Derivation of equivalents for dynamic security assessment

Abstract

A method is described by which the order of interconnected power systems is reduced. When the system under study is composed of a main system and several subsystems connected to the main system, the method gives an equivalent model to each subsystem with far fewer generators, even when each subsystem is connected to the main system at more than one point. The paper also discusses the data that needs to be sent from each subsystem when it is expressed by a reduced-order equivalent model. A numerical example of a 250-bus and 61-machine system shows that the method is effective and causes no loss of accuracy. Although the proposed method provides an accurate reduced-order model, it is rather time-consuming, because it is based on the linearized dynamic equations of the system, and their eigenvectors are needed. This problem must be solved before practical use of the method can proceed.