Electrical Machines Questions and Answers_pag137

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View Answer 
Answer: b 
Explanation: F​r​ is not fixed in synchronous and induction machine. 
9. In all rotating electrical machine, electrical torque is developed when relative speed between 
stator field and rotor field is ____________ 
a) zero 
b) equal to rotor speed 
c) equal and opposite to rotor speed 
d) dependent upon the type of electrical machine 
View Answer 
Answer: a 
Explanation: If the relative speed between stator field and rotor field is not zero, then the load 
angle δ​r​ varies with time. 
From equation T​e​=-(Π/8)P​2​ΦF​r​sinδ​r​ Nm, we can say that average torque over a complete cycle 
is zero, implies T​e​=0. 
This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “MMF 
Produced by Distributed Windings”. 
1. The winding MMF in rotating machines depends on 
a) winding arrangement 
b) winding current 
c) air gap length,slot openings etc 
d) both winding arrangement and winding current 
View Answer 
Answer: d 
Explanation: The winding MMF depends only on the winding arrangement and the winding 
current. 
2. A knowledge of the air gap flux distribution in a machine helps in determining the 
a) generated EMF waveform and its magnitude 
b) electrical torque 
c) winding MMF 
d) both generated EMF waveform and electrical torque 
View Answer 
Answer: d 
Explanation: The winding mmf depends only on the winding arrangement and the winding 
current. 
3. If the current in the coil is DC, then MMF doesn’t vary with ____________ 
a) space 
b) time 
c) both space and time 
d) None of the mentioned 
View Answer 
Answer: c