Most Important Transformer MCQ (50 MCQ)
8) When a 6 V battery is connected across the
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primary of a transformer with a turns ratio of 8,
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the secondary voltage is
A. 48v
1) Oil is provided in an oil filled transformer for
B. 6v
A. Insulation
C. 8v
B. cooling
D. 0
C. both cooling and insulation.
9) The main purpose of performing open circuit
D. Lubrication
test in a transformer is to measure its–
2) The basic function of transformer is to change?
A. core loss
A. the level voltage
B. copper loss
B. the level frequency
C. insulation resistance
C. power factor level
D. total loss
D. power level
3) Transformer is used for—
10) When a 400Hz transformer is operated at 50
Hz, its KVA ratings is–
A. to step down voltage
A. unaffected
B. to step up and step down primary voltage
B. reduced to 1/8
C. to step up voltage
C. Increased by 8 times
D. None of above
D. None of above
4) Breather is provided in a transformer to
A. Absorb moisture of air during breathing.
11) What is the condition for maximum efficiency
of a transformer?
B. filter of transformer oil
A. when copper loss = core loss
C. provide cold air in transformer
B. When transformer run by unity power
D. None of above
5) The leakage flux in a transformer depends upon
A. the load current.
B. the frequency.
factor
C. when copper loss = eddy current loss
D. when copper loss = hysteresis loss
12) Lamination of transformer core is made of
C. the mutual flux.
A. cast iron
D. the applied voltage.
B. silicon steel.
6) What kVA rating is required for a transformer
C. cast steel
that must handle a maximum load current of 8 A
D. aluminium
with a secondary voltage of 2 kV?
A. 32kv
13) Which of the following is minimized by
laminating the core of a transformer?
B. 16kv
A. Eddy current loss.
C. 4kv
B. Hysteresis loss.
D. 8kV
C. Copper loss
7) The copper loss of a transformer at full load is
40W. What would be at half loadA. 20W
D. Stray loss
14) Does the transformer draw any current when
secondary is open?
B. 80W
A. Yes
C. 40W
B. No
D. 10W
15) When the turns ratio of a transformer is 20
D. Voltage and Frequency
and the primary ac voltage is 12 V, the secondary
22) No-load test on a transformer is carried out to
voltage is
determine-
A. 24v
A. copper loss
B. 120v
B. magnetising current and no-load current
C. 240v
C. magnetising current
D. 440v
D. all of above.
16) The input power under no load condition of
23) Which of the following losses varies with load
transformer consists of
in transformer?
A. core losses and very small amount of
copper loss in primary.
A. Copper loss.
B. Core loss
B. copper loss in transformers.
C. Transfomer all losses
C. core loss in transformers.
D. None of above
D. None of above.
17) Transformers operating in parallel will share
the load depending upon their-
24) A transfomer has negative voltage regulation
when its load power factor is–
A. lagging
A. rating
B. leading
B. Percentage impedance.
C. unity
C. Leakage reactance.
D. None of above
D. None of above
25) The essential condition for parallel operation of
18) Which of the following is not a basic element
two single-phase transformer is that they should
of a transformer?
have the same–
A. primary winding
A. polarity
B. secondary winding
B. KVA ratings
C. mutual flux
C. voltage ratio
D. core
D. None of abobe
19) At relatively light load, transformer efficiency
26) Which one is used for constant street light
is low because-
load?
A. transformer losses are high
A. current transformer
B. secondary output is low
B. Constant current transformer
C. fixed loss is high in proportion to the
C. power transformer
output
D. Cu loss is small
20) A transformer transform-
D. potential transformer
27) Which of the following losses remain constant
during normal operation of transformer?
A. voltage and currrent
A. Copper loss
B. voltage
B. Transformer all losses
C. current
C. Core loss
D. frequency
D. None of above
21) When AC supply is given to the transformer,
the flux will depend on…….
A. Current
B. Voltage
C. Frequency
28) Iron loss in transformer can be determined
C. High voltage winding
by…..
