McqMate
Chapters
| 1. |
Which of the following does not change in a transformer ? |
| A. | Current |
| B. | Voltage |
| C. | Frequency |
| D. | All of the above |
| Answer» C. Frequency | |
| 2. |
In a transformer the energy is conveyed from primary to secondary |
| A. | through cooling coil |
| B. | through air |
| C. | by the flux |
| D. | none of the above |
| Answer» C. by the flux | |
| 3. |
A transformer core is laminated to |
| A. | reduce hysteresis loss |
| B. | reduce eddy current losses |
| C. | reduce copper losses |
| D. | reduce all above losses |
| Answer» B. reduce eddy current losses | |
| 4. |
The degree of mechanical vibrations produced by the laminations of a transformer depends on |
| A. | tightness of clamping |
| B. | gauge of laminations |
| C. | size of laminations |
| D. | all of the above |
| Answer» D. all of the above | |
| 5. |
The no-load current drawn by transformer is usually what per cent of the full-load current ? |
| A. | 0.2 to 0.5 per cent |
| B. | 2 to 5 per cent |
| C. | 12 to 15 per cent |
| D. | 20 to 30 per cent |
| Answer» B. 2 to 5 per cent | |
| 6. |
The path of a magnetic flux in a transformer should have |
| A. | high resistance |
| B. | high reluctance |
| C. | low resistance |
| D. | low reluctance |
| Answer» D. low reluctance | |
| 7. |
No-load on a transformer is carried out to determine |
| A. | copper loss |
| B. | magnetising current |
| C. | magnetising current and loss |
| D. | efficiency of the tr |
| Answer» A. copper loss | |
| 8. |
The dielectric strength of transformer oil is expected to be |
| A. | lkV |
| B. | 33 kV |
| C. | 100 kV |
| D. | 330 kV |
| Answer» B. 33 kV | |
| 9. |
Sumpner's test is conducted on trans-formers to determine |
| A. | temperature |
| B. | stray losses |
| C. | all-day efficiency |
| D. | none of the above |
| Answer» A. temperature | |
| 10. |
The permissible flux density in case of cold rolled grain oriented steel is around |
| A. | 1.7 Wb/m2 |
| B. | 2.7 Wb/m2 |
| C. | 3.7 Wb/m2 |
| D. | 4.7 Wb/m2 |
| Answer» A. 1.7 Wb/m2 | |
| 11. |
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 |
| Answer» D. copper losses = iron losses | |
| 12. |
No-load current in a transformer |
| A. | lags behind the voltage by about 75° |
| B. | leads the voltage by about 75° |
| C. | lags behind the voltage by about 15° |
| D. | leads the voltage by about 15° |
| Answer» A. lags behind the voltage by about 75° | |
| 13. |
The purpose of providing an iron core in a transformer is to |
| A. | provide support to windings |
| B. | reduce hysteresis loss |
| C. | decrease the reluctance of the magnetic path |
| D. | reduce eddy current losses |
| Answer» C. decrease the reluctance of the magnetic path | |
| 14. |
Which of the following is not a part of transformer installation ? |
| A. | Conservator |
| B. | Breather |
| C. | Buchholz relay |
| D. | Exciter |
| Answer» D. Exciter | |
| 15. |
While conducting short-circuit test on a transformer the following side is short circuited |
| A. | High voltage side |
| B. | Low voltage side |
| C. | Primary side |
| D. | Secondary side |
| Answer» B. Low voltage side | |
| 16. |
In the transformer following winding has got more cross-sectional area |
| A. | Low voltage winding |
| B. | High voltage winding |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» A. Low voltage winding | |
| 17. |
A transformer transforms |
| A. | voltage |
| B. | current |
| C. | power |
| D. | frequency |
| Answer» C. power | |
| 18. |
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. | a D.C. circuit has more losses |
| C. | Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero |
| D. | none of the above |
| Answer» 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 |
| A. | is always a low voltage winding |
| B. | is always a high voltage winding |
| C. | could either be a low voltage or high voltage winding |
| D. | none of the above |
| Answer» C. could either be a low voltage or high voltage winding | |
| 20. |
Which winding in a transformer has more number of turns ? |
| A. | Low voltage winding |
| B. | High voltage winding |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» B. High voltage winding | |
| 21. |
Efficiency of a power transformer is of the order of |
