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Tech Transition

Utility projects advance the state of the art.

Fortnightly Magazine - July 2009

normally 2,000 amp path can, and sometimes does, jump to 40 kA at 13 kV, or 63 kA at 138 kV and 345 kV. These are realistic fault currents for bolted faults, validated by oscillograph readings.”

The full-scale, 700 foot-long, high temperature superconductor (HTS) cable will run under city streets and connect two Manhattan substations. If there’s a problem at one substation, the connection will allow Con Edison to shift some of its load over to the other.

Common events, such as storms or accidents, can produce large spikes or “faults” in current that can damage electrical equipment or cause power failures. The cable’s fault-limiting capabilities will protect the grid by allowing normal current to pass through unimpeded. If and when it senses fault current, the technology instantly prevents a large increase in the electrical flow, choking off a potentially damaging electrical spike. Once the fault current subsides, the cable will allow standard levels of current to flow, thus protecting the electrical system automatically without human intervention.

“Once we get beyond this economic downturn, we see our electric load increasing substantially. That means there will be more devices on the grid that could contribute to a fault,” Duggan says. “As a utility, we’re hoping superconductor technologies will get smaller and cheaper. This project will demonstrate the cable in an urban environment, at a site under varying conditions that include rats, road salt and voltage transients.”

The project is being funded mainly by the Federal Department of Homeland Security (DHS), which is picking up $25 million of the $39 million tab. DHS is interested in the technology’s capacity and fault-limiting capabilities to prevent an isolated problem from turning into a cascading failure. The rest of the cost is being shared by American Superconductor Corp., which is providing the cable, along with Con Edison and the New York State Energy Research and Development Authority. If the project delivers on its promise for Con Edison, it could pave the way for future utility commercialization of superconductor technology.

“To get a regulator’s approval, you need to explain the project so they can understand all the benefits and why it deserves to be supported,” Duggan says. “If this project proves to be viable, it could help to achieve a breakthrough over the installed cost of copper, if we could use this more compact fault current limiting superconducting cable design to fit these cables within existing ducts, rather than excavating under city streets. We have roughly 94,000 miles of underground cable in our system. Obviously we won’t replace all of it, but superconductor technology could be extremely beneficial at specific points within the system.”

California Microgrid

In August, SDG&E begins a three-year, $12.5 million proof-of-concept pilot, subsidized in part by the DOE, that will determine whether existing information technologies can be used to leverage distributed energy resources and create a true smart grid.

Doing so, the utility says, could allow more power to be delivered through existing infrastructure, thereby reducing the need to build more T&D facilities. Additionally, it might increase reliability by adding elements that make the