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Neutral Distributed / Non Distributed

Nick Parker
Explain me the difference between a neutral not distributed and with neutral distributed.


(3 Phase + 1 Neutral) loads -- > Is this termed as distributed neutral?

(1 Phase + 1 Neutral) loads  -- > Is this termed as distributed neutral?

3 Phase, for example motor  --> Non distributed neutral?

2 Phase, for example lighting fixtures -- > Non distributed neutral?,


I would like to apply the relevant equations to find the short circuit at the end of line. That is why this question came up.

e0ad2d78a7db489c6dec116697fc0792-huge-neutral-distributed-vs-non-distributed.png

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  • 0
    The question asks for the minimum short circuit current.  If we use the BS7671 definition of short circuit that implies that we are dealing with faults between live conductors.


    For a 3 wire 3 phase system the minimum short circuit current is produced by a line to line fault (2 phase fault) and for a 3 phase 4 wire system the minimum short circuit current is produced by a line to neutral fault.


    The equations are basically just I = V/R.


    The numerators are the same apart from the value of  voltage i.e Ur = Rated voltage line to line and U0 = line to earth or in this case line to neutral.

    The 0.8 maybe something to do with voltage regulation and the K terms are generally correction factors for impedance (probably referring to the source)  (in IEC 60909 terms).


    The denominators represent an approximation of line impedance.  For the first case this is line to line and for the second it is line to neutral.


    p.2L/S and p.(1 + m).L/S are both dc resistance (resistivity formula) and the 1.5 is probably a factor to approximate impedance Z (for cables over 300mm^2 1.5 is in the ball park)


    p.(1 + m).L/S probably allows for reduced neutrals i.e if the neutral is the same size as the line m = 1.


    Regards

    Geoff Blackwell
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  • 0
    The question asks for the minimum short circuit current.  If we use the BS7671 definition of short circuit that implies that we are dealing with faults between live conductors.


    For a 3 wire 3 phase system the minimum short circuit current is produced by a line to line fault (2 phase fault) and for a 3 phase 4 wire system the minimum short circuit current is produced by a line to neutral fault.


    The equations are basically just I = V/R.


    The numerators are the same apart from the value of  voltage i.e Ur = Rated voltage line to line and U0 = line to earth or in this case line to neutral.

    The 0.8 maybe something to do with voltage regulation and the K terms are generally correction factors for impedance (probably referring to the source)  (in IEC 60909 terms).


    The denominators represent an approximation of line impedance.  For the first case this is line to line and for the second it is line to neutral.


    p.2L/S and p.(1 + m).L/S are both dc resistance (resistivity formula) and the 1.5 is probably a factor to approximate impedance Z (for cables over 300mm^2 1.5 is in the ball park)


    p.(1 + m).L/S probably allows for reduced neutrals i.e if the neutral is the same size as the line m = 1.


    Regards

    Geoff Blackwell
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