Electrical Machine Design MCQ

61. Gross window area in a transformer is 750 cm². The approximate height of window is

(a) 50 cm
(b) 75 cm
(c) 30 cm
(d) 25 cm [A.M.I.E Design of Electrical Systems 2005]

62. If the insulation material in the window of transformer occupies 70% of window area, the window space factor is

(a) 0.7
(b) 0.3
(c) 0.49
(d) 0.09

63. The inductive reactance of a distribution core type transformer with concentric cylindrical coils of equal length can be reduced by

(a) increasing the window height.
(b) increasing the window width.
(c) decreasing the yoke height.
(d) increasing the operating flux density in the yoke.

64. If all the dimensions of a transformer is doubled its iron loss will be

(a) half.
(b) double.
(c) four times.
(d) 8 times. [A.M.I.E. Elec. Design 1993]

65. The hum in a transformer is due to

(a) magnetostriction.
(b) vibrations developed by laminations depending upon the tightness of clampings.
(c) mechanical vibrations of the tank walls.
(d) all of the above.

66. Humming noise in a transformer can be reduced by

(a) using lower flux densities.
(b) tightening the clampings of laminations.
(c) using suitable cushions, paddings and oil barriers.
(d) all of the above.

67. Cylindrical windings using circular conductors employed in transformers are

(a) multi-layered.
(b) double layered.
(c) triple layered.
(d) single layered.

68. The disadvantage of cylindrical winding is

(a) high copper loss.
(b) poor mechanical strength.
(c) more eddy current loss.
(d) none of the above.

69. In transformers, the cylindrical winding with rectangular conductors is usually used for………..voltage winding.

(a) tertiary
(b) high
(c) low
(d) any of these

70. In transformers cylindrical windings are not used for voltage exceeding

(a) 6 kV
(b) 13 kV
(c) 33 kV
(d) 66 kV

71. The cylindrical windings employing circular conductors are used for current rating of up to

(a) 20 A
(b) 50 A
(c) 80 A
(d) 150 A

72. Helical windings are employed in transformers.

(a) distribution
(b) power
(c) shell type
(d) none of these

73. Multi-layer helical windings are widely employed in the power transformers as hv windings

(a) 25 kV.
(b) up to 66 kV.
(c) 110 kV and above.
(d) 220 kV and above.

74. Disc windings are primarily employed in…………capacity transformers.

(a) low
(b) medium
(c) high
(d) any of these

75. The high voltage winding is usually

(a) continuous disc type winding with rectangular conductors.
(b) cylindrical winding with circular conductors.
(c) crossover winding with either circular or small rectangular conductors.
(d) all of the above .

76. The primary and secondary windings are interlaced for

(a) easiness of coil making.
(b) reduced leakage reactance.
(c) reduced cost.
(d) uniform heating. [A.M.I.E. Elec. Design 1993]

77. It is necessary that magnetic coupling in a transformer is close. This is done to ensure

(a) high efficiency.
(b) good regulation.
(c) good regulation and high efficiency.
(d) good regulation and high power factor. [A.M.I.E Sec B. 2005]

78. The thickness of insulation between lv and hv windings is determined by relation

(a) (5 + 0.9 kV) mm.
(b) ( 9 + 0.5 kV) mm.
(c) (0.9 + 0.5 kV) mm.
(d) (4 + 0.75 kV) mm.

79. What is the arrangement of windings in a core type single- phase transformer?

(a) Half lv inside and half hv outside or each core limb.
(b) LV on one core limb and hv on the other.
(c) Sandwiched lv and by discs on each core limb.
(d) Half hv inside and half lv outside on each core limb. [A.M.I.E. Sec Elec. Design, 1994]

80. With increase in voltage, the window space factor of a transformer

(a) decreases.
(b) increases.
(c) remains constant.
(d) decreases or increases depending upon whether it is a distribution or power transformer. [A.M.I.E Elec. Design 1994]