Power Rating Determination of Electric Motors for Different Application MCQ

1. 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.   

 

2. 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.   

 

3. 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.   

 

4. 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.   

 

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

A, 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.   

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6. 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.   

 

7. Calculate mark to space ratio if the system is on for 20 sec and off for 3 sec.

A. 6.66
B. 4.48
C. 8.2
D. 5.6

Answer: A

Mark to space ratio is Ton÷Toff. It is the ratio of the time for which the system is active and the time for which is inactive.

M = Ton÷Toff=20÷3=6.66.   

 

8. Calculate the average power dissipated if the value of the duty cycle is .5 and Pmax=12 W.

A. 6 W
B. 5 W
C. 4 W
D. 3 W

Answer: A

The average power dissipated can be calculated using the relation

Pavg=D×Pmax.

The value of the average power is .5×12=6 W.   

 

9. Full form of PWM.

A. Pulse width modulation
B. Pulse run modulation
C. Power width modulation
D. Pulse wisdom mode

Answer: A

PWM stands for pulse width modulation. This technique is used to alter the voltage level of the output of the inverter. We can control the voltage level using the PWM technique.   

 

10. What is the correct relationship between the phase voltage and line voltage in Delta connection with the positive sequence?

A. VL=Vp
B. VL=√3Vp
C. VL=√2Vp
D. IL=√2Ip

Answer: A

In the delta connection line voltage is the same as the phase voltage. The line current is √3 times the phase current and leads by 30°.   

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