100 TOP Electrical Machine Design Multiple choice Questions and Answers pdf

81.    The surge phenomenon is particularly important in case of
(a)    low voltage transformers
(b)    medium voltage transformers
(c)    high voltage transformers
(d)    any of the above
Ans: c

82.    Which of the following in an application of D.C. motors?
(a)     Traction
(b)     Drives for process industry
(c)    Battery driven vehicles
(d)    Automatic control
(e)    All of the above
Ans: e

83.    D.C. servomotors are used in
(a)     purely D.C. control systems
(6)     purely AC. control systems
(c)    both D.C. and AC. control systems
(d)    none of the above
Ans: a

84.    The stator of a D.C. machine comprises of
(a)    main poles
(6)    interpoles
(c)    frame
(d)    all of the above
Ans: d

85.    The laminations of the armature of a D.C. machine are usually _____ thick.
(a)    0.1 to 0.2 mm
(b)    0.2 to 0.3 mm
(c)    0.3 to 0.4 mm
(d)    0.4 to 0.5 mm
Ans: d

86.    is usually used for brush rockers
(a)     Mild steel
(b)     Copper
(c)     Aluminium   
(d)     Cast-iron
Ans: d

87. ______ brushes are fragile and cause excessive wear of commutator,
(a)     Natural graphite
(b)     Hard carbon
(c)     Electro graphitic
(d)     Metal graphite
Ans: a

88.   Which of the following brushes can be used for high values of current density ?
(a)    Metal graphite brushes
(b)    Hard carbon brushes
(c)    Electro-graphitic brushes
(d)    Natural graphite brushes
Ans: a

89    ________ is the common method of applying brushes to the commntator.
(a)     Radial
(b)     Trailing
(c)     Reaction
(d)     All of the above
Ans: d

90.    Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?
(a)     Increased I R losses
(b)     Increased core losses
(c)    Poor commutation
(d)    Change in motor parameters
(e)    All of the above
Ans: e

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