BASICS OF TRANSFORMER

MCQS ON TRANSFORMER

   
100. N atural air coo ling is generally restricted for transformers up to
(a) 1.5 MVA
(b) 5 MVA
(c) 15 MVA
(d) 50 MVA
Ans: a
101. A shell-type transformer has
(a) high eddy current losses
(b) reduced magnetic leakage
(c) negligibly hysteresis losses
(d) none of the above
Ans: b
102. A transformer can have regulation closer to zero
(a) on full-load
(b) on overload
(c) on leading power factor
(d) on zero power factor
Ans: c
103. A transformer transforms
(a) voltage
(b) current
(c) current and voltage
(d) power
Ans: d
104. Which of the following is not the standard voltage for power supply in India ?
(a) llkV
(b) 33kV
(c) 66 kV
(d) 122 kV
Ans: d

105. Reduction in core losses and increase in permeability are obtained with transformer
employing
(a) core built-up of laminations of cold rolled grain oriented steel
(b) core built-up of laminations of hot rolled sheet
(c) either of the above
(d) none of the above
Ans: a
106. In a power or distribution transformer about 10 per cent end turns are heavily
insulated
(a) to withstand the high voltage drop due to line surge produced by the shunting
capacitance of the end turns
(b) to absorb the line surge voltage and save the winding of transformer from damage
(c) to reflect the line surge and save the winding of a transformer from damage
(d) none of the above
Ans: a
107. For given applied voltage, with the increase in frequency of the applied voltage
(a) eddy current loss will decrease
(b) eddy current loss will increase
(c) eddy current loss will remain unchanged
(d) none of the above
Ans: c
108. Losses which occur in rotating electric machines and do not occur in trans formers
are
(a) friction and windage losses
(b) magnetic losses
(c) hysteresis and eddy current losses
(d) copper losses
Ans: a
109. In a given transformer for a given applied voltage, losses which remain constant
irrespective of load changes are
(a) hysteresis and eddy current losses
(b) friction and windage losses
(c) copper losses
(d) none of the above
Ans: a
110. Which of the following statements regarding an idel single-phase transformer having
a turn ratio of 1 : 2 and
drawing a current of 10 A from 200 V A.C. supply is incorrect ?
(a) Its secondary current is 5 A
(b) Its secondary voltage is 400 V
(c) Its rating is 2 kVA
(d) Its secondary current is 20 A
(e) It is a step-up transformer
Ans: d
111 The secondary of a current transformer is always short-circuited under operating
conditions because it
(a) avoids core saturation and high voltage induction
(b) is safe to human beings
(c) protects the primary circuit
(d) none of the above
Ans: a
112. In a transformer the resistance between its primary and secondary should be
(a) zero
(b) 10 Q
(c) 1000 Q
(d) infinity
Ans: d
113. A good voltage regulation of a transformer means
(a) output voltage fluctuation from no load to full load is least
(b) output voltage fluctuation with power factor is least
(c) difference between primary and secondary voltage is least
(d) difference between primary and secondary voltage is maximum
Ans: a
114. 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
115. Which of the following protection is normally not provided on small distribution
transformers ?
(a) Overfluxing protection
(b) Buchholz relay
(c) Overcurrent protection
(d) All of the above
Ans: b
116. 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
117. 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
118. Which of the following insulating materials can withstand the highest temperature
safely ?
(a) Cellulose
(b) Asbestos
(c) Mica
(d) Glass fibre
Ans: c
119. Which of the following parts of a transformer is visible from outside ?

(a) Bushings
(b) Core
(c) Primary winding
(d) Secondary winding
Ans: a
120. The noise produced by a transformer is termed as
(a) zoom
(b) hum
(c) ringing
(d) buzz
Ans: b
121. 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
122. 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
123. 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
124. The hum in a transformer is mainly attributed to
(a) load changes
(b) oil in the transformer

(c) magnetostriction
(d) mechanical vibrations
Ans: c
125. 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
126. 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
127. An open-circuit test on a transformer is conducted primarily to measure
(a) insulation resistance
(b) copper loss
(c) core loss
(d) total loss
(e) efficiency
(f) none of the above
Ans: c
128. A no-load test is performed on a transformer to determine
(a) core loss
(b) copper loss
(c) efficiency
(d) magnetising current
(e) magnetising current and loss
Ans: e
129. 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
130. 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
(e) transformer tank
Ans: c