multiple choice questions subject: control of electric

Faculty of Degree Engineering - 083 Department of Electrical Engineering -09

Dr. Subhash Technical Campus- The Jewel of Junagadh

Multiple Choice Questions

Subject: Control of Electric Drives Branch: Electrical Engineering

Subject code: 2160913 Semester: 6th

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) Cost

(e) 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) Speed control range and its nature

(e) 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



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

5 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

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

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

8. Light duty cranes are used in which of the following ? (A) Power houses

(B) Pumping stations

(C) Automobile workshops




9. 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

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

(A) Slow speed motors (B) Continuous duty motors

(C) Short time rated motors (D) None of the above

11 is preferred for synthetic fibre mills.

(A) Synchronous motor

(B) Reluctance motor

(C) Series motor

(D) Shunt motor

12. Ward-Leonard controlled D.C. drives are generally used for excavators.

(A) Light duty

(B) Medium duty

(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




14. Which part of a motor needs maximum attention for maintenance ?

(A) Frame

(B) Rearing

(C) Stator winding

(D) Rotor winding

15 need frequent starting and stopping of electric motors,

(A) Paper mills

(B) Grinding mills

(C) Air-conditioners

(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

17. motor is a constant speed motor.


(B) Schrage motor

(C) Induction motor

(D) Universal 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

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

20 is not a part of ball bearing ?

(A) Inner race

(B) Outer race

(C) Cage

(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

22. Rotor of a motor is usually supported on bearings.



(A) ball or roller

(B) needle

(C) bush

(D) thrust

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

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

25. A reluctance motor

(A) is provided with slip rings

(B) requires starting gear

(C) has high cost

(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

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

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

29. Which of the following is essentially needed while selecting a motor ? (A) Pulley

(B) Starter

(C) Foundation pedal

(D) Bearings

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



31 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

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

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

(A) heavy

(B) medium

(C) normal

(D) low

34. For a motor-generator set which of the following motors will be preferred ?


(B) Slip ring induction motor

(C) Pole changing induction motor

(D) Squirrel cage induction motor

35. Which of the following motors is usually preferred for kiln drives?



(A) Cascade controlled A.C. motor


(C) Three phase shunt wound com-mutator motor


36. Heat control switches are used in

(A) transformers

(B) cooling ranges

(C) three phase induction motors

(D) single phase

37 has relatively wider range of speed control.


(B) Ship ring induction motor


(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

39. In which of the following applications the load on motor changes in cyclic order?

(A) Electric shovels



(B) Cranes

(C) Rolling mills


40. Flame proof motors are used in

(A) paper mills

(B) steel mills

(C) moist atmospheres

(D) explosive atmospheres

41. Which of the following machines has heavy fluctuation of load ?

(A) Printing machine

(B) Punching machine

(C) Planer

(D) Lathe

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


43. Battery operated scooter for braking uses

(A) plugging

(B) mechanical braking

(C) regenerative braking



(D) rheostatic braking

44 has least range of speed control.

(A) Slip ring induction motor


(C) D.C. shunt motor

(D) Schrage motor

45 has the least value of starting torque to full load torque ratio.

(A) D.C. shunt motor



(D) Slip ring 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

47. A pony motor is used for the starting which of the following motors ? (A) Squirel

cage induction motor

(B) Schrage 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

49. In which of the following applications variable speed operation is preferred ?

(A) Exhaust fan

(B) Ceiling fan

(C) Refrigerator

(D) Water pump

50. Heavy duty cranes are used in

(A) ore handling plants

(B) steel plants

(C) heavy engineering workshops

(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

52. Besides a constant speed a synchronous rotor possesses which of the following

advantages ?



(A) Lower cost

(B) Better efficiency

(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


54. Which of the following motors is preferred when quick speed reversal is the main

consideration?


(B) Wound rotor induction motor


(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

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

(D) AC. slip ring motor

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

(A) type of drive

(B) span

(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


59. Which of the following motors is preferred for boom hoist of a travelling crane?

(A) Single phase motor


(C) A.C. slip ring motor

(D) Ward-Leonard controlled D.C. shunt 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


61. Which of the following motors has series characteristics ?

(A) Shaded pole motor

(B) Repulsion motor

(C) Capacitor start 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)


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

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



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

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

(e) None of the above

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

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

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

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


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

(A) Light duty

(B) Medium duty

(C) Heavy duty


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

(A) Synchronous motors

(B) Word Leonard controlled DC motors

(C) None 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

74. A reluctance motor........

(A) Is provided with slip rings

(B) Requires starting gear

(C) Has high cost

(D) Is compact


(A) Crowd motion

(B) Angle of swing

(C) Cubic metres

(D) Travel in metres

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

(A) Heavy

(B) Medium

(C) Normal

(D) Low



77. Flame proof motors are used in

(A) Paper Mills

(B) Steel mills

(C) Moist atmospheres

(D) Explosive atmospheres

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

(A) Slip ring induction motor


(C) DC shunt motor

(D) Schrage motor

79. 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


80. 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




(A) Ore handling plants

(B) Steel plants

(C) Heavy engineering workshops


82. 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


83. Besides a constant speed a synchronous rotor possesses which of the following

advantages ?

