Method and system for calculating temperature of transformer box body by electromagnetic induction heating

Abstract

The invention relates to the technical field of transformers, and discloses a method and system for calculating the temperature of a transformer box through electromagnetic induction heating, and the method comprises the steps: creating a transformer electromagnetic field model calculation formula through an electromagnetic field principle; a transformer solid structure coupling solution electromagnetic field is calculated; transformer coil induction heating calculation; calculating the temperature of the heat conduction box. According to the method for calculating the temperature of the transformer box body through electromagnetic induction heating, a finite element analysis method is combined, temperature distribution of the transformer box body can be accurately calculated, temperature field analysis of the box body under different working conditions is achieved by establishing a three-dimensional model, generating a finite element grid and setting current density, material attributes and boundary conditions, and the temperature of the transformer box body can be accurately calculated. According to the method, the operation efficiency of the transformer can be improved, equipment faults caused by overheating can be effectively prevented, and technical guarantee is provided for safe operation of the transformer.

Description

Technical Field

[0001] The invention relates to the technical field of transformers, and in particular to a method and a system for calculating the temperature of a transformer box by utilizing electromagnetic induction heating. Background Art

[0002] Transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are primary coil, secondary coil and iron core (magnetic core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer), etc. Transformer is the basic equipment for power transmission and distribution, and is widely used in industry, agriculture, transportation, urban communities and other fields. There are about 17 million transformers in operation in my country, with a total capacity of about 11 billion kilovolt-amperes. Transformer loss accounts for about 40% of the power loss in power transmission and distribution, and has great energy-saving potential. In the power system, transformer is a key equipment responsible for voltage conversion and power transmission. However, transformers usually generate a lot of heat during operation, especially under high load or short circuit conditions, which may cause the transformer box temperature to be too high, thus affecting the normal operation and service life of the equipment. The existing temperature measurement method is not accurate, which leads to misjudgment of the temperature of the transformer box, causing the transformer to overheat and fail. For this reason, we propose a method for calculating the transformer box temperature using electromagnetic induction heating. Summary of the invention

[0003] 1. Technical issues to be resolved In view of the shortcomings of the prior art, the present invention provides a method and system for calculating the temperature of the transformer box using electromagnetic induction heating, and uses the eddy current of the electromagnetic field to calculate the induction heating temperature of the transformer box, so as to continuously detect the temperature change of the transformer. It takes a different approach in the normal operation detection of the transformer and provides a universal and continuous transformer operation temperature detection method.

[0004] (II) Technical solution To achieve the above technical purpose, the present invention provides the following technical solution: a method for calculating the temperature of a transformer box using electromagnetic induction heating, comprising the following steps: S1, using the electromagnetic field principle to construct a transformer electromagnetic field model calculation formula and calculate the transformer electromagnetic field; S2, electromagnetic field calculation based on transformer electromagnetic field and transformer solid structure coupling; S3, based on the coupling solution result, the transformer coil induction heating calculation is performed to obtain the electromagnetic induction heat of the coil; S4, obtaining the temperature of the heat conduction box based on the electromagnetic induction heat.

[0005] Preferably, the step 1 comprises the following steps: A1. Settings For transformer multi-connection conduction area, set For the surrounding external insulator area, the and The interface between , Transformer Boundary Set at the outer edge of the transformer box, the transformer boundary The external normal vector is , set the conductivity to , set the magnetic permeability to , set the dielectric constant to , In and ; A2. Under the conditions of step A1, set is the vector potential, set is a scalar potential, and the application condition is , we get the equation system, the expression is as follows:

[0006] in, is the diffusion-free current density, is the rate of change of electric potential with time, Used to calculate the curl of the electric field; A3. Projecting the equations of A2 onto the Nedelec-type basis functions, a linear equation system can be obtained, which is expressed as follows:

[0007] in, is the mass matrix, Represents the change in temperature, is the magnetic matrix of the material, is the diffusion coefficient matrix of the material, is the heat source term, Indicates temperature The rate of change over time.

[0008] Preferably, in step 2, after the electromagnetic field is calculated in step 1, the Lorentz force at each spatial point in the transformer box is obtained, and its expression is as follows:

[0009] Where F is the Lorentz force, is the current density, is the magnetic field strength.

