Local voltage instability monitoring and protection in the presence of self-restoring loads and two-level LTCs

In this paper we give an overview of a local voltage instability monitoring and protection system integrated in the controller of each bulk power delivery LTC transformer. The proposed system identifies imminent voltage instability and subsequently applies corrective measures to restore stable operation by properly adjusting the distribution voltage setpoint of the LTC. The system is extended in this paper to include also the LTCs acting on EHV/HV autotransformers and is checked in the presence of self-restoring loads. Application on a small test system and a 52-bus test system shows the performance of the proposed system and the associated problems and solutions.