Design of Induction Motors — MCQs – EE

1. The main objective in designing an induction motor is to:
(A) Achieve desired torque, efficiency, and power factor with minimum cost
(B) Increase size and weight
(C) Reduce output intentionally
(D) Ignore thermal performance

2. The two main parts of an induction motor are:
(A) Stator and rotor
(B) Armature and field winding
(C) Shaft and bearings
(D) Core and commutator

3. The stator of an induction motor carries:
(A) Three-phase winding supplied by AC source
(B) DC excitation winding
(C) Commutator segments
(D) Permanent magnets

4. The rotor in an induction motor may be:
(A) Squirrel cage type or wound type
(B) Cylindrical or salient pole
(C) Laminated or solid
(D) Field or armature type

5. The stator core of an induction motor is laminated to:
(A) Reduce eddy current losses
(B) Increase mechanical strength
(C) Improve insulation
(D) Increase weight

6. The air gap in an induction motor is kept small to:
(A) Reduce magnetizing current
(B) Increase ventilation
(C) Improve cooling
(D) Reduce speed

7. The synchronous speed of an induction motor depends on:
(A) Supply frequency and number of poles
(B) Voltage only
(C) Rotor resistance
(D) Shaft diameter

8. The slip in an induction motor is defined as:
(A) Difference between synchronous and rotor speed expressed as a percentage of synchronous speed
(B) Ratio of input to output power
(C) Ratio of torque to current
(D) Change in stator flux

9. The rotor bars of a squirrel cage motor are made of:
(A) Aluminum or copper
(B) Iron
(C) Brass
(D) Steel

10. The end rings of a squirrel cage rotor are used to:
(A) Short-circuit the rotor bars
(B) Support the shaft
(C) Carry stator winding
(D) Improve insulation

11. The starting torque of a squirrel cage induction motor is:
(A) Moderate
(B) Very high
(C) Zero
(D) Extremely low

12. The starting torque of a wound rotor motor can be controlled by:
(A) Adding external resistance in rotor circuit
(B) Changing stator winding
(C) Adjusting supply frequency
(D) Increasing cooling

13. The efficiency of an induction motor mainly depends on:
(A) Copper and core losses
(B) Shaft material
(C) Air-gap size
(D) Frame design only

14. The power factor of an induction motor is generally:
(A) Lagging
(B) Leading
(C) Unity
(D) Zero

15. The output equation of an induction motor relates:
(A) Power developed to specific magnetic and electric loadings
(B) Voltage to current
(C) Torque to frequency
(D) Speed to efficiency

16. The specific magnetic loading in induction motor design refers to:
(A) Average flux density in the air gap
(B) Armature current
(C) Rotor slip
(D) Winding turns

17. The specific electric loading refers to:
(A) Total current per meter of stator periphery
(B) Current in one phase
(C) Slip value
(D) Power factor

18. Increasing magnetic loading generally:
(A) Reduces machine size but increases core losses
(B) Increases copper losses
(C) Decreases efficiency
(D) Increases temperature without size change

19. Increasing electric loading results in:
(A) Increased copper losses and temperature
(B) Reduced output
(C) Lower current density
(D) Improved efficiency

20. The stator slots in an induction motor are usually:
(A) Semi-closed or open type
(B) Fully closed
(C) Circular
(D) Triangular

21. The rotor slots in a squirrel cage motor are generally:
(A) Skewed to reduce magnetic locking and noise
(B) Straight for high torque
(C) Circular for simplicity
(D) Open for ventilation

22. The stator winding is generally made of:
(A) Copper conductors insulated with enamel
(B) Aluminum sheets
(C) Iron wire
(D) Graphite rods

23. The temperature rise in an induction motor depends on:
(A) Total losses and cooling system
(B) Supply voltage
(C) Slip only
(D) Power factor

24. The frame of an induction motor is designed to:
(A) Support the core and provide heat dissipation
(B) Carry the load
(C) Store magnetic energy
(D) Reduce rotor losses

25. The insulation class of an induction motor determines:
(A) Maximum permissible temperature rise
(B) Output power
(C) Frequency limit
(D) Starting torque

26. The cooling method of a totally enclosed fan-cooled (TEFC) motor involves:
(A) External fan blowing air over the frame
(B) Internal oil circulation
(C) Open air ventilation
(D) Water cooling

27. The torque developed in an induction motor is proportional to:
(A) Slip and rotor current
(B) Voltage only
(C) Frequency only
(D) Speed only

28. The efficiency of large induction motors is usually in the range of:
(A) 90% to 95%
(B) 70% to 75%
(C) 50% to 60%
(D) 40% to 50%

29. The noise and vibration in an induction motor can be reduced by:
(A) Skewing rotor slots and proper balancing
(B) Increasing slip
(C) Using higher voltage
(D) Reducing insulation thickness

30. The overall design goal of an induction motor is to:
(A) Achieve optimum performance, efficiency, and reliability with minimal cost and size
(B) Maximize weight and losses
(C) Ignore ventilation
(D) Reduce torque intentionally