FINITE-ELEMENT MODELING OF TRANSMISSION-LINE GALLOPING

A computationally efficient, finite element idealization is presented to analyse galloping, which is characterized by large amplitude vibrations of iced, multi-span, electrical transmission lines. A three-node, isoparametric cable element having three translational and a torsional degree-of-freedom at each node is developed to model a conductor. Support insulator strings and remote conductor spans are represented by linear static springs. A transmission line's interactions with a support tower are modelled through the tower's equivalent stiffness at the conductor's suspension point. An expedient time marching scheme is developed to obtain the envelope of galloping. The scheme can be utilized to integrate dynamic equilibrium equations involving not only geometric and material nonlinearities but also nonlinear damping. Time integration is performed in the sub-space to minimize computational effort. The finite element model has been employed to successfully simulate field galloping records. It is shown that it is necessary to consider a multi rather than a single span for a conservative estimate of the galloping amplitudes to enable sufficient clearances to be designed between adjacent conductors.