A. 0.07
B. 1.5
C. 2.5
D. 3.5
Related Mcqs:
- Hydrogen has a heat transfer co-efficient __________ times that of air?
A. 1.5
B. 2.5
C. 3.5
D. 4.5 - The thermal conductivity of hydrogen is _____________ times that of air?
A. 2
B. 3
C. 5
D. 7 - 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 - 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 - 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 of the above - 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 - In direct cooled system using hydrogen both stator and rotor conductors are made____________?
A. solid
B. hollow
C. perforated
D. any ofthe above - 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 - 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 - 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
