Power transmission line state evaluation method and device based on steel-cored aluminum strand stress change analysis

Abstract

The invention discloses a power transmission line state evaluation method and device based on steel-cored aluminum strand stress change analysis, and the method comprises the steps: carrying out the drawing and stranding of a steel-cored aluminum strand of a power transmission line lead through COMSOL simulation software, and constructing a power transmission line lead simulation model; performing grid division and fine solution on the power transmission line conductor simulation model to obtain a three-dimensional stress grid division model; performing coupling of a set physical field on the three-dimensional stress grid division model, and performing simulation calculation on the stress of the power transmission line conductor under the coupling action of the set physical field to obtain a stress change result; generating a stress change cloud picture according to the stress change result; and according to the stress change cloud picture, evaluating the running state of the power transmission line by observing the stress change of the steel-cored aluminum strand stranded layer, and outputting an evaluation result. According to the invention, scientificity, integrity, accuracy and timeliness of state evaluation of the power transmission line can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage transmission line status assessment, and in particular to a transmission line status assessment method and device based on stress change analysis of steel-core aluminum stranded wire. Background Art

[0002] High-voltage transmission lines, as a crucial component of the power system's transmission chain, are not only crucial to the transmission capacity but also to the safe and stable operation of the entire power system. With the continued expansion of power grids, my country's power grid has evolved from being independent, decentralized, and weak to a nationwide interconnected, interoperable, and mutually beneficial one. This has continuously improved grid security, and power supply reliability ranks among the best in the world. The length of transmission lines has also expanded from an initial 6,475 kilometers to 2.425 million kilometers today. Six major regional power grids have emerged across China, encompassing Northeast China, North China, Northwest China, East China, Central China, and Southern China, with asynchronous interconnection between regions. As a crucial component of this system, the health of transmission lines directly impacts the safety and stability of power grid operations.

[0003] However, because high-voltage transmission lines are exposed to the air for long periods of time and outdoor weather conditions are constantly changing, the transmission conductors, primarily made of steel core, aluminum conductors, and anti-corrosion grease, are affected by changes in ambient temperature and the heat generated by the transmission conductors themselves. This can lead to conductor deviation, increased twist gaps, and increased geometric spacing. Furthermore, changes in air temperature can cause internal expansion of transmission conductors, deteriorating insulation performance, and leading to frequent incidents of reduced power transmission quality. However, these issues are difficult to repair, and partial damage to the conductor can necessitate replacement of the entire conductor, resulting in significant economic losses. The combined effects of temperature on transmission conductors exposed to the air can pose significant safety risks to the transmission lines and the safe operation of the power grid.

[0004] Therefore, how to invent a transmission line status assessment method based on stress change analysis of steel core aluminum stranded wire, which can improve the scientificity, completeness, accuracy and timeliness of transmission line status assessment, has become an urgent problem to be solved. Summary of the Invention

[0005] To this end, the present invention provides a transmission line status assessment method and device based on stress change analysis of steel core aluminum stranded conductors. By means of simulation, stress change analysis of the transmission conductors is performed. By analyzing the offset of the twisted conductors, the transmission line status can be assessed in a scientific, targeted, timely, accurate, reliable and well-visualized manner.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for evaluating the state of a transmission line based on stress change analysis of an aluminum-steel cored conductor, comprising:

[0007] Using COMSOL simulation software, the steel-core aluminum stranded wire of the transmission line conductor is drawn and twisted to construct a transmission line conductor simulation model;

[0008] Meshing and refining the transmission line conductor simulation model to obtain a three-dimensional stress meshing model;

[0009] The three-dimensional stress grid division model is coupled with a set physical field, and under the coupling effect of the set physical field, a simulation calculation is performed on the stress of the transmission line conductor to obtain a stress change result; and a stress change cloud map is generated according to the stress change result;

[0010] According to the stress change cloud map, the operation status of the transmission line is evaluated by observing the stress changes in the stranded layers of the steel core aluminum stranded wire, and the evaluation results are output.

[0011] As a preferred solution for the transmission line status assessment method based on stress change analysis of steel core aluminum stranded wire, before constructing the transmission line conductor simulation model, the stress stage of the selected material is determined; and whether the selected material is in the plastic stage is judged according to the yield condition; the yield condition expression is:

[0012] F(σ ij ,ε ij ,t,T)=0

[0013] Where σ ij is the component of stress in the i, j direction; ε ij is the strain component; t is the time component; T is the ambient temperature component;

[0014] When the selected material is in the elastic stage, the yield condition expression is:

[0015] F(kσ ij )=0

[0016] Where k is the strengthening coefficient, which gradually increases during the elastic deformation and stretching process.

[0017] As a preferred solution of the transmission line state assessment method based on stress change analysis of steel core aluminum stranded wire, in the process of meshing and refining the transmission line conductor simulation model, the transmission line conductor simulation model is meshed and refined by the finite element analysis method to obtain the three-dimensional stress meshing model; the analysis steps of the finite element analysis method are as follows:

[0018] According to the set refinement requirements, the transmission line conductor simulation model is divided into a plurality of finite elements;

[0019] Establishing a corresponding mathematical model within the finite element through physical equations to construct a stiffness matrix of the finite element;

[0020] Assembling the stiffness matrices of several finite elements to generate a global equation for the entire structure;

[0021] Solving the global equation to obtain a solution result;

[0022] Visualization and error analysis are performed based on the solution results.

