By Andrew Nusca
Posting in Design
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.
Sep 23, 2009
To Hate Malware - Think about your car when you start moving, especially if it is a manual transmission. When you start in 1st gear, your engine revs up to 2,000 - 5,000 RPM (depending on your vehicle) but you are barely moving. As you gain momentum, your gear ratio gets closer to a 1-to-1. If you have an "overdrive" gear, it is usually a 0.9-to-1 (or less) which is why you get better gas mileage. But you have to have the high torque of the lower gears to break the inertia of your car and start it moving. Once moving, less force is needed to keep it moving (Newton's Laws).
?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. Now i may not be an engineer or even have a degree but from life experience i would say that statement is incorrect. If the "typical" gearbox is a reduction box then yes it is correct, but most i have come across are not and therefore going from low speed to high speed is the norm.
To Lynn110 The direct drive generator has a fairly large diameter and the lines of magnetism inducing power into the coils are a very large number per revolution. The output is conditioned by a follow-on controller which synchronises the frequency and converts the volts and amps to match the grid requirements. The direct drive is more reliable because of its simplicity the only penalty being high cogging forces at start up but this may be alleviated by coil switching.
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.