Civil Engineering Reference
In-Depth Information
FIGURE 5-7
Speed control methods used in small to medium size turbines.
5.2
Turbine Rating
The wind turbines are manufactured in sizes ranging from a few kW for
stand-alone remote applications to a couple of MW each for utility scale
power generation. The grid-connected turbine as large as 2 MW capacity
was installed in 1979 on Howard Knob Mountain in the United States, and
3 MW capacity was installed in 1988 at Berger Hill in the United Kingdom.
The method of assessing the nominal rating of the wind turbine has no
globally acceptable standard. The difficulty arises because the power output
of the turbine depends on the square of the rotor diameter and the cube of
the wind speed. The rotor of a given diameter will, therefore, generate
different power at different wind speed. The turbine that can generate
300 kW at 7 m/s would produce 450 kW at 8 m/s wind. What rating should
then be assigned to this turbine? Should we also specify the “rated speed”?
Early wind turbine designers created a rating system that specified the power
output at some arbitrary wind speed. This method did not work well as
everyone could not agree on one speed to specify the power rating. The “rated”
wind speeds varied from 10 to 15 m/s under this practice. Manufacturers are
