DYNAMIC WARD EQUIVALENTS FOR TRANSIENT STABILITY ANALYSIS

In an effort to reduce the computing time of transient stability asses sment, the paper presents a dynamic equivalent which results from the elimination of the load buses povided with voltage-dependent loads. Th e elimination is performed through a new version of the Ward equivalen cing method. In this approach, the equivalent current injections are e xpressed in terms of the retained bus angles and a sensitivity matrix W. The non-linearity of the load flow model is accounted for through p iecewise linear approximations by updating the W matrix whenever the o perating point moves beyond the validity of the linearization. The pap er also derives the expressions of the incremental changes in the gene rator electric power and the transient energy function for the reduced system. The approach has been tested on several systems with differen t sizes and characteristics.