Investigation On Multi-modal Vibration Response And Coupling Mechanism For Iced-Bundled Transmission Lines

After the transmission lines are iced,galloping phenomenon with low frequency and high amplitude can be produced under the action of wind load,and ice-shedding jump phenomenon with vertical oscillation can be also produced due to the ice falling off,which may trigger flashover and damage transmission lines,fittings and towers.With the development of power construction,compact three-phase transmission lines have been widely used,and the problems that have arisen are more complicated.Therefore,the research on single-phase and three-phase iced transmission lines has important engineering application value.Firstly,the theoretical and experimental studies on single-phase iced-bundled transmission lines are conducted,including galloping stability,multi-modal coupling galloping mechanism and galloping behavior,etc.Meanwhile,the experimental verification is carried out on the continuous iced-bundled transmission lines using designed and built low-speed wind tunnel.Secondly,the experimental research on compact three-phase iced-bundled transmission lines is mainly conducted,including galloping characteristics,dynamic responses of ice-shedding jump and roles of anti-galloping device,etc.The research aspects of this thesis are mainly as follows:(1)The multi-parameter galloping stability analysis of single-phase iced-bundled transmission lines is carried out.Considering geometric and aerodynamic nonlinearities,nonlinear dynamic equations including the first two-order modes of in-plane,out-of-plane and torsional motions are derived by using Hamilton principle and Galerkin spatial discretization.Wind speeds,sags,initial wind attack angles,in-plane damping ratios and torsional damping ratios are selected as bifurcation parameters.By means of eigenvalue analysis and numerical methods,galloping stabilities under the coupling of various three-parameter are investigated and Hopf bifurcation points are obtained.The influence of multi-parameters on the critical condition of galloping is analyzed.Finally,a method for predicting the upper critical wind speed of the system is proposed.(2)The mechanism of multi-modal coupling galloping of single-phase iced-bundled transmission lines is studied.The variation law of galloping frequencies with wind speed and sag are determined by numerical simulation,and it is found that the coupling mechanism among multi-modes under different parameters is obviously different.Furthermore,the variation law of galloping amplitude with wind speed in each mode is investigated as well as the spectrum.The synchronous and limited-amplitude characteristics of same-order modal galloping along in-plane,out-of-plane and torsional directions are found.Multi-modal nonlinear coupling effects under different parameters are explored.Meanwhile,the different energy transition processes are compared and analyzed,thus revealing the energy transition and feedback mechanism among various modes of the iced transmission lines galloping system.(3)The galloping nonlinear response of single-phase iced-bundled transmission lines is studied.By using numerical simulation,the critical conditions of the first two-order modal galloping along in-plane,out-of-plane and torsional directions are determined in parameter plane of wind speed-sag.The influence laws of single-mode galloping and coupled-modes galloping on the galloping behavior are obtained.The variations of galloping amplitude with wind speeds and sags are discussed.Moreover,two dangerous parameter domains and the wind speed region where large amplitude galloping occurs are obtained.Based on the characteristics of parameter domains,different anti-galloping strategies are proposed.(4)A low-speed wind tunnel with wide bore is designed and built to investigate galloping of iced bundled transmission lines on a single span.Based on the designed and built continuous model of iced-bundled transmission lines,galloping experiments including in-plane,out-of-plane and torsional motions are conducted.The vibration signals of iced-bundled transmission lines are obtained by laser displacement sensor,wireless attitude sensor and force sensor.Qualitative verifications of the above theoretical results are carried out through experimental research,including the frequency crossing phenomenon of in-plane symmetrical modes,the synchronous and limited-amplitude galloping characteristics among modes,and the galloping behaviors varying with wind speed.The experimental results are in qualitative agreement with the theoretical results.(5)The continuous model of three-phase iced-bundled transmission lines is designed and made.Using the low-speed wind tunnel,the galloping characteristics of compact three-phase iced-bundled transmission lines and the control effects of interphase spacers on galloping are investigated through the model experiments.A modification method is proposed to determine the similarity condition of galloping frequencies between the aeroelastic model and the prototype.The galloping characteristics varying with wind speed are explored.Four common arrangements of compact interphase spacers(including triangular and V-shaped)are considered.The influence of interphase spacers on the galloping characteristics of each phase conductor is determined.The amplitude comprehensive reduction rate of the first two-order modes,the amplitude reduction rates varying with wind speed and the change of interphase distance are evaluated.Then,the anti-galloping effects of interphase spacers are dertermined and the corresponding arrangements under different conditions are proposed.(6)The influence of the interphase spacer on sudden ice shedding from compact three-phase iced-bundled transmission lines is investigated.The staggered-arrangement groups and compact-arrangement groups(including triangular and V-shaped structures)of interphase spacers are considered.Then,the influence of the interphase spacers on the vibration characteristics of transmission lines during ice shedding is determined through numerical analysis.Furthermore,the corresponding comprehensive evaluation indexes for the different line configurations are proposed.The influence laws of different factors on on each index are determined,including the position and number of transmission lines for the ice-shedding phase and the various possible arrangements of interphase spacers.Then,the efficient and reliable deicing schemes are proposed based on different arrangement groups of interphase spacers.In addition,model experiments during ice shedding are also implemented,and theoretical results are overall consistent with experiments.