# Three Phase Transformer Design

• I design single phase transformers, around 400W - 8000W, but now im lost because i have to design a three phase transformer ( delta - delta connection ).

• I searched, trying to find a page that can provide me the formulas, but I dont find anything.

• For what I know, if its delta-delta:

1. Phase Voltage = Line Voltage
2. Phase Voltage = ( 1/sqrt(3) ) * Line Voltage


• When designing, I will have 3 cores, so the voltage in the three of them will be the same, and the current it will be 1/3 in each one? or it will be 1/sqrt(3) in each one?

• In single phase transformers, a good and easy way to know the maximum power of the core its, measure the interior part, lets say side A, and B. So it will be A * B = Area ( cm*cm), and then the Pmax will be Pmax= Area * Area. How can I do this in the three phase transformers? Its the same? I Can choose the core between some that are in this page: http://www.pryde.com.ar/subcategorias.php?c=1&s=2

-The transformer I want to design its: Voltage input: 380V, Voltage Output: 51V, Secondary Current: 100A, Connection: Delta-Delta. So if im not wrong it will be:

1. Pmax = 51v * 100A * sqrt(3) = 8833W
2. Each Core Pmax = 51v * ( 100A / sqrt(3) )

• @Transistor Yes, im sorry, i didn't know how it was named in english... Jun 12 at 19:17
• Have a look at 3-phase core laminations(?) (for potentially unbalanced loads there used to be cores with 4 or 3 2/2 limbs). As to power/current, it is complicated unless load is balanced. (They managed to screw up the image of UI core sheets?!) Jun 12 at 20:03

Delta-in to delta-out means basically three individual transformers with no core sharing. Treat the design just like three single phase transformers with each handling one-third of the power. Based on this you don't need to worry about $$\\sqrt3\$$ or anything like that.