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本帖最后由 zengxiaodong 于 2009-2-15 18:21 编辑
美国Clipper的介绍
Liberty’s patented quantum distributed generation power-train, “Quantum Drive,” a compact two-stage helical distributed design, offers a breakthrough in trouble-free power-train operation.
Gone are the stresses found in standard three-stage planetary gearboxes typically used in today’s multi-megawatt wind turbines. Through its load-distributing, multiple-path design, a total of four high-speed output shafts split torque loads from the rotor main shaft to the generators by a factor that is four times greater than standard gearboxes.
Liberty also employs two pre-loaded, low-speed tapered-roller main bearings to absorb thrust loads, preventing damage, minimizing downtime and extending turbine life. Unlike standard drive trains, there is no problematic axial motion or main shaft misalignment in Liberty as both are also stabilized through her two robust tapered roller main bearings.
To further reduce long-term operating costs, Liberty’s high-speed gear sets are in “cartridge” form and can be easily replaced with her on-board hoist without removal of the gearbox. Multiple inspection ports simplify routine monitoring by way of easy visual observation in addition to an advanced gearbox health monitoring system.
When it comes to generators, permanent magnet was a simple choice. Unlike the industry’s most commonly-used doubly-fed generators, permanent magnet is simpler, nearly maintenance-free, and operates at higher efficiency over a wider range of power output. Since there is no need for current to be fed into the generator rotor, stray currents are not created, thus pitting and bearing failures are pretty much a thing of the past.
With no brushes, there are none to replace. There’s also no need for coupling or a slip clutch between the gearbox and generator since the unit’s short-circuit current is low; a benefit that results in lower short circuit torque overall, and absorption of fault torques without harm to the gearbox.
The generator’s form-wound Class H insulated stator winding operates at less than a Class F rise in temperature and is rated for medium voltage, another benefit compared to the standard random-wound generator designed only for lower voltage. Liberty’s power-train system can operate with only two or three generators, continuing to deliver at a reduced power output until service can be performed. Compact and lightweight, the generators can be serviced via Liberty’s on-board jib hoist…no need to bring in a large, costly crane. Finally, the permanent magnet generator system, in combination with the Liberty converter, is grid friendly, staying near unity all the way down to five to ten percent of load, minimizing the need for VAR correction.
Available in two configurations: A IP54 totally enclosed water-to air-cooled model offering contamination-free enclosure for harsh environments, including damp, corrosive salt situations; and, the IP54 air-cooled system, with filters that protect the generator from contamination.
Clipper’s patented variable speed system is simpler, more reliable, and meets IEEE 519 high quality power requirements now common in all major electricity power markets. Today, most variable speed systems are based on a doubly-fed generator with the generator rotor wired directly to dual IGBT’s, which, at lower wind speeds, flow current into the generator rotor, and, at higher wind speeds, draw current out to maintain the turbine’s desired power output frequency. As the current is transferred, it is conducted through high power slip rings and brushes which require frequent maintenance due to damaging stray currents induced in the generator rotor shaft. Also, these stray currents often find way to an electrical ground, arcing across generator bearings, causing pitting which can lead to costly failures of the generator, turbine downtime, and expensive crane mobilization.
Through Clipper’s variable speed system, greater efficiency and reliability is made possible by recent advances in larger capacity IGBT’s and the use of proprietary permanent magnet generator technology. Here, power is delivered exclusively from the generator’s stator where it is rectified to DC current. Advanced and more reliable IGBT’s convert the DC power to AC current, simply and efficiently maintaining the unit’s desired power factor. By way of this simplified process, the need for troublesome slip rings and brushes is eliminated.
As you might expect, Liberty’s control system provides high reliability with simplicity. Through the use of high-speed embedded processors, algorithm processing is repeated every 50 milliseconds. Because unity power factor is produced down to a low percentage of rated power, the need for VAR correction at the substation is reduced. Through the system’s line power factor control, Liberty rides through system faults and line outages for up to three seconds. Liberty’s control system has fewer parts, about half in fact, than today’s standard turbine, resulting in higher reliability overall and greater time between failures.
Increasingly, stringent ride-through requirements imposed by regulatory agencies and transmission operators is a factor with which today’s turbine owners must comply. Liberty’s extended low-voltage ride-through capability works through the generator’s stator, completely isolating the generator from the grid, resulting in simpler low voltage, greatly extended ride through capability, immune from grid disturbance.
Minimizing costs associated with unscheduled maintenance is fundamental to Liberty’s design. When storm clouds roll in, Liberty’s lightning receptors at the tip of each blade connect through brushes on the blade bearing and main shaft to carry lighting strike current down the tower to ground. For service crew and machine safety, a nacelle steel-mesh Faraday cage is an added protective measure. Control signal wires are further protected within a second Faraday cage. As has been repeatedly demonstrated, Liberty is able to ride through severe lightning strikes with minimal to no damage or loss of availability. |
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