Quote: " The slower rotational speed of the blades is offset by the
presence of magnets, which spin faster in a larger diameter around the
coil, inducing more current in the generator by increasing the torque."
What does that mean? This explainatiton needs some work. "more
current" and "torque" are not the reasons...The object would be to match
the frequency of the output to be 60 cycles and then maintain that under
varying wind conditions and further to synchronize the output to the power
supply grid.
General Electric is using a major acquisition of a company that makes gearless wind turbines to bolster the promise of alternative energy efforts.
The company’s acquisition of Norway’s ScanWind is a sign of faith in gearless turbines, which use magnets instead of gearboxes to produce electricity.
Gearboxes are used in wind turbines to convert the slow rotations of the blades into faster rotations needed for generators to create electricity.
The problem with conventional wind turbines that their gearboxes, under frequent stress from wind turbulence, must be repaired often. That’s a problem when wind farms are located in hard-to-reach areas, particularly offshore locations.
Technology Review explains the mechanics:
In conventional wind turbines, the blades spin a shaft that is connected through a gearbox to the generator. The gearbox converts the turning speed of the blades–15 to 20 rotations per minute for a large, one-megawatt turbine–into the faster 1,800 rotations per minute that the generator needs to generate electricity. “Wind turbines are very different than any other gearbox application,” says Sandy Butterfield, chief engineer of the wind program at the National Renewable Energy Laboratory in Golden, CO. “You’re going from a very low speed to a high speed.” Typically it’s the opposite.
The multiple wheels and bearings in a wind turbine gearbox suffer tremendous stress because of wind turbulence, and a small defect in any one component can bring the turbine to a halt. This makes the gearbox the most high-maintenance part of a turbine. Gearboxes in offshore turbines, which face higher wind speeds, are even more vulnerable than those in onshore turbines. Butterfield is leading a gearbox-reliability study with turbine makers to identify design weaknesses that could be avoided.
In contrast, ScanWind’s turbine design connects the rotor shaft directly to the generator. The slower rotational speed of the blades is offset by the presence of magnets, which spin faster in a larger diameter around the coil, inducing more current in the generator by increasing the torque.
The tradeoff? For now, direct-drive turbines cost more than gearbox models to install and represent a 15 to 20 percent heavier load. But General Electric expects the downsides to be mitigated by less frequent (and thus less costly) repairs and downtime.
The company’s acquisition of ScanWind, the second-largest wind turbine firm in the world, gains it the infrastructure of a company that sells 50 percent of new turbines in the United States, and has installed more than 12,000 turbines across the globe.
General Electric is initially eying the European market, the most developed for offshore wind installations. The company expects to have a market-ready product ready by late 2012.
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