INDUSTRIAL APPLICATIONS OF ELECTRIC MOTORS

Objective Questions

Short notes

Objective questions (Answers are given below)

A steel mill requires a motor having high
starting torque, wide speed range and precise
speed control. Which one of the following
motors will you choose ?
(a) d.c. shunt motor
(b) synchronous motor
(c) d.c. series motor
(d) slip-ring induction motor.
Heavy-duty steel-works cranes which have
wide load variations are equipped with
…………….. motor.
(a) double squirrel-cage

(b) d.c. series
(c) slip-ring induction
(d) cumulative compound

A reciprocating pump which is required to
start under load will need ………motor.
(a) repulsion
(b) squirrel-cage induction
(c) synchronous
(d) double squirrel-cage induction.
Motors used in wood-working industry have
…………….. enclosure.
(a) screen protected (b) drip proof
(c) TEFC (d) TE
Single-phase synchronous motors are used in
teleprinters, clocks and all kinds of timing
devices becasue of their
(a) low starting torque
(b) high power factor
(c) constant speed
(d) over-load capacity.
Which motor is generally used in rolling mills,
paper and cement industries ?
(a) d.c. shunt motor
(b) double squirrel-cage motor
(c) slip-ring induction motor
(d) three-phase synchronous motor
Direct drive is used for power transmission
only when
(a) negligible slip is required
(b) large amount of power is invloved
(c) speed of the driven machine equals the
motor speed
(d) high-speed motor is to drive a low-speed
machine.
Which type of enclosure will be most suitable
for motors employed in atmospheres containing
inflammable gases and vapours ?
(a) pipe-ventilated
(b) totally enclosed, fan-cool
(c) flame proof
(d) screen-protected.
While plugging d.c. motors, ……………..
connections are reversed
(a) supply
(b) armature
(c) field
(d) both armature and field
During rheostatic braking of a d.c., motor,
(a) its field is disconnected from the supply
(b) its armature is reverse-connected
(c) it works as a d.c. generator
(d) direction of its field current is reversed.
Rheostatic braking may be applied to an
induction motor provided
(a) separate d.c. source for field excitation is
available
(b) it is a squirrel cage type
(c) it is slip-ring type
(d) variable external resistance is available
During regenerative braking of electric motors,
they are
(a) disconnected from the supply
(b) reverse-connected to the supply
(c) made to run as generators
(d) made to stop.
Regenerative braking
(a) can be used for stopping a motor
(b) cannot be easily applied to d.c. series
motors
(c) can be easily applied to d.c. shunt motors
(d) cannot be used wen motor load has overhauling
characteristics
Net energy saved during regenerative braking
of an electric train
(a) increases with increase in specific
resistance
(b) is high with high down gradient
(c) decreases with reduction in train speed due
to braking
(d) is independent of the train weight.
The selection of an electric motor for any
application depends on which of the following
factors?
(a) Electrical characteristics
(b) Mechanical characteristics
(c) Size and reating of motors
(d) cost
(e) All of teh above
For a particular application the type of electric
and control gear are determined by which of
the following considerations?
(a) Starting torque
(b) Conditions of environment
(c) Limitation on starting current
(d) Speed control range and its nature
(e) all of the above
Which of the following motors is preferred for
traction work?
(a) Universal motor
(b) D.C. series motor
(c) Synchronous motor
(d) three-phase induction motor
Which of the following motors always starts on load?

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

……. 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
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
The load cycle for a motor driving a power
press will be …….
(a) variable load
(b) continuous
(c) continuous but periodical
(d) intermittent and variable load
Light duty cranes are used in which of the
following?
(a) Power houses
(b) Pumping station
(c) Automobile workshops
(d) all of the above
While selecting an electric motor for a floor
mill, which electrical characteristics will be of
least significance?
(a) Running characteristics
(b) Starting charasteristics
(c) Efficiency
(d) Braking
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
……. is preferred for synthetic fibre mills.
(a) Synchronous motor
(b) Reluctance motor
(c) Series motor
(d) Shunt motor
Ward-Leonard controlled D.C. drives are
generally used for ……. excavators.
(a) Light duty (b) Medium duty
(c) Heavy duty (d) All of the above
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

