A new node voltage stability index based on local voltage phasors

The paper proposes an equivalent system model (ESM), which includes effects of both local network and system outside the local network. A new node voltage stability index called the equivalent node voltage collapse index (ENVCI), which is based on ESM and uses only local voltage phasors, is presented. The main advantages of ENVCI are accuracy in modeling and calculations, and ease in real time or on-line applications. The simulation results show that the ENVCI can identify not only the weakest node (bus) causing system instability but also the system voltage collapse point when it is near zero. This feature enables us to set an index threshold to monitor and predict system stability on-line so that a proper action can be taken to prevent the system from collapse.