Analytical approaches to determine critical clearing time in multi-machine power systems

In spite of the advances made since 1978 in using direct energy methods for power system stability analysis, the computation of relevant critical energies still poses a problem for on-line applications such as dynamic security assessment. Efforts at simplifying the computations involve (i) trajectory approximations as a power series, and (ii) use of potential energy boundary surface (PEBS) method instead of computing the relevant unstable equilibrium point (u.e.p.). In this paper we indicate improvements on both these issues. Specifically, the introduction of approximations for the post-fault trajectory are proposed as an alternative to the iterative PEBS method.