A COMSOL-based electro-thermal-mechanical coupling simulation analysis method and system for transformer bushings

Abstract

The present invention discloses a method and system for electro-thermal-mechanical coupling simulation analysis of a transformer bushing based on COMSOL, which defines simulation parameters such as the rated voltage, current, and tank temperature of the transformer bushing; establishes a three-dimensional model of the transformer bushing and imports it into COMSOL; defines physical parameters such as the relative permittivity, thermal conductivity, and Young's modulus of the materials in the bushing; adds electrostatic, current, solid heat transfer, solid mechanics, and multi-physics field modules, and sets the boundary conditions of each physical field; determines the mesh accuracy to divide the model and sets the solver parameters; conducts finite element simulation calculations; and draws the distribution of the electric field, temperature, and stress under multi-physics field coupling. The present invention simulates the distribution of each key parameter of the transformer bushing when it works under the rated voltage, considering the multi-physics field coupling environment, and provides a reference standard for judging whether the transformer bushing is working in a normal state.

Description

Technical Field

[0001] The present invention belongs to the technical field of high voltage and insulation, and relates to a method and system for electro-thermal-mechanical coupling simulation analysis of transformer bushings based on COMSOL. Background Art

[0002] Transformer bushings are the main insulation devices outside the transformer tank. They need to insulate the lead wire from the ground and at the same time play the role of fixing the lead wire. Therefore, transformer bushings require good electrical strength and sufficient mechanical strength. At the same time, due to the long-term passage of a large load current during the operation of the transformer, the transformer needs to have good thermal stability and be able to withstand instantaneous overheating when a short-circuit current passes through. Transformer bushings play an extremely important role in the power system, and it is necessary to ensure that all parameters are normal under rated working conditions.

[0003] When the transformer bushing is working, it is in a relatively complex state due to the influence of multiple physical fields such as electricity, heat, and mechanics. The presence of current leads to the generation of Joule heat, and at the same time, the electric field and temperature rise will also generate mechanical forces, thermal stresses, etc., which will have a certain impact on the mechanical structure of the transformer bushing.

[0004] For the transformer bushings with complex working conditions, most of the existing studies conduct simulation analysis for a single physical field. Obviously, this kind of simulation for a single physical field cannot reflect the complete working condition information of the transformer bushing. Therefore, there is an urgent need for a multi-physical field simulation analysis method for transformer bushings that includes the full process. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems in the prior art, and provide a method and system for electro-thermal-mechanical coupling simulation analysis of transformer bushings based on COMSOL, aiming to solve the defective technical problem that for the transformer bushings with complex working conditions in the prior art, most of the simulation analysis is carried out for a single physical field, and the complete working condition information of the transformer bushing cannot be reflected.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A method for electro-thermal-mechanical coupling simulation analysis of transformer bushings based on COMSOL proposed by the present invention is characterized by including the following steps:

[0008] According to the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing, establish a three-dimensional model of the transformer bushing and import the three-dimensional model of the transformer bushing into COMSOL;

[0009] According to the materials of the transformer bushing, respectively determine the material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing;

[0010] Add the physical fields required for electro-thermal-mechanical coupling simulation analysis of the transformer bushing, and set the boundary conditions of each physical field and perform coupling according to the actual conditions and the parameters required for electro-thermal-mechanical coupling simulation analysis of the transformer bushing;

[0011] Set the grid precision to divide the three-dimensional model grid, and set the solver parameters to accelerate the simulation convergence, so as to realize the electro-thermal-mechanical coupling finite element simulation calculation of the transformer bushing.

[0012] Preferably, the parameters required for electro-thermal-mechanical coupling simulation analysis of the transformer bushing include the geometric structure parameters and external variables of the transformer bushing;

[0013] The geometric structure parameters include the height and thickness of the capacitor screen of the transformer bushing, the size and number of umbrellas; the external variables include the rated voltage, current and tank temperature;

[0014] Establish a three-dimensional model of the transformer bushing including the conductor rod, capacitor screen, upper and lower porcelain bushings, flange and grading sphere parts;

[0015] The three-dimensional model of the transformer bushing is simplified to improve the simulation efficiency on the premise of ensuring the simulation accuracy:

[0016] 1) Remove some complex features of the transformer bushing;

[0017] 2) Simplify some rounded corner structures of the transformer bushing into right angle structures;

[0018] 3) Remove the bolts and nuts in the transformer bushing.

