Patent ID: 8816871

Claim:
A method for monitoring a static and/or dynamic stability of a wind turbine having a tower, a nacelle which is supported by the tower, and a rotor which is mounted in or on the nacelle and has at least one rotor blade defining a plane as the rotor blade rotates over an area and said rotor blade being adjustable about its longitudinal axis, the method comprising the steps of: exciting the wind turbine to oscillate with said tower thereof in a z-direction at right angles to said plane by adjusting a blade pitch angle of said at least one rotor blade to its feathered position; detecting a frequency (f m ) of the excited oscillation of said wind turbine including said tower; comparing the detected frequency with a predetermined frequency (f ref ); and, generating an alarm signal when the detected frequency deviates from the predetermined frequency by more than a difference value (Δf).