Extra-high voltage direct current isolation switch thermal characteristic analysis method based on multi-field coupling

Abstract

A multi-field coupling-based thermal characteristic analysis method for an extra-high-voltage direct-current isolating switch comprises the following steps of: 1, establishing a three-dimensional geometric model of a conductive structure of the extra-high-voltage direct-current isolating switch, and simplifying the structure according to a simulation precision requirement; 2, importing the three-dimensional geometric model obtained in the step 1 into simulation software, applying rated current excitation to the conductive structure in the simulation software, and calculating current density distribution in the conductor and Joule thermal power generated by the current density distribution; 3, coupling the thermal power field obtained in the step 2 with a heat conduction field, and constructing an electric-thermal multi-physical field joint simulation model; 4, setting temperature-related physical property parameters and environment boundary conditions of the material, and performing transient thermal analysis to obtain temperature distribution and thermal characteristics of the disconnecting switch in an operation state; through the steps, the thermal characteristic analysis of the extra-high voltage isolation switch based on multi-field coupling is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to the thermal performance evaluation and optimization technology of high-voltage electrical devices of power systems, and specifically relates to a 408kV DC disconnector thermal characteristic analysis method based on COMSOL electro-thermal multi-physical field joint simulation. BACKGROUND

[0002] In an ultra-high voltage DC power transmission system, the disconnector is an important electrical component for realizing system safety isolation and maintenance switching, and its operation reliability is directly related to the stability and safety of the entire power grid. Especially at the 408kV level, the disconnector not only faces higher voltage electric field strength, but also bears greater through-flow current load, thereby causing obvious resistance loss and eddy current loss of the conducting system, and further causing local temperature rise. If this temperature rise exceeds the allowable range of the material, it may not only affect the mechanical strength and contact performance of the device, but also cause arc breakdown, corona discharge, and even fire and other serious consequences.

[0003] Traditional disconnector thermal analysis methods mostly rely on empirical formulas or single thermodynamic qualitative analysis, and do not fully consider the coupling effect between electric field, magnetic field and thermal field, making it difficult to truly reproduce the thermal evolution law of the disconnector under complex operating conditions. With the development of multi-physical field simulation technology, especially the application of COMSOL Multiphysics platform, a new means is provided for the thermal behavior analysis of the disconnector under the coupling conditions of strong electric current, high voltage and complex geometric structure.

[0004] For example, a three-dimensional electromagnetic-thermal coupling model can be established in COMSOL, the current density distribution of the conductor under through-flow state is calculated using the current distribution interface, and the Joule heat power caused by the skin effect, contact resistance, etc. is automatically coupled; the power field is directly loaded as a heat source into the heat conduction module, combined with the heat transfer boundary conditions (including heat conduction, natural convection and radiation), and the temperature rise trend and steady-state response of the key conducting parts can be obtained.

[0005] However, in a DC system, due to the strong continuity of the current and the high voltage level, higher requirements are put forward for the conductor surface treatment, electrical contact performance and insulation structure; at the same time, the setting of boundary conditions (such as convective heat transfer coefficient, surface emissivity) and the simplification of geometric model (such as the omission of bolts and small components) in the simulation process may affect the analysis accuracy. Therefore, the existing methods still have deficiencies in simulation precision, local hot spot identification and result verifiability, and it is still difficult to fully meet the demand of high-precision thermal performance prediction in actual engineering.

[0006] Therefore, it is urgent to propose an electric-thermal multi-physical field coupling analysis method for 408kV high-voltage direct current disconnecting switch, rely on COMSOL multi-physical field simulation platform, combine accurate physical modeling, reasonable structure simplification strategy, fine material parameter setting and experimental verification means, realize the accurate simulation and performance evaluation of the thermal behavior of the main conducting structure of the disconnecting switch under extreme working conditions, so as to provide key support for the research and development, verification and optimization design of high-voltage direct current transmission equipment. SUMMARY

[0007] The present application aims at the technical problem that the existing disconnecting switch thermal analysis method cannot meet the demand of high-precision thermal performance prediction in actual engineering when used in an ultra-high voltage direct current system, because the current continuity is strong, the voltage level is high, the conductor surface treatment, the electrical contact performance and the insulation structure are obviously different, and the setting precision of boundary conditions and the simplification of geometric model are not high in the simulation process, which easily leads to the final analysis precision cannot meet the demand of high-precision thermal performance prediction in actual engineering, and proposes an ultra-high voltage direct current disconnecting switch thermal characteristic analysis method based on multi-field coupling.