[0019] Preferably, the materials required for electro-thermal-mechanical coupling simulation of the transformer bushing include copper laid at the conductor rod, oil paper and aluminum foil laid at the capacitor screen, transformer oil laid inside the bushing and in the tank, ceramics laid at the upper and lower porcelain bushings, and steel laid at the flange and grading sphere;

[0020] The material properties required for electro-thermal-mechanical coupling simulation of the transformer bushing include the relative permittivity and conductivity required in the electric field analysis, the thermal conductivity and constant pressure heat capacity required in the solid heat transfer field analysis, and the Young's modulus and Poisson's ratio required in the solid mechanics analysis;

[0021] During the operation of the transformer bushing, for the influence of the temperature rise generated during the operation of the transformer bushing, a linear resistivity model is used to simulate the change of material resistivity with temperature, and the calculation of the conductivity σ of the material is shown in formula (1):

[0022]

[0023] Among them, ρ0 is the reference resistivity, T ref is the reference temperature, T is the temperature, and α is the temperature coefficient of resistance.

[0024] Preferably, the physical fields required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing include the electrostatic field, the current field, the solid heat transfer field, and the solid mechanics field.

[0025] Preferably, for the transformer bushing, the equations satisfied by the added electrostatic field are shown in Equation (2):

[0026]

[0027] where D is the electric flux density, E is the electric field strength, is the electric potential; according to the equations satisfied by the electrostatic field, the boundaries to be set for the transformer bushing in the electrostatic field simulation are the electric potential, grounding, and charge conservation.

[0028] Preferably, for the transformer bushing, the equations that the added current field needs to satisfy are shown in Equation (3):

[0029]

[0030] where J is the current density vector, σ is the electrical conductivity of the material, and E is the electric field strength; according to the equations satisfied by the current field, the boundaries set for the transformer bushing in the current field simulation are the current, grounding, and contact impedance.

[0031] Preferably, for the transformer bushing, the equation satisfied by the added solid heat transfer field is shown in Equation (4):

[0032]

[0033] where ρ, C p , and k are the density, constant-pressure heat capacity, and thermal conductivity of the material, T is the temperature, u is the fluid flow rate, and Q is the heat source distribution; according to the equations satisfied by the solid heat transfer field, the boundaries to be set for the transformer bushing in the solid heat transfer field simulation are the temperature and the heat flux;

[0034] When coupling the current field and the solid heat transfer field, the electromagnetic heat generated in the current field is calculated as part of the heat source, and the calculation of the Joule heat Q e is shown in Equation (5):

[0035] Q e = J·E (5).

[0036] Preferably, for the transformer bushing, the equation satisfied by the added solid mechanics field is shown in Equation (6):

[0037]

[0038] where S is the stress tensor, F vis the unit volume force; during the simulation of the transformer bushing in the solid mechanics field, it is necessary to add boundary conditions of fixed constraints to the transformer bushing.

[0039] Preferably, when considering the influence of the electrostatic field on the structure of the transformer bushing, analyze the action of electromagnetic stress, add mechanical force in the multi-physics field module and select the electrostatic field and the solid mechanics field, and the electromagnetic stress σ EM is calculated as shown in formula (7):

[0040]

[0041] where δ is the Kronecker function;

[0042] When considering the influence caused by the solid heat transfer field, analyze the thermal expansion caused by the temperature rise, add thermal expansion in the multi-physics field module and select the solid heat transfer and the solid mechanics, and the thermal stress ∈ th is calculated as shown in formula (8):

[0043] ∈ th = α(t)(T - T0) (8)

[0044] where α(t) is the thermal expansion coefficient of the material, and T0 is the initial temperature.

