Method for evaluating oil level adjusting capability of wave wing of oil tank of fully-sealed distribution transformer

Abstract

The invention discloses a method for evaluating the oil level regulation capability of a wave fin of a fully-sealed distribution transformer oil tank, which comprises the following steps: carrying out thermal coupling analysis on the distribution transformer oil tank to obtain the relationship between fatigue cracks of the distribution transformer oil tank and the wave fin and structural deformation and temperature / strain / displacement, and determining temperature / strain / displacement key feature points of a transformer; analyzing and evaluating the fatigue life of the oil tank and the wave fin, and adjusting the structural parameters of the distribution transformer oil tank and the wave fin to meet the oil level position of the distribution transformer oil tank. Fuel tank and wave fin thermal-mechanical coupling analysis is performed by applying a finite element method, fuel tank fatigue life is evaluated according to analysis results and typical fuel tank and wave fin material welding structure basic data, fuel tank structural design is evaluated and guided from the angle of weld fatigue life, and leakage caused by cracking due to weld fatigue crack propagation of the transformer fuel tank is avoided; and flashover is caused and power supply safety is threatened due to insufficient oil level easily caused by combined action of thermal expansion and cold contraction of a transformer oil tank shell and internal transformer oil.

Description

Technical Field

[0001] The invention relates to the technical field of electric transformation, and in particular to a method for evaluating the oil level regulating capability of a fully sealed distribution transformer oil tank wave fin. Background Art

[0002] In recent years, in order to avoid oxidation and moisture of distribution transformer oil, fully sealed distribution transformers are mostly used in Qinghai Province. The oil tank of the fully sealed distribution transformer is one of the key components of the distribution transformer. It mainly relies on the "breathing" effect of the oil tank corrugated fins, that is, the elastic change of the corrugated fins compensates for the change in transformer oil volume caused by temperature rise and fall, thereby alleviating the increase in internal pressure of the transformer.

[0003] However, it is currently found that the oil tank wave wing expands due to the increase in temperature, but cannot shrink normally after the temperature drops. After long-term operation, the transformer oil level drops, and the exposed conductor discharges to the transformer shell, affecting the stable operation of the equipment. Therefore, it is necessary to conduct fatigue life research on the "breathing" of the fully sealed transformer wave wing, analyze the relationship between temperature, deformation, stress and oil level during the use of the oil tank, evaluate the adaptability of the oil tank in Qinghai, and guide the product structure design and quality assessment index formulation of the transformer oil tank. Summary of the invention

[0004] The purpose of the present invention is to provide a method for evaluating the oil level regulating capability of a fully sealed distribution transformer oil tank wave fin to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin comprises: analyzing the thermal-mechanical coupling of the distribution transformer oil tank, obtaining the relationship between fatigue cracks and structural deformation and temperature / strain / displacement of the distribution transformer oil tank and wave fins, determining key characteristic points of transformer temperature / strain / displacement, analyzing and evaluating the fatigue life of the oil tank and wave fins, and adjusting the structural parameters of the distribution transformer oil tank and wave fins to meet the oil level position of the distribution transformer oil tank.

[0007] Furthermore, the thermal-mechanical coupling analysis of the distribution transformer tank and wave fins is carried out based on the finite element method;

[0008] Obtain the relationship between the fatigue cracks of the distribution transformer oil tank and wave fins and the structural deformation and temperature / strain / displacement, determine the key characteristic points of transformer temperature / strain / displacement, and analyze and evaluate the fatigue life of the oil tank and wave fins, including:

[0009] The fatigue behavior caused by thermal expansion and contraction of the oil tank and corrugated fins of the distribution transformer is used as the basis for the fatigue life of the oil tank and corrugated fins. The fatigue behavior is expressed by the fatigue crack growth rate of the oil tank and corrugated fin materials:

[0010]

[0011] Where F is the geometric correction factor, Δp is the stress intensity factor, and Δp m It represents the maximum value of the stress intensity factor range, N represents the number of stress cycles, T represents the deformation temperature of the oil tank and the corrugated fin material, and D represents the crack length of the oil tank and the corrugated fin material.