[0008] In order to solve the above technical problem, the present application proposes the following technical scheme: An ultra-high voltage direct current disconnecting switch thermal characteristic analysis method based on multi-field coupling, comprising the following steps: Step one: establishing a three-dimensional geometric model of the conducting structure of the ultra-high voltage direct current disconnecting switch, and simplifying the structure according to the simulation precision requirement; Step two: importing the three-dimensional geometric model obtained from step one into the simulation software, and applying rated current excitation to the conducting structure in the simulation software, calculating the current density distribution in the conductor and the joule heat power generated thereby; Step three: directly coupling the joule heat power obtained in step two to the Heat Transfer in Solids interface to establish an electric-thermal multi-physical field joint simulation model, realizing the continuous data transmission between the electric field and the thermal field; Step four: setting the temperature-related physical property parameters of the material and the environmental boundary conditions, performing transient thermal analysis, and obtaining the temperature distribution and thermal characteristics of the disconnecting switch in the running state; Through the above steps, the ultra-high voltage disconnecting switch thermal characteristic analysis based on multi-field coupling is realized.

[0009] In step one, based on the structural characteristics of the 408kV direct current disconnecting switch, a three-dimensional geometric model of the conducting structure is constructed in COMSOL, and non-key components and detailed structures are moderately simplified according to the simulation precision requirement, so as to balance the calculation efficiency and model precision.

[0010] In step one, the three-dimensional geometric model is moderately simplified according to the actual structure and the simulation precision requirement; In the simplification process, parts with less influence on simulation and parts not involved in electric conduction or heat transfer are removed to improve simulation efficiency and reduce the consumption of computing resources.

[0011] The parts with less influence on simulation include bolts, clamps, and fillets, and the parts not involved in electric conduction or heat transfer include insulators and bases.

[0012] In the simplification process, multiple complex parts are combined into a unified body through Boolean operation to reduce the complexity of meshing, and parts with less influence on electric conduction or heat transfer such as insulators and bases are deleted to improve simulation efficiency without affecting the accuracy of thermal simulation.

[0013] In step two, the three-dimensional model is imported into the COMSOL multi-physics simulation platform, a direct current or alternating current excitation of 8000 A is applied under the Electric Currents physical field interface, and the current density distribution and Joule heat power field inside the conductive structure are solved based on the Maxwell equation set; When using the COMSOL multi-physics simulation platform, the open domain problem is handled by reasonably setting the simulation domain and boundary conditions, and the current density, power loss, and electric field distribution are extracted to identify the local heating area and hot spot position of the conductive system under the action of the rated current, thereby providing accurate heat source input data for subsequent thermal field simulation.

[0014] In step two, the electric field control equation is established based on the Maxwell equation set, the variable separation is realized by introducing the vector magnetic potential and scalar electric potential, and the Joule heat power density is calculated through the coupling relationship between the current density and the electric field as the heat source input for thermal field analysis; (1) Obtain the relationship between the electric field analysis and control equation: (1); In the formula, D is the electric flux density (C / m 2 ); C / m 3 ) is the charge density; H is the magnetic field intensity (A / m); is the vector differential operator; is the divergence operator, which represents the outflow degree of a field at a point; is the curl operator, which represents the "rotation" property of the field; represents the rate of change of the magnetic field with time, represents the displacement current density, which reflects the virtual current generated by the changing electric field; In order to facilitate solving, the above partial differential equation is transformed into two independent equations of electric field and magnetic field through the separation of variables method; two quantities are defined to realize variable separation, which are the vector magnetic potential A and the scalar electric potential φ, defined as follows: (2); where B is the magnetic induction (T); E is the electric field intensity (V / m); is the magnetic vector potential (Wb / m), which describes a potential of the magnetic field; is the electric potential function (V); in a homogeneous medium, the following relationship exists: (3); where is the permittivity (F / m), is the permeability (H / m), is the permeability (S / m), is the displacement current density (A / m 2 ); Thus, the electric field and the magnetic field can be expressed separately, and the electric field control equation applicable to the direct current steady state condition is obtained, as shown in equation (4); equation (3) is brought into equation (1) for derivation, and the magnetic field partial differential equation and the electric field partial differential equation are obtained, as shown in equation (4): (4); (5); This set of equations reveals the propagation law of electromagnetic waves in a medium, where is the Laplace operator, represents a current source, represents a voltage source; the three second-order partial derivative terms represent the rate of change of temperature, electric potential or electric field in the x, y and z spatial directions, respectively; The boundary condition of the three-dimensional electric field is: (6); where Γ1 is the Dirichlet boundary, g(Γ1) is a position function, Γ2 is the Neumann boundary, g(Γ2) and are general functions, n is the outward normal vector of the boundary Γ2; The eddy current field of the high-voltage disconnector can be expressed as: (7); When the conductive system of the high-voltage disconnector is in a through-flow state, the energy loss of the disconnector is: (8); where q is the energy loss, σ is the electrical conductivity; Formula (8) is the solution equation of the eddy current field in the on-state of the disconnector, which also includes current loss and eddy current loss, and the calculation result is the heat source load of the temperature field; the above equation reveals the quantitative relationship between conductor energy loss and current density, conductivity, providing a basis for subsequent joule heat power calculation; For the DC disconnector contact and the contact finger, the two are tightly connected through a certain assembly relationship. According to the derivation of the above formula (4), when the current flows through the two, the corresponding resistance heat is generated, which exchanges heat through the surrounding air to form the corresponding temperature field. According to the relevant theoretical knowledge of heat exchange, the current density field is derived from the potential, and the heat source Establish a connection: (9); In the formula: J is the current density, σ is the conductivity, E is the electric field strength, V is the potential; The joule heat power density formula is as follows: (10); P is the joule heat power density (W / m³), which represents the heat generated per unit volume per unit time; J is the current density vector (A / m²), which represents the distribution of current in the conductor; E is the electric field strength vector (V / m); σ is the conductivity of the material (S / m), that is, the material's ability to conduct electricity; E is the square of the electric field strength, representing the electric field energy density; Expression (10) realizes the physical coupling between electricity and joule heat, providing a basic step for subsequent joint solution of electric-thermal multi-field.

