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
    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

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

    Is this right?:cool:
  2. theamber

    AAC Fanatic!

    Jun 13, 2008
    Check on this calculator.

    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
    Looks like I messed up in my calculations a bit. Looks like I was dividing by 1.73 when I should have been multiplying.


    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?