GB551450A - Improvements in or relating to insulated electrical conductors - Google Patents

Abstract

551,450. Transformers and inductances. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Oct. 13, 1941, No: 13153. Convention date, Oct. 16, 1940. [Class 38 (ii)] [Also in Group XXXVI] Electric conductors for use immersed in liquid dielectric such as oil or halogenated cyclic hydrocarbon fluids, have applied thereto inner and outer layers of insulation, the inner layer or layers being permeable to the liquid dielectric, and the outer layer comprising a coating of adhesive material impermeable to the dielectric and substantially covering the inner layer or layers but leaving spaces to permit escape of air and entry of the dielectric to said inner layer or layers. In Fig. 1, a copper &c. conductor 12, which may have a coating of oil insoluble varnish, is covered with one or more layers 14 of paper, cambric, cloth, glass fibre material &c. permeable to the dielectric, over which is applied spirally a layer of cloth or paper 16 treated on one or both sides with oil insoluble varnish or other adhesive, preferably thermoplastic, spaces 18 being left between turns for entry of the dielectric to the layers 14 ; the adhesive may comprise shellac, polyvinyl acetate or acetal, plasticized cellulose esters or ethers, or varnishes prepared from thermoplastic resins modified by additions of thermosetting resin such as the phenol-aldehyde type, or polyvinyl alcohol produced by hydrolysingpolyviriyl esters 50 to 75' per cent and dissolved in a 30 to 60 per cent water-ethyl alcohol solvent, a tape coated with the lastnamed substance being rendered adhesive after drying by applying water or an aqueous aldehyde. Adjacent conductors may be bonded together by pressure and heat, the assembly being cooled before the pressure is relieved. In place of, or in addition to, the spaces 18, apertures may be made in the coated strip 16. In other forms, the strip 16 has a discontinuous coating of adhesive, such as spots or parallel bands, the remainder of the strip being permeable, or strips of cellulose acetate, polyvinyl alcohol &c. are applied in spaced turns over an uncoated strip 16, and heat and pressure applied to bond the whole. The conductors may be formed into coils by winding on a mandrel, tying the coils, securing the sides and corners by clamps if required and heating in an oven at 100 to 125‹ C. ; in a transformer, a number of such coils are placed on a laminated magnetic core and spaced as by Fullerboard. In Fig. 6, three coils 30 have their last turns taped with fabric 42 impregnated as above and are spaced by blocks 44 formed.of layers of Fullerboard coated with thermoplastic adhesive, the blocks 44 having keystone-shaped slots 46 to receive supporting members in the transformer casing, the assembly then being heated to 100 to 125 ‹C. ; before or during immersion in the dielectric an evacuating treatment may be used to remove air and moisture.