Electrical Drives Questions and Answers

1. Which of the following motors always starts on load ?

(a) Conveyor motor
(b) Floor mill motor
(c) Fan motor
(d) All of the above


Answer: (d) All of the above.
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2. ……….. is preferred for automatic drives.

(a) Squirrel cage induction motor
(b) Synchronous motors
(c) Ward-Leonard controlled D.C. motors
(d) Any of the above


Answer: (c) Ward-Leonard controlled D.C. motors.
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3. When the load is above …………. a synchronous motor is found to be more economical.

(a) 2 kW
(b) 20 kW
(c) 50 kW
(d) 100 kW


Answer: (d) 100 kW
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4. While selecting an electric motor for a floor mill, which electrical characteristics will be of least significance?

(a) Running characteristics
(b) Starting characteristics
(c) Efficiency
(d) Braking


Answer: (d) Braking
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5. Which of the following motors are preferred for overhead travelling cranes?

(a) Slow speed motors
(b) Continuous duty motors
(c) Short time rated motors
(d) None of the above


Answer: (c) Short time rated motors.
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6. Which of the following motors is used for elevators ?

(a) Induction motor
(b) Synchronous motor
(c) Capacitor start single phase motor
(d) Any of the above


Answer: (d) Any of the above.
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7. Which part of a motor needs maximum attention for maintenance?

(a) Frame
(b) Bearing
(c) Stator winding
(d) Rotor winding


Answer: (b) Bearing
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8. …………need frequent starting and stopping of electric motors.

(a) Paper mills
(b) Grinding mills
(c) Air-conditioners
(d) Lifts and hoists


Answer: (d) Lifts and hoists.
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9. Which feature, while selecting a motor for centrifugal pump, will be of least significance?

(a) Starting characteristic
(b) Operating speed
(c) Horse power
(d) Speed control


Answer: (d) Speed control.
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10. The starting torque in case of centrifugal pumps is generally

(a) less than running torque
(b) same as running torque
(c) slightly more than running torque
(d) double the running torque


Answer: (a) less than running torque.
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11. Which of the following motors are best for the rolling mills ?

(a) Single phase motors
(b) Squirrel cage induction motors
(c) Slip ring induction motors
(d) D.C. motors


Answer: (d) D.C. motors.
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12. The starting torque of a D.C. motor is independent of which of the following?

(a) Flux
(b) Armature current
(c) Flux and armature current
(d) Speed


Answer: (d) Speed
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13. Rotor of a motor is usually supported on …………bearings.

(a) ball or roller
(b) needle
(c) bush
(d) thrust


Answer: (a) ball or roller.
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14. A reluctance motor ………….

(a) is provided with slip rings
(b) requires starting gear
(c) has high cost
(d) is compact


Answer: (d) is compact.
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15. The size of an excavator is usually expressed in terms of

(a) ‘crowd’ motion
(b) angle of swing
(c) cubic metres
(d) travel in metres


Answer: (c) cubic metres.
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16. For blowers which of the following motor is preferred ?

(a) D.C. series motor
(b) D.C. shunt motor
(c) Squirrel cage induction motor
(d) Wound rotor induction motor


Answer: (c) Squirrel cage induction motor.
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17. Belted slip ring induction motor is almost invariably used for

(a) water pumps
(b) jaw crushers
(c) centrifugal blowers
(d) none of the above


Answer: (b) jaw crushers.
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18. Reluctance motor is a…………

(a) variable torque motor
(b) low torque variable speed motor
(c) self starting type synchronous motor
(d) low noise, slow speed motor


Answer: (c) self starting type synchronous motor.
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19. In jaw crushers motor has to often start against………… load.

(a) heavy
(b) medium
(c) normal
(d) low


Answer: (a) heavy.
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20. For a motor-generator set which of the following motors will be preferred ?

(a) Synchronous motor
(b) Slip ring induction motor,
(c) Pole changing induction motor
(d) Squirrel cage induction motor


Answer: (a) Synchronous motor.
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21. Which of the following motor is usually preferred for kiln drives?

(a) Cascade controlled A.C. motor
(b) Slip-ring induction motor
(c) Three phase shunt wound commutator motor
(d) Any of the above


Answer: (d) Any of the above.
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22. Heat control switches are used in

(a) transformers
(b) cooling ranges
(c) three phase induction motors
(d) single phase


Answer: (b) cooling ranges.
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23. In which of the following applications the load on motor changes in cyclic order ?

(a) Electric shovels
(b) Cranes
(c) Rolling mills
(d) All of the above


Answer: (d) All of the above.
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24. Which of the following machines has heavy fluctuation of load ?

(a) Printing machine
(b) Punching machine
(c) Planer
(d) Lathe


Answer: (b) Punching machine.
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25. In…………. the speed can be varied by changing the position of brushes.

(a) slip ring motor
(b) schrage motor
(c) induction motor
(d) repulsion motor


Answer: (b) schrage motor.
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26. In which of the following applications variable speed operation is preferred ?

(a) Exhaust fan
(b) Ceiling fan
(c) Refrigerator
(d) Water pump


Answer: (b) Ceiling fan.
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27. Heavy duty cranes are used in

(a) ore handling plants
(b) steel plants
(c) heavy engineering workshop
(d) all of the above


Answer: (d) all of the above.
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Electrical Drives Questions and Answers

 

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