Method for calculating windage yaw of power transmission tower-line system

Abstract

The invention provides a power transmission tower-line system windage yaw calculation method, and belongs to the technical field of electric power engineering. According to the technical scheme, breeze field characteristics and formation mechanisms of typical power transmission line sections in Qinghai under specific landforms are studied, and based on wind field data under a large amount of micro-topographic conditions, wind tunnel tests and theoretical calculation are combined to analyze wind deflection mechanisms of typical tower structures and possible wind damage tripping and even tower falling rules. Based on theoretical research and wind tunnel test data, a power transmission tower-line system windage yaw calculation model under the micro-topographic condition is established, and breakthrough and innovation are achieved in the aspects of a power transmission line windage yaw mechanism and error prevention and control. The method is beneficial to improving the technical level of disaster prevention and reduction of the power system, provides theoretical guidance for erecting subsequent power transmission lines in similar topographic and geomorphic areas in Qinghai, and further improves the safety and stability of the power system.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power engineering, and further to the analysis and prevention of wind deflection flashover faults in high-voltage transmission lines, and specifically to a method for calculating wind deflection of a transmission tower-line system. Background Art

[0002] Wind deviation is one of the main factors causing transmission line failures, and wind deviation prevention has always been valued by the State Grid Corporation's operation department. In recent years, wind deviation has occurred frequently on Qinghai's transmission lines, causing line tripping, arc burns, line breaks and other faults. Wind deviation prevention and control work needs to be strengthened urgently. The environment of transmission lines with wind deviation faults is usually mountainous or windy. If the local climate conditions are not analyzed in depth during line design, the tower head size will not be consistent with the standard requirements, resulting in frequent wind deviation flashover faults.

[0003] In some micro-topographic areas in Qinghai, once in a strong wind environment, it is very easy to cause squall line winds. Under the action of squall line winds, the spatial distance between the insulator string and the tower will be reduced. Once the minimum voltage requirement for discharge cannot be met, flashover will occur. The wind-induced flashover failure of high-voltage transmission lines that has occurred so far is directly related to disastrous meteorological conditions, especially in weather with strong winds mixed with thunderstorms, which is more likely to cause wind-induced flashover failures. When wind-induced flashover failures occur, the insulation strength of the transmission line will also show a downward trend. In addition, under the action of strong winds, rainwater on the conductor will form a directional intermittent water line with the wind direction. Once it is in the same direction as the discharge flashover path, it will cause the discharge voltage of the air gap to show a downward trend, which is also an important factor in the occurrence of wind deviation in the line. Moreover, in some local areas, at the wind outlet and wind duct, the wind force is relatively concentrated, and these micro-meteorological conditions are also very likely to cause wind-induced flashover failures.

[0004] The occurrence of wind deviation is often related to strong winds. This was also found in the inspection of areas with multiple wind deviation fault discharges. Strong winds on site usually break or uproot large trees, and wind deviation flashover of transmission lines occurs under such strong winds. Because once the conductor is under the action of strong winds, it will have a certain deviation from the specified standard position, and because the gap between the insulator string and the tower head is reduced, the spatial field strength is enhanced, which will cause local high field strength to occur at the tip of the conductor hardware and the tower body, causing discharge at this location. Since wind deviation discharge occurs in transmission lines, the air gap distance between the conductor and the tower or between the conductors is reduced under the action of strong winds, and once the electrical strength of this gap distance does not match the operating voltage specified by the system, it will cause a discharge accident. In order to better prevent the occurrence of wind deviation faults, it is necessary to strengthen the design wind speed design margin, construction and installation technology, tower head size and other aspects. Establishing a wind deviation calculation model for the transmission tower-line system under micro-topography conditions and accurately calculating the wind deviation displacement are the basis for the above design and analysis work. Summary of the invention

[0005] The technical problem to be solved by the present invention is: how to establish a windage calculation model for a transmission tower-line system under micro-topography conditions and accurately calculate the windage displacement.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A method for calculating the windage of a transmission tower-line system, in which the maximum sag f of the transmission line is calculated by the following formula: m :

[0008]

[0009] In the above formula, l is the span, g is the gravity per unit length of the ground wire, and Τ is the horizontal tension of the overhead line. is the height difference angle, γ is the load ratio of the ground conductor, and σ0 is the horizontal stress at each point of the ground conductor;

[0010] The sag f at any point can be calculated by the following formula: x :

[0011]

[0012] In the above formula, x is the horizontal distance from one side of the tower, l is the span, and f m is the maximum sag;

[0013] The horizontal windage displacement x and the vertical windage displacement y of any point are calculated by the following two formulas:

[0014]

[0015] In the above two equations, λ is the length of the insulator string, ξ is the wind deflection angle of the conductor, is the wind deflection angle of the insulator string. Preferably, in this method, the wind load acting on the transmission line is calculated by the following formula:

[0016] W x =α·ω0·μ z ·μ s β c ·d·L p ·sin 2 θ;

[0017] In the above formula, W x is the wind load perpendicular to the line direction, ω0 is the standard value of the reference wind pressure, α is the wind pressure unevenness coefficient, μ z is the wind pressure height variation coefficient, μ s Line shape factor, β c is the wind load adjustment factor, d is the conductor cross-sectional diameter, L p is the horizontal span, θ is the angle between the wind load and the line;

[0018] in:

[0019] ω0=v 2 / 1600;

[0020] v is the wind speed at a reference height of 10 m.

