500kV power cable finite element modeling and conductor temperature simulation method

Abstract

The invention relates to the technical field of power systems, in particular to a 500kV power cable finite element modeling and conductor temperature simulation method. Comprising the steps that firstly, finite element software is used for producing a 500kV power cable geometric model according to data information; secondly, setting corresponding environment boundary conditions and electromagnetic boundary conditions according to different cable laying environments; for a buried type, a multi-layer soil model is established; according to the model, heat convection boundaries and heat conduction boundaries can be set for different sublayer soil models, so that buried boundary conditions are formed; for an overhead type, environment data of different overhead heights are collected and analyzed, and overhead type boundary conditions are set through radiation influence and heat conduction effect; electromagnetic boundary conditions realize setting of an electric field and a magnetic field according to a cable contact medium; and finally, carrying out grid optimization on the key area of the cable through a grid optimization method. According to the method, accurate simulation of the conductor temperature is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a 500kV power cable finite element modeling and conductor temperature simulation method. Background Art

[0002] Power cable is a type of cable used for power transmission and distribution, and is widely used in power networks, industrial construction, buildings, etc. Power cables can be divided according to different voltage levels, including: low-voltage cables for household power transmission; medium-voltage cables are commonly used in distribution networks; high-voltage cables are used for high-voltage power transmission and power transmission between substations; and ultra-high-voltage cables are used for ultra-high-voltage transmission lines, such as 500kV transmission systems.

[0003] 500kV power cable is a type of cable used for ultra-high voltage power transmission, mainly used for long-distance, large-capacity power transmission; the cable structure includes: the conductor usually uses copper or aluminum, the insulation layer usually uses cross-linked polyethylene (XLPE) as the insulation material, which has excellent electrical properties, heat resistance and chemical stability, the shielding layer uses a metal shielding layer, such as copper foil, aluminum foil or woven metal mesh, which is used to reduce electromagnetic interference and prevent the cable from leaking electromagnetic waves, and the protective sheath uses corrosion-resistant and wear-resistant sheath materials, such as polyvinyl chloride (PVC) or polyethylene (PE), to protect the cable from mechanical damage and environmental influences.

[0004] 500kV power cables can adapt to various environmental conditions, such as underground, overhead, high humidity or extreme environments, to ensure long-term stable operation. Therefore, in order to ensure that 500kV power cables can still maintain good performance under various environmental conditions, it is necessary to effectively detect 500kV power cables; during the detection process, determining the cable conductor temperature is a very important aspect for monitoring cable operation. If the temperature of the conductor exceeds the specified standard maximum temperature, it will cause the aging of the insulation material to accelerate, shorten the life of the cable, be detrimental to power transmission, and more likely to cause major safety failures. The temperature of wires and cables is generally detected by using sensing equipment to obtain the temperature of the conductor. However, due to the complex location of the cable laying, it is impossible to accurately collect the temperature data of the cable only through sensing equipment.

[0005] In order to obtain the temperature of 500kV power cables, cable modeling is now implemented through finite element modeling, and conductor temperature simulation experiments are carried out. Among them, finite element modeling, as an engineering analysis method, is widely used to simulate the behavior of complex structures and systems. In the field of power cables, finite element modeling is used to analyze and optimize the structure, electric field distribution, thermal distribution and mechanical stress of cables. However, in the process of simulating the conductor temperature of 500kV power cables using the finite element method, most existing technologies do not pay much attention to the actual laying environment of 500kV power cables, resulting in a large difference between the conductor temperature in the simulation process and the actual application, and it is impossible to achieve accurate simulation of the conductor temperature of 500kV power cables.

[0006] To this end, the present invention proposes a 500kV power cable finite element modeling and conductor temperature simulation method. Summary of the invention

[0007] The purpose of the present invention is to provide a 500kV power cable finite element modeling and conductor temperature simulation method to achieve finite element modeling and temperature simulation of 500kV power cables; mainly from the following points, firstly, the invention collects relevant data of 500kV power cables and uses finite element models to establish a 500kV power cable geometric model; secondly, in order to achieve a true simulation of the conductor temperature of the 500kV power cable, the 500kV power cable geometric model is loaded with environmental boundary conditions and electromagnetic boundary conditions; wherein. The setting of environmental boundary conditions is divided into buried type and overhead type according to the laying environment of the cable in actual circumstances; in the buried type, the soil thermal convection boundary conditions and soil thermal conduction boundary conditions are set by layered modeling of the soil; in the overhead type, the environmental change, radiation and heat conduction conditions are obtained by analyzing the actual overhead environment; in order to obtain accurate conductor temperature distribution; finally, the 500kV power cable geometric model is visualized by inputting current parameters. Temperature distribution display; in addition, a meshing method is also used to divide the model area in the 500kV power cable geometric model.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A 500kV power cable finite element modeling and conductor temperature simulation method, the specific steps include:

[0010] Step 1: Obtain relevant data of the 500kV power cable through data information; wherein the relevant data includes: cable structure (material type and composition of conductor, insulation layer, shielding layer and sheath layer), geometric dimensions (conductor outer diameter information, insulation layer thickness information, shielding layer thickness information and protective sheath thickness information), cable length and layout.

[0011] Step 2: Process the relevant data to obtain standard finite element modeling data; wherein the data processing includes: checking whether there are data errors in the relevant data; when errors occur in the relevant data, correcting them according to the standard parameters of the 500kV power cable to obtain corrected relevant data; converting the corrected relevant data according to the data input format of the finite element software to obtain the standard finite element modeling data.

