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- Posted on August 20, 2010
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WHEN FIRE HIT A RURAL CONNECTICUT HOME AND A DOWNED POWER LINE endangered response teams, the actions of Connecticut Light & Power (CL&P) were anything but routine. With residents trapped inside the burning building, firefighters didn't have to wait the seemingly interminable minutes it would normally take for a utility crew to arrive and cut the electricity. Instead, in a control room nearly 80 miles away, technicians at a CL&P operations center were able to cut power to the structure less than a minute after receiving the emergency call.
That's because CL&P is about three-quarters of the way through an eight-year project to further automate the 17,000 overhead line miles of its distribution network. The distribution supervisory control and data acquisition (DSCADA) system, through a high-powered radio communications network, now enables a centralized operations center to talk to 1,731 of the 3,000 reclosers mounted on poles throughout Connecticut.
Reclosers—or switches that detect faults throughout the distribution system and automatically restore service—have been an essential part of distribution systems for decades. But having the ability to overlay DSCADA throughout the system happened serendipitously.
The ability to deploy a DSCADA system was enabled by decisions made 20 years ago to convert the entire system from lateral distribution to a series of thousands of interconnecting loops. ''In that way, a single customer on one section of a line could be energized from two different paths,'' said E. Bruce Roy, manager of distribution engineering and operations support for CL&P, the dominant utility in the Nutmeg State. The company has determined that the optimal setup in its protection scheme is for each recloser to serve about 500 customers with each recloser located a few dozen yards apart in densely populated cities to perhaps miles in the remotest regions.
Those paths are on display at its system operations center in Berlin, Conn., roughly the geographic center of the state. The system operation center has divided Connecticut into three regions—western, central and eastern—with 11 individual work stations that can be reoriented as the workload demands.
Each monitor can hone in on any color-coded recloser in the system, with red and green signifying those closed and open, and white designating those not yet enabled with DSCADA. In that instance, a truck would have to roll to the site to de-energize a line. A steady stream of single-line messages scroll down another screen, monitoring events in the systems, with bright pink ones indicating messages from 911 that warrant attention and may require immediate action. On routine spring day, the center is fairly quiet, but operators are poised to act, especially when storms gather and system events literally track from west to east in a storm's path.
And with the thunderstorm season upon us, the system is routinely used to cut power to downed lines that threaten trapped motorists and other people who may be endangered.
And there's also an operational benefit that occurs during storms. DSCADA also allows the utility to operate its system using a lightning protection mode. Normally, reclosers can be set to work extremely fast, as fast as one cycle, to detect a fault. But the operators have the ability to adjust a time delay intentionally. ''If we wanted to, we could set the reclosers to as fast as they are capable, but in any fault, that would cause the lights to flicker on and off, which would be a nuisance to our customers,'' said Roy. ''But in lightning mode you would want the reclosers to respond very fast.'' The company developed the logic so when storms occur, the system allows CL&P to reset the reclosers from its operations center in any or all areas of its service territory to prepare the system for lightning strikes—essentially protecting its fuses from blowing during these events. The cost benefit is real, but impossible to quantify. ''We know it's saving, but that's almost like asking for an answer of what didn't happen,'' he added.
Other cost benefits are easier to quantify. ''Historically, before DSCADA, trucks would roll and be sent from trouble spot to trouble spot. Planning would start before the day even began, and that meant overtime,'' Roy stated. ''Last year, there were 60,000 operations through the DSCADA system, which resulted in 10,000 to 12,000 trips by truck, so right there was a cost benefit of well over $1 million.''
The initial outlay for the system is fairly significant. About 1,700 units are installed, each serving about 500 customers. At about $20,000 a unit—essentially a computer installed on a pole—the company already has invested about $3.4 million. At the current rate of installation, CL&P expects to complete the project in about two years.
The overhead deployment started about six years ago with a pilot of about 45 locations in southwestern Connecticut. Around the same time, the accidental death of a firefighter who entered a building that did not have its power cut only underscored the safety benefits. After the pilot, and some improvements from equipment manufacturers, a decision was made with the Connecticut Department of Public Utility Control to introduce the technology statewide.
Deploying DSCADA in CL&P's 6,000 miles of underground distribution is still being contemplated, though not yet mandated by the state regulators. The utility is also looking at installing them in underground systems. Engineering work is now being done, with an assessment of costs and benefits to be made later.
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