What is a nacelle?
The rotating part of a turbine is the rotor (the blades and the hub). Th e intermediate part between the rotor and the tower is the nacelle.
The nacelle does not rotate with the rotor, but it must rotate with respect to the tower. This rotating motion, called yaw, is necessary for directing the turbine to the wind stream, as the direction of wind is not fixed. This motion is provided by the yaw system, which comprises a number of yaw motors and a yaw gear.
The output shaft from the rotating rotor goes inside the nacelle. The shaft transfers the mechanical energy to a generator, to be converted to electrical energy.
In most of today’s turbines this transfer is not direct and there is a gearbox between the main shaft (rotor output) and the high-speed shaft (the generator input). Thus, various equipment are housed inside the nacelle.
Figure below shows the inside of a generic nacelle, indicating the main shaft , the gearbox, the generator, and other components. An overhead crane, also shown, makes lifting and displacement of heavy objects easier during maintenance works.
The nacelle is a compartment not fixed to the tower and not fixed to the hub. “Not fixed” here implies that there are bearings between the two that allow them to move with respect to each other; that is, the assembly of hub and blades rotate with respect to the nacelle, and the nacelle rotates about the tower axis.
The nacelle serves the following purposes:
1. Houses the gearbox, generator, coolers for the gearbox oil, heaters for winter time, turbine brake system, motors and gear for yaw system, the wind direction and speed measurement systems, the transformer for turbine energy supply, and other equipment based on the turbine design.
2. Allows yawing of the turbine; that is, adjusting the turbine orientation to the wind direction.
3. Provides counterweight for the hub and blades’ weight.
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