Power transmission line state evaluation method under different complex meteorological conditions based on analytic hierarchy process

Abstract

The invention discloses a power transmission line state evaluation method based on an analytic hierarchy process under different complex meteorological conditions, and relates to the field of power transmission line state evaluation research. According to the method, a two-dimensional physical model of the power transmission line is established, and a power transmission line state evaluation method under different meteorological conditions is constructed; the meteorological data sets under different complex meteorological conditions describe probabilities corresponding to climate and meteorological conditions, the matching probability is calculated by associating the Bayesian network, and the meteorological data sets are established; a two-dimensional power transmission line conductor model is established, grids are divided by adopting a finite element analysis method, and the convergence of two-dimensional calculation is improved; through an analytic hierarchy process, performing weighted evaluation on meteorological data of the meteorological data set by taking the temperature as a target layer, and by means of a COMSOL simulation model, calculating a stress change and a displacement rate of a power transmission line lead as evaluation indexes, so as to construct a power transmission line evaluation method; and the requirement of power transmission line state evaluation under different complex meteorological conditions is effectively met.

Description

Technical Field

[0001] The invention relates to the field of power transmission line status assessment, and is a method for assessing the status of power transmission lines under different complex meteorological conditions based on artificial intelligence. Background Art

[0002] With the continuous expansion of the power system and the continuous expansion of the power grid, the transmission line, as an important part of the power system, directly affects the safety and stability of the power grid operation. At the same time, with the drastic changes in the global climate, different complex meteorological conditions have led to frequent occurrences of various severe weather conditions, which have a very serious impact on the transmission line. During the operation of the transmission line, various components are exposed to the external environment for a long time. The various equipment that constitutes the transmission line is greatly affected by the meteorological conditions. The operating environment is complex, not only susceptible to the external mechanical force, but also affected by the natural environment such as ice, snow and lightning. In recent years, various types of faults caused by complex meteorological conditions have emerged in an endless stream. Once an irreversible fault occurs in the transmission line, it will cause the associated power system to shut down or directly collapse, resulting in irreversible catastrophic effects. Different complex meteorological conditions have brought unprecedented challenges to the state assessment of transmission lines, and the research on the state assessment method of transmission lines under different complex meteorological conditions has also been further deepened.

[0003] Under this development trend, a method for evaluating the state of power transmission lines under different complex meteorological conditions is studied to improve the scientificity, completeness, accuracy and hierarchy of the state evaluation of power transmission lines. It also promotes the intelligentization and lightweight maintenance of power transmission lines. According to the constituent units and evaluation indicators of the transmission lines, a corresponding relationship diagram is drawn in combination with the meteorological data under different meteorological conditions, and a correlation analysis is performed on them to obtain a method for evaluating the state of power transmission lines under different complex meteorological conditions. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and defects of the prior art and to provide a method for evaluating the status of a transmission line under non-stop meteorological conditions which is highly scientific, accurate, reliable and has a relatively intelligent method.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for evaluating the state of a power transmission line under different complex meteorological conditions based on a hierarchical analysis method, the steps of which are as follows:

[0006] Step 1) Based on the Bayesian network, construct a data set of different complex meteorological conditions, and set different complex meteorological conditions as C i＝1，2，3，4，5 , C1 is temperature, C2 is humidity, C3 is wind speed, C4 is air pressure, C5 is precipitation, and the common complex weather is set as B j＝1，2，3，4, B1 is typhoon, B2 is blizzard, B3 is hail, and B4 is freezing rain; according to the associated Bayesian network theorem, the different meteorological probabilities corresponding to different meteorological conditions are obtained as P;

[0007] 1.1) Use Bayesian network to construct data set and calculate the probability of association between different complex meteorological conditions and different complex meteorological conditions:

[0008] Construct different complex meteorological condition data sets. Different meteorological conditions correspond to different meteorological conditions. The climatic factors corresponding to typhoon climate include wind speed and air pressure; the climatic factors corresponding to blizzard climate include temperature, humidity, and wind speed. i = {1, 2, 3, 4, 5} represents five meteorological factors, with b j = {1, 2, 3, 4} represents four different types of weather, then the associated probability P(C i =c i |B j =b j ), according to Bayes’ theorem, we get

[0009]

[0010] Where P(C i =c i ) is the prior probability of meteorological factors, P(B j =b j |C i =c i ) represents the posterior probability between different meteorological conditions and different weather conditions, P(B j =b j ) is the joint probability between different meteorological conditions and different meteorology;

[0011] The five types of meteorological conditions are independent and have no cross-relationship, so formula (1) can be expressed as:

[0012]

[0013] 1.2) According to Bayes' maximum a posteriori principle, select c i ={1, 2, 3, 4, 5} corresponds to the maximum state of random probability, which is used as the probability result of meteorological conditions. By training data samples, a meteorological data set for transmission lines under different meteorological conditions is constructed.

[0014] Step 2) Calculate the weighted temperature using the analytic hierarchy process, and replace C i＝1，2，3，4，5 Perform weighted evaluation with temperature as the objective function, wherein the scaling method selects the 1-9 scaling method; construct a judgment matrix, solve the weight value, and perform a new weight sorting to obtain a new weighted temperature;

[0015] 2.1) Calculate weighted temperature using AHP:

[0016] 2.1.1) Hierarchicalize complex problems and set target layers for the problems to be solved. The target layer is the factor or element with the largest final weight, which is the ultimate goal of the problem. Then, refine the criterion layer and standard layer to form a dominant relationship network from top to bottom. For overhead transmission lines, hail, heavy snow, and freezing rain weather conditions will cause ice coverage on overhead transmission lines. The main meteorological factor is temperature, so temperature is taken as the final goal.

[0017] 2.1.2) Construct a judgment matrix, and make comparative judgments between different indicators or influencing factors based on the relationship network. Suppose there are 1, 2, 3…m influencing factors, obtain relatively important data, and thus construct an m-order matrix:

[0018]

[0019] a ij Represents the weight values ​​in the judgment matrix (i = 1, 2, 3, ...m; j = 1, 2, 3, ...m). Matrix A is an m-order square matrix and is a judgment matrix;

[0020] 2.1.3) Check the consistency of the judgment matrix: If there is a consistency problem with the judgment matrix, calculate the maximum eigenvalue λ of the matrix A max = b, and λ max The corresponding eigenvector is the ranking weight of each element layer.

[0021] 2.1.4) The judgment matrix is ​​calculated row by row to obtain the weight of the corresponding factor. The factor with the largest weight is the main factor that has the greatest impact on the target factor.

