GB393694A - Improvements in electric cables - Google Patents

Abstract

393,694. Cables. BEAVER, C. J., Bell Place, Stamford Road, Bowden, DAVEY, E. L., 37, Greenway Road, Timperley, both in Cheshire, and GLOVER & CO., Ltd., W. T., Trafford Park, Manchester. Feb. 9, 1932, No. 3842. [Class 36.] To prevent the formation of corona in an impregnated paper cable, the paper is applied about the conductor in such a manners as to leave spaces distributed throughout the insulation which are subsequently charged with a gas under such pressure, substantially greater than atmospheric pressure, that ionization within the gas-filled spaces cannot occur. To ensure that the spaces shall not be filled with free impregnating compound, the impregnation of the paper is effected, prior to its lapping on the conductor, with a compound having a setting point substantially higher than the maximum temperature reached in the working conditions of the cable. Thin lubricating films of highly viscous petroleum jelly may be provided between. the layers of paper lappings. In the construction shown, a stranded conductor 1 formed with a smooth cylindrical surface 2 is lapped with layers of pre-impregnated paper over which is wound a metallized paper layer 6. The layer 6 is preferably perforated. 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 formed by using 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 adjacent turns of the paper strip and by staggering the turns in successive layers. The spaces may increase in size towards the outer layer, the spacing between the turns and the thickness of the paper strip being graded for this purpose. The Figure shows the insulation of the cable formed in sections 3, 4, 5 having gas spaces of progressively increasing dimensions. 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 enclosed in the insulation is evacuated and replaced by dry air or an inert gas, such as nitrogen or carbon dioxide. The filling of the cable with dry air or gas may be facilitated by a repeated flooding and exhaustion of the gas or dry air into and from the cable and by the application of heat, the gas or air being finally forced in under pressure. In a multicore cable free compound is also excluded from the fillers and the belt insulation. 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.