[0023] As a preferred solution for the transmission line status assessment method based on stress change analysis of steel-core aluminum stranded wire, during the simulation calculation of the transmission line conductor stress, heat conduction occurs between the steel core, aluminum layer, and air in the transmission line conductor; the heat conduction method satisfies the three-dimensional heat conduction equation; the expression of the three-dimensional heat conduction equation is:

[0024]

[0025] Where λ is the thermal conductivity of the conductor material; x, y, z are the three-dimensional rectangular coordinates; T is the temperature of the steel core aluminum stranded wire conductor; c is the specific heat capacity of the material; ρ is the density of the material; τ is the time; q is the unit volume heat rate of the steel core aluminum stranded wire q = I 2 R, I is the current flowing through the steel core aluminum stranded wire, and R is the resistance of the steel core aluminum stranded wire per unit volume.

[0026] As a preferred solution of the transmission line status assessment method based on stress change analysis of steel core aluminum stranded wire, the set physical fields include: temperature field, electric field, solid heat transfer field and cable mechanics field.

[0027] The present invention also provides a transmission line status assessment device based on stress change analysis of steel core aluminum stranded wire, based on the above transmission line status assessment method based on stress change analysis of steel core aluminum stranded wire, comprising:

[0028] A transmission line conductor simulation model construction module is used to draw and twist the steel-core aluminum stranded wire of the transmission line conductor using COMSOL simulation software to construct a transmission line conductor simulation model;

[0029] A three-dimensional stress grid division model acquisition module is used to grid the transmission line conductor simulation model and perform a refined solution to obtain a three-dimensional stress grid division model;

[0030] A stress change cloud map generation module is used to couple the three-dimensional stress grid division model with a set physical field, and simulate the stress of the transmission line conductor under the coupling effect of the set physical field to obtain stress change results; and generate a stress change cloud map based on the stress change results;

[0031] The transmission line operation status assessment module is used to assess the operation status of the transmission line by observing the stress changes in the stranded layers of the steel core aluminum stranded wire according to the stress change cloud map, and output the assessment result.

[0032] As a preferred solution of the transmission line state assessment device based on stress change analysis of steel core aluminum stranded wire, in the transmission line conductor simulation model construction module, before constructing the transmission line conductor simulation model, the stress stage of the selected material is determined; and whether the selected material is in the plastic stage is judged according to the yield condition; the yield condition expression is:

[0033] F(σ ij ,ε ij ,t,T)=0

[0034] Where, σ ij is the component of stress in the i, j direction; ε ij is the strain component; t is the time component; T is the ambient temperature component;

[0035] When the selected material is in the elastic stage, the yield condition expression is:

[0036] F(kσ ij )=0

[0037] Where k is the strengthening coefficient, which gradually increases during the elastic deformation and stretching process.

[0038] As a preferred solution of the transmission line state assessment device based on stress change analysis of steel-core aluminum stranded wire, in the three-dimensional stress meshing model acquisition module, in the process of meshing and refining the transmission line conductor simulation model, the transmission line conductor simulation model is meshed and refined by the finite element analysis method to obtain the three-dimensional stress meshing model; the analysis submodule of the finite element analysis method includes:

[0039] A model segmentation submodule is used to segment the transmission line conductor simulation model into a plurality of finite elements according to set refinement requirements;

[0040] A finite element stiffness matrix construction submodule is used to establish a corresponding mathematical model in the finite element through physical equations to construct the stiffness matrix of the finite element;

[0041] A global equation generation submodule, used for assembling the stiffness matrices of several finite elements to generate a global equation for the entire structure;

[0042] A global equation solving submodule, used to solve the global equation and obtain a solution result;

[0043] The visualization and error analysis submodule is used to perform visualization and error analysis based on the solution results.

[0044] As a preferred solution of the transmission line status assessment device based on stress change analysis of steel-core aluminum stranded wire, in the stress change cloud map generation module, during the simulation calculation of the transmission line conductor stress, heat conduction occurs between the steel core, aluminum layer and air in the transmission line conductor; the heat conduction method satisfies the three-dimensional heat conduction equation; the expression of the three-dimensional heat conduction equation is:

[0045]

[0046] Where λ is the thermal conductivity of the conductor material; x, y, z are the three-dimensional rectangular coordinates; T is the temperature of the steel core aluminum stranded wire conductor; c is the specific heat capacity of the material; ρ is the density of the material; τ is the time; q is the unit volume heat rate of the steel core aluminum stranded wire q = I 2 R, I is the current flowing through the steel core aluminum stranded wire, and R is the resistance of the steel core aluminum stranded wire per unit volume.

[0047] As a preferred solution of the transmission line status assessment device based on stress change analysis of steel core aluminum stranded wire, in the stress change cloud map generation module, the set physical fields include: temperature field, electric field, solid heat transfer field and cable mechanics field.

[0048] The present invention has the following advantages: the present invention uses COMSOL simulation software to draw and twist the steel-core aluminum stranded wire of the transmission line conductor to construct a transmission line conductor simulation model; the transmission line conductor simulation model is meshed and refined to obtain a three-dimensional stress meshing model; the three-dimensional stress meshing model is coupled with a set physical field, and under the coupling action of the set physical field, the stress of the transmission line conductor is simulated and calculated to obtain a stress change result; a stress change cloud map is generated based on the stress change result; based on the stress change cloud map, the operating status of the transmission line is evaluated by observing the stress change of the steel-core aluminum stranded wire stranded layer, and the evaluation result is output. The present invention uses the COMSOL modeling and simulation method, uses the finite element calculation method to mesh different stranded layers of the steel-core aluminum stranded wire and perform physical field coupling calculation on them, and evaluates the operating status of the transmission line by observing the stress change cloud map of the transmission line stranded wire cross-section. Using COMSOL to model 3D transmission lines and integrating them with multiphysics coupling significantly improves the invisible response of transmission lines to meteorological factors and enhances the visualization of transmission line operations. The integration of multiphysics coupling more accurately reflects the stress changes in steel-core aluminum stranded conductors under varying convection conditions, enhancing the scientific nature of transmission line evaluation methods. This improves the operational stability, visibility, and controllability of the power grid, strengthens its resilience to various risks and disasters, and shifts from "planned maintenance" to "condition-based maintenance." BRIEF DESCRIPTION OF THE DRAWINGS

[0049] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can, without inventive effort, derive other implementation drawings based on the provided drawings.