[0021] As a preference, the wind pressure unevenness coefficient α is determined according to the design basic wind speed according to Table 1; the wind pressure height variation coefficient μ z Determine according to Table 1; Line shape coefficient μ s , when the conductor diameter is less than 17mm or when ice is applied, μ s =1.2, when the wire diameter is greater than or equal to 17mm, take μ s =1.1; 500KV and 750KV line conductor wind load adjustment factor β c According to the design basic wind speed, determine according to Table 2;

[0022] Table 1

[0023]

[0024] Table 2

[0025]

[0026] Preferably, in the method, the process of computational fluid dynamics comprises:

[0027] 1) Establish the control equation;

[0028] 2) Determine initial conditions and boundary conditions;

[0029] 3) Divide the grid and generate calculation points;

[0030] 4) Establish discrete equations;

[0031] 5) Determine control parameters;

[0032] 6) Solve discrete equations;

[0033] 7) Determine whether it converges, and if it converges, execute the following step 8), and if it does not converge, return to the above step 2);

[0034] 8) Output the calculation results.

[0035] Preferably, the Euler description of the fluid mechanics control equation is as shown in the following four equations:

[0036]

[0037] In the above four equations, ρ is the fluid density, t is the flow time; τ is the viscous stress component existing on the surface of the microelement; is the velocity vector, and its components in the three coordinate directions are u, v, and w respectively; p represents the pressure on the fluid element.

[0038] Preferably, the micro-topographic conditions of the object calculated by the method include: pass-type terrain, high mountain watershed-type terrain, water vapor enhancement-type terrain, terrain lifting-type terrain, and canyon wind channel-type terrain.

[0039] Preferably, in this method, the inlet boundary condition expression of the micro-topography wind field includes a turbulent kinetic energy expression and a dissipation rate expression, wherein the turbulent kinetic energy expression is as follows:

[0040]

[0041] The dissipation rate expression is as follows:

[0042]

[0043] In the above two equations, I(z) represents the turbulence at height z, L u is the turbulence integral scale, C u The value is 0.09 and the value of K is 0.42.

[0044] As a preference:

[0045]

[0046]

[0047] In the above two formulas, z g is the gradient wind height, z in the B type terrainb =5m.

[0048] Preferably, in this method, the surface roughness of the micro-topography wind field is determined by the roughness height parameter k s To describe, the roughness height parameter k s The roughness length z0 satisfies the following relationship:

[0049] k s =20z0;

[0050] where z0 is determined by the Class B landform roughness specification.

[0051] Preferably, after the calculation is completed, the calculation results are verified by a wind tunnel test of the transmission tower-line system.

[0052] The present invention provides a method for calculating the wind deviation of a transmission tower-line system. This technical solution studies the characteristics and formation mechanism of the micro-wind field of a typical transmission line section in Qinghai under specific terrain and landforms. Based on a large amount of wind field data under micro-terrain conditions, combined with wind tunnel tests and theoretical calculations, the wind deviation mechanism of a typical tower structure and the laws of possible wind damage tripping and even tower collapse are analyzed. Based on the data from theoretical research and wind tunnel tests, a wind deviation calculation model for a transmission tower-line system under micro-terrain conditions is established, achieving breakthroughs and innovations in the wind deviation mechanism and error prevention of transmission lines. The present invention is conducive to improving the technical level of disaster prevention and mitigation of power systems, providing theoretical guidance for the subsequent construction of transmission lines in areas with similar terrain and landforms in Qinghai, thereby improving the safety and stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a CFD numerical calculation flow chart in the present invention.

[0054] Figure 2 This is a schematic diagram of the pass-type terrain.

[0055] Figure 3 This is a schematic diagram of the alpine watershed terrain.

[0056] Figure 4 It is a schematic diagram of water vapor enhanced terrain.

[0057] Figure 5 It is a schematic diagram of topographic lift terrain.

[0058] Figure 6 This is a schematic diagram of the canyon wind tunnel type terrain.

[0059] Figure 7 This is the result diagram of the self-maintenance verification of the default wind profile formula.

[0060] Figure 8 This is the verification result diagram of the self-sustaining performance of the corrected wind profile.

[0061] Fig. 9 It is a schematic diagram of the windage displacement of the conductor.

[0062] Fig.10 It is a schematic diagram of the research ideas of wind loads in the field of structural engineering.

[0063] Fig.11 This is a physical picture of the wind tunnel test section.