(A) Lower cost

(B) Better efficiency

(C) High power factor


84. 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


(A) Type of drive



(B) Span

(C) Tonnes


86. 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

87. Which part of a motor needs maximum attention for maintenance?

(A) Frame

(B) Bearing

(C) Stator winding

(D) Rotor winding

88. 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

89. Which off the following motors is used for elevators?



(A) Induction motor


(C) Capacitor start single phase motor


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


(B) Reluctance motor

(C) Series motor

(D) Shunt motor

91. 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


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

reduced

(A) Auto transformer

(B) Star Delta

(C) Slip ring


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

(A) High operation



(B) Variable speed drive

(C) High starting torque

(D) Reversibility

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

(A) Ball or roller

(B) Needle

(C) Thrust

(D) Bush

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

(A) Resistance starting

(B) Auto transformer


(D) Star delta

96. 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

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

(A) Inner race

(B) Outer race

(C) Cage



(D) Bush

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


(B) Schrage motor



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



(C) Squirrel case induction motor

(D) DC shunt motor

100. Heat control switches are used in

(A) Transformers

(B) Cooling ranges

(C) Three phase induction motors

(D) Single face

101. An elevator Drive is required to operate in

(A) One quadrant only

(B) Two quadrants

(C) Three quadrants

(D) Four quadrants



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

(A) High

(B) Low

(C) Medium

(D) Zero

103. 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

104. Light duty cranes are generally used in

(A) Power houses

(B). Pumping stations

(C) Auto mobile workshops



(A) Crowd motion

(B) m 3

(C) Travel in metres

(D) Angle of swing

106. The range of ratings 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 1000 kW

107. When an electric train is moving down a hill the DC motor operates as a DC

(A) Series motor

(B) Series generator

(C) Shunt motor

(D) Shunt generator

108. Speed controlled by variation of field flux results in

(A) Constant power Drive

(B) Variable power Drive

(C) Constant torture Drive

(D) Variable torque Drive

109. The slip power recovery scheme is used in induction motor for speed control in the

range

(A) Above synchronous speed

(B) Below synchronous speed

(C) Both above and below synchronous speed


110. The pair used for frequency converter is

(A) Squirrel cage induction motor and synchronous motor

(B) Sleep ring induction motor and a synchronous motor



(C) Sleep ring induction motor and squirrel cage induction motor


111. The motor in close are used for collieries, chemical plant is

(A) Flame proof type

(B) Splash proof type

(C) Totally enclosed type

(D) Pipe ventilated type

112. The motor enclosure used in wood-working industry is

(A) Protected type

(B) Totally enclosed fan cooled type

(C) Flame proof type

(D) Splash proof type

113. The motor enclosure used for industrial purposes is

(A) Protected type

(B) Drip proof type

(C) Totally enclosed type

(D) Open type

114. Ball-bearings are

(A) Used up to 75 kW motors

(B) Of long life and low friction loss

(C) Costlier and noisy particularly at high speed motor




115. Sleeve bearings

(A) Are normally of bronze

(B) Have self lubricating properties

(C) Are used where noise is to be avoided


116. Hot bearings of a DC motor may be caused by

(A) Poor ventilation

(B) Incorrect voltage

(C) Loose coupling

(D) Lack of or dirty lubricant

117. The least expensive drive is

(A) Belt drive

(B) Rope drive

(C) Chain drive


118. For very high speed ratio the indispensable drive is

(A) Direct drive

(B) Rope Drive

(C) Chain drive


119. 15 minute rated motors are suitable for



(A) Light duty cranes

(B) Medium duty cranes

(C) Heavy duty cranes


120. For medium duty cranes the short time rating motor used is

(A) 10 minutes

(B) 15 minutes

(C) 30 minutes


121. The cost of an induction motor will increase as

(A) Horse power rating increases but rpm decreases

(B) Horse power rating decreases but rpm increases

(C) Horse power rating and operating speed increases

(D) Horse power rating and operating speed decreases

122. Which of the following motors has series characteristics?

(A) Shaded Pole motor

(B) Repulsion motor

(C) Capacitor start motor


123. Which of the following motors is preferred for boom host of a travelling crane?

(A) Single phase motor




(C) AC slip ring motor

(D) Ward Leonard controlled DC shunt motor

124. For crane travel which off the following motors is normally used?


(B) DC differential compound motor

(C) Ward Leonard controlled DC shunt motor

(D) AC slip ring motor

125. Which of the following happens when start Delta starter is used ?

(A) Starting voltage is reduced

(B) Starting current is reduced


(D) Both A and B

126. 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

127. The characteristics of drive for crane hoisting and lowering are which off the

following?

