When conductor sizes for high-voltage underground transmission cables ranged from 500 to 2,000 kcmil, these cables were mostly designed with concentric round stranded copper or aluminum conductors. As energy demands grow, and with it the need for increased power transfer in HV cables, larger conductors with cross-sections of up to 4,000 or 5,000 kcmil are required. In these larger applications, a phenomenon called the skin effect becomes a significant issue as conventional conductors reach their limits.

Thomas Wilki, director of underground transmission for Southwire's Energy Division, describes skin effect as the displacement of current flow toward the surface of the conductor as a result of its magnetic field. This in turn increases the AC resistance, limiting power transfer and increasing conductor losses.

The skin effect can be significantly reduced by changing the conductor design from a regular round design to a Milliken design, typically called a segmental conductor today. The conductor is separated into several individual insulated segments that are cabled together.

Southwire has now introduced this segmental design to its product line based on five separate segments. This will allow utilities to transmit 10% to 30% more power through cables with conductor sizes ranging from 2500 kcmil to 4000 kcmil, as well as reduce losses in the transmission grid. For special applications, segmental conductors with cross-sections as small as 1,750 kcmil may be used. Southwire customers can specify segmental conductors for voltages up to 230 kV with their preferred combination of insulation, shielding and jackets.