Justifying synchrophasors in the smart grid
By Jay Giri, Director of Power Systems Technology and Strategic Initiatives, ALSTOM Grid
Emerging hardware and software technologies will benefit the electric utility industry by making transmission and distribution operations more efficient, reducing the probability of blackouts and brownouts and giving power suppliers the option of deferring costly new construction.
This burst of innovation is partly driven by funding for smart grid programs, and the benefits can be seen today. Technology advances such as synchrophasors and enhanced Energy Management Systems (EMS) will improve operation of the existing grid infrastructure and, in some cases, relieve financial pressure on utilities facing expensive investments in new transmission capacity. The benefits to grid operators include improved utilization of existing transmission grid assets and greater confidence in implementing timely decisions to protect grid integrity.
Synchrophasors are power system measurements made in sub-second intervals at numerous locations across an electric power grid. Time-stamped to a common reference, they typically monitor critical operational parameters such as three-phase voltages and currents, frequency, and rate of change of frequency.
Availability of this vast amount of high-resolution synchrophasor data allows for implementation of new analytical tools and enhancements to EMS to provide control room operators with an unprecedented real-time view of grid conditions. Real-time monitoring of multiple remote points on the electrical grid, in turn, supports corrective responses to sudden disturbances in the grid that must be implemented quickly to prevent large-scale outages.
Synchrophasors are measured by Phasor Measurement Units (PMU). A PMU can be a dedicated device, a meter, or any measuring device that can accept a global time reference and properly time-stamp the power system measurements. A single PMU device typically provides 12 to 16 synchrophasor measurements.
Deferring Infrastructure Investment
Synchrophasor technology and enhanced EMS analytics give utilities the opportunity to make a significant leap in optimizing the utilization of existing transmission assets by improving the models and model data used in EMS tools. This will result in more accurate evaluation of transmission congestion limits so operators can confidently make more aggressive decisions to allow operation closer to the grid's 'true' real-time operating limit. This maximizes utilization of existing transmission assets.
Further, many utilities can reap a windfall in operational efficiency by updating transmission limits dynamically in real-time. A large number of 500 KV transmission systems have restrictive congestion operational limits to protect the grid against sudden unexpected disturbances. Today, the system operator enters these limits manually in the EMS. Once entered, the limits are not changed very often; hence a large, pessimistic safety factor needs to be built in to accommodate the widely varying system conditions that occur throughout the day, week, and month.
Having time-stamped, real-time grid data facilitates enhanced software and hardware that can calculate operational limits in real-time using current system conditions. This reduces the safety factor required and the grid can be operated closer to its current 'true' limit.
Dynamic, real-time limit updates can help utilities avoid investments in new transmission line construction that are driven by unnecessarily wide and pessimistic safety margins. As utility executives are well aware, installing a new transmission line is very expensive and time consuming. Transmission lines traverse hundreds of miles, rights-of-way have to be established, and local 'not in my backyard' resistance is common.
Guarding Against Blackouts
From a financial perspective, operating efficiencies made possible by synchrophasors and advanced EMS are matched in terms of benefit impacts by their ability to stop a cascading blackout in its tracks. The cost of the 2003 East Coast blackout has been estimated at between $6 and $8 billion. Avoiding such costs in the future is more than sufficient justification for investments in new technologies.
In today's control rooms, emergency decision-making starts only after a disturbance on the grid occurs. Before operators can take remedial action, they must assimilate and analyze the disturbance information, and communicate with neighbors to be doubly certain of exactly what happened. This fact-finding process consumes valuable time – more than enough time for a minor event to escalate into a major catastrophe.
Because synchrophasors give control centers real-time insight into the grid, EMS software is now capable of quickly identifying abnormal behavior, and taking corrective action automatically without operator intervention. Two developments are necessary for this to become a reality. First, utilities must have the ability to share synchrophasor data with neighboring control centers. Second, they must have absolute confidence in the validity of the synchrophasor data being fed into their decision support system.
NERC (North American Electric Reliability Corporation) and NASPI (North American Synchrophasor Initiative) are addressing the first issue by promoting development of a NASPInet communications and data sharing network throughout North America.
Data reliability and security present more difficult challenges, but are being addressed as a top-level priority by utilities, government agencies, and regulators. Several projects funded by DOE grants totaling more than $300 million will increase the number of synchrophasors in North America from 200 to more than 1,000 in the next few years. An important focus of these projects will be a rigorous discovery process to understand how to make synchrophasor measurements trustworthy enough for use in prompt, automated decision-making.
Three New Challenges
Seldom in the more than century-long history of the electric utility industry has it been more critical to quickly adopt innovative technologies. The North American grid is aging. As it ages, it is becoming less and less secure, and simultaneously facing new and increasingly complex user demands.
The average transformer is 40 years old and close to exceeding its manufacturer's life expectancy. Meanwhile, mandates to increase deployment of renewable energy resources are introducing more variability and uncertainty in energy supply, which places further inadvertent stress on the grid.
While adopting new technologies is essential to upgrading the grid, technology's fellow traveler, data security, creates another big challenge. Secure, reliable and hack-resistant communication is a mission-critical goal that must be addressed by enhanced cyber security plans, comprehensive monitoring of communications traffic, and strategies to ensure reliable and secure data transport.
Standardization is, of course, a significant challenge but one that can be met with cooperation amongst stakeholders. Automated communication between utilities and data needed for complex EMS analytics requires that data formats, and in many instances software and hardware, utilize a common baseline language. Products from different vendors have to work together, as never before. Development and deployment of standards is vital to the success of harmonious interoperability.
Over the next 5 to 10 years, the promise of new technologies will usher in an exciting golden age for electric utilities. One of the key milestones will be achieved after the next five-year phase of building confidence with PMU measurements and synchrophasor technology. The march toward the smart grid does not stop with enhanced visualization and fast real-time monitoring of grid conditions; the ultimate goal of the smart grid is automating control to quickly protect the grid against unexpected disturbances. That lofty objective can only be achieved after we have established full confidence in the reliability, security and precision of synchrophasor measurements.
About the Author
Jay Giri is the director of Power Systems Technology and Strategic Initiatives at ALSTOM Grid where he leads an engineering team that delivers synchrophasor applications to control centers. He is a member of the IEEE Power & Energy Society (PES) Governing Board.