Electrical Drive MCQ

21. Variable speed operation is preferred in

(a) water pump.
(b) ceiling fan.
(c) exhaust fan.
(d) refrigerator.

22. The application in which the motor is to start with high acceleration is

(a) lifts and hoists.
(b) centrifugal pump.
(c) oil expeller.
(d) flour mill.

23. While selecting a motor for air-conditioner the feature of utmost importance is

(a) type of enclosure.
(b) type of bearing.
(c) noise.
(d) power transmission arrangement.

24. Belt conveyors offer……..starting torque.

(a) high
(b) medium
(c) low
(d) zero

25. The characteristic(s) of drive for crane hoisting anti lowering is are

(a) fast speed control.
(b) smooth movement.
(c) precise control.
(d) all of the above.

26. The capacity of a crane is expressed in terms of

(a) span.
(b) tonnes.
(c) type of drive.
(d) any of the above.

27. The travelling speed of a crane varies from

(a) 20 to 25 m/s.
(b) 10 to 20 m/s.
(c) 1.0 to 2.5 m/s.
(d) 0.2 to 1.0 m/s.

28. Light duty cranes are generally used in

(a) power houses.
(b) pumping stations.
(c) automobile workshops.
(d) all of the above.

29. Heavy duty cranes are employed in

(a) powerhouses and pumping stations.
(b) automobile workshops.
(c) steel plants and ore handling plants.
(d) both (a) and (c).

30. In case of centrifugal pumps the starting torque is usually

(a) less than running torque.
(b) same as running torque.
(c) slightly higher than running torque.
(d) double of running torque.

31. The size of an excavator is usually expressed in terms of

(a) crowd motion.
(b) m³.
(c) travel in metres.
(d) angle of swing.

32. The range of rating of electric motor used for rolling mills is of the order of

(a) 10 to 25 kW
(b) 25 to 85 kW
(c) 85 to 400 kW
(d) 400 to 1,000 kW

33. If the liquid to be pumped has relative density of 1.25, the output power required in comparison to that required for pumping water in case of centrifugal pump will be

(a) 1.25 times.
(b) the same.
(c) 0.8 times.
(d) 15 times (roughly).

34. The load torque decreases with the increase in speed in case of

(a) lathes, boring machines, milling machines.
(b) hoist winches, machine tool feed mechanism.
(c) blowers, fans, centrifugal pumps.
(d) both (a) and (b).

35. In synthetic fiber mills motors with

(a) variable speeds are required.
(b) constant speeds are preferred.
(c) low starting torque are required.
(d) high starting torque are preferred.

36. In case of kiln drives, starting torque is

(a) more than double of the running torque.
(b) almost √2 times of the running torque.
(c) almost equal to running torque.
(d) almost zero.

37. The diameter of the rotor shaft for an electric motor depends upon

(a) speed only.
(b) power output only.
(c) speed and power output.
(d) speed, power output and power factor.

38. Which one of the following is not necessarily the advantage of dc motors over ac motors ?

(a) Low cost.
(b) Excellent torque and speed operating characteristics.
(c) Flexible speed control.
(d) None of the above.

39. An electric train employing a dc series motor is running at a fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in

(a) drop in speed and rise in current.
(b) rise in speed and drop in current.
(c) rise in speed and rise in current.
(d) drop in speed with current unaltered.

40. A dc series motor is used for an overhauling load. It can work stably if

(a) the armature is shunted by a resistor.
(b) the field winding is reversed.
(c) a resistor is put in series with the machine.
(d) a divertor is put across the field.