Transformer coil winding local fine homogenization model calculation method and device

Abstract

The application provides a transformer coil winding local fine homogenization model calculation method and device, and relates to the technical field of coil winding temperature rise calculation of electrical equipment. The application is based on the finite element method, solid and fluid heat transfer, and first obtains a homogenization equivalent model of an actual coil model. On the basis, a highest temperature point position of the coil is obtained through temperature field and fluid field coupling simulation calculation. A local fine homogenization model of the coil winding is proposed on the basis of the highest temperature point, and the coil temperature is recalculated. The method simplifies the structure of the coil model, improves the temperature field calculation speed and efficiency, and can improve the accuracy of the highest temperature point calculation of the coil compared with the traditional coil homogenization model calculation method. The method can provide reliable credentials for the structure optimization, daily operation and maintenance and fault early warning of the transformer, and has certain engineering application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coil winding temperature rise calculation of electrical equipment, and particularly relates to a transformer coil winding local fine homogenization model calculation method and device. BACKGROUND

[0002] As a key equipment in the power system, the operation stability and safety of the power transformer directly affect the reliability and stability of the entire power system operation. In the long-term research on the power transformer, it is generally found that the winding temperature rise of the power transformer is higher than that of other components in the working state, and the uneven distribution of the winding temperature is prone to cause the local overheating of the winding, resulting in the accelerated aging of the insulation and the decline of the insulation performance, thereby bringing hidden dangers to the safe operation. In the long-term service of the equipment, the thermal stability problem of the winding position is particularly prominent: the measured data shows that when the rated load is operated, the hot spot temperature of the transformer coil winding can reach 98-105 DEG C, which is 25-30 DEG C higher than the temperature of the core under the same working condition. This significant temperature gradient is caused by the superposition effect of the eddy current loss and the conductor resistance loss specific to the winding structure.

[0003] At present, the service life of the power transformer follows the "six-degree principle". Therefore, the hot spot temperature of the transformer coil winding is not only a decisive factor affecting the whole life cycle of the transformer, but also the main restrictive factor affecting the current-carrying capacity of the transformer. Accurate calculation of the hot spot temperature of the power transformer coil winding is crucial for power transformer fault early warning, power transformer whole life cycle prediction and power transformer structure design and development. When using finite element simulation software to carry out simulation and calculation, the electromagnetic, flow and thermal multi-physical coupling method is usually used for in-depth research. When facing the temperature rise and hot spot analysis, there is turn-to-turn insulation between the windings, and the thickness of the turn-to-turn insulation is only mm level, which not only increases the complexity of the model construction, but also due to the large difference between the size of the winding and the turn-to-turn insulation, in order to accurately calculate the temperature and the hot spot temperature, the mesh division amount is large, which brings the problems of long calculation time and non-convergence of the results.

[0004] At present, there are many researches on improving the simulation model calculation speed, mainly focusing on the improvement of mesh division and the fast calculation method of matrix. In view of the problem that there is a magnitude difference between the sizes of the transformer components, a simulation model simplification and material parameter equivalent method is proposed, which simplifies the complexity of the model and improves the calculation efficiency, so as to reduce the calculation time while basically keeping consistent with the temperature rise distribution of the complex model. However, this method is not accurate enough in the calculation of the highest temperature point of the transformer, so a local fine homogenization model calculation method is proposed, which selects the actual model structure of the highest temperature point position based on the homogenization model, to improve the calculation accuracy of the highest temperature point temperature. SUMMARY

[0005] The application aims to provide a transformer coil winding local fine homogenization model calculation method and device, which is used to solve the problem of how to accurately obtain the temperature distribution and the highest temperature point position of the transformer coil winding, and can accurately and quickly obtain the temperature distribution and the highest temperature point position of the transformer coil winding.

