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Electrical Engineering Objective Questions { DC Motors }

78.  In a dc machine
A. torque and induced emf are produced both in motor and generator
B. torque is produced in motor and emf is induced in generator
C. torque is produced in generator and emf is induced in motor
D. none of these

79. Function of the interpoles in the dc generators is to
A. neutralize the reactance voltage
B. make commutation sparkles
C. neutralize cross magnetizing effects of a armature reaction.
D. all the above

80. Which of the following is not a cross field machine?
A. Level compound generator with interpoles
B. Amplidyne
C. Rosenberg dynamo
D. Metadyne

81. A d.c. shunt generator has full-load voltage regulation of 10% at rated speed of 1000 r.p.m. If it is now driven at 1250 r.p.m., then its voltage regulation at full load would
A. be more than 10%
B. be less than 10%
C. remain unchanged
D. be 12.5%

82. Load saturation characteristic of a dc generator gives relation between
A. V and Ia
B. E and Ia
C. E0 and If
D. V and la

83. In d.c. machines, constant loss is composed of
A. iron loss and mechanical loss
B. friction windage (FW) and iron loss and field circuit loss
C. iron loss and field circuit loss
D. FW and stray load losses

84. An amplidyne develops an output voltage of 100 volts at an armature speed of n r.p.m. If its armature is now driven at 2n r.p.m., then its output voltage is
A. 100 volts
B. 200 volts
C. 400 volts
D. 50 volts

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