UPTON, NY - A novel method for finding dielectric fluid leaks inunderground high-voltage electric cables protects the environment andprevents street excavations, while saving utilities time and money,according to a new study.
The approach has already been successfully used to pinpoint leaksin power lines contained in fluid-filled pipes under New York City'sstreets. It may also be potentially useful for finding problems in oilpipelines.
And, say researchers from the U.S. Department of Energy'sBrookhaven National Laboratory, the Consolidated Edison Company of New YorkInc. (Con Edison) and the Electric Power Research Institute, the method ismuch more efficient and effective than others in use.
The team describes the method in a paper in the currentTransactions on Power Delivery, published by the Institute of Electricaland Electronics Engineers.
"With this technique, even the tiniest leaks can be located andrepaired as fast as possible, reducing both the impact to the environmentand the interruption to local traffic and power supply," said RussellDietz, the lead Brookhaven researcher on the team.
Added his Con Edison colleague Reza Ghafurian, "The development ofsuch a method has been of prime importance to our industry, and Con Edisonis at the forefront of this area of research. Based on our real-worldtests in New York, we believe this approach is a winner."
The method is based on chemicals called perflurocarbon tracers, orPFTs. Originally developed at Brookhaven 20 years ago for use inatmospheric research, PFTs are inert manmade gases that can be easilydetected using special sensors. Because they do not interact chemicallywith anything, PFTs can be safely added to the fluid, similar to mineraloil, that is used to cool many underground electric cables.
More than 80 percent of the nation's underground power lines arecontained in these fluid-filled pipes under high pressure. The dielectricfluid, as it is called, is required for cooling and insulation of powertransmission cables. But occasionally, corrosion, damage and stray currentcan create holes in the pipes, causing the fluid to leak out.
If there is a leak, the trace amounts of PFTs in the dielectricfluid can be detected in aboveground air by technicians equipped withsensors called dual trap analyzers (DTAs). Con Edison has equipped twospecial "leak hunter" vans for this purpose, which use dual trap analyzersto check for leaks every two minutes along a distance of two city blocks ata time.
"The vans let Con Edison zoom in on a leak first by determining itsposition within a few blocks," said Dietz. "Then, they make tiny boreholesin the street to pinpoint the location to within a few feet. This is farbetter than freezing the dielectric fluid at the cable's midpoint andchecking to see which side is losing pressure, until successive freezespermit a small section to be excavated to find the leak, as is currentlydone with great expense of time and money."
Con Edison has used the method to find many leaks - ranging fromless than one gallon per day up to 50 gallons per hour - in its hundreds ofmiles of underground lines."PFT has been Con Edison's primary method of finding leaks for twoyears," states Patrick Keelan, Con Edison's operations manager in charge ofthe mobile labs. "We have been 100 percent successful in finding all leaksusing this approach. We have drastically reduced the leak-search time fromweeks and days to hours. Now, we are looking into marketing our successand experience to help other utilities find leaks."
PFT concentrations in the dielectric fluid and the surrounding airduring leaks are extremely low, because of the sensitivity of the detectors- even under rainy and windy conditions. PFTs pose no health or safetyrisks.
The research was funded by Con Edison and EPRI, and based on yearsof research at BNL funded by DOE.BNL's first work with PFTs began in the 1970s, when scientistswanted a method to track pollutants in the atmosphere. General discussionswith Con Edison in the 1980s led to cooperative research, which wascontracted through EPRI.
BNL first demonstrated the technology on Con Edison and Britishhigh-voltage fluid-filled underground lines, leading to Con Edison'sdecision to purchase its own PFT sensor equipment. Their dual trapanalyzers were made in cooperation with industrial partners Sentex SystemsInc. and Robotech Inc. The injection system was developed by UndergroundSystems Inc.
Now, BNL is beginning a new project with Con Edison to enhancetheir leak-pinpointing and detection capabilities. The Laboratory may alsocontinue developing PFT techniques for other uses, including detectingleaks in the 200,000 miles of oil pipelines in the U.S. Currently, mostoil lines' leak detection systems cannot measure any leak less than a fewpercent of pipeline capacity, which can be quite large.
And, PFTs will also be again used for their original purpose ofatmospheric research. This summer, BNL scientists will study how airpollution from Mexico affects visibility in some U.S. national parks.The U.S. Department of Energy's Brookhaven National Laboratorycreates and operates major facilities available to university, industrialand government personnel for basic and applied research in the physical,biomedical and environmental sciences, and in selected energy technologies.The Laboratory is operated by Brookhaven Science Associates, a not-for-profit research management company, under contract with the U.S.Department of Energy.
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