Electrical Drive MCQ

81. For a particular type of motor, the heating time constant

(a) increases with the increase in size.
(b) decreases with the increase in size.
(c) same for all sizes.

82. For estimation of power rating of an electric drive, its losses can be considered to be proportional to

(a) power.
(b) (power)².
(c) (power)³.
(d) torque.

83. The heating time constant of a totally enclosed motor is relatively

(a) lower.
(b) higher.
(c) independent of type of enclosure.

84. For a certain industrial application, an overrated ac motor was selected. It will lead to operation with

(a) higher efficiency and better pf.
(b) lower efficiency and poorer pf.
(c) higher efficiency and poorer pf.
(d) lower efficiency and better pf.

85. A flywheel is generally used in

(a) a cement mill drive.
(b) a paper mill drive.
(c) a roiling mill drive.
(d) a sugar centrifuge drive.

86. In overhead travelling cranes

(a) continuous rating motors are used.
(b) continuous minimum rating motors are used.
(c) short-time rating motors are used.
(d) any of the above.

87. 15 minute rated motors are suitable for

(a) light duty cranes.
(b) medium duty cranes.
(c) heavy duty cranes.
(d) all of the above.

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

(a) 10 minutes.
(b) 15 minutes.
(c) 30 minutes.
(d) one hour.

89. Load equalization is desirable in the case of

(a) very large refrigeration and air-conditioning plants.
(b) rolling mills, electric hammers, presses, reciprocating pumps.
(c) lathes, woodworking machines, paper making machines, shapers and slotters.
(d) travelling cranes, lifts.

90. The phase controlled rectifiers used in speed control of dc motors converts fixed ac supply voltage into……….output voltage.

(a) variable dc
(b) variable ac
(c) variable frequency ac
(d) full rectified ac

91. A four quadrant operation requires

(a) two full converters in series.
(b) two full converters connected back to back.
(c) two full converters connected in parallel.
(d) two semi converters connected back to back.

92. The following converters can feed power in any of the four quadrants

(a) semi-converter.
(b) full converter.
(c) dual converter.
(d) combination of a semi and full-converters.

93. For speed control of dc motors using controlled rectifiers, armature voltage control gives speed

(a) above rated speed.
(b) below rated speed.
(c) above as well as below rated speed.

94. Armature of a dc motor is fed from a phase controlled rectifier where as its field is supplied from a constant dc source. To reduce the speed of the motor regeneratively

(a) the firing angle of the converter should be increased.
(b) the polarity of the dc voltage should be reversed.
(c) the polarity of the armature induced voltage should be reversed.
(d) the firing angle should be varied in the range 90° to 80° simultaneously reversing the armature connections.

95. For the speed control of ac drive, the preferred method using thyristors is

(a) phase control.
(b) integral cycle control.
(c) chopper control.
(d) all are equally good.

96. The semiconductor device used for speed control of single phase induction motors in every day domestic use is

(a) SCR.
(b) power transistor.
(c) Triac.
(d) power MOS.

97. Which of the following motor is suitable for driving cranes, hoists, centrifugal pumps, conveyor belt etc. ?

(a) DC series motor.
(b) DC shunt motor.
(c) DC compound wound motor.
(d) Any of the above.

98. Heavy-duty steel-works cranes having wide load variations are equipped with

(a) dc series motors.
(b) plain squirrel cage induction motors.
(c) wound rotor induction motors.
(d) synchronous motors.

99. The most suitable motor for a steel mill requiring a motor having high starting torque, wide speed range and precise speed control is

(a) plain squirrel cage induction motor.
(b) wound rotor induction motor.
(c) dc series motor.
(d) dc shunt motor.

100. For automatic drives the preference is for

(a) synchronous motors.
(b) Wald-Leonard controlled dc shunt motors.
(c) plain squirrel cage induction motors.

101. The type of motor that can be used for hoisting machinery is

(a) dc compound motor.
(b) Ward-Leonard controlled dc shunt motor.
(c) wound rotor induction motor.
(d) any of the above.

102. The motor normally used for crane travel is

(a) wound rotor induction motor.
(b) synchronous motor.
(c) dc differentially compounded motor.
(d) plain squirrel cage induction motor.

103. The drive, that can be used for derricks and winches is

(a) pole-changing squirrel cage induction motor.
(b) ac slip-ring induction motor with variable resistance.
(c) dc shunt motor with Ward-Leonard control.
(d) any of the above.

104. Ward-Leonard controlled dc drives are generally used for……..duty excavators.

(a) light
(b) medium
(c) heavy
(d) none of these.

105. The motor suitable for a reciprocating pump required to start under load is

(a) plain squirrel cage induction motor.
(b) double-squirrel cage induction motor.
(c) synchronous motor.
(d) dc shunt motor.

106. A pole-changing squirrel cage induction motor employed in derricks has four, eight and twenty four poles. The lowest speed is used in

(a) hoisting.
(b) landing the load.
(c) lifting.
(d) lowering.

107. A pole-changing type squirrel cage induction motor employed in derricks has four, eight and twenty four poles. The medium speed is used in

(a) landing the load.
(b) hoisting.
(c) lowering.
(d) lifting.

108. Motor preferred for kiln drive is usually

(a) wound rotor induction motor.
(b) cascaded controlled ac motor.
(c) Ward-Leonard controlled dc shunt motor.
(d) any of the above.

109. The motor used in mines is

(a) flame-proof squirrel cage induction or wound rotor motor.
(b) dc series motor.
(c) dc shunt motor.
(d) any of the above.

110. The motor used in punches, presses and shears is

(a) dc series or shunt motors.
(b) dc cumulative compound motor.
(c) high slip squirrel cage or wound rotor induction motor.
(d) both (b) and (c).

111. A domestic mixer uses the following motor

(a) induction motor.
(b) reluctance motor.
(c) universal motor.
(d) permanent magnet synchronous motor.

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