A method for real time voltage stability monitoring in sub-transmission networks

This paper presents a real-time voltage stability monitoring method based on estimation of maximum power transfer. The approach solely requires information from PMUs installed at concerned load buses at substations in addition to available information of system topology and load power obtained from SCADA/EMS or state estimator. The proposed algorithm estimates the Thevenin impedance seen at the load bus and consequently the maximum loadability. This power transfer limit is used as an indicator for voltage stability assessment when compared to the load power. It is emphasized that only topology of the considered subsystem is needed, not the whole network. This feature makes the method viable for online implementation since the computation requirement is insignificant. In principle, the proposed methodology is not limited to specific grids in terms of voltage level, but it is especially suitable for sub-transmission networks, where loads are supplied by bulk power source and voltage instability is imposed by long transmission lines. The proposed approach is validated by simulations on the Norwegian transmission grid.