[0015] In step four, the temperature-related material property parameters and convective, radiative and other thermal boundary conditions are set, and transient thermal analysis is performed to obtain the temperature distribution and evolution law of the key parts of the disconnector.

[0016] In step three, the current density distribution is directly coupled with the heat conduction equation, and the joint solution of electric-thermal multi-physical field is realized in the COMSOL multi-physical field simulation platform; The specific method is: in the electric-thermal multi-physical field joint simulation model, the current distribution and heat conduction physical field interface are called, the joule heat power is input as the heat source load, the time step, the material temperature-related parameters and the boundary heat exchange conditions are set, and the temperature rise extreme value and its variation law with time of the key parts of the disconnector (including the moving and static contacts, the connecting part of the conductive rod, etc.) are obtained, so as to realize the accurate evaluation of the thermal stability of the disconnector in the operation process.

[0017] In step three, the obtained electric-thermal multi-physical field joint simulation model is specifically: (18); Formula (18) is a thermal model of the conductive part of the 408 kV high-voltage disconnector established based on the heat conduction mechanism; wherein is the conductor temperature (°C or K), is the air environment temperature; is the material density, is the specific heat capacity; , , , are the thermal conductivity coefficients in each direction, reflecting the anisotropic thermal conduction performance of the material; is the convective heat transfer coefficient (h) , used to characterize the convective heat transfer strength between the surface and the air; is a specified heat flow boundary function, defining the known heat flux density boundary on the surface ; is the temperature gradient along the normal direction; is the internal heat generation term (Q) , usually generated by the conductor carrying current.

[0018] Compared with the prior art, the present application has the following technical effects: 1) The present application comprehensively considers the through-flow current, electromagnetic eddy current effect, contact resistance effect and convection and radiation and other heat dissipation boundary conditions borne by the conductive structure in actual operation, constructs an electric-thermal multi-physical field joint simulation model in the COMSOL multi-physical field simulation platform, realizes joint analysis of the temperature field and thermal behavior of the disconnector under high-voltage and large-current through-flow operating conditions, and thus provides accurate data support and theoretical basis for thermal stability design, structure optimization and overheating fault warning of the disconnector; 2) The present application solves the problems of insufficient simulation accuracy, rough model simplification, disconnection between heat source input and electromagnetic distribution and large deviation between simulation and test in the existing disconnector thermal analysis process. By constructing a three-dimensional simulation model of the main conductive system of the high-voltage disconnector on the COMSOL multi-physical field simulation platform, combining joint coupled solution of the electric field and the thermal field, comprehensively analyzing the electric field distribution, current density and temperature evolution process of the disconnector under through-flow operating state, and realizing high-precision qualitative and quantitative prediction of its thermal stability performance; 3) The present application can accurately simulate the current density distribution, power loss and temperature evolution process of the 408 kV DC disconnector under large-current operation by constructing an electric-thermal multi-physical field joint simulation model; 4) Compared with the traditional single thermal analysis method, the method significantly improves the accuracy and engineering applicability of the simulation results, and can effectively identify the high-temperature risk area of the key position, providing a scientific basis for the structural optimization design and safe operation of the disconnecting switch. BRIEF DESCRIPTION OF DRAWINGS

[0019] The application will be further described below in combination with the drawings and examples: Figure 1 is a specific step flow chart of the application; Figure 2 is a 408KV DC disconnecting switch model diagram; Figure 3 is a simplified model diagram of the main conducting system; Figure 4 is a mesh division diagram; Figure 5 is a solution domain setting diagram; Figure 6 is a disconnecting switch through-flow potential distribution diagram; Figure 7 is a disconnecting switch current density distribution diagram; Figure 8 is a disconnecting switch electric field mode distribution diagram; Figure 9 is a disconnecting switch temperature rise simulation distribution diagram; Figure 10 is a disconnecting switch contact temperature rise simulation distribution diagram. DETAILED DESCRIPTION

