Validation of a Model of the NREL Gearbox Reliability Collaborative Wind Turbine Gearbox Authors: C.K. Halse, Z.H. Wright, A.R. Crowther


Gearboxes in the wind industry have been suffering from a poor reputation due to major issues with reliability. There has been a long list of issues; e.g. grind temper, material inclusions, axial cracking in bearings, poor load sharing on shaft­bearing arrangements, significant gear misalignment, bearing ring creep, gear scuffing, gear and bearing micropitting; all of which are common and often serial problems. There has been improvement in the last few years for some of the products, yet it is not uncommon for wind sites built as recently as 2008 to have 20 ­ 40% of gearboxes requiring a component replacement (such as a high speed pinion or intermediate shaft bearing) already (by 2012) and 5­10% complete gearbox failures. An important program for the industry, "The Gearbox Reliability Collaborative" (GRC), has been funded by the US Department of Energy and run by the National Renewable Energy Laboratory for several years to aid the industry in improving the reliability of this key component. The collaborative has brought together manufacturers, academia, national laboratories, engineering consultants and gear and bearing software providers as part of a program to model, build, simulate and test gearboxes with a goal to improve reliability and reduce the cost of energy.
The team at NREL have instrumented two gearboxes with over 125 channels, for measurements such as planetary tooth load distributions, annulus gear hoop strains, planet bearing load distribution, sun orbit and carrier deflection. They were then subjected to a rigorous testing regime, both up­tower and on the NREL 2.5MW dynamometer. Romax Technology have been a collaborator in the GRC Analysis Group and have developed detailed computer simulation models of the gearbox including gear macro and micro­geometry, bearing macro and micro­geometry, structural stiffness of gearbox housing, carrier and annulus gear, system clearances and preloads, and surrounding boundary conditions (such as main shaft, rotor hub and bedplate). The model is used for accurate simulation of the whole system deflections and the prediction of the resulting gear and bearing contact conditions under various loading conditions.
The focus of this paper is a comparison between measurement and simulation for key parameters including gear load distributions, annulus deflection and sun motion. The simulation results that are robust and those that are sensitive to hard­to­predict parameters that include significant effects from manufacturing and assembly variations will be outlined. Lessons learned in how best to apply computer­aided­engineering tools to improve wind turbine gearbox reliability will be described.
ISBN: 1-978-61481-038-4 Pages: 12
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