[0012] Furthermore, the fuel tank and the wave fin material are deformed bodies of arbitrary shapes under force, and their tiny volume elements d x d y d z In the paper, based on the three major variables of displacement, strain and stress, the equilibrium equation, geometric equation and elastic constitutive equation are established. The finite element method is used to discretize the equations and then solve them to obtain the stress and strain of all the integral points in the unit.

[0013] Furthermore, the equilibrium equation is as follows:

[0014]

[0015] Where σ xx , σ yy , σ zz They represent the normal stress of the microelement on the plane perpendicular to the X, Y, and Z axes respectively;

[0016] τ xy , τ yz , τ zx They represent the shear stress along the Y, Z, and X axes on the plane perpendicular to the X, Y, and Z axes of the micro-element respectively;

[0017] They represent the physical force of the tiny element along the X, Y, and Z axes respectively.

[0018] Furthermore, the geometric equation is as follows:

[0019]

[0020] Where ε xx , ε yy , ε zz Respectively represent the positive strain of the microelement along the three directions of X, Y, and Z axes;

[0021] γ xy , γ yz , γ zx They represent the deflection angles of the plane perpendicular to the X, Y, and Z axes toward the Y, Z, and X axes, respectively, and are called engineering shear strain.

[0022] Furthermore, the elastic constitutive equation is as follows:

[0023]

[0024] Where E, μ, and G represent the elastic modulus, Poisson's ratio, and shear modulus of the material, respectively.

[0025] Furthermore, the specific solution process of the finite element method includes the following steps:

[0026] Structural discretization: When performing numerical calculations using the finite element method, the first step is to discretize the continuous structure into a finite number of units that can be connected to each other through nodes. At the same time, each node and unit is numbered one by one, and the corresponding unit type, node number, physical properties, and node coordinate value information are assigned;

[0027] Unit characteristic analysis: each discretized unit is regarded as a separate research object, and the relationship between the node force and node displacement is studied to establish the relevant equations;

[0028] Unit grouping: According to the force balance conditions of the overall structure and the boundary conditions at various locations, the units are regrouped to form the overall finite element equation

[0029] {F}=[K]{η}

[0030] Where {F} is the load matrix; [K] is the overall stiffness matrix; {η} is the node displacement matrix of the entire object;

[0031] Calculate the displacements at unknown nodes: By combining the boundary conditions with the entire system of equations, the general solution of the finite element equations can be solved, thereby deriving the displacements of each node;

[0032] Calculate the stress and strain occurring in the unit: Based on the solved node result data, the stress and strain of all integration points in the unit can be calculated through the selected interpolation function.

[0033] Furthermore, the thermal-mechanical coupling analysis of the distribution transformer oil tank based on the finite element method includes the use of the sequential coupling method to analyze the heat transfer process and the stress process separately. The thermal analysis is performed first, and then the temperature field calculation results obtained by the thermal analysis are applied as thermal loads to the subsequent structural stress analysis. Finally, the thermal analysis results are obtained based on the structural stress analysis.

[0034] Furthermore, basic data of typical fuel tank and wave fin material welding structures are obtained, and the fatigue life of the fuel tank and wave fin is evaluated based on the finite element simulation analysis results and the basic data of typical fuel tank and wave fin material welding structures. The fuel tank and wave fin structure design is evaluated and guided from the perspective of weld fatigue life.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention applies the finite element method to perform thermal-mechanical coupling analysis of the oil tank and the wave fin, evaluates the fatigue life of the oil tank based on the finite element simulation analysis results and the basic data of the welding structure of typical oil tank and wave fin materials, evaluates and guides the oil tank structure design from the perspective of weld fatigue life, avoids the expansion of fatigue cracks in the weld of the transformer oil tank and then cracking and leakage, and in addition, due to the combined effect of thermal expansion and contraction of the transformer oil tank shell and the internal transformer oil, it is easy to cause insufficient oil level, thereby causing flashover, threatening the power supply safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is the finite element analysis flow chart of the present invention.

