Topological and Impedance Element Ranking (TIER) of the Bulk-Power System

The Electricity Modernization Act of the Energy Policy Act of 2005 requires the creation of enforceable reliability standards for users, owners, and operators of the "Bulk-Power System" (BPS). This paper introduces an algorithm based on electrical properties of an electric power network that yields a numeric ranking of its branch elements as a step towards identifying which elements should be considered part of the BPS. This ranking depends solely on network topology and element electrical characteristics, and is wholly independent of generator cost functions and system operating point. Two perspectives for deriving and justifying this ranking algorithm are described: one based on the sensitivity of bus-to-branch Lagrange multipliers and another based on generation shift factors. Summary results obtained from applying the algorithm to a detailed model of the US Eastern Interconnection are reported (with suitable anonymity for any facility specific data, in keeping with Critical Energy Infrastructure Information (CEII) protections).