[0050] The structures, proportions, sizes, etc. illustrated in this specification are intended solely to complement the contents disclosed herein and to facilitate understanding and reading by persons skilled in the art. They are not intended to limit the conditions under which the present invention may be implemented and therefore have no substantive technical significance. Any structural modifications, changes in proportions, or adjustments in sizes, without affecting the efficacy and objectives of the present invention, shall remain within the scope of the technical contents disclosed herein.

[0051] Figure 1 This is a flow chart of a method for evaluating the state of a power transmission line based on stress change analysis of an aluminum-steel core conductor provided in Example 1 of the present invention;

[0052] Figure 2This is a schematic diagram of a specific implementation process of the method for evaluating the state of a transmission line based on stress change analysis of an aluminum-steel core conductor provided in Example 1 of the present invention;

[0053] Figure 3 This is a common grid division diagram in the transmission line status assessment method based on stress change analysis of steel-core aluminum stranded wire provided in Example 1 of the present invention;

[0054] Figure 4 A schematic diagram of meshing refinement in COMSOL in the method for evaluating the state of a transmission line based on stress variation analysis of an aluminum stranded steel conductor provided in Example 1 of the present invention;

[0055] Figure 5 This is a schematic diagram of three-dimensional geometric modeling in the transmission line state assessment method based on stress change analysis of steel-core aluminum stranded wire provided in Example 1 of the present invention;

[0056] Figure 6 A schematic diagram of mesh division for the four-layer geometric modeling of aluminum-cored steel wire in the method for evaluating the state of a transmission line based on stress variation analysis of aluminum-cored steel wire provided in Example 1 of the present invention;

[0057] Figure 7 A schematic diagram of a stress calculation process in a transmission line state assessment method based on stress change analysis of an aluminum-steel core conductor provided in Example 1 of the present invention;

[0058] Figure 8 A schematic diagram of a cloud diagram of stress calculation results in the method for evaluating the state of a transmission line based on stress change analysis of an aluminum-steel core conductor provided in Example 1 of the present invention;

[0059] Figure 9 This is a schematic diagram of a TACSR / AS-150 / 25ACSR 4-layer twisted wire in a possible embodiment provided in Example 1 of the present invention;

[0060] Figure 10 This is a schematic diagram of a cloud diagram of stress calculation results in a possible embodiment provided in Example 1 of the present invention;

[0061] Figure 11 This is a schematic diagram of the architecture of a transmission line status assessment device based on stress change analysis of steel-core aluminum stranded wire provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0062] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0063] Example 1

[0064] See also Figure 1 and Figure 2 Embodiment 1 of the present invention provides a method for evaluating the state of a transmission line based on stress change analysis of an aluminum-steel core conductor, comprising the following steps:

[0065] S1. Using COMSOL simulation software, draw and twist the steel-core aluminum stranded wire of the transmission line conductor to build a transmission line conductor simulation model;

[0066] S2. Meshing and refining the transmission line conductor simulation model to obtain a three-dimensional stress meshing model;

[0067] S3. Couple the three-dimensional stress grid model with a set physical field, and simulate and calculate the stress of the transmission line conductor under the coupling effect of the set physical field to obtain a stress change result; and generate a stress change cloud map based on the stress change result;

[0068] S4. Evaluate the operating status of the transmission line by observing the stress changes in the stranded layers of the steel-core aluminum stranded wire according to the stress change cloud map, and output the evaluation result.

[0069] In this embodiment, in step S1, the steel-core aluminum stranded wire of the transmission line conductor is drawn and twisted by COMSOL simulation software to construct a transmission line conductor simulation model;

[0070] Specifically, a physical simulation model was constructed using COMSOL simulation software based on the components of the transmission line conductors. Conductor models were constructed for different voltage levels, and twisting and stress analysis were performed on the steel-core aluminum stranded wire. Corresponding material properties were assigned to the different components, resulting in a scaled-down physical simulation model of the transmission line conductors.

[0071] In this embodiment, the steel core portion of the steel core aluminum stranded wire is designed. The typical structure of the steel core aluminum stranded wire is that the different aluminum wires between each spiral stranded wire layer are twisted in a layered order. Except for the steel core, the twisting directions of the aluminum wires between adjacent layers are opposite. Due to the relatively complex physical model structure, the present invention uses COMSOL modeling to establish a finite element model of the transmission line conductor. Before establishing the physical model, in order to facilitate the subsequent stress change analysis, it is necessary to consider the elastic stage and yield stage of the material. That is, the yield criterion is used to determine whether the selected material is in the plastic stage. The yield condition is related to the temperature and load time of the model material. Its specific expression is:

[0072] F(σ ij ,ε ij ,t,T)=0

[0073] Where σ ij is the component of stress in the i, j direction; ε ij is the strain component; t is the time component; T is the ambient temperature component;

[0074] However, when the material is in the elastic stage, the stress component is directly proportional to the strain component, and the yield condition expression is:

[0075] F(kσ ij )=0

[0076] Where k is the strengthening coefficient, which gradually increases during the elastic deformation and stretching process.

[0077] In the three-dimensional unit slice stress plane, the yield condition corresponds to an elliptical plane model, while in three-dimensional stress space, it corresponds to a three-dimensional cylinder. Once the stress value exceeds the yield surface function graph, the material yields; otherwise, the material is in the elastic stage.