[0022] 2.2) Constructing a judgment matrix: Before solving the weight of the temperature data, the judgment matrix is ​​set so that the final data fits the actual temperature. Since there are many different influencing factors in the judgment matrix, the influence of each factor is first arranged. When assigning values ​​to multiple factors, the 1-9 scaling method is selected. The weights of each factor are assigned according to the judgment matrix assignment standard to construct different types of judgment matrices.

[0023] 2.3) Recalculation of weight values ​​and weighted temperature calculation: For the influencing factors of the transmission line under complex meteorological conditions, mainly including: temperature, wind speed, humidity, air pressure, precipitation, the importance of temperature exists as the most influential factor, and its weight should be the largest. The judgment matrix is ​​obtained according to the judgment matrix assignment standard.

[0024] According to this judgment matrix, the five meteorological data factors are arranged in a matrix and compared layer by layer and row by row, and the judgment matrix is ​​obtained as follows:

[0025]

[0026] Select the axis function to calibrate the axis, solve different functions along the direction of the axis, and take different values ​​according to the dimensions of different data. For one-dimensional data, the corresponding value of axis is 0; for two-dimensional data, axis takes 0 or 1, and for three-dimensional data, axis takes 0, 1, and 2. In the present invention, the data involves time and space dimensions, and the axis takes 0, 1, and 2. When solving the specific program, only two-dimensional calculations are involved, and axis is selected as 1.

[0027] The weight solution of the AHP method requires the calculation of the maximum characteristic root of the judgment matrix. The 1-9 scaling method is used. In the process of solving the eigenvalue, the square root method is used to calculate the weight of each factor. The product operation is performed on each element in the judgment matrix and then the mth power is taken to obtain:

[0028]

[0029] where a ij is the element in row i and column j of the judgment matrix, r i is the value obtained by multiplying each element to the mth power; weighting formula (5) is sorted, and the calculation formula of the sorting value is:

[0030]

[0031] Where: w i is the new weight value; thus, the weight values ​​corresponding to different meteorological factors are obtained, and various meteorological factors are added according to the weight to obtain the required weighted temperature.

[0032] Step 3) Construct a two-dimensional conductor model of the COMSOL transmission line, build an evaluation system, perform multi-physics field coupling simulation on the conductor model based on the weighted temperature as the basic data, and build an evaluation standard based on the stress change and displacement cloud map.

[0033] In the step 3), the specific method is:

[0034] 3.1) Analysis of conductor thermal effect: Steel-core aluminum stranded wire will produce thermal effect due to its own current carrying capacity. Under the two heat dissipation conditions of natural convection and forced convection, temperature changes will occur. At the same time, there are different gaps between the strands, and thermal expansion caused by thermal effect will produce stress effect. Since the thermal conductivity coefficient of steel and aluminum in steel-core aluminum stranded wire will not change with the change of temperature, assuming that the gap between the steel core and the aluminum layer is ignored, the two-dimensional thermal conductivity equation of steel-core aluminum stranded wire is established:

[0035]

[0036] Where, λ is the thermal conductivity of the material, W / (m·K); t is the steel core temperature, °C; γ 1、 γ2 represents the unit heat rate of the steel core and aluminum layer, x is the position of the wire at this time, ρ is the material density, Kg / m 3 ; c is the specific heat capacity of the object, J / (kg·℃);

[0037] While transmitting electric energy, overhead transmission lines also consume a certain amount of energy and generate thermal effects. The heat of steel-core aluminum stranded wire includes the heat generated by itself under certain current carrying capacity conditions and the heat generated by the external environment.

[0038] The thermal effect of the overhead transmission line itself is:

[0039]

[0040] Among them, Q t is the heat generated by the wire, J; I is the current flowing through the wire, A; R is the unit resistance of the wire, Ω; t is the power-on time, s; ρ is the resistivity of the resistor material, L is the wire length, m; S is the cross-sectional area of ​​the wound wire, m 2 ; The heat dissipation will be different depending on the materials of the steel core and the aluminum layer;

[0041] 3.2) Temperature changes under the influence of external environment When external meteorological factors act on the transmission line, taking into account the temperature, humidity, air pressure, precipitation, and wind speed, the hierarchical analysis method is used to sort the weights of each factor and recalculate the weights to obtain the final weighted temperature measured by temperature as the temperature of the external environment. The heat dissipation of the conductor takes into account the influence of convection heat dissipation and radiation heat dissipation and sets the steel core heating rate to ε m , the heat generation rate of the aluminum layer is set to ε AL , whose expression is:

[0042]

[0043] Where Q is the heat generated per unit time when the current is passed through the material, J; A is the cross-sectional area of ​​each material, m 2 The aluminum layer of the steel core aluminum stranded wire is exposed to the outside. The reason why it is affected by solar radiation is that the solar radiation intensity under normal circumstances is E s , the heating rate of the aluminum wire layer needs to be recalculated as:

[0044]

[0045] Among them, Q AL is the heat per unit time of the aluminum material when the current is passed, J; D is the outer diameter of the conductor, m; that is, the overall diameter of the wire, η S is the absorptivity of the conductor to solar radiation;

[0046] After defining the material of the two-dimensional cross section of the overhead transmission line, the temperature field is applied to the space according to the boundary conditions. At this time, the temperature field scope is all the domains where the transmission line is located. In the steady-state solution environment, the temperature field calculation conditions for the transmission line are:

[0047]

[0048] Where ρ is the medium density, kg / m 3 ; C p is the specific heat capacity of the medium, J / (kg·℃); u is the flow velocity of the medium in the two-dimensional coordinate, m / s; Q ted is the heat source density load, W / m 3 ; T is the temperature function in two-dimensional coordinates, ℃;

[0049] Thermal insulation is set at the boundary between each strand of steel core aluminum stranded wire. Considering that different materials will deform during the stranding process, an assumed equation is made for the boundary condition so that heat conduction does not occur between the conductor materials, thereby establishing a thermal equation:

[0050] -n·q=0 (12)

[0051] Combined with formula (12), the out-of-plane heat flux of the domain is assumed and calculated. The overall out-of-plane heat flux is the algebraic sum of the upper inward heat flux and the lower inward heat flux. Let the upper inward heat flux be q 0,u , the heat flux from the lower side is q 0,d ; The total out-of-plane heat flux is:

[0052]

[0053] Among them, q 0,u ,q 0,d It is the heat exchanged between the solid surface and the fluid per unit area on the upper and lower sides of the material per unit time (heat flux density), W / m 2 ; T ext,u 、T ext,d is the fluid temperature on the solid surface, i.e., the upper and lower sides, K; h u 、h d is the upper and lower side convection heat transfer coefficient, W / (m 2 k);

[0054] The default medium around the outdoor transmission line is air, which generates natural convection. The temperature distribution of the overall temperature field in the two-dimensional plane is obtained in COMSOL by calculating through formulas (11)(12)(13). Since the steel core aluminum stranded wire will generate energy flow under exposed conditions, a solid heat transfer field is added;

[0055] 3.3) COMSOL 2D modeling: 2D geometry drawing is performed in COMSOL. When drawing a single section, the circular section is divided into four boundaries with a span unit of 90°. A temperature degree of freedom is generated at each node. The cross section of the steel core aluminum stranded wire is meshed and arranged according to the rotation geometry with the steel core as the center of the circle. The actual cross section of the overhead transmission line is used as a reference, and a 2D geometry model is constructed according to the national power grid operation and control technical standards.

