Transformers MCQ questions set 1

Transformers MCQ questions

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 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) magnetizing current
   (c) magnetizing current and loss
   (d) the 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
   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
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
    Ans: b
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
    Ans: c
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

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°
    Ans: d
25. In a transformer routine efficiency depends upon
    (a) supply frequency
    (b) load current
    (c) power factor of load
    (d) both (b) and (c)
    Ans: d

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