Electrical Machine 6

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Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Electrical Machine 6

Part 6: List for questions and answers of Electrical Machine I

 

Q1.The maximum torque in a 3-phase induction motor occurs at a slip

a) R2/X2

b) X2/R2

c) R22/X2

d) R22/X22

 

Q2.For high starting torque, the most 3-phase induction motor is

a) Squirrel-cage type

b) Slip-ring type

c) Deep bar squirrel-cage type

d) Double-cage induction motor

 

Q3.The starting torque in a single-phase induction motor is

a) High

b) Low

c) Zero

d) Very low

 

Q4.The efficiency of a single-phase induction motor as compared to a 3-phase induction motor rating is

a) Lower

b) Higher

c) Equal

d) None of these

 

Q5.The starting torque of a 3-phase induction motor can be increased by increasing

a) the rotor reactance

b) the rotor resistance

c) the stator resistance

d) none of these

 

Q6.The maximum starting torque in the induction motor is developed when the rotor reactance is

a) half of the rotor resistance

b) twice of the rotor resistance

c) equal to the rotor resistance

d) none of these 

 

Q7.A change of 55 in the supply voltage of an induction motor will produce a change of approximately

a) 5%

b) 7%

c) 10%

d) 25%

 

Q8.The transformation ratio of an induction motor can be found by

a) blocked rotor test

b) open circuit test

c) slip test

d) stator resistance test

 

Q9.The crawling in the induction motor is caused by

a) improper design of the machine

b) low supply voltage

c) high loads

d) harmonics developed in the motor

 

Q10.Which one of the following motors is most suitable for signalling devices and timers?

a) dc series motor

b) ac series motor

c) induction motor

d) reluctance motor

 

Q11.In case of induction motors the ratio of length to pole pitch for minimum cost, is taken as

a) 1.0

b) 1.5 to 2

c) 2 to 3

d) 3 to 5

 

Q12.The use of double squirrel cage winding on the rotor provides

a) low noise

b) reduced starting torque

c) a large starting torque

d) higher efficiency 

 

Q13.In induction motors, there is large decrease in maximum power factor when the dispersion coefficient is __________

a) decreased

b) increased

c) remains same

d) kept constant to certain value

 

Q14.In induction motor when the length of the air gap is increased, the magnetizing current of the motor increases while the short circuit current ________

a) increased

b) decreased

c) kept constant to certain value

d) remains unchanged

 

Q15.Induction motors have the advantage of

a) all of below

b) less cost

c) simple in construction

d) less maintenance

 

Q16.Slip speed is the

a) difference of synchronous speed and actual rotor speed

b) difference of actual rotor speed and synchronous speed

c) sum of synchronous and rotor speeds

d) half of the sum of synchronous and rotor speeds

 

Q17.At slip s = 1 torque developed in machine is

a) starting torque

b) maximum torque

c) electromagnetic torque

d) none

 

Q18.Why are capacitors used with large AC induction motor?

a) Improve voltage level

b) Improve power factor

c) Improve power level

d) Improve current level 

 

Q19.A three phase induction motor has a synchronous speed of 1500 rpm the machine runs at 1460 rpm at a particular load. The slip at this load is ___________

a) 30 %

b) 1.5 %

c) 2.67 %

d) 5 %

 

Q20.Slip exists in

a) induction motor

b) synchronous motor

c) in both machines

d) none of above 

 

Part 6: List for questions and answers of Electrical Machine I

 

Q1. Answer :a

 

Q2. Answer :b

 

Q3. Answer :c

 

Q4. Answer :a

 

Q5. Answer :b

 

Q6. Answer :c

 

Q7. Answer :d

 

Q8. Answer :a

 

Q9. Answer :d

 

Q10. Answer :d

 

Q11. Answer :b

 

Q12. Answer :

 

Q13. Answer :b

 

Q14. Answer :d

 

Q15. Answer :a

 

Q16. Answer :a

 

Q17. Answer :a

 

Q18. Answer :b

 

Q19. Answer :b

 

Q20. Answer :a