(A) Precise control

(B) Smooth movement

(C) Fast speed control




128. 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

129. In which of the following applications variable speed operation is preferred?

(A) Exhaust fan

(B) Ceiling fan

(C) Refrigerator

(D) Water pump

130. The travelling speed of cranes varies from 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

131. Which of the following motors is preferred when quick speed reversal is the main

consideration?


(B) Wound rotor induction motor


(D) DC motor



132. Which off the following motors is preferred when a smooth and resize speed

control over a wide range is desired?

(A) DC motor


(C)Wound rotor induction motor

(D) Synchronous motor

133. Which of the following machines has heavy fluctuating of load ?

(A) Printing machine

(B) Punching machine

(C) Planer

(D) Lathe

134. Which of the following motors is usually preferred for kiln drives?

(A) Cascade controlled AC motor


(C) Three phase shunt wound commutator motor


135. 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) Start Delta starting



136. Electric drive is becoming more and more popular because

(A) It is simple, cleaned, 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


137. 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

138. Introduction of automation in production process has become possible only

because of the use of

(A) An electric drive

(B) Group drives

(C) Individual and multi motor drives

(D) Individual Drive

139. DC motor 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



140. A typical active load is

(A) Hoist

(B) Lathe

(C) Blower

(D) Pump

141. In jaw crushers, a motor has to often start against

(A) low load

(B) medium load

(C) normal load

(D) heavy load.

142. Motor used for elevators is generally

(A) synchronous motor

(B) induction motor

(C) capacitor start single phase motor

(D) any of the above.

143. In synthetic fibre mills motor with

(A) constant speeds are preferred

(B) high starting torque are preferred

(C) variable speed are preferred

(D) low starting torque are preferred.



144. Which of the following motor is preferred for synthetic fibre mills ? (A) series

motor

(B) reluctance motor

(C) shunt motor

(D) synchronous motor.

145. Reluctance motor is a

(A) self-starting type synchronous motors

(B) low torque variable speed motor

(C) variable torque motor

(D) low noise, slow speed motor.

146. A reluctance motor

(A) is compact

(B) has high cost

(C) requires starting gear

(D) is provided with slip rings.

147. Power factor in case of reluctance motor is

(A) nearly unity

(B) always leading

(C) 0.8

(D) 0.3 to 0.4.

148. The efficiency of reluctance motor is around

(A) 95%



(B) 90%

(C) 75 to 85%

(D) 60 to 75%.

149. A reluctance motor on over-load runs as


(B) induction motor

(C) either of the two.

150. The size of a excavator is usually expressed in terms of

(A) cubic meters

(B) travel in meters

(C) angle of swing

(D) 'crowd' motion

151. Ward-Leonard controlled dc drives are generally used for

(A) light duty excavators

(B) medium duty excavators

(C) heavy duty excavators

(D) all of the above.

152. In case of contactors, the contacts are generally made of

(A) copper

(B) silver

(C) cadmium copper




153. Which electromagnet is preferred for noiseless operation

(A) DC operated

(B) AC operated

(C) Any of the above.

154. For high frequency choppers the device that is preferred is

(A) Thyristor

(B) TRIAC

(C) Transistor

(D) GTO.

155. The number of operations per hour in case of class IV contactor will be around

(A) 100

(B) 600 (C) 900 (D) 1200.

156. In case of contactors, the duty in which the main contacts remain closed for a

period bearing a definition relation to the no-load periods, is known as

(A) Standard duty

(B) Intermittent duty

(C) Temporary duty

(D) Un-interrupted duty.

157. In case of contactors the ratio of the in service period to the entire period,

expressed as a percentage is known as

(A) duty



(B) load factor

(C) class of contact

(D) none of the above.

158. A class I contactor should be mechanically sound to withstand

(A) 0.05 million times

(B) 0.25 million times (C) 1.2 million times (D) 5.0 million times.

159. Which of the following pair is used for frequency converters ?

(A) Squirrel cage induction motor and synchronous motor

(B) Wound rotor induction motor and synchronous motor

(C) Wound rotor induction motor and squirrel cage induction motor

(D) Any of the above.

160. Belted wound rotor induction motors are preferred for

(A) machine tools

(B) gyratory crushers

(C) belt conveyor

(D) water pumps.

161. The cooling time constant is usually

(A) equal to the heating time constant

(B) more than heating time constant

(C) none of these.

162. A motor of less than full load power rating can be used if the load is



(A) continuous duty

(B) short time duty

(C) intermittent periodic duty

(D) none of these.

163. Pole changing method of speed control is used in

(A) slip ring induction motor

(B) dc shunt motor

(C) dc series motor

(D) squirrel cage induction motor.

164. To save the energy during braking

(A) dynamic braking is used

(B) plugging is used

(C) regenerative braking is used

(D) mechanical braking is used.

