Interaction of Transmission Network and Load Phasor Dynamics in Electric Power Systems

This paper is concerned with modeling and analysis of an interconnected electric power system for frequency ranges in which phasor dynamics of transmission lines and loads may be important to include. In most studies, only phasor dynamics of generators are taken into account. Dynamics of all other system components (transmission lines, loads, and generator stator windings) are assumed stable and instantaneous (static). While several papers have examined phasor dynamics of the transmission lines, particularly when these are equipped with FACTS devices, no systematic investigation has been carried out concerning validity of static load models in this case. It is shown in this paper that problems may arise in particular when a static constant power load model is used at the same time that phasor dynamics of transmission lines are included. Standard singular perturbation-based arguments for neglecting load dynamics are shown not to be applicable in this case. More generally, the paper raises a general concern about consistency of electric power system models in frequency ranges where phasor dynamics of the devices typically assumed to be static must be taken into consideration.