[0045] A system for an electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL proposed by the present invention includes:

[0046] A model construction module, which is used to establish a three-dimensional model of the transformer bushing according to the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing and import the three-dimensional model of the transformer bushing into COMSOL;

[0047] A material property determination module required for coupling simulation, which is used to determine the material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing according to the transformer bushing material;

[0048] A physical field boundary condition determination and coupling module, which is used to add the physical fields required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing, and set the boundary conditions of each physical field and perform coupling according to the actual conditions and the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing;

[0049] An electro-thermal-mechanical coupling finite element simulation calculation module for the transformer bushing, which is used to set the grid accuracy to divide the three-dimensional model grid and set the solver parameters to accelerate the simulation convergence, so as to realize the electro-thermal-mechanical coupling finite element simulation calculation of the transformer bushing.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] A method for electro-thermal-mechanical coupling simulation analysis of transformer bushings based on COMSOL proposed by the present invention provides a reference standard for judging whether the transformer bushings are operating in a normal state by considering the distribution of key parameters in an environment of multi-physical-field coupling. It solves the problem that in the prior art, for transformer bushings with complex working conditions, most of the simulation analyses are carried out for a single physical field, and the complete working condition information of the transformer bushings cannot be reflected.

[0052] A system for a method for electro-thermal-mechanical coupling simulation analysis of transformer bushings based on COMSOL proposed by the present invention divides the system into a model construction module, a material property determination module required for coupling simulation, a determination and coupling module for physical field boundary conditions, and a finite element simulation calculation module for electro-thermal-mechanical coupling of transformer bushings. The modular idea is adopted to make each module independent of each other, which is convenient for unified management of each module. Description of the Drawings

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0054] Figure 1 It is a flowchart of electro-thermal-mechanical coupling simulation of transformer bushings based on COMSOL of the present invention.

[0055] Figure 2 It is a three-dimensional model diagram of the transformer bushing of the present invention.

[0056] Figure 3 It is the distribution of electric potential of electro-thermal-mechanical coupling simulation of the transformer bushing of the present invention.

[0057] Figure 4 It is a system diagram of electro-thermal-mechanical coupling simulation of the transformer bushing of the present invention. Detailed Embodiments

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0059] Accordingly, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0060] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0061] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0062] In addition, if the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0063] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if terms such as "set", "installed", "connected", "connected" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0064] The present invention will be further described in detail below with reference to the accompanying drawings:

[0065] As Figure 1 shown, a method for electro-thermal-mechanical coupling simulation analysis of a transformer bushing based on COMSOL proposed by the present invention includes the following steps:

[0066] According to the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing, a three-dimensional model of the transformer bushing is established and imported into COMSOL;

[0067] Determine the material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing according to the transformer bushing material respectively;

[0068] Add the physical fields required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing, and set the boundary conditions of each physical field and perform coupling according to the actual conditions and the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing;

[0069] Set the grid accuracy to divide the three-dimensional model grid, and set the solver parameters to accelerate the simulation convergence to achieve the electro-thermal-mechanical coupling finite element simulation calculation of the transformer bushing;

[0070] Perform post-processing on the results of the simulation calculation. The post-processing processes required include plotting the distribution of the electric potential, electric field, temperature and stress of the transformer bushing under the multi-physical field coupling environment.

[0071] An electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL proposed by the present invention specifically includes the following steps:

[0072] Step 1: Define the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing.

[0073] Considering a 330 kV transformer bushing, the parameters to be defined include two parts: geometric structure parameters and external variables. Among them, the geometric structure parameters include the height and thickness of the capacitor screens of the transformer bushing, the size and number of umbrellas, etc., and the external variables include the rated voltage, current, temperature of the connecting oil tank of the transformer bushing, etc.

[0074] Step 2: Establish a three-dimensional model of the transformer bushing and import it into COMSOL.

[0075] To improve the simulation efficiency while ensuring the simulation accuracy, simplify the model of the transformer bushing, including: removing some small but complex features of the transformer bushing; simplifying the fillet structures of parts such as flanges and umbrellas into right-angle structures; removing non-essential parts for simulation such as bolts and nuts.

[0076] Use three-dimensional modeling software to construct each main part of the transformer bushing in the form of parts, including the bushing rod, capacitor screens, upper and lower porcelain bushings, flanges and grading balls, etc., as Figure 2 shown; and add an infinite element domain to the model, which is represented as being infinitely far away.

[0077] Step 3: Determine the material properties required for the simulation according to the transformer bushing material respectively.

[0078] According to the structure of the transformer bushing, the materials to be laid in each part are determined as follows: copper laid at the guide rod, transformer oil laid inside the bushing and at the oil tank, oil-paper and aluminum foil laid at the capacitor screen, ceramics laid at the upper and lower porcelain bushings, and steel laid at the flange and grading sphere.