[0064] Fig.12 This is a physical picture of the control console for wind tunnel testing.

[0065] Fig.13 It is a comparison chart of the theoretical and measured wind speeds of the transmission tower-line system in a typical topographic turbulent wind field. DETAILED DESCRIPTION

[0066] The specific embodiments of the present invention will be described in detail below. In order to avoid too much unnecessary details, the well-known structures or functions will not be described in detail in the following examples. The approximate language used in the following examples can be used for quantitative expression, indicating that the quantity can be allowed to have a certain change without changing the basic function. Unless otherwise defined, the technical and scientific terms used in the following examples have the same meaning as those generally understood by those skilled in the art to which the present invention belongs.

[0067] 1. Micro-topography high-precision wind field simulation

[0068] 1.1 Computational Fluid Dynamics Theory

[0069] Computational Fluid Dynamics (CFD) is an analytical method and means for solving fluid flow, heat transfer effects and flow field related parameters based on a computer platform. The basic principle of CFD is to divide the overall continuous fluid calculation domain in three-dimensional space into extremely small calculation units. Using finite units as the minimum calculation scale, solve the fluid mechanics control equations on the micro-element and finally obtain the flow field characteristics. The basic process of CFD numerical calculation is as follows: Figure 1 shown.

[0070] Any form of fluid flow always follows the basic physical conservation laws, including the conservation laws of mass, momentum, energy and components. The research object of this invention is the micro-topography wind field, and the heat transfer and chemical components are not considered, that is, the energy conservation equation and the component mass conservation equation are not involved in the calculation. In the default inertial rectangular coordinate system, the Euler description of the fluid mechanics control equation is:

[0071]

[0072] Where ρ is the fluid density and t is the flow time. Due to the viscosity of the molecules, there is a viscous stress component on the surface of the microelement, which is recorded as τ. is the velocity vector, whose components in the three coordinate directions are u, v, and w respectively; p represents the pressure on the fluid element; formula (1) is the continuity equation for conservation of mass, and formulas (2)(3)(4) are the momentum conservation equations.

[0073] The core idea of ​​CFD numerical calculation is to discretize the units in the calculation domain, and then discretize the control equations. The control equations are discretely solved by three discrete methods: finite difference method (FDM), finite element method (FEM) and finite volume method (FVM). Among them, the finite volume method is the most widely used discretization method in most commercial CFD software. The present invention uses the Fluent module in the ANSYS workbench platform to solve the finite volume method.

[0074] The finite volume method divides the computational domain into micro-element control volumes and discretizes and solves differential equations on each micro-element volume. Compared with the finite difference method, the finite volume method does not require the orthogonality of the discrete grid, so unstructured grids can be used extensively to solve complex flow field model problems. In actual calculations, the amount of grid calculation is small, and the memory space occupied is small, so it is possible to divide the flow field details more finely.

[0075] 1.2 Main types of micro-topography

[0076] Transmission lines built in micro-topography and micro-meteorology areas will be affected by the local airflow operating environment and may be adversely affected by extreme wind speeds or increased icing beyond the design. Typical micro-topography and micro-meteorology can be roughly divided into five types.

[0077] (1) Passage type Figure 2 ). In the passes formed between the long mountains, the airflow shows a concentrated acceleration phenomenon. When the power transmission line in the mountainous area crosses the pass, the narrow channel effect will cause the lateral wind speed to increase significantly, and there is also the possibility of a small increase in ice cover.

[0078] (2) High mountain watershed type Figure 3 ). When the line corridor crosses the watershed, the windward slope terrain lifting effect generates strong winds full of water vapor, which can easily lead to the collapse of the windward slope line tower and disconnection. At the top of the mountain and the windward slope, the adiabatic expansion process occurs along the slope under the action of wind, so that the supercooled water is cooled out of the air and attached to the conductor, which aggravates the icing of the conductor. The windward and leeward slopes of the watershed have certain vertical wind speeds, which have a certain impact on the force on the conductor.

[0079] (3) Water vapor growth type ( Figure 4If the transmission line is near a large river or lake, due to the high humidity in the air all year round, once a cold front arrives or the temperature drops below 0°C, it is easy for the overhead transmission wires to be severely covered with ice at all angles, increasing the burden on the wires and insulator strings.

[0080] (4) Terrain uplift type Figure 5 ). It is generally a terrain step in a plain landform, or a basin edge with one side lower and the other side higher, or a stepped hilly slope. Because the basin is low and has sufficient water vapor and high air humidity, cold air easily rises along the hillside with the wind. Similar to the watershed type terrain, clouds and fog form on the top of the hillside, and when the temperature drops during the cold wave, severe ice will appear. At the same time, the terrain-lifting micro-topography will produce obvious vertical wind speed due to the airflow climbing effect, which has a great impact on the force on the conductor.

[0081] (5) Canyon Wind Channel Type Figure 6 ). The line crosses the canyon, and the two banks are very high and steep. The narrow channel effect generates a large and long-lasting local lateral wind speed, which will lead to a significant increase in the wind load on the transmission line.