[0038] Figure 2 The thermal stress diagram of the transformer tank is calculated by the sequential coupling method of the present invention.

[0039] Figure 3 It is the overall implementation roadmap of the present invention. DETAILED DESCRIPTION

[0040] 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.

[0041] See also Figures 1 to 3 , the present invention provides a technical solution:

[0042] The fatigue caused by thermal expansion and contraction of the transformer oil tank belongs to low-cycle fatigue behavior (fatigue life does not exceed 10,000 times). The evolution of low-cycle fatigue damage assumes that the energy damage theory is based on continuum mechanics and thermodynamics, and regards the damage process as an energy conversion process, and this conversion process is irreversible. It reflects the material damage in the process of irreversible changes in the internal structure of the material, is related to the change in the microstructure of the material, and is a change in the state of matter. The energy damage theory is established based on free energy and dissipated potential within a thermodynamic framework with internal variables. The so-called internal variables are used to describe the thermodynamic state of a mechanical system. Some physical quantities can be selected from different perspectives as their internal state variables. These variables are only related to the irreversible thermodynamic processes of the system, such as ε p , ε e , D, etc. The general form of fatigue damage evolution can be expressed as:

[0043]

[0044] Finite element analysis is the earliest calculation method based on structural mechanics. Within the elastic range, it mainly studies how to express the mechanical variables of materials at any position in an elastic deformable body of arbitrary shape when they are in a complex stress state and the relationship between these variables. The specific steps are shown in Figure 1 .

[0045] Any deformed body of any shape under force, in its tiny volume element d x d y d z In the mechanics model, based on the three major variables of displacement, strain and stress, the following three basic mechanical equations can be established:

[0046] Balancing equations

[0047] Where σ xx , σ yy , σ zz —represents the normal stress of the microelement on the plane perpendicular to the X, Y, and Z axes respectively;

[0048] τ xy , τ yz , τ zx —represents the shear stress of the microelement along the Y, Z, and X axes on the plane perpendicular to the X, Y, and Z axes respectively;

[0049] —represents the body force of the tiny element along the three directions of X, Y, and Z axis respectively;

[0050] Geometric equations

[0051] Where ε xx , ε yy , ε zz —represents the normal strain of the microelement along the three directions of X, Y and Z axis respectively;

[0052] γ xy , γ yz , γ zx —represents the deflection angle of the plane perpendicular to the X, Y, and Z axes of the micro-element toward the Y, Z, and X axes, respectively, which is called engineering shear strain;

[0053] Elastic constitutive equation

[0054] Where E, μ, G represent the elastic modulus, Poisson's ratio and shear modulus of the material respectively.

[0055] Finite Element Method (Finite Element Method) is an efficient and approximate numerical calculation method. In the field of scientific computing, it is often necessary to solve various differential equations, and the analytical solutions of many differential equations are generally difficult to obtain. After discretizing the differential equations using the finite element method, a program can be compiled to use computer-aided solutions. The specific solution process of the finite element method usually includes the following steps:

[0056] (1) Structural Discreteness

[0057] When performing numerical calculations using the finite element method, the first step is to discretize the continuous structure into a finite number of units that can be connected to each other through nodes. At the same time, each node and unit is numbered one by one, and the corresponding unit type, node number, physical properties, node coordinate values, and other information are assigned.

[0058] (2) Unit characteristics analysis

[0059] Each discretized unit is regarded as a separate research object, and the relationship between the nodal force and the nodal displacement is studied to establish the relevant equations.

[0060] (3) Unit Group

[0061] According to the force balance conditions of the overall structure and the boundary conditions at various locations, the units are reassembled to form the overall finite element equation.

