GB578869A - Improvements in or relating to dielectric compositions and sealed electrical apparatus impregnated therewith - Google Patents

Abstract

578,869. Electric insulation. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. June 14, 1945, No. 15102. Convention date, June 29, 1944. Drawings to Specification. [Class 36] [Also in Group XXXV] A dielectric composition, for sealed electrical apparatus such as a transformer with electrical elements disposed within and spaced from a hermetically sealed casing, comprises a major volumetric proportion of fine spherical particles of a solid inorganic material having a coefficient of cubical expansion less than that of the casing and elements and a minor proportion of liquid dielectric filling the rest of the space between the casing and elements, the dielectric composition having a coefficient of thermal volumetric expansion so correlated to that of the casing and elements that adverse pressure conditions are not established within the casing over the range of operating temperatures of the apparatus. The spherical particles, which preferably form more than 70 per cent. of the composition and are less than .1 inch in diameter are made of a substance having a coefficient of thermal volumetric expansion of 30 x 10<-6> or less, fused vitreous materials such as glass, porcelain, alumina, silica, silicon carbide and magnesia being especially suitable. The spheres may be all the same size, or smaller ones whose diameter is between .5 and .75 that of the larger ones may be used to fit in the spaces, still smaller ones being used to fit in the remaining spaces, four or more different sizes of spheres being intermixed if desired. Various liquid dielectrics may be used, such as petroleum oils, halogenated cyclic compounds, molten waxes and paraffins, liquid gases and pitches.