GB404412A - Improvements in electric cables - Google Patents

Abstract

404,412. Cables. BEAVER, C. J., Bell Place, Stamford Road, Bowdon, DAVEY, E. L., 37, Greenway Road, Timperley, both in Cheshire, and GLOVER & CO., Ltd., W. T., Trafford Park, Manchester. Sept. 27, 1932, No. 26800. [Class 36.] To prevent corona formation in a hightension cable having laminated insulation, such as paper, impregnatedpaper, or varnished cambric, the insulation is formed with distributed spaces of definite and substantially invariable dimensions which are charged with a gas under a pressure, substantially less than atmospheric pressure, sufficiently low to prevent ionisation within the gas-filled spaces. To ensure that the spaces shall remain free of impregnating compound when impregnated paper insulation is employed, the impregnation of the paper is effected, prior to the lapping of the paper on the conductor, with a compound having a setting point substantially higher than the maximum temperature reached in the cable under working conditions. In a multicore cable free compound is also excluded from the fillers and belt insulation. Thin lubricating films of highly viscous petroleum jelly may be provided between the layers of insulation. In the construction shown, a stranded conductor 1 having a smooth cylindrical surface 2 is lapped with layers of paper strip 3, over which is wound a metallized, and preferably perforated, paper layer 6. A lead sheath 7, which is reinforced by a helically wound metal tape 8 and protected by an impregnated fabric jacket 9, completes the cable. The smooth cylindrical surface 2 may be obtained by the use of shaped wires in the outer layer of the stranded conductor 1, or by winding a metal tape or foil about the conductor or a lead tube may be applied over the conductor. Gas spaces 10 are formed in the paper layers by spacing apart the turns of the strip 3 and by staggering the turns in successive layers. The spaces may increase in size towards the outer layer, as shown, the thickness of the paper strip and the spacing between the turns being graded for this purpose. The paper strip is preferably lapped on the conductor in air which is kept below normal humidity, and, after the application of the sheath 7, the air is evacuated from the cable to the desired extent or is replaced by an inert gas such as nitrogen, carbon dioxide, helium, or neon at the desired pressure. The filling of the cable with gas may be facilitated by a repeated flooding and exhaustion of the gas into and from the cable and by the application of heat, the cable being finally evacuated to the desired low pressure. Specifications 20549/14, 182,510, [both in Class 36, Electricity, Conducting &c.], 318,647, [Class 140, Waterproof &c. fabrics], and 373,697, [Group VIII], are referred to.