Numerical and experimental investigation of the influence of dynamic loads on wet snow shedding from overhead cables

Several types of atmospheric icing deposits may load overhead cables including heavy adherent wet snow, hard rime, large but lightweight soft rime and high-density glaze ice. Snow deposits on exposed structures can be the source of several serviceability, safety and mechanical reliability issues. On overhead power lines in particular, the gravity loads due to heavy snow accretion, coupled with wind-on-snow loads, may lead to structural damages, or failure and even cascading collapse of towers. The shedding of the snow deposit can apply dynamic loads on the line by the initiated cable vibration and results in unbalanced tension between shed and unshed adjacent spans. Therefore, in order to protect the line against loads resulting as a consequence of accreted snow on the line and to ensure the reliability of electrical power delivery networks, the processes of snow shedding have to be profoundly understood and countermeasures have to be taken, e.g., by applying anti-icing and de-icing methods.;The numerical model can serve as a basis to study various failure criteria of wet snow in terms of adhesion. In order to achieve this goal, first the tensile and shear adhesion of snow to cable surfaces were experimentally studied, which are essential to correlate shedding and the adhesive strength between cable and snow, since shedding occurs after adhesion vanishes. These measurements were carried out using material test machine and centrifuge machine. Then, a criterion of wet-snow failure was determined and applied in the numerical model, which simulates vibrations of the cable covered by wet snow due to application of periodic excitation resulting snow shedding process. The periodic excitation is modeled by an input displacement time function at one cable end, making the variation of excitation frequency possible. The challenge is to predict whether the deposit will remain attached to the conductor or fall off during the resulting vibration. The model considers snow shedding by removing snow elements along the cable where the failure criterion is satisfied.;In the experimental study, wet snow sleeves were reproduced on a small-scale span by using a formerly developed technique. Snow loads of different thickness were thus created on this span and periodic loads were applied at the suspension point in order to initiate cable vibration and observe the resulting shedding mechanism. The coincidence of results of numerical model and those of small-scale experimental simulations validates the model and assures its reliability. Finally, the developed snow model with failure criterion is applied in further numerical simulations for real-scale single spans subjected to periodic impact.;This study focuses on the dynamic analysis of snow-covered overhead transmission lines subjected to periodic loads. Such loads may result from the effect of an external periodic load intended to remove accreted snow from the cable, or from such natural effects as wind or load imbalances due to sudden or propagating snow shedding from an adjacent span. The objective is to understand the phenomenon of mechanically-induced snow shedding on overhead cable spans and to simulate the effects of periodic loads on wet snow shedding. In previous studies, the response of the line to instantaneous shedding was modeled, whereas in this research, the propagation of snow shedding along the span as response to a periodic load is studied. In particular, the dynamic response of snow-covered cables to periodic loads is examined by numerical modeling using nonlinear finite element analysis as well as experimentally in a cold chamber.