[0078] According to the stranding rules of steel core aluminum stranded wire, the unit length slice plane is swept, the curved stranding trajectory is designed and the torsion angle is set to construct a three-dimensional transmission line conductor stranding model. The center of the model is a circular steel wire, which serves as a steel core and plays a supporting role. The outer layer of steel core is attached to the steel core and twisted. The curvature of the aluminum wire is set by the depth and torsion degree. The steel core that plays a supporting role is mainly made of a steel core and a twisted outer layer of steel core. The aluminum layer wrapped outside the steel core is divided into an inner aluminum layer and an outer aluminum layer, and the twisting directions are opposite. The COMSOL three-dimensional steel core aluminum stranded wire model of the transmission line is obtained as follows Figure 5 shown.

[0079] In this embodiment, in step S2, the transmission line conductor simulation model is meshed and refined to obtain a three-dimensional stress mesh model;

[0080] Specifically, the transmission line conductor simulation model is meshed and refined, and the finite element method is used for approximate numerical calculation to discretize the complex twisted structure into many small units to obtain a three-dimensional stress mesh model, such as Figure 6 As shown, this facilitates the subsequent coupling and association of different physical fields. Meshing converts calculations originally attached to the physical model into a mesh. The smallest unit of meshing corresponds to geometric accuracy. The smaller the minimum unit of meshing, the higher the corresponding accuracy, which also means longer solution time and more memory required.

[0081] Finite element analysis is a numerical calculation method that uses the idea of discretization to solve complex physical problems. It decomposes complex structures to obtain a number of regular simple units, also known as finite elements, which are then numerically calculated and solved using mathematical models. The main steps of finite element analysis include the following five steps:

[0082] S21. Segmenting the transmission line conductor simulation model according to set refinement requirements to form a plurality of finite elements;

[0083] Specifically, complex problems are divided and appropriate unit types are selected. That is, complex physical models or structures are divided into many small sub-regions. Each small unit is a "finite element". These small units can be divided into triangles, quadrilaterals, tetrahedrons and other structures according to the different requirements of the refinement level of different models. These small units are combined and connected with each other to form a closed grid covering the entire physical model or complex structure. Common grid divisions include Figure 3 shown.

[0084] S22. Establishing a corresponding mathematical model in the finite element through physical equations to construct a stiffness matrix of the finite element;

[0085] Specifically, the unit stiffness matrix is constructed, and the corresponding mathematical model is established in each small unit using physical equations, including equilibrium equations, geometric constraints, material constitutive relations, and unit and global equations. The equation used to describe the equilibrium relationship of forces is called the equilibrium equation, and its expression is:

[0086] ▽·σ+f=0

[0087] Where σ is the stress tensor; f is the material volume stress; and ▽ is the divergence of σ (gradient operator). The equation describing the relationship between material stress and strain is as follows:

[0088] σ=Cε

[0089] Where C is the stiffness matrix of the material, also called the elastic constant matrix; ε is the strain tensor.

[0090] S23, assembling the stiffness matrices of the plurality of finite elements to generate a global equation for the entire structure;

[0091] Specifically, the matrices in each cell are assembled into the global equations of the entire structure or physical system. It is worth noting that the overall stiffness matrix K and the structural point load matrix P are both composed of the unit stiffness matrix K e and the unit equivalent nodal load matrix P e For the common triangular unit element, the stiffness matrix is expressed as:

[0092]

[0093] Where D is the elastic matrix; B is the strain matrix; B T is the transposed matrix of the strain matrix; t is the thickness of the triangular closed unit, which determines the unit's resistance to external forces; A is the cross-sectional area of the triangular closed unit.

[0094] The point load matrix includes the forces exerted by adjacent cells on the cell, and its expression is:

[0095] P e =[P ix P iy P jx P jy P mx P my ] T

[0096] The global system equation of the system is obtained through the collection of unit stiffness matrix and point load matrix, and the global system equation satisfies the following characteristics: symmetry, singularity, and constant positivity of the principal element.

[0097] S24, solving the global equation to obtain a solution;

[0098] Specifically, the system equations are solved to obtain the unknown quantities of each node, thereby determining the response of the entire system.

[0099] S25. Perform visualization and error analysis based on the solution results.

[0100] Specifically, visualization and error analysis are performed based on the solution results.

[0101] In this embodiment, before solving the stress calculation, it is necessary to perform appropriate mesh division on the three-dimensional geometric model. For common three-dimensional geometric models, hexahedral mesh is generally used for mesh division. However, due to the different minimum units obtained by mesh division at different levels of refinement, COMSOL provides the following mesh division methods: Figure 4Different precision settings are shown. Under normal circumstances, conventional partitioning can meet the needs of 3D geometric modeling. However, 3D units require more geometric units than 2D units. The interpolation function is a perfect polynomial of each degree in 3D coordinates. According to the geometric characteristics of 3D tetrahedral units, the volume coordinates of any point P in the unit are obtained as follows:

[0102]

[0103] Furthermore, the voxel volume coordinates L1, L2, L3, and L4 in each plane need to satisfy the condition: L1+L2+L3+L4=1.

[0104] In this embodiment, the transmission line conductor model acts on the temperature field and is affected by heat. The temperature field is not only a function of the spatial domain, but also a function of the time domain. However, the time and space domains are not coupled. Therefore, a partial discretization method is required to establish the finite element mesh format. The general expression of the finite element in the three-dimensional temperature field is:

[0105]

[0106] After partially integrating the above formula, we can get the temperature φ of n nodes i The matrix equation is:

[0107]

[0108] Where, C is the thermal melt matrix; K is the heat conduction matrix; C and K are both symmetric positive definite matrices; P is the temperature load matrix; φ is the temperature matrix; is the array of derivatives of nodal temperature with respect to time.

