Electrical Machines Questions and Answers_pag144

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b) thyrister based excitation system 
c) synchronous motor excitation system 
d) brushless and thyristor based excitation system 
View Answer 
Answer: b 
Explanation: SCRs are used in the rectifier configuration as a static system for excitation for dc 
field winding. 
7. The excitation system and speed of alternator has _______ 
a) linear response 
b) exponential response 
c) rectangular hyperbola response 
d) circular response 
View Answer 
Answer: a 
Explanation: As the excitation energy is directly taken from alternator terminals, excitation 
voltage is directly proportional to speed. 
8. The brushless excitation and conventional DC excitation systems are comparable but one 
significant change is _______ 
a) pilot exciter is brushless permanent magnet motor 
b) three phase rectifier feeds directly to main exciter 
c) a three phase rectifier is fed by main exciter 
d) no direct rectification is provided to the pilot exciter 
View Answer 
Answer: a 
Explanation: The brushless excitation involves a brushless permanent motor which acts as an 
auxiliary exciter. 
9. The main exciter used in DC excitation is ________ 
a) field on stator 
b) armature on stator 
c) field on rotor 
d) field on poles 
View Answer 
Answer: a 
Explanation: The main exciter used in DC excitation is field on stator. 
10. If the DC excitation is suddenly dropped to 0 ,the three phase alternator _________ 
a) runs as motor 
b) stops to zero speed in few seconds 
c) continues to run as motor but at lower speed 
d) no change in the operating conditions 
View Answer 
Answer: a 
Explanation: When the dc excitation is disconnected from the supply, it will start acting as 
synchronous motor as the prime mover will still be mechanically coupled.