Gearboxes in utility scale wind turbines have a reputation for needing repairs long before their maintenance schedules predict they should. The culprit seems to be unexpected loading conditions on the turbine blades. That's why the U.S. Dept. of Energy's National Renewable Energy Laboratory installed a special dynamometer capable of simulating the off-axis loads and related conditions created by wind gusts and other environmental realities.
Recently, the NREL dyno put 12.6 million in-lb of torque on a 185,000-lb wind turbine drive train from Samsung. It was the greatest amount of power ever measured at NREL's dynamometer lab, and the largest full-scale dynamometer test of a wind turbine drive train ever done in the U.S.
NREL's 2.5-MW dynamometer is outfitted with a 3,550-hp electric motor coupled to a three-stage epicyclic gearbox. The motor can produce speeds up to 30 rpm, simulating everything from soft breezes to gales.
NREL is also designing a 5-MW dyno that will be able to test most of the large turbines expected to go into service during the next decade.