Electrical Machines Questions and Answers_pag37

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b) decreasing 
c) either increasing or decreasing 
d) none of the mentioned 
View Answer 
Answer: b 
Explanation: The effect of short pitched coil is to reduce the generated EMF and this reduction 
factor is cosε/2 and is referred to as coil pitch factor. 
8. A winding is distributed in the slots along the air gap periphery 
(i) to add mechanical strength to the winding 
(ii) to reduce the amount of conductor material required 
(iii) to reduce the harmonics in generated EMF 
(iv) to reduce the size of the machine 
(v) for full utilization of iron and conductor materials 
From these, the correct answer is 
a) (i),(iii),(iv),(v) 
b) (i),(ii),(iv),(v) 
c) (i),(ii),(iii),(v) 
d) (i),(iii),(v) 
View Answer 
Answer: d 
Explanation: In rotating electrical machines, the armature turns are usually distributed in slots 
rather than concentrated in single slot. This is essential from the view point of utilizing the 
armature periphery completely, and add mechanical strength. 
9. In an AC machine, the effect of distributing the turns in different slots, results in a further 
reduction of generated EMF by the factor k​d​. This factor is called ____________ 
a) distribution/speed factor 
b) coil pitch factor 
c) winding factor 
d) any of the mentioned 
View Answer 
Answer: a 
Explanation: E = √2πk​p​k​d​f​r​NΦ, k​d​ is the distribution factor. 
10. A polyphase induction motor of the slip ring or wound rotor type can be used ____________ 
a) for high start-up torque applications 
b) as a frequency converter 
c) any of the mentioned 
d) none of the mentioned 
View Answer 
Answer: c 
Explanation: A polyphase induction motor can be used as a frequency converter (or changer) 
for changing the supply frequency f to other frequencies sf and (2-s)f at the slip ring terminals. 
11. The equation for slip speed is ____________ 
a) (ω-ω​r​)/ω