Research On Cascading Failures In Large-scale Power Grid Based On Small-world Network Theory

The complexity of power grid and the fast development of complex network theory have madeit constructive and popular to study the security and reliability of power system from the point ofcomplex network view. Considering the power system as an integrated unit, this paper studies thesmall-world effects, structural load distribution, and characteristics of failure cascading in powergrid, deeply analizies the influences of small-world effects on cascading failures of the power gridand finally establishies a complete analysis system to find the intrinsic reasons for cascading failuresin small-world power grid.Firstly, small-world effects analysis method is proposed and testified for both weightless andweighted power grid models, and the topological characteristics of real power grids are studied. Inlarge-scale power grid, the clustering coefficient is large while the average distance is small, andnumber of connections is relatively equal among nodes, therefore the power grid is a typicalsmall-world network and none of a scale-free network.Secondly, inheterogeneity of nodes is analyzed in particulare with concrete schemes.Experiment results show that the long-edges in small-world power grid are the outcome of thedynamic procedure of transmitting power in the most efficient way. However, the high efficiency isachieved at the cost of high centrality of load on certain nodes, indicating that the influences ofnodes on power system reliability might be much different according to their status in powertransmitting.Thirdly, a comparison of the current cascading failure models is proposed. Compared with theexisting models, where no operation capacity or operation limit are concerned so that nodes canafford limitless load, or merely the conception of operation capability is concerned and the on-linecut measures for failed nodes are ignored, the model which considers both the operation capacity andoperation limit simulates the procedure of failures more accurately.The load loss percentage, which reflects both the numbers of the invalid nodes and theirimportance to power grid, is used to estimate the width and depth of failures. The failure iniatingmodes are improved to study the structural vulnerability of the power grid from two aspects. Thefirst mode is designed to study the dependency of small-world power grid on high degree nodes andhigh load nodes. The second mode is designed to study the reaction of power grid to internal andexternal factors. The reactions of the power grid under the two modes are helpful to find thevulnerable part of the grid and thus present valuable references for valid measures to improve thecapability of the power grid in enduring large-scale blackouts. Fourthly, based on the failure characteristics and the structural characteristics, the paperanalyzes the inherent reason for cascading failures in small-world power grid. In small-world powergrid, the special topological structure of small-world power grid explains the essential reason for itsvulnerability: in small-world power grid, the nodes show strong heterogeneity in load, some of thekey nodes that take over much higher load than others are closely related with those long-edges thathelp to increase the efficiency of electricity transmission. The key nodes, though much meaningfulto the stability of the grid structure, are the vulnerable parts of small-world power grid, once they arefaulted and exit from operation, relative long-edges are broken, large amounts of the shortestelectrical paths are diverted and failures are swiftly extended in the grid.Finally, the paper points out that structural vulnerability of smail-world power grid is theintrinsic reason for failures to cascade in the grid and external factor can hardly improve itsendurance to large-scale cascading failures. More reasonable resource configuration and loaddistribution are meaningful to prevent large-scale cascading failures, thus increase the reliability ofelectricity transmission.