[0020] A 408kV DC disconnecting switch thermal characteristic analysis method based on multi-field coupling, comprising the following steps: Step one: based on the structural characteristics of the 408kV DC disconnecting switch, a three-dimensional geometric model of the conducting structure is constructed in COMSOL, and non-key components and detailed structures are moderately simplified according to the simulation accuracy requirements, so as to balance the calculation efficiency and model accuracy; Step two: apply 8000A rated current excitation to the conducting structure in the Electric Currents interface, solve the current density distribution and Joule heat power field inside the conductor based on the Maxwell equation set, and consider the influence of contact resistance and skin effect on local current distribution; Step three: directly couple the Joule heat power field obtained in step two to the Heat Transfer in Solids interface to establish an electric-thermal multi-physical field joint simulation model, and realize continuous data transmission between the electric field and the thermal field; Step four: set the temperature-related material property parameters and heat boundary conditions such as convection and radiation, perform transient thermal analysis, and obtain the temperature distribution and evolution law of the key position of the disconnecting switch; Through the above steps, the application realizes high-precision analysis of the thermal characteristics of the 408kV DC disconnecting switch based on electro-thermal multi-physical field coupling, can effectively identify the overheating area, and provides reliable basis for structural optimization and thermal stability evaluation.

[0021] In step one, a three-dimensional geometric model of the main conductive system of the 408kV high-voltage disconnecting switch is constructed, and the model is appropriately simplified according to the actual structure and simulation accuracy requirements. In the simplification process, components with less influence on simulation (such as bolts, clamps, fillets, etc.) and components not participating in conduction or heat transfer (such as insulators, bases) are removed to improve simulation efficiency and reduce computing resource consumption. In the process of geometric modeling and simplification, multiple complex components are combined into a unified body through Boolean operation to reduce the complexity of meshing; at the same time, components such as insulators, bases and other structures with little effect on electricity or heat are deleted to improve simulation efficiency without affecting the accuracy of thermal simulation.

[0022] Table 1: Material parameters of disconnecting switch

[0023] In step two, the above three-dimensional model is imported into the COMSOL multi-physical field simulation platform, a 8000A DC current excitation is applied under the Electric Currents physical field interface, and the current density distribution and Joule heat power field inside the conductive structure are solved based on Maxwell's equations; characterized in that: COMSOL three-dimensional electric field simulation module is used for modeling and calculation, the open domain problem is handled by reasonably setting the simulation domain and boundary conditions, and the current density, power loss and electric field distribution are extracted to identify the local heating area and hot spot position of the conductive system under the action of the rated current, thereby providing accurate heat source input data for subsequent thermal field simulation.

[0024] The theoretical basis of the application and the software COMSOL is based on Maxwell's equations, and the control equation for three-dimensional electric field analysis of the disconnecting switch is as follows: (1) Obtain the relationship between electric field analysis and control equation: (1); In the formula, D is the electric flux density (C / m 2 ); H is the magnetic field intensity (A / m); is a vector differential operator; is a divergence operator, which represents the outflow degree of a field at a point; is a curl operator, which represents the "rotation" property of the field; represents the rate of change of the magnetic field with time, represents the displacement current density, which reflects the virtual current generated by the changing electric field; To facilitate the solution, the above partial partial equation is transformed into two independent equations for the electric field and the magnetic field using the method of separation of variables. Two quantities are defined to achieve the separation of variables: the vector magnetic potential A and the scalar electric potential φ, as follows: (2); In the formula, B is the magnetic flux density (T); E is the electric field strength (V / m). Wb / m is the magnetic vector potential, a potential that describes a magnetic field. Let V be the potential function. In a homogeneous medium, the following relationship holds: (3); In the formula, is the dielectric constant (F / m). ρ is the magnetic permeability (H / m). ρ is the magnetic permeability (S / m). Displacement current density (A / m) 2 ); Thus, the electric field and magnetic field can be expressed separately, and the electric field control equation applicable to DC steady-state conditions can be obtained, as shown in equation (4). Substituting equation (3) into equation (1) for derivation, the partial differential equations of the magnetic field and the electric field can be obtained, as shown in equation (4): (4); (5); This set of equations reveals the propagation law of electromagnetic waves in a medium, where, For the Laplace operator, Indicates a current source. This represents a voltage source; the three second-order partial derivative terms represent the rates of change of temperature, potential, or electric field in the three spatial directions of x, y, and z, respectively. The boundary conditions for a three-dimensional electric field are: (6); In the formula, Γ1 is the Dirichlet boundary, g(Γ1) is the position function, Γ2 is the Neumann boundary, and g(Γ2) and It is a general function. n Let Γ2 be the outward normal vector of the boundary.