[0109] The minimum unit divided meets the above conditions, and the iterative process of finite element analysis converges.

[0110] In this embodiment, in step S3, the three-dimensional stress grid division model is coupled with a set physical field, and under the coupling effect of the set physical field, the stress of the transmission line conductor is simulated and calculated to obtain a stress change result; and a stress change cloud map is generated based on the stress change result;

[0111] Specifically, such as Figure 7 As shown in the figure, the transmission line conductor model after meshing is coupled with different physical fields, including temperature field, electric field, solid heat transfer field and cable mechanics field; under the coupling of different fields, the stress of the transmission line conductor is calculated and simulated, and the stress change cloud map is obtained according to its stress change, as shown in the figure. Figure 8 shown.

[0112] In this embodiment, COMSOL three-dimensional multi-physics field coupling is used, which includes temperature field, electric field, solid heat transfer field and cable mechanical field. When coupling different physical fields, it is necessary to pay attention to the need for interaction and mechanical balance between different physical fields. In the solid heat transfer field, it is necessary to consider the mass flow and heat transfer process in the fluid. When coupling physical fields, appropriate boundary conditions need to be set at the interface between different fields, and the dynamic balance of each field needs to be satisfied. At the same time, the steel core aluminum stranded wire of the present invention is respectively provided with a steel core layer, a steel core stranded layer, an aluminum wire stranded layer and an aluminum wire stranded layer from the inside to the outside. When coupling physical fields, the characteristics of different materials must also be considered. The role of the steel core layer and the steel core layer is to provide support, and the tensile coefficient is naturally higher than that of the outer stranded aluminum wire.

[0113] In this embodiment, the thermal effect of steel core aluminum stranded wire is analyzed. Heat conduction occurs between the steel core, aluminum layer, and air in the transmission line. The heat conduction method satisfies the three-dimensional heat conduction equation, so the heat conduction control equation of the transmission line can be established:

[0114]

[0115] Where λ is the thermal conductivity of the conductor material; x, y, z are the three-dimensional rectangular coordinates; T is the temperature of the steel core aluminum stranded wire conductor; c is the specific heat capacity of the material; ρ is the density of the material; τ is the time; q is the unit volume heat rate of the steel core aluminum stranded wire q = I 2 R, I is the current flowing through the steel core aluminum stranded wire, and R is the resistance of the steel core aluminum stranded wire per unit volume.

[0116] Since there is a temperature difference between the surface of the steel core aluminum stranded wire and the surrounding objects or air, heat will be exchanged between the two. This phenomenon is called thermal convection. Thermal convection can be divided into two types: natural convection and forced convection. Thermal convection produces heat exchange, and its heat exchange equation conforms to the convection heat transfer equation. The thermal convection expression is as follows:

[0117] q1=h(T a -T b )

[0118] Where h is the convection heat transfer coefficient between the conductor and the air; T a is the surface temperature of the transmission line; T b is the temperature of the environment surrounding the conductor.

[0119] The wind speed and humidity in the same environment have a greater impact on the convection coefficient between the surface of the steel core aluminum stranded wire and the air. When the wind speed v is less than 0.5m / s, natural convection is mainly in effect. When v is greater than or equal to 0.5m / s, forced convection takes the dominant position. The calculation of the convection coefficient at this time is as follows:

[0120]

[0121] Where λ is the thermal conductivity of air; Nu represents the convective heat transfer intensity; D eq is the equivalent diameter of the conductor.

[0122] In this embodiment, the steel-core aluminum stranded wire is exposed to atmospheric conditions. As wind speed fluctuates, the tension at both ends of the wire fluctuates. This causes the wires to vibrate under the influence of wind, and the stranded structure to undergo various states of tightening and loosening. In these situations, the steel strands provide support and are therefore rigid and less susceptible to deformation. However, the aluminum strands are relatively soft and are susceptible to deformation and extrusion when subjected to stress. Therefore, in practice, the stress variation trend of the aluminum strands is higher than that of the steel strands.

[0123] When stranding steel-core aluminum stranded wire, the axial stress and equivalent stress on the surface of each strand of steel-core aluminum strand are distributed in a spiral pattern, with the spiral direction being the same as the stranding direction. When the strand is subjected to a single tensile load, the strands twist back. The stress it experiences decreases from the inside out. The stress, deformation, and displacement generated by the axial stress of the strand per unit length is recorded as:

[0124]

[0125] Where Δs is the displacement recorded in the experiment; lexp is the effective length of the experimental strand (unit length); l FE is the wire length of the stranded wire finite element model.

[0126] By calculating the deformation displacement and drawing the stress cloud diagram of the transmission line stress simulation model, the natural stress displacement of the stranded wire when it is in the external environment is obtained, thereby formulating the transmission line operation status evaluation standard.

[0127] In this embodiment, in step S4, the operating status of the transmission line is evaluated by observing the stress changes in the stranded layers of the steel core aluminum stranded wire according to the stress change cloud map, and the evaluation result is output.

[0128] Specifically, such as Figure 8As shown in the figure, the stress changes of steel-core aluminum stranded conductors in transmission lines when twisted in different layers are recorded and analyzed. The stress decreases from the inside out. When the second layer of strands experiences a stress change, it inevitably leads to a geometric change in the third layer, either releasing or tightening the strands. However, due to the relatively loose structure of the outermost strands, heat is continuously reduced during air convection, and the probability of stress change itself is not high. However, due to the geometric deformation of the inner strands, they are affected by external forces, resulting in the most obvious displacement changes. Combining the above factors, the operating status of the transmission line is divided into three levels: normal, dangerous, and warning, based on the number of strands of different materials that change in the stress change diagram, and the transmission line operation status is evaluated. Within the unit length slice plane, when one of the strands of the fourth layer of aluminum stranded wire changes, it will squeeze the surrounding aluminum wires. Since the stress change will be absorbed by the gap between the aluminum layers, the change may not be obvious. At this time, the operation status of the transmission line is normal. However, when two strands of wire change due to stress, the deformation resistance of the geometric gap will be critical, which will inevitably cause stress changes in the third and fourth strands. At this time, the operation status of the transmission line is in a dangerous state. When stress changes occur in the inner steel core, the transmission line must be in a warning state.