[0056] The overall meshing includes the default setting, i.e., triangular meshing, and mesh scale function meshing;

[0057] When dividing the overall mesh, the number of meshes determines the time consumed for calculation. The more meshes there are, the longer the calculation time and the more iterations there are. The mesh density is related to the structural part to be divided. The mesh density for places with large bending degrees is different from that for flat and smooth places. The principle of mesh division is that the physical field within a unit will not change dramatically and will not produce large disturbances. For the two-dimensional plane of steel core aluminum stranded wire, quadrilateral mesh is used for mesh division.

[0058] When performing quadrilateral mesh division on the plane of the transmission line, the division is performed in units of mm, the maximum cell is set to 0.514, the minimum cell is set to 0.00193, the maximum and minimum cell growth rates are set to 1.2, and the curvature factor is set to 0.25; the two-dimensional mesh division diagram of the steel core aluminum stranded wire is obtained;

[0059] When solving the temperature field of overhead transmission lines, what is obtained is not a model of a sudden change, but a steady-state model under stable conditions. When adding a study, the steady state is selected for study, with electric current, solid mechanics, and solid and fluid heat transfer as the physical field interfaces.

[0060] 3.4) Evaluation system construction: According to the number of strands of different materials that change in the stress change diagram, the operation status of the transmission line is divided into three levels: good, normal, and dangerous. The operation status of the transmission line is evaluated. Because in the same plane, when one of the materials that enclose the cross-section changes, it will squeeze the surrounding strands, and the stress change will be absorbed by the gap. However, when two strands change due to stress, they will be in a critical state, which will inevitably cause stress changes in the third strand. When stress changes occur in the steel core, the transmission line must be in a dangerous state.

[0061] The evaluation method used in the above 3.4) is as follows: observe whether strand displacement occurs according to the stress change diagram simulated and calculated under the temperature data obtained by weighted hierarchical classification method; if displacement occurs, calculate the displacement amount to obtain the displacement change amount; according to the allowable stress deviation of ±2.5% for voltage levels of 220kV and above, the nominal outer diameter of LGJ-300 / 70 is ±0.63mm; according to the displacement change amount, and whether it is greater than ±0.63mm, the displacement judgment boundary of the steel core aluminum stranded wire is set to: the number of aluminum layer stress change strands in the stress change diagram ≤2 strands, 3 strands ≤ the number of aluminum layer stress change strands in the stress change diagram ≤5 strands, the aluminum layer stress changes greatly, and the steel core has stress offset; give the operation status level of the transmission line at this time according to different situations: good, normal, dangerous; thereby completing an evaluation of the operation status of the transmission line.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention discloses a method for evaluating the state of a transmission line under different complex meteorological conditions based on the hierarchical analysis method, which relates to the research field of transmission line state evaluation. The probability calculation and intensity association of different complex meteorological conditions are performed using an associated Bayesian network to construct a transmission line meteorological data set. Through the hierarchical analysis method, the meteorological data is weighted through three links of data processing, judgment matrix construction, and weight calculation, which has the characteristics of hierarchy, convenience, and accuracy; COMSOL is used to perform two-dimensional modeling of the transmission line, and the two-dimensional transmission line is coupled with multiple physical fields to realize the visualization of the two-dimensional stress changes of the transmission line under different meteorological conditions. The problem of invisible response of the transmission line under the action of meteorological factors is greatly improved, and the operation visualization of the transmission line is improved. The integration of multi-physical field coupling can more accurately reflect the physical changes of the transmission line under different complex meteorological conditions, and improve the scientific nature of the transmission line evaluation method. Thereby constructing a transmission line state evaluation standard under different complex meteorological conditions, and proposing an evaluation method for the transmission line under different complex meteorological conditions. Improve the operational stability, predictability and controllability of the power grid, enhance the ability to resist various risk disasters, and change "planned maintenance" to "condition-based maintenance". BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0064] Figure 1 is the dominance relationship network diagram of Example 1;

[0065] Figure 2 is a convection diagram around the line of Example 1;

[0066] Figure 3 is a two-dimensional transmission line modeling grid division diagram of Example 1;

[0067] Figure 4 is a diagram of the analytic hierarchy process calculation model of Example 1;

[0068] Figure 5 is a schematic diagram of the process of Example 1;

[0069] Figure 6 is a COMSOL modeling calculation convergence curve diagram of Example 2;

[0070] Figure 7 This is a graph showing stress variation results of running the COMSOL modeling under different meteorological conditions in Example 2;

[0071] Figure 8 It is a three-dimensional stress variation diagram under the weighted temperature of the special case of Example 2. DETAILED DESCRIPTION

[0072] The present invention will be further described below using the accompanying drawings and embodiments.

[0073] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0074] Example 1

[0075] Reference Figure 1 to Figure 5 , which is the first embodiment of the present invention, a method for evaluating the state of a power transmission line under different complex meteorological conditions based on the analytic hierarchy process, comprising:

[0076] Step 1): Construct different complex meteorological conditions data sets and set different complex meteorological conditions as C i＝1，2，3，4，5 They are 1: temperature; 2: humidity; 3: wind speed; 4: air pressure; 5: precipitation. Common complex weather conditions are set as B j＝1，2，3，4 , respectively 1: typhoon; 2: blizzard; 3: hail; 4: freezing rain. According to the association Bayesian network theorem, the different meteorological probabilities corresponding to different meteorological conditions are obtained as P.

[0077] The specific method is to establish data sets of different complex meteorological conditions and construct them with the help of associated Bayesian networks.

[0078] The Bayesian network is used to construct the data set. The probability of association between different complex meteorological conditions and different complex meteorological conditions is calculated.