[0010] Preferably, the step three comprises the following steps: B1. The transformer coil induction heating generates Joule heat through eddy current flowing in the conductor, and its expression is:

[0011] in, It's heat. is the eddy current intensity, is the resistor, It’s time; B2. selecting a time step during the induction heating process of the transformer coil; B3. Within a plurality of groups of time steps, using the finite element method to solve the distribution of the electromagnetic field and obtain the intensity of the eddy current; B4. Based on the solved eddy current intensity, calculate the Joule heat power generated in the time period; B5. Average the Joule heat power in several groups of time steps to obtain a stable Joule heat power value; B6. Input the Joule heat power value in step B5 directly into the thermal calculation module to calculate the electromagnetic induction heat of the coil.

[0012] Preferably, in the step B5, at the time step The calculated Joule heat power is expressed as ,in represents the index of the time step, Indicates time points, and then calculate the arithmetic mean of the Joule heat power values, which is calculated as follows:

[0013] in, The number of time steps, is The average Joule heat power over the time step.

[0014] Preferably, the thermal calculation module is a calculation unit for simulating and calculating the heat transfer process, and its calculation method is as follows:

[0015] in, is the temperature field, is the thermal diffusivity, defined as , is the thermal conductivity, is the density, is the specific heat capacity.

[0016] Preferably, in step B3, the finite element method comprises the following steps: C1, is the finite element mesh of the transformer electromagnetic field model; C2, set the electromagnetic equations; C3. Calculate the eddy current density.

[0017] Preferably, in the step C1, a mesh is created using finite element software, and the finite element software is SolidWorks Simulation.

[0018] Preferably, the electromagnetic equation in step C2 is expressed as follows:

[0019] in, is the curl of the electric field, which indicates the local circulation characteristics of the electric field. is the magnetic field strength, is the rate of change of the magnetic field with time.

[0020] Preferably, the eddy current density in step C3 is calculated as follows:

[0021] in, is the current density, is the electric field strength.

[0022] Preferably, in step S4, the Joule heat power calculated by step S3 is added to the existing heat transfer model, the heat transfer model uses the time step to update the temperature, and the heat transfer model uses the isotropic model with phase change to calculate and obtain the transformer box temperature, which is calculated as follows:

[0023] in is the latent heat, Liquid fraction.

[0024] A system for calculating transformer box temperature by electromagnetic induction heating, comprising an electromagnetic field acquisition module, a coupling solution module, an induction heat calculation module and a box temperature calculation module; The electromagnetic field acquisition module uses the electromagnetic field principle to construct the transformer electromagnetic field model calculation formula and calculate the transformer electromagnetic field; The coupling solution module solves the electromagnetic field calculation based on the coupling between the transformer electromagnetic field and the transformer solid structure; The induction heat calculation module calculates the induction heating of the transformer coil based on the coupling solution results to obtain the electromagnetic induction heat of the coil; The box temperature calculation module obtains the heat conduction box temperature based on electromagnetic induction heat.

[0025] Compared with the prior art, the present invention provides a method for calculating the temperature of a transformer box using electromagnetic induction heating, which has the following beneficial effects: The present invention provides a method for calculating the temperature of a transformer box body by using electromagnetic induction heating. By using this method, the temperature problem of the box body can be converted into an electromagnetic problem and a mechanical problem of the box body. The accurate box body temperature method can be calculated by measuring the relevant force parameters of the transformer. This is a data conversion calculation method. This method can realize more accurate calculation of the transformer temperature, make the transformer temperature judgment more accurate, and avoid transformer overheating failure.

[0026] The present invention utilizes the principle of electromagnetic induction to perform heating analysis. Electromagnetic induction heating heats the box body by eddy currents generated when the transformer is working. Combined with the finite element analysis method, the temperature distribution of the transformer box body can be accurately calculated. By establishing a three-dimensional model and generating a finite element mesh, the current density, material properties and boundary conditions are set to achieve temperature field analysis of the box body under different working conditions. This method can not only improve the operating efficiency of the transformer, but also effectively prevent equipment failures caused by overheating, thereby providing technical guarantee for the safe operation of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flowchart of a method for calculating the temperature of a transformer box by using electromagnetic induction heating in an embodiment of the present invention.

