290+ Control of Electric Drives Solved MCQs

1.

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 rating of motors
D. All of the above
Answer» D. All of the above
2.

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. All of the above
Answer» D. All of the above
3.

Which ofthefollowingmotors is preferred for traction work ?

A. Universal motor
B. D.C. series motor
C. Synchronous motor
D. Three-phase induction motor
Answer» B. D.C. series motor
4.

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
5.

is preferred for automatic drives.

A. Squirrel cage induction motor
B. Synchronous motors
C. Ward-Leonard controlled
D. C. motors
Answer» C. Ward-Leonard controlled
6.

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
7.

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
Answer» D. intermittent and variable load
8.

Light duty cranes are used in which of the following ?

A. Power houses
B. Pumping stations
C. Automobile workshops
D. All of the above
Answer» D. All of the above
9.

While selecting an electric motor for a floor mill, which electrical characteristics will be of least significance ?

A. Running characteristic
B. Starting characteristics
C. Efficiency
D. Braking
Answer» D. Braking
10.

Which of the following motors are pre-ferred for overhead travelling cranes ?

A. Slow speed motor
B. Continuous duty motors
C. Short time rated motors
D. None of the above
Answer» C. Short time rated motors
11.

is preferred for synthetic fibre mills.

A. Synchronous motor
B. Reluctance motor
C. Series motor
D. Shunt motor
Answer» B. Reluctance motor
12.

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
Answer» C. Heavy duty
13.

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» A. Induction motor
14.

Which part of a motor needs maximum attention for maintenance ?

A. Frame
B. Rearing
C. Stator winding
D. Rotor winding
Answer» B. Rearing
15.

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
16.

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
Answer» D. Speed control
17.

motor is a constant speed motor.

A. Synchronous motor
B. Schrage motor
C. Induction motor
D. Universal motor
Answer» A. Synchronous motor
18.

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
19.

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
20.

is not a part of ball bearing ?

A. Inner race
B. Outer race
C. Cage
D. Bush
Answer» D. Bush
21.

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
22.

Rotor of a motor is usually supported on bearings.

A. ball or roller
B. needle
C. bush
D. thrust
Answer» A. ball or roller
23.

For which of the following applications D.C. motors are still preferred?

A. High efficiency operation
B. Reversibility
C. Variable speed drive
D. High starting torque
Answer» C. Variable speed drive
24.

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
Answer» C. individual drive is preferred
25.

A reluctance motor

A. is provided with slip rings
B. requires starting gear
C. has high cost
D. is compact
Answer» D. is compact
26.

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
27.

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» B. D.C. shunt motor
28.

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
29.

Which of the following is essentially needed while selecting a motor ?

A. Pulley
B. Starter
C. Foundation pedal
D. Bearings
Answer» B. Starter
30.

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
31.

method of starting a three phase induction motor needs six terminals.

A. Stardelta
B. Resistance starting
C. Auto-transformer
D. None of the above
Answer» A. Stardelta
32.

In method of staging three phase induction motors the starting voltage is not reduced.

A. auto-transformer
B. star-delta
C. slip ring
D. any of the above
Answer» C. slip ring
33.

In jaw crushers a motor has to often start against load.

A. heavy
B. medium
C. normal
D. low
Answer» A. heavy
34.

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
35.

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 wound com-mutator motor
D. Any of the above
Answer» D. Any of the above
36.

Heat control switches are used in

A. transformers
B. cooling ranges
C. three phase induction motors
D. single phase
Answer» B. cooling ranges
37.

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
Answer» D. D.C. shunt motor
38.

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
Answer» A. Resistance in rotor circuit
39.

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
40.

Flame proof motors are used in

A. paper mills
B. steel mills
C. moist atmospheres
D. explosive atmospheres
Answer» D. explosive atmospheres
41.

Which of the following machines has heavy fluctuation of load ?

A. Printing machine
B. Punching machine
C. Planer
D. Lathe
Answer» B. Punching machine
42.

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 con-trol
C. A.C. slip ring motors with variable resistance
D. Any of the above
Answer» D. Any of the above
43.

Battery operated scooter for braking uses

A. plugging
B. mechanical braking
C. regenerative braking
D. rheostatic braking
Answer» B. mechanical braking
44.

has least range of speed control.

A. Slip ring induction motor
B. Synchronous motor
D. C. shunt motor
Answer» B. Synchronous motor
45.

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
Answer» C. Squirrel cage induction motor
46.

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
Answer» D. slip ring induction motor
47.

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
Answer» C. Synchronous motor
48.

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
49.

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
50.

Heavy duty cranes are used in

A. ore handling plants
B. steel plants
C. heavy engineering workshops
D. all of the above
Answer» D. all of the above
51.

The travelling speed of cranes varies from

A. 20 to 30 m/s
B. 10 to 15 m/s
C. 5 to 10 m/s
D. 1 to 2.5 m/s
Answer» D. 1 to 2.5 m/s
52.

Besides a constant speed a synchronous rotor possesses which of the following advantages ?

A. Lower cost
B. Better efficiency
C. High power factor
D. All of the above
Answer» C. High power factor
53.

By the use of which of the followingm D.C. can be obtained from AC?

A. Silicon diodes
B. Mercury arc rectifier
C. Motor generator set
D. Any of the above
Answer» D. Any of the above
54.

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
Answer» D. D.C. motor
55.

Which ofthefollowing 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
Answer» A. D.C. motor
56.

