COUPLINGS & TORQUE LIMITERS
WINDPOWER
COUPLINGS & TORQUE LIMITERS What causes damaging loads in wind turbine drivetrains and how does torsional damping help?
This article provided by Paul Baker, AeroTorque Corp.
THE COST OF PRODUCING wind Transient loads from rotor and energy has steadily declined for the generator inertia are difficult to model past several years. While the increase accurately and almost impossible to in the size of wind turbines has been duplicate on a test stand. But they can one key contributor, improvements be measured in the field, and have been in reliability have also played a major for more than five years on many sizes, role. Hard lessons have been learned types, and brands of turbines. One thing about bearings, gears, generators, and is clear, this is not a turbine specific turbine control systems. Improvements problem, it’s an inertia problem. have been made to bearings, gears, Five years of field-measured data and lubricating oils. Condition from seven different OEMs show that monitoring techniques such as vibration transient loads are daily events to some The WindTC, a torsional control device analysis, wear debris analysis, and lube turbines and monthly to others. What’s for wind turbines drivetrains, comes from sample analysis are improved and in more, many torque reversals have AeroTorque. much wider use than even five years been measured at 1 to 3 times nominal ago. Testing capabilities have also operating torque. Oscillations are often improved with larger and more sophisticated dynamometers at 1.5 times torque (peak to peak) at a frequency of greater and modeling continues to advance as more dynamic models than 1/sec. are developed. The reliability discussion has also evolved from Smooth frictional torque control, one solution, greatly “How can we make turbines more robust?” to “What loads are reduces loads caused by transient events. By absorbing the causing these failures?”. As more people inside the industry energy early in the event, it lets the turbine operate under the come to the realization that it is not normal operating loads loads for which it was designed and tested. The graph, Turbine that are problematic, rather the occasional transient events stopping protocol, demonstrates results of field measurements that are causing the most damaging loads. during a stopping event on side-by-side turbines, one with Before discussing how a torsional damper reduces severe and one without torsional damping, a solution that can be transient loads, it’s important to understand where damaging retrofitted to most modern turbines, easily and with a fast loads come from. Transient events can be caused by nature payback. or related to control systems. Nature induced transients Don’t confuse Torque Limiting with Torque Control. come from wind gusts, ridgeline effect, wake effect, wind Traditional style torque limiters have been employed for years shear, and sudden changes in wind direction. Events related in gearbox to generator couplings. While these can protect to control systems include starting and stopping protocols, the spacer from extreme loads, it has to be set so high that and pitch lube and brake tests. Necessary stopping protocols it cannot protect against torsional reversals. To accomplish intended to protect the turbine often create the worse torsional control, it must react at a lower setting during a transient loads of all. Under normal operation, the drive train torque reversal. masses wind up almost like the rubber band on a toy airplane The WindTC torque controller acts to extend other (huge exaggeration), but they are ‘in sync’. When the system reliability improvements and enables production improvements experiences a sudden change (transient) in dynamics, the while improving reliability. Because the device dissipates the reaction can be a violent torque reversal, a significant torque energy early during the transient event, it protects the drive oscillation, and usually both. These drive train loads react train and the entire turbine from the related reactionary loads through the bedplate and the entire turbine structure down to which may manifest as bedplate cracks, yaw pinion/gear the foundation. problems, tower flange faster tension, and more. 28
WINDPOWER ENGINEERING & DEVELOPMENT — 2017 RENEWABLE ENERGY HANDBOOK
05. Wind REH 17 - Couplings & Torque Limiters V4.indd 28
windpowerengineering.com
12/19/16 2:35 PM