Real-Time External Equivalents for Static Security Analysis

Equivalent models for the external system in online load-flow studies are presented. The main contribution is a simple extension to the Ward-type equivalencing method that solves the boundary-bus designation problem and gives reliable and accurate results. The method can be applied equally well for off-line equivalencing, where it overcomes the need for buffer zones. Variations on this technique are investigated. The models require topology information, but no real-time measurement data, for the external system. The new methods have been verified by simulation on the IEEE 30 and 118 bus load-flow test systems and on the 835-bus interconnected 15 GW power system of S.E. Brazil.