Abstract
Transmission line structures, though designed per code provisions, suffered several failures worldwide in the past. As reported in the body of the available literature, more than 90% of those failures are due to sever localized wind events such as downbursts. Several recent studies emphasised on the importance of the conductor loads and how their forces contribute to the failure of the towers. The velocity profile and loads associated with a downburst wind field vary significantly with the change in its configuration. Previous studies, focused on identifying the critical transmission tower members that are likely to fail during a downburst event and the associated critical downburst configurations. In all these studies, a smooth terrain was assumed where the effect of terrain roughness is not considered. In the current study, an evolutionary optimization algorithm is coupled with a semi-closed form solution technique to predict the maximum conductor’s reactions under downburst wind field and the associated critical downburst configurations. A Large Eddy Simulation (LES) model of downbursts impinging on various exposure conditions, developed in a previous study, has been incorporated to predict wind forces acting on the conductor line. It is believed that the current study is the first of its kind to provide critical downburst configurations that lead to maximum conductors’ reactions while considering the effect of terrain exposure (open, countryside, suburban, and urban). Based on the optimal downburst configuration identified for each type of terrain roughness, a simple and practical approach in the form of simple equations and a set of charts to evaluate maximum reactions has been developed and validated. The simplified approach is suitable for practitioner engineers to accurately and rapidly evaluate maximum conductor reactions under downburst events considering multiple terrain conditions.
Highlights
The transmission line system (TL) has a significant importance as it undertakes the task of transmitting electricity from source of production to end users
The optimization code developed in sections Genetic Algorithm (GA) Optimization Technique and Results and Discussion is capable of predicting the critical downburst configuration associated with maximum conductor reactions for different types of terrain roughness
The simplified approach is based on utilizing the general expression given in Equation (6) to predict maximum conductor reaction Rmax, where Lx is the conductor span length, gpymax is the maximum intensity of the downburst wind load and fmax is a factor that depends on the reaction type, terrain exposure and other factors as will be described later
Summary
The transmission line system (TL) has a significant importance as it undertakes the task of transmitting electricity from source of production to end users. Due to the importance of accounting for the conductor reactions and the challenge in conducting computationally intensive analyses to evaluate those reactions, the current study sought to develop an easy-to-apply method suitable for practicing engineers to predict peak conductor reactions for different terrain exposures under downburst loads.
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