A load shedding scheme against both short- and long-term voltage instabilities in the presence of induction motors

In the presence of induction motors in loads, long-term voltage instability may result in sharp voltage decreases, once the generators supporting transmission voltages have their field currents limited. Furthermore, after a fault, induction motors may fail re-accelerating and their stalling leads to short-term voltage instability. This paper investigates the ability of the load shedding scheme, previously proposed by the authors, to deal with both short and long-term voltage instabilities. The scheme is distributed with minimal amount of information exchange. It is also shown that the selectivity of this protection scheme can be increased by prioritizing in time the various controllers. Detailed time simulations of a test system are reported.