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AssigneeGeneral Cable Corporation
InventorsGeorge Bahder, George S. Eager, Jr., David A. Silver
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High-voltage power cables with extruded dielectric plastic insulation, installed underground, have their life shortened by the formation of electrochemical trees in the insulation. This invention provides a high-voltage power transmission cable constructed with sealant in interstices of a stranded conductor that are not filled by the semi-conducting material of a conductor shield of the cable. The construction prevents or greatly delays the formation of electrochemical trees in the insulation of the cable. The sealant prevents entrance of air into the cable at cable ends, and the passage of the humidity of the air through the conductor shield to an interface between the conductor shield and the inside surface of insulation that surrounds the conductor shield.
A method of making an insulated high-voltage power transmission cable resistant to the formation of electrochemical trees, which cable comprises a multi-stranded metal conductor comprising bare individual strands twisted together along helical paths, and a layer of extruded polyethylene insulation material surrounding the conductor, said insulation being subject to the formation of electrochemical trees starting at the inner surface of the insulation where the voltage stress in the insulation is at a maximum and from which said trees progress away from the inner surface and radially outward, comprising preventing air from entering the cable at the ends thereof by completely filling the spaces between the bare strands of the multistranded conductor and any space between the bare conductor strands and the inside surface of the insulation with a flexible sealant material to eliminate access of air to the inside surface of the extruded polyethylene insulation that surrounds the conductor, said sealant comprising a semi-conducting sealant having a drip point and characteristics required for high voltage power transmitting cables, providing a semi-conducting layer between the conductor and the inside surface of the insulation and maintaining a tight contact between the extruded insulation and such layers of the cable as are adjacent to the insulation to prevent access of air into the cable at the ends thereof.
A method of manufacturing a high voltage power transmission cable having a conductor made of bare metal strands of wire of generally circular cross-section and stranded along helical paths, comprising extruding a semi-conducting layer over the conductor, extruding over the semi-conducting layer a polyethylene insulation that is subject to the formation of electrochemical trees when exposed to high voltage stresses in the presence of at least some moisture, making the cable resistant to the formation of such trees by preventing air from premeating through the semiconducting conductor shield to the interface of the conductor shield and insulation by filling the interstices of the conductor with a sealant material having a drip point higher than 130.degree. C., said sealant material being compatible with the conductor shield and insulation and being flexible at all temperatures to which the cable will be subject when put to its intended use, thereby preventing entry of air into the conductor of the cable at cable ends and during splicing and terminating operations said sealant being extended throughout the full length of the conductor and acting as an air barrier at any location where the cable may be cut to make a shorter length of cable.
Dependencies are inferred from the claim text.