A reduced model for the dynamic analyses of power transmission lines with truss supporting towers

This paper presents some advances in a research program focusing on the dynamic behavior of transmission lines under dynamic environmental excitation. In the paper a reduced model of a vertical double circuit steel transmission tower for a power transmission line is described. The model, consisting in a sequel of beam elements placed along the axis of the tower and of the crossarms, permits to reduce the total number of the degrees of freedom in the dynamic analysis of the tower-conductors coupled system. The equivalent bending, shear and torsional sectional properties of the beam element are completely determined from the geometrical characteristics of the truss tower. The mass of the tower has been reproduced using lumped masses at the ends of each element. The adequacy of the simplified model in reproducing the tower behavior is assessed against a second, more refined, three-dimensional model in which the entire tower has been modeled using beam elements. The ability of the simplified model in simulating the vibrating characteristics of the tower in a power-line is checked comparing the natural frequencies and modal shapes of a portion of a power transmission line.