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Electrical Engineering Objective Questions { DC Motors }

8. The main factor which leads to unstable parallel operation of flat and overcom pound generators is
A. unequal number of turns in their series field windings
B. unequal series field resistances
C. their rising voltage characteristics
D. unequal speed regulation of their prime movers -

9.  If field resistance of a dc shunt generator is increased beyond its critical value, the generator
A. output voltage will exceed its nameplate rating
B. will not build up
C. may burn out if loaded to its nameplate rating
D. power output may exceed its nameplate rating

10.  A dc shunt generator develops a fault in the form of an open armature coil. As a temporary measure, you should
A. disconnect the open coil from the armature
B. use new brushes which can span 3 commutator segments
C. bridge the two commutator bars across which open coil is connected
D. change the armature it self

11. If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shund field
A. to earth
B. to an alternator
C. in reverse
D. to a battery

12.  The sole purpose of commutator in a dc generator is to
A. increase output voltage
B. reduce sparking at brushes
C. provide smoother output
D. convert the induced alternating voltage into unidirectional pulses

13.  All rotating electric machines are basically
A. d.c. machines
B. a.c. machines
C. electro-mechanical convertors
D. machines using electromagnetic induction

14. All rotating electrical machines have
A. rotating armature and fixed field
B. rotating field and fixed armature
C. either (a) or (b) above
D. none of the above

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