A method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator

Abstract

This invention provides a method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator. By performing partitioned equivalent processing on the heat source and heat transfer coefficient, and using the segmented heat transfer coefficient as the core, the flow field and temperature rise are gradually decoupled. Finally, a high-precision simulation method is established to rapidly evaluate the flow field and temperature rise of the generator stator end coil. Compared with existing technologies, this invention solves the problems of low computational efficiency, poor convergence, and insufficient flexibility in traditional coupling methods applied to engineering schemes. It also takes into account the heat dissipation problem caused by localized high losses in the end coil of large generators. It can be used to calculate the flow field and temperature rise of the stator end coil of large-capacity generators and predict the cooling performance of the end coil.

Description

Technical Field

[0001] This invention relates to a step-by-step calculation method for the flow field and temperature rise of the stator end coil of a large-capacity generator in engineering, belonging to the field of generator flow-heat simulation calculation technology. Background Technology

[0002] The stator end coils are subjected to high-intensity electromagnetic loads during operation, and the electromagnetic loss distribution exhibits significant spatial non-uniformity. Simultaneously, the temperature is affected by the motor body coils. Insufficient cooling or uneven temperature distribution can lead to localized overheating, accelerating the aging of insulation materials and, in severe cases, even causing insulation breakdown and other major faults, threatening the safe and stable operation of the unit.

[0003] Directly and strongly coupled calculations of flow field and temperature field face many difficulties in engineering practice:

[0004] First, the end region involves complex fluid-structure interaction problems, making it difficult to solve the governing equations. At the same time, due to the scale differences, it is extremely difficult to perform whole-machine thermal flow simulation. Secondly, the interaction between the flow field and the temperature field requires repeated iterations to achieve convergence, and the complex geometric features at the generator end often result in tens of millions of meshes, making iterative calculations extremely costly. Finally, the nonlinear changes in fluid properties with temperature further increase the difficulty of solving the problem, making numerical oscillations or even divergence more likely. Summary of the Invention

[0005] The purpose of this invention is to propose a multi-physics coupling simulation calculation method that combines high precision, high efficiency and strong robustness to meet the design requirements of stator end coils for large-capacity generators in engineering, thereby solving the pain points of existing technologies.

[0006] To achieve the above objectives, the present invention discloses a method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator, characterized by comprising the following steps: Step 1: Create the end model: A model of the end of a large generator is built based on the generator drawings, and the fluid domain is extracted to obtain a three-dimensional simulation model. Step 2, segmenting the end coil model: Based on the electromagnetic loss calculation results, the generator end coil structure in the three-dimensional simulation model is divided into 5 regions. Step 3, End flow field calculation: The flow characteristics of the cooling medium at the stator end obtained in steps 1 and 2 are solved using computational fluid dynamics. Step 4: Extraction of heat transfer coefficients by zone: Based on the flow field calculation results obtained in step 3, the distribution of the entire fluid domain, including the velocity field, pressure field, and turbulence, is obtained, and the local average surface heat transfer coefficient at each location on the coil surface is extracted in sections. Step 5, Temperature Field Calculation: Using the heat transfer coefficient of the partition obtained in step 4 as the heat transfer boundary condition of the end coil, and the loss value as the initial input, the body coil is solved by fluid-structure interaction using a single-slot model, and finally the temperature distribution of the stator end coil is obtained.

[0007] Preferably, in step 1, the model of the end of the large generator includes a three-dimensional model of the end coil structure and its spatial arrangement, the main cooling air duct and ventilation slot, the end support structure including the support ring, the stator core end face, and the outer contour of the rotor end.

[0008] Preferably, in step 2, the region is reasonably divided according to the winding structure and current distribution characteristics of the coil, and is divided into 5 characteristic segments: the first region - slot opening segment, the second region - R-bend segment, the third region - involute segment 1, the fourth region - involute segment 2, and the fifth region - nose segment.

[0009] Preferably, in step 3, a common grid density is used for flow field calculation, and the physical model of the cooling gas, inlet and outlet boundaries and wall conditions are set. The flow rate of the cooling gas at different outlets is controlled by adjusting the pressure ratio of different outlet boundaries.

[0010] Preferably, in step 4, the average surface heat transfer coefficient of the five characteristic segments from the first region to the fifth region is calculated based on the results of the flow field simulation.

[0011] Preferably, in step 5, coil loss data, including copper loss and iron loss, is obtained by combining electromagnetic field calculations or empirical formulas, and is applied to the corresponding solid region as a volume heat source or surface heat source.

[0012] Preferably, in step 5, the average surface heat transfer coefficient of the partition obtained in step 4 is used as the convection boundary condition of the corresponding region.

