Donald Cooksey: NASA Wind Generation Project
(Page 8 of 9)
May/June 1976
By the Mother Earth News staff
HUB: The rotor blades are connected to the windplant's main low-speed drive shaft by a fixed hub (that is, the hub is rigidly bolted to the shaft and only the blades themselves are allowed to twist—thereby changing their pitch—as the whole assembly rotates). The pitch-change mechanism consists of a hydraulic pump, pressure control valve, actuator, and gears. The pump is mounted separately within the windplant's main housing and its hydraulic fluid is brought into the shaft via rotating seals. The pressure of the fluid pushes the rack of a rack and pinion actuator which, in turn, controls a master gear that feathers and unfeathers the blades through bevel gears.
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DRIVE TRAIN ASSEMBLY
The high torque and low (40) rpm of the rotor is changed to low torque and high (1800) rpm by a 45-to-1 ratio gearbox. The output shaft of this box is then connected to the input shaft of a 100-kw alternator by V-belts. For safety's sake, the gearbox is designed to handle 176 kw (236 horsepower), which is a load approximately one-third greater than the rotor should ever deliver.
ALTERNATOR
The 1800-rpm synchronous alternator is self-cooling and contains a directly connected brushless exciter and regulator (the regulator includes power, potential, and current transformers). The 1,425-pound alternator is rated at 125 kva, 0.8 power factor, and 480 volts, and is a three-phase, 60-hertz, Y-connected unit.
YAW SYSTEM
The rotor, drive train, and alternator of the NASA Wind Turbine Generator (WTG) are all supported on a bedplate that is enclosed in a streamlined fiberglass housing and mounted on bearings so it can be rotated (yawed) by a geared "yaw control" assembly. Through the use of this control, the whole windplant can be turned on top of the tower to "point" the rotor into and out of its proper downwind position as the direction of the wind changes. This rotation can take place even when the machine is not generating electricity.
It's interesting to note that, at only 1/6 rpm, this yawing mechanism does not move fast enough to either overstress the rotor's shaft (the gyroscope-like effect of that giant propeller could snap the shaft like a toothpick if the windplant were turned quickly) or allow the generator to constantly track the light and variable wind shifts that are always taking place. The yaw is plenty quick enough, however, to keep the huge plant's rotor always pointed downstream of the general movement of the passing air mass.
TOWER
The NASA WTG is mounted on top of a tower that is 100 feet tall. The structure is made of steel and is of the "pinned truss" design. The tower alone weighs 40,000 pounds (60,000 pounds, counting ladders and platforms) and is anchored to a concrete foundation. There is far more to this structure than meets the eye: In addition to just holding up the windplant on its top, the tower must with stand wind and rotor-thrust loads—both steady and cyclic—during the generator's operation.
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