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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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    As promised, neutral offset voltage with open PEN.


    3 loads  R1= 230/60 ohms  R2 =230/50 ohms and R3 = 230/40 ohms.


    Let us ground the 40A phase (call it L3 )and consider L1 and L2 to be two phases of 400V relative to it, one at 60 degrees phase offset relative to the other.

    We can transform our voltages back to a 'centre earth' at the end, and I prefer to work with only 2 moving parts in the model.


    V 3 is the drop across the R3 resistor due to the sum of the two currents coming in through R1 and R2. They are not orthogonal and cannot simply be superposed, so we calc current in R3 from V1 with V2 grounded, then current in R3 from V2with V1 grounded, then

    do the in phase and orthogonal thing to get the magnitude and angles.


    see figure below

    08bdd61293a5b04ad2554607fb0f934a-original-neutral_offset.png


Reply
  • 0
    As promised, neutral offset voltage with open PEN.


    3 loads  R1= 230/60 ohms  R2 =230/50 ohms and R3 = 230/40 ohms.


    Let us ground the 40A phase (call it L3 )and consider L1 and L2 to be two phases of 400V relative to it, one at 60 degrees phase offset relative to the other.

    We can transform our voltages back to a 'centre earth' at the end, and I prefer to work with only 2 moving parts in the model.


    V 3 is the drop across the R3 resistor due to the sum of the two currents coming in through R1 and R2. They are not orthogonal and cannot simply be superposed, so we calc current in R3 from V1 with V2 grounded, then current in R3 from V2with V1 grounded, then

    do the in phase and orthogonal thing to get the magnitude and angles.


    see figure below

    08bdd61293a5b04ad2554607fb0f934a-original-neutral_offset.png


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