In this article, we shared the 200 plus electrical transformer MCQ questions and answers to test your knowledge.
Transformer MCQ
The below list provides all the multiple-choice questions related to the transformer’s technical subject.
Answers are available at the bottom of the article.
1. While rising and falling if a wave is not symmetrical, it contains
| A) | none of these answers |
| B) | even harmonics in addition to fundamental |
| C) | odd harmonics in addition to fundamental |
| D) | both odd and even harmonics in addition to fundamental |
2. If the supply frequency to the transformer is increased: the iron loss will
| A) | not change |
| B) | increase |
| C) | decrease |
| D) | any of these answers |
3. Which of the following properties is not necessarily desirable for the material for transformer core?
| A) | High thermal conductivity |
| B) | High permeability |
| C) | Adequate mechanical strength |
| D) | Low hysteresis loss |
4. When a delta connected primary of a 3-phase transformer is connected to 3- phase supply
| A) | none of these answers |
| B) | magnetizing current in phase winding will not contain third harmonics but line current will contain third harmonics |
| C) | magnetizing current in phase winding will contain third harmonics and line current will alsò contain third harmonics |
| D) | magnetizing current in phase winding will carry third harmonics but line current will be free from it |
5. Auto-transformer makes effective saving on copper and copper losses when its transformation ratio is
| A) | less than one |
| B) | approximately equal to one |
| C) | none of these answers |
| D) | great than one |
6. Harmonic currents in a transformer cause
| A) | magnetic interference with protective relays |
| B) | increased loss |
| C) | all of these answers |
| D) | increased core loss |
7. Which of the following test on a transformer provides information about regulation, efficiency, and heating under load conditions?
| A) | Short circuit test |
| B) | Open circuit test |
| C) | Swinburne’s test |
| D) | Back to back test |
8. Simple porcelain bushings are used for transformers up to
| A) | none of these answers |
| B) | 11 kV |
| C) | 132 kV |
| D) | 400 kV |
9. In a transformer the resistance between its primary and secondary is
| A) | zero |
| B) | 1000 ohms |
| C) | 1 ohm |
| D) | infinite |
10. During short-circuit test iron losses are negligible because
| A) | the voltage on secondary side does not vary |
| B) | the voltage applied on primary side is low |
| C) | the current on secondary side is negligible |
| D) | full-load current is not supplied to the transformer |
11. In a transformer overcurrents affect
| A) | insulation life |
| B) | temperature rise |
| C) | all of these answers |
| D) | mechanical stress |
12. Transformer cores are built-up from laminations rather than from solid metal so that
| A) | turn ratio is higher than voltage ratio |
| B) | less insulation is required for the windings |
| C) | eddy current loss is reduced |
| D) | oil penetrates the core more easily |
13. A tap changer is used on a transformer for
| A) | adjustments in secondary voltage |
| B) | adjustments in both primary and secondary voltages |
| C) | adjustments in primary voltage |
| D) | none of these answers |
14. Short circuit test on transformers is conducted to determine
| A) | hysteresis losses |
| B) | eddy current losses |
| C) | copper losses |
| D) | core losses |
15. Transformer rating are usually expressed in terms of
| A) | kW |
| B) | kVA |
| C) | kWh |
| D) | kVAR |
16. Which of the following statement concerning parallel operation of transformers is incorrect ?
| A) | Transformers must have equal voltage ratings |
| B) | Transformers must be operated at the same frequency |
| C) | Transformers must have same transformation ratio |
| D) | Transformers must have equal kVA |
17. The transformer ratings are usually expressed in terms of
| A) | amperes |
| B) | kW |
| C) | volts |
| D) | kVA |
18. For transformers upto a capacity of____ kVA air blast cooling is provided.
| A) | 2500 |
| B) | 10000 |
| C) | 5000 |
| D) | 20000 |
19. Most widely used insulating and cooling transformer liquid is
| A) | askarel |
| B) | water |
| C) | mineral oil |
| D) | none of these answers |
20. Which winding of the transformer has less cross-sectional area?
| A) | Low voltage winding |
| B) | High voltage winding |
| C) | Primary winding |
| D) | Secondary winding |
21. Which of the following acts as a protection against high voltage surges due to lightning and switching?
| A) | Thermal overload relays |
| B) | Breather |
| C) | Horn gaps |
| D) | Conservator |
22. In measuring voltage or current by means of instrument transformer
| A) | only ratio errors need be considered |
| B) | none of these answers |
| C) | either only ratio errors need be considered or both ratio as well as phase angle error need to be considered |
| D) | both ratio as well as phase angle error need to be considered |
23. A common method of cooling a power transformer is
| A) | air blast cooling |
| B) | natural air cooling |
| C) | any of these answers |
| D) | oil cooling |
24. Losses which occur in rotating electric machines and do not occur in transformers are
| A) | friction and windage losses |
| B) | hysteresis and eddy current losses |
| C) | magnetic losses |
| D) | copper losses |
25. The highest voltage for transmitting electrical power in India is
| A) | 132 kV |
| B) | 66 kV |
| C) | 400 kV |
| D) | 33 kV |
26. In a power transformer the efficiency should be maximum at
| A) | 80% full load |
| B) | full load |
| C) | 60% full load |
| D) | 50% of full load |
27. In large transformers, oil is invariably used in order to
| A) | insulate the coils |
| B) | lubricate the core |
| C) | insulate the core |
| D) | none of these answers |
28. In a power or distribution transformer about 10 per cent end turns are heavily insulated
| A) | none of these answers |
| B) | to reflect the line surge and save the winding of a transformer from damage |
| C) | to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns |
| D) | to absorb the line surge voltage and save the winding of transformer from damage |
