Mechanical Characteristics Of Iced Conductor And Dynamic Response Analysis Of Tower-line System

Transmission line accidents caused by ice loads is one of the main hazards for the safe operation of transmission line,which seriously threatens the social production and living.However,the conductor breaking,damge of hardware and tower member,even the progressive collapse occure sometimes for the lack of understanding of mechanisms of ice disasters.Thus,it is necessary to study the mechanism of ice disaster for transmission line.In this paper,two important characteristics of iced conductor(aerodynamic characteristic and torsional stiffness)are studied to investigate the mechanism of galloping.Then the ice-shedding,conductor rupture and insulator breaking with ice-load are simulated to investigate the response and influencing parameter in these ice accidents.The main content and conclusion are as follow:(1)With considering the surface roughness of the iced conductor,12 conductor models with the crescent-shaped ice were fabricated.Then the aerodynamic coefficients of these models were obtained by the wind tunnel tests.The influence of the Reynolds number and the shape parameter,β(defined as the ratio of ice thickness to the diameter),were investigated.In addition,the effect of surface roughness of the iced conductor was discussed.Subsequently,unsteady areas of conductor galloping were calculated according to the Den Hartog criterion and the Nigol criterion.The results indicate that the aerodynamic coefficients of iced conductors change sharply at the attack angles of 20° and 170° with the increasing β.The galloping area increases with the Reynolds number,and the surface roughness of iced conductors changed the range of attack angle,which was influenced by the increase of the Reynolds number.(2)A new method of calculating the torsional stiffness of iced bundled conductors is proposed with consideration of the eccentricity of ice,then the parametric study is conducted.The results show that the eccentricity of ice does have effects on the torsional stiffness and it shouldn’t be neglected;the eccentricity of sector ice has the greatest impact on torsional stiffness among the common ice shape which can cause galloping;under the influence of the icing eccentricity,the torsion stiffness and critical torsional angle of the iced conductor is basically the same as that under the clockwise and anti-clockwise torque,but the critical torque are different.(3)The iced transmission line is modeled by considering the stiffness of ice,and the element birth and death method is used to simulate the ice-shedding.Two typical forms of ice-shedding(i.e.,the shock-load-induced ice-shedding of a single conductor and one sub-conductor ice-shedding from bundle conductors)are studied,and a parametric study is performed to investigate the influence of the transmission line parameter and the external load on the ice shedding.The results show that wind loads should be considered when the span is large;the vibration caused by the ice-shedding of one sub-conductor can accelerate the process of ice shedding of the bundle conductor;the stiffness of ice should be considered in the simulation,otherwise it is not safe.(4)A transmission tower-line system is established for 2 towers and 3 span lines with consideration of the initial eccentricity.Then the nonlinear static stability analysis and nonlinear dynamic stability analysis induced by the conductor breaking are carried out to obtain the load vs.displacement curves,while studying the failure modes of the transmission tower-line system.Moreover,the ice load is considered during the numerical simulation.In addition,a parametric analysis is performed to investigate the influence of span,insulator length and initial tension force on the stability failure of the system.The results show that the dynamic instability will occur earlier than the static instability due to the dynamic impact effect and conductor breaking with ice loads can lead to the progressive collapse of the transmission tower-line system.Finally,the span length has the greatest effect on the response of transmission tower caused by conductor breaking.(5)A finite element model of a transmission tower-line system with 3 towers and 4 span lines under ice loads is established.Dynamic analyses of the tower-line system after insulator breakage with ice load are performed to study the dynamic responses of system and failure process.In addition,a parametric analysis is implemented to investigate the influences of span length and insulator length on the vibration of the system and the failure mode.The results show that a larger ice load can lead to more severe vibration of tower-line system due to the insulator breakage and that as the span length increases,the insulator breakage can result in more serious consequences and even the cascading collapse of transmission tower-line system.