[0012] Step 3: Input the standard finite element modeling data into the finite element software to generate a 500kV power cable geometric model;

[0013] Step 4: Loading the material properties of the 500 kV power cable;

[0014] Step 5: setting boundary conditions according to the working environment of the 500 kV power cable; wherein the boundary conditions include: environmental boundary conditions and electromagnetic boundary conditions; wherein the working environment is obtained according to the arrangement form in the relevant data, including: buried type and overhead type;

[0015] The setting process of the buried boundary condition is as follows:

[0016] The physical and thermodynamic parameters of the buried soil are collated as soil attribute parameters;

[0017] Further, a multi-layer soil model is established using the soil property parameters;

[0018] Further, defining soil characteristics of each layer for the multi-layer soil model, and setting thickness and depth distribution;

[0019] Further, a background temperature is set for the multi-layer soil model according to historical data of soil area monitoring, and the background temperature is adaptively adjusted according to a temperature change curve;

[0020] Further, setting the heat flux density of the buried area of ​​the 500 kV power cable in the multi-layer soil model;

[0021] Furthermore, soil thermal convection boundary conditions and soil thermal conduction boundary conditions are defined respectively; wherein. The soil thermal convection boundary condition definition process includes: obtaining soil environmental data and soil characteristic data; wherein, the soil environmental data includes: temperature and humidity; the soil characteristic data includes: porosity and humidity unit time growth rate; the soil environmental data, the soil characteristic data and the soil convection direction are input into the soil thermal convection model to obtain the soil thermal convection boundary conditions.

[0022] Furthermore, nonlinear effects are introduced to optimize the soil thermal convection boundary conditions and the soil thermal conduction boundary conditions to obtain the buried boundary conditions;

[0023] The process of setting the overhead boundary condition is as follows: collecting overhead environmental data of cable areas at different overhead heights;

[0024] Further, the overhead environment data is input into an environmental analysis model to obtain the law of environmental changes;

[0025] Furthermore, an environmental radiation model is introduced to calculate the radiation impact on the overhead cable; wherein the model function of the environmental radiation model is expressed as:

[0026] I total (x,y,z)=I direct (x,y,z)+I diffuse (x,y,z)+I reflected (x,y,z);

[0027] Among them, I total () represents the radiation impact value; (x, y, z) represents the location of the overhead cable area; I direct () represents direct solar radiation; I diffuse () represents diffuse reflected radiation; I reflected () represents the reflected radiation reflected by the surrounding buildings;

[0028] Further, the heat transfer rates of the overhead cables in different areas are set;

[0029] Furthermore, the environmental change law, the radiation influence and the heat transfer rate are comprehensively modeled to obtain the overhead boundary conditions; wherein the setting process of the electromagnetic boundary conditions includes: obtaining the dielectric data of the working environment and the 500kV power cable; wherein the dielectric data includes: conductivity, dielectric constant and magnetic permeability;

[0030] Further, setting electric field boundary conditions according to the conductivity and the dielectric constant;

[0031] Further, setting magnetic field boundary conditions according to the magnetic permeability;

[0032] Further, the electromagnetic boundary condition is formed by combining the electric field boundary condition and the magnetic field boundary condition;

[0033] Step 6: Loading the environmental boundary conditions and the electromagnetic boundary conditions into the 500 kV power cable geometric model;

[0034] Step 7: Input current parameters;

[0035] Step 8: Meshing the 500 kV power cable geometric model; wherein the specific meshing process includes: defining the size and type of the initial mesh and adjusting it;

[0036] Furthermore, the key areas of the 500kV power cable geometric model with loaded boundary conditions are identified; wherein the key areas include: the cable conductor surface, the cable insulation layer interface, the contact surface between the cable and the surrounding medium, the cable end and the connection point, and the stress concentration area;

[0037] Further, adding the initial grid to the key area;

[0038] Furthermore, the initial grid is dynamically adjusted according to the recognition result of the key area; wherein the dynamic adjustment process includes: extracting feature data of the key area; performing error estimation on the feature data and marking the key area as a key adjustment area when the error exceeds an error threshold; adjusting the density and shape of the initial grid of the key adjustment area according to the grid adjustment coefficient; running a simulation on the adjusted initial grid to obtain a running result; performing error calculation on the running result to evaluate the running effect after adjustment; and optimizing the grid adjustment coefficient using a gradient method according to the running effect.

[0039] Step 9: Run finite element simulation to calculate the conductor temperature distribution;

[0040] Step 10: Visualize the conductor temperature distribution in the 500 kV power cable geometric model and save the data.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention proposes a method for setting buried conditional boundaries according to a 500kV power cable in an underground environment; the method sets soil thermal convection boundary conditions and soil thermal conduction boundary conditions of different sub-layers of soil by establishing a multi-layer soil model; the soil thermal conductivity analysis process is calculated according to the environmental data of each layer of soil and the soil characteristic data to obtain the influence relationship of adjacent soil layers, and the boundary conditions are corrected through nonlinear effects, so that the 500kV power cable can achieve accurate conductor temperature simulation in the buried case.

[0043] 2. The present invention proposes a method for setting overhead boundary conditions according to the overhead environment of 500kV power cables; the method collects and analyzes environmental data of different cable overhead heights to obtain the influence rules on cable performance; and introduces an environmental radiation model, which analyzes the temperature changes caused by radiation in different areas of the cable; overhead boundary conditions are established by analyzing environmental changes, radiation effects, and the influence of ambient temperature and cable temperature; the method realizes the accurate simulation of the conductor temperature of 500kV power cables in overhead conditions.

[0044] 3. The present invention proposes a method for setting electromagnetic boundary conditions; the method collects and analyzes data of the medium in contact with the cable, including: conductivity, dielectric constant and magnetic permeability; and sets electric field boundary conditions and magnetic field boundary conditions according to the collected medium data; the two boundary conditions are combined to form electromagnetic boundary conditions under the corresponding environment; the method can reduce the calculation errors caused by improper boundary condition setting, thereby improving the calculation efficiency and conductor temperature simulation accuracy.