29. For a transformer, operating at constant load current, maximum efficiency will occur at
| A) | zero power factor |
| B) | unity power factor |
| C) | 0.8 leading power factor |
| D) | 0.8 lagging power factor |
30. Which of the following is the main advantage of an auto-transformer over a two winding transformer ?
| A) | Copper losses are negligible |
| B) | Saving in winding material |
| C) | Eddy losses are totally eliminated |
| D) | Hysteresis losses are reduced |
31. The power transformer is a constant
| A) | current device |
| B) | voltage device |
| C) | power device |
| D) | main flux device |
32. For given applied voltage, with the increase in frequency of the applied voltage
| A) | eddy current loss will remain unchanged |
| B) | eddy current loss will increase |
| C) | none of these answers |
| D) | eddy current loss will decrease |
33. No-load current of a transformer has
| A) | has high magnitude and low power factor |
| B) | has high magnitude and high power factor |
| C) | has small magnitude and low power factor |
| D) | has small magnitude and high power factor |
34. In which of the following the highest rating transformer is likely to find application ?
| A) | Distribution |
| B) | Transmission |
| C) | Generator |
| D) | Sub station |
35. The efficiency of two identical transformers under load conditions can be determined by
| A) | back-to-back test |
| B) | any of these answers |
| C) | short-circuit test |
| D) | open circuit test |
36. The saving in copper achieved by converting two winding transformer into an auto-transformer is determined by
| A) | voltage transformation ratio |
| B) | load on the secondary |
| C) | size of the transformer core |
| D) | magnetic quality of core material |
| E) | none of these answers |
37. The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be
| A) | 400 W |
| B) | 800 W |
| C) | 1600 W |
| D) | 6400 W |
38. The function of a conservator in a transformer is
| A) | to reduce copper as well as core losses |
| B) | to cool the transformer oil |
| C) | to project against internal fault |
| D) | to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings |
39. Which of the following parts of a transformer is visible from outside ?
| A) | Primary winding |
| B) | Secondary winding |
| C) | Core |
| D) | Bushings |
40. Which of the following is not a fitting on a transformer ?
| A) | Breather |
| B) | Buchholz’s relay |
| C) | Conservator |
| D) | Commutator |
41. Greater the secondary leakage flux
| A) | less will be the primary terminal voltage |
| B) | none of these answers |
| C) | less will be the primary induced e.m.f. |
| D) | less will be the secondary induced e.m.f. |
42. In a transformer, electric power is transferred from one coil to the other coil in a transformer
| A) | physically |
| B) | electromagnetically |
| C) | electrically |
| D) | magnetically |
43. The iron losses of a transformer can be calculated by knowing the weights of
| A) | cores and yokes |
| B) | yokes only |
| C) | cores only |
| D) | copper winding only |
44. In core-type transformers, the concentric windings are used with
| A) | low voltage winding on the outerside |
| B) | high voltage winding on the outerside |
| C) | low voltage winding placed next to core |
| D) | high voltage winding placed next to core |
45. In a transformer routine efficiency depends upon
| A) | load current |
| B) | power factor of load |
| C) | both load current and power factor of load |
| D) | supply frequency |
46. The place of transformer installation is selected such that
| A) | location is not subject to damage from men and material traffic |
| B) | location is not too warm |
| C) | all of these answers |
| D) | plenty of dry and clean air is available and wet conditions are not encountered |
47. Helical coils are very well suited for
| A) | high voltage winding of large rating transformers |
| B) | none of these answers |
| C) | high voltage winding of small rating transformers |
| D) | low voltage winding of large rating transformers |
48. For power purpose sine wave shape is preferred because
| A) | it gives least copper losses |
| B) | it is easy to generate e.m.f. of this wave shape |
| C) | it is stable wave shape as the line parameters cannot change it |
| D) | none of these answers |
49. For given effective applied voltage of constant frequency eddy current losses
| A) | become less with peaked wave shape of applied voltage |
| B) | either become less with peaked wave shape of applied voltage or are independent of the wave shape of the applied voltage |
| C) | are independent of the wave shape of the applied voltage |
| D) | none of these answers |
50. In a transformer, if the magnitude of magnetizing current is more
| A) | its power factor will become low on lagging side |
| B) | its power factor will become low on leading side |
| C) | it has no effect on the power factor of the transformer |
| D) | none of these answers |
51. The humming sound in a transformer is mainly due to
| A) | walls of the tank |
| B) | laminations of the transformer |
| C) | magnetostriction |
| D) | oil of the transformer |
52. Dust should never be allowed to accumulate on the windings and core of a dry type transformer because it
| A) | absorbs oil and grease |
| B) | tends to corrode the metal surface |
| C) | reduces dissipation of heat |
| D) | may short-circuit the windings |
53. Buchholz’s relay gives warning and protection against
| A) | none of these answers |
| B) | electrical fault outside the transformer in outgoing feeder |
| C) | either electrical fault inside the transformer itself or electrical fault outside the transformer in outgoing feeder |
