Cascade Failure of Transmission Lines under Downbursts
Abstract
Downburst belongs to a category of localized windstorm, called High Intensity Wind (HIW) events that happen during thunderstorms. Because of their extensive length, transmission line structures are vulnerable to failure when a downburst happens with their long paths. The failure can be costly since the collapse of one tower often triggers the collapse of many towers along the line. This is one of the major problems facing the electrical utility industry worldwide. While previous research studies have investigated the behavior and failure of a single tower, the research conducted in this thesis is first to consider the analysis and progression of failure of a segment of a transmission line, including multiple towers and the in-between conductors, under downbursts. A unique numerical model is developed in this thesis to achieve this task. This numerical model consists of various components and their formulation and validation are reported in various parts of the thesis. The model developed to predict the failure of a single tower is first presented in Chapter 2. Once a tower fails at a certain location, a mechanism is formed, and the rotation of the unstable part tends to increase the conductor tension forces, which can bring the tower into a new state of equilibrium. As such, an analytical solution based on three-dimensional catenary theory was developed in Chapter 3 to predict the conductor’s forces with unlevelled ends horizontally and vertically. The comprehensive numerical model that can predict the progress of failures of the entire line is presented in Chapter 4. The model starts by identifying the downburst configuration most critical to the tower. It predicts the failure mode of the tower, including the post failure new equilibrium state and the associated conductor forces transmitted to adjacent towers. The analysis similarly proceed to subsequent towers till covering the entire segment. Case studies involving studying of the failure of a single tower as well as a segment of a line are presented in the thesis together with a parametric study conducted to assess the effect of downburst jet velocity, the span and the insulator length on the cascade failure of a line.