An improved transient stability index for dynamic security assessment using a marginally unstable injection (MUI) approach

This paper is about hybrid methods of combining energy function analysis and conventional time-domain simulation for transient stability assessment. In particular, a new approach called marginally unstable injection (MUI) for developing a more accurate transient stability index is presented. An energy margin for transient stability assessment based on a reduced energy function is formulated. One implementation of the proposed approach is to use a feedback-controlled sequence of short pseudo-faults to impel the stable system to a marginally unstable state. The conceptual differences between MUI and some earlier approaches of hybrid methods are discussed. For illustrative purposes, the technique developed is applied to a 700-bus North America system. Some numerical results are presented