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Homework Help: Max Fault Current XFMR-need help quickly if possible

  1. Apr 11, 2013 #1
    Hi, I have a power systems protection assignment and I wanted to get some simple calcs verified.

    XFMR - 30MVA, 132kV:22kV; Star/Delta respectively. star neutral is floating, not that it matters for this part.

    reactance is 8% and resistance is 0.5% on the 30MVA base.

    Basically I am trying to choose CT's and I don't want them saturated so I need the max line current (obviously the XFMR will trip on OC so I need max current up to 140%30MVA = 42MVA)

    I have: [tex] I= \frac{42MVA}{\sqrt{3}*22kv} = 1.102kA [/tex] on the LV delta side. I'm not sure if this is correct though???? why have the specified the transformer impedance???
    I also need the max line current on the star side for diff protection but I think that that should just be reduced by the turns ration,,,, may have to account for the star delta configuration????

    Thanks for any help.
  2. jcsd
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