Loss of Neutral

Discussion in 'General Electronics Chat' started by Appeagyei, Nov 7, 2013.

  1. Appeagyei

    Thread Starter New Member

    Oct 16, 2013
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    Dear Members,

    As far as I know neutral loss in a 3 phase system causes the voltage of the phase with less load to rise and that with higher load to fall.

    Please i want explanation as to why and how this happens.

    thank you
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    The Completed Projects Forum is for Completed Projects only. It is meant to allow members to show plans for projects they built so other members can duplicate them if desired. New threads are also automatically moderated per Moderator review for this reason. Your thread does not belong in this forum, and was moved here.
     
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Draw it out. Loose your neutral and your loads are in series. Apply the math and reconsider the question.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    For me that statement is too general. The loss of neutral connection, such that current is unable to return to the 3-phase source via the neutral conductor, immediately imposes the condition that the line currents must re-adjust to allow for the loss of neutral current. The vector addition of the individual 3-phase line currents must be zero to satisfy this outcome. This may, for instance, result in a lower total 3-phase power delivery from the source in relation to the case with the neutral intact.

    As suggested by GDI this really requires one to undertake a full circuit analysis having regard to the changed circuit conditions both with and without the neutral connection. Whilst a little challenging in execution it boils down to AC circuit analysis using complex algebra.
     
  5. GetDeviceInfo

    Senior Member

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    Or just some simple deduction. Regardless of the value, a poly phase system with neutral will keep the voltages equal across the individual loads. Loss of neutral puts the loads in series, where classical voltage drop equations paints the picture. Don't worry about the numbers themselves, but the relationships.
     
  6. t_n_k

    AAC Fanatic!

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    An interesting concept. Perhaps you could give a specific example of conditions in an unbalanced 3-phase system before & after neutral loss. I imagine something like an unbalanced 3-phase Wye connected load fed by a balanced Wye connected 3-phase source with the Wye load neutral point returned to the source neutral in one case and not returned in the other case.
     
    Last edited: Nov 8, 2013
  7. GetDeviceInfo

    Senior Member

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    take your common 208/120 3 phase. Take a 1 ohm load from A to neutral, and a 10 ohm load from B to neutral. Now take the neutral away and calculate series current/voltage drops across the series loads. Compare the two conditions and consider the original question.

    Could be way off though. I'm sure if it was some wye/wye connection it would need to be mentioned.
     
    Last edited: Nov 8, 2013
  8. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    OK. I see your interpretation of the OP's question differed from mine. In the case of a third phase C with a load to neutral, then problem becomes more complex.
     
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Could have been a more complex y/y connection, but that would have to have been stated
     
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