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MCQ of D.C generators page-9

81. The critical resistance of a dc generator can be increased by

a) Increasing the field current
b) Increasing its speed
c) Increasing the armature resistance
d) All of these

Ans: (b)

82. A series dc generator does not build up voltage. The reason is

a) Short-circuited terminals
b) Reversed terminal of field winding
c) Reversed terminal of armature winding
d) Disconnected load

Ans: (a)

83. D.C. generator have normally an over-all efficiency of the order of

a) 85 – 95 %
b) 75 – 85 %
c) 65 – 75 %
d) 55 – 65 %

Ans: (a)

84. Difference between interpoles and compensation winding is that

a) Interpoles additionally supply mmf for counter acting the reactance voltage induced in the coil under going commutalion
b) Action of interpoles is localized
c) Interpoles also helps in equalizing distribution of current in brushes
d) (Both (a) and b)

Ans: (d)

85. Sparking at the brushes in the d.c. generator is due to

a) High resistance of the brushes
b) Reactance voltage
c) Armature reaction
d) Quick reversal of current in the coil

Ans: (b)

86. Armature magnetic field has the effect that it

a) Cross magnetizes it
b) Demagnetizes it
c) Strengthens the main flux
d) Both (a) and (b)

Ans: (d)

87. Generator is called flat compounded if

a) Rated voltage is less than no load voltage
b) Series field AT produces same voltage at rated and no load
c) Series field AT produces rated voltage grated then and no load
d) Series field AT produces rated voltage less than no load

Ans: (b)

88. Commutation process can be improved by

a) Increasing the resistance of the brushes
b) Reducing the number of turns in armature coil
c) Neutralizing reactance voltage
d) All of these

Ans: (d)

89. When two d.c. series generators are running in parallel, equalizer bar is used

a) To increase the series flux
b) Because both will pass equal currents to the load
c) To reduce combined effect of armature reaction of both
d) To increase speed and hence generated emf.

Ans: (b)

90. In d.c. generator, if field winding attains critical resistance then it will

a) Not develop voltage at all
b) Generate maximum power
c) Generate maximum voltage
d) None of these

Ans: (a)

91.For paralleling two d.c. generators, their

a) Polarities must be same
b) Phase sequence must be same
c) Polarities and voltage must be same
d) Both (b) and (c)

Ans: (d)

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