MCQs on Transformer 21-40

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

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

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°✔

25. In a transformer routine efficiency depends upon
(a) supply frequency
(b) load current
(c) power factor of load
(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

27. Natural oil cooling is used for transformers up to a rating of
(a) 3000 kVA✔
(b) 1000 kVA
(c) 500 kVA
(d) 250 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

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

30. Transformer breaths in when
(a) load on it increases
(b) load on it decreases✔
(c) load remains constant
(d) none of the above

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✔

32. Spacers are provided between adjacent coils
(a) to provide free passage to the cooling oil✔
(b) to insulate the coils from each other
(c) both (a) and (b)
(d) none of the above

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

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

35. The power transformer is a constant
(a) voltage device
(b) current device
(c) power device
(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

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

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

39. If the percentage impedances of the two transformers working in parallel are different, then
(a) transformers will be overheated
(b) power factors of both the transformers 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✔

40. In a transformer the tappings are generally provided on
(a) primary side
(b) secondary side
(c) low voltage side✔
(d) high voltage side