Electrical Machines Questions and Answers_pag343

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a) effective rotor resistance is very large compared to reactance 
b) rotor resistance is equal to stator resistance 
c) rotor resistance is equal to rotor reactance 
d) rotor reactance almost equal to stator reactance 
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Answer: a 
Explanation: It is because effective resistance value(r2/s) is far more than reactance and so the 
torque is linear in this region. 
16. If a 3-phase induction motor is fed from the rotor short circuiting the stator terminals, 
frequency of the current flowing in the short-circuited stator is 
a) slip frequency 
b) supply frequency 
c) zero 
d) frequency corresponding to the rotor speed 
View Answer 
Answer: a 
Explanation: In the stator the flux developed will revolve with a speed of slip frequency. 
17. A constant torque variable power drive of induction machine has 
a) constant air gap flux. 
b) constant slip 
c) variable air gap flux, constant slip 
d) constant slip, constant air gap flux 
View Answer 
Answer: d 
Explanation: A constant torque drive should have constant flux and hence constant air gap flux. 
Also it should have constant slip. 
18. If an emf at slip frequency is injected at an angle α with existing rotor induced emf, then 
a) power factor only improves 
b) speed changes 
c) power factor improves and speed changes 
d) power factor worsens and speed changes 
View Answer 
Answer: a 
Explanation: Power factor increases as the net angle decreases. 
18. Questions on Armature Windings 
This set of Basic Electrical Machines Questions and Answers focuses on “Armature Windings”. 
1. Concentrated winding differ from distributed winding with the concern of 
a) identical magnetic axis 
b) two magnetic axis 
c) no magnetic axis 
d) physical spacing 
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