A wind turbine is a rotating machine that transfers kinetic energy from the wind into mechanical energy. If the mechanical energy is used directly by machinery, such as for pumping water, cutting lumber or grinding stones, the machine is called a windmill. If the mechanical energy is instead converted to electricity, the machine may be called a wind turbine generator (WTG), wind power unit (WPU), wind energy converter (WEC), or aerogenerator.
The wind turbine's blades are turned by the wind. This turns a shaft turning slowly, at about 10-20 rpm with a high torque. The shaft goes into a reduction gearbox with a ratio of about 1:50, although some wind turbine gearboxes can have a ratio of 1:100 or more. Some wind turbines may have no reduction gearbox at all and have a ratio of 1:1. The gearbox turns the generator more quickly, at around 1000 rpm, at a low torque. The generator creates electricity. This electricity is combined with any other wind turbines that may be in the same wind farm. This combined electricity may be used locally or adjusted to match the electricity in the power grid and sent to the power grid.

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