GB1043234A - Improvements relating to electric cables - Google Patents

Abstract

1,043,234. Gas insulated cables. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 14, 1963 [June 20, 1962], No. 23782/62. Heading H1A. A compressed gas electric power cable comprises a stranded conductor 1 with a central duct supported within a pressure retaining conduit or sheath 2 by means of an insulating structure comprising inner layer 3, fins 4 and surrounding tube 5 all integrally extruded. To increase the maximum flashover voltage, which occurs along the gas/solid interfaces, the fins 4 extend at an angle to the normal from the conductor surface, a tangential (as shown) or possibly a curved disposition of the fins being preferred. The number of fins 4 may be three, four (as shown) or five and preferably they should not overlap each other. There may be conducting or semi-conducting layers between the cable conductor 1 and the layer 3 and also round the outside of the insulating structure, i.e. screen 6. The interior space of the hollow conductor 1, spaces 7, and any spaces between the insulating structure and the conduit or sheath 2 are filled with gaseous insulating medium under pressure, e.g. mixtures of sulphur hexafluoride or difluoro-dichloromethane with nitrogen. The insulating structure may be extruded polythene or polypropylene and the pressure retaining conduit or sheath 2 may be reinforced lead, aluminium, aluminium alloy' either plain or corrugated, or copper, steel or zinc or their alloys. A multi-core cable (Fig. 2, not shown) comprises cable conductors each with an insulating structure 3-4-5 but without an individual pressure retaining conduit 2, loosely accommodated in a common pressure retaining conduit all remaining internal spaces being filled with compressed gaseous insulant,