Problem 1:A 255V shunt motor has an armature resistance of 0.245 Ohm and a field resistance
of 124.9...

Question

Problem 1:A 255V shunt motor has an armature resistance of 0.245 Ohm and a field resistance
of 124.9 Ohm. At no load (1200 r/min), the motor draws a current of 2.041 A. At full load, the
motor draws 54 A. What’s the motor’s full load speed (in r/min)?
Problem 2:Write MATLAB program and plot speed (r/min) vs torque (N-m) characteristic of
Example 8-2 when input current is varied from 20 to 500 A in steps of 10 A.
Bonus Problem:
A 240 V dc shunt motor runs at 820 rpm and takes armature current of 55 A. Find resistance to
be added to the field circuit to increase speed to 1050 rpm at an armature current of 85 A.
Assume flux proportional to field current. Armature resistance = 0.149 ohmand field winding
resistance = 249.5 ohm.

Robert · Accepted Answer

Problem 1:  
A 255V shunt motor has an armature resistance of 0.245 Ohm and a field resistance of 124.9 Ohm. 
At no load (1200 r/min), the motor draws a current of 2.041 A. At full load, the motor draws 54 A. 
What’s the motor’s full load speed (in r/min)? 
 
Solution 1: 
Field current at no load, 
Amps
R
V
I
F
S
NLF 041.2
9.124
255
_   
 
Therefore the armature current at no load is, 
AmpsIII NLFNLLNLA 0)041.2041.2(___   
 
Now at no load, the back EMF is, 
2550255
60
__ 





 ANLASNLNLg RIVN
A
ZP
E

 
Or, 2125.0
1200
255
60






A
ZP
 
 
Now at full load, 
AmpsIII FLFFLLFLA 959.51041.254___     NLFFLF II __   
 
Now at full load, the back EMF is, 
245.0959.51255
60
__ 





 AFLASFLFLg RIVN
A
ZP
E

 
Or,  5.955
2125.0
245.0959.51255
60
_











A
ZP
RIV
N
AFLAS
FL

 r/min 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Problem 2:  
Write MATLAB program and plot speed (r/min) vs torque (N-m) characteristic of Example 8-2 when 
input current is varied from 20 to 500 A in steps of 10 A.

Problem 1: A 255V shunt motor has an armature resistance of 0.245 Ohm and a field resistance of 124.9 Ohm. At no load (1200 r/min), the motor draws a current of 2.041 A. At full load, the motor draws...

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