[0025] The eddy current field of a high-voltage disconnector can be expressed as: (7); When the conductive system of a high-voltage disconnector is in a current-carrying state, the energy loss of the disconnector is as follows: (8); In the formula, q For energy loss,σ for conductivity; Equation (8) is the solution equation of the eddy current field in the on-state of the disconnector, which also includes current loss and eddy current loss, and the calculation result is the heat source load of the temperature field. The above equation reveals the quantitative relationship between conductor energy loss and current density, conductivity, providing a basis for subsequent joule heat power calculation.

[0026] For DC disconnector contacts and contact fingers, they are tightly connected through a certain assembly relationship. According to the above formula derivation, when current flows through them, corresponding resistance heat is generated, which exchanges heat through the surrounding air to form a corresponding temperature field. According to the relevant theoretical knowledge of heat exchange, the current density field is derived from the electric potential, and the heat source Establish a connection: (9); In the formula: is the current density, is the conductivity, is the electric field strength, is the electric potential; The joule heat power density formula is as follows: (10); is the joule heat power density (W / m³), which represents the heat generated per unit volume per unit time; is the current density vector (A / m²), which represents the distribution of current in the conductor; is the electric field strength vector (V / m); is the conductivity of the material (S / m), i.e. the material's ability to conduct electricity; is the square of the electric field strength, representing the electric field energy density.

[0027] The above expression realizes the physical coupling between electricity and joule heat, providing a theoretical basis for subsequent joint solution of electricity-heat multi-field.

[0028] In step three, the current density distribution is directly coupled with the heat conduction equation, and the joint solution of the electricity-heat field is realized in the COMSOL multi-physical field simulation platform; In the same model, the current distribution and the thermal conduction physical field interface are called, the joule heat power is automatically input as the heat source load, the time step, the material temperature related parameters and the boundary heat exchange conditions are set, and the temperature rise extreme value of the disconnector key parts (including the moving and static contacts, the connecting part of the conductive rod, etc.) and its variation with time are obtained, so as to realize the accurate evaluation of the thermal stability of the disconnector in the operation process.

[0029] The basic theory of temperature field analysis is the three laws of thermodynamics, for thermal analysis problem, the energy conservation law is suitable for any form of energy, according to the second law of thermodynamics, heat is always transferred from the object with higher temperature to the surrounding medium or the object with lower temperature, and the process of heat transfer is irreversible.

[0030] The temperature field is the collection of instantaneous temperatures of each point in the object, which is the function of time and spatial coordinates, and the corresponding mathematical expression of three-dimensional transient temperature field in the application is: (11); In the formula, (x, y, Z) is a spatial Cartesian coordinate.

[0031] There are generally three ways of heat transfer: heat conduction, heat convection and heat radiation, the empirical formula is derived by considering the three forms of heat transfer, and the following is the explanation of the heat conduction formula of the application: (1) heat conduction: The phenomenon that heat of a high-temperature object is transferred to a low-temperature object is called heat conduction, and the analysis of the process can be calculated according to Fourier's law: (12); In the formula, is the heat flow density (w / m2) under heat conduction, and Φ is the heat size, S is the unit area.

[0032] (2) heat convection: Heat convection is the phenomenon of heat transfer due to the mixing of cold and hot fluids, and there are two heat transfer modes: natural convection and forced convection.

[0033] When heat convection is analyzed, the Newton cooling equation is satisfied: (13); In the formula, is the heat transfer coefficient of heat convection; is the convection heat transfer coefficient, T s , and T b are the temperatures of the solid and the fluid respectively.

[0034] (3) heat radiation: Heat radiation is the phenomenon that the object generates radiation energy due to heating, and itself can transfer heat to another system through electromagnetic radiation without medium. The higher the temperature of the object itself, the stronger the generated radiation energy.

[0035] The radiation heat exchange between objects can be represented by Stefan-Boltzman law: (14); In the formula, The heat transfer coefficient is the coefficient of thermal radiation. ε Grayscale coefficient; This is the Stefan–Boltzmann constant, and its value is... , which is the fundamental constant of radiative heat transfer; , These represent the absolute temperatures (in K) of two mutually radiating surfaces. The radiative heat transfer is proportional to the fourth power difference between the temperatures of the two surfaces.

[0036] Fourier's law, also known as the fundamental law of heat conduction, is generally expressed as: (15); In the formula, This is the heat flux density vector (W / m²), representing the rate of heat transfer per unit area; λ Thermal conductivity (W / (m℃)); t The absolute temperature is (K). It represents the unit length in the tangential direction of heat transfer; This represents the unit normal vector. Since heat energy always flows from the hotter object to the colder object during heat conduction, a negative sign is needed.