[0129] In a possible embodiment, a specific verification example is provided as follows:

[0130] Taking TACSR / AS-150 / 25ACSR as an example, a 4-layer twisted cable is established.

[0131] The parameters of the steel core aluminum stranded wire are shown in Table 1:

[0132]

[0133]

[0134] Table 1 Geometric parameters of steel core aluminum stranded wire 3D modeling material parameters are shown in Table 2:

[0135]

[0136] Table 2 Material parameter settings

[0137] Establish a COMSOL 3D geometric model of the steel core aluminum stranded wire for transmission lines. Figure 9As shown, multi-physics field coupling simulation calculations are performed on it. Under the premise that the current flowing through the wire generates Joule heat, heat convection is generated between the wire and the air environment temperature. Through heat exchange, as the Joule heat of the different current-carrying strands themselves is balanced with the external environment temperature, when the temperature reaches the critical point where the strands can produce thermal expansion or cold contraction, the steel-core aluminum stranded wire of the transmission line produces geometric deformation. However, the geometric deformation of the transmission line due to the heat or temperature change generated by the Joule heat of the transmission line itself and the external convection is actually rare in reality. However, in order to make a complete and comprehensive assessment and fault warning of the transmission line, it is still very important to study the stress and geometric deformation of the conductor caused by temperature change.

[0138] The steel core aluminum stranded wire at 500A is now tested for ambient temperature changes. As the ambient temperature changes, it continuously exchanges heat with the Joule heat generated by itself, thereby observing the geometric deformation of the conductor strands in the simulation and then evaluating the status of the transmission line. Figure 10 As shown in the figure: when the external environment is 15℃, due to the thermal effect of the conductor itself, the heat exchange effect causes the overall temperature to rise, so its convection temperature rises, and the steel core aluminum stranded wire does not experience any stress offset or deformation; when the external environment temperature is 30℃, only the outer layer of the steel core aluminum stranded wire undergoes a slight geometric displacement, but it does not affect the inner layer of the stranded wire. Figure 2 The evaluation method shown in the figure shows that the four groups of pictures are all in normal operating status.

[0139] The test results show that the stress and displacement of the steel-core aluminum stranded wires vary continuously due to Joule heating from the current differential energy and thermal convection from the external environment. However, due to the strong ductility of aluminum, the deformation effect is not obvious. This is consistent with the laws of natural science and the actual operating conditions of power transmission lines. Therefore, the present invention is considered feasible. This method can provide guidance for the evaluation of power transmission lines, which is conducive to strengthening the resilience of power grids to various risks and disasters, and changing "planned maintenance" to "condition-based maintenance."

[0140] In summary, the present invention has the following advantages: the present invention uses COMSOL simulation software to draw and twist the steel core aluminum stranded wire of the transmission line conductor to construct a transmission line conductor simulation model; the transmission line conductor simulation model is meshed and refined to obtain a three-dimensional stress mesh division model; the three-dimensional stress mesh division model is coupled with a set physical field, and under the coupling action of the set physical field, the stress of the transmission line conductor is simulated and calculated to obtain a stress change result; a stress change cloud map is generated according to the stress change result; according to the stress change cloud map, the operating status of the transmission line is evaluated by observing the stress change of the steel core aluminum stranded wire twisted layer, and the evaluation result is output. The present invention uses the COMSOL modeling and simulation method, and through the finite element calculation method, meshes the different twisted layers of the steel core aluminum stranded wire and performs physical field coupling calculation on them, and evaluates the operating status of the transmission line by observing the stress change cloud map of the transmission line stranded wire cross-section. Using COMSOL to model 3D transmission lines and integrating them with multiphysics coupling significantly improves the invisible response of transmission lines to meteorological factors and enhances the visualization of transmission line operations. The integration of multiphysics coupling more accurately reflects the stress changes in steel-core aluminum stranded conductors under varying convection conditions, enhancing the scientific nature of transmission line evaluation methods. This improves the operational stability, visibility, and controllability of the power grid, strengthens its resilience to various risks and disasters, and shifts from "planned maintenance" to "condition-based maintenance."

[0141] It should be noted that the method of the embodiments of the present disclosure can be performed by a single device, such as a computer or server. The method of the embodiments of the present disclosure can also be applied in a distributed scenario, where multiple devices cooperate to perform the method. In such a distributed scenario, one of the multiple devices may only perform one or more steps of the method of the embodiments of the present disclosure, and the multiple devices will interact with each other to complete the method.

[0142] It should be noted that the above description is limited to some embodiments of the present disclosure. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in an order different from that described in the above embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0143] Example 2

[0144] See also Figure 11 Embodiment 2 of the present invention further provides a transmission line status assessment device based on stress change analysis of steel core aluminum stranded wire, comprising:

[0145] The transmission line conductor simulation model construction module 001 is used to draw and twist the steel-core aluminum stranded wire of the transmission line conductor using COMSOL simulation software to construct a transmission line conductor simulation model;

[0146] A three-dimensional stress mesh model acquisition module 002 is used to mesh and refine the transmission line conductor simulation model to obtain a three-dimensional stress mesh model;

[0147] The stress change cloud map generating module 003 is used to couple the three-dimensional stress grid division model with a set physical field, and simulate the stress of the transmission line conductor under the coupling effect of the set physical field to obtain stress change results; and generate a stress change cloud map based on the stress change results;

[0148] The transmission line operation status assessment module 004 is used to assess the transmission line operation status by observing the stress changes in the stranded layers of the steel core aluminum stranded wire according to the stress change cloud map, and output the assessment result.

