Section II: Modification of Bus Impedance Matrix

• Adding a New Bus to the Reference Bus
• Adding a New Bus to an Existing Bus through an Impedance
• Adding an Impedance to the Reference Bus from an Existing Bus
• Adding an Impedance between two Existing Buses
• Direct Determination of Z_bus Matrix

Modification of Bus Impedance Matrix

Equation (3.1) gives the relation between the bus impedance and admittance matrices. However it may be possible that the topology of the power system changes by the inclusion of a new bus or line. In that case it is not necessary to recompute the Y_bus matrix again for the formation of Z_bus matrix. We shall discuss four possible cases by which an existing bus impedance matrix can be modified.

Let us assume that an n -bus power system exists in which the voltage-current relations are given in terms of the bus impedance matrix as

(3.30)

The aim is to modify the matrix Z_orig when a new bus or line is connected to the power system.