Integration of low-cost accelerometers for condition monitoring of wind turbine blades

Wind turbine blades are structurally composed of different types of materials. Some of which include; wood and/or steel used for constructing the main-spar and glass reinforced plastic (GRP) for building the downwind and upwind sides of the blade. During manufacture and over the operation lifetime of wind turbine blades, they are subject to defects and degradation which can result to deformation/fault occurrence (such as cracks) and subsequent failure. The wide-spread of materials used in their construction makes it difficult for predictions on lifetime health to be made, thus the importance of condition monitoring. Condition monitoring of wind turbines is an effective method for improving the maintenance and subsequent operation of wind turbine systems. In this paper, non-destructive evaluations were conducted using vibration/modal analysis, low-cost MEMS (Micro Electro-Mechanical Systems) accelerometers and signal processing techniques to detect defects and variations in the health of small wind turbine blades. A healthy (new) and an unhealthy (old) Rutland 913 Windcharger blade were tested in a small scale experiment and comparisons were made. Results showed that the presence of a crack and the overall deterioration in the structural health of the old blade increased its modal frequency from that of the new blade and an edge crack decreased the local stiffness of the wind turbine blade. Experiments were conducted on a 4.5m blade to show how the results extend to larger blades. In conclusion, these low-cost accelerometers have the ability to detect high and low blade resonance frequencies and have the potential to be integrated easily either retrofitted externally or embedded in blades at manufacture for condition monitoring at marginal cost.