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Electrical Engineering Objective Questions { DC Motors }

71. In separately excited dc generator supplying rated load, the armature reaction
A. is always absent
B. is always present
C. may be sometimes present
D. none of these

72. 72. With flux remaining constant, if the speed of a shunt dc generator is doubled, its generated emf
A. doubles
B. becomes half
C. remain unchanged
D. become 4 times as large

73.  The armature reaction ofan unsaturated dc machine is
A. nonmagnetising
B. magnetizing
C. demagnetizing
D. cross-magnetising

74. Electromagnetic torque and speed are in opposite directions in the case of
A. shunt generators
B. shunt motors
C. series motors
D. all of these

75.  The function of a starter in a dc machine is to
A. avoid excessive current at starting
B. avoid armature reaction
C. control the speed
D. avoid excessive heating

76.  In dc machines, the armature reaction mmf is.
A. stationary with respect to the armature
B. rotating with respect to the stator
C. stationary with respect to the stator
D. rotating with respect to brushes

77. A cumulatively compound dc generator supplies 15 A at 240 V. No if the series field winding is short circuited, the terminal voltage
A. will remain unaltered at 240 V
B. will rise to 260 V
C. will shoot up to a very high value
D. will reduce below 240 V

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