[0079] Construct different complex meteorological conditions data sets. Different meteorological conditions correspond to different meteorological conditions. The climatic factors corresponding to typhoon climate include wind speed and air pressure; the climatic factors corresponding to blizzard climate include temperature, humidity, and wind speed. Therefore, different complex meteorological conditions are set as C i＝1，2，3，4，5 They are 1: temperature; 2: humidity; 3: wind speed; 4: air pressure; 5: precipitation, then use c i ={1, 2, 3, 4, 5} represents five meteorological factors. Set the common complex weather as B j＝1，2，3，4 , respectively: 1: typhoon; 2: blizzard; 3: hail; 4: freezing rain. j = {1, 2, 3, 4} represents four different types of weather, then the associated probability P(C i =c i |B j =b j ). According to Bayes' theorem, we can get

[0080]

[0081] Where P(C i =c i ) is the prior probability of meteorological factors, P(B j =b j |C i =c i ) represents the posterior probability between different meteorological conditions and different weather conditions, P(B j =b j ) is the joint probability between different meteorological conditions and different meteorology.

[0082] The five types of meteorological conditions are independent and have no cross-relationship, so formula (1) can be expressed as:

[0083]

[0084] According to Bayes' maximum a posteriori principle, c is selected i ={1, 2, 3, 4, 5} corresponds to the maximum state of random probability, which is used as the probability result of meteorological conditions. By training the data samples, a meteorological data set of transmission lines under different meteorological conditions is constructed.

[0085] Step 2): Calculate the weighted temperature using the AHP method. i＝1，2，3，4，5 Perform weighted evaluation with temperature as the objective function, where the scaling method is 1-9 scaling method. Construct a judgment matrix, solve the weight value, and perform a new weight sorting to obtain a new weighted temperature.

[0086] The specific method is: use the hierarchical analysis method to analyze and process the meteorological data to obtain the weighted temperature with temperature as the target layer.

[0087] 2.1) Calculate weighted temperature using the AHP. The AHP is essentially a way of thinking about decision-making, which gives the algorithm the characteristics of human thinking analysis, judgment and synthesis. The implementation of the AHP is mainly divided into four steps:

[0088] The first step is to hierarchize the complex problems and set the target layer for the problem to be solved. The target layer is the factor or element with the largest final weight, which is the ultimate goal of the problem. Then, the criterion layer and the standard layer are refined to form a dominance relationship network from top to bottom. For overhead transmission lines, hail, heavy snow, and freezing rain weather conditions will cause ice coverage on overhead transmission lines. The main meteorological factor is temperature, so temperature is taken as the final goal. Its dominance relationship network is as follows: Figure 1 shown.

[0089] The second step is to construct a judgment matrix. On the basis of the relationship network, different indicators or influencing factors are compared and judged (assuming there are 1, 2, 3...m influencing factors) to obtain relatively important data, thereby constructing an m-order matrix:

[0090]

[0091] a ij The matrix A represents the weight values ​​(i=1, 2, 3...m; j=1, 2, 3...m) in the judgment matrix. It is an m-order square matrix and is a judgment matrix.

[0092] The third step is to check the consistency of the judgment matrix. If there is a consistency problem with the judgment matrix, calculate the maximum eigenvalue λ of the matrix A max = b, and λ max The corresponding eigenvector is the ranking weight of each element layer.

[0093] The fourth step is to calculate the judgment matrix row by row to obtain the weights of the corresponding factors. The factor with the largest weight is the main factor that has the greatest impact on the target factor.

[0094] 2.2) Construction of the judgment matrix. Before solving the weights of the temperature data, the judgment matrix needs to be reasonably set so that the final temperature obtained is consistent with the actual situation. When constructing the judgment matrix, the consistency of the judgment matrix reflects the consistency of people's thinking and judgment. Maintaining its consistency is the key to making correct decisions. However, since there are many different influencing factors in the judgment matrix, the influence of each factor should be arranged first. When assigning values ​​to multiple factors, different scaling methods are often used. Common scaling methods include: three-scaling method, 1-9 scaling method, 9 / 9-9 / 1 scaling method, and 90 / 9-99 / 9 scaling method. Although the three-scaling method can ensure the orderliness of various elements, it lacks precision. Although the 9 / 9-9 / 1 scaling method and the 90 / 9-99 / 9 scaling method perform well in weight fitting, they do not have good scaling uniformity. The 1-9 scaling method has good scaling uniformity under the premise of ensuring orderliness. For an element of the upper layer, all elements in this layer are evaluated in pairs, and hierarchical sorting is carried out to arrange them in order of importance. Since the present invention aims to consider the influence of various factors on overhead transmission lines, it is necessary to evenly consider the influence of various factors. Therefore, the 1-9 scaling method with better scaling uniformity is selected, and the weights of various factors are assigned according to the judgment matrix assignment standard, thereby constructing different types of judgment matrices.

[0095] 2.3) Recalculation of weight values ​​and weighted temperature calculation. The factors affecting the transmission line under complex meteorological conditions mainly include: temperature, wind speed, humidity, air pressure, and precipitation (arranged according to the five meteorological elements). The importance of temperature is the most influential factor, and its weight should be the largest. The judgment matrix is ​​obtained according to the judgment matrix assignment standard.

[0096] According to this judgment matrix, the five meteorological data factors are arranged in a matrix and compared layer by layer and row by row. The judgment matrix is:

[0097]

[0098] When calculating the weight value, since the solution process involves the calculation of rows and columns, the axis (define axis function) function is selected to calibrate the axis, so that different functions are solved along the axis direction, and different values ​​are taken according to the dimensions of different data. For one-dimensional data, the corresponding value of axis is 0; for two-dimensional data, axis can take 0 and 1, and for three-dimensional data, its value can take 0, 1, 2. In the present invention, the data involves time and space dimensions, so its value can take 0, 1, 2. The present invention only involves two-dimensional calculations when solving specific programs, so axis is selected as 1.

[0099] The weight solution of the analytic hierarchy process (AHP) requires the calculation of the maximum eigenvalue of the judgment matrix. The present invention adopts the 1-9 scaling method. In the process of solving the eigenvalue, the square root method is used to calculate the weight of each factor. The product operation is performed on each element in the judgment matrix and then the m-th power is taken to obtain:

[0100]

[0101] The formula (3) is weighted and the calculation formula of the ranking value is:

[0102]

[0103] Thus, the weight values ​​corresponding to different meteorological factors are obtained, and various meteorological factors are added and calculated according to the weights, so as to obtain the weighted temperature required by the present invention.

