Wind hazard reliability assessment of a transmission tower-line system incorporating progressive collapse

Wind-induced progressive collapse is the primary factor triggering large-scale failure of transmission tower line systems (TTLS), which seriously affects the reliable operation of the power system. The core innovation of this paper is incorporating the progressive collapse into the wind hazard reliability assessment of TTLS. First, a semi-analytical solution (SAS) is derived to quantify the nonlinear tensions in a multi-span conductor-insulator system, taking into account the high nonlinearity of insulators. During this process, a multi-dimensional nonlinear system of equations is constructed, with conductor reaction forces and insulator swinging displacements as variables. Subsequently, an efficient SAS-based progressive collapse analysis method is developed by simplifying the failed tower as a multi-segment rigid body model and coupling the two-dimensional overturning angles into the SAS, where the impact of the post-failure equilibrium on progressive collapse is highlighted. Afterwards, uncertain TTLS models are established, and the progressive collapse fragility is estimated using Monte Carlo simulation and SAS. A comprehensive sensitivity analysis is performed to rank the importance of uncertainty parameters affecting the model outcomes. Finally, both the yearly failure probability and reliability index before and after considering the progressive collapse are calculated. Numerical validation demonstrates the excellent reliability of the proposed method; neglecting progressive collapse leads to an overestimation of the reliability index.