GB439980A - Improvements in electric cables - Google Patents

Abstract

439,980. Cables. CALLENDER'S CABLE & CONSTRUCTION CO., Ltd., and ROBINSON, D. M., Hamilton House, Victoria Embankment, London. June 22, 1934, No. 18437. [Class 36] To prevent breakdown of the innermost layers of dielectric in a high tension cable having an impregnated fibrous dielectric, the conductor is formed with a smooth non- re-entrant surface and a thin continuous sheath of homogeous insulating material impervious to the impregnating compound is interposed between the conductor and the impregnated dielectric. The impervious sheath is built up of one or more helical lappings of strip of thickness not exceeding 2 mils and may consist of cellulose esters or ethers, polystyrenes, or oil-resisting rubber-like compounds, such as olefine polysulphide compounds. The smoothing of the surface of the conductor may be effected by building it, or the outer part of it, from wires of a section appropriate to give a continuous cylindrical form. Alternatively a conductor formed of stranded round wires may be lapped with metal tape or metallized paper, or provided with an extruded lead sheath ; or the inner surface of the impervious layer may be metallized. In the construction shown, a stranded conductor 11 is enclosed in a tubular metal sheath 18 over which is applied the thin impervious insulating sheath 15 and a thick body of impregnated paper insulation 13. A small gap is left between adjacent turns of the strip forming the sheath 15 and the turns in adjacent layers of the strip are staggered. To prevent breakdown of the outer layers of the insulation 13, a thin impervious insulating sheath 16, similar to the sheath 15, is disposed between the outer surface of the insulation 13 and the usual metallized layer 17 which surrounds the insulation. Specifications 175,753, [Class 36], and 407,718 are referred to.