501 MCQ Questions on Transformer

36. The equivalent resistance of the primary of a transformer having K = 5 and R₁ = 0.1Ω, when referred to secondary becomes ……….. ohms.

(a) 0.5                
(b) 0.02
(c) 0.004            
(d) 2.5

37. It is desired to measure parameters of 230 V/ 115 V, 2 kVA single-phase transformer. The following wattmeters are available in a laboratory:

W1 250 V, 10 A, Low power factor
W2 250 V, 5 A, Low power factor
W3 150, 10 A, High power factor
W4 150 V, 5 A, High power factor
The wattmeters used in open-circuit test and short-circuit test of the transformer will respectively be
(a) W1 and W2           
(b) W2 and W4
(c) W1, and W4          
(d) W2 and W3

38. In a transformer, the primary and the secondary voltages are

(a) 60° out of phase
(b) 90° out of phase
(c) 180° out of phase
(d) Always in phase

39. The dielectric strength of transformer oil is expected to be

(a) 1 kV                        
(b) 33 kV
(c) 100 kV          
(d) 330 kV

40. 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

41. 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.

42. 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.

43. 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/√K
(b) R₂/K²
(c) R₂² /K²
(d) R₂²/K

44. The use of higher flux density in the transformer design

(a) reduces weight per kVA.
(b) reduces iron losses.
(c) reduces copper losses.
(d) increase part load efficiency.

45. The chemical used in breather is

(a) asbestos fibre
(b) silica sand
(c) sodium chloride
(d) silica gel

46. Star/star transformers work satisfactorily when

(a) load is unbalanced only.
(b) load is balanced only.
(c) on balanced as well as unbalanced loads.
(d) none of the above.

47. During open circuit test of a transformer

(a) primary is supplied rated voltage.
(b) primary is supplied full-load current.
(c) primary is supplied current at reduced voltage.
(d) primary is supplied rated kVA.

48. The size of a transformer core will depend on

(a) frequency.
(b) area of the core.
(c) flux density of the core material.
(d) both (a) and (c).

49. Minimum voltage regulation occurs in transformer when the power factor of the load is

(a) unity
(b) lagging
(c) leading
(d) zero

50. A pole pitch in electrical machine is:

(a) equal to 180° electrical
(b) equal to 180° mechanical
(c) less than 180° electrical
(d) greater than 180° electrical    [DMRC JE-2016]

51. Which of the following are constant losses in transformers?

(a) Winding losses
(b) Core losses
(c) Both Winding & core losses
(d) None of these                 [DMRC JE-2016]

52. Two transformers with identical voltage ratings are working in parallel to supply common load. The percentage impedance of one transformer is higher compared to that of other. The load sharing between the two transformer will:

(a) be proportional to their percentage impedance.
(b) be independent of their percentage impedance.
(c) be inversely proportional to their respective impedance.
(d) depend on the resistance to leakage reactance ratio of each transformer. [DMRC JE-2016]

53. When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their

(a) kVA rating are identical.
(b) efficiencies are equal.
(c) pu impedance are equal.
(d) equivalent impedance are equal.    [DMRC JE-2016]

54. Hysteresis loss in a transformer depends upon

(a) frequency.
(b) supply voltage.
(c) square of the frequency alone.
(d) square of the voltage alone.   [DMRC JE-2016]

55. Which of the following is determined by the turns ratio?

(a) Ratio of primary and secondary voltages .
(b) Ratio of primary and secondary currents.
(c) Both (a) and (b).
(d) None of these.

56. The turns ratio of a step down transformer is

(a) equal to one.
(b) less than 1.
(c) more than 1.
(d) more than that of the step-up transformer.

57. Which of the following is true with a transformer?

(a) The same transformer can be used as a step up or step down.
(b) The primary winding and the secondary winding are connected through a central tap.
(c) Both (a) and (b)
(d) None of these.

58. Which of the following is true with transformers?

(a) They work on the principle of induction.
(b) The voltage can be either stepped-up or stepped down.
(c) Both (a) and (b)
(d) None of these.

59. What is the secondary power of a transformer having a 2 : 1 voltage ratio, if the primary power is 200 W?

(a) 400 W
(c) 200 W
(b) 100 W
(d) None of these

60. A transformer with 1 : 1 turns ratio is called

(a) isolation transformer.
(b) equitable transformer.
(c) isotopic transformer.
(d) none of these.

61. Which of the following is true in a Y-Y configuration?

(a) The phase current, line current and load current are equal in each phase.
(b) The phase current and line current are equal and load current is double of line current.
(c) The phase current double of line current but, load current and line current are equal.
(d) None of these.

62. Which of the following statements is true about the windings of a transformer? [UPPCL JE 2014]

(a) Windings are conductively linked.
(b) Windings are inductively linked.
(c) Windings are not linked at all.
(d) Windings are electrically linked.

63. Five limb core construction is preferred over three limb construction because in this type of construction

(a) hysteresis loss is reduced.
(b) eddy current loss is reduced.
(c) magnetic reluctance of the three phases can be balanced.
(d) copper losses can be reduced.  [RRB SSE 2015]

64. The principle of mutual induction is applied in case of

(a) Alternator
(b) Synchronous motor
(c) Wattmeter
(d) Transformer [UPPCL JE 2014]

65. Which of the following is not a type of construction used for single phase transformer? [UPPCL JE 2014]

(a) Core type
(b) Shell type
(c) Berry type
(d) Roof type

66. If in a transformer, ‘P_m‘ denotes the maximum value of the flux, ‘f’ is the frequency of the supply voltage, ‘N₁,’ is number of primary winding turns, ‘E₁ is RMS value of the primary induced emf, then one of the equations of the transformer would be:

(a) E₁ = 4.44 fP_mN₁
(b) E₁ = 2.35 fP_mN₁
(c) E₁ = 1.23 fP_mN₁
(d) E₁ = 7.8 fP_mN₁

67. An ideal transformer has

(a) very high losses.
(c) moderate losses.
 (b) very low losses.
(d) no losses. [UPPCL JE 2014]

68. The no-load current of a transformer is 20A at a power factor of 0.20 lagging, when connected to 400 V, 50 Hz supply. Calculate the magnetizing component of no-load current. [UPPCL JE 2014]

(a) 13.4 A
(b) 16.8 A
(c) 19.6 A
(d) 18.2 A

69. Which of the following statement/s is/are true?

1. DC supply cannot be used for transformers.
2. The transformer works on the principle of mutual induction.

Choose the correct answer from the options given below.
(a) Only I
(b) Both I and II
(c) Only II
(d) Neither I nor II [UPPCL JE 2014]

70. On which of the following do the eddy current losses depend? [UPPCL JE 2014]

1. Nature of the material
2. Maximum flux density

III. Frequency
Choose the correct answer from the options given below.
(a) I, II and III
(b) II and III
(c) I and II
(d) I and III