| D) | electrical fault inside the transformer itself |
54. In high frequency transformer ferrite cores are used because a ferrite core has
| A) | low permeability |
| B) | high resistance |
| C) | low resistance |
| D) | high hysteresis |
55. Current transformers for meters and relays usually have
| A) | 5 : 1 ratio |
| B) | 15-A secondaries |
| C) | 5-A secondaries |
| D) | 1 : 2 ratio |
56. Buchholz’s relay gives warning and protection against
| A) | electrical fault inside the transformer itself |
| B) | none of these answers |
| C) | electrical fault outside the transformer in outgoing feeder |
| D) | for both outside and inside faults |
57. The principle of working of a transformer is
| A) | dynamic induction |
| B) | self induction |
| C) | mutual induction |
| D) | static induction |
58. A no-load test is performed on a transformer to determine
| A) | copper loss |
| B) | magnetising current and loss |
| C) | efficiency |
| D) | magnetising current |
| E) | core loss |
59. A transformer oil must be free from
| A) | sludge |
| B) | gases |
| C) | odour |
| D) | moisture |
60. Delta/star transformer works satisfactorily when
| A) | load is balanced only |
| B) | on balanced as well as unbalanced loads |
| C) | none of these answers |
| D) | load is unbalanced only |
61. Buchholz relay is used on
| A) | furnace transformers |
| B) | air-cooled transformers |
| C) | welding transformers |
| D) | oil cooled transformers |
62. Iron loss of a transformer can be measured by
| A) | unity power factor wattmeter |
| B) | any type of wattmeter |
| C) | frequency meter |
| D) | low power factor wattmeter |
63. The path of a magnetic flux in a transformer should have
| A) | high reluctance |
| B) | low reluctance |
| C) | low resistance |
| D) | high resistance |
64. The reactance of a transformer depends on
| A) | size of the tank |
| B) | all of these answers |
| C) | leakage flux |
| D) | size of the core |
65. Silicon steel used in laminations mainly reduces
| A) | copper losses |
| B) | hysteresis loss |
| C) | all of these answers |
| D) | eddy current losses |
66. The transformer oil should have ____ volatility and ____ viscosity.
| A) | high, low |
| B) | high, high |
| C) | low, high |
| D) | low, low |
67. The degree of mechanical vibrations produced by the laminations of a transformer depends on
| A) | all of these answers |
| B) | tightness of clamping |
| C) | gauge of laminations |
| D) | size of laminations |
68. A transformer designed for installation in a tropical country if installed in a cold country
| A) | neither of these answers |
| B) | is to be loaded below the name plate kVA rating |
| C) | can be loaded in excess of the name plate kVA rating |
| D) | either is to be loaded below the name plate kVA rating or can be loaded in excess of the name plate kVA rating |
69. Spiral core transformer which has core made up of steel strip has the following advantage.
| A) | Less weight |
| B) | All of these answers |
| C) | Lighter construction |
| D) | Minimum losses |
70. Which of the following is the most likely source of harmonics in a transformer ?
| A) | Loose connections |
| B) | Core saturation |
| C) | Overload |
| D) | Poor insulation |
71. In Scott connections the main transformer has centre tap on
| A) | secondary windings |
| B) | both primary and secondary windings |
| C) | primary winding |
| D) | none of these answers |
72. Helical coils can be used on
| A) | high voltage side of small capacity transformers |
| B) | high voltage side of high kVA rating transformers |
| C) | low voltage side of high kVA transformers |
| D) | high frequency transforraers |
73. Which of the following parts of a transformer is likely to suffer maximum damage due to excessive temperature rise ?
| A) | Winding insulation |
| B) | Dielectric strength of oil |
| C) | Copper winding |
| D) | Core laminations |
74. In which of the following transformer part of primary winding also serves as the secondary winding ?
| A) | Auto transformer |
| B) | Step-up transformer |
| C) | Potential transformer |
| D) | Current transformer |
75. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in
| A) | short-circuiting of the secondaries |
| B) | loading of the transformers not in proportion to their kVA ratings |
| C) | power factor of one of the transformers is leading while that of the’ other lagging |
| D) | transformers having higher copper losses will have negligible core losses |
76. An ideal transformer is one which has
| A) | core of stainless steel and winding of pure copper metal |
| B) | interleaved primary and secondary windings |
| C) | a common core for its primary and secondary windings |
| D) | no losses and magnetic leakage |
77. H.R.C. fuses on a transformer provide protection against
| A) | low oil level |
| B) | insulation failure |
| C) | external faults |
| D) | internal faults |
78. For parallel operation of two single phase transformers the essential condition is that they should have the same
| A) | polarity |
| B) | phase sequence |
| C) | percentage impedance |
| D) | voltage ratio |
79. Open circuit test on transformers is conducted to determine
| A) | eddy current losses |
| B) | core losses |
| C) | hysteresis losses |
| D) | copper losses |
80. A transformer can have zero voltage regulation at
| A) | leading power factor |
| B) | unity power factor |
| C) | zero power factor |
| D) | lagging power factor |
81. The output current corresponding to the maximum efficiency for a transformer having core loss of 200 W and equivalent resistance referred to secondary of 0.5 ohm is
| A) | 20 A |
| B) | 15 A |
| C) | 10 A |
| D) | 5 A |
82. When a given transformer is run at its rated voltage but reduced frequency, its
| A) | core flux density is increased |
| B) | iron losses are reduced |
| C) | core flux density is reduced |
| D) | flux density remains unaffected |
83. The short-circuit voltage of a transformer mainly depends on the
| A) | cross-sectional area of the iron core |
| B) | ohmic resistance of secondary winding |
| C) | ohmic resistance of primary winding |
| D) | magnitude of leakage flux |
84. Which of the following statements is correct ?
| A) | A transformer operate at a power factor depending on the power factor of the load |
| B) | A transformer operates at power factor below a particular value |
| C) | A transformer operates always at unity power factor |
| D) | A transformer has its own power factor |
85. 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
| A) | Breather |
| B) | Conservator |
| C) | Bushings |
| D) | Buchholz relay |
86. Power transformers are designed to have maximum efficiency at
| A) | no load |
| B) | 70% full load |
| C) | nearly full load |
| D) | 50% full load |
87. In an actual transformer the iron loss remains practically constant from no load to full-load because
| A) | value of transformation ratio remains constant |
| B) | secondary voltage remains constant |
| C) | core flux remains practically constant |
| D) | permeability of transformer core remains constant |
| E) | primary voltage remains constant |
88. The distribution transformers are designed to keep the iron-losses minimum because
| A) | iron losses may damage the insulation |
| B) | iron-losses will heat up the coil |
| C) | none of these answers |
| D) | the primary of distribution transformer is energised for all the twenty four hours |
