1. The no-load current drawn by the transformer is usually what percent of the full-load current?
(a) 0.2 to 0.5 percent
(b) 2 to 5 percent
(c) 12 to 15 percent
(d) 20 to 30 percent
Ans: b
2. Sumpner’s test is conducted on transformers to determine
(a) temperature
(b) stray losses
(c) all-day efficiency
(d) none of the above
Ans: a
3.In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are
(a) friction and windage losses
(b) copper losses
(c) hysteresis and eddy current losses
(d) none of the above
Ans: c
4. The function of a conservator in a transformer is
(a) To protect against internal fault
(b) To reduce copper as well as core losses
(c) To cool the transformer oil
(d) To take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings
Ans: d
5.Greater the secondary leakage flux
(a) less will be the secondary induced e.m.f.
(b) less will be the primary induced e.m.f.
(c) less will be the primary terminal voltage
(d) none of the above
Ans: a
6. Two transformers operating in parallel will share the load depending upon their
(a) leakage reactance
(b) per unit impedance
(c) efficiencies
(d) ratings
Ans: b
7.If the percentage impedances of the two transformers working in parallel are different, then
(a) transformers will be overheated
(b) power factors of both the transformers will be same
(c) parallel operation will be not possible
(d) parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load
Ans: d
8. The thickness of laminations used in a transformer is usually
(a) 0.4 mm to 0.5 mm
(b) 4 mm to 5 mm
(c) 14 mm to 15 mm
(d) 25 mm to 40 mm
Ans: a
9.Star/star transformers work satisfactorily when
(a) load is unbalanced only
(b) load is balanced only
(c) on balanced as well as unbalanced loads
(d) none of the above
Ans: b
10.Delta/star transformer works satisfactorily when
(a) load is balanced only
(b) load is unbalanced only
(c) on balanced as well as unbalanced loads
(d) none of the above
Ans: c
11.Buchholz’s relay gives warning and protection against
(a) electrical fault inside the transformer itself
(b) electrical fault outside the transformer in outgoing feeder
(c) for both outside and inside faults
(d) none of the above
Ans: a
12. The chemical used in breather is
a) Asbestos fibre
b) Silica sand
c) Sodium chloride
d) Silica gel
Ans: d
13. Helical coils can be used on
A. Low voltage side of high kVA transformers
B. High-frequency transformers
C. High voltage side of small capacity transformers
D. High voltage side of high kVA rating transformers
Ans: a
14.In an ideal transformer
a) windings have no resistance
b) core has no losses
c) core has infinite permeability
d) all of these
Ans; c
15. The efficiency of a transformer is maximum when
a) It runs at half of full load
b) it runs at full load
c) its Cu loss equal iron loss
d) it runs overload
Ans; c
16. A 400V/100V, 10KVA two winding transformer is reconnected as an auto-transformer across a suitable voltage source. The maximum rating of such an arrangement could be
a)50KVA
b)15KVA
c)12.5KVA
d)8.75KVA
Ans: a
17. A transformer can have zero voltage regulation at
(a) leading power factor
(b) lagging power factor
(c) unity power factor
(d) zero power factor
Ans; a
18. Losses which occur in rotating electric machines and do not occur in transformers are
(a) friction and windage losses
(b) magnetic losses
(c) hysteresis and eddy current losses
(d) copper losses
Ans: a
19. In an autotransformer if the power transferred inductively is equal to the power conducted through, then transformation ratio is given by
a. 1
b. 0.5
c. 2
d. 0
Ans: b
20.If a two winding transformer is converted into an autotransformer by applying additive polarity and subtractive polarity which results in the secondary voltages of 1840 and 1810 volts. Then the primary and secondary voltages of transformer are
a. 1800V, 50V
b. 1810V, 40V
c. 1820V, 30V
d. 1825V, 15V
Ans: d
21. A 600 kVA transformer has iron losses of 400 kW and copper losses of 500 kW. Its kVA rating for maximum efficiency is given by
a. 537 kVA
b. 548 kVA
c. 555 kVA
d. 585 kVA
Ans; a
22. The transformer core is laminated to
A. Reduce the copper losses
B. Reduce the core losses
C. Reduce the eddy current losses
D. None of these
Ans; c
23. In a two winding transformer, the primary and secondary induced emf E1 & E2 are always
a) equal in magnitude
b) anti-phase with each other
c) in phase with each other
d) determined by load on transformer secondary
Ans; c
24.No load test on a transformer is carried out to find
A. Copper loss
B. magnetising current
C. Magnetising current and const. loss
D. Efficiency of the transformer
Ans: c
25.The efficiency of a transformer will be maximum when
A. copper losses = hysteresis losses
B. Hysteresis losses = eddy current losses
C. Eddy current losses = copper losses
D. Copper losses = iron losses
Ans: d
26.Cross over windings are used in
A. Low voltage side of high kVA rating transformers
B. Current transformers
C. High voltage side of high kVA rating transformers
D. High voltage side of low kVA rating transformers
Ans: d
27.When a 400Hz transformer is operated at 50Hz its KVA rating is
a) Reduced to 1/8
b) Increased 8 times
c) Unaffected
d) Increased 64 times
Ans: a
28.In a transformer the resistance between its primary and secondary is
a) Zero
b) 1Ω
c) 1000 Ω
d) Infinite
Ans: d
29.A Buchholz relay can be installed on
a) Auto-transformers
b) Air-cooled transformers
c) Welding transformers
d) Oil cooled transformers
Ans: d
30.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
31.For a single phase no load transformer, which among the following losses will be minimum?
