Page 227 - Solutions Manual to accompany Electric Machinery Fundamentals

From Figure P8-1, this field current would produce an internal generated voltage E of 271 V at a speed
Ao
n of 1200 r/min. At no-load conditions, the minimum internal generated voltage E  V = 120 V.
o A A
Therefore, the speed n with a voltage of 120 V would be
E A  n
E Ao n o
 E   120 V 
n   A  n o    1200 r/min   531 r/min
 E Ao   271 V 
For Problems 8-10 to 8-11, the motor is connected cumulatively compounded as shown in Figure P8-4.

8-10. If the motor is connected cumulatively compounded with R adj = 175 :

(a) What is the no-load speed of the motor?
(b) What is the full-load speed of the motor?
(c) What is its speed regulation?

(d) Calculate and plot the torque-speed characteristic for this motor. (Neglect armature effects in this
problem.)

SOLUTION At no-load conditions, E  V  240 V . The field current is given by
T
A
V 240 V 240 V
I  T    0.960 A
R  F adj R F 175   75  250 

From Figure P8-1, 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
E A  n
E Ao n o
 E   240 V 
n   A  n o    1200 r/min  1195 r/min
 E Ao   241 V 

At full load conditions, the armature current is
V

I  A I  L I  F I  L R  R F  110 A 0.96 A  109 A
T
adj
The internal generated voltage E is
A
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