Wind

8 Signs of damage around the bottom flange of the embedded ring were identified in a large 9 number of existing onshore concrete foundations. As a result, the embedded ring experienced 10 excessive vertical displacement. A wireless structural integrity monitoring (SIM) technique was 11 developed and installed in the field to monitor the stability of these turbines by measuring the 12 displacement patterns and subsequently alerting any significant movements of the embedded ring. This was achieved by using wireless displacement sensors located in the bottom of the turbine. A wind turbine was used as a test bed to evaluate the performance of the SIM system under field operating conditions. The results obtained from the sensors and supervisory control 16 and data acquisition (SCADA) showed that the embedded ring exhibited significant vertical movement especially during periods of turbulent wind speed and during shut down and start up 18 events. The measured displacement was variable around the circumference of the foundation as a result of the wind direction and the rotor uplift forces. The excessive vertical movement was 20 observed in the side where the rotor is rotating upwards. The field test demonstrated that the 21 SIM technique offers great potential for improving the reliability and safety of wind turbine 22 foundations.