[0037] Based on the above equation, establish the corresponding heat flux density vector in the three-dimensional temperature field: (16); Equation (14) is an extended form of Fourier's law in three-dimensional space, where For temperature gradient operators, These are unit vectors in the x, y, and z directions, respectively. Let be the rate of temperature change in each direction. This formula characterizes the way heat diffuses along the temperature gradient in a three-dimensional temperature field.

[0038] The thermal differential equation for the disconnector switch is: (17); Equation (15) is the unsteady-state heat conduction differential equation, where Material density ( ), Specific heat capacity ( ), For time (s) The volumetric internal heat power density ( The term , typically representing the Joule heat generated by an electric current passing through a conductor, is shown. The three terms on the right-hand side of the equation represent the heat conduction contributions in the x, y, and z directions, respectively, reflecting the dynamic changes in temperature over space and time.

[0039] According to the heat transfer principle, the electric-thermal multi-physical field joint simulation model of the 408KV high-voltage disconnecting switch in the application is: (18); Formula (18) is a thermal model of the conductive part of the 408KV high-voltage disconnecting switch established based on the heat conduction mechanism: wherein is the conductor temperature (°C or K), is the air environment temperature; is the material density, is the specific heat capacity; , , , respectively, are the thermal conductivity coefficients in each direction, reflecting the anisotropic thermal conduction performance of the material; is the convective heat transfer coefficient (h), for characterizing the convective heat transfer strength between the surface and the air; is the specified heat flow boundary function, defined on the known heat flux density boundary of the surface ; is the temperature gradient along the normal direction; is the internal heat generation term (Q), usually generated by the conductor carrying current.

[0040] Embodiment: In order to further illustrate the technical scheme of the patent, the specific embodiments of the high-voltage disconnecting switch main conductive system temperature rise simulation analysis method described in the patent will be described below in combination with the drawings.

[0041] In this example, the actual 408KV DC disconnecting switch model of a certain manufacturer is used, and the model structure diagram is shown in Figure 1 , and the model is simplified 1. Model and pre-processing; In order to ensure the feasibility of the simulation calculation, the three-dimensional model is reasonably simplified under the premise of not affecting the accuracy of the thermal field analysis: (1) Ignore the insulator structure (insulator does not flow and is an insulator, which has little effect on temperature rise); (2) Ignore the base structure (the base does not flow and has little effect on temperature rise); (3) The simplified main conductive system model is shown in the attached Figure 2 .

[0042] The material parameters thereof are shown in the following table: Table 1: disconnecting switch material parameters

[0043] Table 2: disconnecting switch material physical parameters

[0044] 2. Solution domain setting; Since both electric field analysis and thermal field analysis belong to open domain problems, a solution domain needs to be constructed outside the isolator model. The boundary distance of the solution domain should be set at least 3-5 times the distance from the device center to the farthest point, so as to achieve a balance between calculation amount and accuracy. A schematic diagram of the solution domain is shown in FIG. 2. Figure 3

[0045] 3. Boundary conditions and excitation loading; In the simulation calculation, a DC current of 8000 A is applied to the left terminal block of the model, the right terminal block is used as the outflow end, and the remaining surfaces are set as convective and radiative coupling boundaries.

[0046] 4. Result analysis; The simulation results show that when the 408 kV DC isolator is operated under the excitation of a rated current of 8000 A, the electric field intensity inside the conductive structure is generally low and uniformly distributed, with a maximum value of only about 0.157 kV / m. As shown in the electric field mode distribution diagram, the electric field is mainly concentrated at the connection between the conductive tube and the support structure and the transition zone of the contact, and there is a slight electric field concentration phenomenon in the local area. This distribution pattern shows that the electrical gap design of the device under high current flow conditions is reasonable and has good electric field uniformity; the local electric field enhancement is mainly related to the structural corner, current contraction effect and contact resistance, which indicates that this area is a potential breakdown and heat accumulation risk point.

[0047] The potential distribution results further reveal the electric energy transmission law of the conductive path. The potential decreases linearly along the conductive system from the input end to the output end, and the overall trend is continuous and smooth, which conforms to the basic law under DC current flow. In the moving and static contact and the connection clamping area, the potential contour is significantly dense, indicating that the potential gradient at these positions is large, and there is a local current density concentration phenomenon, which is highly consistent with the electric field distribution characteristics. Therefore, the contact area of the contact is the main energy loss and Joule heat generation area, which provides a physical basis for subsequent thermal field analysis.

