Improving wind turbine drivetrain bearing reliability through pre-misalignment

Abstract

This is the peer reviewed version of the following article: Whittle, M., Trevelyan, J., Shin, W. and Tavner, P. (2013), Improving wind turbine drivetrain bearing reliability through pre-misalignment. Wind Energy, 17 (8): 12171230 which has been published in nal form at http://dx.doi.org/10.1002/we.1629. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractImproving the reliability of wind turbines (WT) is an essential component in the bid to minimise the cost of energy, especially for offshore wind due to the difficulties associated with access for maintenance. Numerous studies have shown that WT gearbox and generator failure rates are unacceptably high, particularly given the long downtime incurred per failure. There is evidence that bearing failures of the gearbox high speed stage (HSS) and generator account for a significant proportion of these failures. However, the root causes of these failure data are not known and there is, therefore, a need for fundamental computational studies to support the valuable 'top down' reliability analyses. In this paper a real (proprietary) 2 MW geared WT was modelled in order to compute the gearbox-generator misalignment and predict the impact of this misalignment upon the gearbox HSS and generator bearings. At rated torque misalignment between the gearbox and generator of 8500 µm was seen. For the 2 MW WT analysed the computational data show that the L 10 fatigue lives of the gearbox HSS bearings were not significantly affected by this misalignment but that the L 10 fatigue lives of the generator bearings, particularly the drive-end bearing, could be significantly reduced. It is proposed to apply a nominal offset to the generator in order to reduce the misalignment under operation thereby reducing the loading on the gearbox HSS and generator bearings. The value of performing integrated systems analyses has been demonstrated and a robust methodology has been outlined.

Gearbox Reliability Collaborative Investigation of Gearbox Motion and High-Speed-Shaft Loads

“…One of the factors suspected to contribute to both gearbox HSS and generator bearing failures is misalignment between the gearbox and generator [19,20]. Misalignment is a condition in which the centerlines of coupled shafts do not coincide, resulting in a deviation of relative shaft position from a collinear axis of rotation.…”

“…Misalignment can be a pre-existing condition or can be induced during operation through relative motion of the coupling bodies, both statically and dynamically in operation. Operational misalignment between the gearbox and generator typically results from the compliance of the gearbox torque arm mounts [20]. For the GRC, the rubber bushings within the trunnion mounts deform during operation, causing the gearbox to both displace and rotate (subject to torque and rotor moments); thus, the gearbox and generator are typically not perfectly aligned in operation, as shown in Figure 8.…”

“…For the GRC, the rubber bushings within the trunnion mounts deform during operation, causing the gearbox to both displace and rotate (subject to torque and rotor moments); thus, the gearbox and generator are typically not perfectly aligned in operation, as shown in Figure 8. Other reasons for operational misalignment include compliance in the main frame and the gearbox housing but these are not typically significant relative to motion of the gearbox [20]. Misalignment changes the loads on HSS bearings depending on the weight of the brake disk and the coupling stiffness.…”

Experimental investigation of bearing slip in a wind turbine gearbox during a transient grid loss event

“…These misalignments are non‐constant and change with loading. Generator bearings are susceptible to skidding caused by misalignment, whereas gearbox bearings should be less influenced by radial misalignment . During transient events, these alignments can change and possibly influence bearing life.…”

“…Generator bearings are susceptible to skidding caused by misalignment, whereas gearbox bearings should be less influenced by radial misalignment. 12 During transient events, these alignments can change and possibly influence bearing life. Strugg et al similarly conclude that rapid load variations combined with misaligned gear shafts in the HSS can lead to undesired axial load cycles at the bearings.…”