Performance of supersmooth, extra clean semiconductive shields in XLPE insulated power cables

Abstract

Materials StudiedUnderground, XLPE insulated, power cable is intended to provide a service life of 40 years. There are many critical factors that determine the life of such a cable. One critical element is the perfection of the interface between the insulation and the semiconductive shields. Imperfections at these interfaces can result in an increased electrical stress concentration, thereby promoting tree growth in the insulation and premature failure of the cable. These imperfections can arise from voids, contaminants in the semiconductive shield, or protrusions of the semiconductive shield into the insulation. In addition, recent work has shown that the many ions commonly present in the commercial semiconductive shields will migrate into the insulation through the action of an electric field and water. A role by these ions in the development of water trees has been suggested by several researchers. Now, a new class of semiconductive shield has become available. When extruded, this material has a supersmooth surface, free of the many small irregularities common to the current semiconductive shields used in underground cable. In addition, a low moisture content reduces the tendency for die drool and the associated macro protrusions that result. This new semiconductive shield technology is also extra-clean with ionic contaminants in the low ppm range. In several accelerated cable aging tests, cables using this new semiconductive shielding technology as conductor shields have demonstrated marked improvements in performance. Clearly, this new semiconductive technology provides an opportunity t o substantially increase the life expectancy of XLPE and TR-XLPE insulated power cables.

Interface tailoring for charge injection control in polyethylene

“…Efforts were devoted to avoid field intensification at the interface due to the surface roughness of the semicon. HVDC grade semicon was developed using a specific quality of carbon black with less ionic impurities and with percolated structure [16].…”

Underground cable specification advances and installation practices of the largest investor-owned utilities

“…This imparts a smoother surface to the extruded conductor shield and has been reported to increase cable life in wet accelerated aging tests. [10], [11]. However, improvements in conventional semiconductive XLPE compounds over the past 10 yr have narrowed the performance differences between the two materials [12].…”