Wind Turbines - Wind Energy: Renewable Energy and the Environment - page 79

Generator

Hub

Gear
box

Main drive shaft

Disc brake High

speed
shaft

Gear
box

Gear
box
cutaway

Low
speed
shaft

Blade
mounting
ring

Pitch
drive
motors

FIGURE 5.10 Photos of components, Suzlon, 64 m diameter, 1,000 kW, induction generator 4/6 pole. Bottom
right: Cutaway of gearbox, Winergy.

5.5 AERODYNAMICS
The moving blades of the wind turbine convert part of the power in the wind to rotational power.

P T q (5.1)

where T is the torque (N-m) and q (rad/s) is the angular velocity. The same power can be trans-
ferred with a large T and small q , or a small T and large q . The torque- q characteristics of the rotor
should be matched to the torque- q characteristics of the load.

Note: 1 is the angle, where units are degrees or radians. A radian is the angle where the arc of the
circle equals the radius, so circumference 360° 2π radians, or 1 radian 57.3°. Angular veloc-
ity, q Δ1/Δ t . Linear velocity of the tip of the blade is given by v q * r , where r radius of the
blade. For the same angular velocity, the larger the radius, the faster the tip of the blade is moving.
However, for the same tip speed ratio, an increased rotor size will result in slower rpm for the rotor.
That is why small-diameter rotors have large revolutions per minute (rpm) and large-diameter rotors
have small rpm.