Field vibrational analysis of a full scale horizontal-axis wind turbine in actual operating conditions

Wind farm operation reliability is becoming a key asset for wind energy conversion systems in the framework of grid-parity energy market. Consequently, experimental methods for characterizing the vibration behaviour of wind turbines in real operating conditions are going to play a fundamental role in order to improve the correct estimation of the RUL (Remaining Useful Life) of the components as well as the whole system. For this reason, in the present work a new experimental approach for the identification of the most important mechanical parameters through field acceleration measurements has been developed and tested on a full scale three bladed wind turbine with a rated power of 200 kW and a rotor diameter of 31 m. The main goal of the identification procedure was to give the correct estimation of important vibration parameters of the structure and the machine. As for example the tower structural eigenfrequencies and the structural damping. The experimental setup included three accelerometers on the nacelle (two for the tower and one for the main bearing) and up to four sensors on along the tower and in the foundation. The structural eigeinfrenquencies have been studied through machine emergency stops while the operational condition were studied capturing steady-state events. The study demonstrates that the experimental data post-processing can represent a fruitful and quick approach for defining the most important structural and dynamic parameter even when the full details of the wind turbine are not available and this can be particularly useful for refurbished technology.