Modeling and Prediction of Failure of Transmission Lines Due to High Intensity Winds

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Abstract
The high intensity winds (HIW) associated with thunderstorm outflows (downbursts, tornados) have profile shapes that differ greatly from the straight line winds in conventional atmospheric boundary layers that form the basis of the design wind loads for electricity transmission line systems. Evidence from line failures, such as Manitoba Hydro's (MH) on 5th September 1996, that caused failure of 19 towers and a 5-day line outage, suggests that many are the result of HIW, due to a combination of extreme wind speed and an off-design wind load distribution. Whilst the complete upgrading of any given line system to withstand the severest storms is not feasible, some critical locations (e.g. major river / road / rail crossings) could benefit from remediation based on a thorough understanding of HIW loads. The authors have completed the first phase of a comprehensive research program aimed at quantifying these HIW wind fields, their loading on transmission line tower and line components and the resultant response of the transmission line system. The main outcomes from that phase were 1 Formulation of a computational fluid dynamics (CFD) model of downburst and tornado wind fields validated by small-scale laboratory experiments and a theoretical / analytical model 2 Derivation of a loading model for downburst winds and application of this model to fully non-linear finite element (FE) models of a MH Type A guyed tower / line system. Identification of some of the critical members and failure mechanisms. A second phase of work is currently in progress that is concerned with the validation and implementation of the previously developed concepts, encompassing 1 Design and construction of a large scale downburst simulator (based on a 2-D wall jet concept) 2 Testing of tower/line physical models in the large-scale downburst simulator, with comparison to loads derived from atmospheric boundary layer wind profile model testing. 3 Improving the downburst and the tornado numerical models by introducing atmospheric parameters and comparison with Doppler radar atmospheric data.

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