GB972067A - Improvements in or relating to electrical insulating materials for cables - Google Patents

Abstract

972,067. Cable insulation. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Dec. 20, 1960 [Jan. 4, 1960], No. 231/60. Heading H1A. An electric power cable comprises one or more conducting cores embedded in or surrounded by a mass of insulating material which consists of a thermoplastic material having improved thermal conductivity by virtue of a content of up to 50% by weight of powdered alumina therein. In the simplified three-core cable illustrated the layers of insulation are made from homogeneous mixtures largely of polythene and alumina powder, there being at least 20 parts by weight of alumina to 100 parts of polythene. The cores within their individual insulating layers A are embedded in a mass C within a protective sheath B of similar insulating material. The proportion of alumina to polythene may be varied in the three parts A, B, C of the insulation. For example, the core insulation A may have less alumina than the general insulation C in order to improve the electrical characteristics near the cores, and the proportion of alumina in the outer sheath B may be restricted so that good mechanical properties, such as resistance to abrasion, may be obtained. The mechanical properties may be improved in known manner by the addition of a proportion of polyisobutylene or butyl rubber. Similar cables may be made using other thermoplastic materials, especially using polyvinylchloride. Plasticizers may be added to polyvinyl chloride mixes to counteract the hardening effect caused by loading with alumina.