Tree-Partitioning as an Emergency Measure to Contain Cascading Line Failures

Abstract

This paper proposes to replace controlled islanding, which is a defense mechanism against cascading failures, by tree partitioning whereby some of the tie-lines connecting the clusters are still connected in such a way that the cluster-level graph forms a tree. Tree-partitioning prevents line failures from spreading between clusters, similarly as for islanding, but keeps the clusters connected. That results in three main advantages. Power transfers between the clusters can still take place, helping to balance each cluster and limiting any necessary load shedding. Fewer lines are cut, which reduces the shock to the system. There is no need to resynchronize the clusters after the emergency. This paper offers a simple graph-theoretic justification for tree-partitioning, rather than one based on the spectral analysis of network Laplacian proposed in the literature. It also proposes a two-stage methodology, which utilizes spectral clustering, for splitting a network into tree-connected clusters. Test results performed on the 118 node IEEE test network have confirmed the usefulness of the methodology.

A Spectral Representation of Power Systems with Applications to Adaptive Grid Partitioning and Cascading Failure Localization

“…Intentional controlled islanding is a rather extreme response to large-scale cascading failures. In [7] the author propose as an alternative emergency measure beside precisely on the core properties of the bridge-block decomposition. Several other mitigation strategies less drastic than ICI could be adopted, but they often require more detailed cascade models.…”

“…Dynamically creating a bridge-block decomposition is proposed in [7] as a less drastic emergency measure in alternative to controlled islanding. The authors also classical spectral k-way clustering techniques to identify the optimal clusters to be transformed into bridge-blocks.…”

“…Lastly, we remark that an optimization problem similar to OBS is proposed in [7] to refine the bridge-block decomposition as emergency measure. In their formulation, however, the objective is to minimize the total weight of the spanning tree (G E ) P of the reduced graph rather than minimizing the congestion in the post-switching network.…”

“…Let E be non-cut set outage for the power network G = (V, E, b). Then the two submatrices D −EE and D EE of the PTDF matrix defined in(7) decompose as follows:…”

An integrated approach for failure mitigation & localization in power systems

“…A topological representation for the LODF is proposed in [16] and the authors further prove that LODF is zero if the sub-grids are connected in a tree structure in [10]. The failure localization of tree partitioning has been proposed in [17] to replace controlled islanding as a defense mechanism to arrest cascading failure. However, a power network with tree-connected sub-grids is less practical as it creates a single point of failure.…”