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The smoothness of the interface between the insulation layer and the semiconductive conductor shields is very important to provide a uniform electrical stress gradient preserving the long term electrical performance of power cables. Any convolutions or protrusions from the semiconductive conductor shield into the insulation layer can result in localized electrical stress and induce undesired treeing or electrical degradation. An investigation of the compound melt rheology and its relationship to conductor shield convolution will be described. It will be shown that the inherent rheological properties of the semiconductive conductor shield compound in combination with the fabrication conditions in the continuous vulcanization of power cable manufacturing process determine the tendency for convolutions to develop.

New formulation technologies have been developed for application in semiconductive conductor shield compounds. These technologies offer several advantages for conductor shields relative to the traditional polyethylene copolymers of alkyl-acrylate, or vinyl-acetate, that have been in commercial use for over 30 years. New semiconductive conductor shield compounds have been tested extensively both in the laboratory and on insulated power cables. A conventional shield class of product was produced with the new technology utilizing a furnace black. It was used to manufacture a commercial scale 15 kV cable with XLPE insulation. This cable was then tested in long term wet aging under 4,4' ACLT conditions and found to exhibit excellent performance. The cable extrusion study showed excellent processability in comparison to conventional shields.

The electroluminescence test is a relatively new technique to investigate the dielectric performance of semiconductive shields and crosslinked polyethylene insulation interfaces. It is based on the electric field (voltage) at which light emission occurs as a result of charge injection and carriers recombination for a given sample geometry. A standardized sample geometry with a semicon needle-plane electrode was utilized under amplified voltage in a dry condition to monitor the electroluminescence inception voltages of crosslinked polyethylene (XLPE) and tree retardant crosslinked polyethylene insulation (TR XLPE). It resulted that EL inception voltage of TR XLPE is higher than that of XLPE. In water tree growth test, TR XLPE demonstrated to retard water tree growth under the wet aging condition.