A Possible Relation between Wind Conditions, Advanced Control and Early Gearbox Failures in Offshore Wind Turbines

AbstractDuring the past decades, great efforts have been undertaken to make wind power a competitive source for electrical energy. By the end of 2012, global installed wind capacity had risen to 264GW, almost a tenfold increase of the capacity in 2002. Nevertheless, the wind energy sector is still far too expensive to be profitable, especially the strong growing offshore branch. However, a significant part (about 25%) of the cost is related to operation and maintenance (O&M), in particular the failures of the main components (i.e. gearbox and drivetrain) resulting in long downtimes and hence high O&M costs. Various studies today discuss if condition monitoring systems, which allow the forecasting of failures at a very early stage, might be the cure to the problems related to the reliability of the gearbox. Rather than formulating yet another methodology to forecast upcoming failures, the aim of this paper is to identify the underlying cause of the reliability issues related to the gearbox

Validation of four LES and a vortex model against stereo-PIV measurements in the near wake of an actuator disc and a wind turbine

In this paper we report the results of a workshop organised by the Delft University of Technology in 2014, aiming at the comparison between different state-of-the-art numerical models for the simulation of wind turbine wakes. The chosen benchmark case is a wind tunnel measurement, where stereoscopic Particle Image Velocimetry was employed to obtain the velocity field and turbulence statistics in the near wake of a two-bladed wind turbine model and of a porous disc, which mimics the numerical actuator used in the simulations. Researchers have been invited to simulate the experimental case based on the disc drag coefficient and the inflow characteristics. Four large eddy simulation (LES) codes from different institutions and a vortex model are part of the comparison. The purpose of this benchmark is to validate the numerical predictions of the flow field statistics in the near wake of an actuator disc, a case that is highly relevant for full wind farm applications. The comparison has shown that, despite its extreme simplicity, the vortex model is capable of reproducing the wake expansion and the centreline velocity with very high accuracy. Also all tested LES models are able to predict the velocity deficit in the very near wake well, contrary to what was expected from previous literature. However, the resolved velocity fluctuations in the LES are below the experimentally measured values

Performance characteristics of a micro wind turbine integrated on a noise barrier

tract Micro wind turbines can be structurally integrated on top of the solid base of noise barriers near highways. A number of performance factors were assessed with holistic experiments in wind tunnel and in the field. The wind turbines underperformed when exposed in yawed flow conditions. The theoretical cosθ theories for yaw misalignment did not always predict power correctly. Inverter losses turned out to be crucial especially in standby mode. Combination of standby losses with yawed flow losses and low wind speed regime may even result in a net power consuming turbine. The micro wind turbine control system for maintaining optimal power production underperformed in the field when comparing tip speed ratios and performance coefficients with the values recorded in the wind tunnel. The turbine was idling between 20%–30% of time as it was assessed for sites with annual average wind speeds of three to five meters per second without any power production. Finally, the field test analysis showed that inadequate yaw response could potentially lead to 18% of the losses, the inverter related losses to 8%, and control related losses to 33%. The totalized loss led to a 48% efficiency drop when compared with the ideal power production measured before the inverter. Micro wind turbine’s performance has room for optimization for application in turbulent wind conditions on top of noise barriers. https://doi.org/10.3390/en1405128