GB497618A - Improvements in or relating to electric cables - Google Patents

Abstract

497,618. Cables. CALLENDER'S CABLE & CONSTRUCTION CO., Ltd., and LUNT, R. W. Sept. 28, 1937, No. 26254. [Class 36] To prevent breakdown of a high tension cable having an oil- or compound-impregnated fibrous dielectric, a composite layer consisting of an inner portion of semi-conductive material and an outer portion of homogeneous insulating material impervious to the oil or compound is interposed between the conductor and the inner surface of the dielectric. The two portions of the layer are as far as possible in complete contact throughout their adjacent surfaces. The semi-conducting inner portion may be formed by oxidizing the surface of the conductor, when this is of copper; alternatively the inner portion may consist of a graphite coating on the conductor. The outer portion may be formed of insulating varnishes, gum dammar, vinyl chloride, styrene, methacrylic ester, vitreous enamel, or siliceous material. When using copper oxide as semi-conductive material and vitreous enamel for the outer portion of the layer precautions must be taken to limit the reaction between the oxide coating and the vitreous material. Where the outer portion of the layer is of siliceous material this portion may be applied as a varnish consisting of a solution of silica as described in Specification 494,448. Specifications 439,980, 484,777, and 290,717, [Class 1 (i)], also are referred to.