Transformer: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY
& Others competitive]
91. The efficiency of a transformer, under heavy loads, is comparatively low because
(a) copper loss becomes high in proportion to the output
(b) iron loss is increased considerably
(c) voltage drop both in primary and secondary becomes large
(d) secondary output is much less as compared to primary input
Ans: a
92. An open-circuit test on a transformer is conducted primarily to measure
(a) insulation resistance
(b) copper loss
(c) core loss
(d) total loss
Ans: c
93. A no-load test is performed on a transformer to determine
(a) core loss
(b) efficiency
(c) magnetising current
(d) magnetising current and loss
Ans: d
94. The voltage transformation ratio of a transformer is equal to the ratio of
(a) primary turns to secondary turns
(b) secondary current to primary current
(c) secondary induced e.m.f. to primary induced e.m.f.
(d) secondary terminal voltage to primary applied voltage
Ans: c
95. Part of the transformer which is most subject to damage from overheating is
(a) iron core
(b) copper winding
(c) winding insulation
(d) frame or case
Ans: c
96.For a transformer, operating at constant load current, maximum efficiency will occur at …
(a) 0.8 leading power factor
(b) 0.8 lagging power factor
(c) zero power factor
(d) unity power factor
Ans: d
97. Which of the following protection is normally not provided on small distribution transformers?
(a) Over fluxing protection
(b) Buchholz relay
(c) Overcurrent protection
(d) All of the above
Ans: b
98.Which of the following acts as a protection against high voltage surges due to lightning and switching?
(a) Horn gaps
(b) Thermal overload relays
(c) Breather
(d) Conservator
Ans: a
99.The efficiency of two identical transformers under load conditions can be determined by
(a) short-circuit test
(b) back-to-back test
(c) open circuit test
(d) any of the above
Ans: b
100.Which of the following insulating materials can withstand the highest temperature safely?
(a) Cellulose
(b) Asbestos
(c) Mica
(d) Glass fibre
Ans: c
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