89. Which winding in a transformer has more number of turns?
| A) | Secondary winding |
| B) | Low voltage winding |
| C) | High voltage winding |
| D) | Primary winding |
90. The rating of a transformer is given in kVA instead of kW because
| A) | load power factor is often not known |
| B) | kVA is fixed whereas kW depends on load p.f. |
| C) | total transformer loss depends on VA |
| D) | it has become customary |
91. The colour of fresh dielectric oil for a transformer is
| A) | colourless |
| B) | dark brown |
| C) | white to grey |
| D) | pale yellow |
92. The main reason for generation of harmonics in a transformer could be
| A) | poor insulation |
| B) | saturation of core |
| C) | fluctuating load |
| D) | mechanical vibrations |
93. If a transformer core is made of copper and coils are made up of steel wire, then
| A) | magnetising current will be reduced |
| B) | copper losses in the windings will be more |
| C) | eddy current losses will be less |
| D) | all of these answers |
94. Which of the following is not a part of transformer installation ?
| A) | Conservator |
| B) | Buchholz relay |
| C) | Breather |
| D) | Exciter |
95. Natural oil cooling is used for transformers up to a rating of
| A) | 1000 kVA |
| B) | 3000 kVA |
| C) | 250 kVA |
| D) | 500 kVA |
96. Two transformers operating in parallel will share the load depending upon their
| A) | ratings |
| B) | per unit impedance |
| C) | efficiencies |
| D) | leakage reactance |
97. The function of an instrument transformer is to
| A) | act as a radio device to enable the use of standardized low range instruments |
| B) | act as an isolating device to protect equipment and operation personnel from high voltages |
| C) | any of these answers |
| D) | none of these answers |
98. In a transformer minimum voltage regulation occurs when the power factor of the load is
| A) | unity |
| B) | leading |
| C) | 0.8 |
| D) | lagging |
99. A transformer having a turn ratio 1 : 5 and a resistance of 1000 ohms is connected across the secondary terminals, the resistance offered to a current flowing in the primary will be
| A) | 60 Ω |
| B) | 20 Ω |
| C) | 40 Ω |
| D) | 10 Ω |
100. While conducting short-circuit test on a transformer the following side is short-circuited
| A) | Secondary side |
| B) | High voltage side |
| C) | Low voltage side |
| D) | Primary side |
101. The noise resulting from vibrations of laminations set by magnetic forces, is termed as
| A) | hum |
| B) | zoom |
| C) | magnetostrication |
| D) | boo |
102. The no-load current drawn by the transformer is usually what percent of the full-load current?
| A) | 2 to 5 percent |
| B) | 12 to 15 percent |
| C) | 0.2 to 0.5 percent |
| D) | 20 to 30 percent |
103. Which of the following 3-phase connections of transformer create disturbances in communication systems
| A) | star/star |
| B) | delta/star |
| C) | delta/delta |
| D) | star/delta |
104. Which type of winding is used in 3- phase shell-type transformer?
| A) | Circular type |
| B) | Cylindrical type |
| C) | Sandwich type |
| D) | Rectangular type |
105. Which of the following: statements about a transformer having a small short-circuit voltage is true ?
| A) | The transformer has a small transformation ratio |
| B) | The transformer has high copper losses during the operation |
| C) | A low short-circuit current flows through the transformer |
| D) | The transformer has high iron losses during the operation |
| E) | A high short-circuit current flows through the transformer |
106. The efficiencies of transformers compared with that of electric motors of the same power are
| A) | about the same |
| B) | much higher |
| C) | much smaller |
| D) | somewhat smaller |
| E) | none of these answers |
107. Which value of flux is involved in the e.m.f. equation of the transformer?
| A) | Critical value |
| B) | Average value |
| C) | Maximum value |
| D) | R.M.S. value |
108. The yoke sections of transformers using hot-rolled laminations is made 15 per cent greater than that of the core so as to
