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MCQ of Electrical Machines page-5

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81. Swinburne’s test is applied to

Those machines in which the flux is practically constant.
(b) Those machines in which flux is varying.
(c) Those machines in which flux is proportional to armature current.
(d) None of the above.

82. The retardation test is applicable to shunt motors and generators and is used to find

the stray losses.
(b) the copper losses.
(c) the eddy current losses.
(d) the friction losses.

83. In the load Field’s test the two similar d.c. series machines are mechanically coupled. The output of the generator is fed to the resistance and hence is called regenerative test.

(a) true.

84. The use of higher flux density in the transformer design

Reduce the weight per KVA.
(b) Increases weight per KVA.
(c) Has no relation with the weight of the transformer.
(d) Increases the weight per KW.

85. The oil used in the small transformer provides

(a) cooling only.
(b) insulation only.
insulation and cooling both .
(d) lubrication only.

86. The oil used in the transformer should be free from moisture because

(a) Moisture will reduce the density of the oil which is slightly undesirable.
Moisture will reduce the dielectric strength of the oil and hence insulation is weakened.
(c) Moisture will reduce the lubricating property of the oil.
(d) Moisture will develop rust.

87. ASKARELS is the trade name given to

(a) Natural mineral oil used in the transformer.
Synthetic insulating fluids used in the transformer.
(c) Insulating materials for transformers.
(d) Insulating materials for motors and generators.

88. The conservator is used in the transformer

(a) To supply oil to transformer whenever needed.
To protect transformer from damage when oil expands due to rise in temperature. It stores the increasing volume of the oil.
(c) To provide the fresh air cool down the oil.
(d) To store ware for transformer cooling.

89. Which of the following statement is correct ?

(a) Induction coil works on A.C.
(b) Transformer is used to step up the potential of d.c.
The output current of induction coil is nearly unindirectional.
(d) In the step down transformers, the transformation ratio is always greater than one.

90. The induced e.m.f. in the transformer secondary will depend on

(a) Frequently of the supply only.
(b) Number of turns in secondary only.
(c) Maximum flux in core and frequency only.
Frequency, flux and number of turns in the secondary.

91. No load primary input is practically equal to the iron loss in the transformer because primary current is very small.

(b) false.

92. If R2 is the resistance of secondary winding of the transformer and K is transformation ratio than the equivalent secondary resistance referred to primary will be

(a) R2/K2.
(b) R2/2/K2.
(d) R2/√K.

93. A transformer with magnetic leakage is equivalent to an ideal transformer with inductive coils connected in both primary and secondary.

b) false.

94. The leakage flux links both of the winding of transformer and hence contributes to the transfer of energy from primary of the transfer of energy from primary of the transformer to secondary.

(a) true.

95. The vector diagram of the three phase transformer is equivalent to the vector diagram of three phase induction motor with short circuited secondary. If the secondary of the transformer is wounded on a shaft and treated as rotor and primary is fed three phase supply, the rotor will run and behaves like an induction motor.

(a) true.

96.The short circuit test in the transformer is used to determine

(a) The iron loss at any load.
The copper loss at any load or at full load.
(b) The hysteresis loss.
(c) The eddy current loss.

97. If the power factor is leading the regulating of a good transformer will be higher than when it is lagging.

(a) true.

98. A good transformer must have regulation as high as possible.

(a) true.

99. The percentage resistance, reactance and impedance have the same whether referred to primary or secondary of the transformer.

b) false.

100. Which of the following electrical machines has the highest efficiency ?

(a) D.C. shunt motor.
(c) Induction motor.
(d) Synchronous motor.

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