[0079] For the above materials, the material properties to be set in the electro-thermal-mechanical coupling simulation include the relative permittivity, conductivity, etc. required in the electric field analysis, the thermal conductivity, constant-pressure heat capacity, etc. required in the solid heat transfer field analysis, and the Young's modulus, Poisson's ratio, etc. required in the solid mechanics analysis.

[0080] During the operation of the transformer bushing, due to electromagnetic heat, the temperature of each component will rise, resulting in a change in the resistivity of the material. Here, a linear resistivity model is used to simulate the change of resistivity with temperature. The calculation of the conductivity σ of the material is shown in formula (1):

[0081]

[0082] where ρ0 is the reference resistivity, T ref is the reference temperature, and α is the temperature coefficient of resistance.

[0083] Step 4: Add the physical fields required for the simulation analysis, and according to the actual conditions and the defined simulation parameters, set the boundary conditions of each physical field and perform coupling.

[0084] In COMSOL, add the electrostatic, current, solid heat transfer, and solid mechanics physical field modules, and add a multi-physical field module for coupling between physical fields.

[0085] In the electrostatic field, the equations that the transformer bushing needs to satisfy are shown in formula (2):

[0086]

[0087] where D is the electric flux density, E is the electric field strength, is the electric potential.

[0088] According to the equations, the boundary conditions to be set in the electrostatic field simulation of the transformer bushing are as follows: Add at the guide rod; set the grounding conditions at the flange and infinity; set the low-permittivity thin-gap condition at the junction of the layered structure of the capacitor screen, where the relative permittivity is the same as that of aluminum; set the charge conservation for air and transformer oil.

[0089] For the transformer bushing, the equations that the added current field needs to satisfy are shown in formula (3):

[0090]

[0091] Among them, J is the current density vector, and σ is the electrical conductivity of the material.

[0092] For the transformer bushing, the conditions that the added current field needs to meet are as follows: Add a current terminal with a size of 1250 A at the upper end of the conductor rod, and form a closed loop through grounding at the lower end; Set the contact impedance at the junction of the layered structure of the capacitive screen, where the electrical conductivity and relative permittivity are the same as those of aluminum.

[0093] The equation conditions that the transformer bushing needs to meet in the solid heat transfer module are shown in formula (4):

[0094]

[0095] Among them, ρ, C p , and k are the density, constant-pressure heat capacity, and thermal conductivity of the material respectively, T is the temperature, u is the fluid flow velocity, and Q is the heat source distribution.

[0096] The boundary conditions that need to be set in the temperature field simulation of the transformer bushing are as follows: Set the regions with materials of air and transformer oil in the transformer bushing model as the boundary conditions of the fluid; Set the temperature of the transformer oil to be constant at 90 degrees at the oil tank; Add a heat flux condition to the infinite element domain, select the convective heat flux and set the corresponding heat transfer coefficient h = 8.

[0097] When coupling the current field and the solid heat transfer field, it is necessary to add electromagnetic heat in the multi-physics field module and select the current field and solid heat transfer, which means that the electromagnetic heat generated in the current field is used as a part of the heat source for calculation. The calculation of Joule heat Q e is shown in formula (5):

[0098] Q e = J·E (5)

[0099] For the transformer bushing, the equation that the solid mechanics field needs to meet is shown in formula (6):

[0100]

[0101] Among them, S is the stress tensor, F v is the body force per unit volume.

[0102] During the simulation process of the solid mechanics field, it is necessary to add fixed constraints as boundary conditions on the solid contact surface of the transformer bushing.

[0103] In the coupled analysis of the physical fields related to stress, it mainly includes electromagnetic stress and thermal stress.

[0104] When considering the influence of the electrostatic field on the structure of the transformer bushing and analyzing the action of electromagnetic stress, add mechanical force in the multi-physics field module and select the electrostatic field and the solid mechanics field. The electromagnetic stress σEM The calculation of

[0105]

[0106] is shown in Formula (7), where δ is the Kronecker function.

[0107] When considering the influence caused by the solid heat transfer field, analyze the thermal expansion caused by the temperature rise, add thermal expansion in the multi-physics field module and select solid heat transfer and solid mechanics, and the thermal stress ∈ th The calculation of

[0108] ∈ th = α(t)(T - T0) (8)

[0109] where α(t) is the thermal expansion coefficient of the material, and T0 is the initial temperature.

