MCQOPTIONS
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MCQOPTIONS
This section includes 123 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
Which type of winding is used in 3 phase shell type transformer? |
| A. | Circular type |
| B. | Sandwich type |
| C. | Cylindrical type |
| D. | Rectangular type |
| Answer» C. Cylindrical type | |
| 52. |
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» C. Paper | |
| 53. |
The changes in volume of transformer cooling oil due to variation of atmospeheric temperature during day and night is taken care of by which part of transformer? |
| A. | Conservator |
| B. | Breather |
| C. | Bushings |
| D. | Buchholz relay |
| Answer» B. Breather | |
| 54. |
Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results |
| A. | Short-circuiting of the secondaries |
| B. | Power factor of one of the transformers is leading while that of the other lagging |
| C. | Transformers having higher copper losses will have negligible core losses |
| D. | Loading of the transformers not in proportion to their kVA ratings. |
| Answer» E. | |
| 55. |
Power transformers are generally designed to have maximum efficiency around |
| A. | No load |
| B. | Half load |
| C. | Near full load |
| D. | 10% overload |
| Answer» D. 10% overload | |
| 56. |
The full load copper loss of a transformer is 1600W. At half-load the copper loss will be |
| A. | 6400W |
| B. | 1600W |
| C. | 800W |
| D. | 400W |
| Answer» E. | |
| 57. |
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» E. | |
| 58. |
High frequency transformers sometimes make use of ferrite cores because it has |
| A. | High specific gravity |
| B. | High resistance |
| C. | High hysteresis |
| D. | low permeability |
| Answer» C. High hysteresis | |
| 59. |
Silicon steel used in laminations mainly reduces |
| A. | Hysteresis loss |
| B. | . Eddy current losses |
| C. | Copper loss |
| D. | All of the above |
| Answer» B. . Eddy current losses | |
| 60. |
In case there are burrs on the edges of the laminations of the transformer, it is likely to result in |
| A. | Vibrations |
| B. | Noise |
| C. | Higher eddy currents loss |
| D. | Higher hysteresis loss |
| Answer» D. Higher hysteresis loss | |
| 61. |
The path of a magnetic flux in a transformer should have |
| A. | High resistance |
| B. | High reluctance |
| C. | Low resistance |
| D. | Low reluctance |
| Answer» E. | |
| 62. |
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 transformer oil |
| Answer» C. Cleansing the transformer oil | |
| 63. |
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» C. primary side | |
| 64. |
No-load current in a transformer |
| A. | Lags behind the voltage by about 75 deg |
| B. | leads the voltage by about 75 |
| C. | lags behind the voltage by about 15 |
| D. | leads the voltage by about 15 |
| Answer» B. leads the voltage by about 75 | |
| 65. |
During the short-circuit test on a small transformer the frequency is increased from 50-200Hz. The copper losses will increase by a factor of |
| A. | 16 |
| B. | 4 |
| C. | 1 |
| D. | . 1/4 |
| Answer» B. 4 | |
| 66. |
The dielectric strength of transformer oil is expected to be |
| A. | 1kV |
| B. | 33kV |
| C. | 100kV |
| D. | 330 kV |
| Answer» C. 100kV | |
| 67. |
The no-load current drawn by transformer is usually........percent of the full-load current? |
| A. | 0.2 to 0.5 % |
| B. | 2 to 5% |
| C. | 12 to 15 % |
| D. | 20 to 30 % |
| Answer» C. 12 to 15 % | |
| 68. |
The degree of mechanical vibrations produced by the laminations of a transformers depends on |
| A. | Tightness of clamping |
| B. | Gauge of laminations |
| C. | Size of laminations |
| D. | All of the above |
| Answer» E. | |
| 69. |
The noise resulting from vibrations of laminations set by magnetic force, is termed as |
| A. | magnetostriction |
| B. | boo |
| C. | hum |
| D. | zoom |
| Answer» D. zoom | |
| 70. |
If a pump motor is run on 2/3rd of its supply voltage, it will |
| A. | Continue to deliver same power |
| B. | burn |
| C. | stall |
| D. | continue to run at lower speed |
| Answer» D. continue to run at lower speed | |
| 71. |
In a transformer the resistance between its primary and secondary is |
| A. | Zero |
| B. | 1Ω |
| C. | 1000 Ω |
| D. | Infinite |
| Answer» E. | |
| 72. |
Which of the following does not change in a transformer? |
| A. | Current |
| B. | Voltage |
| C. | . Frequency |
| D. | All of the above |
| Answer» D. All of the above | |
| 73. |
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 |
| Answer» B. Increased 8 times | |
| 74. |
In operating a 400hz transformer at 50Hz |
| A. | Only voltage is reduced in the same proportion as the frequency |
| B. | Only KVA rating is reduced in the same proportion as the frequency |
| C. | Both voltage and KVA rating are reduced in the same proportion as frequency |
| D. | None of the above |
| Answer» C. Both voltage and KVA rating are reduced in the same proportion as frequency | |
| 75. |
The iron loss of the transformer is negligible during short circuit test because |
| A. | The entire input is just sufficient to meet Cu losses only |
| B. | Flux produced is a small fraction of the normal flux |
| C. | Iron core becomes fully saturated |