| A) | to provide better cooling |
| B) | to increase the size of the transformers |
| C) | to reduce the copper loss |
| D) | to reduce the iron loss in yoke and magnetizing current |
109. The kVA rating ratio of transformers operating in parallel, as a general rule, should be within
| A) | 3 : 1 |
| B) | 2 : 1 |
| C) | 5 : 1 |
| D) | 4 : 1 |
110. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are
| A) | copper losses |
| B) | none of these answers |
| C) | friction and windage losses |
| D) | hysteresis and eddy current losses |
111. In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are
| A) | friction and windage losses |
| B) | hysteresis and eddy current losses |
| C) | none of these answers |
| D) | copper losses |
112. Oil impregnated paper condenser bushing is generally used on transformers operating at
| A) | 33 kV |
| B) | 66 kV |
| C) | 11 kV |
| D) | 132 kV |
113. In an ideal transformer, on no-load, the primary voltage is balanced by
| A) | the primary induced e.m.f. |
| B) | the secondary voltage |
| C) | the drop across resistances and reactances |
| D) | the secondary induced e.m.f. |
114. A transformer transforms
| A) | voltage |
| B) | power |
| C) | frequency |
| D) | current |
115. Burden of a current transformer is usually expressed in
| A) | volts |
| B) | amperes |
| C) | volt amperes |
| D) | kilowatt |
116. In a transformer maximum voltage regulation occurs when the power factor of the load is
| A) | 0.4 |
| B) | unity |
| C) | leading |
| D) | lagging |
117. The dielectric strength of transformer oil is expected to be
| A) | 330 kV |
| B) | 100 kV |
| C) | 33 kV |
| D) | 1 kV |
118. The type of load for which the voltage regulation of a transformer is negative is
| A) | resistive |
| B) | inductive |
| C) | capacitive |
| D) | none of these answers |
119. If a transformer is switched on to a voltage more than the rated voltage
| A) | its power factor will increase |
| B) | its power factor will be zero |
| C) | its power factor will remain unaffected |
| D) | its power factor will deteriorate |
120. Which of the following materials is suitable for the manufacture of transformer and large turboalternator ?
| A) | Hot rolled grain oriented steel |
| B) | Cast steel |
| C) | Cast iron |
| D) | Cold rolled grain oriented steel |
121. When 240 V D.C. supply is given to an unloaded 220 V, 50 Hz transformer
| A) | secondary will carry heavy current |
| B) | we will get A.C. voltage on secondary side according to turn ratio |
| C) | primary will carry heavy current and may possibly burn |
| D) | we will get high voltage on secondary side |
122. What is the typical use of an autotransformer ?
| A) | Isolating transformer |
| B) | Control transformer |
| C) | Variable transformer |
| D) | Toy transformer |
123. The use of higher flux density in the transformer design
| A) | reduces weight per kVA |
| B) | reduces copper losses |
| C) | reduces iron losses |
| D) | increases part load efficiency |
124. In the transformer, the function of a conservator is to
| A) | provide fresh air for cooling the transformer |
| B) | none of these answers |
| C) | supply cooling oil to the transformer in time of need |
| D) | protect the transformer from damage when oil expands due to heating |
125. The purpose of a breather in a transformer is to
| A) | provide cooling to the winding |
| B) | extract moisture from the air |
| C) | provide insulation to the winding |
| D) | take insulting oil from the conservator |
126. The efficiency of a transformer will be maximum when
| A) | eddy current losses = copper losses |
| B) | hysteresis losses = eddy current losses |
| C) | copper losses = iron losses |
| D) | copper losses = hysteresis losses |
127. Which of the following does not change in a transformer?
| A) | Current |
| B) | Frequency |
| C) | All of these answers |
| D) | Voltage |
128. A sinusoidal e.m.f.
| A) | leads the flux inducing it by 90° |
| B) | lags the flux inducing it by 90° |
| C) | lags the flux inducing it by 180° |
| D) | leads the flux inducing it by 180° |
129. When a 440/220 V transformer is connected to 400 V D.C. supply
| A) | the transformer may burn |
| B) | the output will be zero volt |
| C) | the output will be 220 V |
| D) | the output will be less than 230 V |
130. The maximum load that a power transformer can carry is limited by its
| A) | copper loss |
| B) | voltage ratio |
| C) | temperature rise |
| D) | dielectric strength of oil |
131. An auto-transformer is preferred to a conventional 2-winding transformer
| A) | where it is required to isolate the two windings electrically |
| B) | where ratio of transformation is low |
| C) | because it is much safer to use an auto-transformer |
| D) | where large number of secondary taps are needed |
132. An increase in secondary current of a transformer brings about an increase in primary current. This is possible because
| A) | primary and secondary windings are conductively coupled |
| B) | primary and secondary windings are capacitively coupled |
| C) | primary and secondary windings are inductively coupled |
| D) | none of these answers |
133. A current transformer is
| A) | an instrument to transform A.C. current to D.C. current |
| B) | a magnetic component to change current level |
| C) | none of these answers |
| D) | a magnetic component to change voltage level |
134. Which of the following transformers is smallest ?
| A) | 2 kVA, 400 Hz |
| B) | 2 kVA, 500 Hz |
| C) | 2kVA, 50 Hz |
| D) | 2 kVA, 200 Hz |
135. Distribution transformers are generally designed for maximum efficiency around
| A) | 90% load |
| B) | 25% load |
| C) | zero load |
| D) | 50% load |
136. A transformer cannot raise or lower the voltage of a D.C. supply because
| A) | there is no need to change the D.C. voltage |
| B) | none of these answers |
| C) | a D.C. circuit has more losses |
| D) | Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero |
137. In a transformer an insulating material may fail due to
| A) | dust |
| B) | any of these answers |
| C) | voids in the winding |
| D) | moisture |
138. Delta-delta power transformer is protected by current transformer having
| A) | delta/delta connections |
| B) | delta/star connections |
| C) | star/star connections |
| D) | star/delta connections |
139. The core used in high frequency transformer is usually
| A) | mild steel core |
| B) | copper core |
| C) | air core |
| D) | cast iron core |
140. The noise produced by a transformer is termed as
| A) | zoom |
| B) | buzz |
| C) | hum |
| D) | ringing |
141. While performing a short-circuit test on a transformer, usually low-voltage side is shortcircuited because it has
| A) | low insulation |
| B) | more number of turns |
| C) | easy access |
| D) | lower terminal voltage and higher current rating |
142. Which of the following is not the standard voltage for power supply in India ?
| A) | 33 kV |
| B) | 122 kV |
| C) | 66 kV |
| D) | 11 kV |
143. A transformer is working at its full load and its efficiency is also maximum. Its iron loss is 1 kW, its copper loss at half load will be
| A) | 0.1 kW |
| B) | 0.5 kW |
| C) | 0.2 kW |
| D) | 0.25 kW |
144. While rising and while falling, if a wave is symmetrical, it contains
| A) | odd harmonics in addition to fundamental |
| B) | even harmonics in addition to fundamental |
| C) | none of these answers |
| D) | both odd and even harmonics in addition to fundamental |
145. The magnetizing current, for sinusoidal voltage applied, will be
| A) | sinusoidal or non-sinusoidal depending upon the saturation point |
| B) | always non-sinusoidal |
| C) | none of these answers |
| D) | always sinusoidal |
146. In a transformer, the resistance between its primary and secondary should be
| A) | infinity |
| B) | 1000 Ohm |
| C) | zero |
| D) | 1 Ohm |
147. A transformer can have regulation closer to zero
| A) | on leading power factor |
| B) | on overload |
| C) | on zero power factor |
| D) | on full-load |
148. Noise level test in a transformer is a
| A) | special test |
| B) | routine test |
| C) | none of these answers |
| D) | type test |
149. The material used for construction of transformer core is usually
| A) | aluminium |
| B) | copper |
| C) | silicon steel |
| D) | wood |
150. The path of the magnetic flux in the transformer should have
| A) | high resistance |
| B) | low resistance |
| C) | high reluctance |
| D) | low reactance |
151. Which of the following statements regarding an ideal 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 rating is 2 kVA |
| B) | Its secondary voltage is 400 V |
| C) | It is a step-up transformer |
| D) | Its secondary current is 20 A |
| E) | Its secondary current is 5 A |
152. An ideal transformer will have maximum efficiency at a load such that
| A) | copper loss = iron loss |
| B) | copper loss < iron loss |
| C) | copper loss > iron loss |
| D) | none of these answers |
153. Leakage fluxes of a transformer may be minimized by
| A) | reducing the reluctance of the iron core to the minimum |
| B) | avoiding overloads |
| C) | keeping magnetizing current to the minimum |
| D) | sectionalizing and interleaving the primary and secondary windings |
| E) | minimizing the number of turns both on primary and secondary |
154. Cross-over windings are used for
| A) | high voltage winding of small rating transformers |
| B) | none of these answers |
| C) | high voltage winding of large rating transformers |
| D) | low voltage winding of small rating transformers |
155. Power transformers are generally designed to have maximum efficiency around
| A) | 10% overload |
| B) | half-load |
| C) | near full-load |
| D) | no-load |
156. The efficiency of a power transformer is of the order of
| A) | 25 percent |
| B) | 50 percent |
| C) | 98 percent |
| D) | 100 percent |
157. A distribution transformer has low flux density because
| A) | it is normally a small transformer |
| B) | it is required to give better power factor |
| C) | iron is quite cheap |
| D) | it is constantly connected to the supply |
158. When two single phase transformers are running in parallel and if the impedance triangles of the transformers are not identical in shape and size then
| A) | power factors at which the transformers operate will be different from one another and again these will be different from power factor of common load |
| B) | power factors at which the transformers operate will be same but different from power factor of common load |
| C) | power factors at which the transformers operate and power factor of common load-all will be same |
| D) | power factor of one transformer and power factor of common load will be same |
