Kwh Calculations for a balanced 3 Phase circuit

Discussion in 'General Electronics Chat' started by Houdini, Sep 22, 2008.

  1. Houdini

    Thread Starter Member

    Dec 13, 2007
    10
    0
    Quick question,

    I'm trying to find the Kwh of a 3 phase machine. It is a balanced 3 phase resistive load. To find the Kwh that the machine draws do I multiply the line to line voltage and the current then divide by 1.73? Then multiply that by how many hours it has ran?

    eg: Voltage = 480 Volts
    Current = 57 Amps
    Run 15 Hours
    Resistive Load
    balanced

    = ((480 x 57) /1000) / 1.73) * 15
    = 237 Kwh

    Is this right?:cool:
     
  2. theamber

    Active Member

    Jun 13, 2008
    318
    0
    Check on this calculator.
    http://www.dieselserviceandsupply.com/Power_Calculator.aspx

    If the 57A current is per leg and to be more accurate if you know the PF rating should multiply it too.
    KW=VOLTS X AMPS X PF X 1.73 /1000
    37.86624*15= 568Kwh. I think it this.
     
  3. Houdini

    Thread Starter Member

    Dec 13, 2007
    10
    0
    Looks like I messed up in my calculations a bit. Looks like I was dividing by 1.73 when I should have been multiplying.

    So.....

    For 3 phases, then, the total power is 3 times the power in any phase. 3 x the line to line voltage x the line current divided by the square root of 3. AND since 3 divided by the Sq root of 3 simplifies to just the Sq root of 3. Multiplying that , as you noted , would give me the watts of a 3 phase circuit (assuming the power factor is 1).

    Sound right?

    Thanks!

    :D
     
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