In one case, a series of active soil cracks started to appear around the wind tower foundations at a Texas wind farm, indicating foundation movements that affected the performance of the wind towers, reducing their power generation capacity due to frequent shutdown of turbines. In order to investigate the root cause of the problem and to develop a repair plan, the owner hired CTLGroup for foundation crack monitoring as well as load monitoring and frequency measurement on selected towers.
CTLGroup developed a monitoring system using a high-speed data acquisition system and an array of sensors including tiltmeters, displacement sensors, strain gages, and accelerometers located at specific locations on the tower foundation and inside the tower. CTLGroup performed wind tower load monitoring to identify bending moments and longitudinal stress magnitudes near tower base ring, under different wind speeds and operating conditions. These stresses and moments were then compared with the design values to determine whether the tower was being overloaded. In one particular situation, load monitoring was conducted during standard operating conditions and during emergency stops on a wind tower with extensive soil cracks in the vicinity of tower foundation.
The monitoring system designed and installed by CTLGroup indicated no overloading of the tower structure but pointed towards potential problems with the digging operation during foundation construction that, over time, resulted in excessive displacement at the top of the tower thus frequent turbine shut downs.