Page 91 - Solutions Manual to accompany Electric Machinery Fundamentals

4-3. Assume that the field current of the generator in Problem 4-2 has been adjusted to a value of 5 A.
(a) What will the terminal voltage of this generator be if it is connected to a -connected load with an
impedance of 24 25    ?
(b) Sketch the phasor diagram of this generator.

(c) What is the efficiency of the generator at these conditions?
(d) Now assume that another identical -connected load is to be paralleled with the first one. What
happens to the phasor diagram for the generator?
(e) What is the new terminal voltage after the load has been added?

(f) What must be done to restore the terminal voltage to its original value?
SOLUTION
(a) If the field current is 5.0 A, the open-circuit terminal voltage will be about 16,500 V, and the open-
circuit phase voltage in the generator (and hence E A ) will be 16,500 / 3  9526 V .

The load is -connected with three impedances of 24 25  . From the Y- transform, this load is
equivalent to a Y-connected load with three impedances of 
8 25  . The resulting per-phase equivalent
circuit is shown below:

0.20 ? j2.5 ? I A

+

+ 825 


E A - V ? Z

-

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