AC and impulse performance of medium voltage ethylene propylene- rubber cables with over 25 years of in-service aging in a wet underground environment

Many electric utilities, including Memphis Light, Gas & Water (MLGW), began installing underground residential electric (URD) facilities in the late 1960s. The earliest URD customers at MLGW were served by paper-insulated lead-covered (PILC) type cable which has a very good service history but was expensive and time-consuming to install. In an effort to install URD facilities at a comparable cost to traditional overhead facilities, direct buried high-molecular weight polyethylene (HMWPE) insulated cables were utilized. These unjacketed cables were constructed with a #2 AWG copper conductor, 6.1 mm (240 mils) of HMWPE insulation, and copper concentric neutrals. Unjacketed feeder cables were constructed with a 380 mm2 (750 kcmil) aluminum conductor, 6.1 mm (240 mils) of cross-linked polyethylene (XLPE) insulation, and copper concentric neutrals. Initially, feeder cables were direct buried but by the mid-1970s were installed in conduit. All cables were operated at either 12 kV or 23 kV phase-to-phase system voltages.