Page 281 - Solutions Manual to accompany Electric Machinery Fundamentals

P  3 V cos     3 480 V 73.2 A cos21.2    56.7 kW
I
T L
Q  3 V sin     3 480 V 73.2 A sin 21.2    22 kvar
I
T L
The phasor diagram of the ac machine before and after the change in dc machine field current is shown
below.
E
A2
E A1

jX I
S A
I A2 V

I
A1
(d) The real power flow through an ac-dc motor-generator set can be controlled by adjusting the field
current of the dc machine. (Note that changes in power flow also have some effect on the reactive power
of the ac machine: in this problem, Q dropped from 36.8 kvar to 22 kvar when the real power flow was
adjusted.)

The reactive power flow in the ac machine of the MG set can be adjusted by adjusting the ac machine’s
field current. This adjustment has basically no effect on the real power flow through the MG set.

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