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Test your caliber
1. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be _____.
E/2
2E
slightly less than E
E
2. In a D.C. generator the actual flux distribution depends upon ______.
size of air gap
shape of the pole shoe
clearance between tips of the adjacent pole shoes
all of the above
3. The armature core of a D.C. generator is usually made of _____.
silicon steel
copper
non-ferrous material
cast-iron
4. Satisfactory commutation of D.C. machines requires _____.
brushes should be of proper grade and size
brushes should smoothly run in the holders
smooth, concentric commutator properly undercut
all of the above
5. Open circuited armature coil of a D.C. machine is _____.
identified by the scarring of the commutator segment to which open circuited coil is connected
indicated by a spark completely around the commutator
both (a) and (b)
none of the above
6. In a D.C. machine, fractional pitch winding is used _____.
to increase the generated voltage
to reduce sparking
to save the copper because of shorter end connections
due to (b) and (c) above
7. For the parallel operation of two or more D.C. compound generators, we should ensure that _____.
voltage of the incoming generator should be same as that of bus bar
polarity of incoming generator should be same as that of bus bar
all the series fields should be run in parallel by means of equilizer connection
series fields of all generators should be either on positive side or negative side of the armature
8. D.C. series generator is used _____.
to supply traction load
to supply industrial load at constant voltage
voltage at the toad end of the feeder
for none of the above purpose
9. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
series generator
shunt generator
compound generator
self-excited generator
10. Interpole flux should be sufficient to _____.
neutralise the commutating self induced e.m.f.
neutralise the armature reaction flux
neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
perform none of the above functions
11. D.C. generator generally preferred for charging automobile batteries is _____.
series generator
shunt generator
long shunt compound generator
any of the above
12. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when _____.
r.p.m. is more than 300
r.p.m. is less than 300
number of poles is 4
number of poles is 2
13. Permeance is the reciprocal of _____.
flux density
reluctance
ampere-turns
resistance
14. In D.C. generators the polarity of the interpoles _____.
is the same as that of the main pole ahead
is the same as that of the immediately preceding pole
is opposite to that of the main pole ahead
is neutral as these poles do not play part in generating e.m.f.
15. The e.m.f. generated in a D.C. generator is directly proportional to _____.
flux/pole
speed of armature
number of poles
all of the above
16. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when _____.
there is no load on|he generator
the generator runs on full load
the generator runs on overload
the generator runs on designed speed
17. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except _____.
interpoles
dummy coils
compensating winding
shifting of axis of brushes
18. In D.C. generators on no-load, the air gap flux distribution in space is _____.
sinusoidal
triangular
pulsating
flat topped
19. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly _____.
150 V
175 V
240 V
290 V
20. The purpose of providing dummy coils in a generator is _____.
to reduce eddy current losses
to enhance flux density
to amplify voltage
to provide mechanical balance for the rotor
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