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SymbolsTransformerRelayPower-SystemBasic-electricalACSR-ConductorCircuit-BreakerInterview-questions-of-Basic-ElectricityInterview-questions-of-transformerInsulatorCurrent-TransformerMCQMCQ-powersystemThermal-power-stationInterview-questions-of-Power-SystemPower-ElectronicsInterview-questions-of-Underground-CableInterview-questions-of-IlluminationIlluminationMCQ-of-ElectronicsMCQ-of-Basic-ElectricalMCQ-of-Transformers MCQ-of-D.C-motor MCQ-of-D.C-generators

MCQ of D.C generators page-4

31. Equalizer rings in lap wound armatures are used to

a) Get sparking commutation
b) Avoid unequal current distribution at brushes
c) Both (a) and (b)
d) To neutralize the armature reaction

Ans: (c)

32. In a dc generator, sparking at brushes results due to

a) Winding distribution
b) Armature reactance
c) High constant resistance of the brushes
d) Reactance voltage in coil undergoing commutation
Ans: (d)

33. The maximum number of brushes which may be used in an electrical machine is equal to

a) Number of poles in the machine
b) 4
c) 2
d) Either (a) or (c)
Ans: (d)

34. The commutator pitch of a quadruplex lap winding in a dc generator is

a) 1
b) 2
c) 4
d) 8

Ans: (c)

35. Commutator of a dc machine acts as a

a) Fullwave rectifier
b) Halfwave rectifier
c) Inverter
d) Controlled rectifier

Ans: (a)

36. Carbon brushes are used in dc machines to

a) Brush off carbon deposits in the commutator
b) Provide a path for flow of current
c) Prevent overheating of armature winding
d) Prevent sparking during commu-tation

Ans: (b)

37. Brushes for commutators for 220 V dc generator are generally made of

a) Copper
b) Carbon copper
c) Electrographite
d) Graphite copper

Ans: (c)

38. In a dc machine commutator, pre-ssure on the brush is usually

a) Less than 1 kg/cm2
b) About 3 kg/cm2
c) About 5 kg/cm2
d) About 10 kg/cm2

Ans: (a)

39. In a dc generator, rapid brush wear may be due to

a) Rough commutator surface
b) Severe sparking
c) Imperfect contact with commutator
d) Any of these

Ans: (d)

40. Generators are often run in parallel because it

a) Keeps stability of supply
b) Gives facility of repair which results in fewer breakdown
c) Gives facility of an additional unit to be installed as and when required
d) All of these

Ans: (d)

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