McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 51. |
The design of electromagnets is based upon which of the following fundamental equations ? |
| A. | Force equation |
| B. | Magnetic circuit equation |
| C. | Heating equation |
| D. | All of the above |
| Answer» D. All of the above | |
| 52. |
When the two coil sides forming a coil are spaced exactly one pole pitch apart they are said to be of |
| A. | short pitch |
| B. | full pitch |
| C. | either of the above |
| D. | none of the above |
| Answer» B. full pitch | |
| 53. |
are always double layer type. |
| A. | Closed windings |
| B. | Open windings |
| C. | Either of the above |
| D. | None of the above |
| Answer» A. Closed windings | |
| 54. |
The distance between the starts of two consecutive coils measured in terms of coil sides is called |
| A. | front pitch |
| B. | winding pitch |
| C. | commutator pitch |
| D. | back pitch |
| Answer» B. winding pitch | |
| 55. |
The winding where dummy coils are used is sometimes called |
| A. | duplex winding |
| B. | triplex winding |
| C. | forced winding |
| D. | none of the above |
| Answer» C. forced winding | |
| 56. |
Dummy coil should not be used in |
| A. | small machines |
| B. | large machines |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» B. large machines | |
| 57. |
Power transformers have rating |
| A. | equal to 50 kVA |
| B. | equal to 100 kVA |
| C. | above 200 kVA |
| D. | none of the above |
| Answer» C. above 200 kVA | |
| 58. |
Power transformers should be designed to have maximum efficiency |
| A. | at one-fourth load |
| B. | at one-half load |
| C. | at or near full load |
| D. | any of the above |
| Answer» C. at or near full load | |
| 59. |
In transformers using hot rolled steel, the cross-section of the yoke is made about _____ greater than that of the core |
| A. | 5 percent |
| B. | 10 percent |
| C. | 15 percent |
| D. | 30 percent |
| Answer» C. 15 percent | |
| 60. |
Yokes with rectangular cross-section are used for |
| A. | small capacity transformers |
| B. | medium capacity transformers |
| C. | large capacity transformers |
| D. | any of the above |
| Answer» A. small capacity transformers | |
| 61. |
The cold rolled grain oriented steel has ______ permeability in the direction of the grain orientation. |
| A. | minimum |
| B. | maximum |
| C. | nil |
| D. | none of the above |
| Answer» B. maximum | |
| 62. |
Cylindrical windings using circular conductors, employed in transformers, are |
| A. | single layered |
| B. | double layered |
| C. | multi-layered |
| D. | none of the above |
| Answer» C. multi-layered | |
| 63. |
Helical windings are used in |
| A. | distribution transformers |
| B. | power transformers |
| C. | shell type transformers |
| D. | none of the above |
| Answer» B. power transformers | |
| 64. |
Multi-layer helical windings are commonly used in the transformers as high voltage windings |
| A. | upto 20 kV |
| B. | upto 50 kV |
| C. | upto 80 kV |
| D. | for 110 kV and above |
| Answer» D. for 110 kV and above | |
| 65. |
Disc windings are primarily used in |
| A. | short capacity transformers |
| B. | medium capacity transformers |
| C. | high capacity transformers |
| D. | any of the above |
| Answer» C. high capacity transformers | |
| 66. |
The heat dissipating capability of transformers of ratings higher than 30 kVA in increased by providing which of the following ? |
| A. | Corrugations |
| B. | Fins |
| C. | Tubes |
| D. | All of the above |
| Answer» D. All of the above | |
| 67. |
Transformers with a capacity of upto _____ have a cooling radiator system with natural cooling |
| A. | 2 MVA |
| B. | 5 MVA |
| C. | 7.5 MVA |
| D. | 10 MVA |
| Answer» D. 10 MVA | |
| 68. |
