ETHYLENE PROPYLENE RUBBER AND CROSSLINKED POLYETHYLENE AS INSULATIONS FOR 90-DEGREES-C RATED MEDIUM VOLTAGE CABLES

Results of an experimental study are presented which show that amorphous ethylene propylene rubber insulated power cables are more stable under high temperature conditions than crystalline crosslinked polyethylene insulated cables. The properties of amorphous EP rubbers are little affected by temperature from minus 30 to 150 degree C; those of crystalline XLPE fall off as temperature exceeds the melting point (around 100 degree C) of the crystalline regions. Reinforced amorphous EP rubber insulated cables are expected to be more stable in wet locations than unfilled XLPE insulated cables. They do not fail by the formation of water trees as the primary mechanisms, since the bonds between filler and polymer are stronger than the forces responsible for water trees forming in XLPE cables in service. The reinforcing effect of fillers in EP rubber makes questionable any extrapolation from high stress treeing studies of unreinforced PE, XLPE, or EP polymers. For the longest possible life in wet locations insulation should be protected by a water impermeable metallic sheath, which must be protected against corrosion, mechanical damage, fatigue cracks, etc.