Effects of transient loading on wind turbine drivetrains
This project aims to tackle some of the fundamental issues with modelling the drivetrain of the wind turbine. Reliability data shows that gearboxes and generators have higher failure rates than expected, in particular the high speed bearings which are shown to be most problematic. Models of gearboxes are generally isolated from the rest of the structure and loading applied at boundaries to the model. This may not adequately represent conditions that bearings encounter and in certain cases bearings fail due to under prediction of loads. A full drivetrain model is created showing how flexibility of certain subcomponents affects loading on other parts of the drivetrain. Stiffness of the gearbox mounts, the bedplate and the coupling is revealed to have a large effect on the loading that high speed bearings experience. Transient loading is also examined to discover if this has a significant effect on high speed bearing loading. Static models have been used to analyse drivetrains using predicted inputs applied at the boundaries but this cannot include any contributions from the structural modes. Transient events such as a grid loss emergency stop are performed on a model of a 2 MW wind turbine and sensitivities of the control strategies are found in relation to LSS torque and rotor speed. Findings show that static models are able to predict general motion of the drivetrain structure so long as the response follows the input conditions; transient models of the drivetrain showed significant differences in the response between loading predicted by static models and transient models. Finally, medium speed drivetrains are analysed showing how design of the drivetrain can reduce the susceptibility of the drivetrain bearings to vibrational modes of the structure. Findings show problematic bearings are removed and drivetrain bearings become insensitive to loading concluding that medium speed drivetrains could improve reliability.
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