Region of attraction in a power system with discrete LTCs

This paper extends some previously obtained results on load tap changer (LTC) stability and derives detailed conditions for the stability of a dynamical system consisting of discrete LTC transformers based on Lyapunov's direct method and its extension according to LaSalle's Invariance Principle. The exact region of attraction of a two LTC system is constructed based upon tap position and controlled voltage values. Generalizations and extensions are finally discussed in the framework of extracting rules for post-load-shedding stability.