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Electrical Engineering Objective Questions { DC Motors }

85. A short-shunt cumulatively compounded d.c. generator builds up a voltage of 220 V at no load and rated speed. If it is operated as a differentially compounded generator, other things remaining the same, then it would build up
A. 1,2
B. Ia
C. speed
D. a constant

86. A dc shunt motor is rotating in clockwise direction as viewed from one end. The polarity of connection of the armature and field winding are reversed simultaneously. The motor will
A. not rotate at all
B. rotate in anti-clockwise direction
C. rotate in clockwise direction.
D. None of above

87. A self-excited d.c. shunt motor is ranning at no load at 1000 rpm. If the terminal voltage is reduced to 50% of its original value, the no-load speed of the otor will be?rpm.

88. lithe applied voltage of a dc shunt motor is halved with the load torque doubled, the following approximate changes will be observed. Speed is
A. doubled and armature current is halved
B. the same and armature current is doubled
C. same and armature current increases four-fold
D. halved and armature current is same

89. A d.c. shunt motor is running with a certain load. The effect of adding an external resistance in the field circuit is to
A. reduce the motor speed
B. increase the motor speed
C. reduce the armature current of the motor
D. stop the motor

90. Which of the following motor has high starting torque?
A. ac series motor
B. dc series motor
C. induction motor
D. synchronous motor

91. A d.c. series motor with rated voltage of 230 volts is connected to an a.c. supply of 230 volts. It will
A. run
B. not run
C. run with less efficiency
D. run with more efficiency

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