[0149] In this embodiment, in the transmission line conductor simulation model construction module 001, before constructing the transmission line conductor simulation model, the stress stage of the selected material is determined; and whether the selected material is in the plastic stage is judged according to the yield condition; the yield condition expression is:

[0150] F(σ ij ,ε ij ,t,T)=0

[0151] Where σ ij is the component of stress in the i, j direction; ε ij is the strain component; t is the time component; T is the ambient temperature component;

[0152] When the selected material is in the elastic stage, the yield condition expression is:

[0153] F(kσ ij )=0

[0154] Where k is the strengthening coefficient, which gradually increases during the elastic deformation and stretching process.

[0155] In this embodiment, in the three-dimensional stress meshing model acquisition module 002, in the process of meshing and refining the transmission line conductor simulation model, the transmission line conductor simulation model is meshed and refined by the finite element analysis method to obtain the three-dimensional stress meshing model; the analysis submodule of the finite element analysis method includes:

[0156] The model segmentation submodule 021 is used to segment the transmission line conductor simulation model into a plurality of finite elements according to the set refinement requirements;

[0157] The finite element stiffness matrix construction submodule 022 is used to establish a corresponding mathematical model in the finite element through physical equations to construct the stiffness matrix of the finite element;

[0158] A global equation generation submodule 023 is used to assemble the stiffness matrices of the finite elements to generate a global equation for the entire structure;

[0159] The global equation solving submodule 024 is used to solve the global equation and obtain a solution result;

[0160] The visualization and error analysis submodule 025 is used to perform visualization and error analysis based on the solution results.

[0161] In this embodiment, in the stress change cloud map generation module 003, during the simulation calculation of the transmission line conductor stress, heat conduction occurs between the steel core, the aluminum layer, and the air in the transmission line conductor; the heat conduction method satisfies the three-dimensional heat conduction equation; the expression of the three-dimensional heat conduction equation is:

[0162]

[0163] Where λ is the thermal conductivity of the conductor material; x, y, z are the three-dimensional rectangular coordinates; T is the temperature of the steel core aluminum stranded wire conductor; c is the specific heat capacity of the material; ρ is the density of the material; τ is the time; q is the unit volume heat rate of the steel core aluminum stranded wire q = I 2 R, I is the current flowing through the steel core aluminum stranded wire, and R is the resistance of the steel core aluminum stranded wire per unit volume.

[0164] In this embodiment, in the stress variation cloud map generation module 003, the set physical fields include: temperature field, electric field, solid heat transfer field and cable mechanics field.

[0165] It should be noted that the information interaction, execution process, etc. between the modules of the above-mentioned system are based on the same concept as the method embodiment in Example 1 of the present application, and the technical effects they bring are the same as those of the method embodiment of the present application. For specific contents, please refer to the description in the method embodiment shown above in the present application, and no further details will be given here.

[0166] Example 3

[0167] Embodiment 3 of the present invention provides a non-transitory computer-readable storage medium, in which the program code of a transmission line status assessment method based on stress change analysis of steel-core aluminum stranded conductor is stored. The program code includes instructions for executing embodiment 1 or any possible implementation thereof.

[0168] Computer-readable storage media can be any available medium that can be accessed by a computer or a data storage device such as a server or data center that includes one or more available media. The available media can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid-state drives (SSDs)).

[0169] Example 4

[0170] Embodiment 4 of the present invention provides an electronic device, including: a memory and a processor;

[0171] The processor and the memory communicate with each other via a bus; the memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the transmission line status assessment method based on steel-core aluminum stranded wire stress change analysis of Example 1 or any possible implementation thereof.

[0172] Specifically, the processor can be implemented by hardware or by software. When implemented by hardware, the processor can be a logic circuit, an integrated circuit, etc.; when implemented by software, the processor can be a general-purpose processor, which is implemented by reading software code stored in a memory. The memory can be integrated into the processor or located outside the processor and exist independently.

[0173] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable systems. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website, computer, server or data center to another website, computer, server or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode.

[0174] Obviously, those skilled in the art will appreciate that the various modules or steps of the present invention described above can be implemented using a general-purpose computing system. They can be centralized on a single computing system or distributed across a network of multiple computing systems. Alternatively, they can be implemented using program code executable by a computing system, and thus, they can be stored in a storage system and executed by the computing system. In some cases, the steps shown or described herein can be performed in a different order than that shown, or they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module. Thus, the present invention is not limited to any particular combination of hardware and software.

[0175] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for evaluating the state of a transmission line based on stress change analysis of an aluminum-steel core conductor, characterized in that: include: Using COMSOL simulation software, the steel-core aluminum stranded wire of the transmission line conductor is drawn and twisted to construct a transmission line conductor simulation model; Meshing and refining the transmission line conductor simulation model to obtain a three-dimensional stress meshing model; The three-dimensional stress grid division model is coupled with a set physical field, and under the coupling effect of the set physical field, a simulation calculation is performed on the stress of the transmission line conductor to obtain a stress change result; and a stress change cloud map is generated according to the stress change result; According to the stress change cloud map, the operation status of the transmission line is evaluated by observing the stress changes in the stranded layers of the steel core aluminum stranded wire, and the evaluation results are output.

