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.Management Sciences
Category: Electrical Machine Design
Which of the following is an advantage of hydrogen cooling ?
A. Increase in efficiency
B. Increase in ratings
C. Increase in life
D. Smaller size of coolers
E. All of the above
____________are used for construction of core of electromagnets?
A. Soft magnetic materials
B. Hard magnetic materials
C. Either A. or B.
D. None of the above
__________ has a low relative permeability and is used principally in field frames when cost is of primary importance and extra weight is not objectionable?
A. Cast steel
B. Aluminium
C. Soft steel
D. Cast iron
electromagnets generally function as holding magnets ?
A. Tractive
B. Portative
C. Either of the above
D. None of the above
The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc?
A. conduction
B. convection
C. radiation
D. any of the above
Yokes with rectangular cross-section are used for_______________?
A. small capacity transformers
B. medium capacity transformers
C. large capacity transformers
D. any of the above
The weight of copper of both armature and field windings decreases with __________ in number of poles?
A. increase
B. decrease
C. either of the above
D. none of the above
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
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 of the above
D.C. machines designed with a large value of air gap length have_____________?
A. worst, ventilation
B. poor ventilation
C. better ventilation
D. none of the above
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