Wind gust 10 to 15 knots, the term "gusts" is used while "strong gusts" is used for departure of 15 to 25 knots, and "violent gusts" when it exceeds 25 knots. Wind gust A gust or wind gust is a brief increase in the speed of the wind, usually less than 20 seconds. It is of a more transient character than a squall, which last minutes, and is followed by a lull or slackening in the wind speed. Generally, winds are least gusty over large water surfaces and most gusty over rough land and near high buildings. The wind is measured using
Variable speed wind turbine As of 2003, nearly all grid-connected wind turbines operate at an exactly constant speed (synchronous generators) or within a few percents of constant speed (induction generators). Below is an illustration of the formula_8 curve for a typical wind turbine. Maximum efficiency occurs at one tip-speed ratio only. Since the tip-speed ratio is given by the aforementioned expression, variable speed wind turbines can operate at maximum efficiency over all wind speeds (ideally). For a wind turbine, the power harvested is given by the following formula: formula_9 where formula_10 is the power, formula_11 is the density of the air, formula_3 is the