[0045] 4. The present invention proposes a grid planning method for planning a 500kV power cable geometric model; the method locates the temperature distribution of the main area by identifying the key area of ​​the cable; and obtains the adjustment coefficient by calculating the error of the characteristic data of the key area, adjusts the shape and density of the grid, and makes the error value approach convergence through continuous iterative optimization, so that the subtle changes in temperature distribution can be captured more accurately, thereby improving the accuracy of temperature simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of a 500kV power cable finite element modeling and conductor temperature simulation method provided in an embodiment of the present invention;

[0047] Figure 2 The embodiments of the present invention provide fluctuations in cable performance at different heights. DETAILED DESCRIPTION

[0048] 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.

[0049] 500kV power cable is an ultra-high voltage power transmission cable, mainly used for long-distance, large-capacity power transmission; the cable consists of a conductor, an insulation layer, a shielding layer and a protective sheath;

[0050] 500kV power cables can adapt to various environmental conditions, such as underground, overhead, high humidity or extreme environments, to ensure long-term stable operation. Therefore, in order to ensure that 500kV power cables can still maintain good performance under various environmental conditions, it is necessary to effectively detect 500kV power cables; during the detection process, determining the cable conductor temperature is a very important aspect for monitoring cable operation. If the temperature of the conductor exceeds the specified standard maximum temperature, it will cause the aging of the insulation material to accelerate, shorten the life of the cable, be detrimental to power transmission, and more likely to cause major safety failures. The temperature of wires and cables is generally detected by using sensing equipment to obtain the temperature of the conductor. However, due to the complex location of the cable laying, the temperature data of the cable cannot be well collected by sensing equipment alone.

[0051] In the process of calculating the conductor temperature of 500kV power cables, conductor temperature simulation can be achieved through finite element modeling; finite element modeling can be used to accurately simulate and analyze the temperature of 500kV power cable conductors. By establishing a detailed cable geometry model and defining appropriate boundary conditions and material properties, the thermal behavior of the cable under different working conditions can be simulated. This includes considering factors such as the current load of the conductor, thermal conductivity, thermal properties of the insulation material, and ambient temperature. Through in-depth analysis of these parameters, the finite element model can provide detailed predictions of the conductor temperature, helping to optimize the cable design to ensure its safety and performance stability.

[0052] In the prior art, when finite element models are used to simulate the conductor temperature of 500kV power cables, most methods are not fully combined with the laying environment of the power cables, resulting in insufficient accuracy in the temperature calculation of the conductor during the simulation process. For this reason, the present invention proposes a 500kV power cable finite element modeling and conductor temperature simulation method. The following will describe in detail two embodiments.

[0053] Embodiment 1:

[0054] In the embodiments of this application, according to Figure 1 The implementation steps given are used to perform finite element modeling of buried 500 kV power cables and the resulting temperature; Figure 1The implementation steps mainly include: Step 1: Get the relevant data of 500kV power cable; Step 2: Process the relevant data to obtain standard finite element modeling data; Step 3: Input the standard finite element modeling data into the finite element software to generate a 500kV power cable geometric model; Step 4: Load the material properties of the 500kV power cable; Step 5: Set the boundary conditions of the 500kV power cable; Step 6: Load the boundary conditions to the 500kV power cable geometric model; Step 7: Input current parameters; Step 8: Mesh the 500kV power cable geometric model; Step 9: Run finite element simulation to calculate the conductor temperature distribution; Step 10: Visualize the conductor temperature distribution and save the data. The following is based on Figure 1 Specific implementation process;

[0055] according to Figure 1 Step 1: obtaining relevant data of the 500kV power cable through data information; wherein the relevant data includes: cable structure (material type and composition of conductor, insulation layer, shielding layer and sheath layer), geometric dimensions (conductor outer diameter information, insulation layer thickness information, shielding layer thickness information and protective sheath thickness information), cable length and layout form;

[0056] In the embodiment of the present application, relevant data of the 500kV power cable is obtained through data information, including: cable structure, geometric dimensions, cable length and layout form, so as to ensure that the simulation results can accurately reflect the actuality of the cable.

[0057] Refer to Table 1 for the relevant data of the 500kV power cable in the application example;

[0058] Table 1500kV power cable related data

[0059]

[0060] Table 1 gives a detailed description of the relevant data of the 500kV power cable, including not only the composition structure and material information of the cable, but also the outer diameter and thickness information of each layer structure. In this way, finite element modeling can more accurately reflect the actual performance of the 500kV power cable, optimize thermal management and electrical performance analysis, and improve the accuracy of the model and the reliability of the simulation results.

[0061] Further, the acquired relevant data is processed according to the content of the above step 2 to obtain standard finite element modeling data; wherein the main contents of the data processing include: checking whether there are data errors in the relevant data; when errors occur in the relevant data, correcting them according to the standard parameters of the 500kV power cable to obtain corrected relevant data; converting the corrected relevant data according to the data input format of the finite element software to obtain the standard finite element modeling data;

[0062] In the embodiment of the present application, the relevant data obtained are processed by the above method, which can significantly improve the accuracy of finite element modeling and the reliability of simulation results. The accuracy of data and the correctness of the format directly affect the quality of finite element analysis, and the optimized model can provide more reliable prediction results, thereby providing more powerful support for the design, evaluation and optimization of power systems.

[0063] Further, according to step 3, the processed relevant data is input into the finite element software to generate a 500kV power cable geometric model; in the embodiment of the present application, COMSOL Multiphysics software is used for finite element modeling, which supports multi-physics field simulation and is suitable for complex electrical and thermal analysis;

[0064] Furthermore, according to the content of step 4, material properties are loaded for the 500 kV power cable geometric model through finite element software; see Table 2 for a list of material properties.