The forced oil and air circulation method is usual one for transformers of capacities |
| A. | upto 5 MVA |
| B. | upto 10 MVA |
| C. | upto 20 MVA |
| D. | 30 MVA upwards |
| Answer» D. 30 MVA upwards | |
| 69. |
The flash point of transformer oil should be higher than |
| A. | 40°C |
| B. | 60°C |
| C. | 80°C |
| D. | 104°C |
| Answer» D. 104°C | |
| 70. |
The voltage control in electric supply networks in required on account of which of the following reasons ? |
| A. | Adjustment of voltage at consumers premises within statutory limits |
| B. | Control of active and reactive power |
| C. | Adjustment of short period daily and seasonal voltage variations in accordance with variations of load |
| D. | All of the above |
| Answer» D. All of the above | |
| 71. |
D.C. windings are |
| A. | sometimes 2-layer type |
| B. | never 2-layer type |
| C. | always 2-layer type |
| D. | none of the above |
| Answer» C. always 2-layer type | |
| 72. |
The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are |
| A. | 0.5 to 0.8 Wb/m2 |
| B. | 0.8 to 1.0 Wb/m2 |
| C. | 1.1 to 1.35 Wb/m2 |
| D. | 1.4 to 1.8 Wb/m2 |
| Answer» C. 1.1 to 1.35 Wb/m2 | |
| 73. |
For 275 kV transformers, using cold rolled grain oriented steel, which of the following values of flux density may be used? |
| A. | 1.0 Wb/m2 |
| B. | 1.1 Wb/m2 |
| C. | 1.3 Wb/m2 |
| D. | 1.6 Wb/m2 |
| Answer» D. 1.6 Wb/m2 | |
| 74. |
For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used ? |
| A. | 1.0 to 1.2 A/mm2 |
| B. | 1.5 to 2.0 A/mm2 |
| C. | 2.2 to 3.2 A/mm2 |
| D. | 3.2 to 4.2 A/mm2 |
| Answer» C. 2.2 to 3.2 A/mm2 | |
| 75. |
A current density of _____ is ilsed for large power transformers with forced circulation of oil or with water cooling coils |
| A. | 1.5 to 2.5 A/mm2 |
| B. | 3.5 to 4.5 A/mm2 |
| C. | 4.0 to 5.0 A/mm2 |
| D. | 5.4 to 6.2 A/mm2 |
| Answer» D. 5.4 to 6.2 A/mm2 | |
| 76. |
The high voltage winding is usually which of the following type ? |
| A. | Cylindrical winding with circular conductors |
| B. | Cross-over winding with either circular or small rectangular conductors |
| C. | Continuous disc type winding with rectangular conductors |
| D. | All of the above types |
| Answer» D. All of the above types | |
| 77. |
Which of the following is the basic consideration in the design of insulation ? |
| A. | Electrical considerations |
| B. | Mechanical considerations |
| C. | Thermal considerations |
| D. | All of the above |
| Answer» D. All of the above | |
| 78. |
A practical formula for determining the thickness of insulation between low voltage and high voltage windings is |
| A. | 1 + 0.2 kVmm |
| B. | 2 + 0.5 kVmm |
| C. | 4 + 0.7 kV mm |
| D. | 5 + 0.9 kV mm |
| Answer» D. 5 + 0.9 kV mm | |
| 79. |
The insulation between windings and grounded core and the insulation between the windings of the same phase is called |
| A. | minor insulation |
| B. | major insulation |
| C. | either of the above |
| D. | none of the above |
| Answer» B. major insulation | |
| 80. |
The cylindrical windings using circular conductors are used for current rating of |
| A. | upto 20 A |
| B. | upto 40 A |
| C. | upto 60 A |
| D. | upto 80 A |
| Answer» D. upto 80 A | |
| 81. |
The surge phenomenon is particularly important in case of |
| A. | low voltage transformers |
| B. | medium voltage transformers |
| C. | high voltage transformers |
| D. | any of the above |
| Answer» C. high voltage transformers | |
| 82. |
Which of the following in an application of D.C. motors? |
| A. | Traction |
| B. | Drives for process industry |
| C. | Battery driven vehicles |
| D. | All of the above |
| Answer» D. All of the above | |
| 83. |
D.C. servomotors are used in |
| A. | purely D.C. control systems |
