Electric cables of reduced micro-voids in the extruded insulation

Claim 1

An electric cable for use at medium and high voltages, said cable comprising a conductor surrounded by a first semi-conductive layer which is surrounded by solid insulation which in turn is surrounded by second semi-conductive layer, said solid insulation being an extruded, peroxide cross-linked, plastic material which has been treated subsequent to the cross-linking thereof by subjecting it to heat at a temperature in the range from about 120° C. to 150° C. and an ambient pressure less than 10 mm. Hg. to remove decomposition products and reduce the number of micro-voids formed during the cross-linking, said insulation being characterized by a perforation gradient better than the same insulation which has not been so treated, being substantially free of said decomposition products and having a number of micro-voids less than the same insulation which has not been so treated and less than 10 3 per mm 3 whereby the perforation gradient is improved and the stability of the insulating properties of the insulation remains substantially constant with use over a period of time.