[0065] Table 2 Description of 500kV power cable material properties

[0066] property Conductor layer Insulation layer Shielding Sheath layer Conductivity 58×10^6S / m - 58×10^6S / m - Resistivity 1.72×10^-8Ω·m - 1.72×10^-8Ω·m - Insulation resistance - 10^10Ω - - Thermal conductivity 401W / (m·K) 0.35W / (m·K) 401W / (m·K) 0.15W / (m·K) Specific heat 385J / (kg·K) 1500J / (kg·K) 385J / (kg·K) 1000J / (kg·K) Expansion coefficient 16×10^-6 / K 100×10^-6 / K 16×10^-6 / K 50×10^-6 / K Elastic modulus 110×10^9Pa 0.5×10^9Pa 110×10^9Pa 2×10^9Pa Poisson's ratio 0.34 0.45 0.34 0.35 Yield Strength 210×10^6Pa - 210×10^6Pa 40×10^6Pa Dielectric constant - 2.5 - 4.0 Loss tangent - 0.005 - 0.02 Magnetic Permeability 1 - 1 -

[0067] Further, according to the content of step 4, boundary conditions are set for the 500kV power cable geometric model; wherein the boundary conditions include: environmental boundary conditions and electromagnetic field boundary conditions;

[0068] Among them, the environmental boundary conditions are divided into buried and overhead types according to the 500kV power cable laying environment; according to actual judgment, the 500kV power cable laying environment in the embodiment of the present application is buried, so the buried boundary conditions are set;

[0069] In the embodiment of the present application, during the conductor temperature simulation of the 500kV power cable geometric model, the environmental boundary conditions are divided into buried type and overhead type according to the laying environment of the cable, so that the temperature distribution of the cable under different environments can be better evaluated according to the actual laying environment. This helps to optimize the cable design.

[0070] The process of setting the buried boundary conditions includes: collecting the physical and thermal parameters of the soil in different buried areas of the 500kV power cable;

[0071] Furthermore, the physical parameters and the thermal parameters are sorted according to the soil type to obtain soil property parameters;

[0072] Furthermore, a multi-layer soil model is established according to soil attribute parameters; wherein the multi-layer soil model is expressed as: MuLSM = {Layer i |1≤i≤3}; where MuLSM represents the sub-model set in the multi-layer soil model; Layer i It is represented as the i-th layer soil sub-model; in the embodiment of the present application, three layers of sub-models are established for the multi-layer soil model, namely: Layer1 is the first layer sub-model, the soil depth is 0-1m; Layer2 is the second layer sub-model, the soil depth is 1-3m; Layer3 is the third sub-model, the soil depth is 3-4m;

[0073] Further, the soil characteristics of each layer are defined for the multi-layer soil model, and the thickness and depth distribution are set; see Table 3;

[0074] Table 3 Soil characteristics

[0075]

[0076] Furthermore, the background temperature of the multi-layer soil model is set according to the monitoring data of the 500kV power cable buried area; the background temperature in each sub-layer is different; in order to further realize the true simulation of the temperature in the soil environment, the temperature change curve can be obtained by collecting the historical soil temperature and historical meteorological data of the 500kV power cable buried area in the past year for temperature analysis; the temperature change curve is used to adaptively adjust the multi-layer soil model over time series;

[0077] Furthermore, the heat flux density of the 500 kV power cable buried area in the multi-layer soil model is set; in the embodiment of the present application, the heat flux density of Layer 1 is set to 200 W / m 2 ; According to the principle of heat conduction, the heat flux density of Layer2 and Layer3 is calculated as follows: Among them, QLayer i Represented as Layer i The heat flux density of QLayer1 is the heat flux density of Layer1; kLayer i Represented as Layer i The thermal conductivity of kLayer1 is Layer iThermal conductivity; According to the calculation, the heat flux density of Layer2 is 233.3W / m 2 , the heat flux density of Layer 3 is 266.7W / m 2 ;

[0078] Furthermore, soil thermal convection boundary conditions and soil thermal conduction boundary conditions are defined respectively; wherein the definition process of the soil thermal convection boundary conditions is as follows:

[0079] Acquire soil environment data and soil property data; wherein the soil environment data includes: temperature and humidity; the soil property data includes: porosity and humidity unit time growth rate; refer to Table 4;

[0080] Table 4 Soil environment data and soil property data

[0081]

[0082] The soil environment data, the soil characteristic data and the soil convection direction are input into the soil thermal convection model to obtain the soil thermal convection boundary conditions; specifically:

[0083] (1) Set the soil convection direction to vertically downward;

[0084] (2) Boundary condition setting;

[0085] Upper boundary condition: upper boundary of layer 1, temperature T top =22℃;

[0086] Lower boundary condition: lower boundary of layer 3, temperature T bottom =18℃;

[0087] (3) The soil thermal convection model is set as a one-dimensional steady-state heat conduction model. The steady-state heat conduction equation is as follows: Where k0 represents the reference thermal conductivity; T represents the temperature;

[0088] (4) Calculate the reference heat flow coefficient of each layer;

[0089] The calculation formula of parameter heat flow coefficient is: Where L represents the thickness of the soil layer; Nu represents the Nusselt number, which is set to 1.5;

[0090] The soil thermal convection boundary conditions obtained according to the above process are shown in Table 5;

[0091] Table 5 Soil thermal convection boundary condition settings

[0092] Layer Number Thermal conductivity (W / (m·K)) <![CDATA[Heat convection coefficient (W / (m 2 ·K))]]> Temperature(℃) 1 1.2 1.8 22 2 1.4 1.05 20 3 1.6 1.2 18

[0093] The definition of soil heat conduction boundary conditions for each layer is as follows: If there is heat convection between the surface and the air, the surface boundary condition can use the heat convection boundary condition, and the formula is: T surface Expressed as soil surface temperature; T air Represents the air temperature; if there is no heat convection between the surface and the air, it can be set to the known surface temperature of the soil; for the bottom boundary condition, if there is no heat flow at the bottom of the soil, it can be assumed to be an adiabatic boundary condition, that is, the heat flow is zero; if the bottom temperature is known, it can be set to a constant.

[0094] In the embodiment of the present application, in order to define the soil thermal convection boundary conditions of the buried cable, the soil environment data and soil characteristic data of the soil model sublayer are correspondingly obtained, and the relevant data are input into the soil thermal convection model. By analyzing the thermal convection conditions of different sublayers, the heat flow conditions of different soil layers can be accurately grasped.

