GB1401347A - Capacitors - Google Patents

Abstract

1401347 Capacitors IMPERIAL CHEMICAL INDUSTRIES Ltd 25 Sept 1973 [18 Oct 1972 9 Feb 1973] 47917/72 and 6398/73 Heading H1M In a wound capacitor at least one of the dielectric spacers separating the electrodes comprises thermoplastic polymeric material having a thermal shrinkage in the longitudinal direction of from 5 to 10% and a ratio of thermal shrinkage in the longitudinal direction to that at right angles of from 1À7 : 1 to 10 : 1, and a sleeve covering at least 75% of the exposed surface area of the winding has a thermal shrinkage in the direction corresponding to the longitudinal direction of the spacer at least 1À02 times that of the spacer in this direction. Shrinkages are measured by heating a freely suspended film at the temperature at which the winding will be heat stabilized for 15 minutes and observing the contraction between reference points. The electrodes may be aluminium or tin foils or vacuum deposited layers of aluminium, zinc, silver, gold or nickel, and contact thereto may be by means of connection tags or by metal coatings on the end faces of the roll. The spacer material may be polypropylene or other polyolefins, polycarbonate, polysulphone, polyethylene terephthalate or polyethylene-1,2- diphenoxyethane-4,4<SP>1</SP>-dicarboxylate. The films may be manufactured by rolling, pressing, casting or preferably extruding using the bubble process, and may be treated by known methods to improve slip characteristics. The sleeve may be a cylindrical sheath slipped on to the roll but preferably comprises 10 to 50 turns of a web wound round the roll. The sleeve material is preferably the same as the spacer material, or has an equal or greater co-efficient of thermal expansion. The capacitor may be impregnated with, e.g. mineral oil, castor oil, cottonseed oil, silicone oil, chlorinated diphenyls or polybutene, or gases such as nitrogen or sulphur hexafluoride, prior to heat stabilizing.