separately excited dc motor

Discussion in 'Homework Help' started by Amanda_Riley, May 9, 2011.

  1. Amanda_Riley

    Thread Starter New Member

    May 12, 2010
    22
    0
    Can someone tell me how armature current is found if you know:

    Vt = 240
    Ra = 0.25
    pout = 30k
    efficiency = 92%
     
  2. majsyd2010

    Member

    Aug 29, 2010
    61
    1
    Follow below;

    Ia = Et - Ecemf / Ra

    where
    Ia = armature current
    Et = terminal voltage
    ECEMF = counter EMF
    Ra = armature resistance
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    You might need a bit more thought on that.

    You know the mechanical output is Pout=30kW, with an overall efficiency of 92% [η=0.92]. Also given Ra=0.25 with a DC input Vd=240V.

    Steps required

    1. Calculate the electrical input power to the air gap emf, i.e. Pe. [Pe=Pout/η]
    2. Set up the equation for the armature circuit. [Vd=Ia*Ra+Pe/Ia]
    3. Solve the quadratic equation from step 2 above to find Ia. Only one of the quadratic roots will give the correct value for Ia.
     
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