Phasor Measurement Unit - Technical Overview

Technical Overview

A phasor is a complex number that represents both the magnitude and phase angle of the sine waves found in electricity. Phasor measurements that occur at the same time are called "synchrophasors", as are the PMU devices that allow their measurement. In typical applications phasor measurement units are sampled from widely dispersed locations in the power system network and synchronized from the common time source of a global positioning system (GPS) radio clock. Synchrophasor technology provides a tool for system operators and planners to measure the state of the electrical system and manage power quality.

Synchrophasors measure voltages and currents at principle intersecting locations (critical substations) on a power grid and can output accurately time-stamped voltage and current phasors. Because these phasors are truly synchronized, synchronized comparison of two quantities is possible, in real time. These comparisons can be used to assess system conditions-such as; frequency changes, MW, MVARs, kVolts, etc. The monitored points are preselected through various studies to make extremely accurate phase angle measurements to indicate shifts in system (grid) stability. The phasor data is collected either on-site or at centralized locations using Phasor Data Concentrator technologies. The data is then transmitted to a regional monitoring system which is maintained by the local Independent System Operator (ISO). These ISO's will monitor phasor data from individual PMU's or from as many as 150 PMU's - this monitoring provides an accurate means of establishing controls for power flow from multiple energy generation sources (nuclear, coal, wind, etc.).

The technology has the potential to change the economics of power delivery by allowing increased power flow over existing lines. Synchrophasor data could be used to allow power flow up to a line's dynamic limit instead of to its worst-case limit. Synchrophasor technology will usher in a new process for establishing centralized and selective controls for the flow of electrical energy over the grid. These controls will affect both large scale (multiple-states) and individual transmission line sections at intersecting substations. Transmission line congestion (over-loading) and protection and controls will there fore be improved on a multiple region scale (US, Canada, Mexico) through interconnecting ISO's.