D. Low voltage winding
A. open circuit test.
36) In a given transformer for given applied
B. short circuit test.
voltage, losses which remain constant irrespective
29) Transformer core are laminated in order to-
of load changes are
A. simplify it's construction
A. core losses
B. minimize eddy current loss
B. copper losses
C. reduce cost
C. both A and B
D. reduce hysteresis loss
D. none of the above
30) The main purpose of performing short circuit
37) Power transformers are designed to have
test in a transformer is to measure its–
maximum efficiency at
A. Copper Loss
A. 80% full load
B. Core Loss
B. 50% full load
C. Total Loss
C. nearly full load
D. Insulation resistance
D. no load
31) The path of a magnetic flux in a transformer
38) The maximum efficiency of a distribution
should have
transformer is
A. low resistance
A. at full load
B. low reluctance
B. at 70% full load
C. high resistance
C. at 50% full load
D. high reluctance
D. at no load
32) No-load current in a transformer
39) Flash point of transformer insulating oil should
A. lags behind the voltage by about 75°
be more than
B. leads the voltage by about 75°
A. 100°C.
C. lags behind the voltage by about 15°
B. 140°C.
D. leads behind the voltage by about 25°
C. 45°C.
33) Which of the following is not a part of
D. 35°C.
transformer?
40) Noise of transformer mainly due to
A. Breather
A. noise generated by cooling fans.
B. Conservator
B. magnetostriction in iron core.
C. Exciter
C. mechanical vibration.
D. Buchholz relay
D. all of above
34) While conducting short-circuit test on a
41) The tap changer in an electrical power
transformer the following side is short circuited
transformer is provided on
A. Low voltage side
A. LV winding.
B. High voltage side
B. HV winding.
C. Primary side
C. either LV or HV winding.
D. Secondary side
D. both LV and HV winding.
35) Which winding in a transformer has more
42) The transformer ratings are usually expressed
number of turns ?
in terms of
A. Primary winding
A. KVA
B. Secondary winding
B. KW
C. KVAR
49) Which of the following loss in a transformer is
D. Volts
zero even at full load ?
43) A Buchholz relay can be installed on-
A. Hysteresis loss
A. welding transformers
B. Eddy current loss
B. air cooled transformers
C. Core loss
C. oil cooled transformers
D. Friction loss
D. all of above
50) If supply frequency of a transformer increases,
44) In a transformer the resistance between its
the secondary output voltage of the transformer -
primary and secondary is
A. remains same.
A. zero
B. increases.
B. infinite
C. decreases.
C. 1 ohm
D. any of the above
D. 10000 ohm
45) If the supply frequency to the transformer is
Ans Sheet:
increased, the iron loss will
1C – 2A – 3B - 4A – 5A – 6B – 7D – 8D – 9A -10B –
A. remain same
11A – 12B – 13A – 14A – 15C- 16A – 17A – 18C –
B. decrease
19C – 20A – 21D -22B – 23A – 24B – 25A – 26B –
C. increase
27C – 28A – 29B – 30A - 31B - 32A - 33C - 34A -
D. any of the above
35C - 36A - 37C - 38C - 39B - 40B - 41B - 42A - 43C
46) Which type of winding is used in 3phase shell-
- 44B - 45C - 46D - 47A - 48A - 49D - 50A.
type transformer ?
A. Cylindrical type
B. Circular type
C. Rectangular type
D. Sandwich type
47) The secondary winding of which of the
Why is transformer rating in KVA?
Copper loss of a transformer depends on current
following transformers is always kept closed ?
and iron loss on voltage. Hence, total transformer
A. CT
loss depends on volt-ampere (VA) and not on
B. PT
phase angle between voltage and current i.e.
C. Step-up transformer
independent of load power factor. That is why
D. Step-down transformer
48) The efficiency of two identical transformers
under load conditions can be determined by
A. back-to-back test
B. short circuit test
C. open circuit test
D. none of above
rating of transformers is in KVA and not in KW.
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