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Answers Please. Electrical Technology.

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1. A load of 2.5kW takes a current of 12 Amp from a 230 Volt supply. Calculate the power factor.


2. Three single phase loads are to be connected to a three phase supply. All at unity power factor. The loads are,


i, 60 Amp.


ii, 50 Amp.


iii, 40 Amp.


By any method determine the neutral current.


Z.
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    Thanks Mike

    My software considers a broken neutral with all the phases intact.


    I used Millman's theorem to calculate the various voltages and currents.  In this example it is not too dramatic as the loads are not too far out of balance (worst case voltage is Vbs ( voltage between blue phase and the star point of the transformer - blue phase whats that!) = 254V @ 123º.  Hardly destructive but this is usually a dynamic system so things could go pear shaped.


    The voltage between the transformer star point and the neutral on the consumers side of the break Vsn =27v @ 330º.  So well below the 70 V maximum for EV systems.


    Regards

    Geoff Blackwell
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  • 0
    Thanks Mike

    My software considers a broken neutral with all the phases intact.


    I used Millman's theorem to calculate the various voltages and currents.  In this example it is not too dramatic as the loads are not too far out of balance (worst case voltage is Vbs ( voltage between blue phase and the star point of the transformer - blue phase whats that!) = 254V @ 123º.  Hardly destructive but this is usually a dynamic system so things could go pear shaped.


    The voltage between the transformer star point and the neutral on the consumers side of the break Vsn =27v @ 330º.  So well below the 70 V maximum for EV systems.


    Regards

    Geoff Blackwell
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