First and second order methods for voltage collapse assessment and security enhancement

The paper deals with the applications of steady-state approaches to the assessment of the maximum loadability of the electric system and to the determination of control actions suitable to avoid the voltage collapse. Following current research trends, first order indicators, derived by the linearization of the load flow (LF) equations and by the eigen/singular value analysis are adopted to determine the distance from the voltage collapse. In addition, a new second order performance index, obtained by the maximum singular value of the inverse LF Jacobian and by its sensitivities with respect to the system parameters, is proposed. The same second order information is adopted in a procedure for the security enhancement. It allows preventive rescheduling in alarm states and load shedding in emergency. The performances of the investigated indices are shown with reference to a small test network and to the large EHV Italian system.