Modeling effects of system frequency variation in long-term stability studies

This paper describes a fundamental study into modeling the effects of frequency variation on network and shunt impedances in long term power system stability simulations. The focus is on extreme post-fault situations where significant generation-load mismatch causes wide excursions in power system frequency. A novel application of singular perturbations is presented. This method is compared with the "constant reactance" technique, the "variable reactance" method in which the network reactances are varied with system frequency, and a method in which the network transients are fully simulated. Stability simulations for an interconnected two-area power system employing the different modeling techniques show that a two time scale analysis using the singular perturbation method is a feasible technique for accurate prediction of long term post fault system behaviour.