Method and system for calculating bushing electric field distribution based on two-dimensional axial symmetry model

Abstract

The invention provides a method and system for calculating bushing electric field distribution based on a two-dimensional axial symmetry model, and belongs to the technical field of power equipment simulation, and the method comprises the steps: 1, carrying out the dimension reduction processing of an actual transformer bushing three-dimensional structure according to the actual geometric structure symmetry of a transformer bushing, and obtaining an actual transformer bushing electric field distribution value; extracting a transformer bushing two-dimensional axisymmetric model capable of reflecting the actual structure of the bushing; 2, establishing a temperature field simulation model based on the two-dimensional axisymmetric model of the transformer bushing extracted in the step 1, and calculating the two-dimensional temperature field distribution of the transformer bushing; 3, establishing an electric field simulation model based on the two-dimensional axisymmetric model of the transformer bushing extracted in the step 1, coupling the temperature distribution of the transformer bushing obtained in the step 2 into the electric field simulation model, and calculating the two-dimensional electric field distribution of the transformer bushing; and 4, performing circumferential scanning on the calculation result of the two-dimensional electric field distribution of the transformer bushing, restoring the three-dimensional electric field distribution of the transformer bushing, and obtaining the three-dimensional electric field distribution of the transformer bushing.

Description

Technical Field

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

[0002] Bushing is an insulating device that introduces live conductors into electrical equipment or passes through walls. Insulation performance is one of the core indicators of bushings, and electric field distribution is an indispensable parameter for reflecting the insulation performance of bushings. General bushings have the need for digital twinning of electric field distribution; for the sake of convenience, take transformer bushings as an example. Transformer bushings are an indispensable and important part of the power industry and are usually used in conjunction with transformers. Once a transformer bushing fails, it will affect the safe and stable operation of the transformer, and then affect the normal operation of the power grid. Accurate calculation of the electric field distribution of transformer bushings is an important part of the transformer bushing structure design, optimization, and status assessment. Especially with the rise of digital twins of substations, higher requirements are placed on the accuracy and speed of transformer bushing electric field distribution calculations. Therefore, accurate and rapid calculation of transformer bushing electric field distribution is of great significance.

[0003] Prior art CN114254481A discloses a method and device for analyzing bubble defects in transformer bushings. The potential distribution function and relative dielectric constant distribution function corresponding to the three-dimensional model of the transformer bushing with bubble defects are Fourier transformed to obtain function data corresponding to the two-dimensional model; a weak form partial differential equation is established based on the data corresponding to the two-dimensional model; the parameters to be solved in the potential distribution function corresponding to the two-dimensional model are obtained through the weak form partial differential equation and the relative dielectric constant distribution function corresponding to the two-dimensional model; the potential distribution function corresponding to the two-dimensional model is inversely Fourier transformed to obtain the parameters to be solved in the potential distribution function corresponding to the three-dimensional model, so as to obtain the influence of the bubble defect on the potential distribution of the transformer bushing through the parameters to be solved in the potential distribution function corresponding to the three-dimensional model.

[0004] The shortcoming of the existing technical documents is that the influence of temperature on the electric field distribution of the bushing is not considered, and the calculation results are not accurate enough. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a method and system for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model. The present invention adopts the following technical solution.

[0006] A first aspect of the present invention provides a method for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model, comprising the following steps: 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, establishing a temperature field simulation model based on the two-dimensional axisymmetric model of the transformer bushing extracted in step 1 and calculating the two-dimensional temperature field distribution of the transformer bushing; Step 3, establishing an electric field simulation model of the transformer bushing based on the two-dimensional axisymmetric model extracted in step 1, and coupling the temperature distribution of the transformer bushing obtained in step 2 to the electric field simulation model to calculate the two-dimensional electric field distribution of the transformer bushing; 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.

[0007] Optionally, 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.

[0008] Optionally, the 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, calculate and obtain the temperature field distribution of the transformer bushing.

[0009] Optionally, in step 2.1, the thermal material parameters include density, specific heat capacity and thermal conductivity.

[0010] Optionally, 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.

[0011] Optionally, the 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.

[0012] Optionally, 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.

[0013] Optionally, in step 3.3, performing grid independence verification on 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.

[0014] Optionally, 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.

[0015] A second aspect of the present invention provides a system for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model, which is used to execute the method for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model according to the first aspect of the present invention. The system comprises: 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.

[0016] The beneficial effects of the present invention are as follows: 1. Compared with the three-dimensional model used in traditional methods, the present invention reduces its dimension, greatly reduces the amount of calculation, reduces the memory usage, and improves the calculation speed; 2. Coupling the temperature field on the basis of the original transformer bushing electric field simulation model 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 under the influence of temperature gradient low. Therefore, the traditional method often ignores the influence of temperature gradient when calculating the bushing electric field. The present invention considers the influence of temperature gradient on electric field distribution after reducing the dimension of the transformer bushing electric field simulation model, so that the electric field calculation result is closer to reality and more accurate.

