Wind-induced Vibration Response Analysis Of Substation Downlead Structure Under Strong Wind Environment

With the continuous improvement of the voltage level requirements,the design of the down lead structure of the substation is also constantly changing.More and more down conductors are arranged from double bundling to multi bundling.However,the existing research and codes always follow the traditional cable structure theory for the wind-induced vibration design of downlead.The downlead damage accidents caused by special climate occur frequently,especially the damage caused by wind-induced vibration of downlead under strong wind environment,so it is necessary to study the wind-induced vibration response characteristics of downlead structure.Based on an example of the down lead structure of a 750 k V substation,this paper establishes a finite element model according to the functional equation of conductor configuration considering the rigidity.The nonlinear time history analysis of windinduced vibration response of four bundled tube bus downlead structure and double bundled tube bus downlead structure is carried out by ANSYS.According to the principle of response equivalence,the response wind-induced vibration coefficient based on the time history response result is analyzed and calculated.The main research contents are as follows:1)Based on the layout characteristics of the down lead with small span and short line length and the section characteristics of the down lead with enlarged diameter,the configuration function of the down lead considering bending stiffness under different boundary conditions is established,and compared with the experiment to verify the correctness of the configuration model of the conductor.The finite element model of the tubular bus downlead structure is established through the configuration model,and the influence of the conductor stiffness,Span height ratio,number of spacers and other factors on the structure stress under the static wind is analyzed.The conductor stiffness,redundancy and conductor tension are negatively related;the number of spacers mainly affects the overall stiffness of the structure,the less the number of spacers,the greater the conductor tension.2)In this paper,the harmonic synthesis method is used to simulate the threedimensional wind speed time history as the time history load,and the non equal height traverse motion equation considering bending stiffness is established according to the energy method and coordinate rotation.According to the modal theory,the corresponding modal theory of traverse frequency equation is given,and the basic characteristics of traverse modal state are analyzed.Based on this,the modal characteristics of the downlead and the tubular bus system are analyzed by ANSYS.The results show that the modal distribution of the conductor is related to the inclination angle of the conductor,and the in-plane natural frequency decreases with the increase of the inclination angle;With the increase of the number of splits,the fundamental frequency of the downlead structure increases,which is higher than the natural frequency of the long-span transmission line;the influence of the wire stiffness and the number of spacer on the modal is larger,and the influence of the span height ratio is smaller.The influence of wind field characteristics and structure characteristics on the wind-induced vibration of the downlead structure is analyzed.The analysis results of wind field characteristics show that the downlead is mainly affected by the downwind load,and the fluctuating wind load in the crosswind has a certain impact,so it is necessary to use 3D wind field as the wind load;The influence of aerodynamic damping on the wind-induced response of structures is positively related to the wind speed and negatively related to the natural frequency;the wind-induced vibration response of the downlead structure with five wind directions is analyzed.The wind direction angle of 0 ° is the most unfavorable condition of the response of the four bundled downlead structure,and the wind direction angle of 90 ° is the most unfavorable condition of the displacement response of the four bundled downlead structure.The results of structural characteristic analysis show that the reduction of conductor stiffness and the decrease of spacer number can significantly change the stiffness of the structure and increase the response peak value of the structure.With the increase of the ratio of span to height,the main change is the shape of the conductor,increasing the reaction response of the structure and reducing the displacement response of the structure.At the same time,the frequency spectrum analysis of the two structural responses is carried out,both of which are based on the low-order mode along the wind direction.3)Based on the time history response,the response wind-induced vibration coefficient of the structure is calculated,and the calculation method of the wind-induced vibration coefficient of the downlead structure is proposed.According to the different responses,the wind-induced vibration coefficients of the structural reaction(the combined force of axial force and shear force)and displacement response are calculated,and the distribution characteristics of the wind-induced vibration coefficients of the downlead structure are analyzed and studied.The results show that there is little correlation between the two types of wind-induced coefficients,and the wind-induced coefficients of the vertex reaction are larger than those of the displacement response.The mechanical design of the down lead mainly considers the stress of the conductor constraint point and the wind deflection displacement of the conductor.Therefore,different types of wind-induced vibration coefficients should be selected according to the design requirements.The wind-induced vibration coefficient is controlled by aerodynamic damping,wind direction angle,wind speed and so on.At the same time,the reduction of structural stiffness will not only increase the wind-induced vibration response of the structure,but also reduce the corresponding wind-induced vibration coefficient.Finally,the response of the model is tested according to the response windinduced vibration coefficient method,the wind-induced vibration coefficient calculation method of the building load code and the wind-induced vibration coefficient calculated by the load factor method,The results show that the response wind-induced vibration coefficient has an excellent precision and can effectively guide the wind resistance design of the downlead structure.