Detection and Location of Dielectric Fluid Leaks on Pipe-Type Cable Systems

In the late 1940's high voltage pipe-type feeders were first installed in the United States. Since that time, over 2360 circuit miles of underground high voltage pipe-type cables have been installed throughout the country. Con Edison has approximately 652 circuit miles of high pressure pipe-type cable on its system, operating at 69, 138 or 345 kV. The typical pipe-type cable system is comprised of a steel pipe, containing 3 cables, with splices located at intervals of approximately 2000 feet. The pipe is filled with dielectric fluid which is maintained at a nominal operating pressure of 200 psig. Pressurization on the feeder is maintained automatically by pumping plants. For the 345 kV system, these plants sometimes include cooling capability. As the pipe type cable system grows older, leaks of dielectric fluid develop. The major causes of leaks are corrosion, contractor damages, effects of stray currents and localized pipe wear due to vibration. Quick detection and location of dielectric fluid leaks, particularly without the need to deenergize the feeder, is of prime importance to the utility industry. Raychem Corporation has been involved with the development of sensor cables for the detection and location of fluid leaks such as water and gasoline. This technology has been enhanced to address the problem of pipe type cable dielectric fluid leaks and a new system has been developed. The new system uses a sensor cable which is buried in the trench with the pipe type cable.