The windwheel of (10–70 CE) marks one of the first recorded instances of wind powering a machine. However, the first known practical wind power plants were built in , an Eastern province of (now Iran), from the 7th century. These "" were vertical axle windmills, which had long vertical with rectangular blades. Made of six to twelve covered.
[pdf] Mechanical brakes use callipers and discs to create friction and slow a rotor’s motion, designed to withstand the high torque of turbines and harsh conditions. By braking, the blades slow down, keeping the turbine rotating at a safe speed even in fast winds without expelling too much energy.
[pdf] The current wind turbines adopt forced air cooling and liquid cooling prevalently, among which, the wind generating set with power up to 750 kW usually takes forced air cooling as a main cooling method.
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