GB1022183A - Improvements in or relating to electric cables - Google Patents

Abstract

1,022,183. Cable conduits; cable joints and terminations; electric transmission systems. BRITISH INSULATED CALLENDER'S CABLES Ltd. May 7, 1964 [May 8, 1963], No. 18252/63. Headings H2C, H2E and H2H. [Also in Division HI], In an electric power transmission system using a concentric cable, more than one separate concentric conductor is provided for some or all of the phases, and the allocation of the phases to the various conductors of differing radii is made so that they are systematically intermingled. As described, a three-phase cable (Fig. 1, not shown) comprises five conductors A1, A2 (phase 1), B (phase 2), C1, C2 (phase 3) with insulation between adjacent conductors and over the outermost, A2. The current-carrying capacity of conductor B is twice that of any other conductor. The mean radii a 1 , a 2 , b, c 1 , c 2 of conductors A1, A2, B, C 1 , C 2 , respectively, may be such that, substantially, a 1 a 2 = b<SP>2</SP> = c 1 c 2 . A central channel 1 is defined by a steel spiral 2 upon which copper wires 3 are laid up to form conductor A1. The insulation 5 is built up from lappings of transversely serrated polycarbonate tape, applied butting. Conductor C1 consists of copper wires, whilst conductor B consists of copper wires B1 overlaid with aluminium wires B2, and conductors C2, A2 consist of aluminium wires only. A perforated metal screen 6 is applied over the last layer of insulation and is followed by an open turn lapping 7 of non- ferrous D-section tape. This core is drawn into a steel pipe 8 having an anti-corrosive serving 9. The cable may be cooled by the evaporation of liquid refrigerant introduced into the channel 1, as described in Specification 988,030, when straight-through joints and terminations are made in sealed enclosures 12, 13, Fig. 2 (not shown), which communicate with refrigerating apparatus. Clamps 10 embrace each concentric conductor and connectors 11 are used either to make through connections or, at a termination, to join conductors of the same phase, when conducting stalks 14 continue through porcelain insulators 15 to provide terminals. In an alter. native, a three-phase cable comprises six conductors, each of the same current-carrying capacity, i.e., the conductor B, Fig. 1, may be considered as split into two concentric conductors with insulation between them. In another alternative, suitable for single-phase A.C. or for D.C., a triple-concentric cable is used.