Yaw system

The yaw system of wind turbines is the component responsible for the orientation of the wind turbine rotor towards the wind.

The task of orienting the rotor into the wind was a complicated issue already for historical windmills. The first windmills able to rotate in order to "face" the wind appeared in the mid-18th century. Their rotatable nacelles were mounted on the main structure of the windmill using primitive wooden gliding bearings lubricated with animal fat. The necessary yawing torque was created by means of animal power, human power or even wind power (implementation of an auxiliary rotor known as fantail).

Vertical axis wind turbines (VAWT) do not need a yaw system since their vertical rotors can face the wind from any direction and only their self rotation gives the blades a clear direction of the air flow.Horizontal axis wind turbines however need to orient their rotors into and out of the wind and they achieve that by means of passive or active yaw systems.

Horizontal axis wind turbines employ some sort of yaw system which can be passive or active. Both passive and active systems have advantages and disadvantages and various design solutions (both active and passive) are being tried in order to find the optimal design for each wind turbine depending on its size, cost and purpose of operation.

The active yaw systems are equipped with some sort of torque producing device able to rotate the nacelle of the wind turbine against the stationary tower based on automatic signals from wind direction sensors or manual actuation (control system override). The active yaw systems are considered to be the state of the art for all the modern medium and large sized wind turbines, with a few exceptions proving the rule (e.g. Vergnet). The various components of the modern active yaw systems vary depending on the design characteristics but all the active yaw systems include a means of rotatable connection between nacelle and tower (yaw bearing), a means of active variation of the rotor orientation (i.e. yaw drive), a means of restricting the rotation of the nacelle (yaw brake) and a control system which processes the signals from wind direction sensors (e.g. wind vanes) and gives the proper commands to the actuating mechanisms.

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Wikipedia