[0028] Figure 2 It is a schematic diagram of the isotropic heat transfer model of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In modern power systems, transformers play a vital role, and their performance is directly related to the efficiency of power transmission and distribution. However, during the operation of the transformer, heat will be generated due to the flow of current, especially under high load and short circuit conditions, which may cause the temperature of the transformer box to rise significantly, thereby affecting the stability and service life of the equipment. In order to effectively control the temperature rise of the transformer and optimize its operating conditions, a transformer box temperature calculation method based on electromagnetic induction heating is proposed. This method includes multiple steps, has unique advantages, and is significantly innovative and practical compared with the existing technology.

[0031] See also Figure 1-2A method for calculating the temperature of a transformer box using electromagnetic induction heating comprises the following steps: S1. Design the transformer electromagnetic field related formula based on the transformer spatial structure and electromagnetic induction principle: Implementation method: 1.1 Create a geometric model of the transformer, including the core, winding, insulation material and casing, and select CAD software to implement the modeling; 1.2 Settings For transformer multi-connection conduction area, set is the surrounding external insulator area, and The interface between , Transformer Boundary Set at the outer edge of the transformer box, the transformer boundary The external normal vector is , set the conductivity to , set the magnetic permeability to , set the dielectric constant to , In and ; 1.3 Settings is the vector potential, set is a scalar potential, and the application condition is , we get the equation system, the expression is as follows:

[0032] in, is the diffusion-free current density, is the rate of change of electric potential with time, Used to calculate the curl of the electric field; 1.4 Projecting the system of equations in 1.3 onto the Nedelec-type basis functions, we obtain a system of linear equations expressed as follows:

[0033] in, is the mass matrix, Represents the change in temperature, is the magnetic matrix of the material, is the diffusion coefficient matrix of the material, is the heat source term, Indicates temperature The rate of change over time.

[0034] Design transformer electromagnetic field related formulas based on the transformer spatial structure and electromagnetic induction principle. This step accurately models the geometric structure of the transformer and combines the electromagnetic induction principle to form effective electromagnetic field equations, providing a basis for subsequent calculations.

[0035] S2. Use electromagnetic field related formulas to design eddy current calculation equations.

[0036] According to the electromagnetic field distribution, the eddy current density is derived and current density The relationship between them is expressed as follows:

[0037] in, is the current density, is the electric field strength, is the conductivity.

[0038] Based on the principle of electromagnetic induction, the relationship between the heat generated by eddy current and the applied electric field is derived, and the power generated by eddy current can be expressed as:

[0039] in, is the power generated by the eddy current, Represents volume Integrate a physical quantity within to calculate the overall power output. refers to the entire volume area considered, is the current density, is the electric field strength, Represents a tiny part of a volume and is used for volume division during integration.

[0040] The above equations are transformed into a form suitable for numerical solution and solved using the finite element method (FEM).

[0041] The eddy current calculation equations are designed using electromagnetic field related formulas. The generation of eddy current is closely related to the electromagnetic field. By establishing the relationship between eddy current density and electric and magnetic fields, this link lays a theoretical foundation for the subsequent heat generation analysis.

[0042] S3, transformer solid structure coupling and electromagnetic field calculation: Combining the electromagnetic field model with the solid mechanics model, in the design of the transformer, taking into account the influence of electromagnetic force on the core and winding, the mechanical equilibrium equation is used to describe the stress state of the core and winding, and the electromagnetic force generated by eddy current is considered. The equation form is: 0 in is the divergence, which indicates the divergence of a vector field. is the stress tensor, which describes the internal force state of the material. It is a second-order tensor that contains the stress distribution information of the material after being subjected to force, including normal stress and shear stress. is the volume force, which represents the external force acting on a unit volume.

[0043] After the electromagnetic field is calculated through step 1, the Lorentz force at each spatial point in the transformer box is obtained, and its expression is as follows:

[0044] Where F is the Lorentz force, is the current density, is the magnetic field strength.

