Transformer mcqs part-1

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

Ans: c

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

Ans: c

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

Ans: b

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
Ans: d

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

Ans: b

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

Ans: d

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

Ans: c

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

Ans: b

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

Ans: a

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

Ans: a

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

Ans: d

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°

Ans: a

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

Ans: c

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

Ans: d

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

Ans: b

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

Ans: a

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

Ans: c

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

Ans: c

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

Ans: c

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

Ans: b