Judgment criteria for significant wind speed-up regions in natural complex terrain

Flashover incidents due to wind-induced motion of overhead power line components are a not uncommon phenomenon during very strong winds, e.g. typhoons, and an important contributing factor is the speed-up effect caused by small-scale topographic features. In this study, wind speed-up ratios and significant speed-up regions in natural complex terrain are comprehensively analyzed from three perspectives: analysis of landform characteristics of flashover locations, Computational Fluid Dynamics (CFD) simulation, and wind tunnel experiments. Through the analysis of flashover locations, judgment criteria based on the elevation coefficient of variation are proposed to attempt to identify significant speed-up regions in natural complex terrain. Wind tunnel experiments and CFD simulations are conducted to analyze the wind speed-up ratios in 12 wind directions for both a small isolated mountainous area and a large continuous mountainous area. The significant speed-up regions are determined by consolidating the speed-up ratios from all 12 wind directions. The reliability of the judgment criteria is then validated. The results confirm that significant speed-up ratios are predominantly concentrated at the edges of mountainous areas, particularly at peaks and high ridges around areas with larger elevation coefficient of variation. These regions largely coincide with the locations where flashover incidents mainly occurred and the results from wind tunnel experiments and CFD simulations. In summary, the clearly identified significant speed-up regions include (1) small isolated mountainous areas; (2) peaks and high ridges around areas with larger elevation coefficient of variation within large continuous mountainous areas, and the higher crests within these regions. Based on these findings, the study suggests that wind speed-up ratios in design standards should be amplified in the vicinity of these regions to enhance safety measures. •The judgment criteria are proposed to attempt to rapidly identify significant speed-up regions based on the elevation coefficient of variation.•The spatial distribution pattern and landform characteristics of 66 flashover incidents are analyzed.•The significant speed-up regions for two types of terrain features in natural complex terrain are explored.