[0006] In order to achieve the above-mentioned purpose, in the first aspect, the application provides a transformer coil winding local fine homogenization model calculation method, comprising:

[0007] A transformer coil homogenization model is built in a finite element simulation software according to the actual structure of the transformer, the transformer comprising a transformer coil and a transformer core;

[0008] The transformer coil homogenization model is meshed;

[0009] Material parameters, boundary conditions and heat source excitation of the transformer coil homogenization model are set;

[0010] A full-coupling solver of temperature field and fluid field is selected, a direct coupling calculation mathematical equation between the heat-flow coupling physical fields is constructed according to the bidirectional coupling equation groups of the temperature field and the fluid field, so as to realize the bidirectional coupling simulation of the transformer;

[0011] The temperature distribution and the highest temperature point position of the transformer coil under the transformer coil homogenization model are obtained based on the coupling calculation results of the temperature field and the fluid field;

[0012] The axial or radial direction of the highest temperature point position of the transformer coil is finely modeled, and the remaining part is still modeled by the homogenization method, so as to obtain the transformer coil winding local fine homogenization model;

[0013] The temperature distribution and the highest temperature point position of the transformer coil are recalculated based on the transformer coil winding local fine homogenization model.

[0014] According to the transformer coil winding local fine homogenization model calculation method provided by the application, the transformer coil comprises a high-voltage coil and a low-voltage coil;

[0015] The transformer coil homogenization model is built, comprising:

[0016] According to the structures of the high-voltage coil and the low-voltage coil, homogenization is respectively performed; first, the distribution areas of the coil winding and the epoxy resin are determined and equivalent to a single material cylinder, and then the equivalent material parameters are calculated according to the structure parameters and the thermal conductivity of the coil winding and the epoxy resin and loaded on the single material cylinder to form the transformer coil homogenization model.

[0017] The application provides a transformer coil winding local fine homogenization model calculation method.

[0018] The application provides a transformer coil winding local fine homogenization model calculation method.

[0019] The application provides a transformer coil winding local fine homogenization model calculation method.

[0020] The air material parameters include density, thermal conductivity, dynamic viscosity and specific heat capacity.

[0021] The transformer core material parameters include thermal conductivity and specific heat capacity.

[0022] The high-voltage coil and the low-voltage coil material parameters include thermal conductivity and specific heat capacity.

[0023] The application provides a transformer coil winding local fine homogenization model calculation method.

[0024] The application provides a transformer coil winding local fine homogenization model calculation method.

[0025] According to the temperature distribution of the high-voltage coil and the low-voltage coil, the highest temperature point positions of the high-voltage coil and the low-voltage coil are extracted. m When the highest temperature point position of the high-voltage coil pie type winding structure is located at the actual coil model first layer, the high-voltage coil winding local fine homogenization model is re-established. m The actual structure of the high-voltage coil winding 1st layer, 2nd layer and +1st layer is reserved based on the actual coil model. m The actual structure of the high-voltage coil winding 1st layer, 2nd layer and +1st layer is reserved based on the actual coil model. m The actual structure of the high-voltage coil winding 1st layer, 2nd layer and +1st layer is reserved based on the actual coil model.m -2 layers form a homogenized structure, m +2 to k layers form a homogenized structure; for a foil-shaped winding structure of a low-voltage coil winding, when the temperature maximum position is located at the first n layer of the actual coil model, the local fine homogenization model of the low-voltage coil winding is re-established, that is, the low-voltage coil winding n -1 layer, n layer, n +1 layer of the actual structure, the 1 to n -2 layers of the low-voltage coil winding form a homogenized structure, n +2 to p layers form a homogenized structure; wherein, k , m , n , p is a positive integer.

[0026] According to the transformer coil winding local fine homogenization model calculation method provided by the application, the calculation process of the equivalent thermal conductivity and the equivalent specific heat capacity is:

[0027] Under the condition of unit area, the thermal resistance of the material is related to the thickness and thermal conductivity of the material as follows:

[0028] (1)

[0029] In the formula, R m is the thermal resistance of the material, d is the thickness of the material, k is the thermal conductivity of the material;

[0030] If the epoxy resin is embedded in the gap of the transformer coil, the equivalent thermal resistance of the transformer coil in the radial direction is:

[0031] (2)

