1. Which of the following does not change in a transformer ?
Correct : C. Frequency
2. In a transformer the energy is conveyed from primary to secondary
Correct : C. by the flux
3. A transformer core is laminated to
Correct : B. reduce eddy current losses
4. The degree of mechanical vibrations produced by the laminations of a transformer
depends on
Correct : D. all of the above
5. The no-load current drawn by transformer is usually what per cent of the full-load
current ?
Correct : B. 2 to 5 per cent
6. The path of a magnetic flux in a transformer should have
Correct : D. low reluctance
7. No-load on a transformer is carried out to determine
Correct : A. copper loss
8. The dielectric strength of transformer oil is expected to be
Correct : B. 33 kV
9. Sumpner's test is conducted on trans-formers to determine
Correct : A. temperature
10. The permissible flux density in case of cold rolled grain oriented steel is around
Correct : A. 1.7 Wb/m2
11. The efficiency of a transformer will be maximum when
Correct : D. copper losses = iron losses
12. No-load current in a transformer
Correct : A. lags behind the voltage by about 75°
13. The purpose of providing an iron core in a transformer is to
Correct : C. decrease the reluctance of the magnetic path
14. Which of the following is not a part of transformer installation ?
Correct : D. Exciter
15. While conducting short-circuit test on a transformer the following side is short
circuited
Correct : B. Low voltage side
16. In the transformer following winding has got more cross-sectional area
Correct : A. Low voltage winding
17. A transformer transforms
Correct : C. power
18. A transformer cannot raise or lower the voltage of a D.C. supply because
Correct : C. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
19. Primary winding of a transformer
Correct : C. could either be a low voltage or high voltage winding
20. Which winding in a transformer has more number of turns ?
Correct : B. High voltage winding
21. Efficiency of a power transformer is of the order of
Correct : B. 98 per cent
22. In a given transformer for given applied voltage, losses which remainconstant
irrespective of load changes are
Correct : C. hysteresis and eddy current losses
23. A common method of cooling a power transformer is
Correct : C. oil cooling
24. The no load current in a transformer lags behind the appliedvoltage by an angle of
about
Correct : D. 75°
25. In a transformer routine efficiency depends upon
Correct : D. both (b) and (c)
26. In the transformer the function of a conservator is to
Correct : C. protect the transformer from damage when oil expends due to heating
27. Natural oil cooling is used for transformers upto a rating of
Correct : A. 3000 kVA
28. Power transformers are designed to have maximum efficiency at
Correct : A. nearly full load
29. The maximum efficiency of a distribution transformer is
Correct : B. at 50% full load
30. Transformer breaths in when
Correct : B. load on it decreases
31. No-load current of a transformer has
Correct : D. has small magnitude and low powerfactor
32. Spacers are provided between adjacent coils
Correct : A. to provide free passage to the cool¬ing oil
33. Greater the secondary leakage flux
Correct : A. less will be the secondary induced e.m.f.
34. The purpose of providing iron core in a step-up transformer is
Correct : C. to decrease the magnitude of mag-netizing current
35. The power transformer is a constant
Correct : D. main flux device
36. Two transformers operating in parallel will share the load depending upon their
Correct : B. per unit impedance
37. If R2 is the resistance of secondary winding of the transformer and K is the
transformation ratio then the equivalent secondary resistance referred to primary will be
Correct : B. R2IK2
38. What will happen if the transformers working in parallel are not connected with
regard to polarity ?
Correct : B. Incorrect polarity will result in dead short circuit
39. Ifthe percentage impedances of the two transformers working in parallel aredifferent, then
Correct : A. transformers will be overheated
40. In a transformer the tappings are generally provided on
Correct : C. low voltage side
41. The use of higher flux density in the transformer design
Correct : A. reduces weight per kVA
42. The chemical used in breather for transformer should have the quality of
Correct : A. ionizing air
43. The chemical used in breather is
Correct : D. silica gel
44. The transformer ratings are usually expressed in terms of
Correct : D. kVA
45. The noise resulting from vibrations of laminations set by magnetic forces, is termedas
Correct : C. hum
46. Hysteresis loss in a transformer varies as CBmax = maximum flux density)
Correct : B. Bmax1-6
47. Material used for construction of transformer core is usually
Correct : D. silicon steel
48. The thickness of laminations used in a transformer is usually
Correct : A. 0.4 mm to 0.5 mm
49. The function of conservator in a transformer is
Correct : A. to project against'internal fault
50. The highest voltage for transmitting electrical power in India is
Correct : D. 400 kV
51. In a transformer the resistance between its primary and secondary is
Correct : D. infinite
52. A transformer oil must be free from
Correct : D. moisture
53. A Buchholz relay can be installed on
Correct : A. auto-transformers
54. Gas is usually not liberated due to dissociation of transformer oil unless the oil
temperature exceeds
Correct : D. 150°C
55. The main reason for generation of harmonics in a transformer could be
Correct : D. saturation of core
56. Distribution transformers are generally designed for maximum efficiency around
Correct : D. 50% load
57. Which of the following property is not necessarily desirable in the material for
transformer core ?