[0104] Step 3): Construct a two-dimensional wire model of the COMSOL transmission line and build an evaluation system. On this basis, use the weighted temperature as the basic data to perform multi-physics field coupling simulation on the wire model, and build an evaluation standard based on its stress change and displacement cloud map.

[0105] The specific method is to construct a two-dimensional conductor model of the COMSOL transmission line and build an evaluation system.

[0106] 3.1) Analysis of conductor thermal effect. Steel core aluminum stranded wire will produce thermal effect due to its own current carrying capacity. Under the two heat dissipation conditions of natural convection and forced convection, temperature changes will occur. At the same time, there are different gaps between the strands, and thermal expansion due to thermal effect will produce stress effect. However, since the thermal conductivity coefficient of steel and aluminum in steel core aluminum stranded wire does not change with temperature, assuming that the gap between the steel core and the aluminum layer is ignored, the two-dimensional thermal conductivity equation of steel core aluminum stranded wire is established:

[0107]

[0108] Note: λ is the thermal conductivity of the material, W / (m·K); t is the steel core temperature, ℃; γ 1、 γ2 represents the unit heat rate of the steel core and aluminum layer, x is the position of the wire at this time, ρ is the material density, Kg / m 3 ; c is the specific heat capacity of the object, J / (kg·℃);

[0109] While transmitting electric energy, overhead transmission lines also consume a certain amount of energy and produce thermal effects. The heat of their steel-core aluminum stranded wires mainly includes the heat generated by themselves under certain current-carrying conditions and the heat generated by the external environment.

[0110] The thermal effect of the overhead transmission line itself is:

[0111]

[0112] Note: Q t is the heat generated by the wire, J; I is the current flowing through the wire, A; R is the unit resistance of the wire, Ω; t is the power-on time, s; ρ is the resistivity of the resistor material, L is the wire length, m; S is the cross-sectional area of ​​the wound wire, m 2 ; Depending on the materials of the steel core and the aluminum layer, there will be different heat dissipation.

[0113] 3.2) Temperature changes under the influence of external environment When external meteorological factors act on the transmission line, taking into account temperature, humidity, air pressure, precipitation, wind speed and other factors, the hierarchical analysis method is used to sort the weights of each factor and recalculate them to obtain the final weighted temperature measured by temperature as the temperature of the external environment. The heat dissipation of the conductor takes into account the influence of convection heat dissipation and radiation heat dissipation. The heat rate of the steel core is set to and the heat rate of the aluminum layer is set to. The expression is:

[0114]

[0115] Where Q is the heat generated per unit time when the current is passed through the material, J; A is the cross-sectional area of ​​each material, m 2 The aluminum layer of the steel core aluminum stranded wire analyzed in this invention is exposed to the outside, so considering the reason why it is exposed to solar radiation, the solar radiation intensity under normal circumstances is E s , generally 1000W / m 2 , so the heating rate of the aluminum wire layer needs to be recalculated as:

[0116]

[0117] Note: Q AL is the heat per unit time of the aluminum material when the current is passed, J; D is the outer diameter of the conductor, m; that is, the overall diameter of the wire, η S is the absorptivity of the conductor to solar radiation;

[0118] After defining the material of the two-dimensional cross section of the overhead transmission line, the temperature field is applied to the space according to its boundary conditions. At this time, the temperature field scope is all the domains where the transmission line is located. In the steady-state solution environment, the temperature field calculation conditions for the transmission line are:

[0119]

[0120] Where ρ is the medium density, kg / m 3 ; C p is the specific heat capacity of the medium, J / (kg·℃); u is the flow velocity of the medium in the two-dimensional coordinate, m / s; Q ted is the heat source density load, W / m 3 ; T is the temperature function in two-dimensional coordinates, ℃;

[0121] Thermal insulation is set at the boundary between each strand of steel core aluminum stranded wire. Considering that different materials will deform during the stranding process, an assumed equation is made for its boundary conditions so that no heat conduction occurs between the conductor materials, thereby establishing a thermal equation:

[0122] -n·q=0 (12)

[0123] Combined with formula (12), the out-of-plane heat flux of the domain is assumed and calculated. The overall out-of-plane heat flux is the algebraic sum of the upper inward heat flux and the lower inward heat flux. Let the upper inward heat flux be q 0,u , the heat flux from the lower side is q 0,d ; The total out-of-plane heat flux is:

[0124]

[0125] Note: 0,u ,q 0,d It is the heat exchanged between the solid surface and the fluid per unit area on the upper and lower sides of the material per unit time (heat flux density), W / m 2 ; T ext,u 、T ext,d is the fluid temperature on the solid surface, i.e., the upper and lower sides, K; h u 、h d is the upper and lower side convection heat transfer coefficient, W / (m 2 k);

[0126] By default, the medium surrounding the outdoor transmission line is air, which generates natural convection, such as Figure 2 By calculating the above formula, the temperature distribution of the overall temperature field in the two-dimensional plane can be obtained in COMSOL. Since the steel core aluminum stranded wire will produce energy flow under the exposed condition, it is necessary to add a solid heat transfer field.

[0127] 3.3) COMSOL 2D modeling. 2D geometry drawing is performed in COMSOL. When drawing a single section, the circular section is divided into four boundaries with a span of 90°. A temperature degree of freedom is generated at each node. The steel core aluminum stranded wire section is meshed and arranged according to the rotation geometry with the steel core as the center. As shown in the figure, the actual cross-section of the overhead transmission line is used as a reference. According to the national power grid operation and control technical standards, a 2D geometry model is constructed.

[0128] Meshing is an important part of multi-physics simulation. The overall meshing mainly includes default setting (triangular meshing) and mesh scale function. When meshing, the number of meshes determines the time consumption of calculation. The more meshes there are, the longer the calculation time and the more iterations. The mesh density is related to the part of the structure to be divided. The mesh density is different for places with large bending and places with flat and smooth surfaces. An important principle of meshing is that the physical field within a unit will not change dramatically and will not cause large disturbances. Commonly used meshing methods are triangular or quadrilateral meshing. Triangular meshing is more commonly used for long stress and constant strain units and for meshing three-dimensional geometry. Quadrilateral meshes are often used for units with very stress and very strain and for the division of two-dimensional planes. Therefore, quadrilateral meshes are used for meshing the two-dimensional plane of steel core aluminum stranded wire.

[0129] When the quadrilateral mesh is divided for the plane of the transmission line, it is divided in mm, the maximum cell is set to 0.514, the minimum cell is set to 0.00193, the maximum and minimum cell growth rates are set to 1.2, and the curvature factor is set to 0.25; the two-dimensional mesh division diagram of the steel core aluminum stranded wire is obtained as shown in Figure 3 shown.

