Electrical Machine 5

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Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Electrical Machine 5

Part 5: List for questions and answers of Electrical Machine I

 

Q1.The rotational losses in d.c. machines is equal to the

a) Kinetic energy of armature

b) Half of the kinetic energy of armature

c) Square of the kinetic energy of armature

d) Rate of change of kinetic energy

 

Q2.Slip ring induction motor has

a) Low starting torque

b) Medium starting torque

c) High starting torque

d) None of these

 

Q3.The frequency of rotor current in an induction motor is

a) slip times the frequency of stator current

b) slip times the frequency of supply

c) One by slip times the frequency of stator current

d) One by slip times the frequency of supply

 

Q4.Slip of an induction motor increases with

a) increase in current and decrease in torque

b) increase in current and torque

c) decrease in current and torque

d) decrease in current and increase in torque

 

Q5.In an induction motor, rotor speed is always

a) Less than the stator speed

b) More than the stator speed

c) Equal to the stator speed

d) None of these

 

Q6.The frequency of the induced emf in an induction motor is

a) Greater than the supply frequency

b) Lesser than the supply frequency

c) Same as the supply frequency

d) None of these 

 

Q7.The resultant flux in an induction motor is equal to the

a) Maximum value of flux due to any phase

b) Twice of the maximum value of flux due to any phase

c) 0.5 times the maximum value of flux due to any phase

d) 1.5 times the maximum value of flux due to any phase

 

Q8.Slip ring induction motor are employed only for

a) Speed control

b) High starting torque

c) Both (a) and (b)

d) None of these

 

Q9.The advantage of skewing in induction motor is / are

a) Motor runs smoothly as the magnetic hum is reduced

b) The tendency of the rotor teeth to remain under the stator teeth due to direct

magnetic attraction is reduced

c) More uniform torque is obtained while running

d) All of these

 

Q10.In induction motor, greater the number of poles

a) Lesser the speed

b) Greater the speed

c) Lesser the frequency

d) All of these

 

Q11.For induction motors,

a) Should be essentially a constant speed motor

b) Its speed reduces to some extent with increase in load

c) Does not need to be synchronized

d) All of these

 

Q12.The slip speed of an induction motor may be defined as the:

a) Number of pairs of poles divide by frequency

b) Rotor speed – synchronous speed

c) Rotor speed + synchronous speed

d) Synchronous speed – rotor speed 

 

Q13.The slip speed of an induction motor depends upon:

a) Armature current

b) Supply voltage

c) Mechanical load

d) Eddy currents

 

Q14.The starting torque of a simple squirrel-cage motor is:

a) Low

b) Increases as rotor current rises

c) Decreases as rotor current rises

d) High

 

Q15.The slip speed of an induction motor:

a) is zero until the rotor moves and then rises slightly

b) is 100 per cent until the rotor moves and then decreases slightly

c) is 100 per cent until the rotor moves and then falls to a low value

d) is zero until the rotor moves and then rises to 100 per cent

 

Q16.The speed at which the rotating magnetic field produced by stator currents rotates in an induction motor is

a) Synchronous speed

b) Rotor speed

c) Greater than synchronous speed

d) None of these

 

Q17.A 3-phase 50 Hz induction motor runs at speed of 940 RPM; the speed of the rotating magnetic field will be:

a) 940 RPM

b) 1000RPM

c) 1050 RPM

d) 1100 RPM

 

Q18.The no-load speed of an induction motor is of the order of

a) 8%

b) 4%

c) 2%

d) 6% 

 

Q19.Iron losses in the rotor of a 3-phase induction motor are negligible, because

a) Frequency of rotor emf is too low

b) Flux linking the rotor is of constant magnitude

c) Flux density in the rotor parts is too low

d) None of these

 

Q20.Full-load copper losses in a 3-phase 50 Hz 4-pole induction motor running at 1455 rpm are 300 W. The rotor input is

a) 5 kW

b) 10 kW

c) 20 kW

d) 50 kW

 

Part 5: List for questions and answers of Electrical Machine I

 

Q1. Answer :d

 

Q2. Answer :c 

 

Q3. Answer :b

 

Q4. Answer :b

 

Q5. Answer :a

 

Q6. Answer :c

 

Q7. Answer :d

 

Q8. Answer :c

 

Q9. Answer :d

 

Q10. Answer :a

 

Q11. Answer : d

 

Q12. Answer :d

 

Q13. Answer : c

 

Q14. Answer : a

 

Q15. Answer : c

 

Q16. Answer :

 

Q17. Answer :b

 

Q18. Answer :c

 

Q19. Answer :a

 

Q20. Answer :b