165. To get speed higher than the base speed of the dc shunt motor

(A) armature resistance control is used

(B) field resistance control is used

(C) armature voltage control is used

(D) none of these.

166. Rotor resistance speed control is used in

(A) squirrel cage induction motor

(B) synchronous motor



(C) slip ring induction motor

(D) dc shunt motor.

167. Effect of friction torque is more pronounced

(A) when the drive is running on full speed

(B) when the drive is being started

(C) when the drive is being stopped

(D) when the drive at half of its normal speed.

168. The equilibrium speed of a motor load system is obtained

(A) when motor torque equals the load torque

(B) when motor torque is less than the load torque

(C) when motor torque is more than the load torque

(D) none of the these.

169. Most commonly used ac motor is




(D) ac commutator induction motor.

170. The motor commonly used in computers and digital systems is

(A) dc shunt motor

(B) Induction motor

(C) Stepper motor

(D) Synchronous motor.



171. Regenerative braking mode can be achieved in which quadrant (V-I curve)?

(A) Third

(B) Second

(C) Fourth

(D) First

172. Fan type of loads exhibits which type of load torque characteristics?

(A) Constant torque characteristics

(B) Linearly rising torque characteristics

(C) Non-Linearly rising torque characteristics

(D) Non-Linearly decreasing torque characteristics

173. Type-A chopper is used for obtaining which type of mode?

(A) Motoring mode

(B) Regenerative braking mode

(C) Reverse motoring mode

(D) Reverse regenerative braking mode

174. Boost converter is used to _________

(A) Step down the voltage

(B) Step up the voltage

(C) Equalize the voltage

(D) Step up and step down the voltage

175. Reverse motoring mode is available in fourth quadrant.



(A) True

(B) False

View Answer

176. Which one is an example of variable loss?

(A) Windage loss

(B) Hysteresis loss

(C) Armature copper loss

(D) Friction loss

177. Load torques can be classified into how many types?

(A) Three

(B) Two

(C) Four

(D) Five

178. Rolling mills exhibit what type of load torque characteristics?

(A) Constant torque characteristics

(B) Linearly rising torque characteristics

(C) Non-Linearly rising torque characteristics

(D) Non-Linearly decreasing torque characteristics

179. What is the relationship between torque and speed in constant type loads?

(A) Torque is independent of speed

(B) Torque linearly increases with increase in speed

(C) Torque non-linearly increases with an increase in speed



(D) Torque non-linearly decreases with an increase in speed

180. Torque inversely varies with the speed in the windage load torque component.

(A) True

(B) False

181. What type of force handles for active torques?

(A) Strong nuclear forces

(B) Weak nuclear forces

(C) Gravitational forces

(D) Electrostatic forces

182. Passive torques always oppose the motion of the driven machine.

(A) True

(B) False

183. Among the following which one exhibits linearly rising load torque characteristics?

(A) Elevators

(B) Rolling Mills

(C) Fan load

(D) Separately excited dc generator connected to the resistive load

184. What is the condition for the steady-state operation of the motor?

(A) Load torque > Motor torque

(B) Load torque <<<< Motor torque

(C) Load torque = Motor torque



(D) Load torque < Motor torque

185. Choose the correct one. (* stands for multiplication, J represents the moment of

inertia, w represents angular spee(D).

(A) J*d(w)/dt = Load torque – Motor torque

(B) J*d(w)/dt = Load torque + Motor torque

(C) J*d(w)/dt = Motor torque – Load torque

(D) J*d(w)/dt = Load torque * Motor torque

186. In DC chopper, the waveform for input and output voltages is respectively

__________

(A) Discontinuous and Continuous

(B) Continuous and Discontinuous

(C) Both continuous

(D) Both discontinuous

187. A chopper behaves as a __________

(A) DC equivalent of AC switching device

(B) DC equivalent of AC transformer

(C) DC equivalent of AC relay

(D) AC equivalent of circuit breaker

188. A DC chopper feeds an RLE load. If the value of E is increased by 20%, the

current ripple ________

(A) increases by 20%

(B) decreases by 20%

(C) increases only 20%



(D) remains the same

189. The conduction loss versus device current characteristic of a power MOSFET is

best approximated by

a ________

(A) Straight line

(B) Rectangular hyperbola

(C) Parabola

(D) Exponential decaying functions

190. Which of the following device is NOT suitable for parallel operation?

(A) MOSFET

(B) BJT

(C) IGBT

(D) TRIAC

191. SCR is uni-directional in nature.

(A) True

(B) False

192. Which of the following device should be used as a switch in a low power switched

mode power

supply (SMPS)?

