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This paper presents the results of an investigation to develop the technology required to manufacture chemically crosslinked polyethylene insulated power cables in the voltage range 138 to 345 kV, and having insulation thicknesses approximately equal to oil-impregnated paper insulated cables. Background studies are presented using miniature cable models to demonstrate the effect on voltage breakdown strength of irregularities at the conductor shield, contaminants in the insulation, and of type of insulation. A pilot extrusion line which incorporates the new technology for extrusion of full-size cables rated 138-345 kV is described. Data taken on full-size model cables, having 230 mils (5.8 mm) insulation thickness, manufactured on this pilot line are presented which demonstrate short time voltage breakdown average stresses in excess of 800 v/mil (32 kV/mm). This indicates that the technology appears feasible for manufacture of crosslinked polyethylene insulated cables rated 138, 230 and 345 kV, having insulation thicknesses of 500 mils (12.7 mm), 760 mils (19.3 mm) and 1050 mils (26.7 mm), respectively.