[0048] In the thermal field analysis, the temperature distribution of the conductive tube main body is uniform, and the overall temperature is maintained at 30-40°C, indicating that the overall heat dissipation performance of the system is good. In the connection between the moving and static contacts and the transition area of the conductive tube and the support structure, the temperature increases significantly, reaching a maximum of 50.8°C, forming a typical hot spot distribution area. The local enlargement result shows that the heat is mainly generated by the contact resistance and the Joule heat caused by the current contraction, and gradually diffuses along the axial direction to the heat dissipation components. In summary, the electric field, potential and temperature distributions have good physical consistency, proving that the established electric-thermal multi-physical field coupling model accurately reflects the electromagnetic and thermal behavior of the isolator under high voltage and large current operation, providing a reliable basis for structure optimization and thermal stability design.​

[0049] In summary, the multi-field coupling simulation results of the UHV DC disconnector under 8000 A excitation condition are reasonable. The overall low electric field distribution indicates that the insulation design is sufficient. The potential distribution and local electric field concentration reflect that the contact connection area is the typical site of current constriction and resistance concentration. The meshing ensures the simulation accuracy. The temperature rise distribution verifies that the contact and connection area are the heat spots. This series of results confirm each other, showing the physical reasonableness of the simulation. It is worth noting that although the overall temperature rise is not too high, the local hot spot is close to 50℃. In the actual operating environment, if the external climatic factors and long-term electrical aging effects are superimposed, overheating problems may still occur. Therefore, the subsequent research should focus on the optimization of contact structure, the improvement of conductive materials and the heat dissipation measures to improve the long-term operation reliability of the disconnector in UHV DC transmission projects. In summary, the COMSOL-based electro-magnetic-thermal multi-field coupling simulation effectively reveals the electric field distortion, current constriction and temperature rise evolution law of the 408 kV DC disconnector under large current conditions. The research results not only verify the physical consistency of the hot spot area, but also provide a theoretical basis for structure optimization and insulation design. In the follow-up work, the geometric transition form of the contact and conductive connection part can be further optimized to improve the heat conduction channel and surface convective heat dissipation capacity, thereby further reducing the local temperature rise and enhancing the operation reliability and life of the equipment in the high voltage and large current environment.

Claims

1. A method for analyzing thermal characteristics of an ultra-high voltage direct current disconnector based on multi-field coupling, characterized in that, The method comprises the following steps: Step one: establishing a three-dimensional geometric model of the conductive structure of the UHV DC disconnector, and simplifying the structure according to the simulation accuracy requirement; Step two: importing the three-dimensional geometric model obtained from step one into a simulation software, and applying a rated current excitation to the conductive structure in the simulation software to calculate the current density distribution inside the conductor and the Joule heat power generated thereby; Step three: directly coupling the Joule heat power obtained in step two to a heat conduction interface to establish an electro-thermal multi-physical field joint simulation model, and realizing continuous data transmission between the electric field and the thermal field; Step four: setting the temperature-related physical property parameters of the material and the environmental boundary conditions, and performing transient thermal analysis to obtain the temperature distribution and thermal characteristics of the disconnector in the operating state. Through the above steps, the thermal characteristic analysis of the UHV disconnector based on multi-field coupling is realized.

2. The method of claim 1, wherein, In step one, the UHV DC disconnector is a 408kV DC disconnector, and a three-dimensional geometric model of the conductive structure is constructed in COMSOL based on the structural characteristics of the 408kV DC disconnector, and non-key components and detailed structures are moderately simplified according to the simulation accuracy requirement, so as to balance the calculation efficiency and the model accuracy.

3. The method of claim 2, wherein, In step one, the three-dimensional geometric model is moderately simplified according to the actual structure and the simulation accuracy requirement; In the simplification process, components with less influence on simulation and components not participating in conduction or heat transfer are removed to improve the simulation efficiency and reduce the consumption of calculation resources.

4. The method of claim 3, wherein, The components with less influence on simulation include bolts, clamps and fillets, and the components not participating in conduction or heat transfer include insulators and bases.

5. The method of claim 3, wherein, In the simplification process, multiple complex components are merged into a unified body through Boolean operation to reduce the grid division complexity, and components such as insulators and bases with less influence on electricity or heat are deleted to improve the simulation efficiency without affecting the accuracy of thermal simulation.

6. The method of claim 1, wherein, In step two, the three-dimensional model is imported into the COMSOL multi-physical field simulation platform, a 8000A DC or AC current excitation is applied under the current distribution physical field interface, and the current density distribution inside the conductive structure and the Joule heat power field are solved based on the Maxwell equation set; When using the COMSOL multi-physical field simulation platform, the simulation domain and boundary conditions are reasonably set to handle the open domain problem, and the current density, power loss and electric field distribution are extracted to identify the local heating area and hot spot position of the conductive system under the action of the rated current, thereby providing accurate heat source input data for subsequent thermal field simulation.