Which part of a motor needs maximum attention
for maintenance?
(a) Frame (b) Bearing
(c) Stator winding (d) Rotor winding
……. need frequent starting and stopping of
electric motors.
(a) Paper mills
(b) Grinding mills
(c) Air-conditioners
(d) Lifts and hoists
Which feature, while selecting a motor for
centrifugal pump, will be of least significance?
(a) Starting characteristics
(b) Operating speed
(c) Horse power
(d) Speed control
…… motor is a constant speed motor.
(a) Synchronous motor
(b) Schrage motor
(c) Induction motor
(d) Universal motor
The starting torque is 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
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
……. is not a part of ball bearing?
(a) Inner race (b) Outer race
(c) Cage (d) Bush
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
Rotor of a motor is usually supported on …….
bearings.
(a) ball or roller (b) needle
(c) bush (d) thrust
For which of the following applications D.C.
motors are still preferred?
(a) High efficiency operation
(b) Reversibility

In a paper mill where constant speed is required
(a) synchronous motors are preferred
(b) A.C. motors are preferred
(c) individual drive is preferred
(d) group drive is preferred
A reluctance motor ……
(a) is provided with slip rings
(b) requires starting gear
(c) has high cost
(d) is compact
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
For blowers which of the following motors in
preferred?
(a) d.C. series motor
(b) D.C. shunt motor
(c) Squirrel cage induction motor
(d) Wound rotor induction motor
Belted slip ring induction motor is almost
invariably used for
(a) water pumps
(b) jaw crushers
(c) centrifugal blowers
(d) none of the above
Which of the following is essentially needed
while selecting a motor?
(a) Pulley (b) Starter
(c) Foundation pedal (d) Bearings
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
……. method of starting a three phase induction
motor needs six terminals.
(a) Star-delta
(b) Resistance starting
(c) Auto-transformer
(d) None of the above
In ……. method of starting three phase induction
motors the starting voltage is not reduced.
(a) auto-transformer
(b) star-delta
(c) slip ring
(d) any of the above
In jaw crushers a motor has to often start against
…… load.
(a) heavy (b) medium
(c) normal (d) low
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
Which of the following motors is usually
preferred for kiln drives?
(a) Cascade controlled A.C. motor
(b) slip ring induction motor
(c) three phase shunt would commutator motor
(d) Any of the above
Heat control switches are used in ……..
(a) transformers
(b) cooling ranges
(c) three phase induction motors
(d) single phase
…….. has relatively wider range of speed control
(a) Synchronous motor
(b) Ship ring induction motor
(c) Squirrel cage induction motor
(d) D.C. shunt motor
In squirrel cage induction motors which of the
following methods of starting cannot be used?
(a) Resistance in rotor circuit
(b) Resistance in stator circuit
(c) Auto-transformer starting
(d) Star-delta starting
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
Flame proof motors are used in
(a) paper mills
(b) steel mills
(c) moist atmospheres
(d) explosive atmospheres
Which of the following machines has heavy
fluctuation of load?
(a) Printing machine
(b) Punching machine
(c) Planer
(d) Lathe
For derries and winches which of the following
drives can be used?
(a) Pole changing squirrel cage motors
(b) D.C. motors with Ward-leonard control

Battery operated scooter for braking uses
(a) plugging
(b) mechanical braking
(c) regenerative braking
(d) rheostatic braking
……. has least range of speed control.
(a) Slip ring induction motor
(b) Synchronous motor
(c) D.C. shunt motor
(d) Schrage motor
……. has the least value of starting torque to
full load torque ratio.
(a) D.C. shunt motor
(b) D.C. series motor
(c) Squirrel cage induction motor
(d) Slip ring induction motor
In case of ……. speed control by injecting e.m.f.
in the rotor circuit is possible.
(a) d.c. shunt motor
(b) schrage motor
(c) synchronous motor
(d) slip ring induction motor
A pony motor is used for the starting which
of the following motors?
(a) Squirel cage induction motor
(b) Schrage motor
(c) Synchronous motor
(d) None of the above
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
In which of the following applications variable
speed operation is preferred?
(a) Exhaust fan
(b) Ceiling fan
(c) Refrigerator
(d) Water pump
Heavy duty cranes are used in
(a) ore handling plants
(b) steel plants
(c) heavy engineering workshops
(d) all of the above
the travelling speed of cranes varies from
(a) 20 to 30 m/s
(b) 10 to 15 m/s

