The appearance and propagation of fatigue cracks in the main shafts of wind turbines may lead to the shaft breaking and even the collapse of the rotor.
The appearance and propagation of fatigue cracks in the main shafts of wind turbines may lead to the shaft breaking and even the collapse of the rotor. Manual ultrasonic inspection is one solution but it requires stopping the machine and limits the remaining useful life of the shaft to 50%.
The design, development and validation of an autonomous system to evaluate the residual useful life based on ultrasound is presented as an alternative to the implementation of condition-based maintenance.
The entire system consists of an annular array of transducers secured to the front of the shaft, along with electronics controlled by firmware. It is based on the results of a root cause analysis (RCA). The firmware includes the detection method and the algorithm that estimates the useful life. It is based on the crack size measured by the system, and programmes different alert levels; from initial detection to foresee having a new shaft in stock, and the replacement operation; up to the alert indicating that the maximum crack size has been reached so as to recommend shutting down the wind turbine.
The system was initially installed in ten wind turbines and was later extended to one hundred. After three years in operation, the system has proven to offer even better detection capabilities than manual inspection, which is not able to detect cracks located in the compression zone of the shaft, and increases the shaft's useful life from 50% to 96%.
The methodology used is based on a Root Cause Analysis (RCA) of the shafts, and on the development of a new detection system via customised low-cost ultrasound: linked to the shaft from its accessible head, incorporating RCA knowledge.
Further information
ThePDF of the technical article published in Number 94 of the Spanish Non-destructive Testing Association’s magazine explains the methodology followed in greater detail.