7. The method according to one of claims 1 to 6, characterized in that, In step two, the electric field control equation is established based on the Maxwell equation set, the variable separation is realized by introducing the vector magnetic potential and the scalar electric potential, the Joule heat power density is calculated through the coupling relationship between the current density and the electric field, and the Joule heat power density is used as the heat source input for thermal field analysis; the specific expression is as follows: (1) the relationship between the electric field analysis and the control equation is obtained: （1）； where D is the electric flux density; is the charge density; H is the magnetic field strength; is the vector differential operator; is the divergence operator, indicating the outflow of a field at a point; is the curl operator, indicating the "twisting" nature of a field; represents the rate of change of the magnetic field with time, represents the displacement current density, reflecting the fictitious current produced by a changing electric field; In order to facilitate the solution, the above partial differential equation is converted into two independent equations of electric field and magnetic field through the separation of variables; two quantities are defined to realize the variable separation, which are the vector magnetic potential A and the scalar electric potential φ, and are defined as follows: （2）； where B is the magnetic induction; E is the electric field intensity; is the magnetic vector potential, a potential describing the magnetic field; is the electric potential function; in a homogeneous medium, the following relationship holds: （3）； wherein is the dielectric constant, is the magnetic permeability, is the magnetic permeability, is the displacement current density; Thus the electric field and magnetic field can be separated, and the electric field control equation under the condition of direct current steady state can be obtained, as shown in equation (4); equation (3) is substituted into equation (1) to obtain the partial differential equation of the magnetic field and the electric field, as shown in equation (4): （4）； （5）； This set of equations reveals the propagation law of electromagnetic wave in medium, where, is the Laplace operator, represents the current source, represents the voltage source; the three second-order partial derivatives represent the rate of change of temperature, electric potential or electric field in the x, y, z spatial directions, respectively; The boundary condition of three-dimensional electric field is: （6）； where Γ1 is the Dirichlet boundary, g(Γ1) is the position function, Γ2 is the Neumann boundary, g(Γ2) and are general functions, n is the outward normal vector to the boundary Γ2; The eddy current field of high-voltage disconnecting switch can be expressed as: （7）； When the conductive system of high-voltage disconnecting switch is in the on-flow state, the energy loss of the disconnecting switch is: （8）； wherein q is the energy loss, σ is the electrical conductivity; Equation (8) is the solution equation of the eddy current field of the disconnecting switch in the on-flow state, which also includes the current loss and the eddy current loss, and the calculation result is the heat source load of the temperature field; Equation (8) reveals the quantitative relationship between the energy loss of the conductor and the current density and the conductivity, which provides a basis for subsequent calculation of joule heat power; For the DC disconnector contact and the contact finger, they are connected closely through certain assembly relationship. According to the derivation of formula (7) and formula (8), when the current flows through them, the corresponding resistance heat is generated, which exchanges heat through the surrounding air to form the corresponding temperature field. According to the relevant theoretical knowledge of heat exchange, the current density field is derived from the electric potential, and the temperature field is derived from the heat source Establish a connection: （9）； wherein: is the current density, is the electrical conductivity, is the electric field strength, is the electric potential; The formula of joule heat power density is as follows: （10）； J is the Joule heat power density, representing the heat generated per unit volume per unit time; J is the Joule heat power density, representing the heat generated per unit volume per unit time; E is the electric field strength vector; σ is the electrical conductivity of the material, i.e. the material's ability to conduct electricity; E2is the square of the electric field strength, representing the electric field energy density; Expression (10) realizes the physical coupling between electricity and joule heat, which provides a basic step for subsequent joint solution of electric-thermal multi-field.

8. The method of claim 1, wherein, In step four, the temperature-related physical parameters of the material and the heat boundary conditions such as convection and radiation are set, and transient thermal analysis is performed to obtain the temperature distribution and evolution law of the key parts of the disconnecting switch.

9. The method of claim 7, wherein, In step three, the current density distribution is directly coupled with the heat conduction equation, and the joint solution of electric-thermal multi-physical field is realized in the COMSOL multi-physical field simulation platform; The specific method is: in the electric-thermal multi-physical field joint simulation model, the current distribution and the heat conduction physical field interface are called, the joule heat power is input as the heat source load, the time step, the temperature-related parameters of the material and the boundary heat exchange conditions are set, and the temperature rise extreme value and its variation law with time of the key parts of the disconnecting switch are obtained, so as to realize the accurate evaluation of the thermal stability of the disconnecting switch in the operation process.

10. The method according to claim 1 or 8 or 9, characterized in that, In step three, the obtained electric-thermal multi-physical field joint simulation model is as follows: （18）； Equation (18) is the thermal model of the 408 kV high-voltage disconnecting switch conductive component based on the heat conduction mechanism; where is the conductor temperature, is the air ambient temperature; is the material density, is the specific heat capacity; , , , are the thermal conductivities in each direction, reflecting the anisotropic thermal conduction performance of the material; is the convective heat transfer coefficient, used to characterize the convective heat transfer intensity between the surface and the air; is the specified heat flux boundary function, defined on the surface with a known heat flux density boundary; is the temperature gradient along the normal direction; is the internal heat generation term, usually generated by the conductor carrying current.

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