[0130] When solving the temperature field of overhead transmission lines, what is obtained is not a model of a sudden change, but a steady-state model under stable conditions. When adding a study, the steady state is selected for study, with electric current, solid mechanics, and solid and fluid heat transfer as the physical field interfaces.

[0131] 3.4) Evaluation system construction. The present invention has matched a more appropriate judgment matrix through data training. According to this judgment matrix, the following Figure 4 The calculation model shown. According to the Electric Power Industry Standard of the People's Republic of China - Operating Code for Overhead Transmission Line, when calculating the damaged cross-section of aluminum stranded wire, the total area of ​​the conductor is used as the base for calculation; when calculating the sag, the temperature data after operation obtained by weighted temperature is used for calculation, and the influence caused by current and solar radiation can be ignored in the calculation. Combining the above elements, the operating status of the transmission line is divided into three levels: good, normal, and dangerous according to the number of strands of different materials that have changed in the stress change diagram, and the operating status of the transmission line is evaluated. Because in the same plane, when one of the materials that enclose the cross-section changes, it will squeeze the surrounding strands, and the stress change will be absorbed by the gap. However, when two strands of the line change due to stress, it will be in a critical state, which will inevitably cause stress changes in the third strand of the line. When the steel core has stress changes, the transmission line must be in a dangerous state. The final evaluation method is constructed as follows Figure 5 shown.

[0132] Example 2

[0133] Reference Figure 6 to Figure 8 ,In order to verify the feasibility of the transmission line status assessment method under ,different complex meteorological conditions based on the analytic hierarchy method proposed in ,the present invention, the meteorological data of the LGJ-150 / 35 overhead transmission line and a ,region on February 10 with a step span of hours are taken as ,an example to carry out status assessment verification.

[0134] The parameters of steel core aluminum stranded wire are shown in the table:

[0135] Table 1 Geometric parameters of steel core aluminum stranded wire

[0136]

[0137] The material parameters for 2D modeling are shown in the table:

[0138] Table 2 Material parameter setting table

[0139]

[0140] Different weighted temperatures are input in COMSOL for calculation, and the stress change diagram corresponding to different weighted temperatures is solved. The operation status of the transmission line is judged according to the stress change diagram. In the calculation process, since a nonlinear solver is selected, there is a jump at the starting position of each iteration in its convergence diagram, and each iteration will return to the normal accuracy range (1-0.1) at the end. The calculation convergence diagram is shown as follows: Figure 6 As shown, according to the design method of the present invention, two-dimensional modeling and calculation of the transmission line are performed. It can be seen that the model has good convergence, reflects the different components of the steel core aluminum stranded wire, and has certain feasibility.

[0141] In order to verify the feasibility of the power transmission line status evaluation method under different complex meteorological conditions based on the hierarchical analysis method proposed by the present invention, meteorological data under different meteorological conditions are selected to evaluate the operation status of the power transmission line under these meteorological conditions. According to the image comparison, the weighted temperature data is input into COMSOL to calculate the temperature field to obtain the stress diagram of the two-dimensional cross section of the overhead power transmission line. The stress cross-sectional diagram of group 1-group 2 has no change. Under this weighted temperature, the corresponding temperature, wind speed and air pressure are relatively stable, and the operation status of the transmission line is stable; in the stress cross-sectional diagram of group 3-group 9, a certain aluminum layer has a stress deviation, and a certain deviation has occurred in the original stress position. Among them, the stress situation of group 4, group 5, and group 8 is more obvious when the wind speed changes continuously. Groups 10, 13, 15, and 18 have obvious stress changes, but there is no abnormal phenomenon. The main reason is that the wind speed has a large fluctuation under the temperature change, causing the twisted conductors to dance and slightly deform. In actual conditions, the corresponding transmission line of this group is in good operation and no fault occurs. Therefore, this model can be used as an evaluation model for the operation status of the transmission line. In order to make the results more realistic, when the stress of the steel core aluminum stranded wire changes, the stress change displacement is derived to obtain the displacement change data at each coordinate of the two-dimensional transmission line section. Origin is used to draw a three-dimensional image to intuitively see the degree and position of the stress change, thereby obtaining a three-dimensional graph of the displacement data of the stress change. Take the weighted temperature of 34.85374921 as an example to display the displacement data, such as Figure 7 As shown. Based on the displacement change data, the displacement change data at each point of the two-dimensional cross section is derived, and the data is imported into Origin for three-dimensional image processing, as shown below. Figure 8 The three-dimensional graph shown in the figure, a is a scatter plot of the displacement of the aluminum wire in the stranded wire, and b is a 3D surface graph of the displacement of the aluminum wire in the stranded wire. The two graphs can more intuitively observe the displacement of each strand of the line. At this time, the three strands of aluminum wire have undergone displacement changes. The statistical displacement data shows that the maximum displacement data at this time is 0.09265mm. At this time, the transmission line is operating normally. The allowable stress deviation of the steel core aluminum stranded wire at a voltage level of 220kV and above is ±2.5%, which is ±0.63mm for the nominal outer diameter of LGJ-300 / 70. That is, when the maximum displacement data does not exceed ±0.63mm, the line is operating normally.

[0142] The test results show that the evaluation results of the transmission line under this meteorological condition are consistent with the actual line operation results. It can be considered that the transmission line status evaluation method under different complex meteorological conditions based on the hierarchical analysis method proposed in this invention has certain feasibility. Based on this method, it can provide guidance for the evaluation of other components of the transmission line, which is conducive to improving the operational stability and controllability of the power grid, enhancing the resilience to various risk disasters, and changing "planned maintenance" to "condition maintenance".

[0143] The specific implementation methods of the present invention are not exhaustive and do not constitute a limitation on the scope of protection of the claims. Based on the inspiration gained from the embodiments of the present invention, those skilled in the art can think of other substantially equivalent alternatives without creative work, all of which are within the scope of protection of the present invention.

