MCQ on DC grnerator 81-100

81. 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

82. 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

83. 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

84. 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) damagnetising the center of all poles
(d) magnetising the center of all poles

85. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
(a) Series field
(b) Compensating field
(c) Inter pole field✔
(d) Shunt field

86. 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

87. The critical resistance of the D.C. generator is the resistance of
(a) field✔
(b) brushes
(c) armature
(d) load

88. When two D.C. series generators are running in parallel, an equilizer 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

89. 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

90. 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

91. 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✔

92. 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

93. 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

94. 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

95. 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

96. 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

97. 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

98. 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
ohmic drop – armature reaction
(d) magnetisation characteristic = external characteristic
99. With a D.C. generator which of the following regulation is preferred ?
(a) 100% regulation
(b) infinite regulation
(c) 50% regulation
(d) 1% regulation✔
100. 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