| A. | 100 per cent |
| B. | 98 per cent |
| C. | 50 per cent |
| D. | 25 per cent |
| Answer» B. 98 per cent | |
| 22. |
In a given transformer for given applied voltage, losses which remainconstant irrespective of load changes are |
| A. | friction and windage losses |
| B. | copper losses |
| C. | hysteresis and eddy current losses |
| D. | none of the above |
| Answer» C. hysteresis and eddy current losses | |
| 23. |
A common method of cooling a power transformer is |
| A. | natural air cooling |
| B. | air blast cooling |
| C. | oil cooling |
| D. | any of the above |
| Answer» C. oil cooling | |
| 24. |
The no load current in a transformer lags behind the appliedvoltage by an angle of about |
| A. | 180° |
| B. | 120" |
| C. | 90° |
| D. | 75° |
| Answer» D. 75° | |
| 25. |
In a transformer routine efficiency depends upon |
| A. | supply frequency |
| B. | load current |
| C. | power factor of load |
| D. | both (b) and (c) |
| Answer» D. both (b) and (c) | |
| 26. |
In the transformer the function of a conservator is to |
| A. | provide fresh air for cooling the transformer |
| B. | supply cooling oil to transformer in time of need |
| C. | protect the transformer from damage when oil expends due to heating |
| D. | none of the above |
| Answer» C. protect the transformer from damage when oil expends due to heating | |
| 27. |
Natural oil cooling is used for transformers upto a rating of |
| A. | 3000 kVA |
| B. | 1000 kVA |
| C. | 500 kVA |
| D. | 250 kVA |
| Answer» A. 3000 kVA | |
| 28. |
Power transformers are designed to have maximum efficiency at |
| A. | nearly full load |
| B. | 70% full load |
| C. | 50% full load |
| D. | no load |
| Answer» A. nearly full load | |
| 29. |
The maximum efficiency of a distribution transformer is |
| A. | at no load |
| B. | at 50% full load |
| C. | at 80% full load |
| D. | at full load |
| Answer» B. at 50% full load | |
| 30. |
Transformer breaths in when |
| A. | load on it increases |
| B. | load on it decreases |
| C. | load remains constant |
| D. | none of the above |
| Answer» B. load on it decreases | |
| 31. |
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 high power factor |
| D. | has small magnitude and low powerfactor |
| Answer» D. has small magnitude and low powerfactor | |
| 32. |
Spacers are provided between adjacent coils |
| A. | to provide free passage to the cool¬ing oil |
| B. | to insulate the coils from each other |
| C. | both (a) and (b) |
| D. | none of the above |
| Answer» A. to provide free passage to the cool¬ing oil | |
| 33. |
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 |
| Answer» A. less will be the secondary induced e.m.f. | |
| 34. |
The purpose of providing iron core in a step-up transformer is |
| A. | to provide coupling between primary and secondary |
| B. | to increase the magnitude of mutual flux |
| C. | to decrease the magnitude of mag-netizing current |
| D. | to provide all above features |
| Answer» C. to decrease the magnitude of mag-netizing current | |
| 35. |
The power transformer is a constant |
| A. | voltage device |
| B. | current device |
| C. | power device |
| D. | main flux device |
| Answer» D. main flux device | |
| 36. |
Two transformers operating in parallel will share the load depending upon their |
| A. | leakage reactance |
| B. | per unit impedance |
| C. | efficiencies |
| D. | ratings |
| Answer» 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 |
| A. | R2/VK |
| B. | R2IK2 |
| C. | R22!K2 |
| D. | R22/K |
| Answer» B. R2IK2 | |
| 38. |
What will happen if the transformers working in parallel are not connected with regard to polarity ? |
| A. | The power factor of the two trans-formers will be different from the power factor of common load |
| B. | Incorrect polarity will result in dead short circuit |
| C. | The transformers will not share load in proportion to their kVA ratings |
| D. | none of the above |
| Answer» B. Incorrect polarity will result in dead short circuit | |
| 39. |
Ifthe percentage impedances of the two transformers working in parallel aredifferent, then |
| A. | transformers will be overheated |
| B. | power factors of both the trans-formers 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 tr |
