Abstract: A method of manufacturing an electric wire insulated with a foamed plastic. The method includes steps of introducing a foaming agent into a fluororesin in a molten state to allow the foaming agent to dispersed in the molten resin, and extruding the molten resin having the foaming agent dispersed therein onto a conductor wire to allow foaming. A fluorine-based foaming agent contains as a main component at least one kind of a fluorocarbon having a molecular weight of about 338 to 488 is used as a foaming agent.

Abstract: A cryogenic power cable of a cryoresistive type having a conductor which is cooled with a cooling medium to permit large capacity power transmission by reducing thereby the electric resistance and the joule loss of the conductor. The temperature of the cable core is controlled through an ingenious arrangement comprising the conductor which incorporates therein a passage for the cooling medium, an electric insulation layer made of an ordinary electric insulating material and a thermal insulating material layer. The cable not only makes ultra-high voltage transmission of 500 to 1000 KV possible but also is advantageous on account of a simple and economic structure.