Dynamic response of guyed towers in transmission lines submitted to broken conductors

The article approaches the numerical structural response of a Transmission Line (TL) section due to an occurrence of a broken cable. TLs are subjected to various types of dynamic loads. One of these loads is due to the rare event of a broken conductor or a bundle of sub-conductors. This load case assumes an important role in designing suspension towers, which are the most frequent structures in TL and, consequently, also play an important role in evaluating structural system reliability. An incorrect evaluation of such load case may result in a TL weakness causing a cascade failure event. The standard design practice is to obtain the structural response to a load case which is not more than an equivalent static load, in other words, the residual load after the cable rupture. Therefore, the actual response of the tower is not taken into account since the dynamic nature of the load is not modeled nor the restriction of the remaining cables. In this paper, an entire section of the TL is modeled, including towers, cables and insulator strings. The methodology for the development of the numerical models applied to simulate this dynamic analysis is presented, considering the discretization of the structural model using the finite element method (FEM) and the solution of the dynamic problem by direct integration of the motion equations using the Newmark method. Special attention is devoted to guyed towers, which are very often used in TL due to their relative low installation costs. The dynamic loading due to cable rupture is simulated by a deactivation of a conductor's finite element. Dynamic structural responses are shown in terms of forces acting on tower members, conductors and guys. Finally, they are compared to the responses obtained by static analysis, which is usually the standard practice.