Communications of the ACM
Resilient Electric Grid Project Develops the ltimate Surge Protector
Oak Ridge National Laboratory tests the interface between a surge-suppressing superconductor cable and traditional copper cables.
Credit: Oak Ridge National Laboratory
On Aug. 14, 2003, more than 40 million people were plunged into darkness when electrical service failed in large portions of the Northeastern and Midwestern United States and Ontario, Canada. Though many workplaces ceased functioning without electricity, New York City's emergency medical services had to deal with a doubling of call volume during the 29-hour blackout, according to a 2006 report in Prehospital and Disaster Medicine.
Cardiac and respiratory complaints increased, likely due to commuters being left without subway transportation or elevators, according to the report. Paramedics responded to a large number of heat-related medical calls because air conditioners could not function. Ambulances struggled to navigate streets that lacked functioning traffic signals and were crowded with commuters walking home.
The U.S. Department of Homeland Security (DHS) Science and Technology Directorate is supporting a technological advance that could reduce the chances of similar blackouts occurring in the future. The Directorate's Homeland Security Advanced Research Projects Agency (HSARPA) helped fund the development of an electrical cable that could be used to link substations, providing backup sources of electricity in the event part of the grid experiences an outage. The Resilient Electric Grid project will help ensure the nation's utilities can withstand power surges that cause blackouts.
According to Sarah Mahmood, program manager for HSARPA, electric utilities have hesitated to connect substations in the past. Although one substation can compensate for another's outage if the two are linked, there is a downside to building an interconnected grid. If an equipment failure, terrorist attack, or lightning strike causes a power surge, also known as a fault current, that fault current can cascade through the grid and knock out every substation and piece of equipment connected to the problem site. Part of the Resilient Electric Grid project is the development of a superconductor cable designed to suppress fault currents that can potentially cause permanent equipment damage. This technology will allow electric companies to link substations without running the risk of fault currents cascading through the electric grid. "This will help [first responders] by keeping that backbone [of the electric grid] up and running," Mahmood says.
In 2007, HSARPA awarded a contract to American Superconductor Corp. to develop an inherently fault-current limiting high-temperature superconductor cable (IFCL-HTS), also known as Secure Super Grids, which was the first of its kind. A superconductor offers no resistance to electricity flowing through it, thus eliminating power loss incurred with regular wires. In order to do this, however, the superconductor must be super cooled to -460°F. According to Jason Fredette, director of corporate communications for American Superconductor, when a large fault current travels through the grid, the superconductor cable heats up and stops conducting, effectively suppressing the power surge. "The wire itself can act as a smart switch," Fredette says.
What makes IFCL-HTS cable unique is that it operates at a higher temperature than traditional superconductors, -320°F, which makes it more practical for use. American Superconductor and its partner Southwire Co. developed a 25-meter IFCL-HTS cable that was tested at Oak Ridge National Laboratory (ORNL) in 2009. According to Christopher Rey, senior staff scientist at ORNL, the lab plans to test an improved version in the near future.
In addition to preventing surges, the IFCL-HTS cable can improve electrical service to dense urban areas, according to David Lindsay, director for distribution engineering at Southwire. Superconductor cables can carry up to 10 times more electricity than a typical copper cable, and superconductor cables transmit electricity with near zero resistance. The added capacity and efficiency is useful for large cities such as New York, where electricity demand is rising and underground space to run additional cables is limited.
The fault current-limiting superconductor cables are best suited for urban markets, according to Lindsay. In rural areas, he explains, it would likely be more affordable to use overhead power lines and other solutions to suppress power surges. As developmental testing of the cable concludes, HSARPA will explore the possibility of installing the IFCL-HTS technology in a selected location in the electric grid for an operational demonstration, according to Mahmood.
Another aspect of DHS's Resilient Electric Grid project focuses on developing a standalone fault current-limiting device that can be installed anywhere on the existing electric grid, according to Mahmood. DHS is collaborating with Silicon Power to develop a Solid State Current Limiter. A semiconductor switch in the device suppresses power surges in electric cables. The technology would allow utilities to incorporate surge protector capabilities into the infrastructure without replacing current cables or existing protection schemes. DHS is scheduled to hold a demonstration of that technology's key elements at the KEMA Inc. testing facility in Chalfont, PA in the fall of 2010.
These solutions would protect critical infrastructure dependent on electrical power from blackouts that not only threaten safety, but commerce as well. Power outages cost the U.S. approximately $100 billion a year, according to HSARPA. Having a resilient electric grid will protect Wall Street and other financial centers from power outages, according to Fredette. "If New York City goes black, that damages our economy," he says. "This project employs superconductor technology to protect our nation's financial centers."
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