[0017] 3. The heat source of the transformer bushing is mainly composed of the ohmic loss of the conductive rod, and the insulating medium loss accounts for a small proportion of the heat source. In addition, considering the influence of dielectric loss will increase the amount of simulation calculations, so traditional methods usually ignore the influence of dielectric loss. But in fact, although the dielectric loss of the insulating medium has little effect on the overall temperature rise of the transformer bushing, it will cause the temperature water in the local area to rise sharply. The present invention optimizes the traditional transformer bushing electric field simulation method and greatly reduces the amount of calculation. In this case, considering the dielectric loss makes the calculation method proposed by the present invention have a low overall calculation amount and high accuracy compared with the traditional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the numerical algorithm calculation process; Figure 2 It is a schematic diagram of the technical route of the present invention; Figure 3 It is a schematic diagram of the transformer bushing dimensionality reduction process of the present invention; Figure 4 Schematic diagram of the geometric structure of the 10kV transformer bushing; Figure 5 A schematic diagram of the transformer bushing potential and electric field lines calculated using the method of the present invention; Figure 6 This is a schematic diagram of the transformer bushing field strength distribution calculated using the method of the present invention; Figure 7 A schematic diagram of three-dimensional electric field intensity distribution of transformer bushing calculated by the method of the present invention; Figure 8 The schematic diagram of the three-dimensional potential distribution of the transformer bushing calculated by numerical calculation method; Fig. 9 This is a schematic diagram of the three-dimensional electric field strength distribution of the transformer bushing calculated using the numerical calculation method. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0020] The present invention is directed to a general bushing. In order to more clearly describe the solution, a transformer bushing is taken as an example.

[0021] Numerical calculation is the most common method for transformer bushing electric field distribution. This method uses numerical calculation methods such as finite element, finite volume, and finite difference to solve the partial differential equations (Equation 1) that describe the temporal and spatial evolution of the transformer bushing electric field to obtain the bushing electric field distribution. Commercial software is often used to implement the above process. The general steps are as follows: Figure 1 shown.

[0022] (1) 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.

[0023] The specific steps for calculating the electric field distribution of transformer bushing are as follows: like Figure 1 As shown in the figure, the first step is geometric modeling. According to the actual structure of the transformer bushing, its three-dimensional geometric model is established. On this basis, the various parts of the geometric model are assigned values ​​according to the actual material properties. Secondly, voltage excitation is set on the bushing conductive rod, the flange and the transformer tank are set to ground potential, the metal shielding layer is set to suspended potential, and the outermost air domain is set to an infinite element domain. After setting the excitation, boundary and initial values, the established three-dimensional geometric model of the transformer bushing is meshed, and the mesh is continuously encrypted. The mesh result when the maximum field strength begins 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.

[0024] In response to the needs of substation digital twins, the present invention makes the calculation process of transformer bushing electric field distribution faster and occupies less memory, improves the rapidity and accuracy of transformer bushing electric field simulation calculation, and improves the numerical calculation method for calculating transformer bushing electric field distribution, including carrying out dimensionality reduction processing of geometric models, considering the influence of temperature on material conductivity and dielectric constant, and considering dielectric loss of insulating medium. Technical route such as Figure 2 As shown, the specific technical solution is as follows: Embodiment 1 of the present invention provides a method for calculating the electric field distribution of a bushing based on a two-dimensional axisymmetric model, taking a transformer bushing as an example, comprising the following steps: 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 to extract a two-dimensional axisymmetric model of the transformer bushing that can reflect the actual structure of the bushing. The process and the final two-dimensional axisymmetric geometric model of the transformer bushing are shown in FIG. Figure 3 As shown; In a preferred but non-limiting embodiment of the present invention, step 1 specifically comprises: 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 appropriately simplified as the transformer bushing two-dimensional axisymmetric model used for subsequent simulation calculations.

[0025] Step 2: Based on the two-dimensional axisymmetric model of the transformer bushing extracted in step 1, a temperature field simulation model is established and the two-dimensional temperature field distribution of the transformer bushing is calculated. The temperature field simulation calculation is performed 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 formula (2): (2) In the formula, It is a 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; In a preferred but non-limiting embodiment of the present invention, step 2 specifically comprises: 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, including three parameters: density, specific heat capacity, and thermal conductivity; Among them, the components of the two-dimensional axisymmetric model of the transformer bushing in step 2.1 are as follows Figure 4 As shown, it includes silicone rubber, epoxy resin, copper guide rods and stainless steel shielding mesh.

