Electrical Machines Questions and Answers_pag143

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c) two stage 
d) feedback based 
View Answer 
Answer: a 
Explanation: The 3 phase synchronous machine has two excitations. Ac excitation at armature 
while dc excitation at field winding. 
2. Field winding of a dc machine 
a) always absorbs power 
b) absorbs real power at lagging load 
c) delivers power while behaving as generator 
d) always delivers power 
View Answer 
Answer: a 
Explanation: Field is always given supply from dc system so it always absorbs power as it is 
necessary to produce the flux. 
3. In large synchronous machine, field winding is placed on ______ and ac supply on ______ 
a) rotor, stator 
b) stator, rotor 
c) armature, slots 
d) pole shoes, stator 
View Answer 
Answer: a 
Explanation: The field winding is placed on the stator as it will carry less current while the ac 
supply is fed at stator as it will have to carry large amount of current. 
4. The pilot exciter in dc exciters is ________ 
a) dc shunt generator feeding field winding of mains 
b) universal motor 
c) stepper motor feeding the field winding of mains 
d) any of the mentioned 
View Answer 
Answer: a 
Explanation: Pilot exciter is dc shunt generator which supplies the field of main winding. 
5. The main problems faced by conventional DC exciters are/is _______ 
a) cooling and maintainance 
b) wear and tear 
c) additional parasitic losses 
d) all of the mentioned 
View Answer 
Answer: d 
Explanation: The conventional dc exciters have all the above mentioned losses which make 
them out dated and least efficient. 
6. The static excitations mainly comprises of _______ 
a) brushless excitation system