Dc Motors(Engineering > Electrical Engineering ) Questions and Answers
Question 1. The efficiency of a d.c. shunt generator is maximum when the
magnetic losses are equal to the mechanical losses
field copper losses are equal to the constant losses
stray losses are equal to the copper losses
armature copper losses are equal to constant losses.
Explanation:-
Answer: Option D. -> armature copper losses are equal to constant losses.
Question 2. A DC generator can be termed as a
rotating amplifier
prime mover
power pump
none of the above
Explanation:-
Answer: Option A. -> rotating amplifier
Question 3. A DC generator generates
DC voltage
AC voltage
DC and ac voltage
pulsating DC
Explanation:-
Answer: Option B. -> AC voltage
Question 4. The essential condition for stable parallel operation of two dc generators having similar characteristics is that they should have
same kilowatt output ratings
drooping voltage characteristics
same percentage regulation
same no-load and full-load speeds
Explanation:-
Answer: Option B. -> drooping voltage characteristics
Question 5. In a dc generator, the brushes on the commutator are shifted from geometrical neutral positions to
obtain highest generator voltage
avoid sparking.
obtain highest generator efficiency
all the above
Explanation:-
Answer: Option B. -> avoid sparking.
Question 6. Which condition out of the five given below is not required for the build-up of a shunt generator?
there must be sufficient residual magnetism in the poles
for the given direction of rotation, shunt field coils should be corectly connected to the armature
if excited on open circuit, the shunt field resistance should be more than the critical resistance
armature speed should be more than the critical speed
Explanation:-
Answer: Option D. -> armature speed should be more than the critical speed
Question 7. 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
80
6
(b) 60
8
Explanation:-
Answer: Option C. -> (b) 60
Question 8. If field resistance of a dc shunt generator is increased beyond its critical value, the generator
output voltage will exceed its nameplate rating
will not build up
may burn out if loaded to its nameplate rating
power output may exceed its nameplate rating
Explanation:-
Answer: Option B. -> will not build up
Question 9. The main factor which leads to unstable parallel operation of flat and overcom pound generators is
unequal number of turns in their series field windings
unequal series field resistances
their rising voltage characteristics
unequal speed regulation of their prime movers -
Explanation:-
Answer: Option C. -> their rising voltage characteristics
Question 10. . If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by connecting its shund field
