Cluster of wind turbines tripping-off from grid occasionally occurred in large scale wind farms recently

which significantly affects the security of the grid. In the past

the research has mainly been focused on the electromagnetic transient processes stimulated by disturbances in the grid. If a disturbance is large enough and triggers Crowbar protection

it will lead to unbalance in the rotor torques of wind turbines

and the rotor speed will be deviated from normal value. If the rotor speed exceeds certain limits

the over-speed protection would be triggered and wind turbines will be tripped off from the grid. The electromechanical transient process of doubly-fed induction generator (DFIG)-based wind turbines equipped with Crowbar is analyzed. The mechanism of DFIG-based wind turbines over-speed tripping-off from grid is revealed and the criterion for checking over-speed is deduced. A case study of DFIG-based wind turbines tripping-off from grid is analyzed

and the results verify that the proposed method is effective.