Refined Analysis Of Wind-induced Conductor Swing And Research Of Equivalent Static Wind Loads On Transmission Lines

Wind-induced conductor swing refers to the phenomenon that overhead transmission line conductors and suspension insulator strings deviate from the vertical position under the action of wind loads.Extreme wind-induced conductor swing will lead to flashover trips,resulting in line outage,seriously affecting the normal and safe operation of the grid.One of the main reasons for the frequent occurance of wind-induced flashover trips in our country in recent years is that the calculation methods for design wind loads on transmission lines and wind-induced conductor swing responses are not completely reasonable.It is of great importance for the normal,safe and stable operation of China's power grid to improve the calculation methods for wind-induced conductor swing responses and design wind loads in the background that the power system speeds up the construction of UHV transmission lines.The main contents of this thesis are as follows:1.Analysis of aerodynamic damping characteristics of transmission conductors under mean wind-induced swing conditions:Taking the relative motion of the conductor and wind in both horizontal and vertical directions and the dynamic characteristics of conductor under the action of wind loads into consideration,the generalized aerodynamic damping matrix of conductor under mean wind loads is derived.Through numerical studies,aerodynamic damping of conductors under different mean wind speed conditions is calculated.Special attention is paid to the variation of aerodynamic damping ratio and non-proportionality of conductors with mean wind speed.The results are compared with those calculated with a previous method.2.Frequency-domain calculation method and response characteristic analysis of dynamic wind-induced swing of transmission conductors:Based on the improvement of aerodynamic damping calculation method,considering the geometric nonlinearity of conductors,taking the static equilibrium configuration and stiffness in mean wind-induced swing state as initial conditions,frequency-domain method is used to calculate the fluctuating wind-induced swing response of the conductor.The validity of the frequency-domain method is verified by comparing the calculation results of time-domain method and frequency-domain method.Based on the nonlinear static analysis method and the frequency-domain calculation method,the mean and fluctuating wind-induced conductor swing response under different reference wind speed conditions are calculated.Characteristics of fluctuating wind-induced conductor swing responses are analysed from the aspects of contributions of different vibration modes to total responses,characteristics of response spectra and the proportion of fluctuating response.3.Influence of variation of structural parameters on the wind-induced conductor swing responses of UHV transmission lines:A refined conductor-insulator string model is established by taking a 1000kV UHV AC test and demonstration transmission line which was once affeceted by a wind-induced flashover trip for example.Based on nonlinear static calculation method and frequency-domain calculation method,the influences of factors such as calculation spans,span length,relative height between suspension points and conductor tension on the static and dynamic wind-induced swing response characteristics of suspension insulator strings are studied.The mean wind-induced swing response characteristics of suspension insulator strings are analyzed from the perspective of the pendulum model to verify its rationality qualitatively.By comparing with the results of the continuous multi-span finite element model,calculation error source of the pendulum model is analyzed theoretically,and suggestions for modification are given.4.Wind-induced swing response analysis of typical iced conductors:Taking circular,D-shaped and crescent iced conductors as study objects,wind-induced swing response characteristics of iced conductors are studied.The influence of ice thickness on the wind-induced swing of circular iced conductors is studied by comparison of dynamic characteristics,aerodynamic damping and wind-induced displacement responses.Static calculation method is used to calculate the mean wind-induced swing responses of typical non-circular cross-sectional iced conductors to qualitatively analyze the adverse influence of non-circular ice coating on the wind-induced swing responses of conductors.5.Equivalent static wind loads and wind load adjustment coefficients of multi-span conductors:The fluctuating wind-induced responses of conductors are calculated with quasi-static method.Considering the mean response and background response components,the equivalent static wind loads on conductors are calculated with Load-Response Correlation method,Gust Loading Envelope method and multiobjective equivalent method.Taking a 1000kV UHV transmission line for example,the equivalent static wind loads for different equivalent objects are calculated.Wind load adjustment coefficient for conductors is redefined from the viewpoint of equivalent static wind load.Variations of wind load adjustment coefficients with span length,suspension height,ground roughness and reference wind speed are studied.The coefficients are compared with those provided by the codes.