Phasor Measurement Unit

A phasor measurement unit, or PMU, is a device that measures the voltage and current phasors, magnitude and phase angle together, at a point on the electricity grid, using GPS or the IEEE 1588 Precision Time Protocol to synchronize its readings with other units elsewhere on the network; the resulting synchronized readings are called synchrophasors, and a PMU can take up to 120 measurements a second, far faster than the one reading every two to four seconds typical of a conventional SCADA system. Charles Proteus Steinmetz introduced the mathematical phasor representation in 1893, Arun G. Phadke and James S. Thorp of Virginia Tech invented the PMU itself in 1988, and Macrodyne built the first commercial unit, the model 1690, in 1992. The Bonneville Power Administration deployed the first comprehensive synchrophasor network in 2000, and PMUs are now considered one of the most important measuring devices for the future power grid, helping detect the frequency imbalances between supply and demand that can lead to outages; India today operates the world largest such network, with 1,950 PMUs in its Wide Area Monitoring System.