Assessment of the Electric Grid Interdiction Problem using a nonlinear modeling approach

- A nonlinear model of the Electric Grid Interdiction Problem is presented.
- The proposed model provides more accurate information than traditional DC models.
- Valuable information is given to the SO regarding vulnerability of the network.
- Protective actions can be taken by the SO based on information provided by the algorithm.
- The algorithm identifies most critical interdiction plans.

This paper addresses the vulnerability assessment of power systems under multiple outages, both unintentional and deliberate. In this context, a new model and solution approach for the Electric Grid Interdiction Problem (EGIP) are proposed. The EGIP is based on the interaction of two agents: a Disruptive Agent (DA) that aims at maximizing load shedding by performing attacks in the power system; and a System Operator (SO), who reacts to these attacks by modifying the generation dispatch in order to minimize load shedding. The interaction of these agents is modeled as a bilevel programming problem. Due to its non-convexity and non-linearity the EGIP has been traditionally approached by means of linearized equivalents of the network and recast as a single-level Mixed Integer Linear Programing (MILP) problem. In this paper the EGIP is formulated as a Mixed Integer Non-Linear Programming (MINLP) problem using an AC modeling of the network, providing more accurate results than traditional DC models. Another distinctive modeling feature is introduced: the possibility of attacks not only on branches but also on generators. The proposed model is solved by means of an Iterated Local Search (ILS) algorithm. Performance of the proposed ILS is compared with a conventional Genetic Algorithm (GA). Several tests were performed on two benchmark IEEE test systems showing the applicability and robustness of the proposed approach.