Q. Briefly explain about Wye-delta transformation?

Certain network configurations cannot be reduced or simplified by series-parallel combinations alone. In some such cases wye-delta (Y-) transformation can be used to replace three resistors in wye configuration by three resistors in delta configuration, or vice versa, so that the networks are equivalent in so far as the terminals (A, B, C) are concerned, as shown in Figure. For equivalence, it can be shown that

For the simple case when R_A = R_B = R_C = R_Y, and R_AB = R_BC = R_CA = R, Equations (1) and 2) become