GB732973A - Improvements in the manufacture of electric cables having oil impregnated insulation - Google Patents

Abstract

732,973. Impregnated electric insulation. BRITISH INSULATED CALLENDER'S CABLES, Ltd. July 30, 1953 [April 30, 1952], No. 10874/52. Class 140. The dielectric or insulation of an electric cable comprises paper impregnated with a mineral oil imbibed or absorbed by the product obtained by subjecting a hydrocarbon oil or a polymerized aliphatic hydrocarbon to radio-active irradiation in such a way that carbon-to-carbon cross-linking takes place, whereby the tendency of oil to drain from the composite dielectric is reduced. The polymerized aliphatic hydrocarbon may be polyethylene, polyisoprene, polybutadiene, polymerised 2: 3-dimethyl butadiene, or natural rubber. The irradiation may consist of slow neutrons associated with fast neutrons and gamma rays as produced in an atomic pile, or it may be produced from a gamma ray source or an atomic or sub-atomic particle accelerator. The imbibing or absorbing material may be added in or on the paper or in the oil, e.g. it may be added as an emulsion or dispersion to paper pulp, a coating on paper strips, or incorporated in the oil as a powder. In an example paper that has been impregnated with a solution of polythene in xylene or made from a pulp containing dispersed polythene is subjected to irradiation in an atomic pile until 0.18 per cent of the carbon atoms are crosslinked. A conductor is insulated by lapping with a number of layers of treated paper, is immersed in mineral oil, and is finally covered with a metallic sheath and, if desired, armouring. Alternatively, the conductor may be axially rotated in a bath of mineral oil whilst paper tapes are applied, the paper having been preimpregnated with mineral oil to cause the irradiated polythene to swell before lapping is commenced.