(A) GTO

(B) BJT

(C) MOSFET



(D) TRIAC

193. Servo motors are an example of which type of load?

(A) Pulsating loads

(B) Short time loads

(C) Impact loads

(D) Short time intermittent loads

194. Load torque of the crane is independent of _________

(A) Speed

(B) Seebeck e�ect

(C) Hall e�ect

(D) Thomson e�ect

195. The unit of angular velocity is rad/s .

(A) True

(B) False

196. R.M.S value of the sinusoidal waveform V=V sin(ωt+α).

(A) V ÷2

(B) V ÷2

(C) V ÷2

(D) V ÷3

197. Calculate the time period of the waveform x(t)=24sin(24πt+π÷4).

(A) .064 sec



(B) .047 sec

(C) .083 sec

(D) .015 sec

198. The turn-o� times of the devices in the increasing order is ___________

I. MOSFET

II. BJT

III. IGBT

IV. Thyristor

(A) I, III, II, IV

(B) I, II, III, IV

(C) III, I, II, IV

(D) III, II, IV, I

199. Which of the following devices should be used as a switch for high power and high

voltage

application?

(A) GTO

(B) MOSFET

(C) TRIAC

(D) Thyristor

200. Calculate the useful power developed by a motor using the given data: P = 3000 W,

I = 60 A, R = .4

Ω. Assume frictional losses are 200 W and windage losses are 400 W.

(A) 970 W



(B) 960 W

(C) 980 W

(D) 990 W

201. The consideration involved in the selection of the type of electric drive for a

particular application depends on

(A) Speed control range and its nature

(B) Starting torque

(C) Environmental conditions

(D) All of the above.

202. Which of the following is preferred for automatic drives ? (A) Synchronous motors


(C) Ward Leonard controlled dc motors


203. Which type of drive can be used for hoisting machinery

(A) AC slip ring motor

(B) Ward Leonard controlled DC shunt motor

(C) DC compound motor


204. The motor normally used for crane travel is






(D) DC differentially compound motor.

205. A wound rotor induction motor is preferred over squirrel cage induction motor

when the major consideration involved is

(A) high starting torque

(B) low starting current

(C) speed control over limited range


206. When smooth and precise speed control over a wide range is desired, the motor

preferred is


(B) squirrel cage induction motor

(C) wound rotor induction motor

(D) dc motor.

207. When quick speed reversal is a consideration, the motor preferred is



(C) wound rotor induction motor

(D) dc motor.

208. Stator voltage control for speed control of induction motors is suitable for

(A) fan and pump drives

(B) drive of a crane

(C) running it as generator



(D) constant load drive.

209. The selection of control gear for a particular application is based on the

consideration of

(A) duty

(B) starting torque

(C) limitations on starting current


210. As compared to squirrel cage induction motor, a wound rotor induction motor is

preferred when the major consideration is

(A) high starting torque

(B) low windage losses

(C) slow speed operation


211. A synchronous motor is found to be more economical when the load is above

(A) 1 kW (B) 10 kW (C) 20 kW (D)100kW.

212. The advantage of a synchronous motor in addition to its constant speed is

(A) high power factor

(B) better efficiency

(C) lower cost


213. In motor circuit static frequency changers are used for



(A) power factor improvement

(B) improved cooling

(C) reversal of direction

(D) speed regulation.

214. In case of traveling cranes, the motor preferred for boom hoist is




(D) Single phase motor.

215. The characteristics of drive for. crane hoisting and lowering is

(A) smooth movement

(B) precise control

(C) fast speed control



(A) Span

(B) Type of drive

(C) Tonnes


217. The traveling speed of cranes varies from

(A) 1 to 2.5 m/s

(B) 5 to 15 m/s



(C) 20 to 22.5 m/s

(D) 25 to 40 m/s.

218. In overhead traveling cranes

(A) continuous duty motors are used

(B) slow speed motors are preferred

(C) short time rated motors arc preferred


219. 15 minute rated motors are suitable for

(A) light duty cranes

(B) medium duty cranes

(C) heavy duty cranes


220. Light duty cranes are generally used in

(A) automobile workshops

(B) pumping stations

(C) power houses



(A) Heavy engineering workshops

(B) Steel plants

(C) Ore handling plants




222. 1/2 hour rated motors are used for

(A) light duty cranes

(B) medium duty cranes

(C) heavy duty cranes


223. Which of the following drive can be used for derricks and winches ? (A) DC motors

with Ward Leonard control

(B) AC slip-ring motors with variable resistance

(C) Pole changing squirrel cage motors


224. The number of sets used in pole changing type squirrel cage motors for derricks

and winches, is

(A) 2 (B) 3 (C) 4 (D) 6.

225. A pole changing type squirrel cage motor used in derricks has four, eight and

twenty four poles. In this the medium speed is used for

(A) lifting

(B) hoisting

(C) lowering

(D) landing the load.

226. A pole changing type squirrel cage motor used in derricks has four, eight and

twenty four poles. In this the lowest speed is used for

(A) lifting



(B) hoisting

(C) lowering

(D) landing the load.

