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Lv 4
? asked in Science & MathematicsEngineering · 8 years ago

4 wire, unbalanced star load. Please help me!?

I'm quite stuck on an assignment.

400V, 3 Phase supply, 4 wire star, 3 resistive loads of - 24kW, 18 kW, 12kW.

I need to find out the current in each line and the current in neutral conductor.

Any help on what I need to do, would be soooo great!

Thankss.

2 Answers

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  • billrussell42
    Lv 7
    8 years ago
    Favorite Answer

    400 volts phase to phase is 231 volts phase to neutral.

    Assuming the loads are connected phase to neutral, then the currents are

    24 kw/231 = 104 amps

    18 kw/231 = 78 amps

    12 kw/231 = 52 amps

    we can add these as vectors to get the current in neutral

    104 amps = 104i

    78 amps = –78isin30 + 78jsin60 = –39i + 67.5j

    52 amps = –52isin30 – 52jsin60 = –26i – 45 j

    sum is 39i + 22.5j

    magnitude is √(39² + 22.5²) = 45 amps

    but check the math

  • -$@Memo Slim Shady
    Lv 4
    8 years ago

    Voltage per phase = 400/sqrt(3) =235 v/ph

    P = V x I x pf

    pf is unity for resistive loads.

    Therefore,

    I1 = 24000/235 = 102.13 A

    I2 = 18000/235 = 76.6 A

    I3 = 12000/235 = 51 A

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