Power system voltage stability assessment employing phasor measurement units

Employing Phasor Measurement Units in wide area monitoring and control of power systems and the availability of phase angles, a new look at the voltage stability indices is performed in this paper. A systematic approach for comparing these indices is presented, where the behavior of different indices to a step load change, for studying long term voltage stability, is compared. This comparison is carried out in two methodologies. First, the accuracy and preciseness of each index, especially in the proximity of voltage collapse point, is evaluated. Then, the effect of error in phase angle measurement on the response of those indices is examined. Finally, an overall ranking for the indices is given that is based on the results of individual comparisons.