Shunt DC Machines (Rotational Losses)

Discussion in 'Homework Help' started by jegues, Dec 15, 2011.

  1. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    See figure attached.

    They give us details of the no load conditions for this shunt DC machine and I assume that's how you are supposed to find the rotational losses but I can't seem to figure it out.

    How do you obtain the rotational losses using the information provided from the no load conditions?

    Thanks again!
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    At no load the motor presumably draws 5A at a set terminal voltage of 230 V.

    The shunt field would take 2A, so the armature has the remaining 3A. The armature resistance drop is 0.3V so the armature emf = 229.7V. The no-load power input is therefore found from the 3A current and 229.7V armature emf - which would correspond to the rotational loss.
     
  3. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
    735
    43
    Thank you very much.

    It wasn't clear to me from the question that the no load condition was indeed at a terminal voltage of 230V.
     
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