Objective Type Question or MCQ of D.C Generators page-6

51. When a dc generator is operating at constant speed, variable load, which loss is likely to vary significantly

A) Copper loss
B) Eddy current loss
C) Bearing friction loss
D) Windage loss.

Ans : (A)

52. In a dc generator the polarity of interpole is

A) Same as the polarity of the main pole that follows in the direction of rotation
B) Same as the polarity of the main pole that precedes in the direction of rotation
C) Always S
D) Always N.

Ans : (B)

53. The commutator in a dc machine can converts

A) dc to ac
B) ac to dc
C) both (A) and (B)
D) none of these.

Ans : (C)

54. Hysteresis loss in a dc shunt generator

A) depends only on the lamination thickness
B) varies as 1.6 power flux density
C) varies as the inverse of flux density
D) can be minimized by laminating the armature.

Ans : (B)

55. In a dc generator if field winding attains the critical resistance

A) the voltage generated will be zero
B) field winding will burn
C) machine will generate maximum power
D) machine will generate maximum voltage.

Ans : (A)

56. If A be the commercial efficiency, B be the electrical efficiency and C be the mechanical efficiency of a dc generator then which of the following relations is valid ?

A) A = B x C
B) C = A + B
C) B = A x C
D) C = A x B.

Ans : (A)

57. Among the series and shunt generators, which generator has the better regulation

A) Shunt generator
B) Series generator
C) Both have identical regulation.

Ans : (A)

58. The armature reaction of an unsaturated dc machine is

A) Cross-magnetizing
B) Demagnetizing
C) Magnetizing
D) Non-magnetizing.

Ans : (A)

59. In a generator, the winding loss is proportional to

A) flux density
B) square of armature speed
C) square of the supply current
D) supply voltage.

Ans : (B)

60. When field resistance of a dc shunt generator is increased beyond its critical value, the generator

A) power output may exceed the rated power
B) winding may burn out
C) will start’s ‘hunting’
D) will not build up.

Ans : (D)

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