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Total Building Load in KVA

Michael Brennan
Hi All,


I have been asked to provide the total electrical load of a building.  The max load per phase is 426.3A, on a 3-phase supply.  The majority of this is made up of 1-phase (230V) loads, with a few 3-phase loads mixed in there.  I have designed the electrical distribution such that the loads are split as equally as possible, but I have a question on how to calculate the total KVA value for this supply.  I'm getting a little confused with the information provided online and thought I would check this with a reliable source (you guys!).  Can someone confirm which of the following is the correct calculation, please?


1) I = 426.3A (per phase).  V = 400V (per phase).  Therefore: (426.3 * 400 * 1.732) / 1000 = (426.3 * 692.8) / 1000 = 295.34KVA


2) I = 426.3A (per phase).  V = 230V (per phase).  Therefore: (426.3 * 230 * 1.732) / 1000 = (426.3 * 398.36) / 1000 = 169.82KVA


Many thanks in advance,


MJB
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    As a sanity check in these cases you can ditch the 1.732 which is just the 400V/230V ratio and not very exactly , and assume all loads are just the sum of the single phases


    (426.3Amps  *230volts ) * 3phases = 294147 watts = 294kW.


    The rounding errors will be dwarfed by the reality of the supply being anything between 240V near the intake, and more like 220 at the outbuildings.

    How are you handling load diversity ? A lot of the time the max demands end up oversized on bigger projects.


    To be unbalanced by 20 to 30% between currents on the phases is not uncommon, agonizing to the hundreds of milliamps is not realistic.

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  • 0
    As a sanity check in these cases you can ditch the 1.732 which is just the 400V/230V ratio and not very exactly , and assume all loads are just the sum of the single phases


    (426.3Amps  *230volts ) * 3phases = 294147 watts = 294kW.


    The rounding errors will be dwarfed by the reality of the supply being anything between 240V near the intake, and more like 220 at the outbuildings.

    How are you handling load diversity ? A lot of the time the max demands end up oversized on bigger projects.


    To be unbalanced by 20 to 30% between currents on the phases is not uncommon, agonizing to the hundreds of milliamps is not realistic.

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