Following reasons the transposition of conductor:
1. Due transposition of conductor inductance of each line is same LA = LB = LC, So drop due to inductive reactance in each line is same so voltage at receiving end between any two line become same.
2. So to obtain same voltage in any two line at receiving end (VRY = VYB = VRB) transposition is necessary.
3. Radio interferences are less due to transposition.
Figure of transposition of conductor: