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A 1-MW turbine may have several hundred sensors.• Stall controller, which starts the machine at set wind speeds of 8 to 15 mph and shuts offat 50 to 70 mph to protect the blades from overstressing and the generator fromoverheating.• Power electronics to convert and condition power to the required standards.• Control electronics, usually incorporating a computer.• Battery for improving load availability in a stand-alone plant.• Transmission link for connecting the plant to the area grid.The following are commonly used terms and terminology in the wind power industry:Low-speed shaft: The rotor turns the low-speed shaft at 30 to 60 rotations per minute(rpm).High-speed shaft: It drives the generator via a speed step-up gear.Brake: A disc brake, which stops the rotor in emergencies. It can be applied mechanically,electrically, or hydraulically.Gearbox: Gears connect the low-speed shaft to the high-speed shaft and increase theturbine speed from 30 to 60 rpm to the 1200 to 1800 rpm required by most generators toproduce electricity in an efficient manner.Because the gearbox is a costly and heavy part, design engineers are exploring slow-speed, direct-drive generators that need no gearbox.Generator: It is usually an off-the-shelf induction generator that produces 50- or 60-HzAC power.Nacelle: The rotor attaches to the nacelle, which sits atop the tower and includes agearbox, low- and high-speed shafts, generator, controller, and a brake. A cover protectsthe components inside the nacelle. Some nacelles are large enough for technicians tostand inside while working.
Pitch: Blades are turned, or pitched, out of the wind to keep the rotor from turning inwinds that have speeds too high or too low to produce electricity.Upwind and downwind: The upwind turbine operates facing into the wind in front of thetower, whereas the downwind runs facing away from the wind after the tower.Vane: It measures the wind direction and communicates with the yaw drive to orient theturbine properly with respect to the wind.Yaw drive: It keeps the upwind turbine facing into the wind as the wind direction changes.A yaw motor powers the yaw drive. Downwind turbines do not require a yaw drive, as thewind blows the rotor downwind.The design and operating features of various system components are described in thefollowing subsections.Nacelle details of a 3.6-MW/104-m-diameter wind turbine. (From GE Wind Energy. With permission.)
A. TOWERThe wind tower supports the rotor and the nacelle containing the mechanical gear, theelectrical generator, the yaw mechanism, and the stall control. Figure depicts thecomponent details and layout in a large nacelle, and Figure shows the installation on thetower. The height of the tower in the past has been in the 20 to 50 m range. For medium-and large-sized turbines, the tower height is approximately equal to the rotor diameter, asseen in the dimension drawing of a 600-kW wind turbine (Figure 4.4). Small turbines aregenerally mounted on the tower a few rotor diameters high. Otherwise, they would sufferfatigue due to the poor wind speed found near the ground surface. Figure 4.5 shows tower