[0045] Transformer solid structure coupling for electromagnetic field calculation. In this stage, the solid part of the transformer is taken into account, and the electromagnetic field and structure are comprehensively analyzed through the coupling method. This innovative coupling method allows the electromagnetic effect and structural response to be monitored and analyzed in real time, thereby improving the accuracy of the calculation.

[0046] S4, obtaining the temperature of the heat conduction box based on the electromagnetic induction heat.

[0047] The eddy current power calculated in step 2 is used as a heat source and input into the heat conduction model. The spatial distribution of the heat source is determined, and the electromagnetic field, eddy currents, and the power generated during the induction heating process are comprehensively calculated using numerical software. The electromagnetic field calculation results are associated with the heat conduction equation, and the electric field, magnetic field, and temperature distribution are iteratively updated.

[0048] Induction heating coupled electromagnetic field calculation. Using the principle of electromagnetic induction, the eddy current generated by the transformer coil is analyzed to quantify the heat generated in the box and form an effective temperature rise model. The calculation results of this stage will directly affect the distribution of heat and are an important part of the optimization design.

[0049] The induction heating of the transformer coil generates Joule heat through the eddy current flowing in the conductor, and its expression is:

[0050] in, It's heat. is the eddy current intensity, is the resistor, It’s time; A time step is selected during the induction heating process of the transformer coil. Within a plurality of groups of the time steps, the finite element method is used to solve the distribution of the electromagnetic field and obtain the intensity of the eddy current. The finite element method includes the following steps: (1) Create a finite element mesh for the transformer electromagnetic field model using SolidWorks Simulation, a module of SolidWorks software that is mainly used for engineering simulation and finite element analysis (FEM). (2) Set the electromagnetic equation as follows:

[0051] in, is the curl of the electric field, which indicates the local circulation characteristics of the electric field. is the magnetic field strength, is the rate of change of magnetic field with time; (3) Calculate the eddy current density as follows:

[0052] in, is the current density, is the electric field strength; Based on the solved eddy current intensity, the Joule heat power generated in this time period is calculated; The Joule heat power in several groups of time steps is averaged to obtain a stable Joule heat power value. The calculated Joule heat power is expressed as ,in represents the index of the time step, Indicates time points, and then calculate the arithmetic mean of the Joule heat power values, which is calculated as follows:

[0053] in, The number of time steps, is The average Joule heat power over the time step.

[0054] For example: Assume that during the simulation, we record the following Joule heat power values ​​in 5 time steps: =10W =12W =15W =11W =13W Calculate the average power: W.

[0055] Induction heating is used to calculate the temperature of the transformer coil. The heat distribution obtained in the previous steps is used to calculate the specific temperature of the transformer coil, providing necessary data support for subsequent heat transfer analysis.

[0056] The temperature field calculated by the coil is coupled with the heat conduction equation of the casing and surrounding media to establish a comprehensive heat conduction model to solve how heat is transmitted from the coil through the insulating material to the casing during the operation of the transformer. In this process, the relationship between the electromagnetic field and the temperature field is regularly updated to ensure the final stable state.

[0057] Heat transfer coupled electromagnetic field calculation. In this step, the heat transfer process between the electromagnetic heat source and the material is combined to establish the heat conduction equation. This link emphasizes the interaction between the electromagnetic effect and the heat conduction process, ensuring the comprehensiveness of the temperature analysis.

[0058] like Figure 2 As shown, the heat transfer module calculates the transformer box temperature: The Joule heat power value in the above steps is directly input into the thermal calculation module to calculate the electromagnetic induction heat of the coil. The thermal calculation module is a calculation unit used to simulate and calculate the heat transfer process. The calculation method is as follows:

[0059] in, is the temperature field, is the thermal diffusivity, defined as , is the thermal conductivity, is the density, is the specific heat capacity.

[0060] The heat transfer module calculates the temperature of the transformer box. Finally, the heat transfer analysis module combines all the previously obtained data to calculate the overall temperature distribution of the transformer box. The results of this stage provide a basis for the temperature control and management of the equipment.

