How to resolve delta connected systems?

Delta connected components of power distribution system should be converted to wye connection before the MVA method for short circuit fault current analysis can be applied. If the new set has values properly selected, the behavior at the end terminals and the performance of the remainder of the system will be unaffected by the substitution. Figure shows three impedances connected in a delta configuration, and three impedances connected in a wye configuration. Looking into any two terminals, the two connections will be equivalent if corresponding input, output and transfer impedances are equal.

Lets D1, D2, D3 assume MVA ratings for the delta connected components. Y1, Y2, Y3 are the wye connected equivalents to be calculated.

delta to wye conversion

The formulas below are suitable for the conversion of loads of equal X/R ratio. The X/R ratio doesn't change upon the conversion:

S = (D1 x D2) + (D2 x D3) + (D3 x D1)

Y1 = S / D1
Y2 = S / D2
Y3 = S / D3