  This paper proposes a methodology to identify and protect vulnerable
components of connected gas and electric infrastructures from malicious
attacks, and to guarantee a resilient operation by deploying valid corrective
actions (while accounting for the interdependency of gas pipeline network and
power transmission network). The proposed mathematical formulation reduces to a
tri-level optimization problem, where the lower level is a multiperiod economic
dispatch of the gas-electric system, the middle level distinguishes the most
threatening attack on the coupled physical infrastructures, and the upper level
provides optimal preventive decisions to reinforce the vulnerable components
and increase the system resilience. By reformulating the lower level problem as
a mixed integer linear programming (MILP), a nested column-and-constraint
generation (C\&CG) algorithm is developed to solve the min-max-min model. Case
studies on two test systems demonstrate the effectiveness and efficiency of the
proposed methodology.
