Electrical Machines Questions and Answers_pag336

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a) starting 
b) standstill 
c) rated speed 
d) any of the mentioned 
View Answer 
Answer: a 
Explanation: At starting when slip is 1, the voltage induced is maximum. 
2. Starters are required in the induction motor because 
a) of high starting current 
b) they are not self starting 
c) torque produced is very low at starting to overcome inertia 
d) all of the mentioned 
View Answer 
Answer: a 
Explanation: Starters are needed in induction motors to limit the starting current. 
3. Full voltage starting of induction motor may cause 
a) dip in the voltages 
b) high inrush current 
c) high losses 
d) all of the mentioned 
View Answer 
Answer: a 
Explanation: Starting induction motor on full load will cause high inrush current which furthe 
causes dip in the bus voltage. 
4. For a 4-pole, 50 Hz induction motor has starting current as 5 times to that of the full load 
current working at a speed of 1450rpm. 
The ratio of starting to full load torque will be 
a) 0.83 
b) 0.17 
c) 0.67 
d) 1 
View Answer 
Answer: a 
Explanation: Tst/Tfl = (Ist/Ifl)^2*slip 
Tst/Tfl= 25*0.033 
 =0.83 
5. Starting methods applicable to both squirrel-cage and slip ring induction motors is/are 
A. DOL starting 
B. Auto transformer starting 
C. Rotor resistance starting 
a) A, B 
b) A, B, C 
c) B, C