Assessment of Behaviour and Cascade Failure of Tangent and End Towers of Transmission Lines Under Downbursts
Abstract
Thunderstorm-related failure incidents of transmission line structures have increased globally, resulting in widespread power outages, disruptions to infrastructure, and economic losses. Downbursts is one of the extreme wind events that occurs during thunderstorms. Failure of a tower during a downburst can trigger a cascade-type of progressive collapse to various towers along a line. Line segment typically consists of several tangent towers bounded by two end towers, which are stronger structures designed to contain the progression of the cascade failure. This Thesis is a part of an extensive research program conducted at the University of Western Ontario to study the behaviour of transmission lines under downbursts. In this Thesis, the effect of the downburst load provisions on transmission towers is compared to the effect of the design synoptic wind loads defined in different standards. This comparison indicates that transmission towers are susceptible to failure during severe downbursts. During the failure, the system experiences dynamic excitation due to the movement of the failed tower. Accordingly, the Thesis investigates the dynamic response of the tower-conductor system during tower failure under downburst loads using nonlinear dynamic analysis. The findings indicate that the conductor's tension force experiences some peaks over a short period of time during the failure so that the adjacent towers are unlikely to respond to such load. Since end towers are critical structures in the line segment, experimental test of a transmission line under simulated downburst is conducted at the Wind Engineering, Energy and Environment (WindEEE) Research Institute to assess the end tower behaviour under downburst loads. Additionally, numerical analysis of the tested line is conducted to assess the adequacy of the wind load provisions on transmission lines in estimating the downburst loads for end towers. A major outcome of this Thesis is the development of an innovative numerical model for conducting quasi-static analysis to study the cascade failure of an entire segment of a transmission line bounded by two end towers. This model can predict where the failure is initiated and how it progresses along the line, with considering different models of tangent and end towers.