WIND ENERGY SYSTEMS - Cd3wd

Chapter 5—Electrical Network 5–60
9. A 500-kW Darrieus wind turbine is equipped with a synchronous generator rated at 480
V line to line and 625 kVA at 0.8 power factor. Rated current is flowing and the current
leads the voltage by 40 o . What are the real and reactive powers being supplied to the
load?
10. A MOD-OA generator is rated at 250 kVA, 60 Hz, and 480 V line to line. It is connected
in wye and each phase is modeled by a generated voltage E in series with a synchronous
reactance X s . The per unit reactance is 1.38. What is the actual reactance per phase?
What is the actual inductance per phase?
11. The generator in the previous problem is connected to a circuit with a chosen base of
1000 kVA and 460 V. Find the per unit reactance on the new base.
12. A three-phase induction generator is rated at 230 V line to line and 14.4 A at 60 Hz.
Find the base impedance, the base inductance, and the base capacitance.
13. A 11.2-kW (15 hp), 220-V, three-phase, 60-Hz, six-pole, wye-connected induction motor
has the following parameters per phase: R 1 = 0.126 Ω, R 2 = 0.094 Ω, X 1 = X 2 = 0.248
Ω, R m =92Ω,andX m = 8 Ω. The rotational losses are accounted for in R m . The
machine is connected to a source of rated voltage. For a slip of 2.5 percent find:
(a) The line current and power factor.
(b) The power output in both kW and hp.
(c) The starting torque (s =1.0).
14. A three-phase, 440-V, 60-Hz, eight-pole, wye-connected, 75-kW (100-hp) induction motor
has the following parameters per phase: R 1 = 0.070 Ω, R 2 = 0.068 Ω, X 1 = X 2
=0.36Ω,R m =57Ω,andX m = 8.47 Ω. For a slip of 0.03 determine the input line
current, the power factor, and the efficiency.
15. A three-phase, 300-kW (400-hp), 2000-V, six-pole, 60-Hz, wye connected squirrel-cage
induction motor has the following parameters per phase that are applicable at normal
slips: R 1 = 0.200 Ω, X 1 = X 2 = 0.707 Ω, R 2 = 0.203 Ω, X m =77Ω,andR m = 308 Ω.
For a slip of 0.015 determine the input line current, the power factor, the torque, and
the efficiency.
16. The induction machine of the previous problem is operated as a generator at a slip of
−0.017. Find I 1 , I 2 , input mechanical power, real and reactive power, and the efficiency.
Comment on any overload.
17. An autotransformer is connected to the motor of problem 7 for starting. The motor
voltage is reduced to 0.7 of its rated value. Find the motor starting current, the line
current at start, and the starting torque. Note that s = 1 at start.
18. The model utility system of Fig. 22 implements a massive conservation and load management
program which reduces the daily peak load an average of 700 MW. Compute
the new annual risk R a , assuming the same 7000 MW of generation as in Fig. 22.
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001