DC Generator
.
- 1.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
- 2.The insulating material used between the commutator segments is normally
- A.
Graphite
- B.
Paper
- C.
Mica
- D.
Insulating varnish
- 3.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
- 4.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.
Equalizing bus bars are used with parallel running of D.C. shunt generators
- 5.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 equalizer rings
- 6.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
- 7.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
- 8.The following constitute short-circuit in the armature winding.
- A.
Insulation failure between two commutator bars
- B.
Insulation failure between two turns of a coil
- C.
Two of more turns of the same coil getting grounded
- D.
All of the above
- 9.In a D.C. machine stray loss is the sum of
- A.
Total copper loss and mechanical loss
- B.
Armature copper loss and iron loss
- C.
Shunt field copper loss and mechanical loss
- D.
Iron loss and mechanical loss
- 10.Which of the following generator will have negligible terminal voltage while running on no-load?
- A.
Series generator
- B.
Shunt generator
- C.
Compound generator
- D.
Separately excited generator
- 11.In a separately excited generator supplying rated load the armature reaction:
- A.
Is always present
- B.
Is always absent
- C.
May be sometimes present
- D.
None of the above
- 12.. When two D.C. series generators are running in parallel, an equalizer bar is used
- A.
To increase the speed and hence generated e.m.f.
- B.
To increase the series flux
- C.
So that two similar machines will pass approximately equal currents to the load
- D.
Efect of armature reaction To reduce the combined of both machines
- 13.A D.C. generator works on the principle of
- A.
Lenz's law
- B.
Ohm's law
- C.
Faraday's law of electromagnetic induction
- D.
None of the above
- 14.Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be
- A.
270 V
- B.
267.5 V
- C.
265 V
- D.
257.4 V
- 15.In a D.C. generator the critical resistance can be increased by
- A.
Increasing its field resistance
- B.
Decreasing its field resistance
- C.
Increasing its speed
- D.
Decreasing its speed
- 16.For both lap and wave windings, there are as many commutator bars as the number of
- A.
Slots
- B.
Armature conductors
- C.
Winding elements
- D.
Poles
- 17.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
- 18.A D.C. welding generator has
- A.
Lap winding
- B.
Wave moving
- C.
Duplex winding
- D.
Any of the above
- 19.DC shunt generator has terminal voltage versus load current characteristic which is
- A.
Constant
- B.
Slightly drooping
- C.
Slightly rising
- D.
Highly drooping
- 20.The material for commutator brushes is generally
- A.
mica
- B.
Copper
- C.
Cast iron
- D.
carbon
- 21.The insulating material used between the commutator segments is normally
- A.
graphite
- B.
Paper
- C.
Mica
- D.
insulating varnish
- 22.3.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
- 23.4.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 mag¬netisation
- C.
Crossmagnetisation as well as demagnetising
- D.
cross magnetisation only
- 24.Armature reaction of an unsaturated D.C. machine is
- A.
crossmagnetising
- B.
Demagnetising
- C.
Magnetising
- D.
none of above
- 25.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
Questions: 8 | Attempts: 11674 | Last updated: Feb 10, 2021
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