Wide area monitoring systems (WAMS) are based on the new data acquisition technology of phasor measurement and allow monitoring transmission system conditions over large areas in view of detecting and further counteracting grid instabilities.

Current, voltage and frequency measurements are taken by Phasor Measurement Units (PMUs) at selected locations in the power system and stored in a data concentrator (PDC) every 100 milliseconds. The measured quantities include both magnitudes and phase angles, and are time-synchronized via Global Positioning System (GPS) receivers with an accuracy of one microsecond. The phasors measured at the same instant provide snapshots of the status of the monitored nodes. By comparing the snapshots with each other, not only the steady state, but also the dynamic state of critical nodes in transmission and sub-transmission networks can be observed. Thereby, a dynamic monitoring of critical nodes in power systems is achieved.

This early warning system contributes to increase system reliability by avoiding the spreading of large area disturbances, and optimizing the use of assets.