GB511698A - Improvements in or relating to air-space insulated electric conductors - Google Patents

Abstract

511,698. Cables. SHEVLIN, J. T. (Siemens & Halske Akt.-Ges.). Feb. 22, 1938, No. 5638. [Class 36] A cable comprises a single inner conductor separated by at least one air-space insulation layer from a surrounding screen or return conductor, the insulation layer, or that insulation layer immediately surrounding the inner conductor being formed by a self-supporting spacing structure composed of at least one self-supporting open helical spacing member of insulating material, the inner conductor lying freely within the spacing structure which has an internal diameter at least fifty per cent. larger than the diameter of the inner conductor. The spacing structure is preferably of polystyrol As shown in Fig. 2, a spacing structure 21 surrounding a conductor 20 consists of a self-supporting open helical thread 22 wound with a thread 23. An insulating band winding 24 surrounds the structure 21, over which winding is successively applied a return conductor 25 formed of metal bands, a retaining winding 26 for the bands of the return conductor, a closed insulating band winding 27 and a waterproof sheath 28. In a modified construction the thread winding 23 is omitted and a second air-space insulation layer may be provided by arranging between the band winding 24 and the return conductor an open cord winding surrounded by a closed band winding. Fig. 6 shows a construction in which a return conductor or screen 65 is formed of metal braid applied over an insulating sheath 63 surrounding the spacing structure 62 and formed by extension or as a closed band winding. The return conductor or screen is surrounded by a woven or extended insulating jacket 66. The sheath 63 may be omitted and the spacing structure 62 may be formed of two coaxial helices. The outer jacket 66 may be permeated or coated with aluminium powder or other substance having a metallic lustre.