[0061] The calculated Joule heat power is added to the existing heat transfer model. The heat transfer model uses the time step to update the temperature. The heat transfer model uses the isotropic model with phase change to calculate and obtain the transformer box temperature. The calculation method is as follows:

[0062] in is the latent heat, Liquid fraction.

[0063] Thus, the transformer box temperature is obtained.

[0064] Compared with the traditional temperature calculation method, the method of the present invention has obvious advantages. In the traditional method, only static heat conduction or simplified heat source model is often considered, lacking in-depth analysis of electromagnetic phenomena. However, this method not only considers the heat change caused by electromagnetic heating, but also combines the thermal conductivity characteristics of the material, making the model more accurate and reflecting the real state of the transformer in actual operation.

[0065] 1. Through comprehensive electromagnetic field and heat conduction coupling analysis, the accuracy of transformer temperature calculation is ensured. Accurate temperature prediction can help engineers identify potential problems early and take reasonable measures to prevent equipment overheating.

[0066] 2. An effective temperature control solution can optimize the operating efficiency of the transformer, reduce energy loss caused by excessive temperature, and improve the overall performance of the transformer.

[0067] 3. Through scientific temperature calculation and control, the working time of the transformer under high temperature conditions can be reduced, which can significantly extend the service life of the equipment and reduce the cost of maintenance and replacement.

[0068] 4. This method is not only applicable to the analysis of traditional transformers, but can also be combined with modern intelligent monitoring systems to achieve real-time monitoring and intelligent management, thereby improving the automation level of substations.

[0069] 5. The application of this method is not limited to transformers, but can also be extended to the calculation and management of heat sources in other electrical equipment, providing a solid foundation for research and practice in related fields.

[0070] In another embodiment of the present invention, a system for calculating the temperature of a transformer box body by using electromagnetic induction heating is provided, comprising an electromagnetic field acquisition module, a coupling solution module, an induction heat calculation module and a box body temperature calculation module; The electromagnetic field acquisition module uses the electromagnetic field principle to construct the transformer electromagnetic field model calculation formula and calculate the transformer electromagnetic field; The coupling solution module solves the electromagnetic field calculation based on the coupling between the transformer electromagnetic field and the transformer solid structure; The induction heat calculation module calculates the induction heating of the transformer coil based on the coupling solution results to obtain the electromagnetic induction heat of the coil; The box temperature calculation module obtains the heat conduction box temperature based on electromagnetic induction heat.

[0071] In another embodiment of the present invention, a terminal device is provided, the terminal device includes a processor and a memory, the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding functions; the processor described in the embodiment of the present invention can be used for the operation of the method for calculating the temperature of the transformer box using electromagnetic induction heating.

[0072] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and the extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the method for calculating the temperature of the transformer box body using electromagnetic induction heating in the above embodiment.

[0073] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0074] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0075] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0076] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0077] In summary, the present invention uses electromagnetic induction heating to calculate the temperature of the transformer box, which integrates the comprehensive technology of electromagnetic field and heat transfer analysis, greatly improving the accuracy and effectiveness of transformer temperature prediction. This method can be used to convert the temperature problem of the box into an electromagnetic problem and a mechanical problem of the box. The accurate box temperature method can be calculated by measuring the relevant force parameters of the transformer. It is a data conversion calculation method. This method can achieve more accurate calculation of the transformer temperature, making the transformer temperature judgment more accurate and avoiding transformer overheating failure. Through optimized design and comprehensive analysis, it can effectively reduce the risk of failure and improve equipment performance, providing a new technical path for the development of the power industry. This innovative method not only meets the requirements of modern power systems for safety and efficiency, but also provides broad prospects for future research and application.

[0078] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for calculating transformer box temperature using electromagnetic induction heating, characterized in that: The steps include: S1, using the electromagnetic field principle to construct a transformer electromagnetic field model calculation formula and calculate the transformer electromagnetic field; S2, electromagnetic field calculation based on transformer electromagnetic field and transformer solid structure coupling; S3, based on the coupling solution result, the transformer coil induction heating calculation is performed to obtain the electromagnetic induction heat of the coil; S4, obtaining the temperature of the heat conduction box based on the electromagnetic induction heat.

