Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Civil and Environmental Engineering
Supervisor
El Damatty, Ashraf
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.
Summary for Lay Audience
Natural hazards endanger the community’s prosperity by causing significant damage to power distribution systems, resulting in widespread power outages with serious socioeconomic consequences such as business downtime, infrastructure disruption, and high repair costs. Downburst is one of the extreme wind events that occurs during thunderstorms. During this event, a jet of cold air falls suddenly on the ground, causing strong outflow wind. The long distances covered by transmission lines increase their probability of being exposed to a downburst event. Transmission lines consist of supporting towers, conductors that transmit electricity, insulators that connect the conductors to the towers, and ground wires for protecting the system from lightning. The line is ended by an end tower which is typically a stronger tower that can limit the failure progression in the line segment. When a tower fails, the new tension forces in the conductors due to the failure affect the adjacent towers, potentially causing them to fail, triggering a chain of failures in transmission towers. In this Thesis, the effect of the downburst design load cases on transmission towers is compared to the effect of the traditional design wind loads. As transmission towers are vulnerable to failure during downbursts, the Thesis investigates the dynamic response of the conductors to transmission tower failure under downburst loads, aiming to examine the effect of that response on the reactions transferred to adjacent towers. The response of end towers, as critical structures in transmission lines, to downburst loads is assessed using numerical analysis and experimental test of a transmission line conducted at the Wind Engineering, Energy and Environment (WindEEE) Research Institute. Finally, a numerical model is developed to analyze the failure propagation in a transmission line segment, while considering the end towers. The developed model is used to study the effect of different line properties on the failure propagation and the behaviour of end towers.
Recommended Citation
Ahmed, Abdelrahman, "Assessment of Behaviour and Cascade Failure of Tangent and End Towers of Transmission Lines Under Downbursts" (2024). Electronic Thesis and Dissertation Repository. 10459.
https://ir.lib.uwo.ca/etd/10459
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