227. For handing fragile articles in a crane

(A) low speed is preferred

(B) medium speed is preferred

(C) high speed is preferred.


228. The range of horse power of electric motor drives for rolling mills is of the order of

(A) 1 to 10 HP

(B) 15 to 25 HP

(C) 50 to 100 HP

(D) 100 to 500 HP.

229. Motors preferred for rolling mill drive is

(A) dc motors

(B) ac slip ring motors with speed control

(C) any of the above


230. The .......motors, because of their inherent characteristics, are best suited for the

rolling mills

(A) dc motors

(B) slip ring induction motors



(C) squirrel cage induction motors

(D) single phase motors.

231. In case of kiln drives

(A) starting torque is almost zero

(B) starting torque and running torque are nearly equal

(C) starting torque is more than double of the running torque.

232. Motor preferred for kiln drives is usually

(A) slip ring induction motor

(B) three phase shunt wound commutator motor

(C) cascade controlled ac motor


233. Belt conveyors offer

(A) zero starting torque

(B) low starting torque

(C) medium starting torque

(D) high starting torque.

234. In case belt conveyors

(A) squirrel cage motors with direct-on-line starters are used

(B) single phase induction motors are used

(C) dc shunt motors are used

(D) induction motors with star-delta starters are used.



235. Which of the following motor is preferred for blowers ?

(A) wound rotor induction motor


(C) dc shunt motor

(D) dc series motor.

236. Centrifugal pumps are usually driven by

(A) dc shunt motors

(B) dc series motors

(C) squirrel cage induction motors


237. In case of centrifugal pumps the starting torque is generally

(A) double the running torque

(B) slightly more than running torque

(C) same as running torque

(D) less than running torque.

238. In a centrifugal pump if the liquid to be pumped has density twice that of water,

then the horse power required

(as compared to that while pumping water) will be

(A) half (B) same (C) double

(D) four times.

239. Wound rotor and squirrel-cage motors with high slip which develop maximum

torque at stand still are used for



(A) machine tools

(B) presses and punches

(C) elevators


240. Belted slip ring induction motor is almost invariably used for

(A) centrifugal blowers

(B) jaw crushers

(C) water pumps

(D) screw pumps.

241. A solar cell converts light energy into __________

(A) Electrical energy

(B) Thermal energy

(C) Sound energy

(D) Heat energy

242. There are three types of the solar cells.

(A) True

(B) False

243. The output power of the centrifugal pump is proportional to the _________ of the

speed.

(A) Square

(B) Cube



(C) Square-root

(D) Cube-root

244. There are four types of Water pumps.

(A) True

(B) False

245. The output of the Solar panel is DC.

(A) True

(B) False

246. Which of the relationship is correct in Permanent magnet DC motor?

(A) T ∝ (I(A)2

(B) T ∝ (I(A)0

(C) T ∝ Ia

(D) T2 ∝ Ia

247. Which of the relationship is correct in Permanent magnet DC motor?

(A) E ∝ (N)

(B) E ∝ (N)

(C) E ∝ N

(D) E2 ∝ N

248. Who made the first solar cell?

(A) Gerald Pearson



(B) Tim Bell

(C) Tim Cook

(D) Nicola Tesla

249. When was the first solar cell invented?

(A) 1950

(B) 1954

(C) 1965

(D) 1952

250. Which of the following is an advantage of electric traction over other methods of

traction ?

(A) Faster acceleration

(B) No pollution problems

(C) Better braking action


251. Which of the following is the voltage for single phase A.C. system ?

(A) 22 V

(B) 440 V

(C) 5 kV

(D) 15 kV

(e) None of the above

252. Long distance railways use which of the following ?

(A) 200 V D.C.



(B) 25 kV single phase A.C.

(C) 25 kV two phase A.C.

(D) 25 kV three phase A.C.

253. The speed of a locomotive is controlled by

(A) flywheel

(B) gear box

(C) applying brakes

(D) regulating steam flow to engine

254. Main traction systems used in India are, those using

(A) electric locomotives

(B) diesel engine locomotives

(C) steam engine locomotives

(D) diesel electric locomotives

(e) all of the above

255. For diesel locomotives the range of horsepower is

(A) 50 to 200

(B) 500 to 1000

(C) 1500 to 2500

(D) 3000 to 5000

256. _______ locomotive has the highest operational availability.

