Vienna University of Technology has developed, in collaboration with Northeastern University, a method to increase the structural damping of stay cables. Advantages with respect to conventional dampers are the simple and robust technology and the fact that all components, required by the new mechanism are located inside the stay cables. The new device works like an impact damper, embedded inside the stay-cable in order to decrease the dynamic hazards in various cables eigenmodes. The passive control is similar to a tuned mass damper, which was originally proposed and studied by Den Hartog. In its simplest form the behaviour can be modelled as a secondary mass-spring dashpot system, attached to the cable. A reduced-order analytical model for free-vibration dynamics of the cables with damping system is currently been developed. A parametric investigation, based on the developed model, will be used to compare the predicted performance with the experimental results. In a full scale field test on stay-cables with 31-meter length, conducted at Vienna University of Technology, the damping ratio of a conventional stay and the one cable equipped with the damping system were compared. Based on the dynamic response of the cables, of damping properties could be determined. The analytical model and the experiments suggest that the innovative damping system is indeed a very effective and cost efficient method to protect stay-cables from wind and wind-rain induced dynamic vibration.