| 摘要 |
1442634 Power cable BICC Ltd 15 March 1974 [16 March 1973] 12717/73 Heading H1A The impregnated dielectric of an electric power cable comprises an inner zone 5 and an outer zone 7 each of only two layers of paper tape and an intermediate zone 6a, 6b of tapes comprising plastics material. The thickness of each paper tape in the inner and outer zone is preferably substantially equal to or slightly less than, and substantially equal to or slightly greater than respectively, the thickness of the thinnest tape of the intermediate zone. The intermediate zone may consist of composite tapes, see Fig. 3, each consisting of a plastics film 13, e.g. of polypropylene, sandwiched between and bonded to two layers of fibrous material, e.g. paper. The butt spaces 15 between tape edges are filled with the impregnant, e.g. C6 insulating mineral oil. In Fig. 2 a steel tape helix 1 defines an oil duct within conductor 2 which is surrounded by a bronze binder tape 3 and conductor screen 4 which is formed of tapes metallized and/or loaded with conductive material. In zone 6a of the insulation the composite tapes consist of a 50 Ám. polypropylene layer sandwiched between two 25 Ám. paper layers, in zone 6b the polypropylene layer may be 60 Ám. and each paper layer 30 Ám. thick. The essential dielectric screen consists in this embodiment of a semiconductive screen 8 followed by a conductive bedding tape 9 of copper wires interwoven with textile threads or glass fibres. The cable is completed by a lead or aluminium sheath 10, bronze tape 11 and a plastics oversheath 12. The laminate of paper and plastics film of the composite tape may be prestressed, that is it is produced by trapping an extruded molten web of plastics material as it leaves an extruder between two paper sheets forming part of the laminate. |