[0032] In the formula, is the thermal resistance of the copper wire in the radial direction of the transformer coil; is the radial thermal resistance of the epoxy resin;

[0033] The total thickness of the transformer coil in the radial direction is:

[0034] (3)

[0035] In the formula, is the total thickness of the copper wire in the radial direction of the transformer coil; is the total thickness of the epoxy resin in the radial direction;

[0036] The formula (1), formula (2) and formula (3) are combined:

[0037] (4)

[0038] The equivalent thermal conductivity of the transformer coil in the radial direction is:

[0039] ;

[0040] The equivalent thermal resistance of the transformer coil in the axial direction is R ea The calculation formula is:

[0041] (5)

[0042] In the formula, is the axial thermal resistance of the transformer copper conductor, is the axial thermal resistance of the epoxy resin;

[0043] The equivalent thermal conductivity of the transformer coil in the axial direction is:

[0044] (6)

[0045] The epoxy resin is wrapped on the coil winding, so:

[0046] (7)

[0047] Wherein, is the equivalent specific heat capacity of the transformer coil; m is the total mass of the transformer coil; is the temperature change of the transformer coil; is the specific heat capacity of the transformer coil conductor layer; is the specific heat capacity of the epoxy resin; m 1 is the total mass of the transformer coil conductor layer; m 2 is the total mass of the epoxy resin.

[0048] According to the transformer coil winding local fine homogenization model calculation method provided by the application, the direct coupling calculation mathematical equation between the heat-flow coupling physical field is:

[0049]

[0050] In the formula, ρ is the fluid density; v is the velocity vector; is the gradient operator; τ is the viscous stress tensor; F is the body force; p is the fluid pressure; T is the temperature; is the divergence operator; Qis a heat source; g is a gravitational acceleration; is a specific heat capacity; is a thermal conductivity.

[0051] In a second aspect, the present application provides a transformer coil winding local refinement homogenization model calculation device, comprising:

[0052] a modeling unit, configured to build a transformer coil homogenization model in finite element simulation software according to the actual structure of the transformer, the transformer comprising a transformer coil and a transformer core;

[0053] a meshing unit, configured to mesh the transformer coil homogenization model;

[0054] a loading unit, configured to set material parameters, boundary conditions and heat source excitation of the transformer coil homogenization model;

[0055] a calculation unit, configured to select a full coupling solver of a temperature field and a fluid field, construct a direct coupling calculation mathematical equation between thermal-fluid coupling physical fields according to a two-way coupling equation group of the temperature field and the fluid field, so as to realize thermal-fluid two-way coupling simulation of the transformer;

[0056] a post-processing unit, configured to obtain a temperature distribution and a highest temperature point position of the transformer coil under the transformer coil homogenization model based on a temperature field and fluid field coupling calculation result;

[0057] a secondary modeling unit, configured to perform fine modeling on an axial or radial direction of the highest temperature point position of the transformer coil, and the remaining part is still modeled by using the homogenization method, so as to obtain a transformer coil winding local refinement homogenization model;

[0058] a secondary calculation unit, configured to re-calculate the temperature distribution and the highest temperature point position of the transformer coil based on the transformer coil winding local refinement homogenization model.

[0059] Compared with the prior art, the present application has at least the following technical effects:

[0060] The application provides a transformer coil winding local fine homogenization model calculation method and device, which is based on finite element method, solid and fluid heat transfer, and first obtains a homogenization equivalent model of an actual coil model, and then obtains a coil temperature highest point position through temperature field and fluid field coupling simulation calculation, and proposes a coil winding local fine homogenization model based on the point, and re-calculates the coil temperature. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0062] In the drawings:

[0063] Figure 1 The flow chart of the transformer coil winding local fine homogenization model calculation method of the present application;

[0064] Figure 2 The temperature result graph of the actual structure of the transformer coil winding of the embodiment of the present application;

[0065] Figure 3 The temperature result graph of the homogenization model of the transformer coil winding of the embodiment of the present application.

