Chattanooga Shows Smart Grid Can Deliver Results

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by David Wade, EPB, and Mike Edmonds, S&C Electric Company

Smart grid deployments gained momentum in recent years, spurred in part by billions of dollars invested as part of the American Recovery and Reinvestment Act of 2009 (ARRA). Deployments, however, aren’t the same as results. It’s more difficult to find projects where smart grid technology provides a measurable impact. Chattanooga, Tenn., invested in smart grid technology and is seeing improved electric power reliability.

Chattanooga is served by EPB, a power distributor that started in the 1930s when the Tennessee Valley Authority (TVA) was established under the New Deal. The sole reason for establishing EPB and other power distributors in the valley was to spur economic development and improve quality of life for underserved Appalachian communities. Now EPB serves more than 170,000 homes and businesses in a 600-square-mile area. The distributor manages 3,900 circuit miles of line, has a summer peak at 1,307 MW and 14 system interconnections to TVA, and operates 118 substations.

EPB began investing in automation technologies during the early 2000s. After years of study, the distributor began implementing a more defined smart grid strategy in 2007. The plan included several components and was slated for a 10-year construction. While implementation was in progress, the utility applied for and was awarded a matching ARRA grant from the Department of Energy (DOE). What would have been a 10-year build out occurred in three years.

Building a Smarter Grid

Chattanooga’s smart grid investments are driven by the goal of improving power reliability and reducing costs for the community—goals consistent with EPB’s mission since inception. Power reliability continues to impact Chattanooga’s economic vitality. That is true for most cities and communities across the U.S. According to a study by the Lawrence Berkeley National Laboratory, power outages cost a community the size of Chattanooga some $100 million annually. Chattanooga put significant emphasis on smart grid technologies that would drive the biggest improvements in reliability.

As part of its smart grid strategy, EPB established an ambitious goal to reduce outage durations 40 percent. EPB implemented self-healing grid automation technology from S&C that provides rapid response to power outages. EPB installed nearly 1,200 IntelliRupters—advanced smart switches—throughout its system. IntelliRupters include integrated microprocessor-based controls that run S&C’s IntelliTeam SG automatic restoration software, which evaluates grid conditions and decides how to reroute power during outages. This distributed decision-making is essential to quick restoration and provides the flexibility to respond to outages on the same part of the grid simultaneously—something common during storms. IntelliRupters also feature Pulseclosing technology. In the event one of the switches opens to interrupt a short circuit, Pulseclosing allows the smart switches to test the line to determine if a fault is still present before closing, which prevents the device from possibly closing back into a fault and again exposing transformers and other grid equipment to the high currents typically associated with a short circuit. As a result, Pulseclosing technology minimizes wear and tear on the grid and extends asset life.

As part of the larger automation solution for the grid, EPB also installed a 100 percent fiber-optic network. The fiber-optic network is linked to every home and business in Chattanooga and supports other EPB smart grid applications. With this infrastructure, EPB could offer high-speed broadband and video services to the community, providing a new revenue stream that offsets the smart grid investment. The smart switches also can communicate data faster on this network.

To fully realize a smarter grid, EPB is implementing other smart grid technologies that will improve energy efficiency and provide greater customer choice and control, such as volt/VAR optimization, advanced metering infrastructure, smart grid management software and a new supervisory control and data acquisition (SCADA) system. Combined, these technologies are creating a stronger, adaptable grid that can support Chattanooga’s economic development efforts and continue to improve quality of life in the community.

Putting Chattanooga’s Smarter Grid to the Test

Chattanooga’s self-healing, automated grid began to provide benefits before it was fully deployed. For instance, during Labor Day weekend 2011, an extended rainstorm hit the community.

At that point, only 54 percent of the planned smart switches were installed, and 20 percent had automatic restoration software configured and running. Of the 63,000 homes and businesses that would have experienced a power interruption prior to the smart grid installation, 16,000, or 25 percent, avoided interruption.

An additional 7 percent, or 9,000 customers, experienced less than a 2-second interruption. Although the automation deployment was partially completed, Chattanooga’s grid automation technology avoided 1.9 million customer minutes of interruption (CMI).

More recently, Chattanooga experienced a July 5 wind storm. Without automation, some 77,000 homes and businesses would have experienced an outage. Instead, 42,000 either did not experience an outage or were restored without a truck roll.

EPB also accelerated its restoration efforts to the 35,000 customers who experienced an extended outage because of the distribution automation technology.

What would have been a five-day restoration took about three and a half days—a 30 percent reduction.

Field crews performed less work switching and reconfiguring the system to temporarily reroute power to facilitate grid repairs where needed. Instead, problem areas were already isolated and allowed crews to get right to work.

The primary benefit of the automation lies in faster power restoration for the Chattanooga area, but EPB also realized lower restoration costs. EPB avoided 500 truck rolls, which was consistent with the reduced scope of the restoration work and saved roughly $1.4 million in restoration costs from this one storm as an added perk to the reliability improvements.

Apart from the direct improvement to EPB’s electric service reliability, EPB also uses the smart grid technology to help customers make on-site adjustments to further improve power quality and reliability. In one instance, a large commercial facility in EPB’s service territory had a problem with computer-controlled equipment losing power. EPB was unaware of issues on the circuit serving the customer, but queried the nearest smart switches to gain more data to help address the customer’s issue. With this data, EPB found that relay settings at the customer’s facility tripped on-site circuit breakers in response to a one-cycle voltage dip, which happened after a fuse operation on a nearby circuit. EPB provided this information to the customer and recommended it review the settings on its equipment and possibly adjust the relay settings to something less sensitive. Such information from grid automation devices likely will continue to grow in importance as customer equipment becomes more automated and sensitive to disruption.

Return on Investment for the Community

Based on Chattanooga’s results, it is expected that EPB’s smart grid approach will help the community realize or exceed its goal of a 40 percent reduction in outage durations, which will put a dent in the $100 million in outage costs incurred annually in the community.


Mike Edmonds is S&C’s vice president of strategic solutions. He is responsible for the strategy, direction and execution of S&C’s portfolio of solutions families. Reach him at or 773-338-1000.

David Wade is executive vice president and chief operating officer of EPB, which serves more than 169,000 homes and businesses in a 600-square-mile area that includes greater Chattanooga, portions of surrounding Tennessee counties and areas of North Georgia. Reach him at

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