Electrical Machines Questions and Answers_pag341

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d) starting torque decreases, maximum torque remains same, smT decrease 
View Answer 
Answer: a 
Explanation: As the resistance has been changed as the aluminium has replaced copper, it will 
not affect the maximum torque. 
7. A 3-phase slip ring IM is has its copper bars changed by the aluminium bars in the machine. 
With the above change, 
a) starting torque remains same 
b) starting torque increase 
c) starting torque decrease 
d) maximum torque increase 
View Answer 
Answer: a 
Explanation: Resistance increase, so the starting torque increase. 
8. A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 
45 complete oscillations in a minute. 
Then the rotor speed and the speed of stator field w.r.t. rotor is 
a) 985, 15 
b) 970, 1000 
c) 985, 985 
d) 985, 970 
View Answer 
Answer: a 
Explanation: Rotor frequency = s*f1 = 45/60 = 0.75 Hz. 
s = 0.75/50 = 0.015 
rotor speed = 1000(1-0.015) = 985 
rpm. 
Speed of stator field w.r.t. rotor = Ns-Nr = 1000-985=15 rpm. 
9. Choose from the below which can be obtained by the equivalent circuit of an electrical 
machine? 
a) Complete performance characteristics of the machine 
b) Temperature coefficients of the machine components 
c) Type of protection to be used in the machine 
d) Design parameters of the windings 
View Answer 
Answer: a 
Explanation: Equivalent circuit can help to give the complete performance characteristics of an 
electrical machine. 
10. If one of the supply fuses blows off and gets open circuited, then for the connected induction 
machine continues to run with increased slip. 
a) True 
b) False 
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