For the 4-bus system, containing transmission lines and transformers. The admittance matrix is Ybus=⎡⎢
⎢
⎢
⎢⎣−j20j2000j20−j60j4000j40−j60j2000j20−j25⎤⎥
⎥
⎥
⎥⎦
If a transmission line having π-equivalent circuit as shown below is connected between 2nd and 4th buses. Then the modified Ybus matrix will be
Where, Zse = series impedance of transmission line.
Ysh= shunt admittance of transmission line.