Abstract

The Overhead Electrical Transmission Lines, used for carrying high voltage electrical power, are held by huge steel towers with large spans. The cables of transmission lines are subjected to three different types of wind-induced vibrations, namely, galloping, aeolian and wake-induced vibrations. During winter, in some cold climates ice is deposited on the cable, making the cross section of the cable asymmetric. When wind blows across the ice accumulated cables, they start vibrating with large amplitudes and at low frequencies. In the present work, such galloping vibrations are analyzed. Neglecting the flexural rigidity and axial rigidity of the wire, two-dimensional equations of motion of the wire are formulated. The effect of torsion of cable is neglected. Fourth-order Runge - Kutta method has been employed to solve the governing equations and to obtain the orbital motions of the transmission line cable. The analytical model includes parameters such as ice inclination angle, angle of incidence of wind on the cable, sag length, angle subtended by the relative wind velocity to horizontal and aerodynamic force coefficients. The effects of these parameters on the orbital motions of the cable are investigated. Validation of analytical studies is carried out by tests on scale models of the actual cable. The models are analyzed and the eigen values and eigen vectors are found out. Experimental investigation is carried on both the actual cable and the scaled model in the wind tunnel and orbital motions are measured. The test results are compared with the numerical simulations and discussed. The galloping motions were essentially orbital in nature. The test results validated the analytical investigations on the galloping phenomena.