[0110] Step 5: Set the grid accuracy to divide the three-dimensional model grid and set the solver parameters to accelerate the simulation convergence.

[0111] Step 6: Perform the electro-thermal-mechanical coupling finite element simulation calculation of the transformer bushing.

[0112] Step 7: Post-process the results of the simulation calculation.

[0113] For the results of the completed calculation, the required post-processing process includes plotting the distribution of the electric potential, electric field, temperature, and stress of the transformer bushing in the multi-physics field coupling environment, as Figure 3 shown.

[0114] A method for electro-thermal-mechanical coupling simulation analysis of a transformer bushing based on COMSOL proposed by the present invention, as Figure 4 shown, includes:

[0115] A model construction module, which is used to establish a three-dimensional model of the transformer bushing according to the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing and import the three-dimensional model of the transformer bushing into COMSOL;

[0116] A material property determination module required for coupling simulation, which is used to determine the material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing according to the transformer bushing material;

[0117] A physical field boundary condition determination and coupling module, which is used to add the physical fields required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing and set the boundary conditions of each physical field and perform coupling according to the actual conditions and the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing;

[0118] The electro-thermal-mechanical coupling finite element simulation calculation module for transformer bushings is used to set the grid precision to divide the three-dimensional model grid and set the solver parameters to accelerate the simulation convergence, so as to realize the electro-thermal-mechanical coupling finite element simulation calculation of transformer bushings.

[0119] A method and system for electro-thermal-mechanical coupling simulation analysis of transformer bushings based on COMSOL proposed by the present invention first defines simulation parameters such as the rated voltage, current, and tank temperature of the transformer bushings; establishes a three-dimensional model of the transformer bushings and imports it into COMSOL; defines physical parameters such as the relative permittivity, thermal conductivity, and Young's modulus of the materials in the bushings; adds electrostatic, current, solid heat transfer, solid mechanics, and multi-physics field modules, and sets the boundary conditions of each physical field; determines the grid precision to divide the model and sets the solver parameters; conducts finite element simulation calculations; and draws the distribution of electric fields, temperatures, and stresses under multi-physics field coupling. The present invention simulates the distribution of key parameters of transformer bushings when operating at the rated voltage under the environment of considering multi-physics field coupling, providing a reference standard for judging whether the transformer bushings are operating in a normal state.

[0120] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A COMSOL-based electro-thermal-mechanical coupling simulation analysis method for transformer bushings, characterized in that It includes the following steps: According to the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing, a three-dimensional model of the transformer bushing is established and imported into COMSOL; According to the materials of the transformer bushing, the material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing are determined respectively; Add the physical fields required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing, and set the boundary conditions of each physical field and perform coupling according to the actual conditions and the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing; Set the grid precision to divide the grid of the three-dimensional model, and set the solver parameters to accelerate the simulation convergence to achieve the electro-thermal-mechanical coupling finite element simulation calculation of the transformer bushing; The materials required for the electro-thermal-mechanical coupling simulation of the transformer bushing include copper laid at the bushing rod, oil paper and aluminum foil laid at the capacitor screen, transformer oil laid inside the bushing and at the oil tank, ceramics laid at the upper and lower porcelain bushings, and steel laid at the flange and grading sphere; The material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing include the relative permittivity and conductivity required for the electric field analysis, the thermal conductivity and constant-pressure heat capacity required for the solid heat transfer field analysis, and the Young's modulus and Poisson's ratio required for the solid mechanics analysis; During the operation of the transformer bushing, considering the temperature rise effect generated during the operation of the transformer bushing, a linear resistivity model is used to simulate the variation of the material resistivity with temperature, and the conductivity of the material is calculated as shown in Equation (1): （1） wherein, is the reference resistivity, is the reference temperature, T is the temperature, is the temperature coefficient of resistance.

2. The electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL according to claim 1, wherein The parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing include the geometric structure parameters and external variables of the transformer bushing; The geometric structure parameters include the height and thickness of the capacitor screen of the transformer bushing, the size and number of umbrellas; the external variables include the rated voltage, current and oil tank temperature; Establishing a three-dimensional model of the transformer bushing includes the bushing rod, capacitor screen, upper and lower porcelain bushings, flange and grading sphere parts; The three-dimensional model of the transformer bushing is simplified to improve the simulation efficiency on the premise of ensuring the simulation accuracy: 1). Remove some complex features of the transformer bushing; 2). Simplify some rounded corner structures of the transformer bushing into right-angle structures; 3). Remove the bolts and nuts in the transformer bushing.

