A FREQUENCY-DOMAIN TRANSIENT STABILITY-CRITERION FOR NORMAL CONTINGENCIES

In a previous paper, a simple frequency - domain stability criterion;w as proposed for networks near the stability limit subjected to a 3 - p hase fault with no loss of line. The criterion can be summarized as fo llows: if a system is stable, the phase angle of the Fourier transform of a network's transient voltage response exhibits a clockwise polar plot behaviour at all buses (i.e. for increasing frequency); if the sy stem is unstable, it exhibits a counterclockwise behaviour in at least one location. Though these results are of interest, the criterion wou ld be of greater practical use in mechanizing dynamic security analysi s if it could be extended to the types of contingencies actually used in security analysis, namely ''normal contingencies''. Normal continge ncies are commonly defined as the loss of any element in a power syste m, either spontaneously or preceded by a fault, and such changes in to pology impact post-contingency steady-state voltages in addition to th eir transient behaviour. The present paper shows how such cases can be treated, thereby extending the applicable range of the criterion to n ormal contingencies.