Gearbox high‐speed‐stage bearing slip induced by electric excitation in a test facility

Abstract

The goal of this paper is to investigate the behaviour of the high-speed stage of a wind turbine gearbox during transient grid-loss events triggered at different power levels in a full-scale nacelle dynamometer test. The gear mesh behaviour and the bearing roller slip during these events are characterized by strain measurements placed in the gear teeth roots and embedded in the outer rings of the tapered roller bearing locating pair. From our experiments, we conclude that the high-speed stage experiences a multidimensional loading consisting of bending and torsional deformation during the transient event. This loading propagates throughout the gearbox and results in unfavourable loading conditions at the bearing that have the potential to go beyond the preload during the torque reversals that occur during the grid-loss event. During the torque reversal, roller slip can occur in the bearings. It is observed that the slip behaviour is directly linked to the initial power level of the generator.Electrically induced excitation that typically leads to dynamic torque events can therefore cause mechanical gearbox degradation.An emergency stop is a good example of a transient event. As a braking mechanism, the blade pitch is changed to its maximum value as fast as possible to stop the turbine and keep it safe. It is suspected that these events significantly influence turbine and subcomponent lifetime. This hypothesis is shared by many researchers. Bruce et al use simulations to show that during emergency stop events, the HSS bearings can be overloaded, thereby causing excessive stress. 7 Also, Heidenreich et al link torque reversals that occur during emergency stops to the thickness of the bearing oil film as a possible explanation for premature failure. 8,9 Further, Greco et al link white etching crack phenomena that causes premature bearing failure to extreme loads as likely being induced by emergency stops or generator power line losses. 10 Most experimental investigations discussed in literature are based on bearing-level test rigs, general experience from the field, or simulations of the whole turbine system. Full-system tests, however, are not documented often. Dynamometer testing can help understand which mechanisms govern the HSS behaviour during the most important dynamic events because the dynamometer environment offers full control of testing conditions. In addition, certain dynamic events can be reproduced by defining the speed and torque inputs, and both external and internal gearbox instrumentation can be used because the gearbox is easier to access. This work focuses on the grid-loss event conducted in a full-scale dynamometer test with the complete nacelle. During this test, the generator currents go to zero almost instantaneously while the gearbox is still at full speed. The grid-loss test is initiated at different power levels to understand the consistency in system response to such an event. We focus particularly on the HSS bearing and gear response to the grid-loss event.

Fleetwide data-enabled reliability improvement of wind turbines

“…Laboratory testing using dedicated dynamometer setups [37] shows the link between unfavorable (dynamic) loads and bearing failures in the field [36,38]. These test results show that a large majority (71%) of the HSS bearing failures appears to be caused by axial cracking resulting from local microstructural changes.…”

“…It has been shown in literature that this slipping can be induced by dynamic events [20], but with only limited demonstration on a full-scale test article. Specifically, roller slip induced by dynamic load cases is investigated [43,44,38]. Dynamic loads can be induced by certain control actions or erroneous turbine responses, such as blade pitching, startup, emergency braking or yawing [45], during dynamic wind or grid events.…”

Wind Turbine Drivetrain Reliability and Wind Plant Operations and Maintenance Research and Development Opportunities

“…An early attempt at developing design life calculations was undertaken for yaw and pitch bearings by Harris, Rumbarger, and Butterfield (2009). Failure modes related to load-sharing in planetary shaft bearings (LaCava et al 2013;Guo, Keller, and Parker 2014;Guo, Keller, and LaCava 2015;Keller and Wallen 2015;Keller et al 2018;) and high-speed shaft bearings (Helsen et al 2016;Guo and Keller 2018;Helsen, Guo, and Keller 2018) and rating of splined gear-couplings (Guo et al 2016) were investigated in early DRC efforts from 2010 to 2017. Significant research has also been devoted to characterizing bearing WEC failures starting in 2017 (Keller, Gould, and A. Greco.…”

A comparative study on the dynamic behaviour of 10 MW conventional and compact gearboxes for offshore wind turbines

“…However, the gearbox performance should be assessed from its whole life cycle perspective, in which the reliability assessment is a crucial part. Many studies on dynamic analysis of conventional gearboxes have been conducted (e.g., Guo et al; 7 Helsen et al; 8 Mo et al; 9 Bhardwaj et al 10 ), while very limited information about the dynamic performance of the compact gearbox is available in the open literature.…”