Electrical - Wind Energy: Renewable Energy and the Environment - page 148

3. The maximum power rating of the Carter 25 is 30 kW, and it has a single-phase, 240 V
generator. What is the maximum current produced? Remember the difference between
root mean square values and peak values.
4. What are the peak voltages for 110, 240, and 480 VAC?
5. If the phase angle in a 240 VAC, 20-amp circuit is 20°, how much is the power reduced
from maximum power?
6. What does a three-phase generator mean?
7. What is the angular velocity for 60 Hz frequency?
8. The synchronous point on an induction generator is 1,200 rpm. If the generator is rated at
500 kW, what is the shaft torque into that generator?
9. Look at Figure 7.8 . At what slip is the efficiency maximized for generator operation?
10. If a 25 kW (rated) wind turbine has a three-phase, 480 V generator, what minimum size
wire will be needed for each phase to connect the wind turbine to a load that is 50 m
away? Remember, you need to count the length of wire down the tower, 25 m tall. Peak
power can be 30 kW. Calculate maximum current and reduce it by a factor of 1.7 since it
is a three-phase system. Each leg (wire) of the three-phase system carries 1/3 of the cur-
rent. Use Table 7.1 .
11. A 100 kW, 480 V generator, three-phase, is connected to a transformer within 10 m of
the base of a wind turbine. Peak power can be 120 kW. Remember, you need to count the
length of wire down the tower, 30 m tall. What minimum size wire is needed for each
phase? Calculate current and reduce it by a factor of 1.7, since it is a three-phase system.
Each leg of the three-phase system carries part of the current. Use Table 7.1.
12. What is power factor? What affects the value of the power factor for a wind farm?
13. List two advantages and two problems with induction generators, constant rpm, and stall
control.
14. List two advantages and two disadvantages with doubly fed induction generators, vari-
able rpm, and pitch control.
15. What happens at the wind farm when there are faults on the utility line?
16. Why are SCADAs used in wind farms?
17. What type of wind turbines use power electronics? Why?
18. List three functions for a wind turbine controller.
19. What is the function of an inverter? What type and size of wind turbines use inverters?
20. Lightning strikes a blade and essentially destroys it. If you have Internet access, use refer-
ence 17 and estimate the cost for replacing that blade.