Page 225 - Solutions Manual to accompany Electric Machinery Fundamentals

The resulting plot is shown below:

For Problems 8-8 and 8-9, the shunt dc motor is reconnected separately excited, as shown in Figure P8-3. It has a
fixed field voltage V of 240 V and an armature voltage V that can be varied from 120 to 240 V.
F
A

8-8. What is the no-load speed of this separately excited motor when R adj = 175  and (a) V = 120 V, (b)
A
V A = 180 V, (c) V = 240 V?
A
SOLUTION At no-load conditions, E  V . The field current is given by
A
A
V 240 V 240 V
I  F    0.96 A
R  F adj R F 175   76  250 

From Figure P9-1, this field current would produce an internal generated voltage E of 241 V at a speed
Ao
n o of 1200 r/min. Therefore, the speed n with a voltage of 240 V would be

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