Joint Wind and Ice Effects on Transmission Lines in Mountainous Terrain
Abstract
Atmospheric icing on mountainous terrain can produce catastrophic damages to transmission lines when incoming particles impinge and accrete on the cable surface of the system. The first challenge in wind-ice loading is determining joint statistics of wind and ice accretion on transmission lines. This study analyzes the weather characteristics for a specific site of study using 15 years of historical data to use as inputs for ice accretion modeling. The joint wind and ice hazard is characterized by simulating 500 years of icing events from the fitted probability distributions of ice accretion and wind on ice velocities. The second challenge of wind and ice loading is to deal with the wind induced vibrations when the iced conductors present complex asymmetrical shapes. The vertical galloping, characterized by high amplitude and low frequency motions, produce extra tension to the transmission towers which is not considered in the Canadian standard (CSA-C22.3) for the design of wind and ice loads for overhead transmission lines. For the dynamic analysis, the Den Hartog’s principle is applied to identify potential instabilities and the linear theory of free vibrations of a suspended cable is performed for the estimation of the extra tension produced by the free stream velocity acting on the one-degree-of-freedom iced conductor. The static and dynamic loading resulting from the present study are compared with the wind and ice design cases based on the Canadian standard (CSA-C22.3).