[0026] Step 2.2, set the excitation conditions and boundary conditions; In terms of excitation conditions, ohmic loss and dielectric loss are given as heat sources on the conductive rod and insulating medium respectively. The calculation formulas of ohmic loss and dielectric loss are shown in equations (3) and (4) respectively: (3) (4) 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; 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. Given the convection heat transfer coefficient, the natural convection heat transfer coefficient is generally 5~25J / (m·K) according to experience; Step 2.3, meshing the two-dimensional axisymmetric model of the transformer bushing; Step 2.4, select a suitable algorithm for calculation to obtain the temperature field distribution of the transformer bushing.

[0027] Exemplarily, in step 2.4, the appropriate algorithm selected includes the finite element method.

[0028] Step 3: Establish an electric field simulation model based on the two-dimensional axisymmetric model of the transformer bushing. By writing the dielectric constant of the bushing insulation material as a function of temperature, the temperature distribution of the transformer bushing is coupled to the electric field simulation model. The two-dimensional electric field distribution of the transformer bushing is calculated. The electric field simulation calculation is performed on the two-dimensional axisymmetric model of the transformer bushing. The electric field control equation is shown in Formula (5): (5) 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; In a preferred but non-limiting embodiment of the present invention, step 3 specifically comprises: 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, as shown in formula (6): (6) 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; Step 3.2, set the excitation conditions, boundary conditions and initial values; 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 in step 3.2 is the electric field distribution of the casing in the initial state, which is usually set to 0 kV / mm; 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; 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 result will change each time the grid is encrypted. When the grid is encrypted to a certain extent and the casing electric field calculation result does not change, the grid result divided at this time is taken as the final grid. Step 3.4, after the final grid is determined through grid independence verification, a suitable algorithm is selected to calculate the electric field of the transformer bushing to obtain the two-dimensional electric field distribution of the transformer bushing.

[0029] Exemplarily, in step 3.4, the appropriate algorithm selected includes finite element, finite volume and finite difference methods, etc.

[0030] Step 4, performing circumferential scanning on the calculation result of the two-dimensional electric field distribution of the transformer bushing, restoring its three-dimensional electric field distribution, and obtaining the three-dimensional electric field distribution of the transformer bushing; In a preferred but non-limiting embodiment of the present invention, step 4 specifically comprises: 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.

[0031] 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: 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.

[0032] Embodiment 3 of the present invention takes a 10kV transformer bushing as an example. The structure of the transformer bushing is as follows: Figure 4 As shown, the electric field distribution is calculated. Compared with the above numerical calculation method, the calculation speed is increased by 98 times and the memory usage is reduced by four times. Using the method and numerical calculation method proposed in this patent, the field strength distribution and potential distribution of this 10kV transformer bushing are calculated as follows: Figure 5-9 shown.

[0033] 1. Compared with the three-dimensional model used in the numerical calculation method, this patent reduces its dimension, greatly reduces the amount of calculation, reduces the memory usage, and improves the calculation speed; 2. Coupling the temperature field on the basis of the original transformer bushing electric field simulation model will increase the amount of calculation to a certain extent, and the numerical calculation 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 under the influence of temperature gradient low. Therefore, the numerical calculation method often ignores the influence of temperature gradient when calculating the bushing electric field. This patent reduces the dimension of the transformer bushing electric field simulation model and considers the influence of temperature gradient on the electric field distribution, making the electric field calculation results closer to reality and more accurate.

[0034] 3. The heat source of the transformer bushing is mainly composed of the ohmic loss of the conductive rod, and the insulating medium loss accounts for a small proportion of the heat source. In addition, considering the influence of dielectric loss will increase the amount of simulation calculations, so the numerical calculation method usually ignores the influence of dielectric loss. But in fact, although the dielectric loss of the insulating medium has little effect on the overall temperature rise of the transformer bushing, it will cause the temperature of the local area to rise sharply. This patent optimizes the numerical calculation method of the transformer bushing electric field simulation method and greatly reduces the amount of calculation. In this case, considering the dielectric loss makes the calculation method proposed in this article have a low overall calculation amount and high accuracy compared to the numerical calculation method.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection 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, establishing a temperature field simulation model based on the two-dimensional axisymmetric model of the transformer bushing extracted in step 1 and calculating the two-dimensional temperature field distribution of the transformer bushing; Step 3, establishing an electric field simulation model of the transformer bushing based on the two-dimensional axisymmetric model extracted in step 1, and coupling the temperature distribution of the transformer bushing obtained in step 2 to the electric field simulation model to calculate the two-dimensional electric field distribution of the transformer bushing; 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 1, characterized in that: The 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, calculate and obtain the temperature field distribution of the transformer bushing.

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

5. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 3, 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.

6. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 3, characterized in that: The 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.

7. The method for calculating the electric field distribution of the casing based on a two-dimensional axisymmetric model according to claim 6, 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.

8. The method for calculating the electric field distribution of a casing based on a two-dimensional axisymmetric model according to claim 3 or 6, 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.

9. 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.

10. 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 9, 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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