Voltage instability alarm by real-time predictive indicators

This paper proposes real time voltage instability risk indicators based on a reliable identification, through bus local phasor measurements at fast sampling rate, of the Thevenin equivalent seen at any instant by the bus. The effectiveness of the indicator is shown at EHV load and “transit” buses. The prediction criterion is substantially based on the on-line and true real-time recognition of the system operation approaching the nose tip on the PV real curve seen by the considered bus. Moreover the prediction can be anticipated or delayed by the tuning of the identification algorithm speed and of the proposed indicators derivative terms as well. The identification algorithm performance and related predictive indicators are presented through a detailed simulation analysis in different grids. The paper also provides considerations on the single bus voltage instability indicator use to a case of wide area multi-buses system, through the elaboration and coordination of information coming from the PMUs installed in the main system busses, with the aim to recognize the higher risk zones in the area and to enforce the prediction of the overall wide are voltage collapse risk.