Mitigation of transient torque reversals in indirect drive wind turbine
drivetrains
Abstract
Bearing failure in wind turbine gearboxes is one of the significant
sources of downtime. While it is well known that bearing failures cause
the largest downtime, the failure cause(s) is often elusive. The
bearings are designed to satisfy their Rolling Contact Fatigue (RCF)
life. However, they often undergo sudden and rapid failure within a few
years of operation. It is well known that these premature failures are
attributed to different types of surface damage. In that regard,
transient torque reversals (TTRs) in the drivetrain have emerged as one
of the primary triggers of surface damage, as explained in this paper.
The risk associated with TTRs motivates the need to mitigate TTRs
arising in the drivetrain due to various transient events. This paper
investigates three TTR mitigation methods. First, two existing devices,
namely, the torsional tuned mass damper and the asymmetric torque
limiter, are studied. Then, a novel idea of open-loop high-speed shaft
mechanical brake control is proposed. The results show that while the
torsional tuned mass damper and the asymmetric torque limiter can
improve the torsional vibration characteristics of the drivetrain, they
cannot mitigate TTRs in terms of eliminating the bearing slip risk
associated with TTRs. However, the novel approach proposed here can
mitigate TTRs both in terms of improving the torque characteristic in
the high-speed shaft and reducing the risk of bearing slip. Furthermore,
the control method is capable of mitigating TTRs with the mechanical
limitations of a pneumatic actuator in terms of bandwidth and initial
dead time.