Wind Turbines - Wind Energy: Renewable Energy and the Environment - page 78

5.4 Description of the system
The total system consists of the wind turbine and load. A typical wind turbine consists of the rotor
(blades and hub), speed increaser (gearbox), conversion system, controls, and tower (Figure 5.9).
The nacelle is the covering or enclosure. The output of the rotor, rotational kinetic energy, can be
converted to electrical, mechanical, or thermal energy. Generally, it is electrical energy, so the con-
version system is a generator.
Blade configuration may include a nonuniform platform (blade width and length), twist along the
blade, and variable (blades can be rotated) or fixed pitch. The pitch is the angle of the chord at the tip
of the blade to the plane of rotation. The chord is the line from the nose to the tail of the airfoil.
Components for a large unit mounted on a bedplate are shown in Figure 5.10. Most large wind
turbines, which are pitch regulated, have full-span (blade) control, and in this case, electric motors
are used to rotate, change the pitch of the blades. All blades must have the same pitch for all opera-
tional conditions.
For units connected to the utility grid, 50 or 60 Hz, the generators can be synchronous or induc-
tion connected directly to the grid, or a variable-frequency alternator or direct current generator
connected indirectly to the grid through an inverter. Most direct current (DC) generators and per-
manent magnet alternators on small wind turbines do not have a speed increaser. One type of large
wind turbine has no gearbox, which means it has very large generators. Some HAWTs use slip
rings to transfer power and control signals from the top of the tower to ground level, while others
have wire cords that have extra length for absorbing twist. After so much twist, it must be removed
by yawing the turbine or by a manual disconnect. For large wind turbines, the transformer or a
winch may be located in the nacelle. A total system is called a wind energy conversion system
(WECS).

Pitch

Rotor
(blades, hub)

Low-speed
shaft

Gear box

Hub

Stator
Rotor

Anemometer

Controller

Wind
direction

Brake

Yaw drive

Vane

High
speed
shaft

Nacelle

Yaw motor

Blade

Generator

Tower

figure 5.9 Schematic of major components for large wind turbine.