Passive Damage Monitoring of Wind Turbine Rotor Blades Using Cyclic Signal Processing

As of Q1 2011, 41,400 MW of wind energy had been installed in the US and those installations are on pace to achieve the US DOE goal of 20% wind energy by 2030. With this increased level of penetration from wind generation, the stability of the electrical grid will become dependent on the reliability of offshore and terrestrial wind turbines. Structural health monitoring (SHM) integrated into the Operations & Maintenance (O&M) strategy of wind plants has the ability to both increase reliability and reduce O&M costs. Sandia National Laboratories Wind Energy Technologies Department (SNL) has been actively researching SHM technologies at the sub-component, component, and full system levels in both computational and experimental efforts for both terrestrial and offshore wind plants. SNL commissioned the fabrication of a Sensored rotor blade during Spring 2008 as a test bed for promising wind rotor monitoring technologies, including strain gages, fiber Bragg gratings, RTD temperature sensors and accelerometers. Following operational testing, the rotor blade was shipped to the National Renewable Energy Laboratory National Wind Technology Center to test structural health monitoring techniques during a fatigue to failure rotor blade test. To understand the structural state of the rotor blade, a method was devised to estimate Frequency Response Functions from the fatigue excitation and response. The results showed that the method for estimating FRFs could be used to monitor the fatigue test magnitude, phase and structural characteristics throughout the 2M cycle test.