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Homework Help: 3 Phase Synchronous Machine

  1. Aug 17, 2010 #1
    1. The problem statement, all variables and given/known data

    A star-connected, 3-phase, 100kVA, 415V, 50Hz synchronous motor having a synchronous reactance of 1.2ohms and negligible resistance operates at its rated terminal voltage, rated current and per-phase field-induced emf of 228V. Determine the power factor.

    The excitation is adjusted until the numerical value of the power factor is the same as initially but the sign of the reactive power is changed. Determine the new value of field induced emf.

    2. Relevant equations

    Power = 3 Vp.Ip.PF.

    Complex Power = Vl.Il/root3

    V = Ef + jIaXs

    Vl = Vp. root 3

    Complex Power = S = P + jQ

    3. The attempt at a solution

    I calculated the following(correctly, I think):

    The synchronous angular velocity is 100.pi rad/s.

    The line current is 46.37 Amps

    IaXs = 55.65V

    Phase Voltage = 239.6V

    I can't seem to find the power factor though.

    The answers are PF = 0.89, New value of field induced emf = 365V

    As always any help would be greatly appreciated. Thank you
  2. jcsd
  3. Aug 21, 2010 #2
    Hi Guys,

    Been thinking about the problem a lot and I still can't figure out an answer to this problem.

    If somebody could please help me with this I would be extremely grateful.

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