Three Phase Voltage Calculations

Discussion in 'General Electronics Chat' started by Sajid, May 13, 2006.

  1. Sajid

    Thread Starter New Member

    Jul 30, 2005
    3
    0
    Hi,

    In a 4-wire, three phase unbalanced voltage system, where the following voltages are known :

    RN, YN and BN,

    where R, Y and B are the three phases and N is the neutral point.

    How can we calculate the RMS voltage between RY, YB and BR ?

    Please note that the voltages are not balanced or else the following formula could be used :

    RY = R*1.732 and so on...

    I have searched so many sites but could not find it, so a little help here, would be highly appreciated.

    Thanks all,
    Sajid.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    We use trigonometry and the Pythagorean theorem.

    √3 is used for balanced loads because 3 =0.75 + 2.25 = ( √3 / 2)^2 + (1+.5)^2

    The sine of 60 degrees is half of √3 (about .866) and the cosine of 60 degrees is exactly .5

    RY = sqrt( (YN*.866)^2 + (RN+YN*.5)^2 ) = sqrt( (RN*.866)^2 + (YN+RN*.5)^2 )

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  3. Sajid

    Thread Starter New Member

    Jul 30, 2005
    3
    0
    Thanks a lot, Thingmaker3.

    U really are a great help. May God bless U.

    Sajid
     
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