Jan. 22, 1999 UPTON, NY - A novel method for finding dielectric fluid leaks in underground high-voltage electric cables protects the environment and prevents street excavations, while saving utilities time and money, according to a new study.
The approach has already been successfully used to pinpoint leaks in power lines contained in fluid-filled pipes under New York City's streets. It may also be potentially useful for finding problems in oil pipelines.
And, say researchers from the U.S. Department of Energy's Brookhaven National Laboratory, the Consolidated Edison Company of New York Inc. (Con Edison) and the Electric Power Research Institute, the method is much more efficient and effective than others in use.
The team describes the method in a paper in the current Transactions on Power Delivery, published by the Institute of Electrical and Electronics Engineers.
"With this technique, even the tiniest leaks can be located and repaired as fast as possible, reducing both the impact to the environment and the interruption to local traffic and power supply," said Russell Dietz, the lead Brookhaven researcher on the team.
Added his Con Edison colleague Reza Ghafurian, "The development of such a method has been of prime importance to our industry, and Con Edison is at the forefront of this area of research. Based on our real-world tests in New York, we believe this approach is a winner."
The method is based on chemicals called perflurocarbon tracers, or PFTs. Originally developed at Brookhaven 20 years ago for use in atmospheric research, PFTs are inert manmade gases that can be easily detected using special sensors. Because they do not interact chemically with anything, PFTs can be safely added to the fluid, similar to mineral oil, that is used to cool many underground electric cables.
More than 80 percent of the nation's underground power lines are contained in these fluid-filled pipes under high pressure. The dielectric fluid, as it is called, is required for cooling and insulation of power transmission cables. But occasionally, corrosion, damage and stray current can create holes in the pipes, causing the fluid to leak out.
If there is a leak, the trace amounts of PFTs in the dielectric fluid can be detected in aboveground air by technicians equipped with sensors called dual trap analyzers (DTAs). Con Edison has equipped two special "leak hunter" vans for this purpose, which use dual trap analyzers to check for leaks every two minutes along a distance of two city blocks at a time.
"The vans let Con Edison zoom in on a leak first by determining its position within a few blocks," said Dietz. "Then, they make tiny boreholes in the street to pinpoint the location to within a few feet. This is far better than freezing the dielectric fluid at the cable's midpoint and checking to see which side is losing pressure, until successive freezes permit a small section to be excavated to find the leak, as is currently done with great expense of time and money."
Con Edison has used the method to find many leaks - ranging from less than one gallon per day up to 50 gallons per hour - in its hundreds of miles of underground lines. "PFT has been Con Edison's primary method of finding leaks for two years," states Patrick Keelan, Con Edison's operations manager in charge of the mobile labs. "We have been 100 percent successful in finding all leaks using this approach. We have drastically reduced the leak-search time from weeks and days to hours. Now, we are looking into marketing our success and experience to help other utilities find leaks."
PFT concentrations in the dielectric fluid and the surrounding air during leaks are extremely low, because of the sensitivity of the detectors - even under rainy and windy conditions. PFTs pose no health or safety risks.
The research was funded by Con Edison and EPRI, and based on years of research at BNL funded by DOE. BNL's first work with PFTs began in the 1970s, when scientists wanted a method to track pollutants in the atmosphere. General discussions with Con Edison in the 1980s led to cooperative research, which was contracted through EPRI.
BNL first demonstrated the technology on Con Edison and British high-voltage fluid-filled underground lines, leading to Con Edison's decision to purchase its own PFT sensor equipment. Their dual trap analyzers were made in cooperation with industrial partners Sentex Systems Inc. and Robotech Inc. The injection system was developed by Underground Systems Inc.
Now, BNL is beginning a new project with Con Edison to enhance their leak-pinpointing and detection capabilities. The Laboratory may also continue developing PFT techniques for other uses, including detecting leaks in the 200,000 miles of oil pipelines in the U.S. Currently, most oil lines' leak detection systems cannot measure any leak less than a few percent of pipeline capacity, which can be quite large.
And, PFTs will also be again used for their original purpose of atmospheric research. This summer, BNL scientists will study how air pollution from Mexico affects visibility in some U.S. national parks. The U.S. Department of Energy's Brookhaven National Laboratory creates and operates major facilities available to university, industrial and 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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