| B. | purely AC. control systems |
| C. | both D.C. and AC. control systems |
| D. | none of the above |
| Answer» A. purely D.C. control systems | |
| 84. |
The stator of a D.C. machine comprises of |
| A. | main poles |
| B. | interpoles |
| C. | frame |
| D. | all of the above |
| Answer» D. all of the above | |
| 85. |
The laminations of the armature of a D.C. machine are usually _____ thick. |
| A. | 0.1 to 0.2 mm |
| B. | 0.2 to 0.3 mm |
| C. | 0.3 to 0.4 mm |
| D. | 0.4 to 0.5 mm |
| Answer» D. 0.4 to 0.5 mm | |
| 86. |
is usually used for brush rockers |
| A. | Mild steel |
| B. | Copper |
| C. | Aluminium |
| D. | Cast-iron |
| Answer» D. Cast-iron | |
| 87. |
______ brushes are fragile and cause excessive wear of commutator, |
| A. | Natural graphite |
| B. | Hard carbon |
| C. | Electro graphitic |
| D. | Metal graphite |
| Answer» A. Natural graphite | |
| 88. |
Which of the following brushes can be used for high values of current density ? |
| A. | Metal graphite brushes |
| B. | Hard carbon brushes |
| C. | Electro-graphitic brushes |
| D. | Natural graphite brushes |
| Answer» A. Metal graphite brushes | |
| 89. |
________ is the common method of applying brushes to the commntator. |
| A. | Radial |
| B. | Trailing |
| C. | Reaction |
| D. | All of the above |
| Answer» D. All of the above | |
| 90. |
Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ? |
| A. | Increased I R losses |
| B. | Increased core losses |
| C. | Poor commutation |
| D. | All of the above |
| Answer» D. All of the above | |
| 91. |
The weight of copper of both armature and field windings decreases with _____ in number of poles. |
| A. | increase |
| B. | decrease |
| C. | either of the above |
| D. | none of the above |
| Answer» A. increase | |
| 92. |
In a D.C. machine the number of brush arms is _____ the number of poles. |
| A. | less than |
| B. | equal to |
| C. | greater than |
| D. | none of the above |
| Answer» B. equal to | |
| 93. |
In a D.C. machine the current per brush arm should not be more than |
| A. | 100 A |
| B. | 200 A |
| C. | 300 A |
| D. | 400 A |
| Answer» D. 400 A | |
| 94. |
In a D.C. machine, the value of peripheral speed should not, normally, exceed |
| A. | 10 m/s |
| B. | 20 m/s |
| C. | 30 m/s |
| D. | 40 m/s |
| Answer» C. 30 m/s | |
| 95. |
In D.C. machines the width of the duct is usually |
| A. | 4 mm |
| B. | 6 mm |
| C. | 8 mm |
| D. | 10 mm |
| Answer» D. 10 mm | |
| 96. |
D.C. machines designed with a large value of air gap length have |
| A. | worst, ventilation |
| B. | poor ventilation |
| C. | better ventilation |
| D. | none of the above |
| Answer» C. better ventilation | |
| 97. |
In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, the field mmf must be made |
| A. | equal to that of armature mmf |
| B. | less in comparison with the arma¬ture mmf |
| C. | large in comparison with the arma-ture mmf |
| D. | none of the above |
| Answer» C. large in comparison with the arma-ture mmf | |
| 98. |
In D.C. machines, the ____ in field mmf results in increase in size and cost of machines. |
| A. | increase |
| B. | decrease |
| C. | either of the above |
| D. | none of the above |
| Answer» A. increase | |
| 99. |
The operation of a D.C. machine with large air gap lengths is comparatively |
| A. | quiet |
| B. | noisy |
| C. | either of the above |
| D. | none of the above |
| Answer» A. quiet | |
| 100. |
Which of the following methods may be adopted to reduce the effects of armature reaction ? |
| A. | Increase in length of air gap at pole tips |
| B. | Increasing reluctance of pole tips |
| C. | Compensating windings |
| D. | All of the above |
| Answer» D. All of the above | |
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