Manufacturing and performance criteria for medium voltage power cable semiconducting shields [Feature article]

The subject of semiconducting shield (screen) layers for shielded power cable is interesting as a result of the many technical requirements that must be met simultaneously and that will be described in this article. This contribution is timely in that the IEEE Insulated Conductors Committee (ICC) has a Working Group developing a Guide on cable shields. One purpose of this article is to show that the carbon black is not necessarily the dominant issue in the formulation of shield compounds. Processing and compatibility with the overall cable system is as, or more, important to the shield properties and stability in service than the carbon black used. Through held experience, one commercial conductor shield compound used during the 1990s was unstable in the field as a result of high sensitivity to shear, which resulted in the shield layer going essentially nonconductive in service. Another purpose of this contribution is to show that shield layers are not "mix and match". The shield layer must be suitable for the process and dielectric with which it is used. Shields that are designed for use with XLPE dielectric are often not suitable for use with EPR dielectric, and vice versa. Likewise, the appropriate shield depends on the configuration of the extrusion line on which the cable is manufactured.