Motor Duty Classes MCQ [Free PDF] – Objective Question Answer for Motor Duty Classes Quiz

11. Calculate the value of the angular acceleration of the Heavy-duty crane using the given data: J = 5 kg-m2, load torque = 30 N-m, motor torque = 80 N-m.

A. 10 rad/s2
B. 20 rad/s2
C. 30 rad/s2
D. 50 rad/s2

Answer: A

Using the dynamic equation of motor J×(angular acceleration)

= Motor torque – Load torque: 5×(angular acceleration)

= 80-30=50, angular acceleration=10 rad/s2.   

 

12. Calculate the value of the angular acceleration of the machine using the given data: J = .541 kg-m2, load torque = 10 N-m, motor torque = 2 N-m.

A. 45 rad/s2
B. The machine will fail to start
C. 30 rad/s2
D. 51 rad/s2

Answer: B

Using the dynamic equation of motor J×(angular acceleration)

= Motor torque – Load torque: .541×(angular acceleration)

= 2-10=-8, angular acceleration=-14.78 rad/s2.

The load torque is greater than the motor torque. The motor will fail to start.   

 

13. The direction of the single-phase IM can be reversed by using which one of the methods?

A. By interchanging the supply terminals
B. By removing the capacitor
C. By changing the direction of auxiliary winding current
D. By removing the main winding

Answer: A

The direction of the single-phase IM can be reversed by changing the direction of the auxiliary winding or main winding current. The net torque developed in the IM is ImIasin(Φ).   

 

14. Which motor is preferred for overhead traveling cranes?

A. Intermittent periodic motor
B. Continuous duty motor
C. Slow speed duty motor
D. Short time rated motor

Answer: A

An intermittent periodic motor is preferred for overhead traveling cranes. Cranes require high starting torque for a short interval of time. Intermittent periodic motors have low synchronous speed.   

 

15. Which one of the following motors is a 1-Φ AC motor?

A. Synchronous motor
B. Series motor
C. Shunt motor
D. Capacitor run

Answer: D

The capacitor run motor is a 1-Φ AC motor. The capacitor is used to provide a 90° phase difference between the currents of main and auxiliary winding.   

 

16. Current rating of the IM depends upon the cross-section area of the conductors.

A. True
B. False

Answer: A

The current rating of the Induction motor depends upon the cross-section area of the conductors.

Resistance ∝ 1÷Area, I ∝Area.   

 

17. Voltage rating of the IM depends upon the insulation level.

A. True
B. False

Answer: A

The voltage rating of the IM depends upon the insulation level. The insulation level is also decided based on the over-voltages.   

 

18. 450-seconds rated motor is preferable for __________

A. Light duty cranes
B. Medium duty cranes
C. Intermittent duty cranes
D. Heavy-duty cranes

Answer: A

Light-duty cranes are used in power plants and compressor plants. The 450-seconds rated motor is preferable for light-duty cranes. They can safely operate for 450-seconds without exceeding the specified temperature.   

 

19. Calculate the 3-∅ power developed in the IM using the following data: VL=20 V, IL=5A cosΦ=.8.

A. 138.56 W
B. 128.41 W
C. 163.78 W
D. 177.59 W

Answer: A

The power developed in the IM is √3VLILcos∅. The power is independent of time and frequency.

P=√3VLILcos∅

=√3×20×5×.8=138.56 W.   

 

20. The unit of the moment of inertia is Joule.

A. True
B. False

Answer: B

The moment of inertia is taken as the sum of the product of the mass of each particle with the square of their distance from the axis of the rotation. The unit of the moment of inertia is kg×m2=kgm2.   

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