501 MCQ Questions on Transformer

71. Hysteresis loss is ……… proportional to the area under the hysteresis curve. Also, it is ………. proportional to the number of cycles of magnetization per second. [UPPCL JE – 2014]

(a) directly, inversely
(b) inversely, directly
(c) directly, directly
(d) inversely, inversely

72. A 2000/200 V, 20 kVA transformer has 66 turns in the secondary. The number of primary turns are

(a) 660
(b) 440
(c) 770
(d) 330

73. Open circuit test on a transformer gives:

(a) total loss.
(b) insulation resistance.
(c) core loss.
(d) cu loss.

74. High silicon content steel is used for transformer core construction, to

(a) improve cooling of core and yoke.
(b) reduce hysteresis loss.
(c) reduce eddy current loss.
(d) reduce weight of steel.

75. A magnetizing force of 800 AT/m will produce a flux density of ………. in air. [NMRC JE-2017]

(a) 0.5 Wb/m²
(b) 1 Wb/m²
(c) 10 mWb/m²
(d) 1 mWb/m²

76. The rating of transformers is expressed in

(a) kVA
(c) HP
(b) kW
(d) kWh

77. The voltage regulation of a transformer at full load 0.9 p.f. lagging is 5%. For a full load at 0.9 p.f. leading, it will

(a) remain the same.
(b) become negative.
(c) reduce and may even become negative.
(d) increase.

78. Transformer core is laminated in order to

(a) decrease copper losses.
(b) decrease entire core losses.
(c) decrease only eddy current losses.
(d) decrease only hysteresis losses.

79. To conduct Sumpners test on a transformer

(a) only one transformer is sufficient.
(b) two identical transformers are needed.
(c) two un-identical transformers are needed.
(d) at least three transformers are necessary.

80. Iron loss of a transformer can be measured by

(a) low power factor wattmeter.
(b) unity power factor wattmeter.
(c) frequency meter.
(d) any type of wattmeter.

81. Distribution transformers have core losses

(a) more than full load copper losses.
(b) equal to full load copper losses.
(c) less than full load copper losses.
(d) negligible compared to full load copper losses.

82. The minus sign in the expression, e = -Ndφ/dt is  due to:

(a) Fleming’s rule
(b) Thumb’s rule
(c) Faraday’s law
(d) Lenz’s law

83. The following statements associated with Buchholtz relays is not true.

(a) It is a gas actuated device.
(b) It is a current operative device.
(c) It is placed between the transformer tank and the conservator.
(d) It causes alarm for minor fault and tripping for major fault.

84. Which of the following combination of 3-phase transformers can be successfully operated in parallel?

(a) Δ-Y and  Δ-Y
(b) Y-Y and  Δ-Y
(c) Δ -Δ and  Δ-Y
(d) Y-Δ and  Δ-Δ

85. Three phase step-up transformer installed at power house, just before commencement of transmission line, have

(a) DELTA-DELTA connection.
(b) STAR-STAR connections.
(c) STAR-DELTA connections.
(d) DELTA-STAR connections.

86. Hysteresis loss in a transformer depends upon

(a) both voltage and frequency.
(b) voltage alone.
(c) frequency alone.
(d) none of these.

87. During a short-circuit test, the iron losses are negligible, because

(a) mutual flux is small.
(b) current is high.
(c) power factor is low.
(d) none of these.

88. A transformer has maximum efficiency at 3/4 full load. The ratio of its iron losses and full load copper loss is

(a) 16/9
(b) 4/3
(c) 3/4
 (d) 9/16

89. Which two values are plotted on a B-H curve graph?

(a) Reluctance and flux density
(b) Permeability and reluctance
(c) Magnetizing force and permeability
(d) Flux density and magnetizing force

90. What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV?

(a) 4 kVA
(b) 0.25 kVA
(c) 16 kVA
 (d) 8 kVA

91. The hysteresis cycle for the material of a transformer is

(a) tall and narrow.
(b) tall and wide.
(c) short and narrow.
(d) short and wide.

92. Which of the following transformers is smallest?

(a) 1 kVA, 50 Hz
(b) 1 kVA, 200 Hz
(c) 1 kVA, 400 Hz
(d) 1 kVA, 600 Hz

93. In a 3-φ transformer Δ-connected, one of the phase has burnt up, then it works with

(a) zero output
(b) rated output
(c) 60% of its rated output
(d) 86.6% of its rated output

94. The magnetizing current in a transformer is rich in

(a) 3rd harmonic
(b) 5th harmonic
(c) 7th harmonic
 (d) 8th harmonic

95. Varnishes protect the insulating materials against

(a) dust and oil.
(b) moisture, dirt and oil.
(c) moisture and fire hazards.
(d) none of the above. [UPPCL JE – 2007]

96. A transformer having 1000 turns in primary winding is connected to a single phase 250 V a.c. supply. For inducing 400 V in secondary winding, the number of turns in secondary winding must be

(a) 1600
(b) 1250
 (c) 400
(d) 250 [UPPCL JE 2007]

97. A 10 kVA, 220 V/220 V, 50 Hz transformer shows 340 W in short circuit test and 168 W in open circuit test. Its efficiency at full load and 0.8 power factor lagging is approximately

(a) 92%
(b) 94%
(c) 96%
 (d) 98% [UPPCL JE 2007]

98. At light load, efficiency of a transformer is low. It is because

(a) copper loss is small.
(b) copper loss is high.
(c) secondary output is low.
(d) fixed loss is high with respect to output.

99. The essential condition for parallel operation of two single phase transformers is that they should have the same

(a) polarity
(b) kVA rating
(c) voltage ratio
(d) percentage impedance [UPPCL JE 2007]

100. A transformer transforms

(a) frequency only .
(b) voltage only.
(c) current only.
(d) voltage and current. [UPPCL JE 2007]

101. A transformer has negative voltage regulation when its load power factor is

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

102. The no load current in a transformer lags the supply voltage by

(a) 0°
(b) 90°
(c) 110°
(d) about 75° [UPPCL JE 2007]

103. The heat run test of a transformer without its loading is performed by means of

(a) short circuit test.
(b) open circuit test.
(c) half time short circuit test and half time open circuit test.
(d) Sumpner’s test. [UPPCL JE 2007]

104. Distribution transformers must be designed to have maximum efficiency at

(a) full load.
(b) no load.
(c) about 90% of the full load.
(d) about 50% of the full load. [UPPCL JE 2016]

105. In transformer, occurrence of dimensional changes both perpendicular and parallel to the direction of magnetisation is referred to as

(a) damping
(b) magnetostriction
(c) coupling
(d) oscillation [UPPCL JE 2016]