Besides a constant speed a synchronous rotor
possesses which of the following advantages?
(a) Lower cost
(b) Batter efficiency
(c) High power factor
(d) All of the above
By the use of which of the following D.C. can
be obtained from A.C.?
(a) Silicon diodes
(b) Mercury are rectifier
(c) Motor generator set
(d) any of the above
Which of the following motors is preferred
when quick speed reversal is the main
consideration?
(a) Squirrel cage induction motor
(b) Wound rotor induction motor
(c) Synchronous motor
(d) D.C. motor
Which of the following motors is preferred
when smooth and precise speed control over
a wide range is desired?
(a) D.C. motor
(b) Squirrel cage induction motor
(c) Wound rotor induction motor
(d) Synchronous motor
For crane travel which of the following motors
is normally used?
(a) Synchronous motor
(b) D.C. differentially compound motor
(c) Ward-Leonard controlled D.C. shunt motor
(d) A.C. slip ring motor
The capacity of a crane is expressed in terms
of
(a) type of drive
(b) span
(c) tonnes
(d) any of the above
the characteristics of drive for crane hoisting
and lowering are which of the following?
(a) Precise control
(b) Smooth movement
(c) Fast speed control
(d) All of the above
Which of the following motors is preferred for
boom hoist of a travelling crane?
(a) Single phase motor
(b) Synchronous motor
(c) A.C. slip ring motor (d) Ward-Leonard controlled D.C. shunt motor

A wound rotor induction motor is preferred,
as compared to squirrel cage induction motor,
when major consideration is
(a) slop speed operation
(b) high starting torque
(c) low windage losses
(d) all of the above
Which of the following motors has series
characteristics?
(a) Shadel pole motor
(b) Repulsion motor
(c) Capacitor start motor
(d) None of the above
Which of the following happens when stardelta
starter is used?
(a) Starting voltage is reduced
(b) Starting current is reduced
(c) Both (a) and (b)
(d) None of the above
For a D.C. shunt motor which of the following
is incorrect?
(a) Unsuitable for heavy duty starting
(b) Torque varies as armature current
(c) Torque-armature current is a straight line
(d) Torque is zero for zero armature current
For which of the following applications motor
has to start with high acceleration?
(a) Oil expeller
(b) Floor mill
(c) Lifts and hoists
(d) centrifugal pump
Which of the following types of motor
enclosure is safest?
(a) totally enclosed
(b) Totally enclosed fan cooled
(c) Open type
(d) Semi closed
While selecting motor for an air conditioner
which of the following characteristics is of
great importance?
(a) Type of bearings
(b) Type of enclosure
(c) Noise
(d) Arrangement for power transmission
(e) None of the above
The diameter of the rotor shaft for an electric
motor depends on which of the following?
(a) r.p.m. only
(b) Horse power only
(c) Horse power and r.p.m.
(d) Horse power, r.p.m. and power factor
Which of the following alternatives will be
cheaper?
(a) A 100 H.P. A.C. three phase motor
(b) Four motors of 25 H.P. each
(c) Five motors of 20 H.P. each
(d) Ten motors of 10 H.P. each
The cost of an induction motor will increase
as
(a) horsepower rating increases but r.p.m.
decreases
(b) horsepower rating decreases but r.p.m.
increases
(c) horsepower rating and operating speed
increases
(d) horsepower rating and operating speed
decreases
in series motor which of the following methods
can be used for changing the flux per pole?
(a) Tapped field control
(b) Diverter field control
(c) Series-parallel control
(d) Any of the above

(c) 2. (b) 3. (d) 4. (c) 5. (c) 6. (d) 7. (c) 8. (c) 9. (b) 10. (c) 11.(a) 12. (c) 13. (c) 14. (b) 15. (e) 16. (e) 17. (b) 18. (d) 19. (c) 20. (d) 21.(d) 22. (d) 23. (d) 24. (c) 25. (b) 26. (c) 27. (a) 28. (b) 29. (d) 30. (d) 31.(a) 32. (a) 33. (d) 34. (d) 35. (d) 36. (a) 37. (c) 38. (c) 39. (d) 40. (c) 41.(c) 42. (b) 43. (b) 44. (c) 45. (a) 46. (c) 47. (a) 48. (a) 49. (d) 50. (b) 51.(d) 52. (a) 53. (d) 54. (d) 55. (b) 56. (d) 57. (b) 58. (b) 59. (c) 60. (d)61(c) 62. (b) 63. (b) 64. (d) 65. (d) 66. (c) 67. (d) 68. (c) 69. (a) 70. (d) 71(c) 72. (d) 73. (c) 74. (b) 75. (b) 76. (c) 77. (a) 78. (c) 79. (b) 80. (c) 81.(c) 82. (a) 83. (a) 84. (d)

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