Power lines Snow. (266) скачать в хорошем качестве

Power lines Snow. (266)

When ice precipitations accrete on the conductors, the severity of the two phenomena can increase dramatically. Moreover, aeolian vibration of conductors coated with ice may then occur in frequency ranges outside damper capabilities. Galloping, another wind-induced instability, also occurs on ice-accreted conductors and may result in spectacular conductor displacements. Galloping is a movement-induced excitation and its mechanism will be described on both single and bundle conductors. This review of the combined effects of ice or wet snow and wind on overhead power lines includes serious loadings and instabilities such as the rebound of conductors following ice drop and the rolling of bundles due to accumulated glaze or rime ice and wind action in exposed spans or in elevated mountain routes. Direct observation of the effects of icing on overhead power lines is an absolutely necessary preliminary to any understanding of the many phenomena that can occur. Without such observations, unrealistic assumptions about the mechanisms in presence could be made and lead to incorrect or incomplete solutions based on analysis. Since the number of variables such as the overhead line designs, the thickness and density of the ice or snow deposits, and the wind loadings to name a few, is large, an overview of the state of the art of these different phenomena will be presented here. Measurements conducted on transmission lines or test lines with natural or artificial ice are included to better understand and quantify those phenomena. Many of these effects have partial or approximate models supported by field data, to assist in reducing the damage. However, there is a need for more work for complete understanding, including cooperative ventures employing the different resources available to universities and utilities. (266)