensures the physical rationality of the magnetic field distribution.

[0024] Step 3, establish time-harmonic traveling wave field analysis at end losses Using finite element method (FEM) software, a time-harmonic traveling wave field analysis was performed on the complete end model formed in step 2 under a given operating condition. The distribution of the electromagnetic field and eddy currents at the generator end structure and end coils was calculated. This analysis process further includes the following specific steps: Step 3.1: Based on the actual materials used, set the corresponding material properties for the end bars, end structural components, iron core, rotor coil, and shaft structure, including resistivity ρ and permeability μ or BH curves. The accurate setting of material properties determines the propagation, reflection, and loss characteristics of electromagnetic fields in different media, and is the physical basis for calculating eddy current losses. Step 3.2: Based on the different components in the model structure, the model formed in Step 2 is meshed, and the generator end structure model is discretized into a numerical model. The meshing accuracy directly affects the numerical error of the magnetic field calculation. For areas with high magnetic permeability, such as steel end structure components, and areas with large eddy current losses in the end coil, local meshing is required to accurately capture the skin effect. Step 3.3: Apply the parallel magnetic field line condition to the iron core end face and the outer boundary of free space to simulate the effective limit of the magnetic field. This boundary condition works in conjunction with the solid model established in Step 1 to ensure that the magnetic field is reasonably distributed in the computational domain and to avoid numerical distortion caused by boundary reflection. Step 3.4: Divide the stator windings into three phases. Based on the actual working load, apply a specific current to each stator coil conductor of phases A, B, and C in the model. The current excitation of the stator windings and the current excitation of the rotor windings in step 3.5 form a spatial superposition relationship. Step 3.5: Based on the actual operating load, apply alternating current with a phase difference of 120° between each pair of the rotor three-phase windings. This step is coordinated with the circumferentially staggered three-phase coil arrangement in Step 2. Through the correspondence between electrical phase difference and spatial position difference, a rotating rotor magnetic field is synthesized in the circumferential direction, replacing the traditional method of passing DC current through the rotating rotor. This virtual rotating magnetic field is superimposed on the magnetic field generated by the stator winding in Step 3.4 in the end region to form a rotating composite magnetic field, which in turn induces eddy currents in the end structure. This equivalent method transforms the traditional transient rotation calculation into a time-harmonic field calculation, significantly reducing the computational complexity and hardware requirements. Step 3.6: Set the calculation duration and step size to obtain the time-harmonic end magnetic field, and calculate the eddy current loss of the end structure and end coil. Reasonable setting of calculation parameters ensures the numerical convergence and accuracy of the time-harmonic analysis.

[0025] Step 4, Results Analysis The specific magnetic flux density and loss distribution on the end structure are obtained through result processing. This step transforms the electromagnetic field numerical solution obtained in step 3 into loss distribution data that can be used in engineering, providing a basis for end heating assessment and structural optimization design.

[0026] In the above implementation process, steps 1 and 2 together construct a complete electromagnetic computational geometric model. The virtual three-phase winding design in step 2 is a key structural feature for achieving the technical effect of this invention. Steps 3.1 to 3.6 constitute a complete time-harmonic traveling wave field calculation process. The 120° spatial offset arrangement of steps 3.5 and 3.5 forms a dual spatial-electrical correspondence, ensuring the correct synthesis of the rotating magnetic field. The current settings in steps 3.4 and 3.5 together define the electromagnetic excitation source. Together with the material properties in step 3.1, the mesh discretization in step 3.2, and the boundary conditions in step 3.3, they form a stable and solvable electromagnetic field boundary value problem. Step 4 completes the transformation from numerical calculation results to engineering analysis data.

[0027] Through the organic collaboration of geometric modeling, physical property setting, boundary condition definition, excitation load application, and numerical solution, the study of end losses of large synchronous steam turbine generators is transformed from transient field to time-harmonic field. This significantly shortens the calculation time, reduces the requirements for computing hardware, and improves the fault tolerance and engineering practicality of the calculation method while ensuring calculation accuracy.

