Electrical Machines Questions and Answers_pag30

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d) emf is produced by the leakage flux 
View Answer 
Answer: c 
Explanation: In an electrical machine, armature winding is one in which the working emf is 
induced by the working flux. 
10. Why is the air gap between stator and rotor should be kept as small as mechanically 
possible in induction motor? 
a) to reduce the leakage flux between stator and rotor 
b) as it leads to better operating power factor of the induction motor 
c) reduce the eddy current losses 
d) both, to reduce leakage flux between stator and rotor, and also for better operating power 
factor 
View Answer 
Answer: d 
Explanation: The leakage flux and power factor depends on the air gap and it should be as 
small as possible. 
This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on 
“Constructional Features of Rotating Electrical Machines-2”. 
1. Which type of slots are used in the construction of large size and small size induction motors 
respectively? 
a) open slots and semiclosed slots 
b) semiclosed slots and open slots 
c) open slots and open slots 
d) semiclosed slots and semiclosed slots 
View Answer 
Answer: a 
Explanation: Large size motors use open slots, so that already prepared and properly insulated 
coils can be inserted in open slots. Small size induction motors use semiclosed slots, so as to 
reduce the effective gap length between stator and rotor. 
2. In which of the following applications, wound rotor type of induction motor is used? 
a) where the driven load requires speed control 
b) where high starting torque is required 
c) when external resistance is to be inserted 
d) any of the mentioned 
View Answer 
Answer: d 
Explanation: Only in wound rotor type of induction motor, external resistance can be inserted in 
series with the rotor winding, for speed and starting torque control. 
3. For an induction motor, 
(i) squirrel cage type is simpler and more economical in construction 
(ii) wound rotor type requires less maintenance 
(iii) squirrel cage type is more rugged and requires less maintenance 
(iv) no external resistance can be inserted in the rotor circuit of squirrel cage induction motor