Advanced Wind Turbine Program Next Generation Turbine ... - NREL

cluded that the same would likely be true for squirrel cage and synchronous machines. It can be
expected that a small savings in generator cost would result.
Furthermore, the costs estimated for the power electronics for conventional-speed versions of
these machines were very similar to the costs estimated for the power electronics for direct-drive
versions of these machines. As a result, the NGT team further concluded that the cost for the
power electronics for variable-speed operation of medium-speed squirrel cage and synchronous
generators would also be similar to the costs for the direct-drive and conventional-speed versions.
As noted in Section 2.1.1.2, these converter costs are substantially greater than power
electronics costs for the wound rotor induction generator and more than offset any savings in
generator cost that result from using squirrel cage or synchronous designs. As a result, it is safe
to conclude that these configurations have no advantage over the wound rotor induction machine
for variable speed systems.
As for fixed speed operation, the same conclusions reached in Section 2.1.1.3 apply to mediumspeed
machines as well. The cost savings from replacing the more expensive wound rotor induction
generator with a synchronous machine and eliminating the power electronics is more than
offset by the loss in energy capture. Furthermore, fixed speed machines are incapable of providing
critical VAR support.
2.1.2.3 Multiple Medium-Speed Generators
The concept of using multiple stand-alone geared, medium-speed generators was not extensively
investigated. However, drawing analogies from the results of Sections 2.1.1.4, 2.1.2.1, and
2.1.2.2, it is safe to conclude that this concept would hold no particular cost or performance advantage
over using one large geared, medium-speed generator.
2.1.3 Direct-Drive Generators
Interest in direct-drive generators derives from the ability to completely eliminate the gearbox.
The latter component is among the most expensive components in a wind turbine, and wind turbine
gearboxes, in general, have been prone to require extensive maintenance industry wide.
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