Experiment Study And Nonlinear Dynamic Investigation On Galloping Of Iced Transmission Line

Galloping of power transmission line is a typical self-excited vibration due to wind action on an ice or wet snow accretion on the electrical conductors. The occurrence of galloping could cause large dynamic tension acting on transmission lines and towers and induce a series of accidents, such as flashover between different interphases, power/ground line and spaceres broken off. Especially during some special climate conditions, several days longer duration of galloping will bring great damage to tower components and even result in whole towers collapse. In recent years, due to the mushroom development of the power grid and frequent appearance of bad weather conditions, the galloping accident frequency and the damage to power system, which severely endanger the transmission of electrical power and stable development of national economy, has been significantly increased. Therefore, it has great engineering significance and economy value to promote the experimental and theoretical investigation on galloping of iced transmission line, improve anti-galloping design method and provide corresponding technical or scientific supports. The following research aspects are included in present paper:1. Study on mechanical features of tower cross arm under static tension of iced conductor:The segmental strain resistant corner tower model with1:4scale whose cross arm has been damaged during ice disaster was made according to similarity relationship, and the corresponding iced-conductor model was also established. Then the static experiment was conducted to simulate the tension of heavy iced-transmission line acting on tower. Meanwhile, the finite element model of middle cross arm was also founded precisely by taking into account the effects of connection eccentric, joint plate and the length of bolts on the force-transfer characteristic of members, then the whole test process was simulated and the comparison with experiment values was also obtained. On this basis, failure mode of cross arm was obtained by using the method of nonlinear bulking analysis.2. Experiment research on dynamic responses of transmission tower-line system and failure mechanism of tower under iced-conductor galloping:Taking a strain resistant corner tower as prototype whose cross arm was seriously damaged under iced-conductor galloping, a tower segmental model with elastic boundary condition and conductor model of different ice thickness were founded on the basis of the similarity theory of dynamic model, and the vibration experimental equipment used to simulate galloping responses of iced-conductor was developed at the first time. Based on that, dynamic tension and vibration features of galloping conductor were reconstructed under the laboratorial conditions. Then galloping experiment of transmission tower line was carried out, the effects of ice thickness, galloping amplitude and frequency on dynamic response of transmission tower-line system were discussed. According to thickness of ice and vibration amplitude obtained by field testing, the dynamic experiment of transmission tower-line was carried out under conductor galloping. Combining with the experimental results of dynamic stress, fatigue life of tower member was estimated. Finally, the real reason for tower collapse under iced-conductor galloping was determined based on the results of tower-line galloping experiment and tower member's fatigue life.3. Nonlinear dynamics and double parametric bifurcation analysis of iced transmission line:A three dimensional galloping model for iced-bundle conductor, considering non-linear coupling effects of vertical, horizontal and torsional direction, was approached to investigate the action mechanism of system parameters in stability and nonlinear dynamic responses based on Lagrange equation. Galerkin integral method and Routh-Hurwitz criterion were introduced to obtain stable and unstable region in parametric space. Choose wind velocity, initial wind attack angle and vertical damping ratio as bifurcation parameters, the reduced equations in the vicinity of bifurcation point were determined through central manifold theory. By regarding bifurcation parameters as state variables, the reduced system with parameters were converted to extended system without parameters, and then Hopf bifurcation equations sectional solution were calculated with the help of normal form theory in polar coordinates. Based on that, the features of simultaneous varieties of galloping in double parametric space were discussed in detail. 4. Nonlinear numerical simulation for iced bundle conductor galloping:A dynamic nonlinear numerical model with the consideration of aerodynamic and geometric nonlinearities was established to simulate the galloping behavior of iced single and bundled conductors with arbitrary number of sub conductors on the basis of Total Lagrange finite element method. The three-node parabolic cable element with torsional degree of freedom was applied to discrete the single conductor. As for bundled conductor, the Euler beam element added into sub-conductors was used to simulate the movement of spacing rod. A high effective bending degree of freedom reduced method was introduced to simulate the coupling effects of cable and beam element. Meanwhile, the unbalance force vectors of beam element during galloping process were derived precisely by employing co-rotational coordinate system method. Finally, based on the aerodynamic force of iced-conductor with crescent shape obtained by wind tunnel experiment, the impact of turbulence, ice thickness and initial ice-coating angle on conductor galloping mechanism and dynamic responses were investigated.5. Numerical simulation of iced-conductor galloping in three dimensional fluctuating wind field:According to random flow generation method and three dimensional wind power spectral density function, the fluctuating wind field around iced transmission line was simulated point by point. Meanwhile, the statistical characteristics of fluctuating wind field, such as divergence free, power spectral density function, temporal correlation function and spatial correlation coefficients, were verified to illustrate the availability and reliability of presented wind filed simulating method. Then the galloping responses of iced bundled-conductor were determined by applying nonlinear finite element method in uniform flow, one dimensional and three dimensional fluctuating wind field. Based on that, the impact of turbulence on transmission line galloping was discussed in detail.