Phasor measurement unit (PMU)

A phasor measurement unit, also called a PMU or a synchrophasor, is a key tool used on electric systems to improve operators’ visibility into what is happening throughout the vast grid network. A PMU measures a quantity called a phasor, which tells the magnitude and phase angle for the AC voltage or current at a specific location on a power line. This information can also be used to determine frequency and is useful for identifying and analyzing system conditions. 

PMUs provide up to 60 measurements per second, which is much more than the typical one measurement every two to four seconds provided by conventional SCADA systems. PMUs have a big advantage over traditional means of collecting data because all PMU data is time-stamped using global positioning system (GPS) data. This means that data collected across a grid is all synchronized by using the same exact method of associating time with data. For this reason, PMUs are sometimes called synchrophasors.

Information provided by two PMUs on opposite sides of a transmission line
Source: Consortium for Electric Reliability Technology Solutions

PMUs provide a detailed and accurate view of power quality across a wide geographic grid. The data collected tells the system operator if the voltage, current, and frequency are within specified tolerances. This capability is used in multiple ways:

  • To improve the accuracy of modeling system conditions
  • To predict and detect stress and instability on the grid 
  • To provide information for event analysis after a disturbance has occurred
  • To identify inefficiencies 
  • To predict and manage line congestion

In recent years, tens of thousands of PMUs have been installed in transmission (and in some cases distribution) grids throughout the world. Coupled with smart controllers, PMUs offer the opportunity to replace typical hands-on adjustments required by SCADA systems with a system that makes decisions and sends control signals autonomously. Such capabilities promise to allow for more robust and efficient integration of renewables, distributed energy resources (DERs), and microgrids. PMUs are becoming a key tool in making our grid more reliable, resilient, and ultimately cleaner.