Electrical Engineering MCQ Multiple Choice Questions and Answers

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
Ans: c

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

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
Ans: a

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
Ans: a

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
Ans: b

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

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
Ans: d

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
Ans: a

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
Ans: a

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
Ans: c

35. The power transformer is a constant
(a) voltage device
(b) current device
(c) power device   
(d) main flux device
Ans: d

36. Two transformers operating in parallel will share the load depending upon their
(a) leakage reactance
(b) per unit impedance
(c) efficiencies
(d)     ratings
Ans: b

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
Ans: b

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
Ans: b

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
Ans: d

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

1 TO 20 Transformer MCQ

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