Effective turns ratio of 3 phase bank

Discussion in 'Homework Help' started by Sparky, Sep 20, 2010.

  1. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
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    0
    Greetings,

    I've been brushing up on my "power" knowledge.

    I found this problem and solution but need a little clarification.

    Problem:
    " The following transformer is composed of 3 single phase transformers or pri:sec voltage ratio 480:120 volts. Each transformer is rated 4.5kVA. The voltage source is a balanced 3phase positive sequence source with VA - 277.1 (0 degrees) v.

    Find the effective 3-phase turns ratio."

    a = VLL_primary / (VLL_Sec) = (VLN_Pri / VLN_Sec) = 2.309

    I guess first question -

    In the solution
    The 480 is labeled the LL_Pri while 120 is labeled LN_Sec

    The LN_Primary is 277.1.

    How do we know the 480 is the LL_Primary and how do we know the 120 is the LN_secondary?

    Thanks
    -Sparky
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    You are not given this explicitly - I guess the implicit assumption is that the transformer is a distribution type with a typical primary line-to-line value of 480V and a typical secondary line-to-neutral value of 120V.

    It would have made the issue abundantly clear if the question had simply stated that this was the case.
     
  3. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
    75
    0
    Thanks

    I was hoping someone would agree with my take on the way the problem was worded.

    -Sparky
     
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