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Electrical Engineering Objective Questions { DC Motors }

1. The efficiency of a d.c. shunt generator is maximum when the
A. magnetic losses are equal to the mechanical losses
B. field copper losses are equal to the constant losses
C. stray losses are equal to the copper losses
D. armature copper losses are equal to constant losses.
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2. In a dc generator, the brushes on the commutator are shifted from geometrical neutral positions to
A. obtain highest generator voltage
B. avoid sparking.
C. obtain highest generator efficiency
D. all the above
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3. A simplex lap-wound 10-pole dc generator has 800 armature conductors. If each pole face covers 75% of pitch, compensating conductors required per pole face are
C.(b) 60
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4. Which condition out of the five given below is not required for the build-up of a shunt generator?
A. there must be sufficient residual magnetism in the poles
B. for the given direction of rotation, shunt field coils should be corectly connected to the armature
C. if excited on open circuit, the shunt field resistance should be more than the critical resistance
D. armature speed should be more than the critical speed
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5. A DC generator generates
A. DC voltage
B. AC voltage
C. DC and ac voltage
D. pulsating DC
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6. A DC generator can be termed as a
A. rotating amplifier
B. prime mover
C. power pump
D. none of the above
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7. The essential condition for stable parallel operation of two dc generators having similar characteristics is that they should have
A. same kilowatt output ratings
B. drooping voltage characteristics
C. same percentage regulation
D. same no-load and full-load speeds
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