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Three phase 400V to 110V transformer formulas

E95

Gents,

Having a bit of a brain meltdown today ..

What's the formula for Ip on a 400V to 110V stepdown transformer in terms of Is, VP, Vs? And is it the same for a centre tapped output?

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    The design will be more or less loss-less, or at least losses will be 10% or less.

    sp take secondary amps times secondary volts  - and if there are 3 outputs then treat them as 3 singles.

    (so  55-0-55 every amp between the two lives is 110 watts. ,if you have 3 lots of 55-0-55 each drawing an amp, then you have 330watts..

    And same for primary/ If you had one winding with 400V between the ends, then the winding current would be not quite 1/4 of the 110V load currents.

    But if you have 3 windings, delta style then as each supply line is covering 2 windings at 120 dedrees, a quick star- to delta conversion shows you that the supply  line current per phase is 1/3 of 1/230 of the total wattage.

    where cos of 120 degrees  = - cos 60 degrees = 230/400 approx

    Then add 10% for losses, and use  a slow breaking MCB for inrush.
    Mike.

Reply
  • 0

    The design will be more or less loss-less, or at least losses will be 10% or less.

    sp take secondary amps times secondary volts  - and if there are 3 outputs then treat them as 3 singles.

    (so  55-0-55 every amp between the two lives is 110 watts. ,if you have 3 lots of 55-0-55 each drawing an amp, then you have 330watts..

    And same for primary/ If you had one winding with 400V between the ends, then the winding current would be not quite 1/4 of the 110V load currents.

    But if you have 3 windings, delta style then as each supply line is covering 2 windings at 120 dedrees, a quick star- to delta conversion shows you that the supply  line current per phase is 1/3 of 1/230 of the total wattage.

    where cos of 120 degrees  = - cos 60 degrees = 230/400 approx

    Then add 10% for losses, and use  a slow breaking MCB for inrush.
    Mike.

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