Question is ⇒ Satisfactory commutation of D.C. machines requires, Options are ⇒ (A) brushes should be of proper grade and size, (B) brushes should smoothly run in the holders, (C) smooth, concentric commutator properly undercut, (D) all of the above, (E) , Leave your comments or Download question paper.

Question is ⇒ Satisfactory commutation of D.C. machines requires, Options are ⇒ (A) brushes should be of proper grade and size, (B) brushes should smoothly run in the holders, (C) smooth, concentric commutator properly undercut, (D) all of the above, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	Satisfactory commutation of D.C. machines requires
A.	brushes should be of proper grade and size [Wrong Answer]
B.	brushes should smoothly run in the holders [Wrong Answer]
C.	smooth, concentric commutator properly undercut [Wrong Answer]
D.	all of the above [Correct Answer]
View Answer 6 -2 Explanation:- Answer : D Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

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⇒ Armature coil is short-circuited by brushes when it lies
along neutral axis
along field axis
in any of the above positions
in none of the above positions

⇒ To avoid formation of grooves in the csommutator of a D.C. machine
the brushes of opposite polarity should track each other
the brushes of same polarity should track each other
brush position has no effect on the commutator grooving

⇒ 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

⇒ Which of the following statements is incorrect in D.C. shunt generators about hysteresis loss ?
It is independent of lamination thickness
It can be minimize by laminating the armature
It depends upon the supply frequency
None of the above

⇒ In a four-pole D.C. machine
all the four poles are north poles
alternate poles are north and south
all the four poles are south poles
two north poles follow two south poles

⇒ The polarity of a D.C. gernerator can be reversed by
reversing the field current
increasing field current
reversing field current as well as direction of rotation
any of the above

⇒ 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

⇒ In a D.C. generator, the armature reaction results in
demagnetisation of the centres of poles
magnetisation of interpoles
demagnetisation of the leading pole tip and magnetisation of the trailing pole tip
magnetisation of the leading tip and demagnetisation of the trailing pole tip

⇒ An external resistance added in the field of a D.C. shunt generator will
decrease the voltage of the generator
increase the voltage of the generator
increase the power delivered
increase the speed of the generator

⇒ In D.C. generators, the cause of rapid brush wear may be
severe sparking
rough commutator surface
imperfect contact
any of the above

⇒ Simple method of increasing the voltage of a D.C. generator is
to increase the length of the armature
to decrease the length of the armature
to increase the speed of rotation
to decrease the speed of rotation

⇒ The e.m.f. generated by a shunt wound D.C. generator is E . 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

⇒ Which one of the following generators is used for charging the batteries ?
Shunt
Series
Compound
Any of the above

⇒ In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
4
8
16
32

⇒ While applying Fleming's right-hand rule to find the direction of induced e.m.f., the thumb points towards
direction of induced e.m.f.
direction of flux
dir ection of motion of the conductor if forefinger points in the direction of generated e.m.f.
direction of motion of conductor, if forefinger points along the lines of flux

⇒ In case of D.C. generators, the armature voltage control is considered as suitable if the machine is driven
at constant load
at constant current
at constant torque
at constant VA

⇒ The demagnetising component of armature reaction in a D.C. generator
reduces generator e.m.f.
increases armature speed
reduces interpoles flux density
results in sparking trouble

⇒ D.C. series generator is used
to supply traction load
to supply industrial load at constant voltage
as a booster to maintain constant voltage at the load end of the feeder
for none of the above purpose

⇒ Which of the following components of a D.C. generator plays vital role for providing direct current of a D.C. generator ?
Dummy coils
Commutator
Eye bolt
Equilizer rings

⇒ The field coils of D.C. generator are usually made of
mica
copper
cast iron
carbon

⇒ A separately excited generator as compared to a self-excited generator
is amenable to better voltage control
is more stable
has exciting current independent of load current
has all above features

⇒ Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be
2 : 3
3 : 1
3 : 2
1 : 3

⇒ The voltage drop for which of the following types of brush can be expected to be least ?
Graphite brushes
Carbon brushes
Metal graphite brushes
None of the above

⇒ The e.m.f. induced in the armature of a shunt generator is 600V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
640 V
620 V
600 V
580 V

⇒ The material for commutator brushes is generally
mica
copper
cast iron
carbon

⇒ D.C. generator generally preferred for charging automobile batteries is
series generator
shunt generator
long shunt compound generator
any of the above

⇒ In a D.C. machine stray loss is the sum of
total copper loss and mechanical loss
armature copper loss and iron loss
shunt field copper loss and mechanical loss
iron loss and mechanical loss

⇒ A series generator can self-excite
only if the load current is zero
only if the load current is not zero
irrespective of the value of load current
none of the above

⇒ With a D.C. generator which of the following regulation is preferred ?
100% regulation
infinite regulation
50% regulation
1% regulation

⇒ 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