[0066] Figure 4 The temperature result graph of the transformer coil winding local fine homogenization model of the embodiment of the present application. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions in the present application will be described clearly and completely in combination with the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0068] The embodiments of the present application will be described in detail in combination with the drawings. The following embodiments and features in the embodiments can be combined with each other without conflict.

[0069] The application selects to use a homogenization simplification method according to the temperature maximum point distribution of the transformer, and meanwhile, the original model structure at the temperature maximum point distribution is reserved, so that the calculation speed is increased and the temperature maximum point is accurately calculated.

[0070] The embodiment of the application provides a homogenization model calculation method and device for local fine transformer coil winding, which comprehensively considers the fast calculation of the temperature of the transformer coil winding and the accurate solution of the temperature maximum point, so that the temperature distribution and heat dissipation process of the transformer are simulated with high calculation efficiency, reliable credentials are provided for the structure optimization, daily operation and maintenance and fault early warning of the transformer, and the method has certain engineering application value.

[0071] Please refer to Figure 1 The embodiment of the application provides a homogenization model calculation method and device for local fine transformer coil winding, which comprehensively considers the fast calculation of the temperature of the transformer coil winding and the accurate solution of the temperature maximum point, so that the temperature distribution and heat dissipation process of the transformer are simulated with high calculation efficiency, reliable credentials are provided for the structure optimization, daily operation and maintenance and fault early warning of the transformer, and the method has certain engineering application value.

[0072] Step S1: building a transformer coil initial homogenization model (referred to as a transformer coil homogenization model) in a finite element simulation software according to the actual structure of the transformer, wherein the transformer includes a transformer coil and a transformer core;

[0073] Specifically, the transformer coil includes a high-voltage coil and a low-voltage coil, and the transformer coil homogenization model is built in the finite element simulation software according to the actual structure of the transformer, that is, the high-voltage coil, the low-voltage coil and the transformer core model are respectively built in the finite element simulation software according to the structure parameters of the transformer components and the actual specifications;

[0074] Step S2: meshing the transformer coil homogenization model;

[0075] Step S3: setting material parameters, boundary conditions and heat source excitation of the transformer coil homogenization model;

[0076] Specifically, the material parameters of the transformer coil homogenization model are set, including:

[0077] The air material parameters include density, thermal conductivity, dynamic viscosity and specific heat capacity.

[0078] The material parameters of the transformer core include thermal conductivity and specific heat capacity.

[0079] The material parameters of the high-voltage coil and the low-voltage coil include thermal conductivity and specific heat capacity; wherein the equivalent thermal conductivity and the equivalent specific heat capacity are set for the transformer coil homogenization part.

[0080] The boundary conditions include the convective heat transfer coefficient of the transformer with the outside world, and the loss is assigned to each component.

[0081] For the transformer coil homogenization model, the heat source excitation is set as the high-voltage coil cylinder, the low-voltage coil cylinder and the transformer core respectively; for the transformer coil winding local refined homogenization model, the heat source excitation is set as the homogenization part of the high-voltage coil cylinder and the low-voltage coil cylinder and the copper conductor of the refined part and the transformer core.

[0082] Step S4: selecting a full-coupling solver of the temperature field and the fluid field, constructing a direct coupling calculation mathematical equation between the heat-flow coupled physical fields according to the two-way coupling equation set of the temperature field and the fluid field, so as to realize the heat-flow two-way coupling simulation of the transformer;

[0083] Step S5: obtaining the temperature distribution and the highest temperature point position of the transformer coil under the transformer coil homogenization model based on the coupling calculation results of the temperature field and the fluid field;

[0084] Step S6: refining the modeling of the axial or radial position of the highest temperature point of the transformer coil, and the remaining part is still modeled by the homogenization method, so as to obtain the transformer coil winding local refined homogenization model;

[0085] Specifically, the transformer coil winding local refined homogenization model is a two-dimensional axisymmetric model of the transformer.

