Chemical-Based Technique Detects Underground Pipe Leaks
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. The method has been successfully tested in New York, say developers from Consolidated Edison Co. of New York (New York City; 212-460-4112); the DOE's Brookhaven National Laboratory (Upton, NY); and the Electric Power Research Institute (EPRI; Palo Alto, CA).
Methodology
Successful Tests
Early Research
The leak-detection method is based on chemicals called perflurocarbon tracers (PFTs). Originally developed at Brookhaven 20 yrs ago for use in atmospheric research, PFTs are inert manmade gases that can be easily detected with sensors. Because they do not interact chemically with anything, PFTs can be safely added to the dielectric fluid that is used to cool and insulate many underground electric cables.
More than 80% of the nation's underground power lines are contained in these high-pressure, dielectric fluid-filled pipes. Occasionally, corrosion, damage, and stray current can create holes in the pipes, causing the fluid to leak.
If there is a leak, trace amounts of PFTs in the dielectric fluid can be detected in aboveground air by technicians equipped with sensors called dual-trap analyzers (DTAs). Consolidated Edison has equipped two special "leak hunter" vans for this purpose, which use dual-trap analyzers to check for leaks every two min along two city blocks at a time.
"The vans let Consolidated Edison zoom in on a leak first by determining its position within a few blocks," says Russell Dietz, lead Brookhaven researcher on the team. "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. This is currently done with great expense of time and money."
The research was funded by Consolidated Edison and EPRI, and based on years of research at Brookhaven. The team describes the method in a paper in the current Transactions on Power Delivery, published by the Institute of Electrical and Electronics Engineers.
Successful Tests (Back to Top)
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. The method is much more efficient and effective than others in use, according to the research team.
"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," Dietz says.
Consolidated Edison has used the method to find many leaks—ranging from less than one gal/day up to 50 gal/hr—in its hundreds of miles of underground lines.
Brookhaven's first work with PFTs began in the 1970s, when scientists wanted a method to track pollutants in the atmosphere. Discussions with Con Edison in the 1980s led to cooperative research, which was contracted through EPRI.
Brookhaven first demonstrated the technology on Consolidated Edison and British high-voltage fluid-filled underground lines, leading to the company'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, Brookhaven is beginning a new project with Consolidated 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 United States. Currently, most oil lines' leak-detection systems cannot measure leaks that are less than a few percent of pipeline capacity. This means that oil can drip undetected for long periods of time.
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