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Graph Theory and Voltage Stability Analysis
In Radial Distribution Systems
Ahmed R. Abul'Wafa
Ain Shams University
Egypt
[email protected]
Tel./Fax 22639022
Aboul’Fotouh El’Garably
El’Shorouk Academy
Egypt
[email protected]
01004881722
Wael A.Fatah Mohamed
El’Shorouk Academy
Egypt
[email protected]
01061326336
ABSTRACT
A graph-based method is reported in this paper to identify nodes that are on the verge
of voltage collapse of radial distribution networks. The voltage stability index is
derived from the bi-quadratic equation which is generally used for the voltage
calculation of distribution load flow algorithms. The proposed method based on
network graphical information allows power flow equations formulation in matrix
form to satisfy the need of distribution automation. A directed graph, of an N-node
radial network is represented by a sparse matrix of an N-by-N matrix. Paths from the
reference node to any node (downstream nodes for each node including the node
itself) are detected by traversing the directed graph in depth-first search form. A
connection matrix (𝑩𝑵) is constructed based on the discovered paths. The proposed
method uses 𝑩𝑵 for dynamic building of a symmetric upper triangular Bus-Injection
to Branch-Current matrix (𝑩𝑰𝑩𝑪) and a Branch-Current to Bus-Voltage matrix
(𝑩𝑪𝑩𝑽) of the system. The authors present a detailed analysis of effects of different
load models on voltage computation and voltage stability.The results of the
applications of the proposed methodology to a set of networks taken from the
literature on the topic along with conclusion are presented.