McqMate
Chapters
| 101. |
A transformer can have regulation closer to zero |
| A. | on full-load |
| B. | on overload |
| C. | on leading power factor |
| D. | on zero power factor |
| Answer» C. on leading power factor | |
| 102. |
A transformer transforms |
| A. | voltage |
| B. | current |
| C. | current and voltage |
| D. | power |
| Answer» D. power | |
| 103. |
Which of the following is not the standard voltage for power supply in India ? |
| A. | llkV |
| B. | 33kV |
| C. | 66 kV |
| D. | 122 kV |
| Answer» D. 122 kV | |
| 104. |
Reduction in core losses and increase in permeability are obtained with transformer employing |
| A. | core built-up of laminations of cold rolled grain oriented steel |
| B. | core built-up of laminations of hot rolled sheet |
| C. | either of the above |
| D. | none of the above |
| Answer» A. core built-up of laminations of cold rolled grain oriented steel | |
| 105. |
In a power or distribution transformer about 10 per cent end turns are heavily insulated |
| A. | to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns |
| B. | to absorb the line surge voltage and save the winding of transformer fromdamage |
| C. | to reflect the line surge and save the winding of a transformer from damage |
| D. | none of the above |
| Answer» A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns | |
| 106. |
For given applied voltage, with the increase in frequency of the applied voltage |
| A. | eddy current loss will decrease |
| B. | eddy current loss will increase |
| C. | eddy current loss will remain unchanged |
| D. | none of the above |
| Answer» C. eddy current loss will remain unchanged | |
| 107. |
Losses which occur in rotating electric machines and do not occur in transformers are |
| A. | friction and windage losses |
| B. | magnetic losses |
| C. | hysteresis and eddy current losses |
| D. | copper losses |
| Answer» A. friction and windage losses | |
| 108. |
In a given transformer for a given applied voltage, losses which remainconstant irrespective of load changes are |
| A. | hysteresis and eddy current losses |
| B. | friction and windage losses |
| C. | copper losses |
| D. | none of the above |
| Answer» A. hysteresis and eddy current losses | |
| 109. |
Which of the following statements regarding an idel single-phase transformerhaving a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ? |
| A. | Its secondary current is 5 A |
| B. | Its secondary voltage is 400 V |
| C. | Its rating is 2 kVA |
| D. | Its secondary current is 20 A |
| Answer» D. Its secondary current is 20 A | |
| 110. |
The secondary of a current transformer is always short-circuited underoperating conditions because it |
| A. | avoids core saturation and high voltage induction |
| B. | is safe to human beings |
| C. | protects the primary circuit |
| D. | none of the above |
| Answer» A. avoids core saturation and high voltage induction | |
| 111. |
In a transformer the resistance between its primary and secondary should be |
| A. | zero |
| B. | 10 Q |
| C. | 1000 Q |
| D. | infinity |
| Answer» D. infinity | |
| 112. |
A good voltage regulation of a transformer means |
| A. | output voltage fluctuation from no load to full load is least |
| B. | output voltage fluctuation with power factor is least |
| C. | difference between primary and secondary voltage is least |
| D. | difference between primary and secondary voltage ismaximum |
| Answer» A. output voltage fluctuation from no load to full load is least | |
| 113. |
For a transformer, operating at constant load current, maximum efficiency will occur at |
| A. | 0.8 leading power factor |
| B. | 0.8 lagging power factor |
| C. | zero power factor |
| D. | unity power factor |
| Answer» D. unity power factor | |
| 114. |
Which of the following protection is normally not provided on smalldistribution transformers ? |
| A. | Overfluxing protection |
| B. | Buchholz relay |
| C. | Overcurrent protection |
| D. | All of the above |
| Answer» B. Buchholz relay | |
| 115. |
Which of the following acts as a protection against high voltage surges due to lightning and switching ? |
| A. | Horn gaps |
| B. | Thermal overload relays |
| C. | Breather |
| D. | Conservator |