[0062] {F}=[K]{η}

[0063] Where {F}—load array;

[0064] [K]—global stiffness matrix;

[0065] {η}—Array of nodal displacements of the entire object.

[0066] (4) Calculate the displacement of unknown nodes

[0067] By combining the boundary conditions with the entire set of equations, the general solution of the finite element equations can be solved, and the displacement of each node can be derived.

[0068] (5) Calculate the stress and strain occurring in the unit

[0069] Based on the solved node result data, the stress and strain of all integration points in the unit can be calculated through the selected interpolation function.

[0070] The thermal stress analysis of the transformer tank structure is a typical example that can be analyzed using the sequential coupling method. The heat transfer process and stress process analysis can be performed separately. The thermal analysis is performed first, and the temperature field calculation results obtained by the thermal analysis are applied as thermal loads to the subsequent structural stress analysis, thereby simplifying the thermal stress coupling solution problem and reducing the large amount of calculation time required for the coupling analysis. The finite element analysis of the thermal-mechanical coupling field uses the sequential coupling method to calculate thermal stress, see Figure 2 .

[0071] Engineering practice focuses on whether the technical principles, fixed installation methods and application environments of temperature displacement sensors, signal collectors and wireless data transmission devices can meet the application requirements of transformer oil tank temperature deformation monitoring.

[0072] 1) Displacement sensor

[0073] A displacement sensor is a device that converts the motion displacement of an object into a measurable electrical quantity. It is usually used to convert physical quantities such as displacement, position, deformation, vibration, and size that are not easy to quantitatively detect and process into electrical quantities that are easy to quantitatively detect, transmit, and process information. Small displacements are usually detected by strain, inductance, differential transformer (LVDT), eddy current, and Hall sensors, while large displacements are often measured by induction synchronizers, gratings, capacitive gratings, magnetic gratings, magnetostrictive gratings, and other sensing technologies.

[0074] Displacement sensors are divided into the following categories according to their working principles: (1) potentiometer displacement sensor; (2) grating displacement sensor; (3) magnetostrictive displacement sensor; (4) LVDT displacement sensor; (5) capacitive displacement sensor; (6) Hall displacement sensor; (7) eddy current displacement sensor; (8) ultrasonic displacement sensor; (9) grating scale displacement sensor; (10) laser displacement sensor, etc.

[0075] Displacement sensors are divided into the following categories according to their mode of movement: (1) linear displacement sensors; (2) angular displacement sensors.

[0076] The research strategy for displacement sensors is mainly to select sensors based on usage requirements such as temperature range, measurement range, radiation resistance and wear resistance, select displacement sensors that basically meet the usage requirements for installation and testing, and select and carry out optimization design based on actual usage effects.

[0077] 2) Temperature sensor

[0078] A temperature sensor is a sensor that can sense temperature and convert it into a usable output signal. The temperature sensor is the core part of a temperature measuring instrument. It can be divided into two categories according to the measurement method: contact and non-contact. It can be divided into two categories: thermal resistors and thermocouples according to the sensor material and electronic component characteristics.

[0079] The detection part of the contact temperature sensor has good contact with the object being measured. The thermometer reaches thermal equilibrium through conduction or convection, so that the reading of the thermometer can directly represent the temperature of the object being measured. Generally, the measurement accuracy is high. Commonly used thermometers include bimetallic thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors and thermocouples. Working principle of contact temperature sensor: (1) Metal expansion; (2) Resistance change; (3) Thermocouple.

[0080] The sensitive element of the non-contact temperature sensor does not contact the object being measured, so it is also called a non-contact temperature measuring instrument. This instrument can be used to measure the surface temperature of moving objects, small targets, and objects with small heat capacity or rapid temperature changes (transients). It can also be used to measure the temperature distribution of the temperature field. The most commonly used non-contact temperature measuring instrument is based on the basic law of blackbody radiation and is called a radiation temperature measuring instrument. The radiation temperature measurement method includes the brightness method (see optical pyrometer), the radiation method (see radiation pyrometer) and the colorimetric method (see colorimetric thermometer).