[0086] According to the temperature distribution of the high-voltage coil and the low-voltage coil, the highest temperature point positions of the high-voltage coil and the low-voltage coil are extracted respectively; for the pie-shaped winding structure of the high-voltage coil, when the highest temperature point position is located at the actual coil model layer m , a local refined homogenization model of the high-voltage coil winding is re-established, that is, based on the actual structure of the high-voltage coil winding, the actual structure of the m -1 layer, m layer, m +1 layer is reserved, the 1 to m -2 layer of the high-voltage coil winding is formed into a homogenization structure, m +2 to k layer is formed into a homogenization structure; for the foil-shaped winding structure of the low-voltage coil, when the highest temperature point position is located at the actual coil model layer n , a local refined homogenization model of the low-voltage coil winding is re-established, that is, based on the actual structure of the low-voltage coil winding, the actual structure of the n -1 layer, n layer, n +1 layer is reserved, the 1 to n -2 layer of the low-voltage coil winding is formed into a homogenization structure, n +2 to p layer is formed into a homogenization structure; wherein, k , m , n , pis a positive integer.

[0087] Step S7: Based on the local fine homogenization model of the transformer coil winding, the temperature distribution and the highest temperature point position of the transformer coil are recalculated. That is, compared with the initial transformer coil homogenization model built before, the local fine homogenization model of the transformer coil winding is obtained in step S6, and then steps S2 to S5 are re-performed, that is, the grid partition, loading, material parameters and boundary conditions of the local fine homogenization model of the transformer coil winding are re-set, and the heat source excitation is respectively set as the copper wires of the homogenization parts and the fine parts of the high-voltage coil cylinder and the low-voltage coil cylinder and the transformer core, and then the temperature distribution and the highest temperature point position of the transformer coil are recalculated, which can realize the double balance of calculation efficiency and the highest temperature point calculation compared with the actual model and the homogenization model.

[0088] Specifically, in step S1, a transformer coil homogenization model is built in a finite element simulation software, including: according to the structure of the high-voltage coil and the low-voltage coil, homogenization is respectively performed; first, the distribution area of the coil winding and the epoxy resin is determined, which is equivalent to a single material cylinder, and then the equivalent material parameters are calculated according to the structure parameters and the thermal conductivity of the coil winding and the epoxy resin and loaded on the single material cylinder to form the transformer coil homogenization model.

[0089] And when building the transformer coil homogenization model, the following assumptions are made:

[0090] The heat sources are the high-voltage coil, the low-voltage coil and the transformer core, without considering other heat sources.

[0091] The high-voltage coil and the low-voltage coil are respectively an integral, without being divided, and there is an air channel between them.

[0092] Specifically, in step S2, the transformer coil homogenization model is meshed, including: using mapping meshing in the high-voltage coil homogenization model and the low-voltage coil homogenization model, the mapping mesh is generated by mapping the regular mesh mode to the geometric body.

[0093] Specifically, the calculation process of the equivalent thermal conductivity and the equivalent specific heat capacity is as follows:

[0094] Under the condition of unit area, the thermal resistance of the material is related to the thickness of the material, the thermal conductivity of the material, and the relationship is as follows:

[0095] (1)

[0096] In the formula, R m The thermal resistance of the material is d The thickness of the material is k The thermal conductivity of the material is

[0097] The equivalent thermal resistance of the transformer coil in the radial direction is:

[0098] (2)

[0099] wherein, Rc is the radial copper wire thermal resistance of the transformer coil; Re is the radial thermal resistance of the epoxy resin;

[0100] The total thickness of the transformer coil in the radial direction is:

[0101] (3)

[0102] wherein, Rct is the total thickness of the copper wire of the transformer coil in the radial direction; Ret is the total thickness of the epoxy resin in the radial direction;

[0103] By combining equation (1), equation (2) and equation (3), we have:

[0104] (4)

[0105] The equivalent thermal conductivity of the transformer coil in the radial direction is:

[0106]

[0107] The equivalent thermal resistance of the transformer coil in the axial direction is R ea The calculation formula is:

[0108] (5)

[0109] wherein, Rca is the axial thermal resistance of the copper wire of the transformer, Rca is the axial thermal resistance of the epoxy resin;

[0110] The equivalent thermal conductivity of the transformer coil in the axial direction is:

[0111] (6)

