(a) case iron
(b) carbon
(c) silicon steel
(d) stainless steel
Ans: c
2. Which of the following could be lamina-proximately the thickness of laminations of a D.C.
machine ?
(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 m
(d) 5 m
Ans: c
3. The armature of D.C. generator is laminated to
(a) reduce the bulk
(b) provide the bulk
(c) insulate the core
(d) reduce eddy current loss
Ans: d
4. The resistance of armature winding depends on
(a)
length of conductor
(b)
cross-sectional area of the conductor
(c)
number of conductors
(d)
all of the above
Ans: d
5. The field coils of D.C. generator are usually made of
(a) mica
(b) copper
(c) cast
iron
(d) carbon
Ans: b
6. The commutator segments are connected to the armature
conductors by means of
(a) copper
lugs
(b) resistance
wires
(c) insulation
pads
(d) brazing
Ans: a
7. In a commutator
(a) copper
is harder than mica
(b) mica
and copper are equally hard
(c) mica
is harder than copper
(d) none
of the above
Ans: c
8. In D.C. generators the pole shoes are fastened to the
pole core by
(a) rivets
(b) counter
sunk screws
(c) brazing (d) welding
Ans: b
9. According to Fleming's right-hand rule for finding the
direction of induced e.m.f., when middle finger points in the direction of
induced e.m.f., forefinger will point in the direction of
(a) motion
of conductor
(b) lines
of force
(c) either
of the above
(d) none of the above
Ans: b
10. Fleming's right-hand rule regarding direction of
induced e.m.f., correlates
(a) magnetic
flux, direction of current flow and resultant force
(b) magnetic
flux, direction of motion and the direction of e.m.f. induced
(c) magnetic
field strength, induced voltage and current
(d) magnetic
flux, direction of force and direction of motion of conductor
Ans: b
11. While applying Fleming's right-hand rule to And
the direction of induced e.m.f., the thumb points towards (a) direction of
induced e.m.f.
(b) direction
of flux
(c) direction
of motion of the conductor if forefinger points in the direction of
generatede.m.f.
(d) direction
of motion of conductor, if forefinger points along the lines of flux
Ans: d
12. The bearings used to support the rotor shafts are
generally
(a) ball
bearings
(b) bush
bearings
(c) magnetic
bearmgs
(d) needle
bearings
Ans: a
13. In D.C. generators, the cause of rapid brush wear may
be
(a) severe
sparking
(b) rough
commutator surface
(c) imperfect
contact
(d) any
of the above
Ans: d
14. In lap winding, the number of brushes is always
(a) double
the number of poles
(b) same
as the number of poles
(a) half
the number of poles
(b) two
Ans: b
15. For a D.C. generator when the number of poles and the
number of armature conductors is fixed, then which winding will give the higher
e.m.f. ?
(a) Lap
winding
(b) Wave
winding
(c) Either
of (a) and (b) above
(d) Depends
on other features of design
Ans: b
16. In a four-pole D.C. machine
(a) all
the four poles are north poles
(b) alternate
poles are north and south
(c) all
the four poles are south poles
(d) two
north poles follow two south poles
Ans: b
17. Copper brushes in D.C. machine are used
(a) where
low voltage and high currents are involved
(b) where
high voltage and small cur-rents are involved
(c) in
both of the above cases
(d) in
none of the above cases
Ans: a
18. A separately excited generator as compared to a
self-excited generator
(a) is
amenable to better voltage con-trol
(b) is
more stable
(c) has
exciting current independent of load current(d) has all above features
Ans: d
19. In case of D.C. machines, mechanical losses are
primary function of (a) current
(b) voltage
(c) speed
(d) none
of above
Ans: c
20. Iron losses in a D.C. machine are independent of
variations in
(a) speed
(b) load
(c) voltage
(d) speed
and voltage
Ans: b
21. In D.C. generators, current to the external circuit
from armature is given through
(a) commutator
(b) solid
connection
(c) slip
rings
(d) none
of above
Ans: a
23. Brushes of D.C. machines are made of
(a) carbon
(b) soft
copper
(c) hard
copper
(d) all
of above
Ans: a
24.
If B is the flux density, I the length of
conductor and v the velocity of conductor, theninduced e.m.f. is given by
(a)Blv
(b)Blv2
(c)Bl2v
(d)Bl2v2
Ans: a
25.
In case of a 4-pole D.C. generator provided with
a two layer lap winding with sixteen coils, the pole pitch will be
(a) 4
(b) 8
(c) 16
(d) 32
Ans: b
26. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast
iron
(d) carbon
Ans: d
27. The insulating material used between the commutator
segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating
varnish
Ans: c
28. In D.C. generators, the brushes on commutator remain in
contact with conductors which
(a)
lie under south pole
(b)
lie under north pole
(c)
lie under interpolar region
(d)
are farthest from the poles
Ans: c
29. If brushes of a D.C. generator are moved in order to
bring these brushes in magnetic neutral axis, there will be
(a)
demagnetisation only
(b)
cross magnetisation as well as magnetisation
(c)
crossmagnetisation as well as demagnetising
(d)