Correct : C. High thermal conductivity
58. Star/star transformers work satisfactorily when
Correct : B. load is balanced only
59. Delta/star transformer works satisfactorily when
Correct : C. on balanced as well as unbalanced loads
60. Buchholz's relay gives warning and protection against
Correct : A. electrical fault inside the transformer itself
61. The magnetising current of a transformer is usually small because it has
Correct : A. small air gap
62. Which of the following does not change in an ordinary transformer ?
Correct : A. Frequency
63. Which of the following properties is not necessarily desirable for the material for
transformer core ?
Correct : C. High thermal conductivity
64. The leakage flux in a transformer depends upon
Correct : A. load current
65. The path of the magnetic flux in transformer should have
Correct : B. low reactance
66. Noise level test in a transformer is a
Correct : C. type test
67. Which of the foJIowing is not a routine test on transformers ?
Correct : C. Radio interference test
68. A transformer can have zero voltage regulation at
Correct : A. leading power factor
69. Helical coils can be used on
Correct : A. low voltage side of high kVA trans¬formers
70. Harmonics in transformer result in
Correct : D. all of the above
71. The core used in high frequency transformer is usually
Correct : C. air core
72. The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be
Correct : D. 400 W
73. The value of flux involved m the e.m.f. equation of a transformer is
Correct : C. maximum value
74. Silicon steel used in laminations mainly reduces
Correct : A. hysteresis loss
75. Which winding of the transformer has less cross-sectional area ?
Correct : D. High voltage winding
76. Power transformers are generally designed to have maximum efficiency around
Correct : C. near full-load
77. Which of the following is the main advantage of an auto-transformer over a two
winding transformer ?
Correct : B. Saving in winding material
78. During short circuit test iron losses are negligible because
Correct : A. the current on secondary side is negligible
79. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in
Correct : A. short-circuiting of the secondaries
80. The changes in volume of transformer cooling oil due to variation of atmospheric
temperature during day and night is taken care of by which part of transformer
Correct : A. Conservator
81. An ideal transformer is one which has
Correct : A. no losses and magnetic leakage
82. When a given transformer is run at its rated voltage but reduced frequency, its
Correct : D. core flux density is increased
83. In an actual transformer the iron loss remains practically constant from noload to fullload because
Correct : C. core flux remains practically constant
84. An ideal transformer will have maximum efficiency at a load such that
Correct : A. copper loss = iron loss
85. If the supply frequency to the transformer is increased,"the iron loss will
Correct : C. increase
86. Negative voltage regulation is indicative that the load is
Correct : A. capacitive only
87. Iron loss of a transformer can be measured by
Correct : A. low power factor wattmeter
88. When secondary of a current transformer is open-circuited its iron core will be
Correct : A. hot because of heavy iron losses taking place in it due to high flux density
89. The transformer laminations are insulated from each other by
Correct : B. thin coat of varnish
90. Which type of winding is used in 3phase shell-type transformer ?
Correct : B. Sandwich type
91. During open circuit test of a transformer
Correct : A. primary is supplied rated voltage
92. Open circuit test on transformers is conducted to determine
Correct : C. core losses
93. Short circuit test on transformers is conducted to determine
Correct : B. copper losses
94. For the parallel operation of single phase transformers it is necessary that they should
have
Correct : B. same polarity
95. The transformer oil should have volatility and viscosity.
Correct : A. low,low
96. The function of breather in a transformer is
Correct : B. to cool the coils during reduced load
97. The secondary winding of which of the following transformers is always kept closed?
Correct : A. Step-up transformer
98. The size of a transformer core will depend on
Correct : D. (a) and (b) both
99. N atural air coo ling is generally restricted for transformers up to