| Answer» A. Horn gaps | |
| 116. |
The efficiency of two identical transformers under load conditionscan be determined by |
| A. | short-circuit test |
| B. | back-to-back test |
| C. | open circuit test |
| D. | any of the above |
| Answer» B. back-to-back test | |
| 117. |
Which of the following insulating materials can withstand the highest temperature safely ? |
| A. | Cellulose |
| B. | Asbestos |
| C. | Mica |
| D. | Glass fibre |
| Answer» C. Mica | |
| 118. |
Which of the following parts of a transformer is visible from outside ? |
| A. | Bushings |
| B. | Core |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» A. Bushings | |
| 119. |
The noise produced by a transformer is termed as |
| A. | zoom |
| B. | hum |
| C. | ringing |
| D. | buzz |
| Answer» B. hum | |
| 120. |
Which of the following loss in a transformer is zero even at full load ? |
| A. | Core loss |
| B. | Friction loss |
| C. | Eddy current loss |
| D. | Hysteresis loss |
| Answer» B. Friction loss | |
| 121. |
Which of the following is the most likely source of harmonics in a transformer ? |
| A. | poor insulation |
| B. | Overload |
| C. | loose connections |
| D. | Core saturation |
| Answer» D. Core saturation | |
| 122. |
If a transformer is continuously operated the maximum temperature rise will occur in |
| A. | core |
| B. | windings |
| C. | tank |
| D. | any of the above |
| Answer» B. windings | |
| 123. |
The hum in a transformer is mainly attributed to |
| A. | load changes |
| B. | oil in the transformer |
| C. | magnetostriction |
| D. | mechanical vibrations |
| Answer» C. magnetostriction | |
| 124. |
The maximum load that a power transformer can carry is limited by its |
| A. | temperature rise |
| B. | dielectric strength of oil |
| C. | voltage ratio |
| D. | copper loss |
| Answer» C. voltage ratio | |
| 125. |
The efficiency of a transformer, under heavy loads, is comparatively low because |
| A. | copper loss becomes high in proportion to the output |
| B. | iron loss is increased considerably |
| C. | voltage drop both in primary and secondary becomes large |
| D. | secondary output is much less as compared to primary input |
| Answer» A. copper loss becomes high in proportion to the output | |
| 126. |
An open-circuit test on a transformer is conducted primarily to measure |
| A. | insulation resistance |
| B. | copper loss |
| C. | core loss |
| D. | total loss |
| Answer» C. core loss | |
| 127. |
A no-load test is performed on a transformer to determine |
| A. | core loss |
| B. | copper loss |
| C. | efficiency |
| D. | magnetising current and loss |
| Answer» D. magnetising current and loss | |
| 128. |
The voltage transformation ratio of a transformer is equal to the ratio of |
| A. | primary turns to secondary turns |
| B. | secondary current to primary current |
| C. | secondary induced e.m.f. to primary induced e.m.f. |
| D. | secondary terminal voltage to primary applied voltage |
| Answer» C. secondary induced e.m.f. to primary induced e.m.f. | |
| 129. |
Part of the transformer which is most subject to damage from overheating is |
| A. | iron core |
| B. | copper winding |
| C. | winding insulation |
| D. | frame or case |
| Answer» C. winding insulation | |
| 130. |
If a transformer is switched on to a voltage more than the rated voltage |
| A. | its power factor will deteriorate |
| B. | its power factor will increase |
| C. | its power factor will remain unaffected |
| D. | its power factor will be zero |
| Answer» A. its power factor will deteriorate | |
| 131. |
Auto-transformer makes effective saving on copper and copper losses, whenits transformation ratio is |
| A. | approximately equal to one |
| B. | less than one |
| C. | great than one |
| D. | none of the above |
| Answer» A. approximately equal to one | |
| 132. |
Minimum voltage regulation occurs when the power factor of the load is |
| A. | unity |
| B. | lagging |
| C. | leading |
| D. | zero |
| Answer» C. leading | |
| 133. |
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. | less than 15 A |
| B. | more than 15 A |
| C. | 15 A |
| D. | none of the above |
| Answer» A. less than 15 A | |
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