Claims

1. A method for evaluating the state of a power transmission line under different complex meteorological conditions based on the analytic hierarchy process, characterized in that: The steps are: Step 1) Based on the Bayesian network, construct a data set of different complex meteorological conditions, and set different complex meteorological conditions as C i＝1，2，3，4，5 , C1 is temperature, C2 is humidity, C3 is wind speed, C4 is air pressure, C5 is precipitation, and the common complex weather is set as B j＝1，2，3，4 , B1 is typhoon, B2 is blizzard, B3 is hail, and B4 is freezing rain; according to the associated Bayesian network theorem, the different meteorological probabilities corresponding to different meteorological conditions are obtained as P; Step 2) Calculate the weighted temperature using the analytic hierarchy process, and replace C i＝1，2，3，4，5 Perform weighted evaluation with temperature as the objective function, wherein the scaling method selects the 1-9 scaling method; Construct a judgment matrix, solve the weight value, and perform a new weight sorting to obtain a new weighted temperature; Step 3) Construct a two-dimensional conductor model of the COMSOL transmission line, build an evaluation system, perform multi-physics field coupling simulation on the conductor model based on the weighted temperature as the basic data, and build an evaluation standard based on the stress change and displacement cloud map.

2. A method for evaluating the state of a power transmission line under different complex meteorological conditions based on the analytic hierarchy process according to claim 1, characterized in that: In the step 1), the specific method is: 1.1) Use Bayesian network to construct data set and calculate the probability of association between different complex meteorological conditions and different complex meteorological conditions: Construct different complex meteorological condition data sets. Different meteorological conditions correspond to different meteorological conditions. The climatic factors corresponding to typhoon climate include wind speed and air pressure; the climatic factors corresponding to blizzard climate include temperature, humidity, and wind speed. i = {1, 2, 3, 4, 5} represents five meteorological factors, with b j = {1, 2, 3, 4} represents four different types of weather, then the associated probability P(C i =c i |B j =b j ), according to Bayes’ theorem, we get Where P(C i =c i ) is the prior probability of meteorological factors, P(B j =b j |C i =c i ) represents the posterior probability between different meteorological conditions and different weather conditions, P(B j =b j ) is the joint probability between different meteorological conditions and different meteorology; The five types of meteorological conditions are independent and have no cross-relationship, so formula (1) can be expressed as: 1.2) According to Bayes' maximum a posteriori principle, select c i ={1, 2, 3, 4, 5} corresponds to the maximum state of random probability, which is used as the probability result of meteorological conditions. By training data samples, a meteorological data set for transmission lines under different meteorological conditions is constructed.

3. The method for evaluating the state of a power transmission line under different complex meteorological conditions based on the analytic hierarchy process according to claim 1 is characterized in that: In the step 2), the specific method is: 2.1) Calculate weighted temperature using AHP: 2.1.1) Hierarchicalize complex problems and set target layers for the problems to be solved. The target layer is the factor or element with the largest final weight, which is the ultimate goal of the problem. Then, refine the criterion layer and standard layer to form a dominant relationship network from top to bottom. For overhead transmission lines, hail, heavy snow, and freezing rain weather conditions will cause ice coverage on overhead transmission lines. The main meteorological factor is temperature, so temperature is taken as the final goal. 2.1.2) Construct a judgment matrix, and make comparative judgments between different indicators or influencing factors based on the relationship network. Suppose there are 1, 2, 3…m influencing factors, obtain relatively important data, and thus construct an m-order matrix: a ij Represents the weight values ​​in the judgment matrix (1=1, 2, 3…m; j=1, 2, 3…m). Matrix A is an m-order square matrix and is a judgment matrix. 2.1.3) Check the consistency of the judgment matrix: If there is a consistency problem with the judgment matrix, calculate the maximum eigenvalue λ of the matrix A max = b, and λ max The corresponding eigenvector is the ranking weight of each element layer. 2.1.4) The judgment matrix is ​​calculated row by row to obtain the weight of the corresponding factor. The factor with the largest weight is the main factor that has the greatest impact on the target factor. 2.2) Constructing a judgment matrix: Before solving the weight of the temperature data, the judgment matrix is ​​set so that the final data fits the actual temperature. Since there are many different influencing factors in the judgment matrix, the influence of each factor is first arranged. When assigning values ​​to multiple factors, the 1-9 scaling method is selected. The weights of each factor are assigned according to the judgment matrix assignment standard to construct different types of judgment matrices. 2.3) Recalculation of weight values ​​and weighted temperature calculation: For the influencing factors of the transmission line under complex meteorological conditions, mainly including: temperature, wind speed, humidity, air pressure, precipitation, the importance of temperature exists as the most influential factor, and its weight should be the largest. The judgment matrix is ​​obtained according to the judgment matrix assignment standard. According to this judgment matrix, the five meteorological data factors are arranged in a matrix and compared layer by layer and row by row, and the judgment matrix is ​​obtained as follows: Select the axis function to calibrate the axis, solve different functions along the direction of the axis, and take different values ​​according to the dimensions of different data. For one-dimensional data, the corresponding value of axis is 0; for two-dimensional data, axis takes 0 or 1, and for three-dimensional data, axis takes 0, 1, and 2. In the present invention, the data involves time and space dimensions, and the axis takes 0, 1, and 2. When solving the specific program, only two-dimensional calculations are involved, and axis is selected as 1. The weight solution of the AHP method requires the calculation of the maximum characteristic root of the judgment matrix. The 1-9 scaling method is used. In the process of solving the eigenvalue, the square root method is used to calculate the weight of each factor. The product operation is performed on each element in the judgment matrix and then the mth power is taken to obtain: where a ij is the element in row i and column j of the judgment matrix, r i is the value obtained by multiplying each element to the mth power; weighting formula (5) is sorted, and the calculation formula of the sorting value is: Where: w i is the new weight value; thus, the weight values ​​corresponding to different meteorological factors are obtained, and various meteorological factors are added according to the weight to obtain the required weighted temperature.

