Utilities are sharply focused on reducing maintenance costs and improving reliability. For years, the underground aluminum 600-V cables feeding street lights, commercial customers and residential customers have had a significant failure rate because of corrosion of aluminum conductors. Data from field failures shows that the cable insulation is nicked during handling, installation or excavations following installation. Cuts allow moisture to enter the cable and provide a path for leakage current to flow into the earth. Failure occurs long after installation crews are gone. With time, corrosion of the aluminum conductor results in a “lights out” trouble call.

Now several major utilities including Dominion Virginia Power (DVP; Richmond, Virginia, U.S.) are looking into the cost-reduction benefits promised by Southwire's (Carrollton, Georgia, U.S.) SureSeal cable. The design consists of a series of discrete channels of sealant encapsulated in the insulation wall. Each channel contains the same precise amount of sealant. When cut, the exposed channel releases an insulating sealant material, which fills the cut, effectively closing off the leakage path and preventing corrosion.

While still stressing proper installation techniques, DVP has been testing SureSeal in a corrosive soil environment for more than six months. A deep cut is placed in the cable prior to energization and the leakage current to ground is recorded. Test results to date are promising.

Testing at the National Electrical Energy Testing Research and Applications Center (NEETRAC) of Georgia Tech has shown that both a #4/0 AWG and a #6 AWG cable with a cut placed across the insulation surface to expose the aluminum conductor, sealed completely, preventing corrosion. It is believed that the NEETRAC test closely represents the type of corrosion-causing damage that these cables most often experience.

Testing at Southwire's Cofer Technology Center has shown the ability of this cable to seal electrical punctures caused by lightning strikes. Impulse testing was used to simulate a lightning strike, creating a small hole. Within minutes, the hole sealed completely and normal impulse testing levels were obtained. A second test demonstrated that after a hole was punctured by overvoltage, the cable was able to withstand the application of 1000 V in water for one week and still met the AC breakdown level requirements for new cable.

Utilities experience thousands of failures of directly buried 600-V aluminum cables each year. Location and repair of these failures is expensive, approaching US$500 or more for each occurrence. SureSeal promises to improve reliability, reduce costs and improve customer satisfaction for customers served by directly buried aluminum 600-V cables.
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