Modal testing of rotating wind turbine rotor using torque input

A method for modal test of rotating wind turbine rotors using torque input is presented. A hydraulic continuously rotating shaker is used for excitation of the rotor and the input torque is measured and used as the reference signal. Accelerometers are mounted on the wind turbine wings and used as response signals. The rotor diameter is 52 m. Different types of excitation were considered in order to maximise the signal to noise ratio without spending too much time on the testing. If too much time were spent on testing the ambient conditions would change and cause different kinds of problems with consistency of data. The ambient conditions were measured and logged carefully during the testing. Problems with the non-symmetric frequency response matrix, non-linearity introduced by different wind loading of the rotor and other effects caused by the ambient conditions are discussed briefly. The wind turbine was changed considerably in order to make the measurements possible. These changes have also been simulated using a finite element model. Later the test results will be used for updating of this model.