A method and system for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model

Abstract

The present invention provides a method and system for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model, belonging to the technical field of power equipment simulation. The method includes: Step 1, according to the symmetry of the actual geometric structure of the transformer bushing, perform dimensionality reduction processing on the three-dimensional structure of the actual transformer bushing, and extract a two-dimensional axisymmetric model of the transformer bushing that can reflect the actual structure of the bushing; Step 2, establish a temperature field simulation model based on the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1 and calculate the two-dimensional temperature field distribution of the transformer bushing; Step 3, establish an electric field simulation model of the transformer bushing based on the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1, and couple the temperature distribution of the transformer bushing obtained in Step 2 into the electric field simulation model to calculate the two-dimensional electric field distribution of the transformer bushing; Step 4, perform a circumferential scan on the calculation result of the two-dimensional electric field distribution of the transformer bushing to restore its three-dimensional electric field distribution and obtain the three-dimensional electric field distribution of the transformer bushing.

Description

Technical Field

[0001] The present invention belongs to the technical field of power equipment simulation, and particularly relates to a method and system for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model. Background Art

[0002] A bushing is an insulating device that introduces a live conductor into an electrical equipment or penetrates a wall. Insulation performance is one of the core indicators of a bushing, and the electric field distribution is an essential parameter reflecting the insulation performance of the bushing. Generally, there is a need for digital twin of the electric field distribution for bushings; for the sake of convenience of explanation, take the transformer bushing as an example. The transformer bushing is an important and indispensable part of the power industry and is usually used in conjunction with a transformer. Once a transformer bushing fails, it will affect the safe and stable operation of the transformer, and further affect the normal operation of the power grid. Accurately calculating the electric field distribution of a transformer bushing is an important link in the structural design and optimization of the transformer bushing and its condition assessment. Especially with the rise of digital twin of substations nowadays, higher requirements are put forward for the accuracy and rapidity of calculating the electric field distribution of transformer bushings. Therefore, accurately and rapidly calculating the electric field distribution of transformer bushings is of great significance.

[0003] The prior art document CN114254481A discloses a method and device for analyzing bubble defects of a transformer bushing. The potential distribution function and the relative permittivity distribution function corresponding to the three-dimensional model of the transformer bushing with bubble defects are subjected to Fourier transform to obtain the function data corresponding to the two-dimensional model; based on the data corresponding to the two-dimensional model, a weak form partial differential equation is established; through the weak form partial differential equation and the relative permittivity distribution function corresponding to the two-dimensional model, the unknown parameters in the potential distribution function corresponding to the two-dimensional model are obtained; the inverse Fourier transform is performed on the potential distribution function corresponding to the two-dimensional model to obtain the unknown parameters in the potential distribution function corresponding to the three-dimensional model, so as to obtain the influence of the bubble defects on the potential distribution of the transformer bushing through the unknown parameters in the potential distribution function corresponding to the three-dimensional model.

[0004] The deficiency of the prior art document is that it does not consider the influence of temperature on the electric field distribution of the bushing, and the calculation result is not accurate enough. Summary of the Invention

[0005] To solve the deficiencies in the prior art, the present invention provides a method and system for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model.

[0006] The present invention adopts the following technical solutions.

[0007] The first aspect of the present invention provides a method for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model, including the following steps:

[0008] Step 1: According to the actual geometric structure symmetry of the transformer bushing, perform dimensionality reduction on the three-dimensional structure of the actual transformer bushing, and extract a two-dimensional axisymmetric model of the transformer bushing that can reflect the actual structure of the bushing.

[0009] Step 2: Based on the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1, establish a temperature field simulation model and calculate the two-dimensional temperature field distribution of the transformer bushing.

[0010] Step 3: Based on the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1, establish its electric field simulation model, and couple the temperature distribution of the transformer bushing obtained in Step 2 into the electric field simulation model to calculate the two-dimensional electric field distribution of the transformer bushing.

[0011] Step 4: Perform a circumferential scan on the calculation results of the two-dimensional electric field distribution of the transformer bushing to restore its three-dimensional electric field distribution and obtain the three-dimensional electric field distribution of the transformer bushing.