159. An ideal transformer has infinite values of primary and secondary inductances. The statement is
| A) | False |
| B) | True |
160. Which of the following protection is normally not provided on small distribution transformers?
| A) | Overcurrent protection |
| B) | Buchholz relay |
| C) | All of these answers |
| D) | Overfluxing protection |
161. Which of the following does not change in an ordinary transformer?
| A) | Any of these answers |
| B) | Frequency |
| C) | Current |
| D) | Voltage |
162. The chemical used in breather is
| A) | silica gel |
| B) | sodium chloride |
| C) | silica sand |
| D) | asbestos fibre |
163. No-load on a transformer is carried out to determine
| A) | magnetising current |
| B) | magnetising current and loss |
| C) | copper loss |
| D) | efficiency of the transformer |
164. The purpose of providing an iron core in a transformer is to
| A) | reduce eddy current losses |
| B) | reduce hysteresis loss |
| C) | decrease the reluctance of the magnetic path |
| D) | provide support to windings |
165. Negative voltage regulation is indicative that the load is
| A) | none of these answers |
| B) | inductive or resistive |
| C) | inductive only |
| D) | capacitive only |
166. Scott connections are used to convert
| A) | three-phase supply to D.C. supply |
| B) | three-phase supply to single-phase supply |
| C) | three-phase supply to two-phase supply |
| D) | three-phase supply to three-phase supply |
167. As the supply frequency of a transformer increases its rating
| A) | decreases |
| B) | none of these answers |
| C) | increases |
| D) | remains unchanged |
168. In the transformer following winding has got more cross-sectional area
| A) | Primary winding |
| B) | Low voltage winding |
| C) | High voltage winding |
| D) | Secondary winding |
169. The transformation ratio of a transformer, for a given application
| A) | depends on secondary load |
| B) | none of these answers |
| C) | is fixed but not constant |
| D) | is constant but not fixed |
170. In a transformer, the energy is conveyed from primary to secondary
| A) | none of these answers |
| B) | through cooling coil |
| C) | by the flux |
| D) | through air |
171. Reduction in core losses and increase in permeability are obtained with transformer employing
| A) | none of these answers |
| B) | core built-up of laminations of cold rolled grain oriented steel |
| C) | either core built-up of laminations of cold rolled grain oriented steel or core built-up of laminations of hot rolled sheet |
| D) | core built-up of laminations of hot rolled sheet |
172. If the percentage impedances of the two transformers working in parallel are different, then
| A) | power factors of both the transformers will be same |
| B) | transformers will be overheated |
| C) | 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 |
| D) | parallel operation will be not possible |
173. The efficiency of a transformer, under heavy loads, is comparatively low because
| A) | iron loss is increased considerably |
| B) | voltage drop both in primary and secondary becomes large |
| C) | secondary output is much less as compared to primary input |
| D) | copper loss becomes high in proportion to the output |
174. For the parallel operation of single-phase transformers it is necessary that they should have
| A) | same polarity |
| B) | same number of turns on the secondary side. |
| C) | same efficiency |
| D) | same kVA rating |
175. As per the name plate of a transformer, the secondary normal voltage is 220 V. Which of the following statements about it is correct ?
| A) | The secondary voltage increases with increasing load |
| B) | At a load which draws the rated current the voltage becomes less than 220 V |