cross magnetisation only
Ans: c
30. Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising
(d) none
of aboveAns: a
31. D.C. generators are connected to the busbars or
disconnected from them only under the floating condition
(a) to
avoid sudden loading of the primemover
(b) to
avoid mechanicaljerk to the shaft
(c) to
avoid burning of switch contacts
(d) all
above
Ans: d
32. Eddy currents are induced in the pole shoes of a D.C.
machine due to
(a) oscillating
magnetic field
(b) pulsating
magnetic flux
(c) relative
rotation between field and armature
(d) all
above
Ans: c
33. In a D.C. machine, short-circuited field coil will
result in
(a)
odour of barning insulation
(b)
unbalanced magnetic pull producing vibrations
(c)
reduction of generated voltage for which
excitation has to be increased to maintain the voltage (d) all above Ans:
34. Equilizer rings are required in case armature is
(a) wave
wound
(b) lap
wound
(c) delta
wound
(d) duplex
wound
Ans: b
35. Welding generator will have
(a) lap
winding
(b) wave
winding
(c) delta
winding
(d) duplex
wave winding
Ans: a
36. In case of D.C. machine winding, number of commutator
segments is equal to
(a) number
of armature coils
(b) number
of armature coil sides
(c) number
of armature conductors
(d) number
of armature turns
Ans: a
37. For a D.C. machines laboratory following type of D.C.
supply will be suitable
(a)
rotary converter
(b)
mercury are rectifier
(c)
induction motor D.C. generator set
synchronous motor D.C. generator set
Ans: c
38. The function of pole shoes in the case of D.C.
machine is (a) to reduce the reluctance of the magnetic path
(b) to
spread out the flux to achieve uniform flux density
(c) to
support the field coil
(d) to
discharge all the above functions
Ans: d
39. In the case of lap winding resultant pitch is
(a) multiplication
of front and back pitches
(b) division
of front pitch by back pitch(c) sum of front and back pitches
(d) difference of front and back pitches Ans: d
40. A D.C. welding generator has
(a) lap
winding
(b) wave
moving
(c) duplex
winding
(d) any
of the above
Ans: a
41. Which of the following statement about D.C. generators
is false ?
(a)
Compensating winding in a D.C. machine helps in
commutation
(b)
In a D. C. generator interpoles winding is
connected in series with the armature winding
(c)
Back pitch and front pitch are both odd and
approximately equal to the pole pitch (d) Equilizing bus bars are used with
parallel running of D.C. shunt generators
Ans: d
42. The demagnetising component of armature reaction
in a D.C. generator (a) reduces generator e.m.f.
(b) increases
armature speed
(c) reduces
interpoles flux density
(d) results
in sparking trouble
Ans: a
43. Magnetic field in a D.C. generator is produced by
(a) electromagnets
(b) permanent
magnets
(c) both
(a) and (b)
(d) none
of the above
Ans: a
44. The number of brushes in a commutator depends on
(a)
speed of armature
(b)
type of winding
(c)
voltage
(d)
amount of current to be collected Ans: d
45. Compensating windings are used in D.C. generators
(a)
mainly to reduce the eddy currents by providing
local short-circuits
(b)
to provide path for the circulation of cooling
air
(c)
to neutralise the cross-magnetising effect of
the armature reaction
(d)
none of the above
Ans: c
46. Which of the following components of a D.C, generator
plays vital role for providing direct current of a D.C. generator ?
(a) Dummy
coils
(b) Commutator
(c) Eye
bolt
(d) Equilizer
rings
Ans: b
47. In a D.C. generator the ripples in the direct e.m.f.
generated are reduced by
(a)
using conductor of annealed copper
(b)
using commutator with large number of segments
(c)
using carbon brushes of superior quality
(d)
using equiliser rings
Ans: c
48. In D.C. generators, lap winding is used for
(a) high
voltage, high current
(b) low
voltage, high current
(c) high
voltage, low current
(d) low
voltage, low current
Ans: b
49. 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
(a) 2 :
3
(b) 3 :
1
(c) 3
: 2
(d)1 : 3 Ans: b
50. The voltage drop for which of the following types of
brush can be expected to be least ?
