Civil Engineering Reference
In-Depth Information
FIGURE 7-1
Rotor power coefficient versus tip-speed ratio has a single maximum.
forces produced in the rotor blades under such speeds can mechanically
destroy the rotor. Moreover, the generator producing power above its rated
capacity may electrically destroy the generator. For these reasons, the turbine
speed and the generator power output must be controlled.
7.1
Speed Control Regions
The speed and the power controls in the wind power systems have three
distinct regions:
•
the optimum constant Cp region.
•
the speed-limited region.
•
the power-limited region.
These regions are shown in
Figure 7-3
.
Typically the turbine starts operat-
ing (cut in) when the wind speed exceeds 4-5 m/s, and is shut off at speeds
exceeding 25 to 30 m/s. In between, it operates in one of the above regions.
At a typical site, the wind-turbine may operate about 70 to 80 percent of the
time. Other times, it is off due to wind speed too low or too high.