[0112] The epoxy resin is wrapped on the coil winding, so we have:

[0113] (7)

[0114] wherein, Cp is the equivalent specific heat capacity of the transformer coil; m M is the total mass of the transformer coil; ΔT is the temperature change of the transformer coil; ​Cp is the specific heat capacity of the transformer coil conductor layer; Cp is the specific heat capacity of the epoxy resin; m 1 is the total mass of the transformer coil conductor layer; m 2 is the total mass of the epoxy resin;

[0115] Specifically, in step S4, the direct coupling calculation mathematical equation between the heat-flow coupled physical fields is as follows:

[0116]

[0117] In the formula, p is the fluid density; v is the velocity vector; is the gradient operator; τ is the viscous stress tensor; F is the body force; p is the fluid pressure; T is the temperature; is the divergence operator; Q is the heat source; g is the gravitational acceleration; is the specific heat capacity; is the thermal conductivity.

[0118] Based on the same inventive concept, another embodiment of the present application provides a transformer coil winding local refinement homogeneous model calculation device, which corresponds to the method of the foregoing embodiment, and comprises:

[0119] a modeling unit, configured to build a transformer coil homogeneous model in finite element simulation software according to the actual structure of the transformer, the transformer comprising a transformer coil and a transformer core;

[0120] a meshing unit, configured to mesh the transformer coil homogeneous model;

[0121] a loading unit, configured to set material parameters, boundary conditions and heat source excitation of the transformer coil homogeneous model;

[0122] a calculation unit, configured to select a full coupling solver of a temperature field and a fluid field, construct a direct coupling calculation mathematical equation between heat-flow coupled physical fields according to a two-way coupling equation group of the temperature field and the fluid field, and thus realize two-way coupling simulation of the transformer;

[0123] a post-processing unit, configured to obtain temperature distribution and a highest temperature point position of the transformer coil under the transformer coil homogeneous model based on a coupling calculation result of the temperature field and the fluid field;

[0124] a secondary modeling unit, configured to perform fine modeling on an axial direction or a radial direction of the highest temperature point position of the transformer coil, and the remaining part is still modeled by using the homogeneous method, so as to obtain a transformer coil winding local refinement homogeneous model.

[0125] A secondary calculation unit is configured to re-calculate the temperature distribution and the position of the highest temperature point of the transformer coil based on the local fine homogenization model of the transformer coil winding.

[0126] The application is simulated and verified as follows. The re-constructed local fine homogenization model of the transformer coil winding is calculated to obtain the temperature field distribution cloud diagram under the model, and the highest temperature point temperature of the transformer coil is accurately calculated. The comparison results of the model calculation under different heat dissipation conditions are shown in Table 1.

[0127] Table 1 Comparison results of model calculation under different heat dissipation conditions

[0128]

[0129] As shown in Table 1, the local fine homogenization model of the transformer coil winding reduces the number of grid divisions, reduces the model calculation time, and can accurately calculate the highest temperature point.

[0130] In summary, the local fine homogenization model calculation method and device of the transformer coil winding provided by the application comprehensively considers the fast calculation of the temperature of the transformer coil winding and the accurate solution of the highest temperature point, simulates the temperature distribution and heat dissipation process of the transformer with high calculation efficiency, provides reliable credentials for the structure optimization, daily operation and fault early warning of the transformer, and has certain engineering application value.

[0131] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. The specification and examples given herein are not intended to be exhaustive or limiting, and other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. The title of this application is intended to be interpreted broadly to include any and all embodiments of the application. It is contemplated that the use of the word "for" in the claim "for the method of calculating the local fine homogenization model of the transformer coil winding" is intended to be interpreted broadly to include any and all embodiments of the application. It is further contemplated that the use of the word "for" in the claim "for the method of calculating the local fine homogenization model of the transformer coil winding" is intended to be interpreted broadly to include any and all embodiments of the application. The scope of the application is to be limited only by the claims.

