Direct current cable with resistivity graded insulation, and a method of transmitting direct current electrical energy

An electrical cable for the transmission of high voltage direct current electrical energy which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes comprising an elongated metal electrical conductor enclosed within a resistivity graded, composite body of polymeric dielectric insulation, said composite dielectric insulation comprising the combination of an inner layer of polymeric insulation of relatively low resistivity, the inner layer of the polymeric insulation being composed of cross-linked polyethylene containing about 50 parts by weight of clay filler per 100 parts by weight of the polyethylene and the contiguous outer layer of the polymeric insulation being composed of cross-linked polyethylene containing about 50 parts by weight of clay filler and about 5 parts by weight of carbon black per 100 parts by weight of the polyethylene.

An electrical cable for the transmission of high voltage direct current electrical energy which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes comprising an elongated metal conductor enclosed within a resistivity graded, composite body of polymeric dielectric insulation, said composite dielectric insulation comprising the combination of an inner layer of polymeric insulation of relatively high resistivity and a contiguous outer layer of polymeric insulation of relatively low resistivity, the inner layer of the polymeric insulation being composed of cross-linked polyethylene and said contiguous outer layer of polymeric insulation being composed of cross-linked ethylene-propylene copolymer containing about 96 parts by weight of clay filler per 100 parts by weight of the copolymer.

An improved method of transmitting high voltage direct current electrical energy with an insulated conductor which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes, comprising providing an elongated metal electrical conductor enclosed within a resistivity graded, composite body of polymeric dielectric insulation composed of the combination of an inner layer of polymeric insulation of relatively high resistivity and a contiguous outer layer of filled polymeric insulation of relatively low resistivity, said inner layer of polymeric insulation comprising a polymeric material consisting essentially of cross-linked polyethylene and said outer layer of filled polymeric insulation consisting essentially of cross-linked ethylene-containing polymer selected from the group consisting of polyethylene and copolymers of ethylene and propylene containing about 25 to about 150 parts by weight of at least one filler selected from the group consisting of clay and titanium dioxide per 100 parts by weight of the polymer, and transmitting direct current electricity through said insulated conductor.

An improved method for transmitting high voltage direct current electrical energy with an insulated conductor which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes, comprising providing an elongated metal electrical conductor enclosed within a resistivity graded, composite body of polymeric dielectric insulation comprising the combination of an inner layer of polymeric insulation of relatively high resistivity and a contiguous outer layer of polymeric insulation of relatively low resistivity, said inner layer of polymeric insulation being composed of cross-linked polyethylene containing about 50 parts by weight of clay filler per 100 parts by weight of the polyethylene and said contiguous outer layer of polymeric insulation being composed of cross-linked polyethylene containing about 50 parts by weight of clay filler and about 5 parts by weight of carbon black per 100 parts by weight of the polyethylene, and transmitting direct current electricity through said insulated conductor.

An improved method of transmitting high voltage direct current electrical energy with an insulated conductor which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes, comprising providing an elongated electrical conductor enclosed within a resistivity graded, composite body of polymeric dielectric insulation comprising the combination of an inner layer of polymeric insulation of relatively high resistivity and a contiguous outer layer of polymeric insulation of relatively low resistivity, said inner layer of polymeric insulation being composed of cross-linked polyethylene and said contiguous outer layer of polymeric insulation being composed of cross-linked ethylene-propylene copolymer containing about 96 parts by weight of clay filler per 100 parts by weight of the copolymer, and transmitting direct current electricity through said insulated conductor.

An improved method of transmitting high voltage direct current electrical energy with an insulated conductor which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes, comprising providing an elongated electrical conductor enclosed within a resistivity graded, composite body of polymeric dielectric insulation comprising the combination of an inner layer of polymeric insulation of relatively high resistivity and a contiguous outer layer of filled polymeric insulation of relatively low resistivity, said inner layer of polymeric insulation being composed of cross-linked polyethylene and said outer layer of polymeric insulation being composed of cross-linked polyethylene containing about 115 parts by weight of titanium dioxide filler per 100 parts by weight of the polyethylene, and transmitting direct current electricity through said insulated conductor.

An improved method of transmitting high voltage direct current electrical energy with an insulated conductor which minimizes disproportional direct current induced electrical stresses through the insulation due to temperature changes, comprising providing an elongated metal electrical conductor enclosed within a resistivity graded, composite body of polymeric insulation composed of the combination of an inner layer of polymeric insulation of relatively high resistivity and a contiguous outer layer of polymeric insulation of relatively low resistivity said inner layer of polymeric insulation consisting essentially of cross-linked polyethylene and said contiguous outer layer of polymeric insulation consisting essentially of cross-linked ethylene-propylene rubber containing about 96 parts by weight of clay filler per 100 parts by weight of the ethylene-propylene rubber, and transmitting direct current electricity through said insulated conductor.