| Answer» A. transformers will be overheated | |
| 40. |
In a transformer the tappings are generally provided on |
| A. | primary side |
| B. | secondary side |
| C. | low voltage side |
| D. | high voltage side |
| Answer» C. low voltage side | |
| 41. |
The use of higher flux density in the transformer design |
| A. | reduces weight per kVA |
| B. | reduces iron losses |
| C. | reduces copper losses |
| D. | increases part load efficiency |
| Answer» A. reduces weight per kVA | |
| 42. |
The chemical used in breather for transformer should have the quality of |
| A. | ionizing air |
| B. | absorbing moisture |
| C. | cleansing the transformer oil |
| D. | cooling the tr |
| Answer» A. ionizing air | |
| 43. |
The chemical used in breather is |
| A. | asbestos fibre |
| B. | silica sand |
| C. | sodium chloride |
| D. | silica gel |
| Answer» D. silica gel | |
| 44. |
The transformer ratings are usually expressed in terms of |
| A. | volts |
| B. | amperes |
| C. | kW |
| D. | kVA |
| Answer» D. kVA | |
| 45. |
The noise resulting from vibrations of laminations set by magnetic forces, is termedas |
| A. | magnetostrication |
| B. | boo |
| C. | hum |
| D. | zoom |
| Answer» C. hum | |
| 46. |
Hysteresis loss in a transformer varies as CBmax = maximum flux density) |
| A. | Bmax |
| B. | Bmax1-6 |
| C. | Bmax1-83 |
| D. | B max |
| Answer» B. Bmax1-6 | |
| 47. |
Material used for construction of transformer core is usually |
| A. | wood |
| B. | copper |
| C. | aluminium |
| D. | silicon steel |
| Answer» D. silicon steel | |
| 48. |
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 |
| Answer» A. 0.4 mm to 0.5 mm | |
| 49. |
The function of conservator in a transformer is |
| A. | to project against'internal fault |
| B. | to reduce copper as well as core losses |
| C. | to cool the transformer oil |
| D. | to take care of the exp |
| Answer» A. to project against'internal fault | |
| 50. |
The highest voltage for transmitting electrical power in India is |
| A. | 33 kV. |
| B. | 66 kV |
| C. | 132 kV |
| D. | 400 kV |
| Answer» D. 400 kV | |
| 51. |
In a transformer the resistance between its primary and secondary is |
| A. | zero |
| B. | 1 ohm |
| C. | 1000 ohms |
| D. | infinite |
| Answer» D. infinite | |
| 52. |
A transformer oil must be free from |
| A. | sludge |
| B. | odour |
| C. | gases |
| D. | moisture |
| Answer» D. moisture | |
| 53. |
A Buchholz relay can be installed on |
| A. | auto-transformers |
| B. | air-cooled transformers |
| C. | welding transformers |
| D. | oil cooled tr |
| Answer» A. auto-transformers | |
| 54. |
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 |
| Answer» D. 150°C | |
| 55. |
The main reason for generation of harmonics in a transformer could be |
| A. | fluctuating load |
| B. | poor insulation |
| C. | mechanical vibrations |
| D. | saturation of core |
| Answer» D. saturation of core | |
| 56. |
Distribution transformers are generally designed for maximum efficiency around |
| A. | 90% load |
| B. | zero load |
| C. | 25% load |
| D. | 50% load |
| Answer» D. 50% load | |
| 57. |
Which of the following property is not necessarily desirable in the material for transformer core ? |
| A. | Mechanical strength |
| B. | Low hysteresis loss |
| C. | High thermal conductivity |
| D. | High permeability |
| Answer» C. High thermal conductivity | |
| 58. |
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 |
| Answer» B. load is balanced only | |
| 59. |
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 |
| Answer» C. on balanced as well as unbalanced loads | |
| 60. |
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 |
| Answer» A. electrical fault inside the transformer itself | |
| 61. |
The magnetising current of a transformer is usually small because it has |
| A. | small air gap |
| B. | large leakage flux |
| C. | laminated silicon steel core |
| D. | fewer rotating parts |
| Answer» A. small air gap | |
| 62. |
Which of the following does not change in an ordinary transformer ? |
| A. | Frequency |
| B. | Voltage |
| C. | Current |
| D. | Any of the above |
| Answer» A. Frequency | |
| 63. |
Which of the following properties is not necessarily desirable for the material for transformer core ? |