| C) | 220 V is the no-load voltage |
| D) | The no-load voltage is more than 220 V |
176. Natural air cooling is generally restricted for transformers up to
| A) | 5 MVA |
| B) | 15 MVA |
| C) | 50 MVA |
| D) | 1.5 MVA |
177. The secondary of a current transformer is always short-circuited under operating conditions because it
| A) | none of these answers |
| B) | avoids core saturation and high voltage induction |
| C) | is safe to human beings |
| D) | protects the primary circuit |
178. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of
| A) | none of these answers |
| B) | 15 A |
| C) | less than 15 A |
| D) | more than 15 A |
179. Which of the following is not a routine test on transformers?
| A) | Core insulation voltage test |
| B) | Radio interference test |
| C) | Polarity test |
| D) | Impedance test |
180. In a three-phase delta transformer, one of the phases burns up. The transformer will supply
| A) | zero output |
| B) | its full output rating |
| C) | 40 percent of its output rating |
| D) | none of these answers |
| E) | 20 percent of its output rating |
181. All day efficiency is the ratio of output to input in
| A) | kWh during 24 hours |
| B) | kVA at a particular instant |
| C) | kW at particular instant |
| D) | kVARh at particular instant |
182. The value of useful flux least depends on
| A) | magnetomotive force |
| B) | all of these answers |
| C) | voltage |
| D) | load |
183. A transformer, as compared to an amplifier, cannot increase
| A) | the output voltage |
| B) | the output power |
| C) | the output current |
| D) | none of these answers |
184. The purpose of providing iron core in a step-up transformer is
| A) | to decrease the magnitude of magnetizing current |
| B) | to provide coupling between primary and secondary |
| C) | to increase the magnitude of mutual flux |
| D) | all of these answers |
185. During open circuit test of a transformer
| A) | primary is supplied full-load current |
| B) | primary is supplied rated kVA |
| C) | primary is supplied rated voltage |
| D) | primary is supplied current at reduced voltage |
186. Which of the following property is not necessarily desirable in the material for transformer core ?
| A) | High permeability |
| B) | High thermal conductivity |
| C) | Mechanical strength |
| D) | Low hysteresis loss |
187. The primary winding of a transformer
| A) | none of these answers |
| B) | is always a high voltage winding |
| C) | could either be a low voltage or high voltage winding |
| D) | is always a low voltage winding |
188. A transformer transforms
| A) | voltage |
| B) | current |
| C) | power |
| D) | current and voltage |
189. A transformer is used to change the value of
| A) | power |
| B) | frequency |
| C) | power factor |
| D) | voltage |
190. Which of the following can be reduced when the flux density in the transformer core is increased ?
| A) | Output frequency |
| B) | None of these answers |
| C) | Size of the transformer |
| D) | Copper losses |
191. The leakage flux in a transformer depends upon
| A) | load current, voltage and frequency |
| B) | load current and voltage |
| C) | load current |
| D) | load current, voltage, frequency and power factor |
192. A Buchholz relay can be installed on
| A) | oil cooled transformers |
| B) | welding transformers |
| C) | air-cooled transformers |
| D) | auto-transformers |
193. What will happen if the transformers working in parallel are not connected with regard to polarity ?
| A) | none of these answers |
| B) | Incorrect polarity will result in dead short circuit |
| C) | The transformers will not share load in proportion to their kVA ratings |
| D) | The power factor of the two transformers will be different from the power factor of common load |
194. The magnetizing current of a transformer is usually small because it has
| A) | small air gap |
| B) | fewer rotating parts |
| C) | large leakage flux |
| D) | laminated silicon steel core |
195. In a transformer on no-load, the input voltage
| A) | leads the magnetizing current by 90° |
| B) | lags the magnetizing current by 90° |
| C) | is always at 60° to the magnetizing current |
| D) | is in phase with magnetizing current |
196. The maximum efficiency of a distribution transformer is
| A) | at no load |
| B) | at 80% full load |
| C) | at 50% full load |
| D) | at full load |
197. The no load current in a transformer lags behind the applied voltage by an angle of about
| A) | 120° |
| B) | 180° |
| C) | 75° |
| D) | 90° |
198. A shell-type transformer has
| A) | none of these answers |
| B) | negligibly hysteresis losses |
| C) | reduced magnetic leakage |
| D) | high eddy current losses |
199. A transformer core is laminated to
| A) | all of these answers |
| B) | reduce hysteresis loss |
| C) | reduce eddy current losses |
| D) | reduce copper losses |
200. Spacers are provided between adjacent coils
| A) | none of these answers |
| B) | to insulate the coils from each other |
| C) | to provide free passage to the cooling oil |
| D) | both to provide free passage to the cooling oil and to insulate the coils from each other |
201. Which of the following loss in a transformer is zero even at full load ?
| A) | Hysteresis loss |
| B) | Friction loss |
| C) | Core loss |
| D) | Eddy current loss |
202. Minimum voltage regulation occurs when the power factor of the load is
| A) | leading |
| B) | zero |
| C) | unity |
| D) | lagging |
203. In some transformers, the tappings are provided on
| A) | H.V. side |
| B) | L.V. as well as on H.V. side |
| C) | L.V. side |
| D) | in the middle of both windings |
204. An open-circuit test on a transformer is conducted primarily to measure
| A) | copper loss |
| B) | efficiency |
| C) | insulation resistance |
| D) | core loss |
| E) | total loss |
205. A step-up transformer increases
| A) | frequency |
| B) | current |
| C) | voltage |
| D) | power |
206. The transformer laminations are insulated from each other by
| A) | mica strip |
| B) | paper |
| C) | any of these answers |
| D) | thin coat of varnish |
207. While performing back-to-back test, the amount of power consumed is equal to
| A) | iron and copper losses of two transformers at full load |
| B) | none of these answers |
| C) | rated output of two transformers and iron and copper losses of transformers at full load |
| D) | full load rated output of the two transformers |
208. The hum in a transformer is mainly attributed to
| A) | oil in the transformer |
| B) | load changes |
| C) | magnetostriction |
| D) | mechanical vibrations |
209. A transformer is working at its maximum efficiency. Its iron loss is 1 kW. Its copper loss will be
| A) | 0.2 kW |
| B) | 0.5 kW |
| C) | 0.25 kW |
| D) | 1 kW |
210. Harmonics in transformer result in
| A) | magnetic interference with communication circuits |
| B) | increasedlosses |
| C) | all of these answers |
| D) | increased core losses |
211. The nominal short-circuit voltage of the transformer is defined as the percentage of
| A) | the test voltage |
| B) | the nominal transformation ratio |
| C) | the rated secondary voltage |
| D) | none of these answers |
| E) | the rated primary voltage |
212. Transformer for constant voltage applications is considered good if its voltage regulation is
| A) | high |
| B) | zero |
| C) | none of these answers |
| D) | low |
213. Gas is usually not liberated due to the dissociation of transformer oil unless the oil temperature exceeds
| A) | 150°C |
| B) | 80°C |
| C) | 100°C |
| D) | 50°C |
214. In a transformer frictional loss is
| A) | 20% of total loss |
| B) | 10% of total loss |
| C) | 5% of total loss |
| D) | any of these answers |
215. Part of the transformer which is most subject to damage from overheating is
| A) | copper winding |
| B) | transformer tank |
| C) | iron core |
| D) | winding insulation |
| E) | frame or case |
216. The chemical used in breather for transformer should have the quality of
| A) | absorbing moisture |
| B) | cooling the transformer oil. |
| C) | ionizing air |
| D) | cleansing the transformer oil |
217. The value of flux involved in the e.m.f. equation of a transformer is
| A) | average value |
| B) | instantaneous value |
| C) | r.m.s. value |
| D) | maximum value |
218. A good voltage regulation of a transformer means
| A) | difference between primary and secondary voltage is least |
| B) | output voltage fluctuation with power factor is least |
| C) | difference between primary and secondary voltage is maximum |
| D) | output voltage fluctuation from no load to full load is least |
219. When secondary of a current transformer is open-circuited its iron core will be
| A) | hot because of heavy iron losses taking place in it due to high flux density |
