PSE&G identifies faults with advanced loop scheme
Published In: Intelligent Utility Magazine November/December 2010
Pacific Service Electric & Gas (PSE&G) has long been proud of its reputation of delivering reliable electricity to 2.1 million customers throughout New Jersey. So when industry reliability metrics SAIFI (System Average Interruption Frequency) and MAIFI ( Momentary Average Interruption Frequency) started to decline about 10 years ago, PSE&G started looking for a solution, which Dick Wernsing, PSE&G's reliability-centered maintenance expert, attributes to weather, tree interference with power lines and aging infrastructure.
"PSE&G customers demand reliable electric service, driving the utility's data-driven approach to improve system performance," said Wernsing. "We owe it to customers to continually improve our performance. To do so we were looking for a methodology to markedly improve SAIFI and eliminate MAFI (flickering lights) while simultaneously preparing for future AMI system growth."
Improving communications among reclosers
In early 2008, PSE&G developed a concept to improve performance through intelligent automation, called the advanced loop scheme (ALS), which builds an intelligent infrastructure using high speed communications between reclosers in a distribution loop circuit. A traditional loop scheme incorporates a circuit breaker at a substation, a feeder recloser halfway through the circuit and a tie recloser at the end. A fault in the first part of the circuit trips the breaker and initiates a reclose attempt which, if unsuccessful, opens the feeder recloser to isolate the fault. The tie recloser will feed alternative power to the second portion of the customers. But that's still a lot of customers experiencing a momentary or a longer power outage.
ALS increases the number of reclosers on a loop circuit and breaks customers served by a particular segment of the circuit into smaller sections. Microprocessors installed in each recloser are connected via a fiber optics network, which can automate communication capabilities between them. "A fault anywhere along the circuit can then be quickly identified and isolated by means of local reclosers speaking to each other in a decentralized manner," Wernsing explained. Such a strategy can significantly reduce the number of customers impacted by an outage.
Isolating power outages so they affect hundreds of customers instead of several thousand would seem an obvious benefit, but few utilities have thus far adopted it. "Our means of isolating an outage is considered unusual in the industry," said Wernsing. "We close the tie point before opening the faulted section, which works for us because of the speed at which we clear faults, eliminating the on-off flicker that people hate."
While the advanced loop scheme is primarily intended to improve reliability, the smart grid implications of intelligent circuits have not escaped the utility. Last year, PSE&G pursued $76 million in stimulus funding through the Department of Energy's Smart Grid Investment Program. Unfortunately, the bid was unsuccessful.
"Reviewers may have been searching for key words and concepts more commonly associated with smart grid such as advanced metering [AMI] ," Wernsing said. "Our bid articulated the benefits of intelligent infrastructure to improve reliability and, oh, by the way, we provide a communications backbone for smart meters, too. We may not have brought front-and-center what reviewers expected."
Despite that disappointment, Wernsing is still happy to expound the benefits of intelligent automation and how it enables communications opportunities including advanced metering infrastructure, opportunities for distributed generation from wind turbines and solar panels, and an intelligent SCADA system.
Asset management benefits
PSE&G is particularly suited for an advanced loop scheme because of its location in the New York-New Jersey metropolitan area. The distance between facilities is only six to 10 miles and fiber optic communications upgrades are less cost prohibitive than they would be for another utility in a less concentrated region with stations and customers further apart.
"We remain vigilant in both the advanced loop scheme and AMI areas. When AMI starts to be deployed, the fiber optic communications of ALS will be cost justified," said Wernsing. "Fiber optics is also part of PSE&G's system upgrade, including serving as replacement cables as older static wires are removed."
Wernsing finished by emphasizing reliable power delivery. "The more electronic our society becomes, the greater the inconvenience of even a momentary outage. Households and businesses have to reset clocks, computers, etc." But soon he was musing again about the asset management benefits of an intelligent automation systems and the smart grid.
Author's note: As a Bronx-born New Yorker familiar with the region, I am personally fascinated by the idea of the smart grid setting a foundation for windmills in Newark (where PSE&G is based). Who could have predicted an intelligent utility even a few decades ago? And who could have thought that smart grid would have happened `oh, by the way' as a utility follows some other goal? But that is what PSE&G is moving toward as it emphasizes power reliability as the primary driver for advanced loop schemes and an intelligent infrastructure.