[0013] Preferably, in step 5, a single-slot model is used to establish a three-dimensional heat transfer model that includes multiple materials such as the main coil, insulation layer, and stator core. The thermal properties of each material, including thermal conductivity and specific heat capacity, are considered. By solving the steady-state heat conduction equation, the temperature distribution of the end coil is finally obtained.

[0014] This invention proposes a method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator. Based on the equivalent partitioning of heat source and heat transfer coefficient, a flow field-temperature rise co-simulation method is used to gradually decouple the flow field and temperature rise through segmented heat transfer coefficients, thereby enabling rapid evaluation of the flow field and temperature rise of the large generator coil.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1) Balancing accuracy and efficiency in engineering calculations: The partitioned averaging method greatly simplifies the data processing flow, retains the main physical information required for the project, and avoids the complexity caused by excessive refinement; it improves the repeatability of calculations, making the entire two-stage calculation process more controllable and efficient. 2) Convergence: The method of partition averaging is essentially a physical "filtering" of the flow field calculation results. It filters out local numerical fluctuations and minor details, while retaining the main heat transfer characteristics of each region of the generator stator end coil. The numerical stability is better and a convergent solution can be obtained. 3) Flexibility: The method disclosed in this invention has high flexibility, which facilitates parametric analysis and optimization design. The average heat transfer coefficient can be used as an independent design parameter or boundary condition to quickly perform parameter scanning and multi-scheme comparison. By adjusting the heat transfer coefficient of a specific region (simulating the effect of local enhanced or weakened cooling), its impact on the end coil temperature field can be quickly evaluated, thereby guiding the optimization design of the cooling system. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the implementation of the generator end coil flow field and temperature rise calculation method in this invention. Figure 2 This is an enlarged schematic diagram of the end region of the model in this invention and a schematic diagram of the flow field calculation model. The left side is an enlarged schematic diagram of the end region of the model, and the right side is a schematic diagram of the flow field calculation model. Figure 3 This is a schematic diagram of the fluid domain model in this invention; Figure 4 This is a schematic diagram of the stator end coil partitioning in this invention; Figure 5 This is a schematic diagram of the model for calculating the temperature field of a single tank in this invention; Figure 6 This is a partially enlarged schematic diagram of the core cross-section in this invention; Figure 7 This is a partially enlarged schematic diagram of the stator slot in this invention; Figure 8 This is a schematic diagram of the temperature field of the stator end coil in this invention.

[0017] In the diagram, 1—stator end coil, 1-1—slot outlet section, 1-2—R-bend section, 1-3—involute section 1, 1-4—involute section 2, 1-5—nose end section, 2—stator connecting copper busbar, 3—support ring structure, 4—pressure ring, 5—rotor, 6—frame housing, 7—air duct, 8—frame middle wall, 9—fluid domain composed of cooling medium, 10—flow field inlet, 11—flow field outlet, 12—back area of ​​the core, 13—stator core, 14—core radial air duct, 15—air gap, 16—stator body coil, 17—stator coil insulation layer, 18—stator bar, 19—interlayer spacer, 20—stator slot wedge. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] This invention discloses a method for calculating the flow field and temperature rise of the stator end coils in a large-capacity generator. It employs the idea of ​​decoupling a strongly coupled multi-physics problem into two relatively independent but logically related calculation stages. The end coils are divided according to the loss distribution, and the heat transfer coefficients of the cooling medium at the stator end are calculated. Heat transfer data of the end coils is transferred through boundaries, and then a temperature field simulation considering the influence of the coils within the slots is performed. Finally, the temperature distribution of the end coils is obtained. Figure 1 As shown, the specific steps include: Step 1: Create the end model: Model and extract the fluid domain to obtain a three-dimensional simulation model, referencing... Figures 2-3 Based on the generator drawings, a model was created using 3D modeling software. The stator end structure of the generator was reasonably simplified. The 3D simulation model includes: stator end coil 1, stator connecting copper busbar 2, support ring structure 3, pressure ring 4, rotor 5, frame housing 6, air guide ring 7, frame middle wall 8. The above structures form the flow boundary, and the flow area of ​​the cooling medium 9 is extracted.

[0020] Step 2, segmenting the end coil model: The stator end coils are located in a complex leakage magnetic field environment, resulting in significant spatial non-uniformity in electromagnetic loss distribution. Furthermore, the heat dissipation conditions and structural characteristics differ fundamentally across different regions. Therefore, the stator end coils are partitioned according to their loss distribution, referencing... Figure 4 The generator end coil structure is divided into 5 regions: The first area: the slot section 1-1, from 100mm inside the stator slot to the starting point of the end involute; The second area: R-curve segment 1-2, from the starting point of the involute curve to the end of the involute transition circle; The third and fourth regions: from the end of the involute transition circle to the starting point of the nose arc, are divided into two equal parts according to the axial length, namely the third region involute segment 1-3 and the fourth region involute segment 2-4. The fifth region: nasal segment 1-5, from the starting point of the nasal arc to the end point of the end coil.

