Real-time identification and prevention of voltage instability using synchronized phasor measurements

This paper presents a novel measurement-based voltage stability indicator suited for real-time monitoring at the transmission level. Building upon a previously defined approach that uses variations in apparent power and impedance, the proposed indicator includes significant modifications; in particular, an adaptive estimation algorithm designed to improve robustness to random variations, measurement noise and short-term dynamics. A mathematical framework is established as basis for the definition of voltage stability regions of operation and their respective thresholds. Moreover, this paper introduces an emergency control scheme based on load shedding as a means to counteract imminent voltage collapse. Dynamic simulations conducted in the IEEE Nordic Test System evaluate the effectiveness of the combined actions of the proposed indicator and emergency control scheme in identifying and preventing voltage instability. Further validation of the novel indicator is carried out through analysis of synchrophasor data pertaining to a real voltage collapse event in the Nordic Grid. The overall results demonstrate that the developed approach constitutes a promising asset for system operators to ensure sufficient voltage stability margins in transmission networks. • A measurement-based voltage stability indicator is proposed for real-time monitoring. • The novel indicator is used to design a load shedding-based emergency control scheme. • Voltage stability regions and thresholds are derived from the mathematical framework. • Validation is based on simulations in the IEEE Nordic Test System and real PMU data. • Results show the merits of the proposed schemes as assets to control center settings.