ABSTRACT
It can be considered that mechanical viscous losses due to a gearbox are proportional to the operating speed, as indicated by
ω ω
(6.1)
where Pgear,rated is the loss in the gearbox at rated speed (on the order of 3% of rated power) ωmech is the rotor speed (rotation/min) ωmech,rated is the rated rotor speed (rotation/min)
Losses in the gearbox dominate the efciency in most of the wind turbine systems, and simple calculations show that a signicant annual energy dissipation in the generator system is due to the gearbox. Therefore, a good motivation for a more efcient generator would be the elimination of such mechanical device. While for large wind turbines a good gearbox system is employed, it is a common sense that for small wind turbines, for inexpensive applications, the gearbox is not optimized and it is expected higher losses than indicated in the literature because those small turbines must have a very competitive low price.
