WIND ENERGY SYSTEMS - Cd3wd

Chapter 6—Asynchronous Generators 6–30
Curves 1 and 2 intersect at P m = 0.5 pu so we can visualize a curve for a new value of
R L that intersects curve 3 at the same P m . This is shown as curve 4 ′ in Fig. 16. If we are
operating on curve 4 ′ at P m = 0.2 pu, the speed is about 0.8 of rated. As shaft power increases
to P m = 0.5 pu the speed increases to about 0.95 of rated. Additional load can be added
at this speed without causing a transient on the turbine since power remains the same. The
speed then increases at a slower rate to 1.01 pu at P m = 1.0 pu. If the wind is high enough
to produce even greater power, the propeller pitch should be changed, brakes set, or other
overload protection measures taken.
Figure 16: Variation of rotational speed with input shaft power for three well-chosen resistive
loads for a 40-hp self-excited induction generator.
The resistance for curve 4 ′ can be computed from Figs. 14 and 15 and the relationship
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001