Page 238 - Solutions Manual to accompany Electric Machinery Fundamentals

mmf_values = prob8_14_mag(:,1);
ea_values = prob8_14_mag(:,2);
...
Eao = interp1(mmf_values,ea_values,mmf,'spline')

(a) Since full load corresponds to 76 A, this calculation must be performed for armature currents of
25.3 A, 50.7 A, 76 A, and 101.3 A.

If I = 23.3 A, then
A
E  A V  T I A R  A R S   240 V  25.3 A 0.09   0.06    236.2 V


The magnetomotive force is F  NI  A 33 turns 25.3 A   835 A turns , which produces a voltage E
Ao
of 134 V at n o = 900 r/min. Therefore the speed of the motor at these conditions is
E 236.2 V
n  A n   900 r/min  1586 r/min
E Ao o 134 V
The power converted from electrical to mechanical form is

P conv  E I  AA 236.2 V 25.3 A   5976 W

Since the rotational losses are ignored, this is also the output power of the motor. The induced torque is
P 5976 W

  conv   36 N m
ind
 m  1586 r/min    2 rad      1 min 60 s  
1 r 
If I A = 50.7 A, then

E  A V  T I A R  A R S   240 V   50.7 A 0.09   0.06    232.4 V

The magnetomotive force is F  NI  A 33 turns 50.7 A  1672 A turns  , which produces a voltage
E of 197 V at n o = 900 r/min. Therefore the speed of the motor at these conditions is
Ao
E 232.4 V
n  A n    900 r/min  1062 r/min
E Ao o 197 V

The power converted from electrical to mechanical form is
P conv  E I  AA 232.4 V 50.7 A  11,780 W

Since the rotational losses are ignored, this is also the output power of the motor. The induced torque is

P 11,780 W
 ind   m   1062 r/min    2 rad      1 min 60 s    106 N m

conv
1 r 
If I A = 76 A, then

E  A V  T I A R  A R S   240 V   76 A 0.09   0.06    228.6 V


The magnetomotive force is F  NI  A 33 turns 76 A   2508 A turns , which produces a voltage E
Ao
of 229 V at n o = 900 r/min. Therefore the speed of the motor at these conditions is
E 228.6 V
n  A n o    900 r/min  899 r/min
E Ao 229 V
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