[0095] Furthermore, nonlinear effects are introduced to optimize the soil thermal convection boundary conditions and the soil thermal conduction boundary conditions to obtain the buried boundary conditions;

[0096] The specific process is:

[0097] (1) Introducing nonlinear heat conduction: The thermal conductivity of soil may change with temperature, so the thermal conductivity k(T) can be described by a nonlinear function, as follows:

[0098] k(T)=k0(1+α(T-ΔT));

[0099] Where α represents the temperature dependence coefficient of heat conduction; ΔT represents the temperature attenuation error;

[0100] (2) Introducing nonlinear thermal convection: The thermal convection coefficient is related to temperature, so the thermal conductivity h(T) can be described by a nonlinear function, as follows:

[0101] h(T)=h0(1+β(T-ΔT));

[0102] Where β represents the temperature dependence coefficient of thermal convection;

[0103] (3) Optimization of buried boundary conditions:

[0104] Nonlinear convection boundary conditions (upper boundary): The convection heat flux can be corrected according to the soil surface temperature and air temperature;

[0105] -q conv =h(T surface )(T surface -T air );

[0106] Among them, -q conv Expressed as the corrected convective heat flux;

[0107] Nonlinear adiabatic boundary condition (lower boundary): If the lower boundary is adiabatic, the effect of temperature changes in the deep soil layer on heat flow can be considered;

[0108] In the embodiment of the present application, environmental boundary conditions are set for an underground 500kV power cable. In the process of setting the buried boundary conditions, the soil in the cable buried area is modeled in layers, and the corresponding soil thermal convection boundary conditions and soil thermal conduction boundary conditions are calculated based on the soil data of each layer. In order to further simulate the changes in the soil, the soil thermal convection boundary conditions and soil thermal conduction boundary conditions are optimized by introducing nonlinear effects to achieve the most realistic setting of buried boundary conditions.

[0109] Furthermore, the process of setting the electromagnetic boundary conditions includes:

[0110] Obtain the working environment and dielectric data of the 500 kV power cable; wherein the dielectric data includes: conductivity, dielectric constant and magnetic permeability; in the embodiment of the present application, the working environment is soil; therefore, the medium includes: soil and moisture; refer to Table 6, which gives the dielectric data of the 500 kV power cable buried in the soil environment;

[0111] Table 6 Medium data under soil working environment

[0112] Layer Number Depth range(m) Conductivity (S / m) <![CDATA[Dielectric constant (ε r )]]> <![CDATA[Magnetic permeability (μ r )]]> 1 0-1 0.1 8 1 2 1-3 0.2 15 1 3 3-5 0.3 20 1

[0113] Further, setting electric field boundary conditions according to the conductivity and the dielectric constant;

[0114] The process of defining the electric field boundary condition is as follows: Calculate the electric field strength Where V represents the electric potential; the electric field flux density D = εE in the medium is calculated based on the electric field strength; where ε = ε0ε r Expressed as dielectric constant; ε0 is the dielectric constant of vacuum; ε r is the relative dielectric constant;

[0115] Further, setting magnetic field boundary conditions according to the magnetic permeability;

[0116] The process of defining the magnetic field boundary conditions is as follows: Calculate the magnetic induction intensity B = μH; where μ = μ0μ r Expressed as magnetic permeability; μ0 is the vacuum permeability; μ r is the relative magnetic permeability; H represents the magnetic field intensity; wherein, the boundary conditions of the magnetic field intensity (H) involve the tangential and normal components of the magnetic field; at the boundary of different media, the tangential component of the magnetic field intensity is continuous.

[0117] Furthermore, the electromagnetic boundary condition is formed by combining the electric field boundary condition and the magnetic field boundary condition; wherein the electromagnetic boundary condition combines the boundary conditions of the electric field and the magnetic field, and the electromagnetic boundary condition constraint rule is:

[0118] (1) The normal component of the electric field flux density remains continuous in the absence of free current, ε1E 1n =ε2E 2n ; where ε1 and ε2 are the dielectric constants of the soil medium and the water medium respectively; E 1n and E 2n are the normal components of the electric field in the soil medium and the water medium, respectively;

[0119] (2) The normal component of the magnetic induction intensity remains continuous, B 1n =B 2n Among them, B 1n and B 2n They are respectively expressed as the normal components of magnetic induction intensity in soil medium and water medium;

[0120] (3) The tangential components of the electric and magnetic fields remain continuous across the boundaries of different media. E 1t and E 2t are the cutting vectors of the electric field in the soil medium and the water medium respectively; H 1t and H 2t are the cutting vectors of magnetic field in soil medium and water medium respectively;

[0121] Further, according to Figure 1 The content of step 6 in , loading the environmental boundary conditions and the electromagnetic boundary conditions into the 500kV power cable geometric model through finite element software;

[0122] Further, according to the above step 7, the current value is input. In this embodiment, the current value is set to 1500A;

[0123] Furthermore, according to the content of step eight, the 500 kV power cable geometric model after loading the boundary conditions is meshed, specifically including:

[0124] Define the size and type of the initial grid; in this embodiment of the present application, the size of the initial grid is set to 15 mm, and the grid type is a tetrahedral grid;

[0125] The key areas of the 500kV power cable geometric model with loaded boundary conditions are identified; wherein the key areas include: the cable conductor surface, the cable insulation layer interface, the contact surface between the cable and the surrounding medium, the cable end and connection point, and the stress concentration area.

[0126] In the embodiment of the present application, the key areas of the 500kV power cable geometric model are defined as the cable conductor surface, the cable insulation interface, the contact surface between the cable and the surrounding medium, the cable end and the connection point, and the stress concentration area; the accuracy of the temperature distribution is particularly critical in these areas, because the temperature of the conductor surface directly affects the overall thermal performance of the cable. Accurate temperature prediction helps to determine the risk of overheating of the conductor and its impact on the life of the cable.

