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

The shutdown of wind turbines may induce excessive loads on the structures and is an important factor to consider in their design. For pitch-regulated turbines, shutdown calls for blade pitching, and one- or two-blade shutdown may occur during pitch actuator failure. Through coupled analysis, this study investigated the dynamic responses of land-based and spar-type 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 short-term and annual fatigue damages to the structural components were compared against these values under normal operation and parked conditions. Three-blade shutdown is recommended for both turbines. One- or two-blade 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 land-based 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 spar-type turbine are affected more.