[0082] 1.3 Introduction to micro-topography wind field

[0083] (1) Inlet boundary conditions

[0084] The inlet boundary condition setting is the core parameter of CFD analysis. The self-maintenance of the boundary conditions must be ensured to verify the correctness of the simulated wind field. The self-maintenance of the boundary conditions is defined as: the inlet boundary wind profile needs to remain unchanged throughout the flow of the flow field before reaching the target. Some studies have obtained three methods for maintaining the inlet profile through the self-maintenance of boundary conditions. The inlet wind profile can be maintained by adjusting the coefficients of the inlet profile expression, adjusting the empirical coefficients of the turbulence model, or using a modified wall function.

[0085] The inlet wind profile is the combination of the mean wind profile and the turbulent wind profile.

[0086] The turbulence profile mainly includes two parameters: turbulent kinetic energy and dissipation rate. In general mean flow field analysis, it is assumed that turbulence is isotropic. The initial turbulent kinetic energy expression and dissipation rate expression are:

[0087]

[0088] Where I(z) represents the turbulence at height z, L u is the turbulence integral scale. There is no clear formula for turbulence intensity and integral scale in the current standards of my country. According to the research results of this invention, C u The value is 0.09 and the value of K is 0.42.

[0089]

[0090] Where z g is the gradient wind height, z in the B type terrain b =5m. The default formula is used to define the inlet wind profile of the calculation domain for calculation, and the wind speed profile reaching 1km is selected. The comparison results are as follows: Figure 7 shown.

[0091] from Figure 7 It can be seen that the eddy viscosity value parameter of the default turbulence formula of Fluent is relatively large, and the near-ground wind profile has undergone a large deformation before it touches the mountain. The horizontal wind speed has increased to a certain extent within 200m above the ground; and above 200m above the ground, the wind speed has decreased relatively. Due to the high eddy viscosity value in the near-ground area, the profile wind speed tends to be evenly distributed. The expression of the eddy viscosity value in the k-ε turbulence model is:

[0092]

[0093] Formula (9) shows that the eddy viscosity value is proportional to the square of the turbulent kinetic energy and inversely proportional to the turbulent dissipation rate. By adjusting the turbulent kinetic energy and turbulent dissipation rate parameter coefficients, the influence of the eddy viscosity value on the near-surface wind field is reduced. After adjusting the coefficients, the self-sustaining property of the wind profile is verified, and the following boundary condition expression is obtained after iterative adjustment:

[0094]

[0095] Formulas (10) and (11) with adjusted coefficients are used as the inlet boundary conditions in the numerical model. The wind speed profile at the position 1 km in front of the micro-topography mountain is extracted and compared with the inlet wind speed profile. The results are as follows: Figure 8 The results show that by adjusting the turbulent kinetic energy and turbulent dissipation rate, thereby reducing the near-ground eddy viscosity value, the defined wind profile can be more accurately applied to the mountain terrain, and the self-maintenance of the wind profile is relatively stable. The numerical calculation process of the flat terrain wind field and the micro-terrain wind field of the present invention will adopt the inlet boundary condition setting.

[0096] (2) Surface roughness

[0097] When analyzing the wind field characteristics of mountainous terrain, the definition of surface roughness in aerodynamics is used: due to the influence of the undulation of the surface or the geometric shape of the landform itself, the position where the wind speed is zero on the wind speed profile is higher than the height of the ground surface at 0, and this height is defined as the aerodynamic roughness. The roughness length z0 is generally used to describe the surface roughness. In the present invention, the roughness height parameter is used to describe the surface roughness, and the conversion relationship between this parameter and the roughness length z0 is as follows:

[0098] k s =20z0 (12)

[0099] The initial surface roughness height value is 0. Since the present invention analyzes the terrain and wind field, the surface roughness cannot be ignored, and the parameters here need to be modified. Determine z0 according to the Class B landform roughness specification, and then convert the roughness height k according to formula (12): s In order to reflect the difference in surface roughness between flat landform and micro-topography mountain, the present invention takes into account the influence of actual ground vegetation and sets the surface roughness of the mountain to 1.5 times that of the flat landform, i.e., the surface roughness heights of the mountain and flat land are 1.2m and 0.8m respectively.

[0100] (3) Turbulence model

[0101] Navier-Stokes equations, also known as NS equations, are motion equations that describe the conservation of momentum for viscous incompressible fluids. When the unsteady NS equations are used to simulate and solve the fluid, due to the need for finite element analysis, the solution to the flow field equations will be discretized into extremely small time and space steps for separate solutions, which will result in a huge amount of CPU calculations and does not meet the needs of engineering calculations. It is necessary to introduce the Reynolds time-averaged simulation method to simplify the NS equations by time averaging. However, in the obtained time-averaged physical quantity control equations, the Reynolds stress is unknown and unsolvable. In order to make the equations solvable, it is necessary to introduce a hypothetical model to assist in the solution. The model created under this assumption is the turbulence model. There are three commonly used turbulence models for numerical simulation of flow fields in Fluent: the standard k-ε model, the RNG k-ε model, and the Realizable k-ε model.

