  Due to the evolving nature of power systems and the complicated coupling
relationship of power devices, it has been a great challenge to identify the
contingencies that could trigger cascading blackouts of power systems. This
paper provides an effective approach to identifying the initial contingency in
power transmission networks, which are equipped with flexible alternating
current transmission system (FACTS) devices, high-voltage direct current (HVDC)
links and protective relays. Essentially, the problem of contingency
identification is formulated in the framework of nonlinear programming, which
can be solved by the Jacobian-Free Newton-Krylov (JFNK) method to circumvent
the Jacobian matrix and reduce the computational cost. Notably, the proposed
identification approach is also applied to complicated cascading failure models
of power systems. Finally, numerical simulations are carried out to validate
the proposed identification approach on IEEE 118 Bus Systems. The proposed
approach succeeds in reconciling the rigorous optimization formulation with the
practical modelling of cascading blackouts.
