Page 119 - Solutions Manual to accompany Electric Machinery Fundamentals

4-26. Assume that the generator is connected to a 3200-V infinite bus, and that its field current has been
adjusted so that it is supplying rated power and power factor to the bus. You may ignore the armature
resistance R A when answering the following questions.
(a) What would happen to the real and reactive power supplied by this generator if the field flux (and
therefore E A ) is reduced by 5 percent.
(b) Plot the real power supplied by this generator as a function of the flux  as the flux is varied from
80% to 100% of the flux at rated conditions.
(c) Plot the reactive power supplied by this generator as a function of the flux  as the flux is varied
from 80% to 100% of the flux at rated conditions.
(d) Plot the line current supplied by this generator as a function of the flux  as the flux is varied
from 80% to 100% of the flux at rated conditions.

SOLUTION
(a) If the field flux is reduced by 5%, nothing would happen to the real power. The reactive power
supplied would decrease as shown below.
V
T

E E
A2 A1

Q Q I
Q 1 2 Q A1 V jX I
G sys  S A
I
A2 Q  I sin 
A
(b) If armature resistance is ignored, the power supplied to the bus will not change as flux is varied.
Therefore, the plot of real power versus flux is

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