Combined effects of wind and atmospheric icing on overhead transmission lines

A complementary method to the one prescribed by the International Standard (IEC 60826:2003) for estimating combined wind and ice loads on overhead transmission line is proposed in the present study. The design approach in the standard is based on static loads only, which might be inadequate for certain atmospheric conditions causing significant dynamic loads. The current study particularly focuses on the potential development of aerodynamic instability conditions which may yield large amplitude and low frequency cyclic motions, known as galloping. The development of the galloping is investigated on the basis of a statistical approach considering the climatic dataset at the site of interest and field observations of this type of motion. A parametric study in which different combinations of wind and ice loads is therefore conceived to enhance the understanding of the influence of each variable on the occurrence of the related instabilities. The instability conditions are evaluated and compared based on Den Hartog’s and Nigol’s theories. The dynamic response of the system is restricted to the case of vertical galloping, and the amplitude of the vertical oscillation was computed by employing the linear theory of free vibrations of a suspended cable. Eventually, a risk analysis for the site of interest is carried out, which can be used as a useful tool to identify the critical load cases and select appropriate control methods to limit or prevent galloping.