For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used?

Related Mcqs:

1. 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...

2. 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...

3. The forced oil and air circulation method is usual one for transformers of capacities____________?

   A. upto 5 MVA B. upto 10 MVA C. upto 20 MVA D. 30 MVA upwards...

4. The density of hydrogen is __________ times the density of air?

   A. 0.07 B. 1.5 C. 2.5 D. 3.5...

5. 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...

6. The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are______________?

   A. 0.5 to 0.8 Wb/m2 B. 0.8 to 1.0 Wb/m2 C. 1.1 to 1.35 Wb/m2 D. 1.4 to 1.8 Wb/m2...

7. 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...

8. 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...

9. Power transformers should be designed to have maximum efficiency________________?

   A. at one-fourth load B. at one-half load C. at or near full load D. any of the above...

10. Power transformers have rating_______________?

    A. equal to 50 kVA B. equal to 100 kVA C. above 200 kVA D. none of the above...