[0102] The standard k-ε model is the most common model in engineering flow field calculations. It is a semi-empirical formula model. Its accuracy and convergence meet the requirements of engineering calculations for fully turbulent flows, but it is not accurate enough when calculating the results of strongly separated flows, large curvature flows, and strong pressure gradient flows.

[0103] The RNGk-ε model adds turbulent vortex equations compared to the standard k-ε model. The RNG theory includes an analytical formula for low Reynolds number flow viscosity, which makes the model more accurate than the standard model for near-wall analysis. The RNGk-ε model has high accuracy in complex shear flow, swirl and separation flow fields.

[0104] Compared with the standard k-ε model, the Realizable k-ε model adds a turbulent viscosity formula and a transmission equation for the dissipation rate. This model can accurately predict rotational flow, boundary layer flow with strong adverse pressure gradient, flow separation and other occasions. For the simulation of wind field conditions in the atmospheric boundary layer, the Realizable k-ε turbulence model is widely considered to be more accurate. The Realizable k-ε turbulence model is used in the Fluent setting of the present invention for solution.

[0105] (4) Determination of computational domain parameters

[0106] After determining the values ​​of several key parameters, the computational domain of the numerical model can be established. According to the pass-hillside landform characteristics and the actual GPS ranging parameters, the micro-topography of the section is modeled through the ANSYS-Design Modeler platform. In the present invention, the maximum height of the micro-topography mountain is 1km, the maximum length of the micro-topography mountain is 9.8km, and the maximum width of the micro-topography mountain is 7.1km. In order to ensure that the fluid in the computational domain can fully develop and avoid the unnecessary influence of the flow field boundary, the height of the CFD computational domain is 5 times the height of the mountain, the length of the computational domain is 8 times the length of the mountain, and the width is 5 times the width of the mountain, and the blockage ratio is controlled below 5%.

[0107] 2. Transmission line-tower system wind deviation calculation model

[0108] Under the action of wind load, overhead transmission lines and insulator strings will deviate from their initial positions, which may cause the distance between the line and the tower to decrease, or cause the air gap between the line and surrounding trees and buildings to decrease. When the distance between the line and other objects does not reach the electrical safety distance, wind-induced flashover or even discharge to the object may occur. According to the actual operation experience of mountain lines, wind-induced tripping accidents are mostly in the form of wind-induced tripping of a certain line section or a certain tower in the micro-topography area. There is also damage to the ground wire and insulators, and there are fewer tower collapses and dancing. Therefore, in order to ensure the normal operation of transmission lines in micro-topography areas, it is very important to accurately estimate the wind-induced parameters of insulator strings and transmission lines. Combined with the micro-topography wind field obtained by numerical calculation and the finite element model of the tower-line system, the wind-induced response of the tower-line system under micro-topography is studied.

[0109] 2.1 Calculation of wind loads on transmission tower and line systems

[0110] The design of transmission towers usually considers the static wind load as the main load, and loads the dynamic wind load equivalent to the static wind load. The external forces on the transmission tower line system are divided into two main parts: one is the wind load acting on the poles of the tower, which is calculated at different heights and applied to the tower in sections; the other is the wind load acting on the transmission line, which is then transferred to the crossarm of the transmission tower through the insulator string. The concentrated load on the transmission tower is mainly the force applied to the crossarm insulator and the conductor, and the magnitude of the force depends on the load calculation parameters of the conductor.

[0111] For the N45-N46-N47 three-tower two-line system model, under the action of wind load, the wind load on the transmission line is the main load, and the wind load on the transmission tower is the secondary load. The wind load on the insulator string is ignored here. The present invention determines that the wind load acting on the transmission line is calculated according to (Formula 13).

[0112] W x =α·ω0·μ z ·μ s β c ·d·L p ·sin 2 θ (13)

[0113] ω0=v 2 / 1600 (14)

[0114] Among them, W x ——wind load perpendicular to the line direction (kN);

[0115] ω0——standard value of reference wind pressure (kN / m 2 );

[0116] α——wind pressure unevenness coefficient;

[0117] μ z ——wind pressure height variation coefficient;

[0118] μ s ——shape factor of the line;

[0119] β c ——wind load adjustment factor;

[0120] d——conductor cross-sectional diameter. If it is a split conductor, the sum of the diameters is taken (m);

[0121] L p ——Horizontal span (m);

[0122] θ——the angle between wind load and line (°);

[0123] v——wind speed at reference height of 10m (m / s).