(a) Graphite
brushes
(b) Carbon
brushes
(c) Metal
graphite brushes
(d) None
of the above
Ans: c
51. 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
(a) E/2
(b) 2E
(c) slightly
less than E
(d) E
Ans: b
52. In a D.C. generator the actual flux distribution
depends upon
(a) size
of air gap
(b) shape
of the pole shoe
(c) clearance
between tips of the ad¬jacent pole shoes
(d) all
of the aboveAns:
53. The armature core of a D.C. generator is usually made
of
(a)
silicon steel
(b)
copper
(c)
non-ferrous material
(d)
cast-iron
Ans: a
9.63. Satisfactory commutation of D.C. machines requires
(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
Ans: d
54. Open circuited armature coil of a D.C. machine is
(a) identified
by the scarring of the commutator segment to which open circuited coil
isconnected
(b) indicated
by a spark completely around the commutator
(c) both
(a) and (b)
(d)none of the above
Ans: c
55. In a D.C. machine, fractional pitch winding is used
(a)
to increase the generated voltage
(b)
to reduce sparking
(c)
to save the copper because of shorter end
connections
(d) due to (b) and (c) above
Ans:
56. For the parallel operation of two or more D.C. compound
generators, we should ensure that
(a) voltage
of the incoming generator should be same as that of bus bar
(b) polarity
of incoming generator should be same as that of bus bar
(c) all
the series fields should be run in parallel by means of equilizer connection
(d) series
fields of all generators should be either on positive side or negative side of
thearmature
(e) all
conditions mentioned above should be satisfied
Ans: d
57. D.C. series generator is used
(a)
to supply traction load
(b)
to supply industrial load at constant voltage
(c)
voltage at the toad end of the feeder
(d)
for none of the above purpose
Ans: c
58. Following D.C. generator will be in a position to
build up without any residual magnetism in the poles
(a) series generator
(b)
shunt generator
(c)
compound generator
(d)
self-excited generator
Ans: d
59. Interpole flux should be sufficient to
(a) neutralise
the commutating self induced e.m.f.
(b) neutralise
the armature reaction flux
(c) neutralise
both the armature reaction flux as well as commutating e.m.f. induced in
thecoil
(d) perform
none of the above functions
Ans: c
60. D.C. generator generally preferred for charging
automobile batteries is
(a)
series generator
(b) shunt
generator
(c) long shunt compound generator
(a)
any of'the above
Ans: c
61. In a D.C. generator the number of mechanical degrees
and electrical degrees will be the
same when
(a) r.p.m.
is more than 300
(b) r.p.m.
is less than 300
(c) number
of poles is 4
(d) number
of poles is 2
Ans: d
62. Permeance is the reciprocal of
(a) flux
density
(b) reluctance
(c) ampere-turns
(d) resistance
Ans: b
63. In D.C. generators the polarity of the interpoles
(a) is
the same as that of the main pole ahead
(b) is
the same as that of the immediately preceding pole
(c) is
opposite to that of the main pole ahead
(d) is
neutral as these poles do not play part in generating e.m.f.Ans: a
64. The e.m.f. generated in a D.C. generator is directly
proportional to
(a)
flux/pole
(b)
speed of armature
(c)
number of poles
(d)
all of the above
Ans: b
65. In a D.C. generator the magnetic neutral axis coincides
with the geometrical neutral axis, when
(a) there
is no load on|he generator
(b) the
generator runs on full load
(c) the
generator runs on overload
(d) the
generator runs on designed speedAns: a
66. 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
(a) interpoles
(b) dummy
coils
(c) compensating
winding
(d) shifting
of axis of brushes
Ans: b
67. In D.C. generators on no-load, the air gap flux
distribution in space is
(a) sinusoidal
(b) triangular
(c) pulsating
(d) flat
topped
Ans: d
68. 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
(a) 150
V
(b) 175
V
(c) 240
V
(d) 290
V
Ans: c
69. The purpose of providing dummy coils in a generator is
(a) to
reduce eddy current losses
(b) to
enhance flux density
(c) to
amplify voltage
(d) to
provide mechanical balance for the rotor
Ans: d
Ans: d
70. In a shunt generator the voltage build up is generally
restricted by
(a) speed
limitation
(b) armature
heating
(c) insulation
restrictions
(d) saturation
of ironAns:
71. If a D.C. generator fails to build up the
probable cause could not be
(a) imperfect brush contact
(a) imperfect brush contact
(b) field
resistance less than the critical resistance
(c) no
residual magnetism in the generator
(d) faulty
shunt connections tending to reduce the residual magnetism Ans: b
72. Flashing the field of D.C. generator means
(a) neutralising
residual magnetism
(b) creating residual magnetism by a D.C. source
(c) making
the magnetic losses of forces parallel
(d) increasing
flux density by adding extra turns of windings on poles
Ans: b
73. The e.m.f. induced in the armature of a shunt
generator is 600 V. The armature resistance is 0.1 ohm. If the armature current
is 200 A, the terminal voltage will be (a) 640 V
(b) 620
V
(c) 600
V
(d) 580
V
Ans: d
74. In a D.C. generator the critical resistance refers to
the resistance of
(a) brushes
(b) field
(c) armature
(d) load
Ans: b
75. To achieve sparkless commutation brushes of a D.C.
generator are rockedm ahead so as to bring them
(a) just
ahead of magnetic neutral axis
(b) in
magnetic neutral axis
(c) just
behind the magnetic neutral axis
Ans: a
76. Armature coil is short circuited by brushes when it
lies
(a)
along neutral axis
(b)
along field axis
(c)
in any of the above positions
(d)
in none of the above positions
Ans: a
77. A cumulatively compounded long shunt generator when
operating as a motor would be (a) cumulatively compounded long shunt
(b) differentially
compounded long shunt
(c) cumulatively
compounded short shunt
(d) differentially
compounded short shunt
Ans: b
78. To avoid formation of grooves in the commutator of a
D.C. machine
(a) the
brushes of opposite polarity should track each other
(b) the
brushes of same polarity should track each other
(c) brush position has no effect on the commutator
groovingAns: a
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