DC Generator Electrical Engineering Multiple Choice Questions and Answers(PDF)

DC Generator Electrical Engineering Multiple Choice Questions and Answers(PDF)


1.The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: d

2.The insulating material used between the commutator segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating varnish
Ans: c

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
Ans: c

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
Ans: c

5.Armature reaction of an unsaturated D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising
(d) none of above
Ans: a

6.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

7.Iron losses in a D.C. machine are independent of variations in
(a) speed
(b) load
(c) voltage
(d) speed and voltage
Ans: b

8.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

9.Brushes of D.C. machines are made of
(a) carbon
(b) soft copper
(c) hard copper
(d) all of above
Ans: a

10.If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by
(a) Blv
(b) Blv2
(c) Bl2v
(d) Bl2v2
Ans: a

11.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

12.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

13.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

14.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

15.A separately excited generator as compared to a self-excited generator
(a) is amenable to better voltage control
(b) is more stable
(c) has exciting current independent of load current
(d) has all above features
Ans: d

16.In case of D.C. machines, mechanical losses are primary function of
(a) current
(b) voltage
(c) speed
(d) none of above
Ans: c

17.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

18.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 generated e.m.f.
(d) direction of motion of conductor, if forefinger points along the lines of flux
Ans: d

19.The bearings used to support the rotor shafts are generally
(a) ball bearings
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings
Ans: a

20.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

21.In lap winding, the number of brushes is always
(a) double the number of poles
(b) same as the number of poles
(c) half the number of poles
(d) two
Ans: b

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