[0081] 3) Selection of wireless data transmission technology solutions

[0082] With the vigorous development of electronic technology, computer technology and wireless communication technology, various wireless data transmission standards have emerged, each of which has its own advantages and disadvantages and different application scenarios.

[0083] Wireless communication (data) transmission method and technical principle:

[0084] Wireless communication is a communication method that uses the characteristics of electromagnetic wave signals propagating in free space to exchange information. Wireless communication technology has many advantages. It is low-cost. It does not need to establish physical lines, let alone a large number of manpower to lay cables. Moreover, wireless communication technology is not restricted by industrial environments, has strong resistance to environmental changes, and is easier to diagnose faults. Compared with the setting and maintenance of traditional wired communications, wireless network maintenance can be completed through remote diagnosis, which is more convenient. It has strong scalability. When the network needs to be expanded, wireless communication does not require expansion wiring. It has strong flexibility. Wireless networks are not restricted by environmental terrain, etc., and when the use environment changes, wireless networks only need to make few adjustments to adapt to the requirements of the new environment. Common wireless communication (data) transmission methods and technologies are divided into two types: "short-range wireless communication technology" and "long-range wireless transmission technology".

[0085] Short-range wireless communication technology refers to the communication between two parties through the use of radio waves to transmit data, and the transmission distance is within a relatively short range. Its application range is very wide. In recent years, the short-range wireless communication standards that are widely used and have good development prospects include: Zig-Bee, Bluetooth, wireless broadband (Wi-Fi), ultra-wideband (UWB) and near-field communication (NFC).

[0086] The widely used communication technologies for long-distance wireless transmission include GPRS / CDMA, digital radio, spread spectrum microwave, wireless bridge, satellite communication, shortwave communication technology, etc. It is mainly used in remote areas or areas where it is not suitable to lay lines, such as coal mines, offshore, polluted or harsh environmental areas, etc.

[0087] GPRS (General Packet Radio Service) is a wireless packet switching technology based on the GSM communication system developed and operated by China Mobile. It is a technology between the second generation and the third generation, usually called 2.5G. It is a wireless transmission method developed using the concept of packet switching. Packet switching encapsulates data into many independent packets, and then transmits these packets one by one. It is a bit like sending a parcel. Its advantage is that it will only occupy bandwidth when there is data to be transmitted, and it is priced by the amount of data, which effectively improves the utilization rate of the network. The GPRS network supports both circuit-type data and packet-switched data, so that the GPRS network can be easily connected to the Internet. Compared with the original GSM network's circuit-switched data transmission method, GRRS's packet switching technology has the advantages of real-time online, volume-based billing, and high-speed transmission.

[0088] CDMA (the abbreviation of Code Division Multiple Access) is a new wireless communication system based on code division technology and multiple access technology operated by China Telecom. Its principle is based on spread spectrum technology.

[0089] Digital wireless data transmission radio adopts digital signal processing, digital modulation and demodulation, and has functions such as forward error correction and equalization soft decision. The working frequency of digital radio mostly uses the frequency band of 220--240MHz or 400--470MHz, and has the advantages of digital and voice compatibility, good real-time data transmission, dedicated data transmission channel, one-time investment, no operation fee, suitable for harsh environment, good stability, etc. The effective coverage radius is about tens of kilometers, which can cover a city or a certain area. It usually provides a standard RS-232 / RS-485 data interface, which can be directly connected to computers, data collectors, RTUs, PLCs, data terminals, GPS receivers, digital cameras, etc. It has been widely used in various industries, such as aerospace, railways, electricity, petroleum, meteorology, earthquake, etc., and has also made great progress and development in the fields of SCADA such as remote control, telemetry, shaking letters, and remote sensing.

