Research Of Wind-induced Response Of Transmission Line Under Mountain Wind Field

With the continuous development of power grid construction,more and more transmission lines built in the mountains.There are significant differences between mountain wind field and flat terrain wind field,and the average wind acceleration effect of the local position is significant,which leads to the increase of the average wind load,and the fluctuating wind load will further exacerbate this adverse effect.Therefore,flashover,tower collapses and other wind disaster accidents are very likely to occur in the transmission line which goes through the area with obvious acceleration effect.The influence of changes in wind field characteristic on the wind-induced response of transmission line is worthy of study.Typical mountain terrains are established based on the mountain range model.The 3D wind field characteristics of mountain terrain are studied by combining CFD numerical simulation with wind tunnel test.The results indicate that the longitudinal mean wind acceleration effect is significant in the near ground in the vicinity of the canyon and the peak.Local position has a considerable horizontal and vertical wind speed.The characteristics of fluctuating wind field are complex and extremely irregular in space.On this basis,the three-dimensional fluctuating wind speed time-histories in mountain wind field of double circuit transmission lines and transmission towers are generated synchronous by POD method.The continuous three-span model of each transmission line is established,which goes arcoss the canyon or ridge,and its direction is perpendicular to the direction of the incoming flow.The wind-induced response in mountain wind field is calculated by time domain method.Then the influence of the variation of wind field on wind-induced conductor swing and hanging point reaction forces of transmission lines is analyzed.The results indicate that the wind-induced conductor swing and hanging point reaction force increase significantly under the influence of the mean wind acceleration effect and fluctuating wind load.The rising airflow mainly affects the vertical displacement of the transmission line and makes it greater.The mean value of wind-induced conductor swing should be increased 22%-50%value according to the design value in flat terrain,and the upper limit should be taken when the transmission line is arranged along the ridge and its height from the ground surface is smaller.The wind vibration coefficient of wind-induced conductor swing should be 1.2～1.3.When the load of hanging point in different directions is calculated,the wind speed correction coefficient should be 1.11～1.49,and the wind vibration coefficient should be 1.10～1.66.When the wind speed correction coefficient is larger,the wind vibration coefficient should be smaller.The model of the 220kV tangent tower is established,which is located at the top of the mountain,and the direction of cross arm is parallel to the direction of the incoming flow.The wind-induced response in the mountain wind field is calculated by the time domain method.The the influences of the variati,on of wind field on along wind displacement and the internal force of the members are analyzed.The results indicate that along wind displacement and the internal force of the members increase significantly under the influence of the mean wind acceleration effect and the fluctuating wind load.The fluctuating load of the transmission lines has a significant effect on the displacement of the tower and the internal force of the members.The influence of the mountain wind field on the internal force of the tower is mainly concentrated in the main members at the lower part of the tower,and the four columns are of great difference.When designing the control members,the wind speed correction coefficient should be 1.19～1.34,and the upper limit should be taken when the transmission line is arranged along the ridge and the height of the member from the ground surface is smaller.The tower wind vibration coefficient is close to the tower structure design criterion,and should be about 1.4 in the whole tower height.The transmission line which goes arcoss the canyon is taken as an example.Taking into account the material nonlinearity and geometric nonlinearity,the finite element model of the tangent tower at the top of the mountain is established.Considering the influence of the along-wind wind load of tower and the three-dimensional load of the transmission lines,and the static non-linear buckling analysis of the transmission tower is carried out.The results indicate that the first instability occurs in a compressed main member,which is located between the tower body and the tower legs.At this point the wind speed is only 79%of the design wind speed,and most members of the transmission tower are still in the elastic state.