| D. | Supply frequency is held constant |
| Answer» C. Iron core becomes fully saturated | |
| 76. |
A transformer has 1000 primary turns, connected to 250V ac supply. To get 400V secondary voltage the no of secondary turns should be |
| A. | 1600 |
| B. | 250 |
| C. | 400 |
| D. | 1250 |
| Answer» B. 250 | |
| 77. |
A transformer has negative voltage regulation when its load power factor is |
| A. | Zero |
| B. | Unity |
| C. | Leading |
| D. | Lagging |
| Answer» D. Lagging | |
| 78. |
The open circuit test is carried out in a transformer to find the |
| A. | Cu loss |
| B. | Core loss |
| C. | Total loss |
| D. | Insulation resistance |
| Answer» C. Total loss | |
| 79. |
During light loads, the transformer efficiency is low because |
| A. | Secondary output is low |
| B. | Transformer losses are high |
| C. | Fixed loss is high in proportion to the output |
| D. | Cu loss is small |
| Answer» D. Cu loss is small | |
| 80. |
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 |
| Answer» E. | |
| 81. |
The core used in high frequency transformer is usually |
| A. | Copper core |
| B. | Cost iron core |
| C. | Air core |
| D. | Mid steel core |
| Answer» D. Mid steel core | |
| 82. |
The function of 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 |
| Answer» E. | |
| 83. |
The highest voltage for transmitting electrical power in India is |
| A. | 33kV |
| B. | 66kV |
| C. | 132kV |
| D. | 400kV |
| Answer» E. | |
| 84. |
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» D. reduce eddy current losses | |
| 85. |
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» E. | |
| 86. |
Which loss is not common between a transformer and rotating machines? |
| A. | Eddy current loss |
| B. | Copper loss |
| C. | Windage loss |
| D. | Hysteresis loss |
| Answer» B. Copper loss | |
| 87. |
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» D. None of the above | |
| 88. |
In the autotransformer obtained in Question 57, the current in each coil is |
| A. | Coil-1 is 25A and Coil-2 is 10A |
| B. | Coil-1 is 10A and Coil-2 is 25A |
| C. | Coil-1 is 10A and Coil-2 is 15A |
| D. | Coil-1 is 15A and Coil-2 is 10A |
| Answer» B. Coil-1 is 10A and Coil-2 is 25A | |
| 89. |
The coils are to be connected to obtain a single phase, 400/1000V, auto-transformer to drive a load of 10kVA. Which of the options given should be exercised to realize the required auto-transformer? |
| A. | Connect A and D; Common B |
| B. | Connect B and D; Common C |
| C. | Connect A and C; Common B |
| D. | Connect A and C; Common D |
| Answer» B. Connect B and D; Common C | |
| 90. |
If the waveform of i(t) is changed to i(t)= 10 sin(100πt)A, the peak voltage across A and B with S closed is |
| A. | 400V |
| B. | 240V |
| C. | 320V |
| D. | 160V |
| Answer» B. 240V | |
| 91. |
The peak voltage across A and B, with S open is |
| A. | 400/ πV |
| B. | 800 πV |
| C. | 4000/π V |
| D. | 800/ πV |
| Answer» E. | |
| 92. |
With S2 closed and S1 open, the current waveform in the delta winding will be |
| A. | a sinusoidal at fundamental frequency |
| B. | . flat-topped with third harmonic |
| C. | only third-harmonic |
| D. | none of these |
| Answer» D. none of these | |
| 93. |
With both S1 and S2 open, the core flux waveform will be |
| A. | a sinusoidal at fundamental frequency |
| B. | flat-topped with third harmonic |
| C. | peaky with third-harmonic |
| D. | . none of these |
| Answer» C. peaky with third-harmonic | |
| 94. |
In performing the short circuit test of a transformer |
| A. | high voltage is usually short circuited |
| B. | low voltage side is usually short circuited |
| C. | any side is short circuited with preference |
| D. | none of the above |
| Answer» C. any side is short circuited with preference | |
| 95. |
In transformer terminology, the ratio 20:1 indicates that |
| A. | there are 20 turns on primary one turn on secondary |
| B. | secondary voltage is 1/20th of the primary |
| C. | primary current is 20 times greater than the secondary current |
| D. | for every 20 turns on primary, there is one turn on secondary |
| Answer» C. primary current is 20 times greater than the secondary current | |
| 96. |
In a two winding transformer, the emf /turn in secondary winding is always......the induced emf power turn in primary |
| A. | equal to k times |
| B. | equal to 1/k times |
| C. | equal |
| D. | greater than |
| Answer» D. greater than | |
| 97. |
In a transformer, the leakage flux of each winding is proportional to the current in that winding because |
| A. | Ohms law applies to magnetic circuits |
| B. | Leakage paths do no saturate |
| C. | the two windings are electrically isolated |
| D. | mutual flux is confined to the core |
| Answer» C. the two windings are electrically isolated | |
| 98. |
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 |
| Answer» D. determined by load on transformer secondary | |
| 99. |
A step up transformer increases |
| A. | voltage |
| B. | current |
| C. | power |
| D. | . frequency |
| Answer» B. current | |
| 100. |
Transformer cores are laminated in order to |
| A. | simplify its construction |
| B. | minimise eddy current loss |
| C. | reduce cost |
| D. | reduce hysteresis loss |
| Answer» C. reduce cost | |