McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 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 transformer |
| Answer» C. magnetising current and 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 remain constant 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 applied voltage 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 power factor |
| Answer» D. has small magnitude and low power factor | |
| 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 are different, 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 transformers operate will be different from the power factor of the common load |
| Answer» D. 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 | |
| 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 transformer oil. |
| Answer» B. absorbing moisture | |
| 43. |
The chemical used in breather is |
| A. | asbestos fibre |
| B. | silica sand |
| C. | sodium chloride |
| D. | silica gel |
| Answer» D. silica gel | |
| 44. |
An ideal transformer has infinite values of primary and secondary inductances. The statement is |
| A. | true |
| B. | false |
| C. | none |
| D. | none |
| Answer» B. false | |
| 45. |
The transformer ratings are usually expressed in terms of |
| A. | volts |
| B. | amperes |
| C. | kW |
| D. | kVA |
| Answer» D. kVA | |
| 46. |
The noise resulting from vibrations of laminations set by magnetic forces, is termed as |
| A. | magnetostrication |
| B. | boo |
| C. | hum |
| D. | zoom |
| Answer» C. hum | |
| 47. |
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 | |
| 48. |
Material used for construction of transformer core is usually |
| A. | wood |
| B. | copper |
| C. | aluminium |
| D. | silicon steel |
| Answer» D. silicon steel | |
| 49. |
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 | |
| 50. |
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 expansion and contraction of transformer oil due to variation of temperature of sur-roundings |
| Answer» D. to take care of the expansion and contraction of transformer oil due to variation of temperature of sur-roundings | |
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