Got a question on 3 phase power

Discussion in 'Homework Help' started by purdub, Nov 14, 2006.

  1. purdub

    Thread Starter New Member

    Nov 14, 2006
    5
    0
    in lecture last week, our instructor gave us an extra credit problem that we had no clue how to solve. i have gotten most of the wye diagram done, and am confused on what to do with the angle at the end.

    heres the problem...

    A balanced three phase load consisting of 4+j3 ohms per pahse is connected to a 208Y/120V source. Calculate the (1)current per phase, (2)power per phase, and (3)total three phase power for the wye connected load. Repeat for a delta connected load.

    for the wye diagram, i got
    Ian=41.6A at -36.87 degrees
    Ibn=41.6A at -156.87 degrees
    Icn=41.6A at 83.13 degrees

    Pan=8.65kW at -36.87 degrees
    Pbn=8.65kW at 96.87 degrees
    Pcn=8.65kW at -23.13 degrees

    how do i solve for Ptot? would it be 25.95kW+jQ? and what goes in the place of j and Q?
     
  2. purdub

    Thread Starter New Member

    Nov 14, 2006
    5
    0
    im not even sure if i did the first 2 parts right now

    can someone give me an outline on how to do it?
     
  3. subtech

    Senior Member

    Nov 21, 2006
    123
    4
    I'm a little late getting here.
    Your calcs are somewhat off.
    If you still want to do this, I'll be glad to help you.
    Post again and let me know.........
     
  4. purdub

    Thread Starter New Member

    Nov 14, 2006
    5
    0
    i eventually figured it out after a lot of reading and calculations

    thanks
     
  5. subtech

    Senior Member

    Nov 21, 2006
    123
    4
    Although the site is supposedly "for professional engineers only-no students" you can find some interesting reading here- www.eng-tips.com
    The electric power engineering forum gets interesting at times.
    Be prepared for some abrupt and downright hostile posts occasionally.
     
  6. purdub

    Thread Starter New Member

    Nov 14, 2006
    5
    0
    i tried posting it there...they didnt like it
    also didnt find much helpful info on 3 phase power
     
  7. subtech

    Senior Member

    Nov 21, 2006
    123
    4
    Sorry you had a bad time at eng-tips.
    I can recommend a couple of super good books that cover 3 phase power, motors, transformers and such if you are interested. Or, if you would care to post some specific questions, I'd be glad to try to help. I should warn you however, I'm not an engineer. I'm a journeyman lineman and a protective relay technician. My math is not on the level of a nuclear physicist.
     
  8. purdub

    Thread Starter New Member

    Nov 14, 2006
    5
    0
    thanks for the help/offer, but weve finished going over three phase stuff for now. and im not really liking that topic either.
    im actually in ME, but we are required to have some experience with electrical components, so i thought i would take this class.
    im hopin to get it back next week with a good grade on it. it was worth up to 100 extra credit quiz points :D

    and it was basically my fault at eng-tips. i didnt read their rules about posting HW help
     
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