The nation’s electricity transmission system, which consists of three grids (one in the West, one in the East, and one in Texas), is one of the biggest and most complex machines ever constructed. Commonly referred to as “the grid”, it carries large amounts of electricity, sometimes over hundreds or thousands of miles, allowing generators in Indiana, for example, to contribute to the power supply of both Chicago and Washington, D.C.
Despite its massive scale, the grid needs to be kept in a state of delicate balance, with operators of the grid re-routing power when abnormal conditions develop. On August 14, 2003, drooping transmission lines in Ohio contacted overgrown trees, causing each line to trip offline. Over the course of the next two hours, additional lines became overloaded and tripped, causing many power plants to shut down as well. At the time, none of the grid operators in the affected area had a clear view of grid conditions, so no one was able to identify the problem and begin coordinating preventive action. The cascading event blacked out an estimated 50 million people in the United States and Canada. More recently, on September 8, 2011, an operator error in Arizona led to series of failures that blacked out much of Arizona, southern California, and northern Mexico. Again, the lack of clear, shared visibility into conditions on the grid contributed to this outage.
One of the key means of preventing future failures is better awareness of the health of the grid. Imagine that you could monitor this vast machine and be able to hear it hum and rattle. You would have more time to chase down potential problems before they led to a blackout. Leveraging federally-funded research begun in the 1990s, and expanded after the 2003 blackout, transmission systems owners and operators, in collaboration with the Department of Energy, have been installing advanced devices across the grid to measure and monitor system conditions. These Phasor Measurement Units (PMU), also known as synchrophasors, measure the voltage and current and other data on a transmission line and send the data back to a central system that can display the information in real-time. The result is a high-resolution picture of the conditions of the grid. The targeted investments of the American Recovery and Reinvestment Act of 2009, made in partnership with utilities and transmission operators, have increased the number of PMUs installed on the grid from under 200 in 2007 to about 1,700 today.
This network of PMUs, connected to high-speed communications networks, enables grid operators to amass real-time information about grid conditions across much of the grid, and analyze and share that wide-area information quickly with other grid operators. As a result, the better wide-area information creates better “situational awareness”, allowing for improved grid operations and reliability. When Hurricane Gustav, for example, isolated part of Entergy’s system, Entergy maintained reliable operations for that area using PMU measurements. Collecting wide-area measurements also greatly facilitates analyzing events. The team investigating the 2011 blackout, for example, was able to collect data within days of the event rather than months as in past investigations. These devices also allow system operators to keep their reliability models up to date without taking power plants offline, saving hundreds of thousands of dollars in startup, shutdown, and lost revenue per plant.
Work with these advanced sensors is ongoing across multiple fronts. System operators in the West, for example, are currently using synchrophasors to increase flows of electricity on transmission lines, forestalling investments in new transmission lines and improving asset utilization. In September, 2013, the Department of Energy announced up to $9 million in funding to advance real-time applications of synchrophasors. The Department’s investment requires that the applications be deployed. In addition, utilities and the Department of Energy are exploring the use of synchrophasor systems at the distribution level, to better understand how changing loads affect the grid. And the Department of Energy continues its support for the North American Synchrophasor Initiative, which facilitates information sharing and problem solving among industry, government, and academia.
Synchrophasors are starting a revolution, enabling a level of observation and control never envisioned when the grid was designed. Real-time awareness of the grid’s operating conditions helps to enhance reliability and assists in integrating clean energy technologies. The Department of Energy continues its commitment to working with industry to turn the data from PMUs into actionable information to support control room operations, asset management, and myriad other applications that lay the groundwork for the 21st Century electric grid.