[0028] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating the losses of end structural components and end coils in a large generator, characterized in that, Includes the following steps: Step 1: Establish a realistic 3D model of the end section. The realistic 3D model of the end section includes the stator end structural components, stator end coils, and rotor structure. Step 2: Establish a virtual rotor end coil three-phase model in the real end three-dimensional model. The virtual rotor end coil includes three-phase coils that are staggered by 120° in the circumferential position. Step 3: Perform time-harmonic traveling wave field analysis on the complete end model composed of Step 1 and Step 2 to calculate the end electromagnetic field and eddy current loss distribution; wherein, apply alternating current with a phase difference of 120° between each pair of three-phase coils to form a rotating rotor magnetic field, thereby converting the nonlinear transient rotation analysis into a linear time-harmonic analysis.

2. The method for calculating the end structure component and end coil loss of a large generator according to claim 1, characterized in that, The actual end 3D model in step 1 includes part of the iron core, stepped iron core, pressure ring, tooth pressure plate, stator end coil and rotor shaft structure, which are accurately created according to the actual drawings using CAD computer-aided design software.

3. The method for calculating the end structure component and end coil loss of a large generator according to claim 1, characterized in that, In step 2, the three-phase coils of the virtual rotor coil are evenly distributed circumferentially in space, with each phase coil spaced 120° apart. This arrangement lays the foundation for generating a rotating magnetic field electrically.

4. The method for calculating the end structure component and end coil loss of a large generator according to claim 1, characterized in that, Step 3, the time-harmonic traveling wave field analysis, also includes: setting corresponding material properties for the end bars, end structural components, iron core, rotor coils and shaft structure according to the actual materials used, including resistivity, relative permeability or BH magnetization curve.

5. The method for calculating the end structure component and end coil loss of a large generator according to claim 4, characterized in that, Step 3, the harmonic traveling wave field analysis, also includes: performing finite element mesh generation on the complete end model, discretizing the generator end structure model into a numerical model, and implementing local mesh refinement for the steel end structure with high magnetic permeability and the end coil region with high eddy current loss.

6. The method for calculating the end structure component and end coil loss of a large generator according to claim 5, characterized in that, Step 3, harmonic traveling wave field analysis, also includes applying parallel magnetic field lines boundary conditions to the core end face and the outer boundary of free space to simulate the effective limit of the magnetic field and avoid numerical distortion caused by boundary reflection.

7. The method for calculating the end structure component and end coil loss of a large generator according to claim 6, characterized in that, Step 3, harmonic traveling wave field analysis, also includes: dividing the stator windings into three phases, and applying specific current excitation to each stator coil conductor of phases A, B, and C in the model according to the actual working load conditions. The current excitation of the stator windings and the current excitation of the rotor three-phase coils form a spatial superposition relationship.

8. The method for calculating the end structure component and end coil loss of a large generator according to claim 1, characterized in that, The nonlinear transient rotational analysis is equivalent to the linear time-harmonic analysis as follows: the electrical rotating magnetic field of the three-phase coil of the virtual rotor is used to replace the mechanical rotation of the real rotor, and the nonlinear transient electromagnetic field analysis of the generator end model is transformed into a linear time-harmonic field analysis. By setting impedance boundary conditions and magnetic field equivalence, the eddy current losses of the end structure and the end coil are calculated.

9. The method for calculating the end structure component and end coil loss of a large generator according to claim 1, characterized in that, Step 3 is followed by step 4: post-processing the calculation results of the time-harmonic traveling wave field analysis to obtain specific magnetic flux density distribution and eddy current loss distribution data on the end structure, and using the data for end heating assessment and structural optimization design.

10. The method for calculating the end structure component and end coil loss of a large generator according to claim 1, characterized in that, The NX software was used to establish a three-dimensional model of the real end and a three-phase model of the virtual rotor end coil. The finite element CAE software was used to perform time-harmonic traveling wave field analysis. The virtual rotor end coil and the real end structure form a complete electromagnetic calculation domain.

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