Answered Questions

  • What is the power ratio between power in Star and Delta circuit?

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    • Member Since Jul-2006 | Jul 13th, 2006

    The power ratio between Star to Delta is 1:3



    Let?s suppose Vs be the supply voltage per phase.

    So the line voltage of the supply will be ?3Vs.

    Now assume any type of load; for simplicity I?m assuming it a only resistive load.

    And let it be ?R? per phase.


    For Delta connected load:


    Calculation for per phase power; PD= I2R


    Where I ? load current (per phase)


    I = ?3Vs/R       {as line voltage of the supply is directly applied to the phase of the delta load}


                Pd = (?3Vs/R )2R = 3Vs2/R  watts per phase.

    For 3 phases:

                P3D = 3Pd = 3*3Vs2/R = 9Vs2/R watts.


    Now for Star connected load:


    PS = I2R = (Vs/R)2R = Vs2/R watts

    For 3 phases: P3S = 3PS = 3 Vs2/R watts



    P3S / P3D  =  3Vs2/R / 9Vs2/R = 1/3

    It may be better concluded by drowing figures. If any variations, can connect to me through  


    • Feb 3rd, 2018

    Well first you assumed voltage per phase as Vs and Line voltage as sqrt(3) x Vs: Which is for star connection. Then, you assumed the same thing for Delta Connection(where line and phase voltages are t...

    Anbumozhi R

    • Dec 3rd, 2017

    Power is Same. Whether it is star to Delta conversion or Delta to star conversion. Power is 1:1

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