What is a Phasor Measurement Unit (PMU)?

A device that measures phasor (magnitude and phase angle of voltage and current) and related data from a specific location on the electrical grid.

  • The measurement is synchronized to a common time source. The time-synchronized estimated phasor is called a synchrophasor.
  • Time synchronizing sources:
    • IRIG-B – Global Positioning Satellite (GPS)
    • Precision Time Protocol (PTP) – IEEE 1588
  • Multiple PMUs transmit the synchrophasors and related data to a phasor data concentrator (PDC), which aggregates and time-aligns the data for real time and post analysis.
Phasor Measurement Unit

Why do you need Synchrophasor measurements?

Synchrophasors provide instantaneous voltage, current, and frequency at specific locations on the grid, allowing  immediate decisions, such as actions to prevent power outages.

Phasor Measurement Unit (PMU) APPLICATIONS

Transmission / Sub-Transmission:

  • Voltage stability assessment
  • Improve grid resiliency and reliability
  • Determine instability through ROCOF and voltage stability monitoring
  • Monitor reactive margin, phase angle and power oscillation
  • Determine dynamic line impedance
Phasor Measurement Unit
Phasor Measurement Unit

Distribution System Applications

  • Distribution state measurement
  • Enable proactive island detection to prevent outages and ensure reliable power to customers
  • Apparatus monitoring
  • Smart inverter control
  • Volt-VAR optimization
  • Broken wire detection

Power Generation: Traditional and Alternative

  • Provide real time frequency, detection of oscillation and low damping conditions
  • Facilitate post event analysis through correlating status and analogs
  • Provide data for power system modeling and validation studies
Phasor Measurement Unit
Phasor Measurement Unit

Distributed Energy Resource Monitoring

  • DER monitoring
  • DER system angular difference to facilitate long distance check sync
  • Rapid islanding detection  for remedial actions

Phasor Measurement Unit (PMU) Benefits

Phasor Measurement Unit
  • Provide wide-area situational awareness for system operators with improved visibility into dynamic grid conditions.
  • Determine stress points of the electric power system.
  • Detect and aid in restoring an islanded section of the grid after a storm or major outage disturbance.
  • Instantaneous measurements provide early warning detection alerts that SCADA systems miss. 
  • Built in system wide PMU analysis for future implementation of big data analytics, artificial intelligence and machine learning to proactively improve power systems and prevent outages. 

Real World Example:

Phasor Measurement Unit

Result of Undetected Phase Angle Divergence in September 2011 Southwest US Outage

  • 11-minute cascading outage in Pacific Southwest.
  • Initiated when a single 500 kV line tripped.
  • Power was redistributed, increasing flow, dropping voltages, and overloading equipment.
  • Led to tripping lines, generators, etc.

Power Quality Meters – NEXUS® 1500+ METER PMU IMPLEMENTATION

The PMU provides the following Synchronized Measurements:

  • Individual voltage/current phasors (VA, VB, VD, IA, IB, IC)
  • Symmetrical components phasors (V0, V1, V2, I0, I1, I2)
  • Frequency and Rate of Change of Frequency (ROCOF)
  • Built-in digital inputs
  • Analog 
    • Fundamental power: (watt total and per phase, VA total and per phase, VAR total and per phase)
    • Displacement power factor: (total and per phase)

Supports P (Fast Response) or M (Precise Measurement) classes, user selectable

Data frame rates for 50 Hz:

  • 10/25/50 frames per second; for 60 Hz: 10/12/15/20/30/60 frames per second

Data format:

  • Configurable float or integer, polar or rectangular

Time sync standard:

  • IRIG-B or IEEE 1588 PTPv2

Number of sessions:

  • up to 2 simultaneous clients

Supports Ethernet or Fiber over Ethernet:

  • TCP communication for header, configuration, and command;
  • UDP communication for data, including unicast, broadcast, and multicast.