[0021] Step 3, End flow field calculation: The flow field of the model obtained in steps 1 and 2 is calculated using simulation software: meshes are divided in the main body region and near the wall region respectively, and the mesh density is set using general meshing and the mesh quality is checked; the physical properties of the cooling medium are set, the flow field inlet 10 is set as the mass flow rate inlet boundary, and the flow field outlet 11, which includes the exhaust pipe and air gap, is set as the pressure outlet boundary.

[0022] Step 4: Extraction of heat transfer coefficients by zone: Based on the flow field calculation results, the distribution of velocity field, pressure field and turbulence in the entire fluid domain is obtained, and the local average surface heat transfer coefficient of the coil surface is extracted according to the partitioning results of step 2.

[0023] Step 5: Temperature field calculation: Establish a simplified model of a single stator slot, such as Figures 5-7 The solid domain includes the stator core 13, stator end coils 1, stator body coils 16, interlayer spacers 19, and stator slot wedges 20. The stator end coils 1 and stator body coils 16 are composed of stator coil insulation layers 17 and stator bars 18. The fluid domain includes the back region of the core 12, the radial air duct of the core 14, and the air gap 15. The internal portion of the stator slot is calculated using a heat-fluid coupling method. The surface of the insulation layer of the stator end coils is set as a convective boundary condition, and the partitioned heat transfer coefficient obtained in step 4 is input. The stator bars 18 and stator core 13 are heat source loading terms, and corresponding loss densities are set. The fluid domain is given the physical properties of the cooling medium, and calculations are performed to obtain the temperature distribution of the stator end coils as shown below. Figure 8 As shown.

[0024] The embodiments of the present invention have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the present invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the present invention, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator, characterized in that, Includes the following steps: Step 1: Create the end model: A model of the end of a large generator is built based on the generator drawings, and the fluid domain is extracted to obtain a three-dimensional simulation model. Step 2, segmenting the end coil model: Based on the electromagnetic loss calculation results, the generator end coil structure in the three-dimensional simulation model is divided into 5 regions. Step 3, End flow field calculation: The flow characteristics of the cooling medium at the stator end obtained in steps 1 and 2 are solved using computational fluid dynamics. Step 4: Extraction of heat transfer coefficients by zone: Based on the flow field calculation results obtained in step 3, the distribution of the entire fluid domain, including the velocity field, pressure field, and turbulence, is obtained, and the local average surface heat transfer coefficient at each location on the coil surface is extracted in sections. Step 5, Temperature Field Calculation: Using the heat transfer coefficient of the partition obtained in step 4 as the heat transfer boundary condition of the end coil, and the loss value as the initial input, the body coil is solved by fluid-structure interaction using a single-slot model, and finally the temperature distribution of the stator end coil is obtained.

2. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 1, the model of the end of the large generator includes a three-dimensional model of the end coil structure and its spatial arrangement, the main cooling air duct and ventilation slot, the end support structure including the support ring, the stator core end face, and the outer contour of the rotor end.

3. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 2, the region is reasonably divided according to the winding structure and current distribution characteristics of the coil, and is divided into 5 characteristic segments: the first region - slot opening segment, the second region - R-bend segment, the third region - involute segment 1, the fourth region - involute segment 2, and the fifth region - nose segment.

4. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 3, a common grid density is used for flow field calculation. The physical model of the cooling gas, inlet and outlet boundaries and wall conditions are set. The flow rate of the cooling gas at different outlets is controlled by adjusting the pressure ratio of different outlet boundaries.

5. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 4, based on the results of the flow field simulation, the average surface heat transfer coefficient of the five characteristic segments from the first region to the fifth region is calculated respectively.

6. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 5, coil loss data, including copper loss and iron loss, is obtained by combining electromagnetic field calculations or empirical formulas, and is applied to the corresponding solid region as a volume heat source or surface heat source.

7. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 5, the average surface heat transfer coefficient of the partition obtained in step 4 is used as the convection boundary condition of the corresponding region.

8. The method for calculating the flow field and temperature rise of the stator end coil of a large-capacity generator according to claim 1, characterized in that: In step 5, a single-slot model is used to establish a three-dimensional heat transfer model that includes multiple materials such as the main coil, insulation layer, and stator core. The thermal properties of each material, including thermal conductivity and specific heat capacity, are considered. By solving the steady-state heat conduction equation, the temperature distribution of the end coil is finally obtained.

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