N atural air coo ling is generally restricted for transformers up to__________?

Related Mcqs:

1. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in____________?

   A. short-circuiting of the secondaries
   B. power factor of one of the transformers is leading while that of the other lagging
   C. transformers having higher copper losses will have negligible core losses
   D. loading of the transformers not in proportion to their kVA ratings

2. Distribution transformers are generally designed for maximum efficiency around________________?

   A. 90% load
   B. zero load
   C. 25% load
   D. 50% load

3. Power transformers are generally designed to have maximum efficiency around__________?

   A. no-load
   B. half-load
   C. near full-load
   D. 10% overload

4. Sumpner’s test is conducted on transformers to determine_____________?

   A. temperature
   B. stray losses
   C. all-day efficiency
   D. none of the above

5. What will happen if the transformers working in parallel are not connected with regard to polarity ?

   A. The power factor of the two trans-formers will be different from the power factor of common load
   B. Incorrect polarity will result in dead short circuit
   C. The transformers will not share load in proportion to their kVA ratings
   D. none of the above

6. If the percentage impedances of the two transformers working in parallel are different, then______________________?

   A. transformers will be overheated
   B. power factors of both the transformers will be same
   C. parallel operation will be not possible
   D. parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load

7. Which of the following is not a routine test on transformers ?

   A. Core insulation voltage test
   B. Impedance test
   C. Radio interference test
   D. Polarity test

8. For the parallel operation of single phase transformers it is necessary that they should have___________?

   A. same efficiency
   B. same polarity
   C. same kVA rating
   D. same number of turns on the secondary side.

9. The efficiencies of transformers compared with that of electric motors of the same power are____________?

   A. about the same
   B. much smaller
   C. much higher
   D. somewhat smaller
   E. none of the above

10. Which of the following protection is normally not provided on small distribution transformers ?

    A. Overfluxing protection
    B. Buchholz relay
    C. Overcurrent protection
    D. All of the above