Online Monitoring of the Electrical Power Transfer Stability and Voltage Profile Stability Margins in Electric Power Transmission Systems Using Phasor Measurement Units Data Sets

An innovative method to monitor the electric power transfer stability on power transmission paths and the voltage profile stability at the power systems nodes in real time modus is proposed. Based on the laws of electric circuit theory, the transfer operating mode of each relevant transmission line is formulated in an active power-voltage PV characteristic. The relevant transmission line parameters and the actual system state phasor measurements are used to calculate the exact point of the maximum secure transfer mode of the given transmission lines at each operating instant, based on the voltage stability criterion. A combination of the transfer characteristic with a flexible voltage stability band allows the simultaneous observation of the voltage profile stability at the system´s buses in the prevalent direction of the lines active power flow. The defined stability margins are directly evaluated on a PV mode without need to specify any loading scenario. The method uses synchronized phasor measurement data as input. It can thus be employed for the wide area stability voltage monitoring of large transmission zones retaining several transmission lines with a reduced number of phasor measurements units. The exactitude and robustness of the method are tested on a two-bus system and on a large power system represented by the western Danish power grid.