Basic Electrical Engineering MCQ-14

Basic Electrical Engineering MCQ-14

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