Machine-translated by Google. Questions are authored in English.
Top

Discussion

A dc generator driven at half its rated speed with rated field current generates

  • A.no emf at all below the rated speed
  • B.about half its rated emf
  • C.about a quarter of its rated emf
  • D.its full rated emf

Answer: B

Correct answer: about half its rated emf

The emf is proportional to speed at constant flux, so half the speed gives half the emf. The relation is linear, not square-law, because it is the rate of cutting flux that generates the voltage - the quarter answer confuses this with an energy quantity. This is also why a self-excited machine has a critical speed: below it the magnetisation curve falls too low to meet the field resistance line.

No comment is present. Be the first to comment.
Loading…

Post your comment

Please log in or register to post a comment.