Objective Electrical Machine Design Questions and Answers pdf

71.    D.C. windings are
(a)    sometimes 2-layer type
(b)    never 2-layer type
(c)    always 2-layer type
(d)    none of the above
Ans: c

72.    The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are
(a)     0.5 to 0.8 Wb/m2
(b)     0.8 to 1.0 Wb/m2
(c)    1.1 to 1.35 Wb/m2
(d)    1.4 to 1.8 Wb/m2
Ans: c

73.    For 275 kV transformers, using cold rolled grain oriented steel, which of the following values of flux density may be used?
(a)     1.0 Wb/m2
(b)     1.1 Wb/m2
(c)     1.3 Wb/m2
(d)     1.6 Wb/m2
(e)    None of the above
Ans: d

74.    For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used ?
(a)    1.0 to 1.2 A/mm2
(b)    1.5 to 2.0 A/mm2
(c)    2.2 to 3.2 A/mm2
(d)    3.2 to 4.2 A/mm2
Ans: c

75.    A current density of _____ is ilsed for large power transformers with forced circulation of oil or with water cooling coils
(a)     1.5 to 2.5 A/mm2
(b)     3.5 to 4.5 A/mm2
(c)    4.0 to 5.0 A/mm2
(d)    5.4 to 6.2 A/mm2
Ans: d

76.    The high voltage winding is usually which of the following type ?
(a)    Cylindrical winding with circular conductors
(b)    Cross-over winding with either circular or small rectangular conductors
(c)    Continuous disc type winding with rectangular conductors
(d)    All of the above types
Ans: d

77.    Which of the following is the basic consideration in the design of insulation ?
(a)     Electrical considerations
(b)     Mechanical considerations
(c)    Thermal considerations
(d)    All of the above
Ans: d

78.    A practical formula for determining the thickness of insulation between low voltage and high voltage windings is
(a)    1 + 0.2 kVmm
(6)    2 + 0.5 kVmm
(c)    4 + 0.7 kV mm
(d)    5 + 0.9 kV mm
Ans: d

79.    The insulation between windings and grounded core and the insulation between the windings of the same phase is called
(a)    minor insulation
(b)    major insulation
(c)    either of the above
(d)    none of the above
Ans: b

80.    The cylindrical windings using circular conductors are used for current rating of
(a)    upto 20 A
(b)    upto 40 A
(c)    upto 60 A
(d)    upto 80 A
Ans: d

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