[0012] Optionally, Step 1 specifically includes:

[0013] Step 1.1: In three-dimensional space, take any plane passing through the axial center line of the bushing conductive rod as the value-taking plane, and the area where the value-taking plane intersects the bushing is the two-dimensional model of the bushing.

[0014] Step 1.2: Take the axial center line of the conductive rod on the value-taking plane as the dividing line, divide the two-dimensional model of the bushing, and take the bushing model on either side of the dividing line after simplification as the two-dimensional axisymmetric model of the transformer bushing used for subsequent simulation calculations.

[0015] Optionally, Step 2 specifically includes:

[0016] Step 2.1: Assign thermal material parameters to each component of the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1 according to the actual material properties.

[0017] Step 2.2: Set excitation conditions and boundary conditions.

[0018] Step 2.3: Perform mesh generation on the two-dimensional axisymmetric model of the transformer bushing.

[0019] Step 2.4: Calculate and obtain the temperature field distribution of the transformer bushing.

[0020] Optionally, in Step 2.1, the thermal material parameters include density, specific heat capacity, and thermal conductivity.

[0021] Optionally, Step 2.2 specifically includes:

[0022] In terms of excitation conditions, set ohmic loss as the heat source of the conductive rod and dielectric loss as the heat source of the insulating medium. The calculation formula for ohmic loss is:

[0023] ,

[0024] Wherein, is the ohmic loss, is the current, is the length of the conducting rod, is the outer diameter of the central conduit of the bushing, is the inner diameter of the central conductor of the bushing, is the resistivity of the current-carrying conductor;

[0025] The calculation formula of the dielectric loss is:

[0026] ,

[0027] Wherein, is the dielectric loss, is the dielectric loss factor, is the electric field frequency, is the electric field strength, is the dielectric constant of the insulating medium;

[0028] In terms of the boundary conditions, the transformer bushing is in contact with air and transformer oil, and natural convection heat transfer exists on the outer surface of the transformer bushing, and the convective heat transfer coefficient is given.

[0029] Optionally, step 3 specifically includes:

[0030] Step 3.1, assign electrical material parameters, including conductivity and dielectric constant, to each component of the two-dimensional axisymmetric model of the transformer bushing according to the actual material properties, wherein the conductivity is a function of temperature, and its formula is:

[0031] ,

[0032] Wherein, is the conductivity of the material at temperature ; is a constant, is the activation energy; is the Boltzmann constant; is the temperature;

[0033] Step 3.2, set the excitation conditions, boundary conditions and initial values;

[0034] Step 3.3, after setting the excitation conditions, boundary conditions and initial values, verify the grid independence of the two-dimensional axisymmetric model of the transformer bushing established in step 2;

[0035] Step 3.4, after determining the final grid through the grid independence verification, calculate and obtain the two-dimensional electric field distribution of the transformer bushing.

[0036] Optionally, in step 3.2, setting the excitation conditions, boundary conditions, and initial values specifically includes:

[0037] In terms of excitation conditions, a voltage is given on the conducting rod, the flange is set to be grounded, and the metal shielding layer is set to a floating potential;

[0038] In terms of boundary conditions, the outermost air domain is set to an infinite element domain;

[0039] The initial value is the electric field distribution in the initial state of the bushing, which is set to 0 kV / mm.

[0040] Optionally, in step 3.3, verifying the grid independence of the two-dimensional axisymmetric model of the transformer bushing specifically includes:

[0041] Based on the mesh divided during the simulation of the bushing temperature field in step 2.3, the mesh is continuously refined, and then the temperature field distribution and electric field distribution of the bushing are recalculated using the refined mesh;

[0042] At this time, each time the mesh is refined, the electric field results will change. Until the mesh is refined to a certain extent and the calculated electric field results of the bushing do not change, the mesh results obtained at this time are taken as the final mesh.

[0043] Optionally, step 4 specifically includes:

[0044] Rotate the two-dimensional electric field simulation result of the transformer bushing obtained in step 3 by 360 degrees around the axis of symmetry. During the scanning process, the two-dimensional distribution result of the electric field is copied and retained in the plane passed through, thereby reconstructing the three-dimensional model of the bushing and obtaining its three-dimensional electric field distribution.

