Electrical Machines Questions and Answers_pag23

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10. In a 4 pole machine, what is the flux per pole produced, if the armature length is l and radius 
is r and B​p​ is peak value of sinusoidal flux? 
a) 4B​p​lr 
b) 2B​p​lr 
c) B​p​lr 
d) B​p​lr/2 
View Answer 
Answer: c 
Explanation: Total flux per pole=4/PB​p​lr, since P=4, Φ=B​p​lr. 
11. The equation for flux per pole Φ=4/PB​p​lr, is valid for _____________ 
a) for salient pole rotor only 
b) for cylindrical pole rotor only 
c) for both cylindrical and salient pole rotor 
d) none of the mentioned 
View Answer 
Answer: c 
Explanation: It does not make any difference whether the field winding is on cylindrical pole 
structure or salient pole structure. 
This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on 
“Rotating Magnetic Field – 1”. 
1. For a p-pole machine, which of the following statements are correct regarding the rotating 
field speed? 
a) The rotating field speed is 1/(p/2) revolutions in one cycle 
b) f/(p/2) revolutions in f cycles 
c) f/(p/2) revolutions in one second 
d) Any of the mentioned 
View Answer 
Answer: d 
Explanation: f/(p/2) revolutions in one second is also correct because f cycles are completed in 
one second. n​s​(rotating field speed in revolutions per second) = 2f/p or N​s​ = 120f/p r.p.m. 
2. The speed at which rotating magnetic field revolves is called 
a) Induction speed 
b) Synchronous speed 
c) Relative speed 
d) Rotating speed 
View Answer 
Answer: b 
Explanation: Rotating field speed (N​s​) = 120f/(p r.p.m) = synchronous speed. 
3. What is the amplitude of rotating MMF produced as a result of m-phase currents flowing in 
m-phase windings? 
a) (2/m)F​m 
b) mF​m 
c) (m/2)F​m