[0124] The wind pressure unevenness coefficient α should be determined according to the design basic wind speed as shown in Table 1; the wind pressure height variation coefficient μ z Determine according to Table 1; Line shape coefficient μ s When the conductor diameter is less than 17 mm or covered with ice (regardless of the conductor diameter), μ s =1.2, the wire diameter is greater than or equal to 17mm, μ s =1.1; 500KV and 750KV line conductor wind load adjustment factor β c It should be determined according to Table 2 based on the design basic wind speed.

[0125] Table 1 Wind pressure unevenness coefficient and wind load adjustment coefficient

[0126]

[0127] Table 2 Variation coefficient of wind pressure height for Class B ground roughness

[0128]

[0129] 2.2 Calculation of conductor windage displacement

[0130] (1) Calculation theory of conductor windage

[0131] Under strong wind conditions, the transmission line will deviate a certain distance from the original state due to the continuous effect of the average wind field. When the wind displacement of the conductor in the gear is too large, the overhead wire may not be within the electrical safety distance from surrounding trees, buildings, other poles and towers, etc., which may lead to discharge. Therefore, it is necessary to pay attention to the maximum wind displacement of the conductor under strong wind conditions, especially under micro-meteorological conditions.

[0132] There are mountains, buildings, trees, etc. near the side conductors of the transmission line. The conductors in the section need to be calibrated for maximum wind deviation based on the maximum wind conditions or icing conditions to meet the clearance distance requirements.

[0133] Calculate the maximum sag f m , generally appears in the middle of the gear span, can be measured from the cross-sectional diagram, or calculated using the formula.

[0134]

[0135] l——spacing, unit: m, obtained from the cross-section diagram or detailed list

[0136] g——self-weight per unit length of ground wire, unit: N / m

[0137] Τ——Horizontal tension of overhead line, unit: N

[0138] ——Elevation angle, unit: °, obtained from the height difference between the front and rear side ground wire hanging points and the gear spacing;

[0139] γ——ground wire load ratio, unit: N / m·mm2

[0140] σ0——Horizontal stress at each point of the ground wire, unit: N / mm2

[0141] Calculate the sag f at any point x , which can be measured from the cross-sectional diagram or calculated using the formula.

[0142]

[0143] x——horizontal distance from one side of the tower, unit: m;

[0144] l——gear spacing, unit: m, f m (i.e. f max )——maximum sag, unit: m.

[0145] Then the horizontal windage displacement x of any point is

[0146]

[0147] The vertical windage displacement y of this point is

[0148]

[0149] Where λ is the length of the insulator string, ξ is the wind deflection angle of the conductor, is the wind deflection angle of the insulator string,

[0150] (2) Comparative analysis between numerical simulation and specifications

[0151] Compare and calculate the maximum windage displacement of the conductor:

[0152] Working condition 1: Based on the line parameters and standard formulas, the maximum windage displacement of the two conductors under the horizontal wind load is calculated respectively;

[0153] Working condition 2: Based on the finite element model of the transmission tower line structure, the conductor is only loaded with horizontal wind load, and the maximum wind displacement of the two-stage conductor is numerically solved;

[0154] Working condition 3: Based on the finite element model of the transmission tower line structure and the micro-topography CFD wind field data, the horizontal wind load under micro-topography conditions is loaded in four sections, and the maximum wind displacement of the two-stage conductor is numerically solved;

[0155] Working condition 4: Based on the finite element model of the transmission tower line structure and the micro-topography CFD wind field data, the horizontal wind load and vertical wind load under micro-topography conditions are loaded in four sections at the same time, and the maximum wind displacement of the two-stage conductors is numerically solved;

[0156] Calculation of maximum windage displacement of conductor in X direction for working conditions 2, 3, and 4 ( Fig. 9 ) and simulation results are shown in Table 3.

[0157] Table 3 Calculation of maximum windage displacement of conductors (unit: m)

[0158]

[0159] It can be seen from the above table that the calculated maximum windage displacement of the conductor in working condition 1 is relatively safe compared with the simulation calculation value of working condition 2; working condition 3 takes into account the horizontal wind load of micro-topography. Compared with the flat terrain wind load in working condition 2, the maximum windage displacement of the conductor is significantly improved due to the acceleration effect of the micro-topography wind field, and the improvement is about 18-19%%; and after considering the vertical wind speed of the micro-topography, the maximum windage displacement of the conductor in working condition 4 is significantly improved by 23%-36% compared with working condition 2. It can be seen that the vertical wind speed caused by the micro-topography airflow climbing effect has a significant adverse effect on the maximum windage displacement of the conductor.

[0160] 3. Wind tunnel test of transmission tower-line system

[0161] 3.1 Theoretical basis

[0162] In terms of structural design of transmission tower-line structures, bridges, and building structures, it is only required that the structures have sufficient strength, rigidity, and stability under wind loads, that is, to ensure the safety, comfort, and durability of bridge structures and building structures; (This is different from the design of aircraft, which strives to minimize the resistance of the moving air around it), and the main focus is on the flow around sharp corners and the separation flow, so it is called "blunt body aerodynamics". Actual structural measurements have been carried out on some towers, buildings, and bridges.