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
Answer» D. C. shunt motor
57.

The capacity of a crane is expressed in terms of

A. type of drive
B. span
C. tonnes
D. any of the above
Answer» C. tonnes
58.

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
Answer» D. All of the above
59.

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
Answer» C. A.C. slip ring motor
60.

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
Answer» B. high starting torque
61.

Which of the following motors has series characteristics ?

A. Shaded pole motor
B. Repulsion motor
C. Capacitor start motor
D. None of the above
Answer» B. Repulsion motor
62.

Which of the following happens when star-delta starter is used ?

A. Starting voltage is reduced
B. Starting current is reduced
C. Both (A) and (B)
D. None of the above
Answer» C. Both (A) and (B)
63.

For a D.C. shunt motor which of the following is incorrect 7

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
Answer» A. Unsuitable for heavy duty starting
64.

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
Answer» C. Lifts and hoists
65.

Which of the following types of motor enclosure is safest ?

A. Totally enclosed
B. Totally enclosed fan cooled
C. Open type
D. Semi closed
Answer» B. Totally enclosed fan cooled
66.

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 transmis¬sion
Answer» C. Noise
67.

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
Answer» C. Horse power and r.p.m.
68.

Which of the following alternatives will be cheaper ?

A. A 100 H.P. AC. 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
Answer» A. A 100 H.P. AC. three phase motor
69.

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
Answer» A. horsepower rating increases but r.p.m. decreases
70.

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
Answer» D. Any of the above
71.

Word Leonard controlled DC Drives are generally used for..... excavators

A. Light duty
B. Medium duty
C. Heavy duty
D. All of the above
Answer» C. Heavy duty
72.

......... is preferred for automatic drives

A. Synchronous motors
B. Word Leonard controlled DC motors
C. None of the above
D. Any of the above
Answer» D. Any of the above
73.

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
Answer» D. Intermittent and variable load
74.

A reluctance motor........

A. Is provided with slip rings
B. Requires starting gear
C. Has high cost
D. Is compact
Answer» D. Is compact
75.

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
76.

In jaw crushers a motor has to often start against....... load

A. Heavy
B. Medium
C. Normal
D. Low
Answer» A. Heavy
77.

........has least range of speed control

A. Slip ring induction motor
B. Synchronous motor
C. DC shunt motor
D. Schrage motor
Answer» B. Synchronous motor
78.

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
Answer» D. Any of the above
79.

Which of the following alternatives will be cheaper ?

A. A 100 HP ac three phase motor
B. Four motors of 25 HP each
C. Five motors of 20 HP each
D. 10 motors of 10 HP each
Answer» A. A 100 HP ac three phase motor
80.

By the use of which of the following DC can be obtained from AC?

A. Silicon diodes
B. Mercury arc rectifier
C. Motor generator set
D. Any of the above
Answer» D. Any of the above
81.

Besides a constant speed a synchronous rotor possesses which of the following advantages ?

A. Lower cost
B. Better efficiency
C. High power factor
D. All of the above
Answer» C. High power factor
82.

Which of the following types of motor and enclosure is safest

A. Totally enclosed
B. Totally enclosed fan cooled
C. Open time
D. Semi closed
Answer» B. Totally enclosed fan cooled
83.

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
Answer» D. Speed control
84.

Which part of a motor needs maximum attention for maintenance?

A. Frame
B. Bearing
C. Stator winding
D. Rotor winding
Answer» B. Bearing
85.

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. Breaking
Answer» D. Breaking
86.

Which off 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» A. Induction motor
87.

...........is preferred for synthetic fibre mails

A. Synchronous motor
B. Reluctance motor
C. Series motor
D. Shunt motor
Answer» B. Reluctance motor
88.

For derries and winches which of the following drives can be used ?

A. Pole changing squirrel cage motors
B. DC motors with word Leonard control
C. AC slip rings motors with a variable resistance
D. Any of the above
Answer» D. Any of the above
89.

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
Answer» C. Slip ring
90.

For which off the following applications DC motors are still preferred?

A. High operation
B. Variable speed drive
C. High starting torque
D. Reversibility
Answer» B. Variable speed drive
91.

Rotor of the motor is usually supported on........... bearings

A. Ball or roller
B. Needle
C. Thrust
D. Bush
Answer» A. Ball or roller
92.

.............method of starting a three phase induction motor needs six terminals

A. Resistance starting
B. Auto transformer
C. None of the above
D. Star delta
Answer» A. Resistance starting
93.

In a paper mill where constant speed is required

A. Synchronous motors are preferred
B. AC motors are preferred
C. Individual drive is preferred
D. Group drive is preferred
Answer» C. Individual drive is preferred
94.

........is not a part of ball bearing

A. Inner race
B. Outer race
C. Cage
D. Bush
Answer» D. Bush
95.

A pony motor is used for the starting which of the following motors ?

A. Squirrel cage induction motor
B. Schrage motor
C. Synchronous motor
D. None of the above
Answer» C. Synchronous motor
96.

........ has relatively wider range of speed control

A. Synchronous motor
B. Slip ring induction motor
C. Squirrel case induction motor
D. DC shunt motor
Answer» D. DC shunt motor
97.

Heat control switches are used in

A. Transformers
B. Cooling ranges
C. Three phase induction motors
D. Single face
Answer» B. Cooling ranges
98.

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
99.

Belt conveyors offer ..........starting torque

A. High
B. Low
C. Medium
D. Zero
Answer» A. High
100.

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
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