| A. | Low hysteresis loss |
| B. | High permeability |
| C. | High thermal conductivity |
| D. | Adequate mechanicalstrength |
| Answer» C. High thermal conductivity | |
| 64. |
The leakage flux in a transformer depends upon |
| A. | load current |
| B. | load current and voltage |
| C. | load current, voltage and frequency |
| D. | load current, voltage, frequency and powerfactor |
| Answer» A. load current | |
| 65. |
The path of the magnetic flux in transformer should have |
| A. | high reluctance |
| B. | low reactance |
| C. | high resistance |
| D. | low resistance |
| Answer» B. low reactance | |
| 66. |
Noise level test in a transformer is a |
| A. | special test |
| B. | routine test |
| C. | type test |
| D. | none of the above |
| Answer» C. type test | |
| 67. |
Which of the foJIowing is not a routine test on transformers ? |
| A. | Core insulation voltage test |
| B. | Impedance test |
| C. | Radio interference test |
| D. | Polarity test |
| Answer» C. Radio interference test | |
| 68. |
A transformer can have zero voltage regulation at |
| A. | leading power factor |
| B. | lagging powerfactor |
| C. | unity power factor |
| D. | zero power factor |
| Answer» A. leading power factor | |
| 69. |
Helical coils can be used on |
| A. | low voltage side of high kVA trans¬formers |
| B. | high frequency transformers |
| C. | high voltage side of small capacity transformers |
| D. | high voltage side of high kVA rating tr |
| Answer» A. low voltage side of high kVA trans¬formers | |
| 70. |
Harmonics in transformer result in |
| A. | increased core losses |
| B. | increased I2R losses |
| C. | magnetic interference with communication circuits |
| D. | all of the above |
| Answer» D. all of the above | |
| 71. |
The core used in high frequency transformer is usually |
| A. | copper core |
| B. | cost iron core |
| C. | air core |
| D. | mild steel core |
| Answer» C. air core | |
| 72. |
The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be |
| A. | 6400 W |
| B. | 1600 W |
| C. | 800 W |
| D. | 400 W |
| Answer» D. 400 W | |
| 73. |
The value of flux involved m the e.m.f. equation of a transformer is |
| A. | average value |
| B. | r.m.s. value |
| C. | maximum value |
| D. | instantaneous value |
| Answer» C. maximum value | |
| 74. |
Silicon steel used in laminations mainly reduces |
| A. | hysteresis loss |
| B. | eddy current losses |
| C. | copper losses |
| D. | all of the above |
| Answer» A. hysteresis loss | |
| 75. |
Which winding of the transformer has less cross-sectional area ? |
| A. | Primary winding |
| B. | Secondary winding |
| C. | Low voltage winding |
| D. | High voltage winding |
| Answer» D. High voltage winding | |
| 76. |
Power transformers are generally designed to have maximum efficiency around |
| A. | no-load |
| B. | half-load |
| C. | near full-load |
| D. | 10% overload |
| Answer» C. near full-load | |
| 77. |
Which of the following is the main advantage of an auto-transformer over a two winding transformer ? |
| A. | Hysteresis losses are reduced |
| B. | Saving in winding material |
| C. | Copper losses are negligible |
| D. | Eddy losses are totally eliminated |
| Answer» B. Saving in winding material | |
| 78. |
During short circuit test iron losses are negligible because |
| A. | the current on secondary side is negligible |
| B. | the voltage on secondary side does not vary |
| C. | the voltage applied on primary side is low |
| D. | full-load current is not supplied to thetr |
| Answer» 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 |
| A. | short-circuiting of the secondaries |
| B. | power factor of one of the trans¬formers is leading while that of the otherlagging |
| C. | transformers having higher copper losses will have negligible core losses |
| D. | loading of the tr |
| Answer» 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 |
| A. | Conservator |
| B. | Breather |
| C. | Bushings |
| D. | Buchholz relay |
| Answer» A. Conservator | |
| 81. |
An ideal transformer is one which has |
| A. | no losses and magnetic leakage |
| B. | interleaved primary and secondary windings |
| C. | a common core for its primary and secondary windings |
| D. | core of stainless steel and winding of pure copper metal |