[0045] The second aspect of the present invention provides a system for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model, which is used to execute the method for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model described in the first aspect of the present invention. The system includes:

[0046] A two-dimensional model extraction module, which is used to extract the two-dimensional axisymmetric model of the transformer bushing;

[0047] A temperature field distribution calculation module, which calculates the two-dimensional temperature field distribution of the transformer bushing;

[0048] An electric field distribution calculation module, which calculates the two-dimensional electric field distribution of the transformer bushing;

[0049] A three-dimensional model reconstruction module, which reconstructs the three-dimensional model of the transformer bushing based on the two-dimensional electric field distribution result and obtains the three-dimensional electric field distribution of the transformer bushing;

[0050] An output module, which is used to output the three-dimensional electric field distribution of the transformer bushing.

[0051] The beneficial effects of the present invention are as follows compared with the prior art:

[0052] 1. Compared with the three-dimensional model used in the traditional method, the present invention reduces its dimension, greatly reducing the amount of calculation, reducing the memory occupancy, and improving the calculation speed;

[0053] 2. Coupling the temperature field on the basis of the original electric field simulation model of the transformer bushing will increase the amount of calculation to a certain extent. The traditional bushing electric field simulation model itself is a three-dimensional model with a large amount of calculation. The superposition of the two makes the calculation efficiency of the three-dimensional electric field simulation model of the transformer bushing considering the influence of the temperature gradient relatively low. Therefore, the traditional method often ignores the influence of the temperature gradient when calculating the bushing electric field. However, after reducing the dimension of the electric field simulation model of the transformer bushing, the present invention considers the influence of the temperature gradient on the electric field distribution, making the electric field calculation result closer to the actual situation and more accurate.

[0054] 3. The heat source of the transformer bushing is mainly composed of the ohmic loss of the conducting rod, and the dielectric loss of the insulating medium accounts for a relatively small proportion in the heat source. In addition, considering the influence of the dielectric loss will increase the amount of simulation calculation. Therefore, the traditional method usually ignores the influence of the dielectric loss. In fact, although the dielectric loss of the insulating medium has little influence on the overall temperature rise of the transformer bushing, it will cause the temperature of the local area to rise sharply. The present invention optimizes the traditional electric field simulation method of the transformer bushing, greatly reducing the amount of calculation. In this case, considering the dielectric loss, the calculation method proposed by the present invention has a lower overall calculation amount and higher accuracy compared with the traditional method. Brief Description of the Drawings

[0055] Figure 1 is the calculation process of the numerical algorithm;

[0056] Figure 2 is the schematic diagram of the technical route of the present invention;

[0057] Figure 3 is the schematic diagram of the dimension reduction process of the transformer bushing of the present invention;

[0058] Figure 4 is the schematic diagram of the geometric structure of the 10 kV transformer bushing;

[0059] Figure 5 is the schematic diagram of the potential and electric field lines of the transformer bushing calculated by the method of the present invention;

[0060] Figure 6 is the schematic diagram of the field strength distribution of the transformer bushing calculated by the method of the present invention;

[0061] Figure 7 is the schematic diagram of the three-dimensional field strength distribution of the transformer bushing calculated by the method of the present invention;

[0062] Figure 8Schematic diagram of the three-dimensional electric potential distribution of a transformer bushing calculated by numerical calculation methods;

[0063] Figure 9 Schematic diagram of the three-dimensional field strength distribution of a transformer bushing calculated by numerical calculation methods. Specific implementation manners

[0064] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only a part of the embodiments of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0065] The present invention is directed to general bushings, and for the sake of more clearly introducing the solution, a transformer bushing is taken as an example.

[0066] Numerical calculation is the most common method for the electric field distribution of transformer bushings. This method uses numerical calculation methods such as finite element, finite volume, and finite difference to solve the partial differential equation group (Equation 1) describing the spatio-temporal evolution law of the electric field of the transformer bushing to obtain the electric field distribution of the bushing. The above process is usually implemented using commercial software, and its general steps are as Figure 1 shown.

