Power grids have become more complex to plan, operate and maintain as they accommodate changes including shifts in generating resource diversity, the character of customer loads and new smart grid technologies. Tools using synchronized measurements based on phasor measurement units (PMUs) can help manage the reliability, performance and security of existing and future power systems.
PMUs record voltage and current at rates of 30 to 120 times per second (100 times faster than existing SCADA systems) and can compute highly accurate parameters such as phase angles and frequencies. When networked together, the resulting "synchrophasors" deliver a real-time, wide-area view of the power system. PMUs are becoming mainstream technology as relays, meters, fault recorders and other IEDs integrate PMU functionality at low cost. And improvements in communications infrastructure now enable networks that can deliver data with required bandwidth, security, latency and reliability.
PMU data are the foundation on which various wide-area monitoring, protection and control applications, including wide-area situational awareness, are being built. Those applications enable early warning of conditions that could lead to catastrophic events, facilitate system restoration, enable accurate component and system models, and speed and improve event analysis. Already synchrophasor data are being used to set alarms and alerts for real-time grid conditions in transmission-owner (TO) and reliability-coordinator (RC) control rooms. Several TOs and RCs are using these data to improve integration and use of renewable generation, with tools enabling validation of generator and system dynamic models (including compliance with NERC standards), better voltage management, oscillation detection and dynamic line loading.
Highly accurate time-stamped data are invaluable for post-event analysis of disturbances, enabling fast reconstruction. Some TOs are using PMUs for fault location and service restoration during severe-weather events. Promising new applications can assess transformer and equipment performance and health, and monitor geomagnetically induced currents.
Wide-area situational awareness will be most effective when multiple owners share the information collected by the technology. The Western Interconnection has built a wide PMU data network and established data-sharing agreements. The Eastern Interconnection Data-Sharing Network is being established to share PMU data later in 2015. This is only the beginning of achieving full benefits of data sharing among TOs and RCs based on well-defined architecture, processes and standards. Several RCs are establishing PMU-based wide-area displays to give all area operators identical real-time information, improving coordination when joint mitigation actions are needed. The need for wide-area situational awareness has motivated the U.S. Department of Energy’s support of synchrophasor technology development and deployment, fulfilling a recommendation from the aftermath of the 2003 blackout.
The last few years have seen major progress worldwide in the adoption of the technology. U.S. deployment was significantly accelerated by the DOE Smart Grid Investment Grant and Demonstration Program funding, yielding more than 1,700 PMUs installed and networked in production-grade systems (including stand-alone industry projects). Coordinated by the North American SynchroPhasor Initiative, the National Institute for Standards and Technology and the IEEE, the industry has developed key standards for synchronized measurement technology: IEEE C37.118 parts 1 and 2 concerning phasor measurements and guides for PMU installation, calibration, synchronization and testing (IEEE C37.242) and for phasor data concentrators (IEEE C37.244).
A well-planned systemwide PMU deployment with a robust data network architecture is necessary to take full advantage of the technology. Once the basic system is in place, the incremental costs of new PMUs and applications are small compared to the added value gained. Many factors contribute to a successful deployment, including designing the system around application requirements and assuring on-going business processes for vendor support, system maintenance, data quality and user training. Realizing benefits also requires extensive baselining using both statistical data and system simulations.
The power industry is also beginning to explore the use of PMUs at the distribution level for power quality, demand response, distributed generation integration and enhanced distribution system visibility. Looking forward, we are approaching an era where all monitoring devices will have data time-synchronized with high precision, but it will take time for full industry-wide adoption of the technology. As the many benefits and uses of time-synchronized data are becoming clear and the technology is implemented into routine business practices, the value of the technology will continue to grow.
David Ortiz is deputy assistant secretary at the DOE.
Alison Silverstein is project manager for the North American Synchro-Phasor Initiative.
Damir Novosel is president of Quanta Technology and president-elect of the IEEE PES.