A Trilevel Model for Segmentation of the Power Transmission Grid Cyber Network

Network segmentation of a power grid's communication system is one way to make the grid more resilient to cyber attacks. We develop a novel trilevel programming model to optimally segment a grid communication system, taking into account the actions of an information technology (IT) administrator, attacker, and grid operator. The IT administrator is given an allowance to segment existing networks, and the attacker is given a fixed budget to attack the segmented communication system in an attempt to inflict damage on the grid. Finally, the grid operator is allowed to redispatch the grid after the attack in order to minimize damage. The resulting problem is a trilevel interdiction problem, which we solve by leveraging current research in bilevel branch and bound. We demonstrate the benefits of optimal network segmentation through case studies on the 9-bus WSCC system and the 30-bus IEEE system. These examples illustrate that network segmentation can significantly reduce the threat.