Latest Electrical Machine Design Multiple choice Questions and Answers pdf

31.    With conventional hydrogen cooling it is possible to increase the rating of a single unit to
(a)     50 MW
(b)     100 MW
(c)    200 MW
(d)    none ofthe above
Ans: c

32.    The noise produced by a ______ cooled machine is less as the rotor moves in a medium of smaller density.
(a)     air
(b)     hydrogen
(c)    either (a) or (b)
(d)    none of the above
Ans: b

33    cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall
(a)    Direct
(b)    Indirect
(c)    Conventional
(d)    Any ofthe above
Ans: a

34.    Machines cooled by direct cooling method may be called
(a)     "supercharged"
(b)     "inner cooled"
(c)    "conductor cooled"
(d)    any of the above
Ans: d

35.    In direct cooled system using hydrogen both stator and rotor conductors are made
(a)    solid
(b)    hollow
(c)    perforated
(d)    any ofthe above
Ans: b

36.    With direct water cooling it is possible to have ratings of about
(a)    200 MW
(b)    300 MW
(c)    400 MW
(d)    600 MW
Ans: d

37.    The resistivity of water should not be less than
(a)    10 Q m
(b)    100 Q m
(c)    1000 Q m
(d)    2000 Q m
Ans: d

38.    Direct water cooling of rotor winding presents
(a)     no mechanical difficulties
(b)     lesser mechanical difficulties
(c)    greater mechanical difficulties
(d)    none of the above
Ans: c

39.    The time taken by the machine to attain 0.632 of its final steady temperature rise is called
(a)     heating time constant
(b)     cooling time constant
(c)    either (a) or (b)
(d)    none of the above
Ans: a

40.    In self cooled motors the cooling time constant is about ______    than the heating time constant because cooling conditions are worse at standstill.
(a)    2 to 3 times greater
(b)    3 to 4 times greater
(c)    4 to 5 times greater
(d)    none of the above
Ans: a

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