[0163] Since scaled geometry leads to a series of problems of physical similarity, the similarity criterion is the theoretical basis of wind tunnel testing. It should be noted that due to the geometric scale of the model, some physical phenomena cannot be accurately reflected, such as the Reynolds number effect. Therefore, when actually designing a model test, a series of trade-offs need to be made to ensure that the main problems can be simulated. Fig.10 shown.

[0164] Before conducting a wind tunnel test on a scaled model, the test model must be designed to meet the similarity criteria of the relevant parameters according to the purpose of the test. Whether the similarity criteria can be met is the key to whether the model test results can be converted to the actual prototype, which is related to the success of the model test. The similarity ratio of the aeroelastic model is determined based on the size of the prototype structure, the size of the wind tunnel test section, and the flow field characteristics of the simulated turbulent wind field. The model design generally needs to meet the principles of flow field similarity, dynamic characteristics similarity, and appearance similarity. Based on the similarity requirements of the flow and the similarity requirements of the dynamic characteristics of the structure's appearance, a series of dimensionless number similarity criteria can be derived from the structural dynamics equations or simple dimensional analysis. The wind tunnel test of the aeroelastic model of the structure in the atmospheric boundary layer requires the dimensionless number similarity shown in the table and the dimensionless number similarity shown in the table below.

[0165] Table 4 Dimensionless parameter similarity requirements

[0166] Dimensionless parameters expression Physical meaning Similar requirements Cauchy number (elasticity parameter) <![CDATA[E / ρU 2 ]]> Structural elastic force / fluid inertia force Strictly similar Density ratio (inertia parameter) <![CDATA[ρ2 / ρ l ]]> Structural elastic force / fluid inertia force Strictly similar Froude number (gravity parameter) <![CDATA[gD / U 2 ]]> Structural gravity / fluid inertia Strictly similar Reynolds number (viscosity parameter) ρUD / μ Fluid inertia force / fluid viscosity force Blunt body is not required Damping ρ Energy dissipated per vibration cycle / total energy dissipated Strictly similar

[0167] In the model test, as long as these three dimensionless parameters are equal for the model and the actual structure, the actual laws of the structure can be truly reflected. This is also the theoretical basis for wind tunnel tests of bridges and structural engineering. Geometric similarity should include similarity of geometric appearance and similarity of vibration mode and amplitude. This is of great significance for the application and promotion of the results of structural wind tunnel tests. With the construction and development of high-voltage and ultra-high-voltage transmission lines, the height of high-voltage transmission towers and the span of lines are getting larger and larger. The transmission tower structure is more prone to aeroelastic instability under external excitation, which leads to large vibration of the transmission tower and even tower collapse accidents, which seriously threatens the safe and stable operation of the transmission line. Due to the particularity of the transmission tower structure and working conditions, it is not easy to use field test research methods. Therefore, it is still a relatively economical and effective research method to determine the aerodynamic characteristics and wind vibration force response of the transmission tower-line structure through aeroelastic model wind tunnel tests.

[0168] The vibration equation of the transmission tower-line structure under the action of fluctuating wind load can generally be expressed as:

[0169]

[0170] Where: Ms, Cs, Ks are the mass matrix, damping matrix, and stiffness matrix of the transmission tower-line structure respectively; x(t), are the displacement, velocity and acceleration vectors of the structure respectively; the items on the left side of the equation represent the inertia force, damping force and elastic force of the structure itself respectively; the right side of the equation represents the horizontal load acting on the structure, including the aerodynamic force caused by fluid pulsation and the self-excited force caused by the movement of the structure itself.

[0171] Since both ends of the equation contain unknowns, it is impossible to solve it directly. Therefore, the following assumptions are made to simplify the equation.

[0172] (1) The amplitude of the wind-induced vibration response of the transmission tower structure is much smaller than the characteristic size of its own structure, and it is considered to satisfy the static determinate assumption proposed by Isyumov N. Therefore, the right side of the above equation can be approximately regarded as:

[0173]

[0174] Where: p(t) is the aerodynamic force caused by the fluid's own pulsation, which can be measured by a rigid model wind tunnel test; It is the self-excited force generated by the structure's own movement.

[0175] (2) The self-excited force generated by the transmission tower's own movement is considered to be caused by the pulsating wind load that is close to the main frequency of the transmission tower structure vibration. By decoupling and ignoring the influence of higher-order terms, the first-order approximate expression of the aerodynamic term can be obtained as follows:

[0176]

[0177] Where: and ρ px Represent the correlation coefficients between wind load and transmission tower structure acceleration, velocity and displacement respectively.

[0178]

[0179] Where: Ma is the additional mass related to the acceleration of the transmission tower structure in the aerodynamic force; Ca is the aerodynamic damping related to the aerodynamic velocity of the transmission tower structure in the aerodynamic force; Ka is the aerodynamic stiffness related to the aerodynamic displacement of the transmission tower structure in the aerodynamic force.