(A) Electric

(B) Diesel

(C) Steam



257. The horsepower of steam locomotives is

(A) upto 1500

(B) 1500 to 2000

(C) 2000 to 3000

(D) 3000 to 4000

258. The overall efficiency of steam locomotive is around

(A) 5 to 10 percent

(B) 15 to 20 percent

(C) 25 to 35 percent

(D) 35 to 45 percent

259. In tramways which of the following motors is used ?

(A) D.C. shunt motor


(C) A.C. three phase motor

(D) AC. single phase capacitor start motor

260. In a steam locomotive electric power is provided through

(A) overhead wire

(B) battery system

(C) small turbo-generator

(D) diesel engine generator

261. Which of the following drives is suitable for mines where explosive gas exists ?



(A) Steam engine

(B) Diesel engine

(C) Battery locomotive


262. Overload capacity of diesel engines is usually restricted to

(A) 2 percent

(B) 10 percent

(C) 20 percent

(D) 40 percent

263. The wheels of a train, engine as well as bogies, are slightly tapered to

(A) reduce frietion

(B) increase friction

(C) facilitate braking

(D) facilitate in taking turns

264. The efficiency of diesel locomotives is nearly

(A) 20 to 25 percent

(B) 30 to 40 percent

(C) 45 to 55 percent

(D) 60 to 70 percent

265. Which of the following is the advantage of electric braking ?

(A) It avoids wear of track

(B) Motor continues to remain loaded during braking



(C) It is instantaneous

(D) More heat is generated during braking

266. Which of the following braking systems on the locomotives is costly ?

(A) Regenerative braking on electric locomotives

(B) Vacuum braking on diesel locomo-tives

(C) Vacuum braking on steam locomo-tives

(D) All braking systems are equally costly

267. Tractive effort is required to

(A) overcome the gravity component of train mass

(B) overcome friction, windage and curve resistance

(C) accelerate the train mass

(D) do all of the above

268. For given maximum axle load tractive efforts of AC. locomotive will be

(A) less than that of D.C. locomotive

(B) more than that of D.C. locomotive

(C) equal to that of D.C. locomotive


269. Due to which of the following co-efficient of adhesion improves ?

(A) Rust on the rails

(B) Dust on the rails

(C) Sand on the rails




270. Which of the following is the disadvantage of electric traction over other systems of

traction ?

(A) Corrosion problems in the under-ground pipe work

(B) Short time power failure interrupts traffic for hours

(C) High capital outlay in fixed instal-lations beside route limitation

(D) Interference with communication lines

(C) All of the above

271. Speed-time curve of main line service differs from those of urban and suburban

services on following account

(A) it has longer free running period

(B) it has longer coasting period

(C) accelerating and braking periods are comparatively smaller


272. The rate of acceleration on suburban orurban services is restricted by the

consideration of

(A) Engine power

(B) Track curves

(C) Passenger Discomfort

(D) Track size

273. The specific energy consumption of a train depends on which of the following ?

(A) Acceleration and retardation

(B) Gradient

(C) Distance covered




274. The friction at the track is proportional to

(A) 1/speed

(B) l/(speed)2

(C) speed


275. The resistance encountered by a train in motion is on account of

(A) resistance offered by air

(B) friction at the track

(C) friction at various parts of the rolling stock


276. Battery operated trucks are used in

(A) steel mills

(B) power stations

(C) narrow gauge traction

(D) factories for material transportation

277. method can bring the locomotive to dead stop.

(A) Plugging braking

(B) Rheostatic braking

(C) Regenerative braking




278. The voltage used for suburban trains in D.C. system is usually

(A) 12 V

(B) 24 V

(C) 220 V

(D) 600 to 750 V

279. For three-phase induction motors which of the following is the least efficient

method of speed control ?

(A) Cascade control

(B) Pole changing

(C) Rheostatic control

(D) Combination of cascade and pole changing

280. Specific energy consumption becomes

(A) more on steeper gradient

(B) more with high train resistance

(C) less if distance between stops is more


281. In main line service as compared to urban and suburban service

(A) distance between the stops is more

(B) maximum speed reached is high

(C) acceleration and retardation rates are low


282. Locomotive having monomotor bogies



(A) has better coefficient of adhesion

(B) are suited both for passanger as well as freight service

(C) has better riding qualities due to the reduction of lateral forces

(D) has all above qualities

283. Series motor is not suited for traction duty due to which of the following account ?

(A) Less current drain on the heavy load torque

(B) Current surges after temporary switching off supply

(C) Self relieving property

(D) Commutating property at heavy load

284. When a bogie negotiates a curve, reduction in adhesion occurs resulting in sliding.

Thus sliding is acute when

(A) wheel base of axles is more

(B) degree of curvature is more

(C) both (A) and (B)


