This document discusses four types of modifications that can be made to an existing power network to revise the Z-bus representation. Type 1 involves adding a branch impedance between a new bus and the reference bus. Type 2 adds a branch between a new bus and an existing bus. Type 3 adds a branch between an existing bus and the reference bus. Type 4 adds a branch between two existing buses. The document presents figures to illustrate each type and provides the corresponding equations to update the Z-bus matrix for the network.

2.  Introduction
 Notations & addition of branch and link
 Type-1 Modification
 Type-2 Modification
 Type-3 Modification
 Type-4 Modification
 Conclusion
 Reference
Karansinh Parmar, M.Tech. Electrical Power System Engineering 2

3.  Step-by-step programmable technique.
 Proceeds branch by branch.
 Advantageous as complete rebuilding not
required.
 Zbus (old) Zb=branch impedance Zbus (new)
Karansinh Parmar, M.Tech. Electrical Power System Engineering 3

4.  Notation: i, j-old buses;
r-reference bus;
k-new bus.
 Addition of branch : For connecting a new bus to
an already existing old bus.
 Addition of link: For connecting two buses which
already exist in partial network.
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Fig.1: Type-1 Modification
• Branch Impedance Zb is added to the
new bus k & the reference bus r.
Vk= Zb * Ik
Zki= Zik = 0; i = 1,2. . . . n
Zkk=Zb
Zbus (new) = Zbus (old)
0
I
I
I
0
Zb0 --- --- ---
0

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Fig.2 : Type-2 Modification
• Zb is added from a new bus k
to old bus j .
Rearranging,

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Fig.3 : Type-3 Modification
• Zb connects an old bus j to the ref. bus r.
Vk= 0
)

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Fig.3 : Type-4 Modification
• Zb connects two old buses i and j.
Vi= Zi1I1 +Zi2I2 + ... +Z1i (Ii+Ik)+Zij(Ij-Ik)+ … +ZinIn
Eliminating Ik we get ,

9.  Step by Step procedure .
 Easiliy computerized procedure.
 Modification employed to revise Z-bus in
case of change in network.
 Opening of line Zij is equivalent to adding a
branch in parallel to it with impedance –Zij.
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10.  “Modern Power System Analysis (4th
edition)”,by D.P.Kothari & I.J.Nagrath.
- Tata McGraw Hill Education Pvt. Ltd.
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