Electrical Machines Questions and Answers_pag231

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Explanation: As the squirrel cage induction motor has more ventilation and more space as 
compares to slip ring induction motor, there will be more efficient ways to cool down the squirrel 
cage motor. 
6. If one of the phases of the supply breaks down, then the connected three phase induction 
motor 
a) continues to run as a single phase induction motor, provided load does does not increase 
beyond 57.7% 
b) stops operating after few seconds 
c) continues to run as single phase induction motor 
d) continues to run as two phase induction motor 
View Answer 
Answer: a 
Explanation: When one of the phases breaks down then the other two phases will supply the 
rated current but the load should be reduced to 57.7%. 
7. If one of the phases of RYB supply gets broken, then the temperature rise of the induction 
motor 
a) remains same as before 
b) reduces as compared to the normal operating temperature 
c) reduces to temperature rise of corresponding single phase induction motor 
d) increases 
View Answer 
Answer: a 
Explanation: The current flowing in the armature will remain same so to maintain the flux 
requirements of the machine.Hence the temperature rise will also remain same as the current 
remains same. 
8. A three phase induction motor is connected to the infinite bus operating at the normal 
conditions. There occurs an unbalancing in the supply, leading to 
a) unequal heating losses 
b) stopping of motor 
c) increase in lower 
d) None of the mentioned 
View Answer 
Answer: a 
Explanation: The unbalancing in the supply phase will create an unbalanced distribution of the 
current in the phases, thereby unequal heating. 
9. A peaky voltage supply is given to the 3 phase power transformer of the connection power 
system. These results into 
a) reduction in iron losses 
b) reduction in copper losses 
c) increase in iron losses 
d) reduction in noise 
View Answer 
Answer: a