Electrical Machines Questions and Answers_pag99

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Answer: a 
Explanation: The d-flux is neutralized by compensating winding at all possible loads as the 
same flux will be produced but in the opposite direction so as to cancel the flux. 
9. In amplidynes, the resultant d-axis flux is 
a) field flux 
b) difference of field flux and main flux 
c) sum of field flux and main flux 
d) cross magnetizing flux 
View Answer 
Answer: a 
Explanation: The resultant d-axis flux lies along the main field poles and are so field flux. The d- 
axis is completely under the control of field winding and is unaffected by direct axis current. 
10. Amplidynes are best applicable in 
a) feedback control systems with regulated power supply. 
b) power supply 
c) speed control of large motors 
d) All of the mentioned 
View Answer 
Answer: a 
Explanation: Amplidynes find applications in feedback systems with large power handling 
requirements. 
11. Interpoles provide mmf more than armature mmf in a dc machine. 
a) True 
b) False 
View Answer 
Answer: a 
Explanation: Interpoles nullify armature cross magnetizing flux and the reactance voltage. So it 
is more than the armature mmf for a good efficient machine. 
12. The delay of the commutation occurs due base cause of emf induced due to 
a) self inductance, mutual inductance 
b) self inductance 
c) mutual inductance 
d) leakage inductance 
View Answer 
Answer: a 
Explanation: The commutation in dc machines is delayed because of the emf induced in the 
coils and the mutual interaction of the field with neighbour coils. 
13. I. DC shunt motor – variable speed application 
II. DC compound generator – constant supply voltage 
III. Differentially compounded motor – welding purposes 
Above are the applications of the dc machines , but all are not matched correctly. Choose the 
wrong marking 
a) III