285. Energy consumption in propelling the train is required for which of the following?

(A) Work against the resistance to motion

(B) Work against gravity while moving up the gradient

(C) Acceleration


286. An ideal traction system should have

(A) easy speed control



(B) high starting tractive effort

(C) equipment capable of with standing large temporary loads


287. have maximum unbalanced forces

(A) Diesel shunters

(B) Steam locomotives

(C) Electric locomotives

(D) Diesel locomotives

288. Specific energy consumption is affected by which of the following factors ?

(A) Retardation and acceleration values

(B) Gradient

(C) Distance between stops


289. In case of ________ free running and coasting periods are generally long.

(A) main-line service

(B) urban service

(C) sub-urban service


290. Overhead lines for power supply to tramcars are at a minimum height of

(A) 3 m

(B) 6 m

(C) 10 m



(D) tO m

291. The return circuit for tramcars is through

(A) neutral wire

(B) rails

(C) cables

(D) common earthing

292. _______ frequency is not common in low frequency traction system

(A) 40 Hz

(B) 25 Hz

(C) 16 Hz

293. For 25 kV single phase system power supply frequency is

(A) 60 Hz

(B) 50 Hz

(C) 25 Hz

(D) 16 Hz

294. Power for lighting in passanger coach, in a long distance electric train, is provided

(A) directly through overhead electric line

(B) through individual generator of bogie and batteries

(C) through rails

(D) through locomotive



295. In India, electrification of railway track was done for the first time in which of the

following years ?

(A) 1820—1825

(B) 1880—1885

(C) 1925—1932

(D) 1947—1954

296. Which of the following happens in Kando system ?

(A) Three phase A.C. is converted into D.C.

(B) Single phase A.C. is converted into D.C.

(C) Single phase supply is converted into three phase system


297. For which of the following locomotives the maintenance requirements are the

least?

(A) Steam locomotives

(B) Diesel locomotives

(C) Electric locomotives

(D) Equal in all of the above

298. Which of the following methods is used to control speed of 25 kV, 50 Hz single

phase traction ?

(A) Reduced current method

(B) Tap changing control of transformer

(C) Series parallel operation of motors




299. The most suitable servo-motor application is __________

(A) AC series motor

(B) DC series motor

(C) AC two-phase induction motor

(D) DC shunt motor

300. the value of the frequency of the DC supply.

(A) 0 Hz

(B) 50 Hz

(C) 20 Hz

(D) 10 Hz



Q Ans. Q Ans. Q Ans. Q Ans. Q Ans. Q Ans.

1 E 51 D 101 D 151 C 201 D 251 A

2 E 52 C 102 A 152 D 202 C 252 B

3 B 53 D 103 C 153 A 203 D 253 D

4 D 54 D 104 D 154 C 204 A 254 E

5 C 55 A 105 B 155 D 205 D 255 C

6 D 56 D 106 C 156 B 206 D 256 A

7 D 57 C 107 B 157 B 207 D 257 A

8 D 58 D 108 A 158 B 208 A 258 A

9 D 59 C 109 C 159 A 209 D 259 B

10 C 60 B 110 A 160 B 210 A 260 C

11 B 61 B 111 A 161 B 211 D 261 C

12 C 62 C 112 B 162 B 212 A 262 A

13 A 63 A 113 A 163 D 213 D 263 D

14 B 64 C 114 D 164 C 214 A 264 A

15 D 65 B 115 D 165 B 215 D 265 A

16 D 66 C 116 D 166 C 216 C 266 A

17 A 67 C 117 A 167 B 217 A 267 D

18 A 68 A 118 B 168 A 218 C 268 B

19 D 69 A 119 A 169 C 219 A 269 D

20 D 70 D 120 C 170 B 220 D 270 C

21 D 71 C 121 A 171 B 221 D 271 D

22 A 72 D 122 B 172 C 222 B 272 D

23 C 73 D 123 C 173 A 223 D 273 C

24 C 74 D 124 D 174 B 224 B 274 C

25 D 75 C 125 D 175 A 225 A 275 D

26 C 76 A 126 C 176 C 226 D 276 D

27 B 77 D 127 D 177 B 227 A 277 A

28 B 78 B 128 B 178 D 228 D 278 D

29 B 79 D 129 B 179 A 229 C 279 C

30 C 80 A 130 D 180 B 230 A 280 D

31 A 81 D 131 D 181 C 231 C 281 D

32 C 82 D 132 A 182 A 232 D 282 D

33 A 83 C 133 B 183 D 233 D 283 B

34 A 84 B 134 D 184 C 234 A 284 C

35 D 85 C 135 A 185 C 235 B 285 D

36 B 86 D 136 D 186 B 236 C 286 D

37 D 87 B 137 B 187 B 237 D 287 B

38 A 88 D 138 C 188 D 238 C 288 D

39 D 89 A 139 A 189 C 239 B 289 A

40 D 90 B 140 A 190 B 240 B 290 C

41 B 91 D 141 D 191 A 241 A 291 B

42 D 92 C 142 B 192 C 242 A 292 A

43 B 93 B 143 A 193 B 243 B 293 B

44 B 94 A 144 B 194 A 244 B 294 B

45 C 95 A 145 A 195 B 245 A 295 C

46 D 96 C 146 A 196 A 246 C 296 C

47 C 97 D 147 D 197 C 247 C 297 B

48 B 98 C 148 D 198 A 248 A 298 B

49 B 99 D 149 B 199 D 249 B 299 D

50 D 100 B 150 A 200 B 250 A 300 A

multiple choice questions subject: control of electric

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