a. hysteresis losses
b. eddy current losses
c. copper losses
d. mechanical losses
Ans: d
32.The most familiar application of zig – zag transformer is as
a) Ground reference on an ungrounded system
b) Converting single phase to two phase
c) Reducing harmonics
d) All of these
Ans: a
33.Scott’s connection is used for the conversion of
a) Single phase to three phase
b) Three phase to single phase
c) three phase to two phase
d) All of these
Ans: c
34)Voltage regulation & efficiency of four transformer A,B,C and D are as given below
A: 5% regulation & 94% efficiency
B: 2% regulation & 96% efficiency
C: 5% regulation & 97% efficiency
D: 2% regulation & 97% efficiency
The transformer that is in a good condition is
1) A 2)B 3)C 4) D
Ans: 4
35.In transformer following winding has got more cross-sectional area
a)Low voltage winding
b)High voltage winding
c)Primary winding
d)Secondary winding
Ans; a
36.Eddy current loss will depends on
a)Frequency
b)Flux density
c)Thickness
d)All of the above
Ans: d
37.The use of higher flux density in the transformer design
a)Reduce weight per KVA
b)Reduces iron losses
c)Reduce copper losses
d)Increases part load efficiency
Ans; a
38.The main advantage of auto transformer over a two winding transformer is
a) Hysteresis losses are reduced b) Saving in winding material
c) Copper losses are negligible
d) Eddy losses are totally eliminated
Ans: b
39.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 induce emf to primary induce emf
d)Secondary terminal voltage to primary applied voltage
Ans: c
40.If K is the transformation ratio of step up autotransformer and Wtw is the total weight of copper in two winding transformer. Then the saving of copper is given by
a) K Wtw
b) Wtw/ K
c) Wtw/ K^ 2
d) K2 Wtw
Ans: a
41.Use of an autotransformer is economical when its transformation ratio is
a) Near unity
b) Much greater than unity
c) Much lesser than unity
d) None of these
Ans; a
42. Two transformers are operated in parallel, the most essential condition to
be satisfied is
a) Polarities should be same
b) Leakage reactance should be equal
c) Turns ratios should be equal
d) Impedances should be in proportion to their kVA rating
Ans; a
43.For the star-star connection of three phase transformer, the phase angle between the phase voltages and line voltages on both primary and secondary side is
a) 0 degree
b) 30 degree
c) 60 degree
d) 120 degree
Ans; b
44.The most commonly used connections for power systems as a step- up and step-down transformers are a) Star-delta, star-star
b) Delta-star, star-delta
c) Star-star, delta-delta
d) Star-delta, delta-star
Ans; b
45.Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds
(a) 50°C
(b) 80°C
(c) 100°C
(d) 150°C
Ans: d
46.Distribution transformers are generally designed for maximum efficiency around
a) 90% load
b) Zero load
c) 25% load
d) 50% load
Ans: d
47.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
48.Which of the following act as a protection against high voltage surges due to lightning and switching?
a) Horn gap
a)Thermal overload relays
b)Breather
c)Conservator
Ans; a
49.The high frequency hum in the transformer is mainly due to
a)Laminations being not sufficiently tight
b)Magnetostriction
c)Oil of the transformer
d)Tank walls
Ans: b
50.Frequency of induced voltage in 1-phase transformer is constant because_____
a)There is no relative motion between coils is present.
b)Relative motion between coil is present
c) Depends upon number of poles
d)Leakage flux is less
Ans; a
51.A transformer is working at full load with maximum efficiency. Its iron loss is 1000W. What will
be its copper loss at half of full load
a)1000W
b)500W
c)250
d)4000W
Ans; c
52.A 50KVA 1000/200V transformer takes 5A current at a power factor of 0.2 lagging, when connected to 1000V side at no load is connected at other side. The core loss in transformer will be
a)1000W
b)250W
c)500W
d)750W
Ans: a
53. In the transformer, the resistive drop is 2% and reactive drop is 5%. What will be its regulation at full load unity power factor?
a)1%
b)3%
c)2%
d)4%
Ans: c
“All power is within you; you can do anything & everything”
-Swami Vivekananda
For detail explanation & solution of each question you must watch this video
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