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Thread: Voltage Unbalance Reason

  1. #11
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    Quote Originally Posted by GoldDigger View Post
    See post #6 for how it can be.
    I sketched it out
    l-n 600/0
    the other x/120
    the sum (rather than subtract as if pol was reversed) being 200/30

    can't find an x that works

  2. #12
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    Gentlemen
    pls re-read post #8 that addresses these issues
    and comment back
    Am I in shape?? I get plenty of exercise pushing my luck!!

  3. #13
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    he has the same set up on the other sets
    n is floating, but the others read ok

    has it ever worked correctly?
    is it a new install being commissioned?

    the only way I can see those magnitudes
    l-n ~600
    l-n ~ 150 with a 300
    is the neut having 600/0 +/- 15-20 deg phasing vs +/- 120 deg
    no idea how you would get that

  4. #14
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    Quote Originally Posted by ATSman View Post
    Gentlemen
    pls re-read post #8 that addresses these issues
    and comment back
    Sometimes I wonder if it is worth challenging someone that is so sure of themself. That's why I thought my suggestion was fair earlier too.
    Ron

  5. #15
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    Quote Originally Posted by mrmuneeb View Post
    dear All,

    Hi, I am having a problem of unbalanced strange values of system voltages in of our power generation plant,
    the disturbance in voltage is being reflected on Low voltage side only,

    system diagram is attached.

    Attachment 20244

    what the system must show at low voltage side is;
    1. P-P 480V
    2.P-N 277V

    but the current scenario on delta side of transformer is;

    L1-L2= 316 V
    L2-L3= 147 V
    L3-L1= 221 V

    L1-N= 594 V
    L2-N= 599 V
    L3-N= 530 V

    neutral is kept floating on both sides, i.e. both LV & MV neutral is floating.
    is there any fault in on of the system phases?
    The vector sum of line or phase voltages, whether balanced or not, of the generator should equal zero i.e they form a closed triangle. If it is not so with your readings i.e a closed triangle is not possible even approximately, it means the phase angle between phase windings are not correct i e the winding issue.

  6. #16
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    Quote Originally Posted by ATSman View Post
    Gentlemen
    pls re-read post #8 that addresses these issues
    and comment back
    a floating neut will not make v l-n 3 x v l-l
    either he made a posting error and v l-l is 600 and v l-n 150-300 or there are major connection issues

    the ONLY way for this to occur
    v l-n for a, b, c ~ 600/0, +15-20, -15-20 deg

    this will give a l-l using a ph ~ +/- 17 deg
    v a + (- v b) = vab
    va = 600 + 0j
    vb = -(575 + 175j)
    vab = 25 + 175j = 175/82
    similarly vac ~ 175/-82

    vbc
    0 + 350j ~ 350/90
    Last edited by Ingenieur; 05-05-18 at 12:06 PM.

  7. #17
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    On occasion I get the feeling that OPs have an moment and don’t bother coming back. I have them often enough.
    Tom
    TBLO

  8. #18
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    Quote Originally Posted by Sahib View Post
    The vector sum of line or phase voltages, whether balanced or not, of the generator should equal zero i.e they form a closed triangle. If it is not so with your readings i.e a closed triangle is not possible even approximately, it means the phase angle between phase windings are not correct i e the winding issue.
    If vector sum of line or phase voltage readings of the generator by OP does not equal zero ie they do not form a closed triangle even approximately, it implies erroneous readings or a break in generator windings.

  9. #19
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    +(vab = 25 + 175j) or 175/82
    -(vac = 25 - 175j) or 175/-82
    -(vbc = 0 + 350j) or 350/90
    = 0 + 0j

    something does not compute
    one machine in reverse rotation
    messed up connections
    etc or some combination

  10. #20
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    I don't understand, if the neutral is kept floating, then aren't any line to neutral voltage readings meaningless?


    If the voltage readings are true, I can't really wrap my head around it either except to speculate that a neutral and a phase are reversed or one generator has its windings in series rather than parallel. I would compare connections to the other six generators that are working fine, try to rule out any obvious errors
    Electricians do it until it Hertz!

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