Wind Tunnel Test On Galloping Of Iced Conductors And Galloping Simulation For Transmission Tower-Line System

Galloping is a low frequency and large amplitude vibration self-excited by single conductor or bundled conductors under mid/low wind velocity. In recent years, the construction of power transmission lines has witnessed great breakthroughs in China, both the voltage level and the construction scale are first-class around the world. However, with rapid development of the power system and frequent occurrence of extreme weather, the frequency and destruction level tend to increase obviously. Consequently, thorough investigation on conductor galloping theory and anti-galloping techniques is of considerable significance to the safety of power transmission lines. In this paper, delicate study including aerodynamic characteristics of iced conductors, galloping of aeroelastic iced conductor model in wind tunnel, numerical galloping simulation of single conductor, bundled conductors and transmission tower-line system as well as the anti-galloping effects of interphase spacer was carried out to obtain further development in conductor galloping theory and anti-galloping techniques. The paper is mainly focused on the following aspects:1.Wind tunnel test study on aerodynamic characteristics of single conductor and bundled conductors with two typical ice-coating sections. As to ultra high voltage transmission conductors with thick ice-coating, truncated conductor models with crescent and D ice-coating sections were made, the aerodynamic coefficients of single conductor and bundled conductors in uniform flow and homogeneous turbulence flow under different attack angles were measured by force balance in wind tunnel. The variation of aerodynamic coefficients with attack angle has been investigated, and the influence of turbulence in the wind field and interference caused by sub-conductors also has been discussed. Based on Den Hartog theory, the ranges of attack angle in which galloping may occur to iced conductors under various cases were calculated respectively. As to single conductor, combined with former test results, the aerodynamic characteristics of the two ice-coating sections were studied and several general principles are received. Moreover, measurement has been conducted on the surface wind pressure distribution of the crescent iced conductor in two types of wind fields, thus further reflects local wind pressure attributes.2.Wind tunnel study on galloping of aeroelastic iced conductor model and identification of its aerodynamic damping. Made in two typical ice-coating section forms(crescent section and D section), aeroelastic models of single conductor and bundled conductors were connected to brackets with springs. The ratio of vertical and rotational self-vibration frequency of the conductor models can be changed by varying spring stiffness, suspension position and additional weight. Galloping of aeroelastic models are excited and recorded respectively in the wind tunnel under appropriate wind speed and attack angles, futher, galloping responses in test were compared with numerical ones from FEM models based on quasi-steady assumption with static aerodynamic coefficients. Vertical and rotational aerodynamic damping in galloping were identified by Hilbert transform, impacts of various factors as wind speed, attack angle, ratio of vertical and rotational self-vibration frequency, iced profile and number of sub conductors on aerodynamic damping were discussed.3. Numerical approach to galloping of single iced conductor. The response of single iced condutor galloping was simulated respectively by analytical model based on assumed-mode method and finite element model which iced conductor was modeled by a three-node, isoparametric cable element with parabolic shape function, a time marching algorithm using Newmar?-?method in conjunction with Newton-Raphson iteration was utilized to integrate dynamic equilibrium equation involving geometric nonlinearities and nonlinear wind load, and results from two methods were compared. Factors influencing galloping were discussed in detailed by parametric analysis with FEM method. Galloping response of three-spans transmission was also derived and compared with response of single span, impacts of insulators and remote spans were discussed.4. Galloping responses of bundled iced conductors and iced transmission tower-line system. The spacers are simulated by two-node beam elements, thus FEM model of bundled conductors with arbitrary number of sub conductors was established, modal analysis was employed to study dynamic property of four bundled conductors and factors impact on it, galloping of four bundled conductors with two types of ice-coating section were obtained. Futhermore, a three-phase four bundled transmission tower-line system with three spans was modeled, galloping responses of one or all phase were acquired when subjected to fluctuating wind load, dynamic loads on insulators and towers due to galloping conductors were determined, some useful conclusion for designing have been found.5.Study on anti-galloping effect of interphase spacer. Firstly, physical models and their implements in finite element method of various interphase spacers were introduced. Then take a 500kV single-circuit three-phase four bundled transmission line with interphase spacer vertically installed for example, the tension increments in sub-conductors with different number and type of interphase spacers were calculated. Also, modal analysis of the transmission line with interphase spacers was conducted. In the end, suppose a certain phase gallops because of ice-coating, comparative analysis of galloping response before and after installing rigid and flexible interphase spacers were carried out.