Y and Delta Network Calculation:
Because of its shape, the network shown in Figure is known as a T (tee) or Y (wye) network. Those are different names for the similar network.
Figure: T or Y Network
The network display in Figure is known as Π (pi) or (delta) ? since the shapes resemble Greek letters Π and ?. These are different names for the same network.
Figure: (pi) or (delta) Network
In the sequence to analyze the circuits, it might be helpful to convert Y to , or to Y, to simplify the solution. The formulas which will be used for these conversions are derived from Kirchhoff's laws. The resistances within these networks are displays in a three-terminal network. One network is equivalent to the other after we use the conversion formulas, because they have equivalent resistances across any one pair of terminals in the Figure.
? to Y conversion:
Ra = R1 R3/ R1 + R2 + R3
Rb = R1 R2/ R1 + R2 + R3
Rc = R2 R3/ R1 + R2 + R3