Aeroelastic Testing to Evaluate Wind Effects on Transmission Systems

Abstract

The transmission infrastructure in the U.S. faces substantial risk from hurricanes. Wind-induced damage poses an immense threat to the electric power grid; such hazards have significantly impacted the supply, generation, and delivery of power to large portions of the U.S. in the past. When exposed to strong winds, critical demands in several elements in transmission tower-line systems may exceed corresponding capacities and trigger various modes of failure. Enhancing the resilience of the transmission grid against increasing threats from hurricanes and strong winds is therefore of critical importance. The results of 1:50 aeroelastic scaled models of a self-supported steel lattice tower and a multi-span transmission lines system under simulated hurricane wind speeds are presented. The aeroelastic tests are conducted at the NSF Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). The models are tested at various wind speeds ranging from 35 m/s to 77 m/s (full-scale) for wind directions varying between normal and parallel to the alignment of the transmission line. Two system identification (SID) techniques are utilized to validate the analytical along-wind aerodynamic damping of the model and provide insights on its crosswind counterpart. A buffeting analysis is conducted to estimate the response of the tower, the conductors and the entire system and compare it to measured values at the WOW. Similarly, drag and moment coefficients are calculated from the measured response, and dynamic amplification factors (DAF) are computed. Results show that the coupling effects between the transmission tower and the conductors are significant. In some instances, such effects are favorable and in others, unfavorable. Other findings also show that there is a need to include the change in turbulence intensity along the height of the tower in the established analytical modeling approach. The drag coefficients are shown to be in agreement with values proposed in the standards. However, there is a need to consider moment in lattice tower design to account for bending in the members that might be introduced by any rigid connection. The resonance contribution is shown to reach a maximum of 18% and 30% of the peak response for the single tower and multi-span transmission lines systems, respectively.