2. The method for calculating the temperature of a transformer box by using electromagnetic induction heating according to claim 1, characterized in that: The S1 comprises the following steps: A1. Settings For transformer multi-connection conduction area, set For the surrounding external insulator area, the and The interface between , Transformer Boundary Set at the outer edge of the transformer box, the transformer boundary The external normal vector is , set the conductivity to , set the magnetic permeability to , set the dielectric constant to , In and ; A2. Under the conditions of step A1, set is the vector potential, set is a scalar potential, and the application conditions are , we get the equation system, the expression is as follows: in, is the diffusion-free current density, is the rate of change of electric potential with time, Used to calculate the curl of the electric field; A3. Projecting the equations of A2 onto the Nedelec-type basis functions, a linear equation system can be obtained, which is expressed as follows: in, is the mass matrix, Represents the change in temperature, is the magnetic matrix of the material, is the diffusion coefficient matrix of the material, is the heat source term, Indicates temperature The rate of change over time.

3. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 1, characterized in that: In S2, after the electromagnetic field is calculated by S1, the Lorentz force at each spatial point in the transformer box is obtained, and its expression is as follows: Where F is the Lorentz force, is the current density, is the magnetic field strength.

4. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 1, characterized in that: The S3 comprises the following steps: B1. The transformer coil induction heating generates Joule heat through eddy current flowing in the conductor, and its expression is: in, It's heat. is the eddy current intensity, is the resistor, It’s time; B2. selecting a time step during the induction heating process of the transformer coil; B3. Within a plurality of groups of time steps, using the finite element method to solve the distribution of the electromagnetic field and obtain the intensity of the eddy current; B4. Based on the solved eddy current intensity, calculate the Joule heat power generated in the time period; B5. Average the Joule heat power in several groups of time steps to obtain a stable Joule heat power value; B6. A computing unit that simulates and calculates the heat transfer process according to the Joule heat power value in step B5, thereby calculating the electromagnetic induction heat of the coil.

5. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 4, characterized in that: In the B5 step, at the time step The calculated Joule heat power is expressed as ,in represents the index of the time step, Indicates time points, and then calculate the arithmetic mean of the Joule heat power values, which is calculated as follows: in, The number of time steps, is The average joule heat power in the time step; The thermal calculation module is a calculation unit used to simulate and calculate the heat transfer process, and its calculation method is as follows: in, is the temperature field, is the thermal diffusivity, defined as , is the thermal conductivity, is the density, is the specific heat capacity.

6. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 4, characterized in that: In step B3, the finite element method includes the following steps: C1, is the finite element mesh of the transformer electromagnetic field model; C2, set the electromagnetic equations; C3. Calculate the eddy current density.

7. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 6, characterized in that: In the step C1, a mesh is created using finite element software, and the finite element software is SolidWorks Simulation.

8. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 6, characterized in that: The electromagnetic equation in step C2 is expressed as follows: in, is the curl of the electric field, which indicates the local circulation characteristics of the electric field. is the magnetic field strength, To express the rate of change of the magnetic field over time, the eddy current density in step C3 is calculated as follows: in, is the current density, is the electric field strength.

9. The method for calculating transformer box temperature by electromagnetic induction heating according to claim 5, characterized in that: In step S4, the Joule heat power calculated in step S3 is added to the existing heat transfer model. The heat transfer model uses the time step to update the temperature. The heat transfer model uses the isotropic model with phase change to calculate and obtain the transformer box temperature. The calculation method is as follows: in is the latent heat, Liquid fraction.

10. A system for calculating transformer box temperature using electromagnetic induction heating, characterized in that: It includes electromagnetic field acquisition module, coupling solution module, induced heat calculation module and box temperature calculation module; The electromagnetic field acquisition module uses the electromagnetic field principle to construct the transformer electromagnetic field model calculation formula and calculate the transformer electromagnetic field; The coupling solution module solves the electromagnetic field calculation based on the coupling between the transformer electromagnetic field and the transformer solid structure; The induction heat calculation module calculates the induction heating of the transformer coil based on the coupling solution results to obtain the electromagnetic induction heat of the coil; The box temperature calculation module obtains the heat conduction box temperature based on electromagnetic induction heat.

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