Power grids exhibit patterns of reaction to outages similar to complex networks. Blackout sequences follow power laws, as complex systems operating near a critical point. Here, the tolerance of electric power grids to both accidental and malicious outages is analyzed in the framework of complex network theory. In particular, the quantity known as efficiency is modified by introducing a new concept of distance between nodes. As a result, a new parameter called net-ability is proposed to evaluate the performance of power grids. A comparison between efficiency and net-ability is provided by estimating the vulnerability of sample networks, in terms of both the metrics.

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Vulnerability analysis in power systems is a key issue in modern society and many efforts have contributed to the analysis. Recently, complex network metrics applied to assess the topological vulnerability of networked systems have been used in power systems, such as betweenness metric, since transmission of power systems is in basis of a network structure. However, a pure topological approach fails to capture the specificity of power systems. This paper redefines, starting from the concept of complex networks, an electrical betweenness metric which considers several of specific features of power systems such as power transfer distribution and line flow limits. The electrical betweenness is compared with the conventional betweenness in IEEE-300 bus network according to the un-served energy after network is attacked. The results show that the tested network is more vulnerable when the components of the network are attacked according to their criticalities ranked by electrical betweenness.