Electrical Power Engineering Multiple Choice Questions and Answers (MCQs) Part 1:
1. The basic elements of an electric drive are :
(a) electric motor and the transmission system.
(b) electric motor, the transmission and control system.
(c) the transmission and control system.
(d) electric motor and conversion equipment.
Answer : (b) electric motor, the transmission and control system.
2. Electric drive is becoming more and more popular because
(a) it is simple, clean, compact and reliable.
(b) it provides easy and smooth control, flexibility in layout, easy starting and facility for remote control.
(c) it is cheaper in initial as well as in maintenance cost.
(d) all of the above.
Answer : (d) all of the above.
3. The main drawback of electric drive is that
(a) it is cumbersome drive.
(b) it is costlier in initial as well as in maintenance cost.
(c) electrical power supply failure makes the drive standstill.
(d) all of the above.
Answer : (c) electrical power supply failure makes the drive standstill.
4. An existing workshop is to be changed over from an engine drive to an electric drive. The type of drive likely to be adopted is
(a) individual drive.
(b) group drive.
(c) multimotor drive.
(d) any of the above.
Answer : (b) group drive.
5. The type of drive used for a paper mill requiring constant speed operation and flexibility of control is
(a) group drive.
(b) multimotor drive.
(c) individual or multimotor drive.
(d) individual drive.
Answer : (c) individual or multimotor drive.
6. Introduction of automation in production processes has become possible only because of use of
(a) an electric drive.
(b) group drives.
(c) individual and multimotor drives.
(d) individual drive.
Answer : (c) individual and multimotor drives.
7. The selection of an electric motor is governed by
(a) nature of load to be handled.
(b) environmental conditions.
(c) nature of electric supply available.
(d) all of the above.
Answer : (d) all of the above.
8. DC motors are still preferred for use in
(a) electric excavators, steel mills and cranes.
(b) lathes and machine tools.
(c) flour mills and jaw crushers.
(d) paper industry.
Answer : (a) electric excavators, steel mills and cranes.
9. The least significant electrical characteristic in selection of electric motor for a flour mill is
(a) starting characteristics.
(b) braking.
(c) running characteristics.
(d) efficiency.
Answer : (b) braking.
10. The least significant feature while selecting a motor for centrifugal pump is
(a) speed control.
(b) power rating of motor.
(c) operating speed.
(d) starting characteristics.
Answer : (a) speed control.
11. A typical active load is
(a) hoist,
(b) blower.
(c) pump.
(d) lathe.
Answer : (a) hoist
12. An elevator drive is required to operate in
(a) one quadrant only.
(b) two quadrants.
(c) three quadrants.
(d) four quadrants.
Answer : (d) four quadrants.
13. Load torque constant at all speeds is represented by a
(a) fan.
(b) compressor.
(c) centrifugal pump load.
Answer : (b) compressor.
14. An example of a motor having short-time duty is found in
(a) centrifugal pumps.
(b) crane drives.
(c) drilling machines.
(d) all of the above.
Answer : (b) crane drives.
15. The load, for which the motor always starts on load is
(a) fan motor.
(b) conveyor motor.
(c) flour mill motor.
(d) all of the above.
Answer : (d) all of the above.
16. The load cycle for a motor driving a power press will be
(a) continuous.
(b) variable.
(c) intermittent and variable.
(d) continuous but periodical.
Answer : (d) continuous but periodical.
17. The application(s) that need(s) frequent starting and stopping is/are
(a) paper mills.
(b) lifts and hoists.
(c) blowers and fans.
(d) grinding mills
Answer : (b) lifts and hoists.
18. An electric motor, in jaw crushers, has to often start against
(a) heavy load.
(b) normal load.
(c) medium load.
(d) low load.
Answer : (a) heavy load.
19. The application(s) in which the load on the motor changes in cyclic order is/are
(a) rolling mills.
(b) cranes.
(c) electric shovels.
(d) all of the above.
Answer : (d) all of the above.
20. The machine having heavy fluctuation of load is
(a) lathe.
(b) planer.
(c) punching machine.
(d) printing machine.
Answer : (c) punching machine.
