Evaluation of the critical load increase direction in voltage collapse studies

This paper investigates the problem of assessing the direction of minimum distance (MD) from the current operating point to the static critical boundary, that is, to the hypersurface describing the maximum loading conditions in the steady-state voltage collapse analysis. The exact calculation of the MD requires a high computational effort. Fast approximated criteria, based on computing the maximum sensitivities of total reactive generation or total losses with respect to the load increase factor, are illustrated and compared in the paper. The theoretical bases of these criteria ate given in the case of a simple two-node system, discussing the possibility of approximating the critical load increase direction, especially when the operating point becomes close to the critical boundary. The extension of the above criteria to the analysis of larger power systems is then discussed and applied to the standard IEEE 30-bus test system. (C) 1997 Elsevier Science S.A.