Electrical Engineering MCQs

Page No. 98

The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ?


aConduction


b Convection


c Radiation


d All of the above


View Answer All of the above

The noise produced by a ___________ cooled machine is less as the rotor moves in a medium of smaller density?


aair


bhydrogen


ceither A. or B.


dnone of the above


View Answer hydrogen

The thermal conductivity of hydrogen is _____________ times that of air?


a 2


b 3


c5


d7


View Answer 7

cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall______________?


aDirect


bIndirect


cConventional


d Any of the above


View Answer Direct

With conventional hydrogen cooling it is possible to increase the rating of a single unit to___________?


a50 MW


b100 MW


c200 MW


dnone of the above


View Answer 200 MW

Hydrogen has a heat transfer co-efficient __________ times that of air?


a1.5


b 2.5


c3.5


d4.5


View Answer 1.5

Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto_______________?


a 10 MW


b30 MW


c60 MW


d150 MW


View Answer 60 MW

The mcrease in heat dissipation by air blasts is due to increase in______________?


aconduction


bconvection


c radiation


dany ofthe above


View Answer convection

On which of the following variables heat convected depends ?


aPower density


bTemperature difference between heated surface and coolant


cGravitational constant


dAll of the above


View Answer All of the above

Which of the following materials is used in the manufacture of resistance grids to be used in the starters of large motors ?


aCopper


bAluminium


cSteel


dCast-iron


View Answer Cast-iron

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