MCQ on DC generator 41-60

41. 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

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

43. 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

44. 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

45. The material for commutator brushes is generally
(a) mica
(b) copper
(c) cast iron
(d) carbon✔

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

47. 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

48. 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

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

50. 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✔

51. 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

52. 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✔

53. Equilizer rings are required in case armature is
(a) wave wound
(b) lap wound✔
(c) delta wound
(d) duplex wound

54. Welding generator will have
(a) lap winding✔
(b) wave winding
(c) delta winding
(d) duplex wave winding

55. 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

56. 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✔
(d) synchronous motor D.C. generator set

57. The function of pole shoes in the case of D.C. machine is
(a) to reduce the reluctance of the mag¬netic 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✔

58. 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✔

59. A D.C. welding generator has
(a) lap winding✔
(b) wave moving
(c) duplex winding
(d) any of the above

60. 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