  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 aims to develop a universal approach for identifying the initial
disruptive contingencies that can result in the worst-case cascading failures
of power grids. The problem of contingency identification is formulated in a
unified mathematical framework, and it can be solved by the Jacobian-Free
Newton-Krylov (JFNK) method in order to circumvent the Jacobian matrix and
relieve the computational burden. Finally, numerical simulations are carried
out to validate the proposed identification approach on the IEEE $118$ Bus
System.