[0067] (1)

[0068] In the formula, D is the electric flux density; ρ e Space charge density; H Magnetic field strength; J Conduction current density; E Electric field strength.

[0069] The specific steps for calculating the electric field distribution of the transformer bushing are as follows:

[0070] As Figure 1 shown, first is geometric modeling, and a three-dimensional geometric model of the transformer bushing is established according to its actual structure. On this basis, each part of the geometric model is assigned values according to the actual material properties. Secondly, a voltage excitation is set on the conductive rod of the bushing, the flange and the transformer oil tank are set to ground potential, the metal shielding layer is set to floating potential, and the outermost air domain is set to an infinite element domain. After setting the excitation, boundaries and initial values, the three-dimensional geometric model of the transformer bushing is meshed, and the mesh is continuously refined. The mesh result when the maximum field strength starts to remain unchanged is taken as the mesh used for electric field calculation. Finally, a suitable algorithm is selected to solve the established electric field simulation calculation model to obtain the electric field distribution of the transformer bushing.

[0071] In response to the requirements of substation digital twins, the present invention improves the calculation process of the electric field distribution of transformer bushings, making it faster and occupying less memory, and enhancing the speed and accuracy of the electric field simulation calculation of transformer bushings. Improvements are made to the numerical calculation method for calculating the electric field distribution of transformer bushings, including operations such as dimensionality reduction of the geometric model, considering the influence of temperature on material conductivity and permittivity, and considering the dielectric loss of the insulating medium. The technical route is as Figure 2 shown, and the specific technical solutions are as follows:

[0072] Embodiment 1 of the present invention provides a method for calculating the electric field distribution of bushings based on a two-dimensional axisymmetric model. Taking a transformer bushing as an example, it includes the following steps:

[0073] Step 1: According to the symmetry of the actual geometric structure of the transformer bushing, perform dimensionality reduction on the three-dimensional structure of the actual transformer bushing, and extract a two-dimensional axisymmetric model of the transformer bushing that can reflect the actual structure of the bushing. The process and the final formed two-dimensional axisymmetric geometric model of the transformer bushing are as Figure 3 shown;

[0074] In a preferred but non-limiting embodiment of the present invention, Step 1 specifically includes:

[0075] Step 1.1: In three-dimensional space, take any plane passing through the axial centerline of the bushing conductive rod as the value-taking plane, and the area where the value-taking plane intersects the bushing is the two-dimensional model of the bushing;

[0076] Step 1.2: Take the axial centerline of the conductive rod on the value-taking plane as the dividing line, divide the two-dimensional model of the bushing, and take the bushing model on either side of the dividing line after appropriate simplification as the two-dimensional axisymmetric model of the transformer bushing for subsequent simulation calculations.

[0077] Step 2: Based on the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1, establish a temperature field simulation model and calculate the two-dimensional temperature field distribution of the transformer bushing. Perform temperature field simulation calculations on the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1. This process is essentially to solve the thermal control equation shown in Equation (2):

[0078] (2)

[0079] In the formula, is the heat source; is the heat capacity; is the external field dependent variable; is the thermal conductivity; is the temperature gradient; is the heat flux density;

[0080] In a preferred but non-limiting embodiment of the present invention, Step 2 specifically includes:

[0081] Step 2.1: Assign thermal material parameters to each component of the two-dimensional axisymmetric model of the transformer bushing extracted in Step 1 according to the actual material properties, including three parameters: density, specific heat capacity, and thermal conductivity.

[0082] Among them, each component of the two-dimensional axisymmetric model of the transformer bushing in Step 2.1 is as Figure 4 shown, including silicone rubber, epoxy resin, copper conductor rod, and stainless steel shielding net.

[0083] Step 2.2: Set the excitation conditions and boundary conditions.