3. The electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL according to claim 1, wherein The physical fields required for adding the electro-thermal-mechanical coupling simulation analysis of the transformer bushing include the electrostatic field, current field, solid heat transfer field and solid mechanics field.

4. The electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL according to claim 3, characterized in that For the transformer bushing, the equations satisfied by the added electrostatic field are shown in formula (2); （2） where D is the electric flux density, E is the electric field strength, is the electric potential; according to the equations satisfied by the electrostatic field, the boundaries that need to be set for the transformer bushing in the electrostatic field simulation are electric potential, grounding, and charge conservation.

5. The electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL according to claim 3, characterized in that For the transformer bushing, the equations that the added current field needs to satisfy are shown in formula (3); （3） Among them, is the current density vector, is the conductivity of the material, and E is the electric field strength; according to the equations satisfied by the current field, in the current field simulation of the transformer bushing, the boundaries set for the transformer bushing are current, grounding, and contact impedance.

6. The electro-thermal-mechanical coupling simulation analysis method of a transformer bushing based on COMSOL according to claim 3, wherein For the transformer bushing, the equation satisfied by the added solid heat transfer field is shown in formula (4); （4） wherein, are the density, constant-pressure heat capacity, and thermal conductivity of the material, respectively, T is the temperature, u is the fluid flow rate, Q is the heat source distribution; according to the equations satisfied by the solid heat transfer field, the boundaries to be set for the transformer bushing in the solid heat transfer field simulation are temperature and heat flux; When coupling the current field and the solid heat transfer field, the electromagnetic heat generated in the current field is calculated as part of the heat source, and the calculation of Joule heat is shown in Equation (5): （5）。 7. The electro-thermal-mechanical coupling simulation analysis method of transformer bushing based on COMSOL according to claim 3, wherein, For the transformer bushing, the equation satisfied by the added solid mechanics field is shown in formula (6); （6） Among them, S is the stress tensor, is the body force per unit volume; during the simulation process of the transformer bushing in the solid mechanics field, it is necessary to add boundary conditions of fixed constraints to the transformer bushing.

8. The electro-thermal-mechanical coupling simulation analysis method of transformer bushings based on COMSOL according to claim 3, characterized in that When considering the influence of the electrostatic field on the structure of the transformer bushing, analyze the action of electromagnetic stress, add mechanical and electrical forces in the multi-physics field module and select the electrostatic field and solid mechanics field, the electromagnetic stress is calculated as shown in formula (7): （7） wherein, is the Kronecker function, is the electric field strength, is the electric displacement vector; When considering the influence caused by the solid heat transfer field, analyze the thermal expansion caused by the temperature rise, add thermal expansion in the multi-physics field module, and select solid heat transfer and solid mechanics, and the thermal stress is calculated as shown in Equation (8): （8） Among them, is the coefficient of thermal expansion of the material, is the initial temperature.

9. A system adopting the COMSOL-based electro-thermal-mechanical coupling simulation analysis method for transformer bushings according to any one of claims 1 to 8, characterized in that, It includes: A model construction module, which is used to establish a three-dimensional model of the transformer bushing according to the parameters required for the electro-thermal-mechanical coupling simulation analysis of the transformer bushing and import the three-dimensional model of the transformer bushing into COMSOL; A module for determining the material properties required for coupling simulation, which is used to determine the material properties required for the electro-thermal-mechanical coupling simulation of the transformer bushing according to the materials of the transformer bushing; Determination of physical field boundary conditions and coupling module, the determination of physical field boundary conditions and coupling module is used to add physical fields required for the electro-thermal-mechanical coupling simulation analysis of transformer bushings, and set the boundary conditions of each physical field and perform coupling according to actual conditions and parameters required for the electro-thermal-mechanical coupling simulation analysis of transformer bushings; Transformer bushing electro-thermal-mechanical coupling finite element simulation calculation module, the transformer bushing electro-thermal-mechanical coupling finite element simulation calculation module is used to set the grid accuracy to divide the three-dimensional model grid, and set the solver parameters to accelerate the simulation convergence to achieve the transformer bushing electro-thermal-mechanical coupling finite element simulation calculation.

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