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US 4,145,567 AGranted
Solid dielectric cable resistant to electrochemical trees
AssigneeGeneral Cable Corporation
InventorsGeorge Bahder, George S. Eager, Jr., Carlos Katz
Life of this patent
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AssigneeGeneral Cable Corporation
InventorsGeorge Bahder, George S. Eager, Jr., Carlos Katz
Estimating the term…
This cable for high-voltage, alternating current power transmission cables not only reduces the access of moisture into the cable but reduces access of moisture to the inner face of the insulation to such an extent as to make the cable highly resistant to the formation of electrochemical trees in the solid extruded insulation of the cable. A compressible layer of closed cell, foamed plastic is extruded over the outside surface of the insulation; and a metallic shield fits tightly around the compressible layer, the metallic shield being a longitudinally folded tape with a lap seam which is preferably bonded to prevent ingress of air or other fluid into the cable. If the conductor is stranded, sealant is used to prevent ingress of moisture, or of air, and the humidity it contains into the cable at cable ends.
A power transmission cable for high-voltage, alternating current and resistant to the formation of electrochemical trees, said cable including in combination a core comprising a conductor with strand sealant throughout the length of the conductor in any interstices of the conductor, a semiconducting conductor shield surrounding the conductor and extruded over the conductor, an extruded solid unfoamed polyolefin insulation extruded over the conductor shield, said insulation having the dimension of its radial thickness as great as the diameter of the conductor, a closed cell, compressible, foamed plastic layer surrounding the outside of the core and in contact therewith, a metal shield around the foamed plastic layer and holding the foamed plastic layer under some compression against the core to ensure intimate surface contact between the metal shield and the compressible layer, the metal shield having a seam with the major component of the direction of extent of the seam extending in the direction of the length of the cable, and means for sealing the seam edge portions together to prevent air or liquid from entering the seam, the compressibility of the foam layer being correlated with the seal of the seam of the metal shield to withstand the high coefficient of thermal expansion of the insulation as compared to the lower coefficient of expansion of the metal, and an extruded outer jacket over the other parts of the cable and fitting snugly around the rest of the cable that the outer jacket encloses.
The method of making a power cable, that has a conductor, a semiconducting conductor shield, an extruded layer of solid polyolefin insulation, a semiconducting insulation shield, a metal shield surrounding the insulation shield and having a lap seam, resistant to the formation of electrochemical trees in the extruded insulation, which method comprises applying between the insulation shield and the metal shield a layer of closed cell, compressible, foamed plastic with a foaming ratio (gas/solid) greater than approximately 20, applying the foamed layer so as to completely surround the circumference of the insulation shield without any gaps in the circumference of the compressible layer, and applying a tape as the metal shield over the compressible layer with a seam where opposite sides of the tape overlap one another, and sealing the lap seam by bonding the overlapping edges of the tape with an airtight bond between the edges.
Dependencies are inferred from the claim text.