Help! Having trouble with OPEN DELTA 3 Phase Connection

Discussion in 'Homework Help' started by MH Ating, Mar 8, 2016.

  1. MH Ating

    Thread Starter New Member

    Feb 9, 2016
    A 3 phase load of two 50hp, 440v, 3phase motors is to be supplied by a transformer connected in Open Delta on a 2300V Line.
    Assume a motor efficiency of 90% and a lagging pf of 85%.
    a. Determine the KVA capacity of each transformer and their transformation ratio.
    I started as 2 x 50 hp = 100hp = 74.57kw
    if i consider 1 motor only, i have 37.285kw
    Efficiency = Pout / Pin

    I = 74.57kw / ((square root of 3) x 440v x 0.85)
    = 115.1

    How would i use the value of Efficiency?
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    Efficiency is going to tell us how much of the power going in is actually going to be converted into usable power out.

    Therefore, Power(out) = Efficiency × Power(in).