A Comparative Study of Shutdown Procedures on the Dynamic Responses of Wind Turbines

Abstract

The shutdown of wind turbines may induce excessive loads on the structures and is an important factor to consider in their design. For pitchregulated turbines, shutdown calls for blade pitching, and oneor twoblade shutdown may occur during pitch actuator failure. Through coupled analysis, this study investigated the dynamic responses of landbased and spartype floating wind turbines (FWTs) during shutdown. We simulated the shutdown procedures by pitching one, two, or three blades, and by varying the pitch rate. The nonpitching blades have a fixed pitch angle during the process. Three generator torque conditions were considered: (1) grid loss, (2) mechanical braking, and (3) grid connection. The extreme response values and shortterm and annual fatigue damages to the structural components were compared against these values under normal operation and parked conditions. Threeblade shutdown is recommended for both turbines. Oneor twoblade shutdown with grid loss may result in a significant rotor overspeed and imbalanced loads acting on the rotor plane. Therefore, unfavorable structural responses are observed. Grid connection or mechanical braking alleviates the situation. The landbased turbine is more sensitive to the pitch rate when considering the tower bottom bending moment, but the blade moments and mooring line loads of the spartype turbine are affected more.