[0090] The distribution transformer oil tank is in typical hot and cold fatigue load conditions in actual use. Due to the structure of the oil tank, there is a large stress concentration at its joints (usually welded structures), which generates cracks (or cracks exist in the tank itself) under the action of hot and cold fatigue loads. As the cracks propagate, the structural strength of the oil tank deteriorates, and the pressure difference causes greater deformation and stress concentration, which in turn affects the crack propagation rate, the service life of the oil tank, and the oil level.

[0091] Conduct theoretical, experimental and computational research on fatigue of distribution transformer oil tank materials within the actual use load range, and obtain basic data such as mechanical properties of the weld area of ​​typical oil tank materials, microstructure of the weld and its heat-affected zone, and fatigue life under typical load conditions;

[0092] 2) Reveal its fatigue life and reveal its crack growth law;

[0093] 3) Apply the finite element method to conduct thermal-mechanical coupling analysis and fluid-solid coupling analysis of the fuel tank. Based on the finite element simulation analysis results and the basic data of the welding structure of typical fuel tank materials, the fatigue life of the fuel tank is evaluated, and the fuel tank structure design is guided from the perspective of weld fatigue life.

[0094] The actual operating conditions of the oil tank structure are complex. Affected by factors such as ambient temperature, solar radiation, and heating of the transformer, the oil tank shell and transformer oil both experience significant thermal expansion and contraction. In addition, there is additional pressure difference deformation due to low air pressure in high altitude areas. It is planned to use the finite element method to perform thermal-mechanical coupling analysis and fluid-solid coupling analysis of the oil tank to obtain the distribution law of temperature stress deformation of the oil tank and the method for evaluating the oil level of the transformer oil tank.

[0095] 1) Study the temperature, deformation and stress distribution of the oil tank in a complex environment, especially the stress deformation at the weld;

[0096] 2) Study the oil level change law of the oil tank shell and transformer oil under thermal expansion and contraction conditions, evaluate the environmental adaptability of the oil tank under different oil filling temperatures and oil filling amounts from the oil level perspective based on finite element simulation analysis technology, conduct experimental verification, and finally formulate an optimized transformer oil tank structure construction assessment method.

[0097] Through finite element simulation and experimental research, the hot and cold deformation law of the distribution transformer oil tank, as well as the relationship between fatigue cracks, structural deformation and temperature, are obtained, the key characteristic points of transformer temperature / strain / displacement are determined, and the formulation of online detection schemes is guided. The overall implementation route of the project is as follows: Figure 3 shown.

[0098] The temperature strain displacement monitoring device is networked by installing temperature sensors and displacement sensors at typical locations of the transformer oil tank and matching data acquisition devices to process the detection signals into standard RS485 interface data. The data is input into the data transmission radio for wireless transmission. The same frequency wireless data transmission radio is used on the host side to receive the signal and input it into the networked computer. The computer (host side) is installed with special software to receive the data and perform special processing. The processed data can be transmitted to the big data platform display terminal through the network.

[0099] The present invention, the undescribed parts are prior art.

[0100] 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 evaluating the oil level regulation capability of the oil tank wave fin of a fully sealed distribution transformer, characterized in that: include: The thermal-mechanical coupling analysis of the distribution transformer oil tank is carried out to obtain the relationship between the fatigue cracks of the distribution transformer oil tank and corrugated fins and the structural deformation and temperature / strain / displacement, determine the key characteristic points of transformer temperature / strain / displacement, analyze and evaluate the fatigue life of the oil tank and corrugated fins, and adjust the structural parameters of the distribution transformer oil tank and corrugated fins to meet the oil level position of the distribution transformer oil tank.

2. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 1, characterized in that: Thermal-mechanical coupling analysis of distribution transformer oil tank and corrugated fin based on finite element method; Obtain the relationship between the fatigue cracks of the distribution transformer oil tank and wave fins and the structural deformation and temperature / strain / displacement, determine the key characteristic points of transformer temperature / strain / displacement, and analyze and evaluate the fatigue life of the oil tank and wave fins, including: The fatigue behavior caused by thermal expansion and contraction of the oil tank and corrugated fins of the distribution transformer is used as the basis for the fatigue life of the oil tank and corrugated fins. The fatigue behavior is expressed by the fatigue crack growth rate of the oil tank and corrugated fin materials: Where F is the geometric correction factor, Δp is the stress intensity factor, and Δp m It represents the maximum value of the stress intensity factor range, N represents the number of stress cycles, T represents the deformation temperature of the oil tank and the corrugated fin material, and D represents the crack length of the oil tank and the corrugated fin material.

3. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 2, characterized in that: The fuel tank and wave fin materials are deformed bodies of arbitrary shapes under force, and their tiny volume elements d x d y d z In the paper, based on the three major variables of displacement, strain and stress, the equilibrium equation, geometric equation and elastic constitutive equation are established. The finite element method is used to discretize the equations and then solve them to obtain the stress and strain of all the integral points in the unit.

4. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 3, characterized in that: The balanced equation is as follows: Where σ xx , σ yy , σ zz They represent the normal stress of the microelement on the plane perpendicular to the X, Y, and Z axes respectively; τ xy , τ yz , τ zx They represent the shear stress along the Y, Z, and X axes on the plane perpendicular to the X, Y, and Z axes of the micro-element respectively; They represent the physical force of the tiny element along the X, Y, and Z axes respectively.

5. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 3, characterized in that: The geometric equation is as follows: Where ε xx , ε yy , ε zz Respectively represent the positive strain of the microelement along the three directions of X, Y, and Z axes; γ xy , γ yz , γ zx They represent the deflection angles of the plane perpendicular to the X, Y, and Z axes toward the Y, Z, and X axes, respectively, and are called engineering shear strain.

6. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 3, characterized in that: The elastic constitutive equation is as follows: Where E, μ, and G represent the elastic modulus, Poisson's ratio, and shear modulus of the material, respectively.

7. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin according to any one of claims 4 to 6, characterized in that: The specific solution process of the finite element method includes the following steps: Structural discretization: When performing numerical calculations using the finite element method, the first step is to discretize the continuous structure into a finite number of units that can be connected to each other through nodes. At the same time, each node and unit is numbered one by one, and the corresponding unit type, node number, physical properties, and node coordinate value information are assigned; Unit characteristic analysis: each discretized unit is regarded as a separate research object, and the relationship between the node force and node displacement is studied to establish the relevant equations; Unit grouping: According to the force balance conditions of the overall structure and the boundary conditions at various locations, the units are regrouped to form the overall finite element equation {F}=[K]}η} Where {F} is the load matrix; [K] is the overall stiffness matrix; {η} is the node displacement matrix of the entire object; Calculate the displacements at unknown nodes: By combining the boundary conditions with the entire system of equations, the general solution of the finite element equations can be solved, thereby deriving the displacements of each node; Calculate the stress and strain occurring in the unit: Based on the solved node result data, the stress and strain of all integration points in the unit can be calculated through the selected interpolation function.

8. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 2, characterized in that: The thermal-mechanical coupling analysis of the distribution transformer oil tank based on the finite element method includes the use of the sequential coupling method to analyze the heat transfer process and the stress process separately. The thermal analysis is performed first, and then the temperature field calculation results obtained by the thermal analysis are applied as thermal loads to the subsequent structural stress analysis. Finally, the thermal analysis results are obtained based on the structural stress analysis.

9. A method for evaluating the oil level regulation capability of a fully sealed distribution transformer oil tank wave fin as claimed in claim 8, characterized in that: Obtain basic data of typical fuel tank and wave fin material welding structures, evaluate the fatigue life of fuel tank and wave fin based on finite element simulation analysis results and basic data of typical fuel tank and wave fin material welding structures, and evaluate and guide the design of fuel tank and wave fin structures from the perspective of weld fatigue life.

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