2. The method for evaluating the state of a transmission line based on stress change analysis of an aluminum-steel core conductor according to claim 1, characterized in that: Before constructing the transmission line conductor simulation model, the stress stage of the selected material is determined; whether the selected material is in the plastic stage is judged according to the yield condition; the yield condition expression is: F(s ij ,he ij ,t,T)=0 Where σ ij is the component of stress in the i, j direction; ε ij is the strain component; t is the time component; T is the ambient temperature component; When the selected material is in the elastic stage, the yield condition expression is: F(kσ ij )=0 Where k is the strengthening coefficient, which gradually increases during the elastic deformation and stretching process.

3. The method for evaluating the state of a power transmission line based on stress change analysis of an aluminum-steel core conductor according to claim 2, wherein: In the process of meshing and refining the transmission line conductor simulation model, meshing and refining the transmission line conductor simulation model by finite element analysis to obtain the three-dimensional stress meshing model; The analysis steps of the finite element analysis method are: According to the set refinement requirements, the transmission line conductor simulation model is divided into a plurality of finite elements; Establishing a corresponding mathematical model within the finite element through physical equations to construct a stiffness matrix of the finite element; Assembling the stiffness matrices of several finite elements to generate a global equation for the entire structure; Solving the global equation to obtain a solution result; Visualization and error analysis are performed based on the solution results.

4. The method for evaluating the state of a power transmission line based on stress change analysis of an aluminum-steel core conductor according to claim 3, characterized in that: During the simulation calculation of the stress of the transmission line conductor, heat conduction occurs between the steel core, the aluminum layer, and the air in the transmission line conductor. The heat conduction method satisfies the three-dimensional heat conduction equation. The expression of the three-dimensional heat conduction equation is: Where λ is the thermal conductivity of the conductor material; x, y, z are the three-dimensional rectangular coordinates; T is the temperature of the steel core aluminum stranded wire conductor; c is the specific heat capacity of the material; ρ is the density of the material; τ is the time; q is the unit volume heat rate of the steel core aluminum stranded wire q = I 2 R, I is the current flowing through the steel core aluminum stranded wire, and R is the resistance of the steel core aluminum stranded wire per unit volume.

5. The method for evaluating the state of a power transmission line based on stress change analysis of an ASCRI according to claim 4, characterized in that: The set physical fields include: temperature field, electric field, solid heat transfer field and cable mechanics field.

6. A transmission line status assessment device based on stress change analysis of steel core aluminum stranded wire, adopting the transmission line status assessment method based on stress change analysis of steel core aluminum stranded wire according to any one of claims 1 to 5, characterized in that: include: A transmission line conductor simulation model construction module is used to draw and twist the steel-core aluminum stranded wire of the transmission line conductor using COMSOL simulation software to construct a transmission line conductor simulation model; A three-dimensional stress grid division model acquisition module is used to grid the transmission line conductor simulation model and perform a refined solution to obtain a three-dimensional stress grid division model; A stress change cloud map generation module is used to couple the three-dimensional stress grid division model with a set physical field, and simulate the stress of the transmission line conductor under the coupling effect of the set physical field to obtain stress change results; and generate a stress change cloud map based on the stress change results; The transmission line operation status assessment module is used to assess the operation status of the transmission line by observing the stress changes in the stranded layers of the steel core aluminum stranded wire according to the stress change cloud map, and output the assessment result.

7. The transmission line status assessment device based on stress change analysis of steel-core aluminum stranded wire according to claim 6, characterized in that: In the transmission line conductor simulation model construction module, before constructing the transmission line conductor simulation model, the stress stage of the selected material is determined; whether the selected material is in the plastic stage is judged according to the yield condition; the yield condition expression is: F(s ij ,he ij ,t,T)=0 Where σ ij is the component of stress in the i, j direction; ε ij is the strain component; t is the time component; T is the ambient temperature component; When the selected material is in the elastic stage, the yield condition expression is: F(kσ ij )=0 Where k is the strengthening coefficient, which gradually increases during the elastic deformation and stretching process.

8. The transmission line status assessment device based on stress change analysis of steel-core aluminum stranded wire according to claim 7, characterized in that: In the three-dimensional stress meshing model acquisition module, in the process of meshing and refining the transmission line conductor simulation model, the transmission line conductor simulation model is meshed and refined by a finite element analysis method to obtain the three-dimensional stress meshing model; The analysis submodule of the finite element analysis method includes: A model segmentation submodule is used to segment the transmission line conductor simulation model into a plurality of finite elements according to set refinement requirements; A finite element stiffness matrix construction submodule is used to establish a corresponding mathematical model in the finite element through physical equations to construct the stiffness matrix of the finite element; A global equation generation submodule, used for assembling the stiffness matrices of several finite elements to generate a global equation for the entire structure; A global equation solving submodule, used to solve the global equation and obtain a solution result; The visualization and error analysis submodule is used to perform visualization and error analysis based on the solution results.

9. The transmission line status assessment device based on stress change analysis of steel-core aluminum stranded wire according to claim 8, characterized in that: In the stress change cloud map generation module, during the simulation calculation of the transmission line conductor stress, heat conduction occurs between the steel core, the aluminum layer, and the air in the transmission line conductor; the heat conduction method satisfies the three-dimensional heat conduction equation; the expression of the three-dimensional heat conduction equation is: Where λ is the thermal conductivity of the conductor material; x, y, z are the three-dimensional rectangular coordinates; T is the temperature of the steel core aluminum stranded wire conductor; c is the specific heat capacity of the material; ρ is the density of the material; τ is the time; q is the unit volume heat rate of the steel core aluminum stranded wire q = I 2 R, I is the current flowing through the steel core aluminum stranded wire, and R is the resistance of the steel core aluminum stranded wire per unit volume.

10. The transmission line status assessment device based on stress change analysis of steel-core aluminum stranded wire according to claim 9, characterized in that: In the stress change cloud map generation module, the set physical fields include: temperature field, electric field, solid heat transfer field and cable mechanics field.

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