| Answer» A. no losses and magnetic leakage | |
| 82. |
When a given transformer is run at its rated voltage but reduced frequency, its |
| A. | flux density remains unaffected |
| B. | iron losses are reduced |
| C. | core flux density is reduced |
| D. | core flux density is increased |
| Answer» D. core flux density is increased | |
| 83. |
In an actual transformer the iron loss remains practically constant from noload to fullload because |
| A. | value of transformation ratio remains constant |
| B. | permeability of transformer core remains constant |
| C. | core flux remains practically constant |
| D. | primary voltage remains constant |
| Answer» C. core flux remains practically constant | |
| 84. |
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 the above |
| Answer» A. copper loss = iron loss | |
| 85. |
If the supply frequency to the transformer is increased,"the iron loss will |
| A. | not change |
| B. | decrease |
| C. | increase |
| D. | any of the above |
| Answer» C. increase | |
| 86. |
Negative voltage regulation is indicative that the load is |
| A. | capacitive only |
| B. | inductive only |
| C. | inductive or resistive |
| D. | none of the above |
| Answer» A. capacitive only | |
| 87. |
Iron loss of a transformer can be measured by |
| A. | low power factor wattmeter |
| B. | unity power factor wattmeter |
| C. | frequency meter |
| D. | any type of wattmeter |
| Answer» A. low power factor wattmeter | |
| 88. |
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 heavy current |
| C. | cool as there is no secondary current |
| D. | none of above will happen |
| Answer» 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 |
| A. | mica strip |
| B. | thin coat of varnish |
| C. | paper |
| D. | any of the above |
| Answer» B. thin coat of varnish | |
| 90. |
Which type of winding is used in 3phase shell-type transformer ? |
| A. | Circular type |
| B. | Sandwich type |
| C. | Cylindrical type |
| D. | Rectangular type |
| Answer» B. Sandwich type | |
| 91. |
During open circuit test of a transformer |
| A. | primary is supplied rated voltage |
| B. | primary is supplied full-load current |
| C. | primary is supplied current at reduced voltage |
| D. | primary is supplied rated kVA |
| Answer» A. primary is supplied rated voltage | |
| 92. |
Open circuit test on transformers is conducted to determine |
| A. | hysteresis losses |
| B. | copper losses |
| C. | core losses |
| D. | eddy current losses |
| Answer» C. core losses | |
| 93. |
Short circuit test on transformers is conducted to determine |
| A. | hysteresis losses |
| B. | copper losses |
| C. | core losses |
| D. | eddy current losses |
| Answer» B. copper losses | |
| 94. |
For the parallel operation of single phase transformers it is necessary that they should have |
| A. | same efficiency |
| B. | same polarity |
| C. | same kVA rating |
| D. | same number of turns on the secondary side. |
| Answer» B. same polarity | |
| 95. |
The transformer oil should have volatility and viscosity. |
| A. | low,low |
| B. | high,high |
| C. | low,high |
| D. | high,low |
| Answer» A. low,low | |
| 96. |
The function of breather in a transformer is |
| A. | to provide oxygen inside the tank |
| B. | to cool the coils during reduced load |
| C. | to cool the transformer oil |
| D. | to arrest flow of moisture when outside air enters thetr |
| Answer» B. to cool the coils during reduced load | |
| 97. |
The secondary winding of which of the following transformers is always kept closed? |
| A. | Step-up transformer |
| B. | Step-down transformer |
| C. | Potential transformer |
| D. | Current tr |
| Answer» A. Step-up transformer | |
| 98. |
The size of a transformer core will depend on |
| A. | frequency |
| B. | area of the core |
| C. | flux density of the core material |
| D. | (a) and (b) both |
| Answer» D. (a) and (b) both | |
| 99. |
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 |
| Answer» A. 1.5 MVA | |
| 100. |
A shell-type transformer has |
| A. | high eddy current losses |
| B. | reduced magnetic leakage |
| C. | negligibly hysteresis losses |
| D. | none of the above |
| Answer» B. reduced magnetic leakage | |
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