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Top 100 MCQ D.C Generator

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60. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f.
in the coil is neutralised by all of the following except..

(a) interpoles

(b) dummy coils

(c) compensating winding

(d) shifting of axis of brushes

Ans: b

 61. In D.C. generators on no-load, the air gap flux distribution in space is

(a) sinusoidal

(b) triangular

(c) pulsating

(d) flat topped

Ans: d

 62. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If thespeed increases to 1200 r.p.m., the generatede.m.f. will be nearly

(a) 150 V

(b) 175 V

(c) 240 V

(d) 290 V

Ans: c

 63. The purpose of providing dummy coils in a generator is

(a) to reduce eddy current losses

(b) to enhance flux density

(c) to amplify voltage

(d) to provide mechanical balance for the rotor

Ans: d

 64. If a D.C. generator fails to build up the probable cause could not be

(a) imperfect brush contact

(b) field resistance less than the critical resistance

(c) no residual magnetism in the generator

(d) faulty shunt connections tending to reduce the residual
magnetism

Ans: b

 65. Flashing the field of D.C. generator means

(a) neutralising residual magnetism

(b) creating residual magnetism by a D.C. source

(c) making the magnetic losses of forces parallel

(d) increasing flux density by adding extra turns of windings on
poles

Ans: b

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66. The e.m.f. induced in the armature of a shunt generator is 600 V. The armatureresistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be

(a) 640 V

(b) 620 V

(c) 600 V

(d) 580 V

Ans: d

 67. In a D.C. generator the critical resistance refers to the resistance of

(a) brushes

(b) field

(c) armature

(d) load

Ans: b

 68. Armature coil is short circuited by brushes when it lies

(a) along neutral axis

(b) along field axis

(c) in any of the above positions

(d) in none of the above positions

Ans: a

 69. A cumulatively compounded long shunt generator when operating as a motor would be

(a) cumulatively compounded long shunt

(b) differentially compounded long shunt

(c) cumulatively compounded short shunt

(d) differentially compounded short shunt

Ans: b

70. To avoid formation of grooves in the commutator of a D.C. machine

(a) the brushes of opposite polarity should track each other

(b) the brushes of same polarity should track each other

(c) brush position has no effect on the commutator grooving

Ans: a

If You Want More Questions Then Click Below

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71. The following constitute short-circuit in the armature winding.

(a) Insulation failure between two commutator bars

(6) Insulation failure between two turns of a coil

(c) Two of more turns of the same coil getting grounded

(d) All of the above

Ans: d

 72. The rapid wear of brushes takes place due to

(a) abrasion from dust

(b) excessive spring pressure

(c) rough commutator bars

(d) all of the above factors

Ans: d

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73. Number of tapings for each equalizer ring is equal to…

(a) number of pole pairs

(b) number of poles

(c) number of parallel paths

(d) number of commutator segments

Ans: a

 74. A 220 V D.C. generator is run at full speed without any
excitation. The open circuit voltage will be

(a) zero

(b) about 2 V

(c) about 50 V

(d) 220 V

Ans: b

 

75. In a
separately excited generator supplying rated load the armature reaction,

(a) is always present

(b) is always absent

(c) may be sometimes present

(d) none of the above

Ans: a

 76. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be

(a) zero

(b) small

(c) the same as rated voltage

(d) high

Ans: a

 77. Armature reaction in a generator results in

(a) demagnetisation of leading pole tip and magnetisation of
trailing pole tip

(b) demagnetisation of trailing pole tip and magnetisation of
leading pole tip

(c) demagnetising the centre of all poles

(d) magnetising the centre of all poles

Ans: a

 78. Wave winding is composed of

(a) any even number of conductors

(b) any odd number of conductors

(c) that even number which is exact multiple of poles + 2

(d) that even number which is exact multiple of poles

Ans: c

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79. The critical resistance of the D.C. generator is the resistance of

(a) field

(b) brushes

(c) armature

(d) load

Ans: a

80. When two D.C. series generators are running in parallel, an equalizer bar is used

(a) to increase the speed and hence generated e.m.f.

(b) to increase the series flux

(c) so that two similar machines will pass approximately equal
currents to the load

(d) to reduce the combined effect of ar-mature reaction of both
machines

Ans: c

81. Which of the following generating machine will offer constant voltage on all loads?

(a) Self-excited generator

(b) Separately excited generator

(c) Level compounded generator.

(d) All of the above

Ans: c

 82. Which of the following generators will be preferred if they are required to be run in parallel?

(a) Shunt generators

(b) Series generators

(c) Compound generators

(d) None of the above

Ans: a

83. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons?

(a) The direction of that generator is reversed

(b) The speed of that generator is increased

(c) The field of that generator is weakened

(d) That generator takes large share of loads   

 

55

Ans: b

84. A D.C. generator works on the principle of 

(a) Lenz’s law

(b) Ohm’s law

(c) Faraday’s law of electromagnetic induction

(d) none of the above

Ans: c

 85. A series generator can self-excite

(a) only if the load current is zero

(b) only if the load current is not zero

(c) irrespective of the value of load current

(d) none of the above

Ans: b

 86. A shunt generator can self-excite

(a) only if the resistance of the field circuit is less than
critical value

(b) only if the resistance of the field circuit is greater than
critical value

(c) irrespective of the value of the resistance in the field
circuit

Ans: a

 87. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be

(a) 150 V

(b) less than 150 V

(c) greater than 150 V

(d) none of the above

Ans: c

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88. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage

(a) will be less than 250 V

(b) will always be 250 V

(c) may be greater or less than 250 V

(d) none of the above

Ans: c

 89. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be?

(a) 270 V

(b) 267.5 V

(c) 265 V

(d) 257.4 V

Ans: b

 90. The essential condition for parallel operation of two D.C. generators is that they have

(a) same kW rating

(b) the same operation r.p.m.

(c) the same drooping voltage characteristics

(d) same percentage regulation

Ans: c

 91. When two D.C. generators are running in parallel an equalizer bar is used

(a) to increase the series flux

(b) to increase the generated e.m.f.

(c) to reduce the combined effect of armature reaction of both
the machines

(d) so that the two identical machines will pass approximately
equal currents to the load

Ans: d

 

92. With a D.C. generator which of the following regulation is preferred?

(a) 100% regulation

(b) infinite regulation

(c) 50% regulation

(d) 1% regulation

Ans: d

 

93.Which generator would you prefer for feeding long D.C. transmission lines?

(a) Series generator

(b) Shunt generator

(c) Over compound generator

(d) Flat compound generator

Ans: c

 

94. In a D.C. generator the critical resistance can be increased by

(a) increasing its field resistance

(b) decreasing its field resistance

(c) increasing its speed

(d) decreasing its speed

Ans: c

 

96. The number of armature parallel paths in a two-pole D.C. generator having duplex
lap winding is

(a) 2

(b) 4

(c) 6

(d) 8

Ans: b

 

97. The series field of a short-shunt D.C. generator is excited by

(a) external current

(b) armature current

(c) shunt current

(d) load current

Ans: d

 

98. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately

(a) 40 percent

(b) 25 percent

(c) 10 percent

(d) 5 percent

Ans: d

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99. Shunt generators are most suited for stable parallel operation because of them

(a) rising voltage characteristics

(b) identical voltage characteristics

(c) drooping voltage characteristics

(d) linear voltage characteristics

Ans: c

 

100. The main factor which leads to unstable parallel operation of flat and over
compounded generators is

(a) their rising voltage characteristics

(b) unequal number of turns in their series field windings

(c) unequal speed regulation of their prime movers

(d) unequal series field resistances

Ans: b


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