Abstract
To remove the mineral oil impregnating the insulating paper present in old, disconnected, underground electrical cables, which represents a threat to the environment, two approaches are investigated at laboratory (1 m) and pilot (10 m) scales. The first one involves in situ polymerization to clog the inner channel of the cables and to enable the washing of the outer paper region impregnated by the oil by axial flow of a displacing fluid (water). The second approach leaves the inner channel open and employs repeated cycles of pressurization and rest to displace the oil contained in the paper by radially pushing the water from the inner channel into the outer layers. The pressurization and rest times were optimized to obtain the highest oil extraction rate. While the first approach showed limitations in terms of required pressures and operating time, which increase with the length of the cables, the second one was effective at removing 97% of the oil impregnating the paper layers within 25 cycles. Even more relevant, this second solution, in contrast to the first one, can be easily scaled up as it does not depend on the length of the cable, and was successfully tested on a 10 m cable, showing 98% oil recovery.
Highlights
Oil-filled electrical cables have been placed underground all over Europe since the late 1950s to distribute electric power throughout the territory, in urban areas
The insulating mineral or synthetic oil contained in the cables may accidentally leak out as a consequence of material deterioration, ground movements, failure at jointures between cables, and damage during drilling/excavations
When feasible, this method would result in high costs due to the manpower needed for the excavations and expensive drilling machinery, as well as long time and interference with the city traffic
Summary
Oil-filled electrical cables have been placed underground all over Europe since the late 1950s to distribute electric power throughout the territory, in urban areas. Despite the first strategy guaranteeing a complete recovery of the oil as well as of the other materials composing the cables, this is seldom applicable due to the inaccessibility of the cables as additional infrastructures may have been built on them, especially in highly populated urban areas When feasible, this method would result in high costs due to the manpower needed for the excavations and expensive drilling machinery, as well as long time and interference with the city traffic. Thebyfirst oneinjection consists in fully clogging channel of thehave cablebeen by indeveloped situ polymerization followed water in fully clogging the inner channel of the cable by in situ polymerization followed by water injection into the paper annular region to remove the impregnating oil by displacement in the axial direction.
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