

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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