4. The method for evaluating the state of a power transmission line under different complex meteorological conditions based on the analytic hierarchy process according to claim 1 is characterized in that: In the step 3), the specific method is: 3.1) Analysis of conductor thermal effect: Steel-core aluminum stranded wire will produce thermal effect due to its own current carrying capacity. Under the two heat dissipation conditions of natural convection and forced convection, temperature changes will occur. At the same time, there are different gaps between the strands, and thermal expansion caused by thermal effect will produce stress effect. Since the thermal conductivity coefficient of steel and aluminum in steel-core aluminum stranded wire will not change with the change of temperature, assuming that the gap between the steel core and the aluminum layer is ignored, the two-dimensional thermal conductivity equation of steel-core aluminum stranded wire is established: Where, λ is the thermal conductivity of the material, W / (m·K); t is the steel core temperature, °C; γ 1、 γ2 represents the unit heat rate of the steel core and aluminum layer, x is the position of the wire at this time, ρ is the material density, Kg / m 3 ; c is the specific heat capacity of the object, J / (kg·℃); While transmitting electric energy, overhead transmission lines also consume a certain amount of energy and generate thermal effects. The heat of steel-core aluminum stranded wire includes the heat generated by itself under certain current carrying capacity conditions and the heat generated by the external environment. The thermal effect of the overhead transmission line itself is: Among them, Q t is the heat generated by the wire, J; I is the current flowing through the wire, A; R is the unit resistance of the wire, Ω; t is the power-on time, s; ρ is the resistivity of the resistor material, L is the wire length, m; S is the cross-sectional area of ​​the wound wire, m 2 ; The heat dissipation will be different depending on the materials of the steel core and the aluminum layer; 3.2) Temperature changes under the influence of external environment When external meteorological factors act on the transmission line, taking into account the temperature, humidity, air pressure, precipitation, and wind speed, the hierarchical analysis method is used to sort the weights of each factor and recalculate the weights to obtain the final weighted temperature measured by temperature as the temperature of the external environment. The heat dissipation of the conductor takes into account the influence of convection heat dissipation and radiation heat dissipation and sets the steel core heating rate to ε m , the heat generation rate of the aluminum layer is set to ε AL , whose expression is: Where Q is the heat generated per unit time when the current is passed through the material, J; A is the cross-sectional area of ​​each material, m 2 The aluminum layer of the steel core aluminum stranded wire is exposed to the outside. The reason why it is affected by solar radiation is that the solar radiation intensity under normal circumstances is E s , the heating rate of the aluminum wire layer needs to be recalculated as: Among them, Q AL is the heat per unit time of the aluminum material when the current is passed, J; D is the outer diameter of the conductor, m; that is, the overall diameter of the wire, η S is the absorptivity of the conductor to solar radiation; After defining the material of the two-dimensional cross section of the overhead transmission line, the temperature field is applied to the space according to the boundary conditions. At this time, the temperature field scope is all the domains where the transmission line is located. In the steady-state solution environment, the temperature field calculation conditions for the transmission line are: Where ρ is the medium density, kg / m 3 ; C p is the specific heat capacity of the medium, J / (kg·℃); u is the flow velocity of the medium in the two-dimensional coordinate, m / s; Q ted is the heat source density load, W / m 3 ; T is the temperature function in two-dimensional coordinates, ℃; Thermal insulation is set at the boundary between each strand of steel core aluminum stranded wire. Considering that different materials will deform during the stranding process, an assumed equation is made for the boundary condition so that heat conduction does not occur between the conductor materials, thereby establishing a thermal equation: -n·q=0 (12) Combined with formula (12), the out-of-plane heat flux of the domain is assumed and calculated. The overall out-of-plane heat flux is the algebraic sum of the upper inward heat flux and the lower inward heat flux. Let the upper inward heat flux be q 0,u , the heat flux from the lower side is q 0,d ; The total out-of-plane heat flux is: Among them, q 0,u ,q 0,d It is the heat exchanged between the solid surface and the fluid per unit area on the upper and lower sides of the material per unit time (heat flux density), W / m 2 ; T ext,u , T ext,d is the fluid temperature on the solid surface, i.e., the upper and lower sides, K; h u 、h d is the upper and lower side convection heat transfer coefficient, W / (m 2 k); The default medium around the outdoor transmission line is air, which generates natural convection. The temperature distribution of the overall temperature field in the two-dimensional plane is obtained in COMSOL by calculating through formulas (11)(12)(13). Since the steel core aluminum stranded wire will generate energy flow under exposed conditions, a solid heat transfer field is added; 3.3) COMSOL 2D modeling: 2D geometry drawing is performed in COMSOL. When drawing a single section, the circular section is divided into four boundaries with a span unit of 90°. A temperature degree of freedom is generated at each node. The cross section of the steel core aluminum stranded wire is meshed and arranged according to the rotation geometry with the steel core as the center of the circle. The actual cross section of the overhead transmission line is used as a reference, and a 2D geometry model is constructed according to the national power grid operation and control technical standards. The overall meshing includes the default setting, i.e., triangular meshing, and mesh scale function meshing; When dividing the overall mesh, the number of meshes determines the time consumed for calculation. The more meshes there are, the longer the calculation time and the more iterations there are. The mesh density is related to the structural part to be divided. The mesh density for places with large bending degrees is different from that for flat and smooth places. The principle of mesh division is that the physical field within a unit will not change dramatically and will not produce large disturbances. For the two-dimensional plane of steel core aluminum stranded wire, quadrilateral mesh is used for mesh division. When performing quadrilateral mesh division on the plane of the transmission line, the division is performed in units of mm, the maximum cell is set to 0.514, the minimum cell is set to 0.00193, the maximum and minimum cell growth rates are set to 1.2, and the curvature factor is set to 0.25; the two-dimensional mesh division diagram of the steel core aluminum stranded wire is obtained; When solving the temperature field of overhead transmission lines, what is obtained is not a model of a sudden change, but a steady-state model under stable conditions. When adding a study, the steady state is selected for study, with electric current, solid mechanics, and solid and fluid heat transfer as the physical field interfaces. 3.4) Evaluation system construction: According to the number of strands of different materials that change in the stress change diagram, the operation status of the transmission line is divided into three levels: good, normal, and dangerous. The operation status of the transmission line is evaluated. Because in the same plane, when one of the materials that enclose the cross-section changes, it will squeeze the surrounding strands, and the stress change will be absorbed by the gap. However, when two strands change due to stress, they will be in a critical state, which will inevitably cause stress changes in the third strand. When stress changes occur in the steel core, the transmission line must be in a dangerous state.

5. The method for evaluating the state of a power transmission line under different complex meteorological conditions based on the analytic hierarchy process according to claim 4 is characterized in that: The evaluation method used in the above 3.4) is specifically as follows: observe whether strand displacement occurs according to the stress change diagram simulated and calculated under the temperature data obtained by weighting by the hierarchical classification method; if displacement occurs, calculate the displacement amount to obtain the displacement change amount; according to the allowable stress deviation of 220kV and above voltage levels of ±2.5%, the nominal outer diameter of LGJ-300 / 70 is ±0.63mm; according to the displacement change amount, according to whether it is greater than ±0.63mm, the displacement judgment boundary of the steel core aluminum stranded wire is set to: the number of aluminum layer stress change strands in the stress change diagram ≤2 strands, 3 strands ≤ the number of aluminum layer stress change strands in the stress change diagram ≤5 strands, the aluminum layer stress change is huge, and the steel core has stress offset; According to different situations, the transmission line is given an operating status level: good, normal, dangerous; This completes an evaluation of the transmission line operation status.

Images