Reducing cost uncertainty in the drivetrain design decision with a focus on the operational phase

Abstract

In order to identify holistically better drivetrain concepts for onshore wind turbine application, their operational behavior needs to be considered in an early design phase. In this paper, a validated approach for estimating drivetrain-concept-specific unplanned operational effort and risk based on open-access data is presented. Uncertain influencing factors are described with distribution functions. This way, the poor data availability in the early design phase can be used to give an indication of the concept's choice influence on the unplanned operational wind turbine behavior. In order to obtain representative comparisons, a Monte Carlo method is applied. Technical availability and drivetrain-influenced unplanned operational effort are defined as evaluation criteria. The latter is constituted by labor, material and equipment expenses. By calculating the range of fluctuation in the evaluation criteria mean values, this approach offers an indication of the inherent risk in the operational phase induced by the drivetrain concept choice. This approach demonstrates that open-access data or expert estimations are sufficient for comparing different drivetrain concepts over the operational phase in an early design stage when using the right methodology. The approach is applied on the five most common state-of-the-art drivetrain concepts. The comparison shows that among those concepts the drivetrain concept without a gearbox and with a permanent magnet synchronous generator performs the best in terms of absolute drivetrain-influenced unplanned operational effort over the drivetrain's lifetime as well as in terms of the inherent risk for the assumptions made. It furthermore makes it possible to give insights into how the different drivetrain concepts might perform in future applications in terms of unplanned operational effort. Exemplarily the impacts of higher torque density in gearboxes, a change to moment bearings and adjusted coil design in electrically excited generators have been analyzed. This analysis shows that the superiority of synchronous-generator concepts manifested in historic data is not entirely certain in future applications. Concluding, this approach will help to identify holistically better wind turbine drivetrain concepts by being able to estimate the inherent risks and effort in the operational phase.