[0127] Adding the initial grid to the key area; dynamically adjusting the initial grid according to the recognition result of the key area;

[0128] The dynamic adjustment process includes: extracting the characteristic data of the key area; referring to Table 7, which shows the characteristic data obtained for each key area;

[0129] Table 7 Characteristic data and description of key areas

[0130]

[0131] Further, the characteristic data is subjected to error estimation, and when the error exceeds an error threshold, it is marked as a key adjustment area; see Table 8, which provides a description of each key area;

[0132] Table 8 Error description of key areas

[0133]

[0134] Furthermore, the density and shape of the initial grid of the key adjustment area are adjusted according to the grid adjustment coefficient; wherein the grid adjustment coefficient is based on the local grid sensitivity analysis, testing the changes in simulation results under different grid densities to determine the sensitivity of the error to the grid density.

[0135] Further, running the simulation on the adjusted initial grid to obtain the running results;

[0136] Further, performing error calculation on the operation result to evaluate the operation effect after adjustment;

[0137] Furthermore, the grid adjustment coefficient is optimized using a gradient method according to the operating effect.

[0138] Wherein, referring to Table 9, the final grid parameters obtained through multiple iterative optimizations in the embodiment of the present application are given in Table 9;

[0139] Table 9 Results of initial grid adjustment for buried type

[0140]

[0141] In the implementation of this application, a grid optimization method for planning a 500kV power cable model is adopted; this method locates the temperature distribution of the main area by identifying the key areas of the cable; and obtains the adjustment coefficient by calculating the error of the characteristic data of the key area, and adjusts the shape and density of the grid. Through continuous iterative optimization, the error value approaches convergence, which can more accurately capture the subtle changes in temperature distribution, thereby improving the accuracy of temperature simulation.

[0142] Further, according to the above step nine, a finite element simulation is run to calculate the conductor temperature distribution;

[0143] Further, according to step ten: the conductor temperature distribution is visualized in the 500 kV power cable geometric model, and the data is saved.

[0144] Embodiment 2:

[0145] In the first embodiment, the present invention realizes the finite element modeling and conductor temperature simulation process of the buried 500kV power cable; in the actual application of 500kV power cable, the buried type is only one of the laying methods, and the overhead type is also included; in the embodiment of the present application, the process of finite element modeling and conductor temperature simulation of the overhead 500kV power cable is described, which mainly includes the following process:

[0146] Step 1: Obtain relevant data of a 500 kV power cable laid overhead through data information; the relevant data of the 500 kV power cable obtained in the embodiment of the present application is the same as that in the first embodiment;

[0147] Step 2: Processing the relevant data to obtain standard finite element modeling data;

[0148] Step 3: Input the standard finite element modeling data into the finite element software to generate a 500kV power cable geometric model;

[0149] Step 4: Loading the material properties of the 500 kV power cable;

[0150] Step 5: setting boundary conditions according to the working environment of the 500kV power cable; wherein, according to the working environment, the overhead laying of the 500kV power cable is usually suspended, and the cable is arranged along a specially designed power tower or supporting structure; therefore, in the finite element simulation process, the environmental boundary conditions are set as overhead boundary conditions;

[0151] The process of setting the overhead boundary condition is as follows:

[0152] Collect overhead environmental data of cable areas at different overhead heights, see Table 10;

[0153] Table 10 Overhead environment data at different overhead heights

[0154]

[0155] Table 11 gives the overhead environmental data for overhead heights ranging from 10 meters to 50 meters.

[0156] Furthermore, the overhead environment data is input into the environment analysis model to obtain the law of environmental change; wherein, in the embodiment of the present application, the model function of the environment analysis model is expressed as:

[0157] P=β0+β1*W+β2*T e +β3*R+β4*S+β5*H+β6*U;

[0158] Where P represents the cable performance index (such as cable temperature increase, tension increase, etc.); W represents the wind speed; T e It represents the ambient temperature; R represents the rainfall; S represents the snow load; H represents the snow load; U represents the ultraviolet intensity;

[0159] Input the data in Table 11 into the model function of the environmental analysis model, and the results are shown in Table 11:

[0160] Table 11 Performance analysis results of different cable overhead heights

[0161] Height(m) Cable performance index (P) 10 20.15 20 21.65 30 21.71 40 22.8 50 21.79

[0162] From the data in Table 11, it can be concluded that when the installation height of 500kV power cable is 10m, the cable performance index is 20.15; when the installation height is 20m, the cable performance index is 21.65; when the installation height is 30m, the cable performance index is 21.71; when the installation height is 40m, the cable performance index is 22.8; when the installation height is 50m, the cable performance index is 21.79; and refer to Figure 2 ,exist Figure 2 The fluctuation of cable performance at different heights is given in;

[0163] Furthermore, an environmental radiation model is introduced to calculate the radiation impact on the overhead cable; wherein the model function of the environmental radiation model is expressed as:

[0164] I total (x,y,z)=I direct (x,y,z)+I diffuse (x,y,z)+I reflected (x,y,z);

[0165] Among them, Itotal () represents the radiation impact value; (x, y, z) represents the location of the overhead cable area; I direct () represents direct solar radiation; I diffuse () represents diffuse reflected radiation; I reflected () represents the reflected radiation reflected by the surrounding buildings; β0 represents a constant term; β1, β2, β3, β4, β5 and β6 represent the influence of each environmental factor on the cable performance index;

[0166] In the embodiment of the present application, direct solar radiation is expressed as: Among them, I solar It is expressed as solar intensity; θ is the angle between the sun's rays and the normal of the cable surface; α is the atmospheric transmittance; diffuse radiation is expressed as: I diffuse (x,y,z)=I diffuse_sky *Svf(x,y,z); where I diffuse_sky It is expressed as diffuse radiation intensity; Svf() is expressed as sky view factor, taking into account the influence of occlusion and terrain; the reflected radiation reflected by surrounding buildings is expressed as: I incident (x i ,y i ,z i ) is expressed as i ,y i ,z i ) incident radiation to the cable surface area; R i Expressed as a reflection coefficient, it depends on the material properties of the surrounding surfaces; Shadow_Factor(x,y,z,x i ,y i ,z i ) is the shadow factor, which calculates the radiation reduction caused by shading by buildings, terrain, etc.; i is the number of the shading object;

[0167] In order to truly simulate the overhead 500kV power cable in the embodiment of the present application, an environmental radiation model is introduced due to the influence of solar radiation on the conductor temperature; this model comprehensively calculates direct solar radiation, diffuse radiation and reflection of surrounding objects, which not only makes the simulation experiment of conductor temperature more realistic, but also ensures the accuracy of the calculation of conductor temperature distribution.

