Transformer: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY
& Others competitive]
81. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is
(a) approximately equal to one
(b) less than one
(c) great than one
(d) none of the above
Ans: a
82. Minimum voltage regulation occurs when the power factor of the load is
(a) unity
(b) lagging
(c) leading
(d) zero
Ans: c
83. In a step-down transformer, there is a change of 15 A in the load
current. This results in change of supply current of
(a) less than 15 A
(b) more than 15 A
(c) 15 A
(d) none of the above
Ans: a
84. The efficiencies of transformers compared with that of electric motors of the same power are
(a) about the same
(b) much smaller
(c) much higher
(d) somewhat smaller
Ans: c
85. The noise produced by a transformer is termed as
(a) zoom
(b) hum
(c) ringing
(d) buzz
Ans: b
86. Which of the following loss in a transformer is zero even at full load ?
(a) Core loss
(b) Friction loss
(c) Eddy current loss
(d) Hysteresis loss
Ans: b
87. Which of the following is the most likely source of harmonics in a transformer ?
(a) poor insulation
(b) Overload
(c) loose connections
(d) Core saturation
Ans: d
88. If a transformer is continuously operated the maximum temperature rise will occur in…
(a) core
(b) windings
(c) tank
(d) any of the above
Ans: b
89. The hum in a transformer is mainly attributed to
(a) load changes
(b) oil in the transformer
(c) magnetostriction
d. mechanical vibrations
Ans: c
90. The maximum load that a power transformer can carry is limited by its
(a) temperature rise
(b) dielectric strength of oil
(c) voltage ratio
(d) copper loss
Ans: c
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