[0084] In terms of the excitation conditions, given the ohmic loss and dielectric loss as heat sources on the conductive rod and the insulating medium respectively, the calculation formulas for the ohmic loss and dielectric loss are shown in Equations (3) and (4) respectively:

[0085] (3)

[0086] (4)

[0087] In the formulas, is the ohmic loss, is the current, is the length of the conductive rod, is the outer diameter of the central conduit of the bushing, is the inner diameter of the central conductor of the bushing, is the resistivity of the current-carrying conductor; is the dielectric loss, is the dielectric loss factor, is the electric field frequency, is the electric field strength, is the relative permittivity of the insulating medium;

[0088] In terms of the boundary conditions, the transformer bushing is in contact with air and transformer oil, and there is natural convection heat transfer on the outer surface of the transformer bushing. Given the convective heat transfer coefficient, the natural convective heat transfer coefficient is generally 5 - 25 J / (m·K) according to experience;

[0089] Step 2.3: Perform mesh generation on the two-dimensional axisymmetric model of the transformer bushing.

[0090] Step 2.4: Select a suitable algorithm for calculation to obtain the temperature field distribution of the transformer bushing.

[0091] Exemplarily, in Step 2.4, the suitable algorithm selected includes the finite element method.

[0092] Step 3: Based on the two-dimensional axisymmetric model of the transformer bushing, establish its electric field simulation model. By writing the relative permittivity of the bushing insulation material as a function of temperature, the temperature distribution of the transformer bushing is coupled into the electric field simulation model to calculate the two-dimensional electric field distribution of the transformer bushing. For the two-dimensional axisymmetric model of the transformer bushing, perform electric field simulation calculations. The electric field control equation is as shown in Equation (5):

[0093] (5)

[0094] In the formula, D is the electric flux density; ρ e is the space charge density; H is the magnetic field strength; J is the conduction current density; E is the electric field strength;

[0095] In a preferred but non-limiting embodiment of the present invention, Step 3 specifically includes:

[0096] Step 3.1: According to the actual material properties, assign electrical material parameters to each component of the two-dimensional axisymmetric model of the transformer bushing, including conductivity and relative permittivity. The conductivity is a function of temperature, as shown in Equation (6):

[0097] (6)

[0098] In the formula, is the conductivity of the material at temperature T; is a constant related to the properties of the material itself, is the activation energy; is the Boltzmann constant; is the temperature;

[0099] Step 3.2: Set the excitation conditions, boundary conditions, and initial values;

[0100] Regarding the excitation conditions, apply a voltage to the conductive rod, set the flange to be grounded, and set the metal shielding layer to a floating potential;

[0101] Regarding the boundary conditions, set the outermost air domain to an infinite element domain;

[0102] Among them, the initial value described in Step 3.2 is the electric field distribution in the initial state of the bushing, which is usually set to 0 kV / mm;

[0103] Step 3.3: After setting the excitation conditions, boundary conditions, and initial values, verify the mesh independence of the two-dimensional axisymmetric model of the transformer bushing established in Step 2;

[0104] Based on the mesh divided during the simulation of the casing temperature field in step 2.3, continuously refine the mesh, and then recalculate the temperature field distribution and electric field distribution of the casing using the refined mesh;

[0105] At this time, each time the mesh is refined, the electric field result will change. Until the mesh is refined to a certain extent and the calculated result of the casing electric field does not change, take the mesh result obtained at this time as the final mesh;

[0106] Step 3.4, after determining the final mesh through mesh independence verification, select a suitable algorithm to calculate the electric field of the transformer casing and obtain the two-dimensional electric field distribution of the transformer casing.

[0107] Exemplarily, in step 3.4, selecting a suitable algorithm includes finite element method, finite volume method, finite difference method, etc.

[0108] Step 4, perform a circumferential scan on the calculation result of the two-dimensional electric field distribution of the transformer casing to restore its three-dimensional electric field distribution and obtain the three-dimensional electric field distribution of the transformer casing;

[0109] In a preferred but non-limiting embodiment of the present invention, step 4 specifically includes:

[0110] Rotate the two-dimensional electric field simulation result of the transformer casing obtained in step 3 by 360 degrees circumferentially around the axis of symmetry. During the scanning process, copy and retain the two-dimensional electric field distribution result in the passing plane, thereby reconstructing the three-dimensional model of the casing and obtaining its three-dimensional electric field distribution.