21. Variable speed operation is preferred in
(a) water pump.
(b) ceiling fan.
(c) exhaust fan.
(d) refrigerator.
Answer : (b) ceiling fan.
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.
Answer : (a) lifts and hoists.
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.
Answer : (c) noise.
24. Belt conveyors offer …….. starting torque.
(a) high
(b) medium
(c) low
(d) zero
Answer : (a) high
25. The characteristic(s) of drive for crane hoisting and lowering is are
(a) fast speed control.
(b) smooth movement.
(c) precise control.
(d) all of the above.
Answer : (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.
Answer : (b) tonnes.
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.
Answer : (c) 1.0 to 2.5 m/s.
28. Light duty cranes are generally used in
(a) power houses.
(b) pumping stations.
(c) automobile workshops.
(d) all of the above.
Answer : (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).
Answer : (c) steel plants and ore handling plants.
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.
Answer : (a) less than 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.
Answer : (b) m3.
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
Answer : (c) 85 to 400 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).
Answer : (a) 1.25 times.
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).
Answer : (a) lathes, boring machines, milling machines.
36. In synthetic fibre 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.
Answer : (b) constant speeds are preferred.
37. 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.
Answer : (a) more than double of the running torque.
38. 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.
Answer : (c) speed and power output.
39. 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.
Answer : (a) Low cost.
40. An unsaturated dc shunt motor drives a constant torque load at a speed at 1,000 rpm taking an armature current of 20 A when 230 V is applied to the motor. If the applied voltage is reduced to 115 V, the motor runs at.
(a) 500 rpm taking an armature current of 20 A.
(b) 1,000 rpm taking an armature current of 20 A.
(c) 500 rpm taking an armature current of 40 A.
(d) 1,000 rpm taking an armature current of 40 A.
Answer : (d) 1,000 rpm taking an armature current of 40 A.
41. 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.
Answer : (a) drop in speed and rise in current.
42. 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.
Answer : (a) the armature is shunted by a resistor.
43. DC series motors are very suitable for heavy duty applications such as electric railways, rolling mills because of
(a) low initial as well as maintenance cost.
(b) high starting torque.
(c) possibility of speed control.
(d) nearly constant speed.
Answer : (b) high starting torque.
44. A flywheel is normally fitted to
(a) dc series motor driving a constant torque load.
(b) separately excited dc motor driving pulsed torque load.
(c) cumulatively compound motor driving pulsed torque load.
(d) differentially compound motor driving pulsed torque load.
Answer : (c) cumulatively compound motor driving pulsed torque load.
45. Which motor should not be used for centrifugal pumps ?
(a) Shunt.
(b) Series.
(c) Cumulatively compound.
(d) Differentially compound.
Answer : (b) Series.
46. For continuously running rolling mills with intermittent loading, the most suitable dc drive is
(a) dc series motor.
(b) dc shunt motor.
(c) dc differentially compounded motor.
(d) dc cumulatively compounded motor.
Answer : (d) dc cumulatively compounded motor.
47. For quick speed reversal the motor preferred is
(a) dc motor.
(b) squirrel cage induction motor.
(c) slip-ring induction motor.
(d) synchronous motor.
Answer : (a) dc motor.
48. The motor, owing to its inherent characteristics, best suited for the rolling mills is
(a) dc shunt motor.
(b) dc cumulative compound wound motor.
(c) squirrel cage induction motor.
(d) synchronous motor.
Answer : (b) dc cumulative compound wound motor.
49. Squirrel cage induction motors with high slip and slip-ring induction motors develop maximum torque at standstill and are used for
(a) elevators.
(b) machine tools.
(c) presses and punches.
(d) all of the above.
Answer : (c) presses and punches.
50. Belted slip-ring induction motor is almost invariably employed for
(a) conveyors.
(b) jaw-crushers.
(c) centrifugal blowers.
(d) water pumps.
Answer : (b) jaw-crushers.
51. Belted wound induction motors are preferred for
(a) gyratory crushers.
(b) screw pumps.
(c) machine tools.
(d) water pumps.
Answer : (a) gyratory crushers.