Claims

1. A method for calculating a locally fine homogenized model of a transformer coil winding, characterized by, The application relates to a transformer winding temperature field and fluid field two-way coupling simulation method. The transformer winding temperature field and fluid field two-way coupling simulation method comprises the following steps: a transformer coil homogenization model is built in finite element simulation software according to the actual structure of the transformer, wherein the transformer comprises a transformer coil and a transformer core; the transformer coil homogenization model is meshed; material parameters, boundary conditions and heat source excitation of the transformer coil homogenization model are set; a full-coupling solver of a temperature field and a fluid field is selected, a direct coupling calculation mathematical equation between the heat-flow coupling physical fields is constructed according to a two-way coupling equation group of the temperature field and the fluid field, and thus the heat-flow two-way coupling simulation of the transformer is realized; the temperature distribution and the highest temperature point position of the transformer coil under the transformer coil homogenization model are obtained based on the coupling calculation results of the temperature field and the fluid field; the axial or radial direction of the highest temperature point position of the transformer coil is finely modeled, and the remaining part is still modeled by using the homogenization method, so that a transformer coil winding local fine homogenization model is obtained; 2. The method of claim 1, wherein the local refinement of the transformer coil winding homogenization model is calculated by, the temperature distribution and the highest temperature point position of the transformer coil are recalculated based on the transformer coil winding local fine homogenization model. The transformer coil comprises a high-voltage coil and a low-voltage coil; the transformer coil homogenization model is built, which comprises the following steps:

3. The method of claim 2, wherein the local refinement of the transformer coil winding homogenization model is calculated by: the high-voltage coil and the low-voltage coil are homogenized respectively; first, the distribution areas of the coil winding and the epoxy resin are determined, the distribution areas are equivalent to single-material cylinders, and then the equivalent material parameters are calculated according to the structure parameters and the thermal conductivities of the coil winding and the epoxy resin, and the equivalent material parameters are loaded on the single-material cylinders to form the transformer coil homogenization model.

4. The method of claim 2, wherein the local refinement of the transformer coil winding homogenization model is calculated by, When the transformer coil homogenization model is built in the finite element simulation software, the heat sources are the high-voltage coil, the low-voltage coil and the transformer core; the high-voltage coil and the low-voltage coil are respectively an integral whole, and there is an air channel between the high-voltage coil and the low-voltage coil.

5. The method of claim 2, wherein the local refinement of the transformer coil winding homogenization model is calculated by, The transformer coil homogenization model is meshed, which comprises the following steps: the high-voltage coil homogenization model and the low-voltage coil homogenization model are meshed by using a mapping mesh; the mapping mesh is generated by mapping a regular mesh mode to a geometric body. The material parameters of the transformer coil homogenization model are set, which comprises the following steps: air material parameters are set, including density, thermal conductivity, dynamic viscosity and specific heat capacity; the material parameters of the transformer core are set, including thermal conductivity and specific heat capacity; 6. The method of claim 1, wherein the local refinement of the transformer coil winding homogenization model is calculated by: the material parameters of the high-voltage coil and the low-voltage coil are set, including thermal conductivity and specific heat capacity; wherein the equivalent thermal conductivity and the equivalent specific heat capacity are set for the transformer coil homogenization part.

7. The method of claim 2, wherein the local refinement of the transformer coil winding homogenization model is calculated by, The boundary conditions comprise a convection heat exchange coefficient of the transformer and the outside world; for the transformer coil homogenization model, the heat source excitation is respectively set as the high-voltage coil cylinder, the low-voltage coil cylinder and the transformer core; for the transformer coil winding local fine homogenization model, the heat source excitation is respectively set as the homogenization part and the fine part of the copper conductor of the high-voltage coil cylinder and the low-voltage coil cylinder and the transformer core. Based on the temperature distribution of the high-voltage and low-voltage coils, the locations of the highest temperature points in the high-voltage and low-voltage coils are extracted respectively. For the pancake winding structure of the high-voltage coil, when the highest temperature point is located at the [missing information]th position in the actual coil model... m During the layering process, a new, refined homogeneous model of the high-voltage coil winding is established, that is, the high-voltage coil winding is retained based on the actual coil model. m -1 floor m layer, m The actual structure of the +1 layer includes the 1st to 1st layer of the high-voltage coil winding. m -2 layers form a homogeneous structure. m +2 to k The layers form a homogenized structure; for the foil winding structure of the low-voltage coil winding, when the highest temperature point is located at the actual coil model... n During the layering process, a new, refined homogeneous model of the low-voltage coil winding is established, that is, the low-voltage coil winding is retained based on the actual coil model. n -1 floor n layer, n The actual structure of the +1 layer is that the low-voltage coil winding 1 to 1 n -2 layers form a homogeneous structure. n +2 to p The layers form a homogeneous structure; among which, k , m , n , p It is a positive integer.