[0111] Embodiment 2 of the present invention provides a system for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model. Based on the method described in Embodiment 1, the system includes:

[0112] Two-dimensional model extraction module, used to extract the two-dimensional axisymmetric model of the transformer casing;

[0113] Temperature field distribution calculation module, calculating the two-dimensional temperature field distribution of the transformer casing;

[0114] Electric field distribution calculation module, calculating the two-dimensional electric field distribution of the transformer casing;

[0115] Three-dimensional model reconstruction model, reconstructing the three-dimensional model of the transformer casing based on the two-dimensional electric field distribution result and obtaining the three-dimensional electric field distribution of the transformer casing;

[0116] Output module, used to output the three-dimensional electric field distribution of the transformer casing.

[0117] Embodiment 3 of the present invention takes a 10kV transformer casing as an example. The structure of this transformer casing is as Figure 4As shown, when calculating its electric field distribution, compared with the above numerical calculation method, the calculation speed is increased by 98 times, and the memory occupancy is reduced by four times. Using the method proposed in this patent and the numerical calculation method, the results such as the electric field distribution and potential distribution calculated for this 10 kV transformer bushing are as Figures 5 - 9 shown.

[0118] 1. Compared with the three-dimensional model used in the numerical calculation method, this patent reduces its dimension, greatly reducing the calculation amount, reducing the memory occupancy, and increasing the calculation speed;

[0119] 2. Coupling the temperature field on the basis of the original transformer bushing electric field simulation model will increase the calculation amount to a certain extent. The numerical calculation of the bushing electric field simulation model itself is a three-dimensional model with a large calculation amount. The superposition of the two makes the calculation efficiency of the three-dimensional electric field simulation model of the transformer bushing considering the influence of the temperature gradient relatively low. Therefore, the numerical calculation method often ignores the influence of the temperature gradient when calculating the bushing electric field. After reducing the dimension of the transformer bushing electric field simulation model in this patent, the influence of the temperature gradient on the electric field distribution is considered, making the electric field calculation result closer to the actual situation and more accurate.

[0120] 3. The heat source of the transformer bushing is mainly composed of the ohmic loss of the conducting rod, and the dielectric loss of the insulating medium accounts for a relatively small proportion in the heat source. In addition, considering the influence of the dielectric loss will increase the simulation calculation amount. Therefore, the numerical calculation method usually ignores the influence of the dielectric loss. However, in fact, although the dielectric loss of the insulating medium has little influence on the overall temperature rise of the transformer bushing, it will cause the temperature of the local area to rise sharply. Optimizing the numerical calculation method of the transformer bushing electric field simulation in this patent greatly reduces the calculation amount. Considering the dielectric loss in this case, the calculation method proposed in this paper has a lower overall calculation amount and higher accuracy compared with the numerical calculation method.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A method for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model, characterized in that: The steps include: Step 1, according to the actual geometric structure symmetry of the transformer bushing, the actual three-dimensional structure of the transformer bushing is reduced in dimension, and a two-dimensional axisymmetric model of the transformer bushing that can reflect the actual structure of the bushing is extracted; Step 2, based on the two-dimensional axisymmetric model of the transformer bushing extracted in step 1, establish a temperature field simulation model and calculate the two-dimensional temperature field distribution of the transformer bushing, wherein step 2 specifically includes: Step 2.1, assigning thermal material parameters to each component of the two-dimensional axisymmetric model of the transformer bushing extracted in step 1 according to actual material properties; Step 2.2, set the excitation conditions and boundary conditions; Step 2.3, meshing the two-dimensional axisymmetric model of the transformer bushing; Step 2.4, calculating and obtaining the temperature field distribution of the transformer bushing; Step 3, based on the two-dimensional axisymmetric model of the transformer bushing extracted in step 1, an electric field simulation model thereof is established, and the temperature distribution of the transformer bushing obtained in step 2 is coupled to the electric field simulation model to calculate the two-dimensional electric field distribution of the transformer bushing. Step 3 specifically includes: Step 3.1, assign electrical material parameters to each component of the two-dimensional axisymmetric model of the transformer bushing according to the actual material properties, including conductivity and dielectric constant, where conductivity is a function of temperature, and its formula is: In the formula, The material is at temperature The conductivity under is a constant, is the activation energy; is the Boltzmann constant; is the temperature; Step 3.2, set the excitation conditions, boundary conditions and initial values; Step 3.3, after setting the excitation conditions, boundary conditions and initial values, verify the mesh independence of the two-dimensional axisymmetric model of the transformer bushing established in step 2; Step 3.4, after the final grid is determined through grid independence verification, the two-dimensional electric field distribution of the transformer bushing is calculated; Step 4: perform circumferential scanning on the calculation result of the two-dimensional electric field distribution of the transformer bushing to restore its three-dimensional electric field distribution and obtain the three-dimensional electric field distribution of the transformer bushing.

2. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 1, characterized in that: The step 1 specifically includes: Step 1.1, in three-dimensional space, any plane passing through the axial center line of the bushing conductive rod is used as a value plane, and the area where the value plane intersects with the bushing is the two-dimensional model of the bushing; Step 1.2, using the axial center line of the conductive rod on the value plane as the dividing line, the bushing two-dimensional model is divided, and the bushing model on any side of the dividing line is simplified as the transformer bushing two-dimensional axisymmetric model used for subsequent simulation calculations.

3. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 2, characterized in that: In step 2.1, the thermal material parameters include density, specific heat capacity and thermal conductivity.

4. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 2, characterized in that: The step 2.2 specifically includes: In terms of excitation conditions, ohmic loss is set as the heat source of the conductive rod, and dielectric loss is set as the heat source of the insulating medium. The calculation formula of ohmic loss is: In the formula, is the ohmic loss, is the current, is the length of the conductive rod, is the outer diameter of the cannula center tube, is the inner diameter of the center conductor of the casing, is the resistivity of the current-carrying conductor; The calculation formula for dielectric loss is: In the formula, is the dielectric loss, is the dielectric loss factor, is the electric field frequency, is the electric field strength, is the dielectric constant of the insulating medium; In terms of boundary conditions, the transformer bushing is in contact with air and transformer oil, and there is natural convection heat transfer on the outer surface of the transformer bushing, and the convection heat transfer coefficient is given.

5. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 1, characterized in that: In step 3.2, setting the excitation conditions, boundary conditions and initial values ​​specifically includes: Regarding the excitation conditions, a voltage was given on the conductive rod, the flange was set to ground, and the metal shielding layer was set to floating potential; Regarding boundary conditions, the outermost air domain was set as an infinite element domain; The initial value is the electric field distribution of the casing in its initial state, which is set to 0 kV / mm.

6. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 1, characterized in that: In the step 3.3, the grid independence verification of the two-dimensional axisymmetric model of the transformer bushing specifically includes: On the basis of the mesh divided during the casing temperature field simulation in step 2.3, the mesh is continuously encrypted, and then the temperature field distribution and electric field distribution of the casing are recalculated using the encrypted mesh; At this time, the electric field results will change each time the grid is encrypted. When the grid is encrypted to a certain extent and the casing electric field calculation results do not change, the grid results divided at this time are taken as the final grid.

7. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 1, characterized in that: The step 4 specifically includes: The two-dimensional electric field simulation result of the transformer bushing obtained in step 3 is rotated 360 degrees around the symmetry axis. During the scanning process, the two-dimensional electric field distribution result is copied and retained in the plane passed through, thereby reconstructing the three-dimensional model of the bushing and obtaining its three-dimensional electric field distribution.

8. A system for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model, used to execute the method for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model according to any one of claims 1 to 7, characterized in that: The system includes: 2D model extraction module, used to extract the 2D axisymmetric model of transformer bushing; Temperature field distribution calculation module, calculates the two-dimensional temperature field distribution of the transformer bushing; Electric field distribution calculation module, calculates the two-dimensional electric field distribution of the transformer bushing; The three-dimensional model reconstruction model reconstructs the three-dimensional model of the transformer bushing based on the two-dimensional electric field distribution results to obtain the three-dimensional electric field distribution of the transformer bushing; Output module, used to output the three-dimensional electric field distribution of the transformer bushing.

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