| B) | hot because primary will carry the heavy current |
| C) | cool as there is no secondary current |
| D) | none of these answers |
220. In order to find the full-load efficiency of a transformer the losses which must be known
| A) | may be found by measuring winding resistances and calculating thelosses |
| B) | may be found by performing open-circuit and short-circuit tests |
| C) | may be found by measuring the input to the primary with secondary open |
| D) | cannot be found except by actually loading the transformer fully. |
221. Which of the following methods is used for cooling of transformers upto a capacity of 10 MVA?
| A) | None of these answers |
| B) | Air blast cooling |
| C) | Forced oil cooling |
| D) | Oil natural cooling |
222. Which of the following insulating materials can withstand the highest temperature safely?
| A) | Cellulose |
| B) | Glass fibre |
| C) | Asbestos |
| D) | Mica |
223. In a transformer the magnitude of mutual flux
| A) | varies at low loads and constant at high loads |
| B) | same at all loads |
| C) | is low at low loads and high at high. Loads |
| D) | is high at low loads and low at high loads |
224. The function of the breather in a transformer is
| A) | to provide oxygen inside the tank |
| B) | to cool the transformer oil |
| C) | to arrest flow of moisture when outside air enters the transformer |
| D) | to cool the coils during reduced load |
225. Sumpner’s test is conducted on transformers to determine
| A) | all-day efficiency |
| B) | temperature |
| C) | stray losses |
| D) | none of these answers |
226. No-load current in a transformer
| A) | leads the voltage by about 75° |
| B) | leads the voltage by about 15° |
| C) | lags behind the voltage by about 15° |
| D) | lags behind the voltage by about 75° |
227. The secondary winding of which of the following transformers is always kept closed ?
| A) | Step-up transformer |
| B) | Potential transformer |
| C) | Current transformer |
| D) | Step-down transformer |
228. If a transformer is continuously operated the maximum temperature rise will occur in
| A) | any of these answers |
| B) | windings |
| C) | core |
| D) | tank |
229. The voltage transformation ratio of a transformer is equal to the ratio of
| A) | secondary terminal voltage to primary-applied voltage |
| B) | primary turns to secondary turns |
| C) | secondary induced e.m.f. to primary induced e.m.f. |
| D) | secondary current to primary current |
230. Buchholz relay is used in
| A) | none of these answers |
| B) | motor protection |
| C) | transformer protection |
| D) | line protection |
231. The size of a transformer core will depend on
| A) | area of the core |
| B) | frequency and area of the core |
| C) | flux density of the core material |
| D) | frequency |
232. For minimum weight of a transformer, the weight of iron should be
| A) | equal to the weight of copper |
| B) | zero |
| C) | greater than weight of copper |
| D) | less than weight of copper |
233. The advantage of putting tappings at the phase ends of a transformer is
| A) | to operate with ease |
| B) | to obtain better regulation |
| C) | to obtain fine variation of voltage |
| D) | to reduce the number of bushings |
234. The secondary winding of a current transformer whose primary is carrying current should
| A) | not be open-circuited |
| B) | none of these answers |
| C) | either not be open-circuited or not be short-circuited |
| D) | not be short-circuited |
235. The thickness of laminations used in a transformer is usually
| A) | 14 mm to 15 mm |
| B) | 0.4 mm to 0.5 mm |
| C) | 4 mm to 5 mm |
| D) | 25 min to 40 mm |
236. Buchhalz’s relay is used in
| A) | generator protection |
| B) | motor protection |
| C) | line protection |
| D) | transformer protection |
237. Star/star transformers work satisfactorily when
| A) | load is balanced only |
| B) | load is unbalanced only |
| C) | none of these answers |
| D) | on balanced as well as unbalanced loads |
238. Star-star power transformer is protected by current transformer having
| A) | star/star connections |
| B) | delta/delta connections |
| C) | star/delta connections |
| D) | delta/star connections |
239. In a transformer, the tappings are generally provided on
| A) | secondary side |
| B) | primary side |
| C) | low voltage side |
| D) | high voltage side |
240. Transformer breaths in when
| A) | load remains constant |
| B) | load on it decreases |
| C) | none of these answers |
| D) | load on it increases |
241. The purpose of performing Sumpner’s test is mainly to find out
| A) | the temperature rise on fill load economically |
| B) | regulation of the transformer |
| C) | none of these answers |
| D) | efficiency of the transformer |
242. In case of transformers using cold rolled grain oriented steel, the area of yoke is taken
| A) | as 15-20% larger than that of core |
| B) | none of these answers |
| C) | equal to that of core |
| D) | as 10-15% larger than that of core |
| E) | as 20-25% larger than that of core |
243. The purpose of providing iron core in a step-up transformer is
| A) | to decrease the magnitude of magnetizing current |
| B) | all of these answers |
| C) | to increase the magnitude of mutual flux |
| D) | to provide coupling between primary and secondary |
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