Cut-In Wind Speed
A minimum wind speed is required to start the rotation of the wind turbine. This wind speed is defined as the start-up wind speed. The cut-in wind speed of most real turbines is around 12 Km/h. This wind speed is classified as Scale no. 3 in the Beaufort Wind Force Scale which is described as “Gentle Breeze”. At this scale, leaves and smaller twigs move in constant motion. The energy content at this wind speed is still very little.
All wind turbines must have some form of over-speed in order to survive high winds. Some turbines use Blade “Flutter” for over-speed protection. The flutter design had the advantage of simplicity and reliability, but had the strong disadvantage of objectionable noise when in flutter. Some turbines uses stall control of the blades. When the blades are stalled, the rotation speed of the turbines reduces dramatically. The stall design reduces wear on the blades and bearings in high winds, thus protects the turbines from damage in high winds.
Blade pitches play an important part in the efficiency of the turbine and what’s more, the protection.
Cut-Out Wind Speed
The maximum wind speed that the wind turbines cannot operate normally is defined as the Cut-off wind speed.