[0168] Furthermore, the heat transfer rate of the overhead cable in different areas is set; setting the heat transfer rate of the overhead cable in different areas usually involves evaluating the thermal conductivity of the cable under different environmental conditions. Heat transfer rate is an important indicator to measure the thermal conductivity of a material, and is usually used to describe the ability of heat to be conducted in a material.

[0169] The heat transfer rate setting process for overhead cables is as follows:

[0170] Obtain the relevant overhead environmental data in Table 11, including: ambient temperature, wind speed, humidity, rainfall, snow load and solar radiation;

[0171] Furthermore, the data is input into the steady-state thermal conduction model, and the corresponding steady-state thermal conduction model formula is: Among them, Q represents the heat rate; c represents the thermal conductivity of the material; A represents the cross-sectional area of ​​heat conduction; ΔsT represents the temperature difference in the overhead environment; d represents the thickness of heat conduction;

[0172] Further, the environmental variation law, the radiation influence and the heat transfer rate are comprehensively modeled to obtain the overhead boundary condition;

[0173] The specific overhead boundary conditions are:

[0174] (1) The thermal boundary condition is defined as: Among them, T c represents the cable temperature; n represents the heat transfer coefficient; p represents the environmental heat transfer rate;

[0175] (2) The radiation boundary condition is expressed as: T c (t) represents the cable temperature at time t; T e (t) represents the ambient temperature at time t; I total (t) represents the radiation impact at time t; R th Expressed as cable resistance;

[0176] (3) Constructing overhead boundary conditions based on thermal boundary conditions and radiation boundary conditions;

[0177] In the embodiment of the present application, an overhead boundary condition is set according to the laying environment of the 500kV power cable; the method analyzes the environmental data of overhead cables at different heights, and calculates the corresponding heat transfer rate and radiation influence, thereby simulating the working environment of the power cable in the real environment, which helps to provide a reasonable experimental scenario for the subsequent conductor temperature simulation.

[0178] Furthermore, the process of setting the electromagnetic boundary conditions includes:

[0179] Obtaining dielectric data of the 500 kV power cable; wherein the dielectric data includes: conductivity, dielectric constant and magnetic permeability; in the embodiment of the present application, the working environment is in the air; therefore, the medium includes: air and moisture in the air;

[0180] Further, setting electric field boundary conditions according to the conductivity and the dielectric constant;

[0181] Further, setting magnetic field boundary conditions according to the magnetic permeability;

[0182] Further, the electromagnetic boundary condition is formed by combining the electric field boundary condition and the magnetic field boundary condition;

[0183] Step 6: Loading the environmental boundary conditions and the electromagnetic boundary conditions into the 500 kV power cable geometric model;

[0184] Step 7: Input current parameters;

[0185] Step 8: Meshing the 500 kV power cable geometric model; wherein the specific meshing process includes: defining the size and type of the initial mesh and adjusting it;

[0186] Furthermore, the key areas of the 500kV power cable geometric model with loaded boundary conditions are identified; wherein the key areas include: the cable conductor surface, the cable insulation layer interface, the contact surface between the cable and the surrounding medium, the cable end and the connection point, and the stress concentration area;

[0187] Further, adding the initial grid to the key area;

[0188] Further, dynamically adjusting the initial grid according to the recognition result of the key area;

[0189] Among them, the dynamic adjustment process includes: extracting the characteristic data of the key area; performing error estimation on the characteristic data, and marking the key area as a key adjustment area when the error exceeds the error threshold; adjusting the density and shape of the initial grid of the key adjustment area according to the grid adjustment coefficient; running a simulation on the adjusted initial grid to obtain the running result; performing error calculation on the running result to evaluate the running effect after adjustment; and optimizing the grid adjustment coefficient using the gradient method according to the running effect.

[0190] Refer to Table 12, which shows the final grid parameters obtained through multiple iterative optimizations in the embodiment of the present application.

[0191] Table 12 Overhead initial grid adjustment results

[0192]

[0193] Step 9: Run finite element simulation to calculate the conductor temperature distribution;

[0194] Step 10: Visualize the conductor temperature distribution in the 500 kV power cable geometric model and save the data.

[0195] In summary, the contents of Example 1 and Example 2 realize the finite element modeling and conductor temperature simulation of 500kV power cable when the laying method is buried and overhead; specifically, the following processes are included: first, relevant data is obtained according to the information of the 500kV power cable, and the relevant data is processed into a specific format and then the cable is modeled using finite element software to obtain a 500kV power cable geometric model; secondly, the environmental boundary conditions and electromagnetic boundary conditions in the temperature simulation process are set according to the laying environment of the cable; when the cable is laid in buried mode, a multi-layer soil model is established; the thermal convection boundary and the thermal conduction boundary of different sub-layers of soil are calculated to form buried boundary conditions; when the cable is laid in overhead mode, the environmental data at different installation heights are collected for environmental simulation. The environmental radiation model is analyzed and the environmental radiation model is introduced to calculate the radiation effect of the sun on the cable; a comprehensive model is built according to the environmental changes, radiation effects, ambient temperature and heat conduction of the cable to obtain the overhead boundary conditions; in the process of setting the electromagnetic boundary conditions, the contact medium of the cable in the installation environment is considered, and the relevant medium data is obtained to analyze the distribution of the electric field and the magnetic field; finally, the environmental boundary conditions and electromagnetic boundary conditions are loaded into the 500kV power cable geometric model for conductor temperature simulation, and a grid planning method is proposed in the simulation process. This method optimizes the density and shape of the grid by calculating the characteristic errors of the key areas, so that the optimized grid can more accurately capture the subtle changes in temperature distribution; the above methods are combined to realize the effective temperature simulation of the 500kV power cable conductor.