[0180] 3.2 Practical Basis

[0181] So far, the technology that can fully simulate the atmospheric boundary layer in the wind tunnel is not sufficient, which requires the structural characteristics of the model to be as similar as possible to the prototype, and also requires the test flow field to be as similar as possible to the actual wind field. The wind tunnel test can be carried out in the North China Electric Power University's two-speed section low-speed return flow boundary layer wind tunnel. The actual objects in the wind tunnel test section are as follows: Fig.11 As shown in the figure, the actual operation console is as follows Fig.12 As shown in the figure, the comparison of the theoretical and measured wind speeds of the transmission tower-line system in a typical turbulent wind field is shown in Fig.13 shown.

[0182] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating windage of a transmission tower-line system, characterized in that: In this method, the maximum sag f of the transmission line is calculated by the following formula m : In the above formula, l is the span, g is the gravity per unit length of the ground wire, and Τ is the horizontal tension of the overhead line. is the height difference angle, γ is the load ratio of the ground conductor, and σ0 is the horizontal stress at each point of the ground conductor; The sag f at any point can be calculated by the following formula: x : In the above formula, x is the horizontal distance from one side of the tower, l is the span, and f m is the maximum sag; The horizontal windage displacement x and the vertical windage displacement y of any point are calculated by the following two formulas: In the above two equations, α is the length of the insulator string, ξ is the wind deflection angle of the conductor, is the wind deflection angle of the insulator string.

2. A method for calculating windage of a transmission tower-line system according to claim 1, characterized in that: In this method, the wind load acting on the transmission line is calculated by the following formula: W x =α·ω0·μ z ·m s ·b c ·d·L p ·sin 2 I; In the above formula, W x is the wind load perpendicular to the line direction, ω0 is the standard value of the reference wind pressure, α is the wind pressure unevenness coefficient, μ z is the wind pressure height variation coefficient, μ s Line shape factor, β c is the wind load adjustment factor, d is the conductor cross-sectional diameter, L p is the horizontal span, θ is the angle between the wind load and the line; in: ω0=v 2 / 1600; v is the wind speed at a reference height of 10 m.

3. A method for calculating windage of a transmission tower-line system according to claim 2, characterized in that: The wind pressure unevenness coefficient α is determined according to the design basic wind speed and Table 1; the wind pressure height variation coefficient μ z Determine according to Table 1; Line shape coefficient μ s , when the conductor diameter is less than 17mm or when ice is applied, μ s =1.2, when the wire diameter is greater than or equal to 17mm, take μ s =1.1; 500KV and 750KV line conductor wind load adjustment factor β c According to the design basic wind speed, determine according to Table 2; Table 1 Table 2 4. A method for calculating windage of a transmission tower-line system according to claim 1, characterized in that: In this method, the computational fluid dynamics process includes: 1) Establish the control equation; 2) Determine initial conditions and boundary conditions; 3) Divide the grid and generate calculation points; 4) Establish discrete equations; 5) Determine control parameters; 6) Solve discrete equations; 7) Determine whether it converges, and if it converges, execute the following step 8), and if it does not converge, return to the above step 2); 8) Output the calculation results.

5. A method for calculating windage of a transmission tower-line system according to claim 4, characterized in that: The Euler description of the fluid dynamics control equation is shown in the following four equations: In the above four equations, ρ is the fluid density, t is the flow time; τ is the viscous stress component existing on the surface of the microelement; is the velocity vector, and its components in the three coordinate directions are u, v, and w respectively; p represents the pressure on the fluid element.

6. A method for calculating windage of a transmission tower-line system according to claim 1, characterized in that: The micro-topographic conditions of the object calculated by this method include: pass-type terrain, high mountain watershed-type terrain, water vapor enhancement-type terrain, terrain lifting-type terrain, and canyon wind channel-type terrain.

7. A method for calculating windage of a transmission tower-line system according to claim 1, characterized in that: In this method, the inlet boundary condition expression of the micro-terrain wind field includes the turbulent kinetic energy expression and the dissipation rate expression, where the turbulent kinetic energy expression is as follows: The dissipation rate expression is as follows: In the above two equations, I(z) represents the turbulence at height z, L u is the turbulence integral scale, C u The value is 0.09 and the value of K is 0.

42.

8. A method for calculating windage of a transmission tower-line system according to claim 7, characterized in that: In the above two formulas, z g is the gradient wind height, z in B-type terrain b =5m.

9. A method for calculating windage of a transmission tower-line system according to claim 1, characterized in that: In this method, the surface roughness of the micro-topography wind field is given by the roughness height parameter k s To describe, the roughness height parameter k s The roughness length z0 satisfies the following relationship: to s =20z0; where z0 is determined by the Class B landform roughness specification.

10. A method for calculating windage of a transmission tower-line system according to claim 1, characterized in that: After the calculation is completed, the calculation results are verified through wind tunnel tests of the transmission tower-line system.

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