MCQs on Transformer 1-20

1. Which of the following does not change in a transformer ?
(a) Current
(b) Voltage
(c) Frequency✔
(d) All of the above

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

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

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✔

5. The no-load current drawn by transformer is usually what per cent of the full-load current ?
(a) 0.2 to 0.5 percent
(b) 2 to 5 percent✔
(c) 12 to 15 percent
(d) 20 to 30 percent

6. The path of a magnetic flux in a transformer should have
(a) high resistance
(b) high reluctance
(c) low resistance
(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

8. The dielectric strength of transformer oil is expected to be
(a) lkV
(b) 33 kV✔
(c) 100 kV
(d) 330 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

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

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✔

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°

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

14. Which of the following is not a part of transformer installation ?
(a) Conservator
(b) Breather
(c) Buchholz relay
(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

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

17. A transformer transforms
(a) voltage
(b) current
(c) power✔
(d) frequency

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

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

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