8. The method of claim 5, wherein the local refinement of the transformer coil winding homogenization model is calculated by, The transformer coil winding local fine homogenization model is obtained, which comprises the following steps: The calculation process of the equivalent thermal conductivity and the equivalent specific heat capacity is as follows: Under the condition of unit area, the thermal resistance of a material is related to the thickness and the thermal conductivity of the material as follows: （1） wherein R m Rth is the thermal resistance of the material, d Rth is the thermal resistance of the material, k Rth is the thermal resistance of the material, The equivalent thermal resistance of the transformer coil in the radial direction is: （2） wherein RthCu is the radial copper conductor thermal resistance of the transformer winding; RthEp is the epoxy radial thermal resistance; The total thickness of the transformer coil in the radial direction is: （3） wherein is the total thickness of the radial copper conductors of the transformer winding; is the total thickness of the radial epoxy; The simultaneous equations (1), (2) and (3) can be obtained: （4） The equivalent thermal conductivity of the transformer coil in the radial direction is: ； Equivalent thermal resistance of transformer coil in axial direction R ea The calculation formula is: （5） wherein is the axial thermal resistance of the transformer copper conductor, is the axial thermal resistance of the epoxy resin; The equivalent thermal conductivity of the transformer coil in the axial direction is: （6） The epoxy resin is wrapped on the coil winding, so that: （7） wherein, Cp is the equivalent specific heat capacity of the transformer coil; m M is the total mass of the transformer coil; DT is the temperature change of the transformer coil; Cp is the specific heat capacity of the conductor layer of the transformer coil; Cp is the specific heat capacity of the epoxy resin; m 1M is the total mass of the conductor layer of the transformer coil; m 2M is the total mass of the epoxy resin.

9. The method of claim 3, wherein the method is characterized by: The direct coupling calculation mathematical equation between the heat-flow coupled physical fields is: where p is the fluid density; v is the velocity vector; is the gradient operator; τ is the viscous stress tensor; F is the body force; p is the fluid pressure; T is the temperature; is the divergence operator; Q is the heat source; g is the gravitational acceleration; is the specific heat capacity; is the thermal conductivity.

10. A device for computing a locally fine homogenized model of a transformer coil winding, characterized by It comprises: A modeling unit is configured to build a homogenization model of a transformer coil in finite element simulation software according to an actual structure of the transformer, the transformer including a transformer coil and a transformer core; A meshing unit is configured to mesh the homogenization model of the transformer coil; A loading unit is configured to set material parameters, boundary conditions and heat source excitation of the homogenization model of the transformer coil; A calculation unit is configured to select a full coupling solver of a temperature field and a fluid field, construct a direct coupling calculation mathematical equation between heat-flow coupled physical fields according to a two-way coupling equation group of the temperature field and the fluid field, and thus realize two-way coupling simulation of the transformer; A post-processing unit is configured to obtain a temperature distribution and a highest temperature point position of the transformer coil under the homogenization model of the transformer coil based on coupling calculation results of the temperature field and the fluid field; A secondary modeling unit is configured to finely model an axial direction or a radial direction of the highest temperature point position of the transformer coil, and the remaining part is still modeled by using the homogenization method, so as to obtain a local fine homogenization model of the transformer coil winding; A secondary calculation unit is configured to re-calculate the temperature distribution and the highest temperature point position of the transformer coil based on the local fine homogenization model of the transformer coil winding.

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