[0196] 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 500kV power cable finite element modeling and conductor temperature simulation method, characterized in that: The following steps are involved: Step 1: Obtain relevant data of the 500kV power cable through data information; Step 2: Processing the relevant data to obtain standard finite element modeling data; Step 3: Input the standard finite element modeling data into the finite element software to generate a 500kV power cable geometric model; Step 4: Loading the material properties of the 500 kV power cable; Step 5: setting boundary conditions according to the working environment of the 500kV power cable; wherein the boundary conditions include: environmental boundary conditions and electromagnetic boundary conditions; wherein the process of setting the electromagnetic boundary conditions includes: obtaining the dielectric data of the working environment and the 500kV power cable; wherein the dielectric data includes: conductivity, dielectric constant and magnetic permeability; setting the electric field boundary conditions according to the conductivity and the dielectric constant; setting the magnetic field boundary conditions according to the magnetic permeability; and forming the electromagnetic boundary conditions by combining the electric field boundary conditions and the magnetic field boundary conditions; Step 6: Loading the environmental boundary conditions and the electromagnetic boundary conditions into the 500 kV power cable geometric model; Step 7: Input current parameters; Step 8: Meshing the 500 kV power cable geometric model; Step 9: Run finite element simulation to calculate the conductor temperature distribution; Step 10: Visualize the conductor temperature distribution in the 500 kV power cable geometric model and save the data.

2. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 1, characterized in that: The relevant data include: cable structure, geometric dimensions, cable length and layout.

3. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 2, characterized in that: The cable structure includes: material types and composition forms of the conductor, insulation layer, shielding layer and sheath layer; the geometric dimensions include: conductor outer diameter information, insulation layer thickness information, shielding layer thickness information and protective sheath thickness information.

4. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 1, characterized in that: The data processing includes: checking whether there are data errors in the relevant data; when errors occur in the relevant data, correcting them according to the standard parameters of the 500kV power cable to obtain corrected relevant data; converting the corrected relevant data according to the data input format of the finite element software to obtain the standard finite element modeling data.

5. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 1, characterized in that: The environmental boundary conditions are set as buried boundary conditions according to the buried type; wherein the setting process of the buried boundary conditions is: data sorting of physical parameters and thermodynamic parameters of the buried soil as soil attribute parameters; establishing a multi-layer soil model using the soil attribute parameters; defining the soil characteristics of each layer for the multi-layer soil model, and setting the thickness and depth distribution; setting the background temperature of the multi-layer soil model according to the historical data of soil area monitoring, and adaptively adjusting the background temperature according to the temperature change curve; setting the heat flux density of the 500kV power cable buried area in the multi-layer soil model; defining the soil thermal convection boundary conditions and the soil thermal conduction boundary conditions respectively; introducing nonlinear effects to optimize the soil thermal convection boundary conditions and the soil thermal conduction boundary conditions to obtain the buried boundary conditions.

6. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 5, characterized in that: The soil thermal convection boundary condition definition process includes: acquiring soil environmental data and soil characteristic data; wherein the soil environmental data includes: temperature and humidity; the soil characteristic data includes: porosity and humidity unit time growth rate; inputting the soil environmental data, the soil characteristic data and the soil convection direction into the soil thermal convection model to obtain the soil thermal convection boundary condition.

7. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 1, characterized in that: The environmental boundary conditions are set as overhead boundary conditions according to the overhead type; wherein the setting process of the overhead boundary conditions is: collecting overhead environmental data of cable areas at different overhead heights; inputting the overhead environmental data into the environmental analysis model to obtain the law of environmental changes; introducing an environmental radiation model to calculate the radiation impact on the overhead cable; setting the heat transfer rate of the overhead cable in different areas; and comprehensively modeling the law of environmental changes, the radiation impact and the heat transfer rate to obtain the overhead boundary conditions.

8. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 7, characterized in that: The model function of the environmental radiation model is expressed as: I total (x,y,z)=I direct (x,y,z)+I diffuse (x,y,z)+I reflected (x,y,z); Among them, I total () represents the radiation impact value; (x, y, z) represents the location of the overhead cable area; I direct () represents direct solar radiation; I diffuse () represents diffuse reflected radiation; I reflected () represents the reflected radiation reflected by the surrounding buildings.

9. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 1, characterized in that: The step eight includes: defining the size and type of the initial grid; identifying the key areas of the 500kV power cable geometric model with loaded boundary conditions; adding the initial grid to the key areas; dynamically adjusting the initial grid according to the identification results of the key areas; wherein the dynamic adjustment process includes: extracting the characteristic data of the key areas; estimating the error of the characteristic data, and marking the key area as a key adjustment area when the error exceeds the error threshold; adjusting the density and shape of the initial grid of the key adjustment area according to the grid adjustment coefficient; running a simulation on the adjusted initial grid to obtain the operation results; calculating the error of the operation results to evaluate the adjusted operation effect; and optimizing the grid adjustment coefficient using the gradient method according to the operation effect.

10. A 500kV power cable finite element modeling and conductor temperature simulation method according to claim 9, characterized in that: The key areas include: the surface of the cable conductor, the interface of the cable insulation layer, the contact surface between the cable and the surrounding medium, the cable end and connection point, and the stress concentration area.

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